TI DAC5687 16-bit, 500 msps 2x-8x interpolating dual-channel digital-to-analog converter (dac) Datasheet

DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
16-BIT, 500 MSPS 2x-8x INTERPOLATING DUAL-CHANNEL
DIGITAL-TO-ANALOG CONVERTER (DAC)
FEATURES
•
•
•
•
•
•
•
•
•
•
•
•
•
500 MSPS
Selectable 2x-8x Interpolation
On-Chip PLL/VCO Clock Multiplier
Full IQ Compensation Including Offset, Gain,
and Phase
Flexible Input Options:
– FIFO With Latch on External or Internal
Clock
– Even/Odd Multiplexed Input
– Single Port Demultiplexed Input
Complex Mixer With 32-Bit NCO
Fixed Frequency Mixer With Fs/4 and Fs/2
1.8-V or 3.3-V I/O Voltage
On-Chip 1.2-V Reference
Differential Scalable Output: 2 mA to 20 mA
Pin Compatible to DAC5686
High Performance
– 81-dBc ACLR WCDMA TM1 at 30.72 MHz
– 72-dBc ACLR WCDMA TM1 at 153.6 MHz
Package: 100-Pin HTQFP
APPLICATIONS
•
•
Cellular Base Transceiver Station Transmit
Channel
– CDMA: W-CDMA, CDMA2000, TD-SCDMA
– TDMA: GSM, IS-136, EDGE/UWC-136
– OFDM: 802.16
Cable Modem Termination System
DESCRIPTION
The DAC5687 is a dual-channel 16-bit high-speed
digital-to-analog converter (DAC) with integrated 2x,
4x, and 8x interpolation filters, a complex numerically
controlled oscillator (NCO), on-board clock multiplier,
IQ compensation and on-chip voltage reference. The
DAC5687 is pin compatible to the DAC5686, requiring only changes in register settings for most applications, and offers additional features and superior
linearity, noise, crosstalk, and PLL phase noise performance.
The DAC5687 has six signal processing blocks: two
interpolate by two digital filters, fine frequency mixer
with 32-bit NCO, a quadrature modulation compensation block, another interpolate by two digital filter
and a coarse frequency mixer with Fs/2 or Fs/4. The
different modes of operation enable or bypass the
signal processing blocks.
The coarse and fine mixers can be combined to span
a wider range of frequencies with fine resolution. The
DAC5687 allows both complex or real output. Combining the frequency upconversion and complex output produces a Hilbert Transform pair that is output
from the two DACs. An external RF quadrature
modulator then performs the final single sideband
up-conversion.
The IQ compensation feature allows optimization of
phase, gain and offset to maximize sideband rejection
and minimize LO feedthrough for an analog quadrature modulator.
The DAC5687 includes several input options: single
port interleaved data, even and odd multiplexing at
half rate, and an input FIFO with either external or
internal clock to ease the input timing ambiguity when
the DAC5687 is clocked at the DAC output sample
rate.
ORDERING INFORMATION
TA
Package Device
-40°C to 85°C
100 HTQFP (1) (P&P) PowerPAD™
Plastic Quad FlatPack
DAC5687IPZP
(1)
Thermal Pad Size: 6 mm × 6 mm.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2005, Texas Instruments Incorporated
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
These devices have limited built-in ESD protection. The leads should be shorted together or the device
placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.
FUNCTIONAL BLOCK DIAGRAM
CLKVDD
CLKGND
LPF
PLLGND PLLVDD
PHSTR
SLEEP
DVDD
CLK2
CLK2C
A
Offset A gain
PLLLOCK
FIR1
FIR2
FIR3
FIR4
IOUTA1
x2
x2
Quardrature Mod
Correction (QMC)
x2
Fine Mixer
Input FIFO/
Reorder/
Mux/Demux
x2
DB[15:0]
SIF
sin
NCO
16-bit DAC
IOUTA2
sin(x)
IOUTB1
x:
x2
cos
TXENABLE
x2
Coarse Mixer:
fs/2 or fs/4
x:
DA[15:0]
16-bit DAC
sin(x)
IOUTB2
B
Offset B gain
SDIO SDO SDENB SCLK
IOGND
IOVDD
100-Pin HTQFP
QFLAG
2
EXTIO
EXTLO
BIASJ
CLK1C
RESETB
1.2-V
Reference
2x−8x
fdata
Internal Clock Generation
and
2x−8x PLL Clock Multiplier
CLK1
DGND
AVDD
AGND
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
IOGND
DB7
DB6
DB5
79
78
77
76
DGND
IOVDD
81
80
DB8
DVDD
83
82
DB10
DB9
85
86
84
DB12
DB11
87
DVDD
DGND
89
88
DB14
DB13
91
92
90
DGND
DB15 (MSB)
93
RESETB
PHSTR
94
96
95
TESTMODE
SLEEP
97
DGND
QFLAG
98
DVDD
99
100
PINOUT
75
DB4
2
74
DB3
AGND
1
AVDD
AVDD
3
73
DB2
AGND
4
72
DB1
IOUTB1
5
71
DB0 (LSB)
IOUTB2
6
70
PLLLOCK
AGND
7
69
DGND
AVDD
8
68
DVDD
AGND
9
67
PLLVDD
AVDD
10
66
LPF
EXTIO
11
65
PLLGND
AGND
12
64
CLKGND
BIASJ
13
63
CLK2C
AVDD
14
62
CLK2
EXTLO
15
61
CLKVDD
AVDD
16
60
CLK1C
AGND
17
59
CLK1
AVDD
18
58
CLKGND
Top View 100 HTQFP
DAC5687
47
48
49
50
IOGND
DA7
DA6
DA5
45
46
DGND
IOVDD
43
44
DA8
41
DA10
DVDD
40
DA11
42
39
DA12
DA9
37
38
DVDD
DGND
35
36
DA14
DA13
DA4
34
51
DA15 (MSB)
25
33
AGND
TXENABLE
DA3
32
DA2
52
DVDD
53
24
31
23
AVDD
SDO
AVDD
30
DA1
SDIO
DA0 (LSB)
54
29
55
22
SCLK
21
AGND
28
IOUTA1
DGND
DVDD
SDENB
DGND
56
26
57
20
27
19
DVDD
AGND
IOUTA2
TERMINAL FUNCTIONS
TERMINAL
I/O
DESCRIPTION
NAME
NO.
AGND
1, 4, 7, 9, 12,
17, 19, 22, 25
I
Analog ground return
AVDD
2, 3, 8, 10, 14,
16, 18, 23, 24
I
Analog supply voltage
BIASJ
13
O
Full-scale output current bias
3
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
TERMINAL FUNCTIONS (continued)
TERMINAL
I/O
DESCRIPTION
59
I
In PLL clock mode and dual clock modes, provides data input rate clock. In external clock mode,
provides optional input data rate clock to FIFO latch. When the FIFO is disabled, CLK1 is not used
and can be left unconnected.
CLK1C
60
I
Complementary input of CLK1.
CLK2
62
I
External and dual clock mode clock input. In PLL mode, CLK2 is unused and can be left
unconnected.
NAME
NO.
CLK1
CLK2C
63
I
Complementary of CLK2. In PLL mode, CLK2C is unused and can be left unconnected.
CLKGND
58, 64
I
Ground return for internal clock buffer
CLKVDD
61
I
Internal clock buffer supply voltage
DA[15..0]
34-36, 39-43,
48-55
I
A-Channel Data bits 0 through 15. DA15 is most significant data bit (MSB). DA0 is least significant
data bit (LSB). Order can be reversed by register change.
DB[0..15]
71-78, 83-87,
90-92
I
B-Channel Data bits 0 through 15. DB15 is most significant data bit (MSB). DB0 is least significant
data bit (LSB). Order can be reversed by register change.
DGND
27, 38, 45, 57,
69, 81, 88, 93,
99
I
Digital ground return
DVDD
26, 32, 37, 44,
56, 68, 82, 89,
100
I
Digital supply voltage
EXTIO
11
I/O
Used as external reference input when internal reference is disabled (i.e., EXTLO connected to
AVDD). Used as internal reference output when EXTLO = AGND, requires a 0.1-µF decoupling
capacitor to AGND when used as reference output
EXTLO
15
I/O
Internal/external reference select. Internal reference selected when tied to AGND, external
reference selected when tied to AVDD. Output only when ATEST is not zero (register 0x1B bits 7
to 3).
IOUTA1
21
O
A-Channel DAC current output. Full scale when all input bits are set 1
IOUTA2
20
O
A-Channel DAC complementary current output. Full scale when all input bits are 0
IOUTB1
5
O
B-Channel DAC current output. Full scale when all input bits are set 1
IOUTB2
6
O
B-Channel DAC complementary current output. Full scale when all input bits are 0
IOGND
47, 79
I
Digital I/O ground return
IOVDD
46, 80
I
Digital I/O supply voltage
LPF
66
I
PLL loop filter connection
PHSTR
94
I
Synchronization input signal that can be used to initialize the NCO, course mixer, internal clock
divider, and/or FIFO circuits.
PLLGND
65
I
Ground return for internal PLL
PLLVDD
67
I
PLL supply voltage. When PLLVDD is 0 V, the PLL is disabled.
PLLLOCK
70
O
In PLL mode, provides PLL lock status bit or internal clock signal. PLL is locked to input clock
when high. In external clock mode, provides input rate clock.
QFLAG
98
I
When qflag register is 1, the QFLAG pin is used by the user during interleaved data input mode to
identify the B sample. High QFLAG indicates B sample. Must be repeated every B sample.
RESETB
95
I
Resets the chip when low. Internal pull-up
SCLK
29
I
Serial interface clock
SDENB
28
I
Active low serial data enable, always an input to the DAC5687
SDIO
30
I/O
Bidirectional serial data in 3-pin interface mode, input only in 4 pin interface mode. Three-pin mode
is the default after chip reset.
SDO
31
O
Serial interface data, uni-directional data output, if SDIO is an input. SDO is 3-stated when the
3-pin interface mode is selected (register 0x08 bit 1).
SLEEP
96
I
Asynchronous hardware power down input. Active High. Internal pull down.
4
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
TERMINAL FUNCTIONS (continued)
TERMINAL
NAME
NO.
I/O
DESCRIPTION
TXENABLE
33
I
TXENABLE has two purposes. In all modes, TXENABLE must be high for the DATA to the DAC to
be enabled. When TXENABLE is low, the digital logic section is forced to all 0, and any input data
presented to DA[15:0] and DB[15:0] is ignored. In interleaved data mode, when the qflag register
bit is cleared, TXENABLE is used to synchronizes the data to channels A and B. The first data
after the rising edge of TXENABLE is treated as A data, while the next data is treated as B data,
and so on.
TESTMODE
97
I
TESTMODE is DGND for the user
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range (unless otherwise noted) (1)
UNIT
Supply voltage range
AVDD (2)
–0.5 V to 4 V
DVDD (3)
–0.5 V to 2.3 V
CLKVDD (2)
–0.5 V to 4 V
IOVDD (2)
–0.5 V to 4 V
PLLVDD (2)
–0.5 V to 4 V
Voltage between AGND, DGND, CLKGND, PLLGND, and IOGND
–0.5 V to 0.5 V
AVDD to DVDD
–0.5 V to 2.6 V
DA[15..0] (4)
–0.5 V to IOVDD + 0.5 V
DB[15..0] (4)
–0.5 V to IOVDD + 0.5 V
SLEEP (4)
Supply voltage range
–0.5 V to IOVDD + 0.5 V
CLK1/2, CLK1/2C (3)
–0.5 V to CLKVDD + 0.5 V
RESETB (4)
–0.5 V to IOVDD + 0.5 V
LPF (4)
–0.5 V to PLLVDD + 0.5 V
IOUT1, IOUT2 (2)
–1.0 V to AVDD + 0.5 V
EXTIO, BIASJ (2)
–0.5 V to AVDD + 0.5 V
EXTLO (2)
–0.5 V to IAVDD + 0.5 V
Peak input current (any input)
20 mA
Peak total input current (all inputs)
30 mA
TA
Operating free-air temperature range (DAC5687I)
–40°C to 85°C
Tstg
Storage temperature range
–65°C to 150°C
Lead temperature 1,6 mm (1/16 inch) from the case for 10 seconds
(1)
(2)
(3)
(4)
260°C
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of these or any other conditions beyond those indicated under recommended operating conditions is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Measured with respect to AGND.
Measured with respect to DGND.
Measured with respect to IOGND.
THERMAL CHARACTERISTICS (1)
over operating free-air temperature range (unless otherwise noted)
Thermal Conductivity
TJ
θJA
θJC
(1)
(2)
Junction
temperature (2)
100 HTQFP
UNIT
105
°C
Theta junction-to-ambient (still air)
19.88
°C/W
Theta junction-to-ambient (150 lfm)
14.37
°C/W
Theta junction-to-case
0.12
°C/W
Air flow or heat sinking reduces θJA and is highly recommended.
Air flow or heat sinking required for sustained operation at 85°C and maximum operating conditions to maintain junction temperature.
5
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
ELECTRICAL CHARACTERISTICS
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 3.3 V, IOVDD = 3.3 V,
DVDD = 1.8 V, IOUTFS = 19.2 mA (unless otherwise noted)
DC SPECIFICATIONS
PARAMETER
TEST CONDITIONS
RESOLUTION
MIN
TYP
MAX
16
UNIT
Bits
DC ACCURACY (1)
INL
Integral nonlinearity
DNL
Differential nonlinearity
1 LSB = IOUTFS/216
TMIN to TMAX
±4
LSB
±4
LSB
±0.04
LSB
±3
LSB
ANALOG OUTPUT
Coarse gain linearity
Worst case error from ideal linearity
Fine gain linearity
Offset error
Mid code offset
Without internal reference
Gain error
With internal reference
With internal reference, dual DAC, and SSB
mode
Gain mismatch
0.01
%FSR
1
%FSR
0.7
%FSR
-2
2
%FSR
current (2)
2
mA
Maximum full-scale output current (2)
20
mA
Minimum full-scale output
Output compliance range (3)
IOUTFS = 20 mA
AVDD
–0.5 V
Output resistance
Output capacitance
AVDD +
0.5 V
V
300
kΩ
5
pF
REFERENCE OUTPUT
Reference voltage
1.14
Reference output current (4)
1.2
1.26
100
V
nA
REFERENCE INPUT
VEXTIO
Input voltage range
0.1
Input resistance
1.25
V
1
MΩ
Small signal bandwidth
1.4
MHz
Input capacitance
100
pF
±1
ppm of
FSR/°C
TEMPERATURE COEFFICIENTS
Offset drift
Gain drift
Without internal reference
±15
With internal reference
±30
Reference voltage drift
ppm of
FSR/°C
ppm of
FSR/°C
±8
POWER SUPPLY
AVDD
Analog supply voltage
DVDD
CLKVDD
IOVDD
I/O supply voltage
PLLVDD
PLL supply voltage
(1)
(2)
(3)
(4)
6
3
3.3
3.6
V
Digital supply voltage
1.71
1.8
2.15
V
Clock supply voltage
3
3.3
3.6
V
3.6
V
3.6
V
1.71
3
3.3
Measured differential across IOUTA1 and IOUTA2 or IOUTB1 and IOUTB2 with 25 Ω each to AVDD.
Nominal full-scale current, IOUTFS , equals 32X the IBIAS current.
The lower limit of the output compliance is determined by the CMOS process. Exceeding this limit may result in transistor breakdown,
resulting in reduced reliability of the DAC5687 device. The upper limit of the output compliance is determined by the load resistors and
full-scale output current. Exceeding the upper limit adversely affects distortion performance and integral nonlinearity.
Use an external buffer amplifier with high impedance input to drive any external load.
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
ELECTRICAL CHARACTERISTICS (continued)
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 3.3 V, IOVDD = 3.3 V,
DVDD = 1.8 V, IOUTFS = 19.2 mA (unless otherwise noted)
DC SPECIFICATIONS
PARAMETER
IAVDD
Analog supply current
current (5)
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Mode 5 (5)
41
mA
Mode 6 (5)
80
mA
6 (5)
IDVDD
Digital supply
587
mA
ICLKVDD
Clock supply current (5)
Mode 6 (5)
5
mA
IPLLVDD
PLL supply current (5)
Mode 6 (5)
20
mA
6 (5)
current (5)
Mode
IIOVDD
IO supply
2
mA
IAVDD
Sleep mode AVDD supply current
Sleep mode (Sleep pin high) CLK2 = 500 MHz
1
mA
IDVDD
Sleep mode DVDD supply current
Sleep mode (Sleep pin high) CLK2 = 500 MHz
2
mA
ICLKVDD
Sleep mode CLKVDD supply current Sleep mode (Sleep pin high) CLK2 = 500 MHz
0.25
mA
IPLLVDD
Sleep mode PLLVDD supply current
Sleep mode (Sleep pin high) CLK2 = 500 MHz
0.6
mA
IIOVDD
Sleep mode IOVDD supply current
Sleep mode (Sleep pin high) CLK2 = 500 MHz
0.6
mA
Mode 1 (5) AVDD = 3.3 V, DVDD = 1.8 V
750
Mode 2 (5) AVDD = 3.3 V, DVDD = 1.8 V
910
PD
Power dissipation
Mode
Mode 3 (5) AVDD = 3.3 V, DVDD = 1.8 V
760
Mode 4 (5) AVDD = 3.3 V, DVDD = 1.8 V
1250
Mode 5 (5) AVDD = 3.3 V, DVDD = 1.8 V
1250
Mode 6 (5) AVDD = 3.3 V, DVDD = 1.8 V
1410
Mode 7 (5) AVDD = 3.3 V, DVDD = 1.8 V
1400
1750
11
20
Sleep mode (Sleep pin high) CLK2 = 500 MHz
APSRR
DPSRR
(5)
Power supply rejection ratio
mW
-0.2
0.2
%FSR/V
-0.2
0.2
%FSR/V
MODE 1 – MODE 7:
a. Mode 1: X2, PLL off, CLK2 = 320 MHz, DACA and DACB on, IF = 5 MHz
b. Mode 2: X4 QMC, PLL on, CLK1 = 125 MHz, DACA and DACB on, IF = 5 MHz
c. Mode 3: X4 CMIX, PLL off, CLK2 = 500 MHz, DACA off and DACB on, IF = 150 MHz
d. Mode 4: X4L FMIX CMIX, PLL off, CLK2 = 500 MHz, DACA off and DACB on, IF = 150 MHz
e. Mode 5: X4L FMIX CMIX, PLL on, CLK1 = 125 MHz, DACA off and DACB on, IF = 150 MHz
f. Mode 6: X4L FMIX CMIX, PLL on, CLK1 = 125 MHz, DACA on and DACB on, IF = 150 MHz
g. Mode 7: X8 FMIX CMIX, PLL on, CLK1 = 62.5 MHz, DACA and DACB on, IF = 150 MHz
7
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
ELECTRICAL CHARACTERISTICS (1)
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 0 V (= 3.3 V for PLL
Clock Mode), IOVDD = 3.3 V, DVDD = 1.8 V, IOUTFS = 19.2 mA, External Clock Mode, 4:1 transformer output termination,
50-Ω doubly terminated load (unless otherwise noted)
AC SPECIFICATIONS
PARAMETER
TEST CONDITIONS
MIN
TYP MAX
UNIT
ANALOG OUTPUT
fCLK
Maximum output update rate
500
ts(DAC)
Output settling time to 0.1%
10.4
ns
tpd
Output propagation delay
3
ns
tr(IOUT)
Output rise time 10% to 90%
2
ns
tf(IOUT)
Output fall time 90% to 10%
2
ns
Transition: Code 0x0000 to 0xFFFF
MSPS
AC PERFORMANCE
SFDR
Spurious free dynamic range (2)
X2, PLL off, CLK2 = 250 MHz, DAC A and DAC B on,
IF = 5.1 MHz, First Nyquist Zone < fDATA/2
78
X4, PLL off, CLK2 = 500 MHz, DAC A and DAC B on,
IF = 5.1 MHz, First Nyquist Zone < fDATA/2
77
X4, CLK2 = 500 MHz, DAC A and DAC B on,
IF = 20.1 MHz, PLL on for Min, PLL off for TYP,
First Nyquist Zone < fDATA/2
SNR
IMD3
IMD
(1)
(2)
(3)
8
Signal-to-noise ratio
Third-order two-tone
intermodulation (each tone at
–6 dBFS)
Four-tone Intermodulation to
Nyquist (each tone at –12
dBFS)
68 (3)
dBc
76
X4, PLL off, CLK2 = 500 MSPS, DAC A and DAC B on,
Single tone, 0 dBFS, IF = 20.1 MHz
73
X4 CMIX, PLL off, CLK2 = 500 MSPS, DAC A and DAC B
on, IF = 70.1 MHz
65
X4 CMIX, PLL off, CLK2 = 500 MSPS, DAC A and DAC B
on, Single tone, 0 dBFS, IF = 150.1 MHz
57
X4 FMIX CMIX, PLL off, CLK2 = 500 MSPS, DAC A and
DAC B on, Single tone, 0 dBFS, IF = 180.1 MHz
54
X4, PLL off, CLK2 = 500 MSPS, DAC A and DAC B
on,Four tone, each -12 dBFS, IF = 24.7, 24.9, 25.1, 25.3
MHz
73
X4, PLL off, CLK2 = 500 MSPS, DAC A and DAC B on,
IF = 20.1 and 21.1 MHz
79
X4 CMIX, PLL off, CLK2 = 500 MSPS, DAC A and DAC B
on, IF = 70.1 and 71.1 MHz
73
X4 CMIX, PLL off, CLK2 = 500 MSPS, DAC A and DAC B
on, IF= 150.1 and 151.1 MHz
68
X4 FMIX CMIX, PLL off, CLK2 = 500 MSPS, DAC A and
DAC B on, IF = 180.1 and 181.1 MHz
67
X4 CMIX, CLK2 = 500 MHz fOUT = 149.2, 149.6, 150.4,
and 150.8 MHz
66
dBc
dBc
Measured single ended into 50-Ω load.
See the Non-Harmonic Clock Related Spurious Signals section for information on spurious products out of band (< fDATA/2).
1:1 transformer output termination.
dBc
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
ELECTRICAL CHARACTERISTICS (continued)
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 0 V (= 3.3 V for PLL
Clock Mode), IOVDD = 3.3 V, DVDD = 1.8 V, IOUTFS = 19.2 mA, External Clock Mode, 4:1 transformer output termination,
50-Ω doubly terminated load (unless otherwise noted)
AC SPECIFICATIONS
PARAMETER
ACLR (4)
Adjacent channel leakage ratio
Noise Floor
(4)
TEST CONDITIONS
MIN
TYP MAX
Single carrier, baseband, X4, PLL Clock Mode,
CLK1 = 122.88 MHz
78.4
Single carrier, baseband, X4, PLL Clock Mode,
CLK2 = 491.52 MHz
78.5
Single carrier, IF = 153.6 MHz, X4 CMIX, External Clock
Mode, CLK2 = 491.52 MHz
70.9
Two carrier, IF = 153.6 MHz, X4 CMIX, External Clock
Mode, CLK2 = 491.52 MHz
67.8
Four carrier, baseband, X4, External Clock Mode,
CLK2 = 491.52 MHz
76.1
Four carrier, IF = 92.16 MHz, X4L, External Clock Mode,
CLK2 = 491.52 MHz
66.8
Single carrier, IF = 153.6 MHz, X4 CMIX, External Clock
Mode, CLK2 = 491.52 MHz, DVDD = 2.1 V
72.2
Two carrier, IF = 153.6 MHz, X4 CMIX, External Clock
Mode, CLK2 = 491.52 MHz, DVDD = 2.1 V
69.3
Four carrier, baseband, X4, External Clock Mode,
CLK2 = 491.52 MHz, DVDD = 2.1 V
68.5
Four carrier, IF = 92.16 MHz, X4L, External Clock Mode,
CLK2 = 491.52 MHz, DVDD = 2.1 V
66.3
UNIT
dBc
50-MHz offset, 1-MHz BW, Single carrier, baseband,
X4, External Clock Mode, CLK1 = 122.88 MHz
92
50-MHz offset, 1-MHz BW, Four carrier, baseband,
X4, External Clock Mode, CLK1 = 122.88 MHz
81
50-MHz offset, 1-MHz BW, Single carrier, baseband,
X4, PLL Clock Mode, CLK2 = 491.52 MHz
88
50-MHz offset, 1-MHz BW, Four carrier, baseband,
X4, PLL Clock Mode, CLK2 = 491.52 MHz
81
dBc
W-CDMA with 3.84 MHz BW, 5-MHz spacing, centered at IF. TESTMODEL 1, 10 ms
ELECTRICAL CHARACTERISTICS (DIGITAL SPECIFICATIONS)
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 3.3 V, IOVDD = 3.3 V,
DVDD = 1.8 V, IOUTFS = 19.2 mA (unless otherwise noted)
DIGITAL SPECIFICATIONS
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
CMOS INTERFACE
VIH
High-level input voltage
2
3
VIL
Low-level input voltage
0
0
IIH
High-level input current
–40
IIL
Low-level input current
–40
Input capacitance
PLLLOCK, SDO, SDIO
Iload = –8 mA
PLLLOCK, SDO, SDIO
Input data rate
µA
40
µA
pF
IOVDD –
0.2
V
0.8 x
IOVDD
V
Iload = 100 µA
VOL
V
40
5
Iload = –100 µA
VOH
V
0.8
Iload = 8 mA
0.2
V
0.22 x
IOVDD
V
External or dual-clock modes
16
250
PLL clock mode
16
160
MSPS
9
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
ELECTRICAL CHARACTERISTICS (DIGITAL SPECIFICATIONS) (continued)
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 3.3 V, IOVDD = 3.3 V,
DVDD = 1.8 V, IOUTFS = 19.2 mA (unless otherwise noted)
DIGITAL SPECIFICATIONS
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
PLL
Phase noise
VCO maximum frequency
VCO minimum frequency
At 600-kHz offset, measured at DAC output,
25 MHz 0-dBFS tone, FDATA = 125 MSPS,
4x interpolation, pll_freq = 1, pll_kv = 0
At 6-MHz offset, measured at DAC output,
25 MHz 0-dBFS tone, 125 MSPS,
4x interpolation, pll_freq = 1, pll_kv = 0
pll_freq = 0, pll_kv = 0
370
pll_freq = 0, pll_kv = 1
480
pll_freq = 1, pll_kv = 0
495
pll_freq = 1, pll_kv = 1
520
133
dBc/Hz
148.5
dBc/Hz
MHz
pll_freq = 0, pll_kv = 0
225
pll_freq = 0, pll_kv = 1
200
pll_freq = 1, pll_kv = 0
480
pll_freq = 1, pll_kv = 1
480
MHz
NCO and QMC BLOCKS
QMC clock rate
320
MHz
NCO clock rate
320
MHz
SERIAL PORT TIMING
ts(SDENB)
Setup time, SDENB to rising edge of SCLK
20
ns
ts(SDIO)
Setup time, SDIO valid to rising edge of
SCLK
10
ns
th(SDIO)
Hold time, SDIO valid to rising edge of
SCLK
5
ns
tSCLK
Period of SCLK
100
ns
tSCLKH
High time of SCLK
40
ns
tSCLK
Low time of SCLK
40
td(Data)
Data output delay after falling edge of SCLK
ns
10
ns
CLOCK INPUT (CLK1/CLK1C, CLK2/CLK2C)
Duty cycle
40%
Differential voltage
0.4
60%
1
V
TIMING PARALLEL DATA INPUT: CLK1 LATCHING MODES
(PLL Mode –Figure 45, Dual Clock Mode FIFO Disabled – See Figure 47, Dual Clock Mode With FIFO Enabled – See Figure 48)
ts(DATA)
Setup time, DATA valid to rising edge of
CLK1
0.5
ns
th(DATA)
Hold time, DATA valid after rising edge of
CLK1
1.5
ns
t_align
Maximum offset between CLK1 and CLK2
rising edges – Dual Clock Mode with FIFO
disabled
1 0.5 ns
2FCLK2
ns
Timing Parallel Data Input (External Clock Mode, Latch on PLLLock Rising Edge, CLK2 Clock Input, See Figure 43 )
ts(DATA)
Setup time, DATA valid to rising edge of
PLLLOCK
72-Ω load on PLLLOCK
0.5
ns
th(DATA)
Hold time, DATA valid after rising edge of
PLLLOCK
72-Ω load on PLLLOCK
1.5
ns
tdelay(Plllock)
Delay from CLK2 rising edge to PLLLOCK
rising edge
72-Ω load on PLLLOCK. Note that PLLLOCK
delay increases with a lower impedance load.
4.5
ns
Timing Parallel Data Input (External Clock Mode, Latch on PLLLock Falling Edge, CLK2 Clock Input, See Figure 44)
ts(DATA)
Setup time, DATA valid to falling edge of
PLLLOCK
High impedance load on PLLLOCK
0.5
ns
th(DATA)
Hold time, DATA valid after falling edge of
PLLLOCK
High impedance load on PLLLOCK
1.5
ns
10
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
ELECTRICAL CHARACTERISTICS (DIGITAL SPECIFICATIONS) (continued)
over recommended operating free-air temperature range, AVDD = 3.3 V, CLKVDD = 3.3 V, PLLVDD = 3.3 V, IOVDD = 3.3 V,
DVDD = 1.8 V, IOUTFS = 19.2 mA (unless otherwise noted)
DIGITAL SPECIFICATIONS
PARAMETER
TEST CONDITIONS
Delay from CLK2 rising edge to PLLLOCK
rising edge
tdelay(Plllock)
MIN
High impedance load on PLLLOCK. Note that
PLLLOCK delay increases with a lower impedance load.
TYP
MAX
4.5
UNIT
ns
Typical Characteristics
8
6
6
4
2
2
Error − LSB
Error − LSB
4
0
−2
0
−2
−4
−4
−6
−8
−6
0
10000 20000 30000 40000 50000 60000 70000
0
10000 20000 30000 40000 50000 60000 70000
Code
Code
G001
G002
Figure 1. Integral Nonlinearity
Figure 2. Differential Nonlinearity
10
10
fdata = 125 MSPS
fin = 20 MHz Real
IF = 20 MHz
4 Interpolation
PLL Off
0
−10
−10
−20
P − Power − dBm
P − Power − dBm
−20
fdata = 125 MSPS
fin = −30 MHz Complex
IF = 95 MHz
4L Interpolation
CMIX
PLL Off
0
−30
−40
−50
−30
−40
−50
−60
−60
−70
−70
−80
−80
−90
−90
0
50
100
150
200
250
f − Frequency − MHz
0
50
100
150
200
G003
Figure 3. Single Tone Spectral Plot
250
f − Frequency − MHz
G004
Figure 4. Single Tone Spectral Plot
11
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Typical Characteristics (continued)
100
10
0
−10
P − Power − dBm
−20
SFDR − Spurious-Free Dynamic Range − dBc
fdata = 125 MSPS
fin = 30 MHz Real
IF = 155 MHz
4L Interpolation
HP/HP
PLL Off
−30
−40
−50
−60
−70
−80
−90
fdata = 125 MSPS
4 Interpolation
PLL Off
95
90
−6 dBFS
85
80
75
0 dBFS
−12 dBFS
70
65
60
0
50
100
150
200
5
250
f − Frequency − MHz
10
15
20
25
30
G005
G006
Figure 5. Single Tone Spectral Plot
Figure 6. In-Band SFDR vs Intermediate Frequency
100
fdata = 125 MSPS
4 Interpolation
PLL Off
85
fdata = 125 MSPS
4L Interpolation
PLL Off
fout = IF 0.5 MHz
95
80
90
75
85
70
IMD3 − dBc
SFDR − Spurious-Free Dynamic Range − dBc
90
0 dBFS
65
60
80
75
0 dBFS
70
55
65
50
60
45
55
40
50
0
50
100
150
200
250
IF − Intermediate Frequency − MHz
0
50
100
150
200
250
IF − Intermediate Frequency − MHz
G007
Figure 7. Out-of-Band SFDR vs Intermediate Frequency
12
35
IF − Intermediate Frequency − MHz
G008
Figure 8. Two Tone IMD vs Intermediate Frequency
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Typical Characteristics (continued)
90
80
IMD3 − dBC
75
−20
−30
70
65
60
−40
−50
−60
55
−70
50
−80
45
−90
40
−35
−30
−25
−20
−15
fdata = 125 MSPS
fin = 20 MHz
0.5 MHz Real
IF = 20 MHz
4 Interpolation
PLL Off
−10
P − Power − dBm
85
0
fdata = 125 MSPS
fin = −30 MHz 0.5 MHz Complex
IF = 95 MHz
4L Interpolation
CMIX
PLL Off
−10
−5
−100
10
0
15
Amplitude − dBFS
20
25
G009
G010
Figure 9. Two Tone IMD vs Amplitude
Figure 10. Two Tone IMD Spectral Plot
90
0
−20
P − Power − dBm
−30
fdata = 125 MSPS
fin = −30 MHz
0.5 MHz Complex
IF = 95 MHz
4L Interpolation
CMIX
PLL Off
fdata = 122.88 MSPS
Baseband Input
DVDD = 1.8 V
85
80
ACLR − dBc
−10
30
f − Frequency − MHz
−40
−50
−60
75
PLL Off
70
65
PLL On
−70
60
−80
55
−90
−100
85
50
90
95
100
105
f − Frequency − MHz
50
100
150
200
250
IF − Intermediate Frequency − MHz
G011
Figure 11. Two Tone IMD Spectral Plot
0
G012
Figure 12. WCDMA ACLR vs Intermediate Frequency
13
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Typical Characteristics (continued)
−10
−20
−30
−20
−30
−40
−50
P − Power − dBm
P − Power − dBm
−40
−10
Carrier Power: −7.99 dBm
ACLR (5 MHz): 81.24 dB
ACLR (10 MHz): 83.79 dB
fdata = 122.88 MSPS
IF = 30.72 MHz
4 Interpolation
−60
−70
−80
−90
−50
−60
−70
−80
−90
−100
−100
−110
−110
−120
−120
−130
18
23
28
33
38
Carrier Power: −7.99 dBm
ACLR (5 MHz): 75.8 dB
ACLR (10 MHz): 80.18 dB
fdata = 122.88 MSPS
IF = 30.72 MHz
4 Interpolation
−130
18
43
23
f − Frequency − MHz
28
33
38
43
f − Frequency − MHz
G013
G014
Figure 13. WCDMA TM1 : Single Carrier, PLL Off,
DVDD = 1.8 V
−20
−30
P − Power − dBm
−40
−50
−10
Carrier Power: −8.7 dBm
ACLR (5 MHz): 75.97 dB
ACLR (10 MHz): 77.47 dB
fdata = 122.88 MSPS
IF = 92.16 MHz
4 Interpolation
CMIX
−20
−30
−40
P − Power − dBm
−10
Figure 14. WCDMA TM1 : Single Carrier, PLL On,
DVDD = 1.8 V
−60
−70
−80
−90
−50
−60
−70
−80
−90
−100
−100
−110
−110
−120
−120
−130
80
85
90
95
100
105
f − Frequency − MHz
Carrier Power: −8.7 dBm
ACLR (5 MHz): 67.43 dB
ACLR (10 MHz): 73.21 dB
fdata = 122.88 MSPS
IF = 92.16 MHz
4 Interpolation
CMIX
−130
80
85
90
95
100
105
f − Frequency − MHz
G015
Figure 15. WCDMA TM1 : Single Carrier, PLL Off,
DVDD = 1.8 V
14
G016
Figure 16. WCDMA TM1 : Single Carrier, PLL On,
DVDD = 1.8 V
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Typical Characteristics (continued)
−20
−30
P − Power − dBm
−40
−50
−10
Carrier Power: −10.35 dBm
ACLR (5 MHz): 72.06 dB
ACLR (10 MHz): 73.21 dB
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−20
−30
−40
P − Power − dBm
−10
−60
−70
−80
−90
−50
−60
−70
−80
−90
−100
−100
−110
−110
−120
−120
−130
141
146
151
156
161
Carrier Power: −10.35 dBm
ACLR (5 MHz): 63.12 dB
ACLR (10 MHz): 69.17 dB
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−130
141
166
146
f − Frequency − MHz
151
156
161
166
f − Frequency − MHz
G017
G018
Figure 17. WCDMA TM1 : Single Carrier, PLL Off,
DVDD = 1.8 V
−20
−30
P − Power − dBm
−40
−50
−10
Carrier Power 1 (Ref): −15.78 dBm
ACLR (5 MHz): 68.19 dB
ACLR (10 MHz): 69.48 dB
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−20
−30
−40
P − Power − dBm
−10
Figure 18. WCDMA TM1 : Single Carrier, PLL On,
DVDD = 1.8 V
−60
−70
−80
−90
−50
−60
−70
−80
−90
−100
−100
−110
−110
−120
−120
−130
138
143
148
153
158
163
168
f − Frequency − MHz
Carrier Power 1 (Ref): −15.78 dBm
ACLR (5 MHz): 61.28 dB
ACLR (10 MHz): 64.61 dB
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−130
138
143
148
153
158
163
168
f − Frequency − MHz
G019
Figure 19. WCDMA TM1 : Two Carrier, PLL Off,
DVDD = 1.8 V
G020
Figure 20. WCDMA TM1 : Two Carrier, PLL On,
DVDD = 1.8 V
15
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Typical Characteristics (continued)
−20
−30
−40
−40
−50
−50
P − Power − dBm
P − Power − dBm
−30
−20
Carrier Power 1 (Ref): −17.41 dBm
ACLR (5 MHz): 69.09 dB
ACLR (10 MHz): 69.34 dB
−60
−70
−80
−90
−100
Carrier Power 1 (Ref): −17.42 dBm
ACLR (5 MHz): 64 dB
ACLR (10 MHz): 65.79 dB
−60
−70
−80
−90
−100
−110
−110
fdata = 122.88 MSPS
IF = 92.16 MHz
4 Interpolation
CMIX
−120
−130
72
77
82
87
92
97
fdata = 122.88 MSPS
IF = 92.16 MHz
4 Interpolation
CMIX
−120
102
107
−130
72
112
77
f − Frequency − MHz
82
87
92
97
102
107
112
f − Frequency − MHz
G021
G022
Figure 21. WCDMA TM1 : Four Carrier, PLL Off,
DVDD = 1.8 V
−20
−30
P − Power − dBm
−40
−50
−10
Carrier Power: −10.35 dBm
ACLR (5 MHz): 73.83 dB
ACLR (10 MHz): 75.39 dB
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−20
−30
−40
P − Power − dBm
−10
Figure 22. WCDMA TM1 : Four Carrier, PLL On,
DVDD = 1.8 V
−60
−70
−80
−90
−50
−60
−70
−80
−90
−100
−100
−110
−110
−120
−120
−130
141
146
151
156
161
166
f − Frequency − MHz
Carrier Power 1 (Ref): −15.77 dBm
ACLR (5 MHz): 69.74 dB
ACLR (10 MHz): 71.17 dB
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−130
138
143
148
153
158
163
168
f − Frequency − MHz
G023
Figure 23. WCDMA TM1 : Single Carrier, PLL Off,
DVDD = 2.1 V
16
G024
Figure 24. WCDMA TM1 : Two Carrier, PLL Off,
DVDD = 2.1 V
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Typical Characteristics (continued)
−20
−30
Carrier Power 1 (Ref): −19.88 dBm
ACLR (5 MHz): 66.6 dB
ACLR (10 MHz): 65.73 dB
−40
P − Power − dBm
−50
−60
−70
−80
−90
−100
−110
fdata = 122.88 MSPS
IF = 153.6 MHz
4 Interpolation
CMIX
−120
−130
133
138
143
148
153
158
163
168
173
f − Frequency − MHz
G025
Figure 25. WCDMA TM1 : Four Carrier, PLL Off,
DVDD = 2.1 V
Test Methodology
Typical ac specifications in external clock mode were characterized with the DAC5687EVM using the test
configuration shown in Figure 26. The DAC sample rate clock fDAC is generated by a HP8665B signal generator.
An Agilent 8133A pulse generator is used to divide fDAC for the data rate clock fDATA for the Agilent 16702A
pattern generator clock and provide adjustable skew to the DAC input clock. The 8133A fDAC output is set to 1
VPP, equivalent to 2-VPP differential at CLK2/CLK2C pins. Alternatively, the DAC5687 PLLLOCK output can be
used for the pattern generator clock.
The DAC5687 output is characterized with a Rohde & Schwarz FSQ8 spectrum analyzer. For WCDMA signal
characterization, it is important to use a spectrum analyzer with high IP3 and noise subtraction capability so that
the spectrum analyzer does not limit the ACPR measurement. For all specifications, both DACA and DACB are
measured and the lowest value used as the specification.
17
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Test Methodology (continued)
1.8 V/2.1 V
200 Ω
Mini Circuits
TCM4−1W
CLK2C
CLK1
CLK1C
PULSE
FREQ. = fdata
10 pF
DVDD
(Pin 56)
SLEEP
CLK2
DVDD
(Not Including Pin 56)
PULSE
FREQ. = fDAC
Ampl. = 1 VPP
1:4
PHSTR
0.01 µF
Agilent 8133A
Pulse Generator
PLLGND
Sinusoid
FREQ. = fDAC
PLLVDD
10 Ω
DGND
HP8665B
Synthesized
Signal
Generator
EXTLO
BIASJ
3.3 V
RBIAS
1 kΩ
PLLLOCK
Agilent 16702B
Mainframe System
With
16702A Pattern
Generator Card
16
Rohde & Schwarz
FSQ8
Spectrum
Analyzer
CEXTIO
0.1 µF
EXTIO
100 Ω
DA[15:0]
3.3 V
1:4
IOUTA1
IOUTA2
16
DB[15:0]
IOUTB1
IOUTB2
TxENABLE
RESETB
IOVDD
3.3 V
AGND
AVDD
LPF
Mini Circuits
T4−1
3.3 V
IOGND
CLKGND
CLKVDD
3.3 V
100 Ω
330 pF
3.3 V
3.3 V
0.033 µF
93.1 Ω
B0039-01
Figure 26. DAC5687 Test Configuration for External Clock Mode
PLL clock mode was characterized using the test configuration shown in Figure 27. The DAC data rate clock
fDATA is generated by a HP8665B signal generator. An Agilent 8133A pulse generator is used to generate a clock
fDATA for the Agilent 16702A pattern generator clock and provide adjustable skew to the DAC input clock. The
8133A fDAC output is set to 1 VPP, equivalent to 2-VPP differential at CLK1/CLK1C pins. Alternatively, the
DAC5687 PLLLOCK output can be used for the pattern generator clock.
18
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Test Methodology (continued)
1.8 V/2.1 V
3.3 V
200 Ω
Mini Circuits
TCM4−1W
CLK1C
CLK2
CLK2C
PULSE
FREQ. = fdata
10 pF
DVDD
(Pin 56)
SLEEP
CLK1
DVDD
(Not Including Pin 56)
PULSE
FREQ. = fdata
Ampl. = 1 VPP
1:4
PHSTR
0.01 µF
Agilent 8133A
Pulse Generator
PLLGND
Sinusoid
FREQ. = fdata
PLLVDD
10 Ω
DGND
HP8665B
Synthesized
Signal
Generator
EXTLO
BIASJ
3.3 V
RBIAS
1 kΩ
PLLLOCK
Agilent 16702B
Mainframe System
With
16702A Pattern
Generator Card
16
Rohde & Schwarz
FSQ8
Spectrum
Analyzer
CEXTIO
0.1 µF
EXTIO
100 Ω
DA[15:0]
3.3 V
1:4
IOUTA1
IOUTA2
16
DB[15:0]
IOUTB1
IOUTB2
IOVDD
3.3 V
AGND
AVDD
LPF
Mini Circuits
T4−1
3.3 V
IOGND
CLKGND
CLKVDD
TxENABLE
RESETB
100 Ω
330 pF
3.3 V
3.3 V
0.033 µF
93.1 Ω
B0039-02
Figure 27. DAC5687 Test Configuration for PLL Clock Mode
WCDMA Test Model 1 test vectors for the DAC5687 characterization were generated in accordance with the
3GPP Technical Specification . Chip rate data was generated using the Test Model 1 block in Agilent ADS. For
multicarrier signals, different random seeds and PN offsets were used for each carrier. A Matlab script performed
pulse shaping, interpolation to the DAC input data rate, frequency offsets, rounding and scaling. Each test vector
is 10 ms long, representing one frame. Special care is taken to assure that the end of file wraps smoothly to the
beginning of the file.
The cumulative complementary distribution function (CCDF) for the 1, 2, and 4 carrier test vectors is shown in
Figure 28. The test vectors are scaled such that the absolute maximum data point is 0.95 (-0.45 dB) of full scale.
No peak reduction is used.
19
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Cummulative Complementary Distribution Function
Test Methodology (continued)
100
10−2
2 Carriers
4 Carriers
1 Carrier
10−4
10−6
3
5
7
9
11
13
15
Peak-to-Average Ratio − dB
G041
Figure 28. WCDMA TM1 Cumulative Complementary Distribution Function for 1, 2, and 4 carriers
DETAILED DESCRIPTION
Modes of Operation
The DAC5687 has six digital signal processing blocks: FIR1 and FIR2 (interpolate by two digital filters), FMIX
(fine frequency mixer), QMC (quadrature modulation phase correction), FIR3 (interpolate by two digital filter) and
CMIX (coarse frequency mixer). The modes of operation, listed in Table 1, enable or bypass the blocks to
produce different results. The modes are selected by registers CONFIG1, CONFIG2, and CONFIG3 (0x02, 0x03,
and 0x04). Block diagrams for each mode (x2, x4, x4L, and x8) are shown in Figure 29 through Figure 32.
Table 1. DAC5687 Modes of Operation
MODE
FIR1
FIR2
FMIX
QMC
FULL BYPASS
–
–
–
X2
–
–
–
X2 FMIX
–
–
X2 QMC
–
X2 FMIX QMC
–
X2 CMIX
X2 FMIX CMIX
CMIX
–
–
–
–
ON
–
ON
–
ON
–
–
–
ON
ON
–
–
ON
ON
ON
–
–
–
–
–
ON
ON
–
–
ON
–
ON
ON
X2 QMC CMIX
–
–
–
ON (1)
ON
ON
X2 FMIX QMC CMIX
–
–
ON
ON (1)
ON
ON
ON
ON
–
–
–
–
FMIX (2)
ON
ON
ON
–
–
–
X4 QMC (2)
ON
ON
–
ON
–
–
X4 FMIX QMC
ON
ON
ON
ON
–
–
X4 CMIX
ON
ON
–
–
–
ON
X4
X4
(1)
(2)
20
FIR3
The QMC phase correction will be eliminated by the CMIX, so the QMC phase should be set to zero.
The QMC gain settings can still be used to adjust the signal path gain as needed.
fDAC limited to maximum clock rate for the NCO and QMC, (See the AC specs).
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Table 1. DAC5687 Modes of Operation (continued)
FIR1
FIR2
FMIX
QMC
FIR3
CMIX
X4L
MODE
ON
–
–
–
ON
–
X4L FMIX
ON
–
ON
–
ON
–
X4L QMC
ON
–
–
ON
ON
–
X4L FMIX QMC
ON
–
ON
ON
ON
–
X4L CMIX
ON
–
–
–
ON
ON
X4L FMIX CMIX
ON
–
ON
ON
ON
X4L QMC CMIX
ON
–
–
ON (2)
ON
ON
X4L FMIX QMC CMIX
ON
–
ON
ON (2)
ON
ON
X8
ON
ON
–
–
ON
–
X8 FMIX
ON
ON
ON
–
ON
–
X8 QMC
ON
ON
–
ON
ON
–
X8 FMIX QMC
ON
ON
ON
ON
ON
–
X8 CMIX
ON
ON
–
–
ON
ON
X8 FMIX CMIX
ON
ON
ON
–
ON
ON
X8 QMC CMIX
ON
ON
–
ON (3)
ON
ON
ON
ON (3)
ON
ON
X8 FMIX QMC CMIX
(3)
ON
ON
The QMC phase correction will be eliminated by the CMIX, so the QMC phase should be set to zero.
The QMC gain settings can still be used to adjust the signal path gain as needed.
A
Offset
DB[15:0]
FIR3
FIR4
16-bit DAC
x2
x
sin(x)
x
sin(x)
16-bit DAC
x2
cos
Coarse Mixer:
fs/2 or fs/4
Quadrature Mod
Correction (QMC)
Fine Mixer
Input Formater
DA[15:0]
A gain
sin
NCO
IOUTA1
IOUTA2
IOUTB1
IOUTB2
B
Offset
B gain
Figure 29. Block Diagram for X2 Mode
21
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
A
Offset
DB[15:0]
x2
x2
Coarse Mixer:
fs/2 or fs/4
x2
FIR4
Fine Mixer
Input Formater
DA[15:0]
FIR2
Quadrature Mod
Correction (QMC)
FIR1
x2
cos
IOUTA1
x
sin(x)
16-bit DAC
x
sin(x)
16-bit DAC
sin
NCO
A.
A gain
IOUTA2
IOUTB1
B
Offset
B gain
A
Offset
A gain
IOUTB2
FMIX or QMC block cannot be enabled with CMIX block.
Figure 30. Block Diagram for X4 Mode (A)
Quadrature Mod
Correction (QMC)
x2
Fine Mixer
Input Formater
DA[15:0]
DB[15:0]
x2
x2
x2
cos
FIR4
Coarse Mixer:
fs/2 or fs/4
FIR3
FIR1
16-bit DAC
x
sin(x)
16-bit DAC
sin
NCO
Figure 31. Block Diagram for X4L Mode
22
IOUTA1
x
sin(x)
IOUTA2
IOUTB1
IOUTB2
B
Offset
B gain
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
A
Offset A gain
FIR2
DB[15:0]
Quadrature Mod
Correction (QMC)
x2
x2
Fine Mixer
Input Formater
DA[15:0]
x2
x2
FIR3
FIR4
x2
x
sin(x)
16-bit DAC
x
sin(x)
16-bit DAC
Coarse Mixer:
fs/2 or fs/4
FIR1
x2
cos
IOUTA1
IOUTA2
IOUTB1
IOUTB2
sin
B
Offset B gain
NCO
Figure 32. Block Diagram for X8 Mode
Programming Registers
REGISTER MAP
Name
Address Default
Bit 7
(MSB)
Bit 6
sleep_daca
sleep_dacb
VERSION
0x00
0x01
CONFIG0
0x01
0x00
CONFIG1
0x02
0x00
qflag
CONFIG2
0x03
0x80
CONFIG3
0x04
SYNC_CNTL
SER_DATA_0
Bit 5
Bit 4
Bit 3
unused
hpla
hplb
pll_freq
pll_kv
interl
dual_clk
twos
nco
nco_gain
qmc
0x00
sif_4pin
dac_ser_dat
a
half_rate
0x05
0x00
sync_phstr
sync_nco
sync_cm
0x06
0x00
dac_data(7:0)
SER_DATA_1
0x07
0x00
dac_data(15:8)
factory use only
0x08
0x00
NCO_FREQ_0
0x09
0x00
freq(7:0)
NCO_FREQ_1
0x0A
0x00
freq(15:8)
pll_div(1:0)
Bit 2
rev_bbus
inv_plllock
fifo_bypass
fir_bypass
full_bypass
cm_mode(3:0)
unused
(LSB)
Bit 0
version(2:0)
interp(1:0)
rev_abus
Bit 1
invsinc
usb
counter_mode(2:0)
sync_fifo(2:0)
unused
unused
NCO_FREQ_2
0x0B
0x00
freq(23:16)
NCO_FREQ_3
0x0C
0x0C
freq(31:24)
NCO_PHASE_0
0x0D
0x00
phase(7:0)
NCO_PHASE_1
0x0E
0x00
phase(15:8)
DACA_OFFSET_0
0x0F
0x00
daca_offset(7:0)
DACB_OFFSET_0
0x10
0x00
DACA_OFFSET_1
0x11
0x00
daca_offset(12:8)
unused
unused
unused
DACB_OFFSET_1
0x12
0x00
dacb_offset(12:8)
unused
unused
unused
QMCA_GAIN_0
0x13
0x00
qmc_gain_a(7:0)
QMCB_GAIN_0
0x14
0x00
qmc_gain_b(7:0)
QMC_PHASE_0
0x15
0x00
QMC_PHASE_GAIN_1
0x16
0x00
DACA_GAIN_0
0x17
0x00
daca_gain(7:0)
DACB_GAIN_0
0x18
0x00
dacb_gain(7:0)
DACA_DACB_GAIN_1
0x19
0xFF
factory use only
0x1A
0x00
atest
0x1B
0x00
dacb_offset(7:0)
qmc_phase(7:0)
qmc_phase(9:8)
qmc_gain_a(10:8)
daca_gain(11:8)
atest
qmc_gain_b(10:8)
dacb_gain(11:8)
phstr_del(1:0)
unused
23
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
REGISTER MAP (continued)
Name
Address Default
DAC_TEST
0x1C
0x00
factory use only
0x1D
0x00
factory use only
0x1E
0x00
factory use only
0x1F
0x00
Bit 7
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
factory use only
(LSB)
Bit 0
phstr_clkdiv_sel
Register Name: VERSION — Address: 0x00, Default = 0x01
BIT 7
BIT 0
sleep_daca
sleep_dacb
hpla
hplb
unused
0
0
0
0
0
version(2:0)
0
1
1
sleep_daca: DAC A sleeps when set, operational when cleared.
sleep_dacb: DAC B sleeps when set, operational when cleared.
hpla:
A side first FIR filter in high-pass mode when set, low-pass mode when cleared.
hplb:
B side first FIR filter in high-pass mode when set, low-pass mode when cleared.
version(2:0): A hardwired register that contains the version of the chip. Read Only.
Register Name: CONFIG0 — Address: 0x01, Default = 0x00
BIT 7
BIT 0
pll_div(1:0)
0
0
pll_freq
pll_kv
0
0
interp(1:0)
0
0
inv_plllock
fifo_bypass
0
0
pll_div(1:0): PLL VCO divider; {00 = 1, 01 = 2, 10 = 4, 11 = 8}.
pll_freq:
PLL VCO center frequency; {0 = low center frequency, 1 = high center frequency}.
pll_kv:
PLL VCO gain; {0 = high gain, 1 = low gain}.
interp(1:0): FIR Interpolation; {00 = X2, 01 = X4, 10 = X4L, 11 = X8}. X4 uses lower power than x4L, but fDAC =
320 MHz max when NCO or QMC are used.
inv_plllock: Multi-function bit depending on clock mode.
fifo_bypass: When set, the internal 4-sample FIFO is disabled. When cleared, the FIFO is enabled.
Table 2. inv_plllock Bit Modes
24
PLLVDD
dual_clk
inv_pllock
fifo_bypass
DESCRIPTION
0V
0
0
1
Input data latched on PLLLOCK pin rising edges, FIFO disabled.
0V
0
1
1
Input data latched on PLLLOCK pin falling edges, FIFO disabled.
0V
0
0
0
Input data latched on PLLLOCK pin rising edges, FIFO enabled
and must be sync’d.
0V
0
1
0
Input data latched on PLLLOCK pin falling edges, FIFO enabled
and must be sync’d.
0V
1
0
1
Input data latched on CLK1/CLK1C differential input. Timing
between CLK1 and CLK2 rising edges must be tightly controlled
(500 ps max at 500-MHz CLK2). PLLLOCK output signal is
always low. The FIFO is always disabled in this mode.
0V
1
1
0
Input data latched on CLK1/CLK1C differential input. No phase
relationship required between CLK1 and CLK2. The FIFO is
employed to manage the internal handoff between the CLK1
input clock and the CLK2 derived output clock; the FIFO must
be sync’d. The PLLLOCK output signal reflects the internally
generated FIFO output clock.
0V
1
0
0
Not a valid setting. Do not use.
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Table 2. inv_plllock Bit Modes (continued)
PLLVDD
dual_clk
inv_pllock
fifo_bypass
DESCRIPTION
0V
1
1
1
Not a valid setting. Do not use.
3.3 V
X
X
1
Internal PLL enabled, CLK1/CLK1C input differential clock is
used to latch the input data. The FIFO is always disabled in this
mode.
3.3 V
X
X
0
Not a valid setting. Do not use.
Register Name: CONFIG1 — Address: 0x02, Default = 0x00
BIT 7
BIT 0
qflag
interl
dual_clk
twos
rev_abus
rev_bbus
fir_bypass
full_bypass
0
0
0
0
0
0
0
0
qflag:
When set, the QFLAG input pin operates as a B sample indicator when interleaved data is enabled.
When cleared, the TXENABLE rising determines the A/B timing relationship.
interl:
When set, interleaved input data mode is enabled; both A and B data streams are input at the
DA(15:0) input pins.
dual_clk:
Only used when the PLL is disabled. When set, two differential clocks are used to input the data to
the chip; CLK1/CLK1C is used to latch the input data into the chip and CLK2/CLK2C is used as the
DAC sample clock.
twos:
When set, input data is interpreted as 2’s complement. When cleared, input data is interpreted as
offset binary.
rev_abus:
When cleared, DA input data MSB to LSB order is DA(15) = MSB and DA(0) = LSB. When set, DA
input data MSB to LSB order is reversed, DA(15) = LSB and DA(0) = MSB.
rev_bbus:
When cleared, DB input data MSB to LSB order is DB(15) = MSB and DB(0) = LSB. When set, DB
input data MSB to LSB order is reversed, DB(15) = LSB and DB(0) = MSB.
fir_bypass: When set, all interpolation filters are bypassed (interp(1:0) setting has no effect). QMC and NCO
blocks are functional in this mode up to fdac = 250 MHz, limited by the input datarate.
full_bypass: When set, all filtering, QMC and NCO functions are bypassed.
Register Name: CONFIG2 — Address: 0x03, Default = 0x80
BIT 7
BIT 0
nco
nco_gain
qmc
1
0
0
cm_mode(3:0)
0
0
invsinc
0
nco:
When set, the NCO is enabled.
nco_gain:
When set, the data output of the NCO is increased by 2x.
qmc:
Quadrature modulator gain and phase correction is enabled when set.
0
0
cm_mode(3:0): Controls fDAC/2 or fDAC/4 mixer modes for the coarse mixer block.
Table 3. Coarse Mixer Sequences
cm_mode(3:0)
Mixing Mode
Sequence
00XX
No mixing
0100
fDAC/2
DAC A = {-A +A -A +A …}
DAC B = {-B +B -B +B …}
0101
fDAC/2
DAC A = {-A +A -A +A …}
DAC B = {+B -B +B -B …}
0110
fDAC/2
DAC A = {+A -A +A -A …}
DAC B = {-B +B -B +B …}
25
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Table 3. Coarse Mixer Sequences (continued)
invsinc:
cm_mode(3:0)
Mixing Mode
Sequence
0111
fDAC2
DAC A = {+A -A +A -A …}
DAC B = {+B -B +B -B …}
1000
fDAC/4
DAC A = {+A -B -A +B …}
DAC B = {+B +A -B -A …}
1001
fDAC/4
DAC A = {+A -B -A +B …}
DAC B = {-B -A +B +A …}
1010
fDAC/4
DAC A = {-A +B +A -B …}
DAC B = {+B +A -B -A …}
1011
fDAC/4
DAC A = {-A +B +A -B …}
DAC B = {-B -A +B +A …}
1100
-fDAC/4
DAC A = {+A +B -A -B …}
DAC B = {+B -A -B +A …}
1101
-fDAC/4
DAC A = {+A +B -A -B …}
DAC B = {-B +A +B -A …}
1110
-fDAC/4
DAC A = {-A -B +A +B …}
DAC B = {+B -A -B +A …}
1111
-fDAC/4
DAC A = {-A -B +A +B …}
DAC B = {-B +A +B -A …}
Enables the invsinc compensation filter when set.
Register Name: CONFIG3 — Address: 0x04, Default = 0x00
BIT 7
BIT 0
sif_4pin
dac_ser_data
half_rate
Unused
usb
0
0
0
0
0
sif_4pin:
counter_mode(2:0)
0
0
0
Four-pin serial interface mode is enabled when set, 3-pin mode when cleared.
dac_ser_data: When set, both DAC A and DAC B input data is replaced with fixed data loaded into the 16 bit
serial interface ser_data register.
half_rate:
Enables half-rate input mode. Input data for the DAC A data path is input to the chip at half speed
using both the DA(15:0) and DB(15:0) input pins.
usb:
When set, the data to DACB is inverted to generate upper side band output.
counter_mode(2:0): Controls the internal counter that can be used as the
{0XX = off; 100 = all 16b; 101 = 7b LSBs; 110 = 5b MIDs; 111 = 5b MSBs}
DAC
data
source.
Register Name: SYNC_CNTL — Address: 0x05, Default = 0x00
BIT 7
BIT 0
sync_phstr
sync_nco
sync_cm
0
0
0
sync_fifo(2:0)
0
0
unused
unused
0
0
0
sync_phstr: When set, the internal clock divider logic is initialized with a PHSTR pin low-to-high transition.
sync_nco:
When set, the NCO phase accumulator is cleared with a PHSTR low-to-high transition.
sync_cm:
When set, the coarse mixer is initialized with a PHSTR low-to-high transition.
sync_fifo(2:0): Sync source selection mode for the FIFO. When a low-to-high transition is detected on the
selected sync source, the FIFO input and output pointers are initialized.
26
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Table 4. Synchronization Source
sync_fifo (2:0)
Synchronization Source
000
txenable pin
001
phstr pin
010
qflag pin
011
db(15)
100
da(15) first transition (one shot)
101
Software sync using SIF write
110
Sync source disabled (always off)
111
Always on
Register Name: SER_DATA_0— Address: 0x06, Default = 0x00
BIT 7
BIT 0
dac_data(7:0)
0
0
0
0
0
0
0
0
dac_data(7:0): Lower 8 bits of DAC data input to the DACs when dac_ser_data is set.
Register Name: SER_DATA_1— Address: 0x07, Default = 0x00
BIT 7
BIT 0
dac_data(15:8)
0
0
0
0
0
0
0
0
dac_data(15:8): Upper 8 bits of DAC data input to the DACs when dac_ser_data is set.
Register Name: BYPASS_MASK_CNTL— Address: 0x08, Default = 0x00
BIT 7
BIT 0
fast__latch
bp_ invsinc
bp_fir3
bp_qmc
bp_fmix
bp_fir2
bp_fir1
nco_only
0
0
0
0
0
0
0
0
These modes are for factory use only – leave as default.
Register Name: NCO_FREQ_0— Address: 0x09, Default = 0x00
BIT 7
BIT 0
freq(7:0)
0
freq(7:0):
0
0
0
0
0
0
0
Bits 7:0 of the NCO frequency word.
Register Name: NCO_FREQ_1— Address: 0x0A, Default = 0x00
BIT 7
BIT 0
freq(15:8)
0
freq(15:8):
0
0
0
0
0
0
0
Bits 15:8 of the NCO frequency word.
Register Name: NCO_FREQ_2— Address: 0x0C, Default = 0x40
BIT 7
BIT 0
freq(23:16)
0
0
0
0
0
0
0
0
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
freq(23:16): Bits 23:16 of the NCO frequency word.
Register Name: NCO_FREQ_3— Address: 0x0B, Default = 0x00
BIT 7
BIT 0
freq(31:24)
0
1
0
0
0
0
0
0
freq(31:24): Bits 31:24 of the NCO frequency word.
Register Name: NCO_PHASE_0— Address: 0x0D, Default = 0x00
BIT 7
BIT 0
Phase(7:0)
0
0
0
0
0
0
0
0
phase(7:0): Bits 7:0 of the NCO phase offset word.
Register Name: NCO_PHASE_1— Address: 0x0E, Default = 0x00
BIT 7
BIT 0
Phase(15:8)
0
0
0
0
0
0
0
0
phase(15:8): Bits 15:8 of the NCO phase offset word.
Register Name: DACA_OFFSET_0— Address: 0x0F, Default = 0x00
BIT 7
BIT 0
daca_offset(7:0)
0
0
0
0
daca_offset(7:0): Bits 7:0 of the DAC A offset word.
28
0
0
0
0
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Register Name: DACB_OFFSET_0— Address: 0x10, Default = 0x00
BIT 7
BIT 0
dacb_offset(7:0)
0
0
0
0
0
0
0
0
dacb_offset(7:0): Bits 7:0 of the DAC B offset word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: DACA_OFFSET_1— Address: 0x11, Default = 0x00
BIT 7
BIT 0
daca_offset(12:8)
0
0
0
0
unused
unused
unused
0
0
0
0
daca_offset(12:8): Bits 12:8 of the DAC A offset word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: DACB_OFFSET_1— Address: 0x12, Default = 0x00
BIT 7
BIT 0
dacb_offset(12:8)
0
0
0
0
unused
unused
unused
0
0
0
0
dacb_offset(12:8): Bits 12:8 of the DAC B offset word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: QMCA_GAIN_0— Address: 0x13, Default = 0x00
BIT 7
BIT 0
qmc_gain_a(7:0)
0
0
0
0
0
0
0
0
qmc_gain_a(7:0): Bits 7:0 of the QMC A path gain word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: QMCB_GAIN_0— Address: 0x14, Default = 0x00
BIT 7
BIT 0
qmc_gain_b(7:0)
0
0
0
0
0
0
0
0
qmc_gain_b(7:0): Bits 7:0 of the QMC B path gain word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: QMC_PHASE_0— Address: 0x15, Default = 0x00
BIT 7
BIT 0
qmc_phase(7:0)
0
0
0
0
0
0
0
0
qmc_phase(7:0): Bits 7:0 of the QMC phase word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: QMC_PHASE_GAIN_1— Address: 0x16, Default = 0x00
BIT 7
BIT 0
qmc_phase(9:8)
0
qmc_gain_a(10:8)
0
0
0
qmc_gain_b(10:8)
0
0
0
0
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
qmc_phase(9:8): Bits 9:8 of the QMC phase word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
qmc_gain_a(10:8) : Bits 10:8 of the QMC A path gain word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
qmc_gain_b(10:8): Bits 10:8 of the QMC B path gain word. Updates to this register do not take effect until
DACA_OFFSET_0 has been written.
Register Name: DACA_GAIN_0— Address: 0x17, Default = 0x00
BIT 7
BIT 0
daca_gain(7:0)
0
0
0
0
0
0
0
0
daca_gain(7:0): Bits 7:0 of the DAC A gain adjustment word.
Register Name: DACB_GAIN_0— Address: 0x18, Default = 0x00
BIT 7
BIT 0
dacb_gain(7:0)
0
0
0
0
0
0
0
0
dacb_gain(7:0): Bits 7:0 of the DAC B gain adjustment word.
Register Name: DACA_DACB_GAIN_1— Address: 0x19, Default = 0xFF
BIT 7
BIT 0
daca_gain(11:8)
1
1
dacb_gain(11:8)
1
1
1
1
1
1
daca_gain(11:8): Four MSBs of gain control for DACA.
dacb_gain(11:8): Bits 11:8 of the DAC B gain word. Four MSBs of gain control for DACB.
Register Name: DAC_CLK_CNTL— Address: 0x1A, Default = 0x00
BIT 7
BIT 0
factory use only
0
0
0
0
0
0
0
0
Reserved for factory use only.
Register Name: ATEST— Address: 0x1B, Default = 0x00
BIT 7
BIT 0
atest(4:0)
0
atest:
30
0
0
phstr_del(1:0)
0
0
0
unused
0
0
Can be used to enable clock output at the PLLLOCK pin according to Table 5. Pin EXTLO must be
open when atest (4:0) is not equal to 00000.
DAC5687
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Table 5.
atest(4:0)
PLLLOCK Output Signal
PLL Enabled (PLLVDD = 3.3 V)
PLL Disabled (PLLVDD = 0 V)
11101
fDAC
Normal operation
11110
fDAC divided by 2
Normal operation
11111
fDAC divided by 4
Normal operation
All others
phstr_del:
Normal operation
Adjusts the initial phase of the fs/2 and fs/4 blocks cmix block after PHSTR.
Register Name: DAC_TEST— Address: 0x1C, Default = 0x00
BIT 7
BIT 0
Factory Use Only
0
0
0
0
phstr_clkdiv_sel
0
0
0
0
phstr_clkdiv_sel: Selects the clock used to latch the PHSTR input when restarting the internal dividers. When
set, the full DAC sample rate CLK2 signal latches PHSTR and when cleared, the divided down
input clock signal latches PHSTR.
Address: 0x1D, 0x1E, and 0x1F – Reserved
Writes have no effect and reads will be 0x00.
Serial Interface
The serial port of the DAC5687 is a flexible serial interface which communicates with industry standard
microprocessors and microcontrollers. The interface provides read/write access to all registers used to define the
operating modes of the DAC5687. It is compatible with most synchronous transfer formats and can be configured
as a 3- or 4-pin interface by sif4 in register config_msb. In both configurations, SCLK is the serial interface
input clock and SDENB is serial interface enable. For 3-pin configuration, SDIO is a bidirectional pin for both
data in and data out. For 4-pin configuration, SDIO is data in only and SDO is data out only.
Each read/write operation is framed by signal SDENB (serial data enable bar) asserted low for 2 to 5 bytes,
depending on the data length to be transferred (1 – 4 bytes). The first frame byte is the instruction cycle which
identifies the following data transfer cycle as read or write, how many bytes to transfer, and what address to
transfer the data. Table 6 indicates the function of each bit in the instruction cycle and is followed by a detailed
description of each bit. Frame bytes 2 to 5 comprise the data transfer cycle.
Table 6. Instruction Byte of the Serial Interface
MSB
LSB
Bit
7
6
5
4
3
2
1
0
Description
R/W
N1
N0
A4
A3
A2
A1
A0
R/W
Identifies the following data transfer cycle as a read or write operation. A high indicates a read
operation from the DAC5687 and a low indicates a write operation to the DAC5687.
[N1 : N0]
Identifies the number of data bytes to be transferred per Table 7. Data is transferred MSB first.
Table 7. Number of Transferred Bytes Within One
Communication Frame
N1
N0
Description
0
0
Transfer 1 Byte
0
1
Transfer 2 Bytes
1
0
Transfer 3 Bytes
1
1
Transfer 4 Bytes
31
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[A4 : A3 : A2 : A1 : A0] Identifies the address of the register to be accessed during the read or write operation.
For multi-byte transfers, this address is the starting address. Note that the address is written to the
DAC5687 MSB first.
Figure 33 shows the serial interface timing diagram for a DAC5687 write operation. SCLK is the serial interface
clock input to the DAC5687. Serial data enable SDENB is an active low input to the DAC5687. SDIO is serial
data in. Input data to the DAC5687 is clocked on the rising edges of SCLK.
Instruction Cycle
SDENB
Data Transfer Cycle(s)
SCLK
SDIO
R/W N1 N0 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0
ts(SDENB)
t(SCLK)
SDENB
SCLK
SDIO
ts(SDIO)
th(SDIO)
t(SCLKL)
t(SCLKH)
Figure 33. Serial Interface Write Timing Diagram
Figure 34 shows the serial interface timing diagram for a DAC5687 read operation. SCLK is the serial interface
clock input to the DAC5687. Serial data enable SDENB is an active low input to the DAC5687. SDIO is serial
data in during the instruction cycle. In 3-pin configuration, SDIO is data out from the DAC5687 during the data
transfer cycle(s), while SDO is in a high-impedance state. In 4-pin configuration, SDO is data out from the
DAC5687 during the data transfer cycle(s). At the end of the data transfer, SDO outputs low on the final falling
edge of SCLK until the rising edge of SDENB when it will 3-state.
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Data Transfer Cycle(s)
Instruction Cycle
SDENB
SCLK
SDIO
R/W N1 N0
A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 0
D7 D6 D5 D4 D3 D2 D1 D0 0
SDO
4-Pin Configuration
Output
3-Pin Configuration
Output
SDENB
SCLK
SDIO
SDO
Data n
Data n−1
td(DATA)
Figure 34. Serial Interface Read Timing Diagram
FIR Filters
Figure 35 shows the magnitude spectrum response for the identical 51-tap FIR1 and FIR3 filters. The transition
band is from 0.4 to 0.6 x FIN (the input data rate for the FIR filter) with < 0.002-dB pass-band ripple and > 80-dB
stop-band attenuation. Figure 36 shows the region from 0.35 to 0.45 x FIN– Up to 0.44 x FIN there is less than
0.5-dB attenuation.
Figure 37 shows the magnitude spectrum response for the 19-tap FIR2 filter. The transition band is from 0.25 to
0.75x FIN (the input data rate for the FIR filter) with < 0.002-dB pass-band ripple and > 80-dB stop-band
attenuation.
The DAC5687 also has an inverse Sinc filter (FIR4) that runs at the DAC update rate (fDAC) that can be used to
flatten the frequency response of the sample and hold output. The DAC sample and hold output set the output
current and holds it constant for one DAC clock cycle until the next sample, resulting in the well known Sin(x)/x
or Sinc(x) frequency response shown in Figure 38 (black solid line). The inverse sinc filter response (Figure 38,
blue dotted line) has the opposite frequency response between 0 to 0.4 x fDAC, resulting in the combined
response (Figure 38, red dashed line). Between 0 to 0.4 x fDAC, the inverse sin filter compensates the sample
and hold rolloff with less than < 0.03-dB error.
The inverse sine filter has a gain > 1 at all frequencies. Therefore, the signal input to FIR4 must be reduced from
full scale to prevent saturation in the filter. The amount of backoff required depends on the signal frequency, and
is set such that at the signal frequencies the combination of the input signal and filter response is less than 1 (0
dB). For example, if the signal input to FIR4 is at 0.25 × fDAC, the response of FIR4 is 0.9 dB, and the signal will
need to be backed off from full scale by 0.9 dB. The gain function in the QMC block can be used to set reduce
amplitude of the input signal. The advantage of FIR4 having a positive gain at all frequencies is that the user is
then able to optimized backoff of the signal based on the signal frequency.
The filter taps for all digital filters are listed in Table 8.
Note that the loss of signal amplitude may result in lower SNR due to decrease in signal amplitude.
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Figure 35. Magnitude Spectrum for FIR1 and FIR3
Figure 36. FIR1 and FIR3 Transition Band
4
3
2
dB
1
0
−1
Sin(x)/x effect
FIR4 response
Corrected spectrum
−2
−3
−4
0
0.1
Figure 37. Magnitude Spectrum for FIR2
0.2
0.3
Fout/Fdac
0.5
Figure 38. Magnitude Spectrum for Inverse Sinc Filter
FIR4 (Versions 1 and 2)
Table 8. Digital Filter Taps
FIR1 and FIR3
34
0.4
FIR2
FIR4 (Invsinc)
Tap
Coeff
Tap
Coeff
Tap
Coeff
1, 51
8
1, 19
9
1, 9
1
2, 50
0
2, 18
0
2, 8
–4
3, 49
–24
3, 17
–58
3, 7
13
4, 48
0
4, 16
0
4, 6
–50
5, 47
58
5, 15
214
5
592
6, 46
0
6, 14
0
7, 45
–120
7, 13
–638
8, 44
0
8, 12
0
9, 43
221
9, 11
2521
10, 42
0
10
4096
11, 41
–380
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Table 8. Digital Filter Taps (continued)
FIR1 and FIR3
FIR2
Tap
Coeff
12, 40
0
13, 39
619
14, 38
0
15, 37
–971
16, 36
0
17, 35
1490
18, 34
0
19, 33
–2288
20, 32
0
21, 31
3649
22, 30
0
23, 29
–6628
24, 28
0
25, 27
20750
26
32768
Tap
FIR4 (Invsinc)
Coeff
Tap
Coeff
Dual Channel Real Upconversion
The DAC5687 can be used in a dual channel mode with real upconversion by mixing with a 1, -1, … sequence in
the signal chain to invert the spectrum. This mixing mode maintains isolation of the A and B channels. There are
two points of mixing: in X4L mode, the FIR1 output is inverted (high-pass mode) by setting registers hpla and
hplb to 1 and the FIR3 output is inverted by setting CMIX to fDAC/2. In X8 mode, the output of FIR1 is inverted by
setting hpla and hplb to 1 and the FIR3 output is inverted by setting CMIX to fDAC/2. In X2 and X4 modes, the
output of FIR3 is inverted by setting CMIX to fDAC/2.
The wide bandwidth of FIR3 (40% passband) in X4L mode provides options for setting four different frequency
ranges, listed in Table 9. For example, with fDATA = 125 MSPS (fDAC = 500 MSPS), setting FIR1/FIR3 to High
Pass/High Pass respectively will upconvert a signal between 25 and 50 MHz to 150 to 175 MHz. With the High
Pass/Low Pass and Low Pass/High Pass setting the upconvertered signal will be spectrally inverted.
Table 9. X4L Mode High-Pass/Low-Pass Options
FIR1
FIR3
Input Frequency
Output Frequency
Bandwidth
Inverted?
Low Pass
Low Pass
0 - 0.4 x fDATA
0 - 0.4 x
fDATA
0.4 x fDATA
No
High Pass
Low Pass
0.2 to 0.4 x fDATA
0.6 - 0.8 x
fDATA
0.2 x fDATA
Yes
High Pass
High Pass
0.2 to 0.4 x fDATA
1.2 - 1.4x
fDATA
0.2 x fDATA
No
Low Pass
High Pass
0 - 0.4 x fDATA
1.6 - 2x
fDATA
0.4 x fDATA
Yes
Limitations on Signal BW and Final Output Frequency in X4L and X8 Modes
For very wide bandwidth signals, the FIR3 pass-band (0 – 0.4 x FDAC/2) can limit the range of the final output
frequency. For example in X4L FMIX CMIX mode (4x interpolation with FMIX after FIR1), at the maximum input
data rate FIN = 125 MSPS the input signal can be ±50 MHz before running into the transition band of FIR1. After
2x interpolation, FIR3 limits the signal to ±100 MHz (0.4 x 250 MHz). Therefore, at the maximum signal
bandwidth, FMIX can mix up to 50 MHz and still fall within the passband of FIR3. This results in gaps in the final
output frequency between FMIX alone (0 MHz to 50 MHz) and FMIX + CMIX with fDAC/4 (75 MHz to 175 MHz)
and FMIX + fDAC/2 (200 MHz to 250 MHz).
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In practice, it may be possible to extend the signal into the FIR3 transition band. Referring to Figure 36 in the
Digital Filter section above, if 0.5 dB of attenuation at the edge of the signal can be tolerated, then the signal can
be extended up to 0.44 x FIN. This would extend the range of FMIX in the example to 60 MHz.
Fine Mixer (FMIX)
The fine mixer block FMIX uses a numerically controlled oscillator (NCO) with a 32-bit frequency register
freq(31:0) and a 16-bit phase register phase(15:0) to provide sin and cos for mixing. The NCO tuning frequency
is programmed in registers 0x09 through 0x0C. Phase offset is programmed in registers 0xD and 0xE. A
block-diagram of the NCO is shown in Figure 39.
32
16
32
Frequency
Register
32
Σ
Accumulator
32
16
16
Σ
sin
Look-Up
Table
16
cos
CLK RESET
16
fDAC
PHSTR
Phase
Register
B0026-01
Figure 39. Block-Diagram of the NCO
Synchronization of the NCO occurs by resetting the NCO accumulator to zero with assertion of PHSTR. See the
Fine Mixer Synchronization section below. Frequency word freq in the frequency register is added to the
accumulator every clock cycle. The output frequency of the NCO is
(freq 2 32) ƒ
freq ƒ
NCO_CLK
NCO_CLK
31
ƒ
for
freq
2
for freq 2 31
ƒ
NCO
NCO
2 32
2 32
where fNCO_CLK is the clock frequency of the NCO circuit. In X4 mode, the NCO clock frequency is the same as
the DAC sample rate fDAC. The maximum clock frequency the NCO can operate at is 320 MHz – in X4 FMIX
mode, where FMIX operates at the DAC update rate, the DAC updated rate will be limited to 320 MSPS. In X2,
X4L and X8 modes, the NCO circuit is followed by a further 2x interpolation and so fNCO_CLK = fDAC/2 and
operates at fDAC = 500 MHz.
Treating channels A and B as a complex vector I + I x Q where I(t) = A(t) and Q(t) = B(t), the output of FMIX
IOUT(t) and QOUT(t) is
IOUT(t) = (IIN(t)cos(2πfNCOt + δ) – QIN(t)sin(2πfNCOt + δ)) x 2(NCO_GAIN – 1)
QOUT(t) = (IIN(t)sin(2πfNCOt + δ) + QIN(t)cos(2πfNCOt + δ)) x 2(NCO_GAIN – 1)
Where t is the time since the last resetting of the NCO accumulator, δ is the initial accumulator value and
NCO_GAIN, bit 6 in register CONFIG2, is either 0 or 1. δ is given by
δ = 2π x phase/216.
The maximum output amplitude of FMIX occurs if IIN(t) and QIN(t) are simultaneously full scale amplitude and the
sine and cosine arguments 2πfNCOt + δ = (2N-1) x π/4 (N = 1, 2, ...). With NCO_GAIN = 0, the gain through FMIX
is sqrt(2)/2 or – 3 dB. This loss in signal power is in most cases undesirable, and it is recommended that the gain
function of the QMC block be used to increase the signal by 3 dB to 0 dBFS by setting qmca_gain and
qmcb_gain each to 1446 (decimal).
With NCO_GAIN = 1, the gain through FMIX is sqrt(2) or + 3 dB, which can cause clipping of the signal if IIN(t)
and QIN(t) are simultaneously near full scale amplitude and should therefore be used with caution.
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Coarse Mixer (CMIX)
The coarse mixer block provides mixing capability at the DAC output rate with fixed frequencies of FS/2 or FS/4.
The coarse mixer output phase sequence is selected by the cm_mode(3:0) bits in register CONFIG2 and is
shown in Table 10.
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Table 10. Coarse Mixer Sequences
cm_mode(3:0)
Mixing Mode
Sequence
00XX
No mixing
0100
fDAC/2
DAC A = {-A +A -A +A …}
DAC B = {-B +B -B +B …}
0101
fDAC/2
DAC A = {-A +A -A +A …}
DAC B = {+B -B +B -B …}
0110
fDAC/2
DAC A = {+A -A +A -A …}
DAC B = {-B +B -B +B …}
0111
fDAC/2
DAC A = {+A -A +A -A …}
DAC B = {+B -B +B -B …}
1000
fDAC/4
DAC A = {+A -B -A +B …}
DAC B = {+B +A -B -A …}
1001
fDAC/4
DAC A = {+A -B -A +B …}
DAC B = {-B -A +B +A …}
1010
fDAC/4
DAC A = {-A +B +A -B …}
DAC B = {+B +A -B -A …}
1011
fDAC/4
DAC A = {-A +B +A -B …}
DAC B = {-B -A +B +A …}
1100
-fDAC/4
DAC A = {+A +B -A -B …}
DAC B = {+B -A -B +A …}
1101
-fDAC/4
DAC A = {+A +B -A -B …}
DAC B = {-B +A +B -A …}
1110
-fDAC/4
DAC A = {-A -B +A +B …}
DAC B = {+B -A -B +A …}
1111
-fDAC/4
DAC A = {-A -B +A +B …}
DAC B = {-B +A +B -A …}
The output of CMIX is complex. For a real output, either DACA or DACB can be used and the other DAC slept,
the difference being the phase sequence.
Quadrature Modulator Correction (QMC)
The quadrature modulator correction (QMC) block provides a means for changing the phase balance of the
complex signal to compensate for I and Q imbalance present in an analog quadrature modulator. The QMC block
is limited in operation to a clock rate of 320 MSPS.
The block diagram for the QMC block is shown in Figure 40. The QMC block contains three programmable
parameters. Registers qma_gain and qmb_gain control the I and Q path gains and are 11 bit values with a
range of 0 to approximately 2. Note that the I and Q gain can also be controlled by setting the DAC full-scale
output current (see below). Register qm_phase controls the phase imbalance between I and Q and is a 10-bit
value with a range of –1/2 to approximately ½.
LO feedthrough can be minimized by adjusting the DAC offset feature described below.
An example of sideband optimization using the QMC block and gain adjustment is shown in Figure 41. The QMC
phase adjustment in combination with the DAC gain adjustment can reduce the unwanted sideband signal from
~40 dBc to > 65 dBc.
Note that mixing in the CMIX block after the QMC correction will destroy the I and Q phase compensation
information from the QMC block.
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qma_gain/210
{0, 1/210 , …, 2 −1/210 }
11
I(t)
Σ
X
X
Q(t)
10
qm_phase/210
{−1/2, −1/2 + 1/210, … , 1/2 −1/210}
X
11
qmb_gain/210
{0, 1/2 10 , …, 2 −1/210 }
Figure 40. QMC Block Diagram
L
O
L
O
sideband
sideband
Uncorrected
Corrected
Figure 41. Example of Sideband Optimization Using QMC Phase and Gain Adjustments
DAC Offset Control
Registers qma_offset and qmb_offset control the I and Q path offsets and are 13-bit values with a range of
–4096 to 4095. The DAC offset value adds a digital offset to the digital data before digital-to-analog conversion.
The qma_gain and qmb_gain registers can be used to backoff the signal before the offset to prevent saturation
when the offset value is added to the digital signal.
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qma_offset
{−4096, −4095, … , 4095 }
13
I
Σ
Q
Σ
13
qmb_offset
{−4096, −4095, … , 4095 }
Figure 42. DAC Offset Block
Analog DAC Gain
The full-scale DAC output current can be set by programming the daca_gain and dacb_gain registers. The DAC
gain value controls the full-scale output current.
16 V
I
fullscale
R
extio
biasj
(GAINCODE 1)
1 FINEGAIN
16
3072
where GAINCODE = daca_gain[11:8] or dacb_gain[11:8] is the coarse gain setting ( 0 to 15) and FINEGAIN =
daca_gain[7:0] or dacb_gain[7:0] (-128 to 127) is the fine gain setting.
Clock Modes
In the DAC5687, the internal clocks (1x, 2x, 4x, and 8x as needed) for the logic, FIR interpolation filters, and
DAC are derived from a clock at either the input data rate using an internal PLL (PLL clock mode) or DAC output
sample rate (external clock mode). Power for the internal PLL blocks (PLLVDD and PLLGND) are separate from
the other clock generation blocks power (CLKVDD and CLKGND), thus minimizing phase noise within the PLL.
The DAC5687 has three clock modes for generating the internal clocks (1x, 2x, 4x, and 8x as needed) for the
logic, FIR interpolation filters, and DACs. The clock mode is set using the PLLVDD pin and dual_clk in register
CONFIG1.
1. PLLVDD = 0 V and dual_clk = 0: EXTERNAL CLOCK MODE
In EXTERNAL CLOCK MODE, the user provides a clock signal at the DAC output sample rate through
CLK2/CLK2C. CLK1/CLK1C and the internal PLL are not used. LPF and CLK1/CLK1C pins can be left
unconnected. The input data rate clock and interpolation rate are selected by the bits interp(1:0) in register
CONFIG0 and is output through the PLLLOCK pin. The PLLLOCK clock can be used to drive the input data
source (such as digital upconverter) that sends the data to the DAC. Note that the PLLLOCK delay relative to the
input CLK2 rising edge (td(PLLLOCK)) in Figure 43 and Figure 44) increases with increasing loads. The input data is
latched on either the rising (inv_plllock = 0) or falling edge (inv_plllock = 1) of PLLLOCK, which is sensed
internally at the output pin.
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PLLLOCK
td(PLLLOCK)
CLK2
th(DATA)
ts(DATA)
DA[15:0]
A0
A1
A2
A3
AN
AN+1
DB[15:0]
B0
B1
B2
B3
BN
BN+1
Figure 43. Dual Bus Mode Timing Diagram for External Clock Mode (PLLLOCK Rising Edge)
PLLLOCK
td(PLLLOCK)
CLK2
th(DATA)
ts(DATA)
DA[15:0]
A0
A1
A2
A3
AN
AN+1
DB[15:0]
B0
B1
B2
B3
BN
BN+1
Figure 44. Dual Bus Mode Timing Diagram for External Clock Mode (PLLLOCK Falling Edge)
2. PLLVDD = 3.3 V (dual_clk can be 0 or 1 and is ignored): PLL CLOCK MODE
In PLL CLOCK MODE, you drive the DAC at the input sample rate (unless the data is mux’d) through
CLK1/CLK1C. CLK2/CLK2C is not used. In this case, there is no phase ambiguity on the clock. The DAC
generates the higher speed DAC sample rate clock using an internal PLL/VCO. In PLL clock mode, the user
provides a differential external reference clock on CLK1/CLK1C.
A type four phase-frequency detector (PFD) in the internal PLL compares this reference clock to a feedback
clock and drives the PLL to maintain synchronization between the two clocks. The feedback clock is generated
by dividing the VCO output by 1x, 2x, 4x, or 8x as selected by the prescaler (div[1:0]). The output of the
prescaler is the DAC sample rate clock and is divided down to generate clocks at ÷ 2, ÷4, and ÷ 8. The feedback
clock is selected by the registers sel(1:0), which is fed back to the PFD for synchronization to the input clock.
The feedback clock is also used for the data input rate, so the ratio of DAC output clock to feedback clock sets
the interpolation rate of the DAC5687. The PLLLOCK pin is an output indicating when the PLL has achieved
lock. An external RC low-pass PLL filter is provided by the user at pin LPF. See the Low-Pass Filter section for
filter setting calculations. This is the only mode where the LPF filter applies.
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CLK2
th(DATA)
ts(DATA)
DA[15:0]
A0
A1
A2
A3
AN
AN+1
DB[15:0]
B0
B1
B2
B3
BN
BN+1
Figure 45. Dual Bus Mode Timing Diagram (PLL Mode)
DIV[1:0]
LPF
CLK1
CLK1C
CLK2
CLK2C
CLK
Buffer
PFD
Charge
Pump
VCO
/1
00
/2
01
/4
10
/8
11
PLLVDD
1
Fdac
CLK
Buffer
0
00
1 ´2
01
0 ´1
10
11
Data
Latch
PLLLOCK
PLLVDD
Fdac/2 ´2
Fdac/4 ´4
/2
0
1
/2
Fdac/4 ´4L
/2
Fdac/8 ´8
Data
Lock
D[15:0]
INTERL
SEL[1:0]
B0053-02
Figure 46. Clock Generation Architecture in PLL Mode
Power for the internal PLL blocks (PLLVDD and PLLGND) are separate from the other clock generation blocks
power (CLKVDD and CLKGND), thus minimizing PLL phase noise.
3) PLLVDD = 0 V and dual_clk = 1: DUAL CLOCK MODE
In DUAL CLOCK MODE, the DAC is driven at the DAC sample rate through CLK2/CLK2C and the input data
rate through CLK1/CLK1C. There are two options in dual clock mode: with FIFO (inv_plllock set) and without
FIFO (inv_plllock clear). If the FIFO is not used, the CLK1/CLK1C input is used to set the phase of the internal
clock divider. In this case, the edges of CLK1 and CLK2 must be aligned to within ±t_align (Figure 47), defined as
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f
align
1
2F
0.5 ns
CLK2
where fCLK2 is the clock frequency at CLK2. For example, talign = 0.5 ns at fCLK2 = 500 MHz and 1.5 ns at fCLK2 =
250 MHz.
If the FIFO is enabled (inv_plllock set) in dual clock mode, then CLK1 is only used as an input latch (Figure 48)
and is independent from the internal divided clock generated from CLK2/CLK2C and there is no alignment
specification. However, the FIFO needs to be synchronized by one of the methods listed in SYNC_CNTL register
and the latency of the DAC can be up to one clock cycle different depending on the phase relationship between
CLK1 and the internally divided clock.
CLK2
CLK1
∆ < talign
DA[15:0]
DB[15:0]
th
ts
Figure 47. Dual Clock Mode Without FIFO
CLK1
DA[15:0]
DB[15:0]
th
ts
Figure 48. Dual Clock Mode With FIFO
The CDC7005 from Texas Instruments is recommended for providing phase aligned clocks at different
frequencies for this application.
Input FIFO
In DAC clock mode, where the DAC5687 is clocked at the DAC update rate, the DAC5687 has an optional input
FIFO that allows latching of DA[15:0], DB[15:0] and PHSTR based on a user provided CLK1/CLK1C input or the
input data rate clock provided to the PLLLOCK pin. The FIFO can be bypassed by setting register fifo_bypass in
CONFIG0 to 1.
The input interface FIFO incorporates a four sample register file, an input pointer, and an output pointer.
Initialization of the FIFO pointers can be programmed to one of seven different sources.
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DA(15:0),
DB(15:0),
PHSTR
q_a
0
1
q_in
D Q
D Q
S
in_sel_a
0
1
q_b
D Q
MUX
S
in_sel_b
1
0
D Q
q_out resynchonized
da(15:0), db(15:0)
and phstr
S
0
1
q_c
D Q
fifo_bypass
S
in_sel_c
0
1
q_d
D Q
sel_q_a
sel_q_b
S
in_sel_d
input
pointer
generation
MUX
sync
sel_q_c
sel_q_d
output
pointer
generation
PLLLOCK
PLL VCO
clk_out
clk_in
clock
generator
CLK2
CLK1
CLK1C
{PLLVDD,
inv_plllock,, dual_clk}
sync source
{TXENABLE, PHSTR, QFLAG, DB(15),
DA(15) oneshot
oneshot, SIF write, always off}
CLK2C
Figure 49. DAC5687 Input FIFO Logic
Initialization of the FIFO block involves selecting and asserting a synchronization source. Initialization causes the
input and output pointers to be forced to an offset of 2; the input pointer will be forced to the in_sel_a state while
the output pointer will be forced to the sel_q_c state. This initialization of the input and output pointers can cause
discontinuities in a data stream and should therefore be handled at startup.
Table 11. Synchronization Source Selection
44
sync_fifo (2:0)
Synchronization Source
000
txenable pin
001
phstr pin
010
qflag pin
011
db(15)
100
da(15) first transition (one shot)
101
sync now with SIF write (always on)
110
sync source disabled (always off)
111
sync now with SIF write (always on)
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All possible sync sources are registered with clk_in and then passed through a synchronous rising edge detector.
D Q
TXENABLE
MUX
000
001
D Q
PHSTR
010
resync_fifo_in
011
1
101
0
110
1
111
D Q
D Q
resync_fifo_out
D Q
D Q
DB(15)
D Q
D Q
100
D Q
QFLAG
D Q
sync
D Q
D Q
D Q
sync_fifo(2:0)
D
DA(15)
Q
D Q
MUX
PLLLOCK
PLL VCO
clk_in
sync_fifo = “100”
DA(15) first rising edge
clk_out
clock
generator
CLK2
CLK1
CLK2C
CLK1C
{PLLVDD, inv_plllock, dual_clk}
Figure 50. DAC5687 FIFO Synchronization Source Logic
For example, if TXENABLE is selected as the sync source, a low-to-high transition on the TXENABLE pin causes
the pointers to be initialized.
Once initialized, the FIFO input pointer advances using clk_in and the output pointer advances using clk_out,
providing an elastic buffering effect. The phase relationship between clk_in and clk_out can wander or drift until
the output pointer overruns the input pointer or vice versa.
Even/Odd Input Mode
The DAC5687 has a double data rate input mode that allows both input ports to be used to multiplex data onto
one DAC channel (A). In the Even/Odd mode, the FIR3 filter can be used to interpolate the data by 2x. The
even/odd input mode is enabled by setting half_rate in CONFIG3. The maximum input rate for each port is 250
MSPS, for a combined rate of 500 MSPS.
Synchronization
The DAC5687 has several digital circuits that can be synchronized to a known state. The circuits that can be
synchronized are the fine mixer (NCO), coarse mixer (fixed fs/2 or fs/4 mixer), the FIFO input and output
pointers, and the internal clock divider.
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Table 12. Synchronization in Different Clock Modes
Clock
Mode
PLLVDD
Pin
Serial Interface Register Bits
Single
External
Clock
without
FIFO
0V
Single
External
Clock with
FIFO
0V
Dual
External
Clock
without
FIFO
0V
1
Dual
External
Clock with
FIFO
0V
PLL
Enabled
3.3 V
DA, DB,
PHSTR, and
TXENABLE
Latch
Description
Signal at the PLLLOCK output pin is used to clock the
PHSTR signal into the chip. The PLLLOCK output
clock is generated by dividing the CLK2/CLK2C input
signal by the programmed interpolation and interface
settings.
fifo_bypass
dual_clk
inv_plllock
1
0
0
PLLLOCK
rising edge
1
PLLLOCK
falling edge
0
PLLLOCK
rising edge
1
PLLLOCK
falling edge
1
0
CLK1/CLK1C
The CLK1/CLK1C input signal is used to clock in the
PHSTR signal. CLK1/CLK1C and CLK2/CLK2C are
both input to the chip and the phase relationship must
be tightly controlled
0
1
1
CLK1/CLK1C
The CLK1/CLK1C input signal is used to clock in the
PHSTR signal. CLK1/CLK1C and CLK2/CLK2C are
both input to the chip, but no phase relationship is
required. The FIFO input circuits are used to manage
the clock domain transfers. The FIFO must be
initialized in this mode.
1
0
0
CLK1/CLK1C
The CLK1/CLK1C input signal is used to clock in the
PHSTR signal. The FIFO must be bypassed when the
PLL is enabled.
0
0
Signal at the PLLLOCK output pin is used to clock the
PHSTR signal into the chip. The PLLLOCK output
clock is generated by dividing the CLK2/CLK2C input
signal by the programmed interpolation and interface
settings. Enabling the FIFO allows the chip to function
with large loads on the PLLLOCK output pin at high
input rates. The FIFO must be initialized first in this
mode.
NCO Synchronization
The phase accumulator in the NCO block (see the Fine Mixer (FMIX) section and Figure 39 for a description of
the NCO) can be synchronously reset when PHSTR is asserted. The PHSTR signal passes through the input
FIFO block, using the input clock associated with the clocking mode. If the FIFO is enabled, there can be some
uncertainty in the exact instant the PHSTR synchronization signal arrives at the NCO accumulator due to the
elastic capabilities of the FIFO. For example, in dual-clock mode with the FIFO enabled, the internal clock
generator divides down the CLK2/CLK2C input signal to generate the FIFO output clock. The phase of this
generated clock will be unknown externally, resulting in an uncertainty of the exact PHSTR instant of as much as
a few input clock cycles.
FIFO
PHSTR
D Q
D Q
phstr sync to NCO
D Q
D Q
MUX
clk_out
PLLLOCK
clk_in
D Q
D Q
clk_nco
clock
generator
PLL VCO
CLK2
CLK2C
CLK1
CLK1C
{PLLVDD, inv_plllock,, dual_clk}}
Figure 51. Logic Path for PHSTR Synchronization Signal to NCO
46
phase
accumulator
reset
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The serial interface includes a sync_nco bit in register SYNC_CNTL, which needs to be set for the PHSTR input
signal to initialize the phase accumulator.
The NCO uses a rising edge detector to perform the synchronous reset of the phase accumulator. Due to the
pipelined nature of the NCO, the latency from the phstr sync signal at the FIFO output to the instant the phase
accumulator is cleared is 13 fNCO clock cycles (fNCO = fDAC in X4 mode, fNCO = fDAC/2 in X2, X4L, and X8 modes).
In 2x interpolation mode with the inverse sinc filter disabled, overall latency from PHSTR input to DAC output is
~100 input clock cycles.
PHSTR
only needs to be asserted for one clk_in period
clk_in
Input delay line + FIFO delay
clk_out
phstr at FIFO
output
clk_nco
phase
accumulator
reset
phase_accum
13 clk_nco cycles
Figure 52. NCO Phase Accumulator Reset Synchronization Timing
Coarse Mixer (CMIX) Synchronization
The coarse mixer implements the fDAC/2 and fDAC/4 (and – fDAC/4) fixed complex mixing operation using simple
complements of the datapath signals to create the proper sequences. The sequences are controlled using a
simple counter and this counter can be synchronously reset using the PHSTR signal.
Similar to the NCO, the PHSTR signal used by the coarse mixer is from the FIFO output. This introduces the
same uncertainty effect due to the FIFO input to output pointer relationship. Bypassing the FIFO and using the
dual external clock mode without FIFO eliminates this uncertainty for systems using multiple DAC5687 devices
when this cannot be tolerated. Using the internal PLL, as with the NCO, allows the complete control and
synchronization of the coarse mixer.
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sync_cm
D Q
PHSTR
D Q
D Q
FIFO
phstr sync to coarse mixer D Q
D Q
D Q
Sequencer
Reset
MUX
clk_cmix
PLLLOCK
clk_in
clk_out
PLL VCO
Clock
Generator
CLK1
CLK2
CLK2C
CLK1C
{PLLVDD, inv_plllock, dual_clk}
Figure 53. Logic Path for PHSTR Synchronization Signal to CMIX Reset
To enable the PHSTR synchronous reset, the serial interface bit sync_cm in register SYNC_CNTL must be set.
The coarse mixer sequence counter will be held reset when PHSTR is low and operates when PHSTR is high.
Only needs to be high for one clk_in period
PHSTR
clk_in
Input delay line + FIFO delay
clk_out
phstr at FIFO
Output
clk_cmix
Sequencer
Reset
Sequencer
fs/2
0 180 0 180
Sequencer
fs/4
0
90 180 270 0
90
Figure 54. CMIX Reset Synchronization Timing
In addition to the reset function provided by the PHSTR signal, the phstr_del(1:0) bits in register ATEST allow
the user to select the initial (reset) state. Changing the cm_mode lower 2 bits produces the same phase shift
results.
Table 13. Initial State of CMIX After Reset
48
Fix Mix Selection
phstr_del(1:0)
fS/2
00 and 10
Initial State at PHSTR
Normal
fS/2
01 and 11
180 degree shift
fS/4
00
Normal
fS/4
01
90 degree shift
DAC5687
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SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Table 13. Initial State of CMIX After Reset (continued)
Fix Mix Selection
phstr_del(1:0)
Initial State at PHSTR
fS4
10
180 degree shift
fS/4
11
270 degree shift
Input Clock Synchronization of Multiple DAC5687s
For applications where multiple DAC5687 chips are used, clock synchronization is best achieved by using
dual-clock mode with the FIFO disabled or the PLL-clock mode. In the dual-clock mode with FIFO disabled, an
appropriate clock PLL such as the CDC7005 is required to provide the DAC and input rate clocks that meet the
skew requirement t_align (see Figure 47). An example for synchronizing multiple DAC5687 devices in dual clock
mode with two CDC7005 is shown in Figure 55. When using the internal PLL-clock mode, synchronization of
multiple using PHSTR is completely deterministic due to the phase/frequency detector in the PLL feedback loop.
All chips using the same CLK1/CLK1C input clock will have identical internal clocking phases.
Ref
fINPUT
CDC7005
#1
Ref
CDC7005
#2
Y0
Y0
Y1
Y1
fINPUT
CLK1
CLK1C
fDAC
CLK2
CLK2C
Y2
Y2
Y3
Y3
fINPUT
CLK1
CLK1C
fDAC
CLK2
CLK2C
Y0
Y0
Y1
Y1
fINPUT
CLK1
CLK1C
fDAC
CLK2
CLK2C
Y2
Y2
Y3
Y3
fINPUT
CLK1
CLK1C
fDAC
CLK2
CLK2C
DAC5687
#1
DAC5687
#2
DAC5687
#3
DAC5687
#4
Figure 55. Block Diagram for Clock Synchronization of Multiple DAC5687 Devices in Dual-Clock Mode
Reference Operation
The DAC5687 comprises a bandgap reference and control amplifier for biasing the full-scale output current. The
full-scale output current is set by applying an external resistor RBIAS to pin BIASJ. The bias current IBIAS
through resistor RBIAS is defined by the on-chip bandgap reference voltage and control amplifier. The full-scale
output current equals 16 times this bias current. The full-scale output current IOUTFS can thus be expressed as:
IOUTFS = 16 × IBIAS = 16 × VEXTIO / RBIAS
where VEXTIO is the voltage at terminal EXTIO. The bandgap reference voltage delivers an accurate voltage of
1.2 V. This reference is active when terminal EXTLO is connected to AGND. An external decoupling capacitor
CEXT of 0.1 µF should be connected externally to terminal EXTIO for compensation. The bandgap reference can
additionally be used for external reference operation. In that case, an external buffer with high impedance input
should be applied in order to limit the bandgap load current to a maximum of 100 nA. The internal reference can
be disabled and overridden by an external reference by connecting EXTLO to AVDD. Capacitor CEXT may hence
be omitted. Terminal EXTIO thus serves as either input or output node.
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The full-scale output current can be adjusted from 20 mA down to 2 mA by varying resistor RBIAS or changing the
externally applied reference voltage. The internal control amplifier has a wide input range, supporting the
full-scale output current range of 20 mA.
DAC Transfer Function
The CMOS DAC’s consist of a segmented array of NMOS current sinks, capable of sinking a full-scale output
current up to 20 mA. Differential current switches direct the current of each current source through either one of
the complementary output nodes IOUT1 or IOUT2. Complementary output currents enable differential operation,
thus canceling out common mode noise sources (digital feed-through, on-chip and PCB noise), dc offsets, even
order distortion components, and increasing signal output power by a factor of two.
The full-scale output current is set using external resistor RBIAS in combination with an on-chip bandgap voltage
reference source (+1.2 V) and control amplifier. Current IBIAS through resistor RBIAS is mirrored internally to
provide a full-scale output current equal to 16 times IBIAS. The full-scale current IOUTFS can be adjusted from 20
mA down to 2 mA.
The relation between IOUT1 and IOUT2 can be expressed as:
IOUT1 = -IOUTFS– IOUT2
We will denote current flowing into a node as - current and current flowing out of a node as + current. Since the
output stage is a current sink the current can only flow from AVDD into the IOUT1 and IOUT2 pins. If IOUT2 = 5 mA and IO(FS) = 20 mA then:
IOUT1 = -20 – (-5) = -15 mA
The output current flow in each pin driving a resistive load can be expressed as:
IOUT1 = IOUTFS × CODE / 65536
IOUT2 = IOUTFS × (65535 – CODE) / 65536
where CODE is the decimal representation of the DAC data input word.
For the case where IOUT1 and IOUT2 drive resistor loads RL directly, this translates into single ended voltages
at IOUT1 and IOUT2:
VOUT1 = AVDD – I IOUT1 I × RL
VOUT2 = AVDD – I IOUT2 I × RL
Assuming that the data is full scale (65535 in offset binary notation) and the RL is 25 Ω, the differential voltage
between pins IOUT1 and IOUT2 can be expressed as:
VOUT1 = AVDD – I -20 mA I x 25 Ω = 2.8 V
VOUT2 = AVDD – I -0 mA I x 25 Ω = 3.3 V
VDIFF = VOUT1 – VOUT2 = 0.5 V
Note that care should be taken not to exceed the compliance voltages at node IOUT1 and IOUT2, which would
lead to increased signal distortion.
Analog Current Outputs
Figure 56 shows a simplified schematic of the current source array output with corresponding switches.
Differential switches direct the current of each individual NMOS current source to either the positive output node
IOUT1 or its complementary negative output node IOUT2. The output impedance is determined by the stack of
the current sources and differential switches, and is typically >300 kΩ in parallel with an output capacitance of 5
pF.
The external output resistors are referred to an external ground. The minimum output compliance at nodes
IOUT1 and IOUT2 is limited to AVDD – 0.5 V, determined by the CMOS process. Beyond this value, transistor
breakdown may occur resulting in reduced reliability of the DAC5687 device. The maximum output compliance
voltage at nodes IOUT1 and IOUT2 equals AVDD + 0.5 V. Exceeding the minimum output compliance voltage
adversely affects distortion performance and integral non-linearity. The optimum distortion performance for a
single-ended or differential output is achieved when the maximum full-scale signal at IOUT1 and IOUT2 does not
exceed 0.5 V.
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DAC5687
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AVDD
RLOAD
RLOAD
IOUT1
IOUT2
S(1)
S(1)C
S(2)
S(2)C
S(N)
S(N)C
S0032-01
Figure 56. Equivalent Analog Current Output
The DAC5687 can be easily configured to drive a doubly terminated 50-Ω cable using a properly selected RF
transformer. Figure 57 and Figure 58 show the 50-Ω doubly terminated transformer configuration with 1:1 and
4:1 impedance ratio, respectively. Note that the center tap of the primary input of the transformer has to be
connected to AVDD to enable a dc-current flow. Applying a 20-mA full-scale output current would lead to a 0.5
VPP for a 1:1 transformer and a 1-VPP output for a 4:1 transformer. The low dc-impedance between the IOUT1 or
IOUT2 and the transformer center tap sets the center of the ac-signal at AVDD, so the 1-VPP output for the 4:1
transformer results in an output between AVDD + 0.5 V and AVDD – 0.5 V.
AVDD (3.3 V)
50 Ω
1:1
IOUT1
RLOAD
50 Ω
100 Ω
IOUT2
50 Ω
AVDD (3.3 V)
S0033-01
Figure 57. Driving a Doubly Terminated 50-Ω Cable Using a 1:1 Impedance Ratio Transformer
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AVDD (3.3 V)
100 Ω
4:1
IOUT1
RLOAD
50 Ω
IOUT2
100 Ω
AVDD (3.3 V)
S0033-02
Figure 58. Driving a Doubly Terminated 50-Ω Cable Using a 4:1 Impedance Ratio Transformer
Combined Output Termination
The DAC5687 DAC A and DAC B outputs can be summed together as shown in Figure 59 to provide a 40-mA
full-scale output for increased output power.
1:1
IOUTA1
RLOAD
50 Ω
IOUTA2
IOUTB1
AVDD (3.3 V)
IOUTB2
S0069-01
Figure 59. Combined Output Termination Using a 1:1 Impedance Ratio Transformer into 50-Ω Load
For the case where the digital codes for the two DACs are identical, the termination results in a full scale swing
of 2 VPP into the 50-Ω load, or 10 dBm. This is 6 dB higher than the 4:1 output termination recommended for a
single DAC output.
There are two methods to produce identical DAC codes. In modes where there is mixing between digital
channels A and B, i.e., when channels A and B are isolated, the identical data can be sent to both input ports to
produce identical DAC codes. Channels A and B are isolated when FMIX is disabled, the QMC is disabled or
enabled with QMC phase register set to 0, and CMIX is disabled or set to fDAC/2. Note that frequency
upconversion is still possible using the high-pass filter setting and CMIX fDAC/2.
Alternatively, by applying the input data on one input port only and setting the other input port to mid-scale (zero),
the NCO can be used to duplicate the output of the active input channel in the other channel by setting the
frequency to zero, phase to 8192 and NCO_GAIN = 1 and QMC gain = 1446. Assuming I(t) is the wanted signal
and Q(t) = 0, this is demonstrated by the simplification of the NCO equations in the Fine Mixer (FMIX) section:
IOUT(t) = (IIN(t)cos(2π x 0 x t + π/4) – 0 x sin((2π x 0 x t + π/4)) x 2(1 –
1)
= IIN(t)cos(π/4) = IIN(t)/2½
QOUT(t) = (IIN(t)sin(2π x 0 x t + π/4) + 0 x cos(2π x 0 x t + π/4)) x 2(1 –
1)
= IIN(t)sin(π/4) = IIN(t)/2½
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Applying the QMC gain of 1446, equivalent to 2½, increases the signal back to unity gain through the FMIX and
the QMC blocks.
Note that with this termination, the DAC side of the transformer is not 50-Ω terminated and therefore may result
in reflections when used with a cable output.
Digital Inputs
Figure 60 shows a schematic of the equivalent CMOS digital inputs of the DAC5687. DA[0..15], DB[0..15],
SLEEP, PHSTR, TXENABLE, QFLAG, SDIO, SCLK, and SDENB have pull-down resistors and RESETB has a
pull-up resistor internal to the DAC5687. See the specification table for logic thresholds.
IOVDD
IOVDD
DA[15:0]
DB[15:0]
SLEEP
PHSTR
TxENABLE
QFLAG
SDIO
SCLK
SDENB
Internal
Digital In
Internal
Digital In
RESETB
IOGND
IOGND
Figure 60. CMOS/TTL Digital Equivalent Input
Clock Inputs
Figure 61 shows an equivalent circuit for the clock input.
CLKVDD
CLKVDD
R1
10 kΩ
Internal
Digital In
CLKVDD
R1
10 kΩ
CLK
CLKC
R2
10 kΩ
R2
10 kΩ
CLKGND
S0028-01
Figure 61. Clock Input Equivalent Circuit
Figure 62, Figure 63, and Figure 64 show various input configurations for driving the differential clock input
(CLK/CLKC).
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DAC5687
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Optional, May Be Bypassed
for Sine Wave Input
Swing Limitation
CAC
0.1 µF
1:4
CLK
RT
200 Ω
CLKC
Termination Resistor
S0029-01
Figure 62. Preferred Clock Input Configuration
Ropt
22 Ω
CAC
0.01 µF
Ropt
22 Ω
1:1
TTL/CMOS
Source
TTL/CMOS
Source
CLK
Optional, Reduces
Clock Feedthrough
CLKC
CLK
CLKC
0.01 µF
Node CLKC Internally Biased
to CLKVDD2
S0030-01
Figure 63. Driving the DAC5687 With a Single-Ended TTL/CMOS Clock Source
CAC
0.1 µF
Differential
ECL
or
(LV)PECL
Source
CLK
+
CAC
0.1 µF
–
100 Ω
CLKC
RT
130 Ω
RT
130 Ω
RT
82.5 Ω
RT
82.5 Ω
VTT
S0031-01
Figure 64. Driving the DAC5687 With Differential ECL/PECL Clock Source
Power Up Sequence
In all conditions, bring up DVDD first. If PLLVDD is powered (PLL on), CLKVDD should be powered before or
simultaneously with PLLVDD. AVDD, CLKVDD, and IOVDD can be powered simultaneously or in any order.
Within AVDD, the multiple AVDD pins should be powered simultaneously.
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DAC5687
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There are no specific requirements on the ramp rate for the supplies.
Sleep Mode
The DAC5687 features a power-down mode that turns off the output current and reduces the supply current to
less than 5 mA over the supply range of 3 V to 3.6 V and temperature range. The power-down mode is activated
by applying a logic level 1 to the SLEEP pin (e.g., by connecting pin SLEEP to AVDD). An internal pull-down
circuit at node SLEEP ensures that the DAC5687 is enabled if the input is left disconnected. Power-up and
power-down activation times depend on the value of external capacitor at node EXTIO. For a nominal capacitor
value of 0.1-µF, power down takes less than 5 µs and approximately 3 ms to power back up.
Application Information
Designing the PLL Loop Filter
Table 14. Optimum DAC5687 PLL Settings
fDAC (MHZ)
pll_freq
pll_kv
pll_div (1:0)
fVCO / fDAC
Estimated GVCO (MHz/V)
25 to
28.125
0
1
11
8
380
28.125 to
46.25
0
0
11
8
250
46.25 to 60
0
1
11
8
300
60 to
61.875
1
0
11
8
130
61.875 to
65
1
1
11
8
225
65 to 92.5
0
0
10
4
250
92.5 to 120
0
1
10
4
300
120 to
123.75
1
0
10
4
130
123.75 to
130
1
1
10
4
225
130 to 185
0
0
01
2
250
185 to 240
0
1
01
2
300
240 to
247.5
1
0
01
2
130
247.5 to
260
1
1
01
2
225
260 to 370
0
0
00
1
250
370 to 480
0
1
00
1
300
480 to 495
1
0
00
1
130
495 to 520
1
1
00
1
225
The optimized DAC5687 PLL settings based on the VCO frequency MIN and MAX values (see the digital
specifications) as a function of fDAC are listed in Table 14. To minimize phase noise at a given fDAC, pll_freq,
pll_kv, and the pll_div have been chosen so GVCO is minimized and within the MIN and MAX frequency for a
given setting.
For example, if fDAC = 245.76 MHz, pll_freq is set to 1, pll_kv is set to 0 and pll_div(1:0) is set to 01 (divide by 2)
to lock the VCO at 491.52 MHz.
The external loop filter components C1, C2, and R1 are set by the GVCO, N = fVCO/fDATA = fVCO x
Interpolation/fDAC, the loop phase margin φd and the loop bandwidth ωd. Except for applications where abrupt
clock frequency changes require a fast PLL lock time, it is suggested that ωd be set to at least 80 degrees for
stable locking and suppression of the phase noise side lobes. Phase margins of 60 degrees or less can be
sensitive to board layout and decoupling details.
C1, C2, and R1 are then calculated by the following equations
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C1 1 1 2
3
C2 1 2
3
where,
K Kvco
1 d 2
tan sec d
d
d
R1 3 2
1 (3 2)
1
2 tan d sec d
(1)
3 d
tan sec d
d
d
(2)
and
charge pump current: iqp = 1 mA
vco gain: KVCO = 2πxGVCO rad/V
FVCO/FDATA: N = {2, 4, 8, 16, 32}
phase detector gain: Kd = iqp × (2 × N) – 1 A/rad
An Excel spreadsheet is provided by Texas Instruments for automatically calculating the values for C1, C2, and
R.
Completing the example given above with:
Parameter
Value
Units
GVCO
1.30E+02
MHz/V
ωd
0.50E+00
MHz
N
4
φd
80
Degrees
C1 (F)
C2 (F)
R (Ω)
3.74E-08
2.88E-10
9.74E+01
The component values are:
As the PLL characteristics are not sensitive to these components, the closest 20% tolerance capacitor and 1%
tolerance resistor values can be used. If the calculation results in a negative value for C2 or an unrealistically
large value for C1, then the phase margin may need to be reduced slightly.
DAC5687 Passive Interface-to-Analog Quadrature Modulators
The DAC5687 has a maximum 20-mA full-scale output and a compliance range of AVDD ±0.5 V. The TRF3701
or TRF3702 analog quadrature modulators (AQM) require a common-mode of approximately 3.7 V and 1.5 V to
2-VPP differential swing. A resistive network as shown in Figure 65 can be used to translate the common mode
voltage between the DAC5687 and TRF3701 or TRF3702. The voltage at the DAC output pins for a full-scale
sine wave is centered at approximately AVDD with a 1-VPP single ended (2-VPP differential). The voltage at the
TRF3701/2 input pins is centered at 3.7 V and swings 0.76-VPP single ended (1.56-VPP differential), or 2.4 dB of
insertion loss.
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GND
5V
205 Ω
205 Ω
50 Ω
50 Ω
15.4 Ω
15.4 Ω
TRF3701
TRF3702
15.4 Ω
15.4 Ω
205 Ω
205 Ω
50 Ω
50 Ω
5V
GND
B0046-01
Figure 65. DAC5687 Passive Interface to TRF3701/2 Analog Quadrature Modulator
Changing the voltage levels and resistor values enable other common-mode voltages at the analog quadrature
modulator input. For example, the network shown in Figure 66 can produce a 1.5-V common mode at the analog
quadrature modulator input, with a 0.78-VPP single-ended swing (1.56-VPP differential swing), or 0.2-dB insertion
loss.
5V
69.8 Ω
−5 V
69.8 Ω
453 Ω
453 Ω
124 Ω
124 Ω
AQM
124 Ω
124 Ω
69.8 Ω
69.8 Ω
5V
453 Ω
453 Ω
−5 V
B0046-02
Figure 66. DAC5687 Passive Interface With 1.5-V Common Mode at AQM Input
Non-Harmonic Clock-Related Spurious Signals
In interpolating DACs, imperfect isolation between the digital and DAC clock circuits generate spurious signals at
frequencies related to the DAC clock rate. The digital interpolation filters in these DACs run at sub-harmonic
frequencies of the output rate clock, where these frequencies are fDAC/2N, N = 1 - 3. For example, for X2 mode
there is only one interpolation filter running at fDAC/2; for X4 and X4L modes, on the other hand, there are two
interpolation filters running at fDAC/2 and fDAC/4. In X8 mode, there are three interpolation filters running at fDAC/2,
fDAC/4, and fDAC/8. These lower-speed clocks for the interpolation filter mix with the DAC clock circuit and create
spurious images of the wanted signal and second Nyquist-zone image at offsets of fDAC/2N.
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To calculate the non-harmonic clock related spurious signals for a particular condition, we first determine the
location of the spurious signals and then the amplitude.
Location of the Spurious Signals
The location of the spurious signals is determined by the DAC5687 output frequency (fSIG) and whether the
output is used as a dual output complex signal to be fed to an analog quadrature modulator (AQM) or as a real
IF signal from a single DAC output.
Figure 67 shows the location of spurious signals for X2 mode as a function of fSIG/fDAC. For complex outputs, the
spurious frequencies cover a range of -0.5 x fDAC to 0.5 x fDAC, with the negative complex frequency indicating
that the spurious signal will fall in the opposite sideband at the output of the QAM from the wanted signal. For the
real output, the phase information for the spurious signal is lost, and therefore what was a negative frequency for
the complex output is a positive frequency for a real output.
For the X2 mode, there is one spurious frequency with an absolute frequency less than 0.5 x fDAC. For a complex
output in X2 mode, the spurious signal will always be offset fDAC/2 from the wanted signal at fSIG - fDAC/2. For a
real output, as fSIG approaches fDAC/4, the spurious signal frequency falls at fDAC/2-fSIG, which will also approach
fDAC/4.
(a) Complex Output in X2 Mode
(b) Real Output in X2 Mode
0.5
0.50
0.4
0.45
0.40
fSIG
0.2
Spurious Frequency/fDAC
Spurious Frequency/fDAC
0.3
0.1
−0.0
−0.1
−0.2
fSIG − fDAC/2
−0.3
0.30
fSIG − fDAC/2
0.25
0.20
0.15
0.10
−0.4
−0.5
0.0
fSIG
0.35
0.05
0.1
0.2
0.3
fSIG/fDAC
0.4
0.5
G026
0.00
0.0
0.1
0.2
0.3
fSIG/fDAC
0.4
0.5
G027
Figure 67. Frequency of Clock Mixing Spurious Images in X2 Mode
Figure 68 shows the location of spurious signals for X4 and X4L mode as a function of fSIG/fDAC. The addition of
the fDAC/4 clock frequency for the first interpolation filter creates three new spurious signals. For a complex
output, the nearest spurious signals are fDAC/4 offset from fSIG. For a real output, the signal due to fSIG - fDAC/4
and fSIG - fDAC x 3/4 falls in band as fSIG approaches fDAC/8 and fDAC x 3/8. This creates optimum real output
frequencies fSIG = fDAC x N/16 (N = 1, 3, 5, and 7), where the minimum spurious product offset from fSIG is fDAC/8.
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(a) Complex Output in X4 and X4L Modes
(b) Real Output in X4 and X4L Modes
0.5
0.4
0.50
fSIG + fDAC/4
0.45
0.2
0.1
fSIG − fDAC/4
0.0
−0.1
fSIG − fDAC/2
−0.2
−0.3
0.35
fSIG
0.30
0.25
fSIG − fDAC/4
0.20
fSIG − fDAC/2
0.15
0.10
fSIG − fDAC*3/4
−0.4
−0.5
0.0
fSIG − fDAC*3/4
0.40
fSIG
Spurious Frequency/fDAC
Spurious Frequency/fDAC
0.3
fSIG + fDAC/4
0.1
0.2
0.05
0.3
0.4
fSIG/fDAC
0.00
0.0
0.5
0.1
0.2
0.3
0.4
fSIG/fDAC
G028
0.5
G029
Figure 68. Frequency of Clock Mixing Spurious Images in X4 and X4L Modes
Figure 69 shows the location of spurious signals for X8 mode as a function of fSIG/fDAC. The addition of the fDAC/8
clock frequency for the first interpolation filter creates four new spurious signals. For a complex output, the
nearest spurious signals are fDAC/8 offset from fSIG. For a real output, the optimum real output frequencies fSIG =
fDAC x N/16 (N = 3 and 5), where the minimum spurious product offset from fSIG is fDAC/8.
(a) Complex Output in X8 Mode
(b) Real Output in X8 Mode
0.5
0.50
fSIG + fDAC/4
0.45
0.3
0.40
0.2
fSIG
fSIG + fDAC/8
Spurious Frequency/fDAC
Spurious Frequency/fDAC
fSIG + fDAC/4
0.4
0.1
fSIG − fDAC/4
−0.0
−0.1
fSIG − fDAC/8
fSIG − fDAC/2
−0.2
−0.3
0.35
0.30
fSIG
fSIG + fDAC/8
0.25
0.20
fSIG − fDAC*3/4
fSIG − fDAC/4
0.15
0.10
fSIG − fDAC/8
fSIG − fDAC*3/4
−0.4
−0.5
0.0
fSIG − fDAC*7/8
0.05
fSIG − fDAC*7/8
0.1
0.2
0.3
fSIG/fDAC
0.4
0.5
G030
0.00
0.0
fSIG − fDAC/2
0.1
0.2
0.3
fSIG/fDAC
0.4
0.5
G031
Figure 69. Frequency of Clock Mixing Spurious Images in X4 and X4L Modes
Amplitude of the Spurious Signals
The spurious signal amplitude is sensitive to factors such as temperature, voltage, and process. Typical worst
case estimates to account for the variation over these factors are provided below as design guidelines.
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Figure 70 and Figure 71 show the typical worst case spurious signal amplitudes vs fDAC for a signal frequency
fSIG = 11 x fDAC/32 in each mode for PLL on (PLL clock mode) and PLL off (external and dual clock modes). Each
spurious signal (fDAC/2, fDAC/4 and fDAC/8) has its own curve. The spurious signal amplitudes can then be
adjusted for the exact signal frequency fSIG by applying the amplitude adjustment factor shown in Figure 72. The
amplitude adjustment factor is the same for each spurious signal (fDAC/2, fDAC/4, and fDAC/8) and is normalize for
fSIG = 11 x fDAC/32.
(b) X4L Mode
100
80
90
80
70
Spurious Amplitude − dBc
Spurious Amplitude − dBc
(a) X2 Mode
90
fDAC/2
60
50
40
30
20
70
fDAC/4
60
fDAC/2
50
40
30
20
10
10
0
0
0
100
200
300
400
fDAC − MHz
500
0
100
G032
400
100
100
90
90
80
80
70
fDAC/2
60
fDAC/4
fDAC x 3/4
40
30
G033
fDAC/4
fDAC x 3/4
70
60
50
fDAC/2
fDAC/8
fDAC x 7/8
40
30
20
20
10
10
0
0
0
100
200
300
fDAC − MHz
400
500
G034
0
100
200
300
400
fDAC − MHz
Figure 70. Clock Related Spurious Signal Amplitude With PLL Off for fSIG = 11 x fDAC / 32
60
500
(d) X8 Mode
Spurious Amplitude − dBc
Spurious Amplitude − dBc
300
fDAC − MHz
(c) X4 Mode
50
200
500
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(b) X4L Mode
60
50
50
Spurious Amplitude − dBc
Spurious Amplitude − dBc
(a) X2 Mode
60
40
fDAC/2
30
20
10
fDAC/2
40
30
fDAC/4
fDAC x 3/4
20
10
0
0
0
100
200
300
400
fDAC − MHz
500
0
100
300
400
fDAC − MHz
G036
(c) X4 Mode
500
G037
(d) X8 Mode
70
70
60
60
Spurious Amplitude − dBc
Spurious Amplitude − dBc
200
50
fDAC/2
40
30
fDAC/4
20
10
fDAC/8
fDAC x 7/8
fDAC/2
50
40
fDAC/4
fDAC x 3/4
30
20
10
0
0
0
100
200
300
fDAC − MHz
400
500
G038
0
100
200
300
400
fDAC − MHz
500
G039
Figure 71. Clock Related Spurious Signal Amplitude With PLL On for fSIG = 11 x fDAC / 32
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40
Amplitude Adjustment − dB
30
20
10
0
−10
−20
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
fSIG/fDAC
G040
Figure 72. Amplitude Adjustment Factor for fSIG
The steps for calculating the non-harmonic spurious signals are:
1. Find the spurious signal frequencies for the appropriate mode from Figure 67, Figure 68, or Figure 69.
2. Find the amplitude for each spurious frequency for the appropriate mode from Figure 70 or Figure 71.
3. Adjust the amplitude of the spurious signals for fSIG using the adjustment factor in Figure 72.
Consider Example 1 with the following conditions:
1. X4 Mode
2. Pll off
3. Complex Output
4. fDAC = 500 MHz
5. fSIG = 160 MHz = 0.32 x fDAC
First, the location of the spurious signals is found for the x4 complex output in Figure 68(a). Three spurious
signals are present in the range -0.5 x fDAC to 0.5 x fDAC: two from fDAC/4 (35 MHz and -215 MHz) and one from
fDAC/2 (-90 MHz). Consulting Figure 70©), the raw amplitudes for fDAC/2 and fDAC/4 are 60 and 58 dBc,
respectively. From Figure 72, the amplitude adjustment factor for fSIG = 0.32 x fDAC is estimated at ~ 1 dB and so
the fDAC/2 and fDAC/4 are adjusted to 61 and 59 dBc.
Table 15. Example # 1 for Calculating Spurious Signals
Spurious Signal
Frequency/fDAC
Frequency
(MHz)
Raw Amplitude (dBc)
Adjusted Amplitude (dBc)
fDAC/4
0.7
35
58
59
fDAC/2
-0.18
-90
60
61
fDAC/4
-0.43
-215
58
59
Now consider Example 2 with the following conditions:
1. X2 Mode
2. PLL on
3. Real output
4. fDAC = 400 MHz
5. fSIG = 70 MHz = 0.175 x fDAC
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First, the location of the spurious signals is found for the X2 real output in Figure 67(b). One spurious signals is
present in the range 0 to 0.5 × fDAC at 0.325 × fDAC (see Table 16). Consulting Figure 71(a), the raw amplitude for
fDAC/2 is 47 dBc. From Figure 72, the amplitude adjustment factor for fSIG = 0.175 x fDAC is estimated at ~ 6 dB,
and so the fDAC/2 and fDAC/4 is adjusted to 53 dBc.
Table 16. Example # 2 for Calculating Spurious Signals
Spurious Signal
Frequency/fDAC
Frequency
(MHz)
Raw Amplitude (dBc)
Adjusted Amplitude (dBc)
fDAC/2
0.325
130
47
53
Schematic and Layout Recommendations
The DAC5687 clock is sensitive to fast transitions of input data on pins DA0, DA1, and DA2 (55, 54, and 53) due
to coupling to DVDD pin 56. The noise-like spectral energy of the DA[0-2] couples into the DAC clock resulting in
increased jitter. This significantly improves by using a 10-Ω resistor between DVDD and pin 56 in addition to
10-pF capacitor to DGND, as implemented on the DAC5687EVM (see the DAC5687 EVM user's guide SLWU017). Pin 56 draws only approximately 2 mA of current and the 0.02-V voltage drop across the resistor is
acceptable for DVDD voltages within the MINIMUM and MAXIMUM specifications. It is also recommended that
the transition rate of the input lines be slowed by inserting series resistors near the data source. The optimized
value of the series resistor depends on the capacitance of the trace between the series resistor and DAC5687
input pin. For a 2-3 inch trace, a 22-Ω to 47-Ω resistor would be recommended.
The effect of DAC clock jitter on the DAC output signal is worse for signals at higher signal frequencies. For low
IF (< 75 MHz) or baseband signals, there is little degradation of the output signal. However, for high IF (> 75
MHz) the DAC clock jitter may result in an elevated noise floor, which often appears as broad humps in the DAC
output spectrum. It is recommended for signals above 75 MHz that the inputs to DA0 and DA1, which are the two
LSBs if input DA[0-15] is not reversed, not be connected to input data to prevent coupling to the DAC rate clock.
The decrease in resolution to 14-bits and increase in quantization noise will not significantly affect the DAC5687
SNR for signals > 75 MHz.
Application Examples
Application Example: Real IF Radio
An system example of the DAC5687 used for a flexible real IF radio is shown in Figure 73. A complex baseband
input to the DAC would be generated by a digital upconverter such as Texas Instruments GC4116, GC5016, or
GC5316. The DAC5687 would be used to increase the data rate through interpolation and flexibly place the
output signal using the FMIX and/or CMIX blocks. Although the DAC5687 X4 mode is shown, any of the modes
(x2, x4L, or x8) would be appropriate.
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DAC5687
DUC
I
2
2
NCO
RF
Processing
DAC
DUC
TRF3750
Q
2
GC4116
GC5016
GC5316
2
CDC7005
B0040-01
Figure 73. System Diagram of a Real IF System Using the DAC5687
With the DAC5687 in external clock mode, a low phase noise clock for the DAC5687 at the DAC sample rate
would be generated by a VCXO and PLL such as Texas Instruments CDC7005, which can also provide other
system clocks at the VCXO frequency divided by 2-n (n = 0 to 4). In this mode, the DAC5687 PLLLOCK pin
output would typically be used to clock the digital upconverter. With the DAC in PLL clock mode, the same input
rate clock would be used for the DAC clock and digital upconverter and the DAC internal PLL/VCO would
generate the DAC sample rate clock. Note that the internal PLL/VCO phase noise may degrade the quality of the
DAC output signal, and will also have higher non-harmonic clock-related spurious signals (see the Non-Harmonic
Clock Related Spurious Signals section).
Either DACA or DACB outputs can be used (with the other DAC put into sleep mode) and would typically be
terminated with a transformer (see the Analog Current Output section). An IF filter, either LC or SAW, is used to
suppress the DAC Nyquist zone images and other spurious signals before being mixed to RF with a mixer.
An alternative architecture uses the DAC5687 in a dual-channel mode to create a dual-channel system with real
IF input and output. This would be used for narrower signal bandwidth and at the expense of less output
frequency placement flexibility (see Figure 74). Frequency upconversion can be accomplished by using the
high-pass filter and CMIX fDAC/2 mixing features.
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DAC5687
RF
Processing
DUC
Ch2
DAC
2
DUC
2
1, −1, 1, ...
1, −1, 1, ...
RF
Processing
DUC
Ch1
DAC
2
DUC
2
GC4116
GC5016
GC5316
TRF3750
CDC7005
B0041-01
Figure 74. System Diagram of a Dual Channel Real IF Radio
The outputs of multiple DAC5687s can be phase synchronized for multiple antenna/beamforming applications.
Application Example: Complex IF to RF Conversion Radio
An alternative to a real IF system is to use a complex IF DAC output with analog quadrature modulator, as
shown in Figure 75. The same complex baseband input as the real IF system in Figure 73 is used. The
DAC5687 would be used to increase the data rate through interpolation and flexibly place the output signal using
the FMIX and/or CMIX blocks. Although the DAC5687 X4 mode is shown, any of the modes (x2, x4L, or x8)
would be appropriate.
TRF3701
TRF3702
DAC5687
I
DAC
2
2
NCO
RF
Processing
CMIX
Q
DAC
2
2
CDC7005
TRF3750
B0042-01
Figure 75. Complex IF System Using the DAC5687 in X4L Mode
Instead of only using one DAC5687 output as for the real IF output, both DAC5687 outputs are used for a
complex IF Hilbert transform pair.
The DAC5687 outputs can be expressed as:
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A(t) = I(t)cos(ωct) - Q(t)sin(ωct) = m(t)
B(t) = I(t)sin(ωct) + Q(t)cos(ωct) = mh(t)
where m(t) and mh(t) connote a Hilbert transform pair and ωc is the sum of the NCO and CMIX frequencies.
The complex DAC5687 output is input to an analog quadrature modulator (AQM) such as the TRF3701 or
TRF3702. A passive (resistor only) interface is recommended between the DAC5687 and TRF3701/2 (See the
Passive Interface to TRF3701/2 section). Upper single-sideband up-conversion is achieved at the output of the
analog quadrature modulator, whose output is expressed as:
RF(t) = I(t)cos(ωc + ωLO)t - Q(t)sin(ωc + ωLO)t
Flexibility is provided to the user by allowing for the selection of -B(t) out, which results in lower-sideband
up-conversion. This option is selected by usb in the CONFIG3 register.
Note that the process of complex mixing in FMIX and CMIX to translate the signal frequency from 0 Hz means
that the analog quadrature modulator IQ imbalance produces a side-band and LO feedthrough that falls outside
the signal.
This is shown in Figure 76, which is the RF analog quadrature modulator (AQM) output of an asymmetric three
carrier WCDMA signal with the properties in Table 17. The wanted signal is offset from the LO frequency by the
DAC5687 complex IF, in this case 122.88 MHz. The nearest spurious signals are ~ 100 MHz away from the
wanted signal (due to non-harmonic clock-related spurious signals generated by the fDAC/4 digital clock),
providing 200 MHz of spurious free bandwidth. The AQM phase and gain imbalance produce a lower sideband
product, which does not affect the quality of the wanted signal. Unlike the real IF architecture, the non-harmonic
clock-related spurious signals generated by the fDAC/2 digital clock fall ±245.76-MHz offset from the wanted
rather than falling inband.
As a consequence, in the complex IF system it may be possible that no AQM phase, gain and offset correction is
needed, instead relying on RF filtering to remove the LO feedthrough, sideband, and other spurious products.
LO
lower sideband
200 MHz
C001
Figure 76. Analog Quadrature Modulator Output for a Complex IF System
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Table 17. Signal and System Properties for Complex IF System Example in Figure 76
Signal
Three WCDMA Carriers, Test Model 1
Baseband Carrier Offsets
-7.5 MHz, 2.5 MHz, 7.5 MHz
DAC5687 Input Rate
122.88 MSPS
DAC5687 Output Rate
491.52 MSPS (4x Interpolation)
DAC5687 Mode
X4 CMIX
DAC5687 Complex IF
122.88 MHz (fDAC/4)
LO Frequency
2140 MHz
The complex IF has several advantages over the real IF architecture such as:
1. Uncalibrated side-band suppression ~ 35 dBc compared to 0 dBc for real IF architecture.
2. Direct DAC - Complex mixer connection - no amplifiers
3. Non-harmonic clock-related spurious signals fall out-of-band
4. DAC 2nd Nyquist zone image is offset fDAC compared with fDAC - 2 x IF for a real IF architecture, reducing the
need for filtering at the DAC output.
5. Uncalibrated LO feed through for AQM is ~ 35 dBc and calibration can reduce or completely remove the LO
feed through.
Application Example: Wide Bandwidth Direct Baseband to RF Conversion
A system example of the DAC5687 used in a wide bandwidth direct baseband to RF conversion is shown in
Figure 77. The DAC input would typically be generated by a crest factor reduction processor such as Texas
Instruments GC1115 and digital predistortion processor. With a complex baseband input, the DAC5687 would be
used to increase the data rate through interpolation. In addition, phase, gain and offset correction of the IQ
imbalance is possible using the QMC block, DAC gain and DAC offset features. The correction could be done
one time during manufacturing (see the TRF3701 data sheet (SLWS145) and the TRF3702 data sheet
(SLWS149)) for the variation with temperature, supply, LO frequency, etc. after calibration at nominal conditions)
or during operation with a separate feedback loop measuring imbalance in the RF signal.
TRF3701
TRF3702
DAC5687
I
DAC
2
2
Phase/
Gain/
Offset
Adjust
GC1115
and DPD
Processor
RF
Processing
Q
DAC
2
2
TRF3750
B0043-01
Figure 77. Direct Conversion System Using DAC5687 in X4L Mode
Operating at baseband has the advantage that the DAC5687 output is insensitive to DAC sample clock phase
noise, so using the DAC PLL clock mode will have similar spectral performance to the External clock mode. In
addition, the non-harmonic clock-related spurious signals will be small due to the low DAC output frequency.
With a complex input rate specified up to 250 MSPS, the DAC5687 is capable of producing signals with up to
200-MHz bandwidth for systems such as digital predistortion (DPD).
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Application Example: CMTS/VOD Transmitter
The DAC5687's exceptional SNR enables a dual-cable modem termination system (CMTS) or video on demand
(VOD) QAM transmitter in excess of the stringent DOCSIS specification, with > 74 dBc and 75 dBc in the
adjacent and alternate channels.
A typical system using the DAC5687 for a cost optimized dual channel two QAM transmitter is shown in
Figure 78. A GC5016 would take four separate symbol rate inputs and provide pulse shaping and interpolation to
~ 128 MSPS. The four QAM carriers would be combined into two groups of two QAM carriers with intermediate
frequencies of approximately 30 MHz to 40 MHz. The GC5016 would output two real data streams to one
DAC5687. The DAC5687 would function as a dual-channel device and provide 2x interpolation to increase the
frequency of the 2nd Nyquist zone image. The two signals are then output through the two DAC outputs, through
a transformer and to an RF upconverter.
DAC5687
QAM1
DUC
Ch2
QAM2
DUC
QAM3
DUC
QAM4
DUC
DAC
2
2
2
2
Ch1
DAC
GC5016
CDC7005
B0044-01
Figure 78. Dual Channel Two QAM CMTS Transmitter System Using DAC5687
The DAC5687 output for a two QAM256 carrier signal at 33-MHz and 39-MHz IF with the signal and system
properties listed in Table 18 is shown in Figure 70. The low DAC5687 noise floor provides better than 75 dBc
(equal bandwidth normalized to one QAM256 power) at > 6-MHz offset.
Table 18. Signal and System Properties for Complex IF System Example in Figure 79
Signal
68
QAM256, 5.36 MSPS, α = 0.12
IF Frequencies
33 MHz and 39 MHz
DAC5687 Input Rate
5.36 MSPS x 24 = 128.64 MSPS
DAC5687 Output Rate
257.28 MSPS (2x Interpolation)
DAC5687 Mode
X2
DAC5687
www.ti.com
SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
C002
Figure 79. Two QAM256 Carriers With at 36-MHz IF
Application Example: High-Speed Arbitrary Waveform Generator
The DAC5687's flexible input allows use of the dual input ports with demultiplexed odd/even samples at a
combined rate of up to 500 MSPS. Combined with the DAC's 16-bit resolution, the DAC5687 allows wideband
signal generation for test and measurement applications.
DAC5687
Odd
Digital
Pattern
Generator
Input
Multiplexer
DAC
Even
B0045-01
Figure 80. DAC5687 in Odd/Even Input Mode
69
DAC5687
www.ti.com
SLWS164B – FEBRUARY 2005 – REVISED JUNE 2005
Revision History
DATE
REV
PAGE (1)
29 JUN 05
B
1
Ordering Information
Added thermal pad dimensions
Reversed "External Clock Mode" and "PLL Clock Mode" in Noise floor test
SECTION
DESCRIPTION
9
AC specifications
31
Register Name: ATEST Changed PLLLOCK Output Signal for PLLVDD = 0 to "Normal Operation" in
Table 5
41
Clock Modes
Reversed ts(DATA) and th(DATA) in Figures 43 and 44
42
Clock Modes
Reversed ts(DATA) and th(DATA) in Figure 45
42
Clock Modes
Updated Figure 46
26 MAR
04
A
–
–
–
12 FEB 03
*
–
–
Original version
(1)
70
Page numbers for previous versions may differ from page numbers in the current version.
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