TI DAC5681

DAC5681
www.ti.com ................................................................................................................................................. SLLS864A – AUGUST 2007 – REVISED JANUARY 2009
16-BIT, 1.0 GSPS
DIGITAL-TO-ANALOG CONVERTER (DAC)
FEATURES
1
•
•
•
•
•
•
•
16-Bit Digital-to-Analog Converter (DAC)
1.0 GSPS Update Rate
16-Bit Wideband Input LVDS Data Bus
– 8 Sample Input FIFO
– On-Chip Delay Lock Loop
High Performance
– 73 dBc ACLR WCDMA TM1 at 180 MHz
On Chip 1.2 V Reference
Differential Scalable Output: 2 to 20 mA
Package: 64-Pin 9 × 9 mm QFN
APPLICATIONS
•
•
•
•
•
•
•
Cellular Base Stations
Broadband Wireless Access (BWA)
WiMAX 802.16
Fixed Wireless Backhaul
Cable Modem Termination System (CMTS)
Medical / Test Instrumentation
Radar Systems
DESCRIPTION
The DAC5681 is a 16-bit 1.0 GSPS digital-to-analog
converter (DAC) with wideband LVDS data input and
internal voltage reference. The DAC5681 offers
superior linearity and noise performance.
The DAC5681 integrates a wideband LVDS port with
on-chip termination, providing full 1.0 GSPS data
transfer into the DAC and lower EMI than traditional
CMOS data interfaces. An on-chip delay lock loop
(DLL) simplifies LVDS interfacing by providing skew
control for the LVDS input data clock.
The current-steering architecture of the DAC5681
consists of a segmented array of current sinking
switches directing up to 20mA of full-scale current to
complementary output nodes. An accurate on-chip
voltage reference is temperature-compensated and
delivers a stable 1.2-V reference voltage. Optionally,
an external reference may be used.
The DAC5681 is characterized for operation over the
industrial temperature range of –40°C to 85°C and is
available in a 64-pin QFN package. The device is pin
upgradeable to the other members of the family: the
DAC5681Z and DAC5682Z. The single-channel
DAC5681Z and dual-channel DAC5682Z both
provide optional 2x/4x interpolation and a clock
multiplying PLL.
ORDERING INFORMATION
TA
–40°C to 85°C
(1)
(2)
(3)
ORDER CODE
PACKAGE DRAWING/TYPE (1) (2) (3)
TRANSPORT MEDIA
DAC5681IRGCT
RGC / 64QFN Quad Flatpack
No-Lead
Tape and Reel
250
Tape and Reel
2000
DAC5681IRGCR
QUANTITY
Thermal Pad Size: 7,4 mm × 7,4 mm
MSL Peak Temperature: Level-3-260C-168 HR
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
website at www.ti.com.
1
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 © 2007–2009, Texas Instruments Incorporated
DAC5681
SLLS864A – AUGUST 2007 – REVISED JANUARY 2009 ................................................................................................................................................. www.ti.com
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.
CLKIN
Clock
Distribution
CLKINC
(3.3V)
AVDD
(1.8V)
VFUSE
(1.8V)
DVDD
(1.8V)
CLKVDD
FUNCTIONAL BLOCK DIAGRAM
EXTIO
1.2V
Reference
FDAC
EXTLO
BIASJ
DCLKP
Sync Disable
Delay Lock
Loop (DLL)
DCLKN
DLL Control
Mode Control
B
A
100
SYNCP
SYNCN
DAC Delay (0-3)
13
SYNC=’0->1'
(transition)
TXEnable=’1'
IOUTA1
16bit
DAC
IOUTA2
4
2
DAC Gain
16
16
Offset
D0N
DDR De-interleave
100
D0P
8 Sample FIFO
16
D15N
Delay Value
100
D15P
Sync & Control
SW_Sync
2
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GND
(3.3V)
IOVDD
RESETB
SCLK
SDENB
SDO
SDIO
FIFO Sync Disable
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DAC5681
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RESETB
AVDD
54
49
AVDD
DVDD
EXTIO
56
55
50
BIASJ
57
51
AVDD
EXTLO
IOUTA2
AVDD
60
59
IOUTA1
AVDD
AVDD
61
53
AVDD
62
52
DVDD
63
58
NC
64
DAC5681
RGC PACKAGE
(TOP VIEW)
CLKVDD
1
48
SDENB
CLKIN
2
47
SCLK
CLKINC
3
46
SDIO
GND
4
45
SDO
SYNCP
5
44
VFUSE
SYNCN
D15P
6
43
D0N
7
42
D0P
D15N
8
41
D1N
DAC5681
31
D5P
32
30
D6N
D5N
28
29
D6P
27
D4P
D7P
33
D7N
16
25
D12N
26
D4N
DCLKP
D3P
34
DCLKN
35
15
23
14
D12P
24
D13N
D8P
D3N
D8N
D2P
36
21
37
13
22
12
D13P
D9P
D14N
D9N
D2N
20
38
D10N
11
19
DVDD
D14P
D10P
DVDD
18
D1P
39
D11N
40
10
17
9
D11P
IOVDD
TERMINAL FUNCTIONS
TERMINAL
I/O
DESCRIPTION
NAME
NO.
AVDD
51, 54, 55,
59–62
I
BIASJ
57
O
Full-scale output current bias. For 20mA full-scale output current, connect a 960 Ω resistor to GND.
CLKIN
2
I
Positive external clock input with a self-bias of approximately CLKVDD/2.
CLKINC
3
I
Complementary external clock input. (See the CLKIN description)
CLKVDD
1
I
Internal clock buffer supply voltage. (1.8 V)
D[15..0]P
7, 11, 13,
15, 17, 19,
21, 23, 27,
29, 31, 33,
35, 37, 40,
42
I
LVDS positive input data bits 0 through 15. Each positive/negative LVDS pair has an internal 100 Ω
termination resistor. Order of bus can be reversed via rev_bus bit in CONFIG5 register. Data format
relative to DCLKP/N clock is Double Data Rate (DDR) with two data samples input per DCLKP/N clock. In
dual-channel mode, data for the A-channel is input while DCLKP is high.
D[15..0]N
8, 12, 14,
16, 18, 20,
22, 24, 28,
30, 32, 34,
36, 38, 41,
43
Analog supply voltage. (3.3V)
D15P is most significant data bit (MSB) – pin 7
D0P is least significant data bit (LSB) – pin 42
LVDS negative input data bits 0 through 15. (See D[15:0]P description above)
I
D15N is most significant data bit (MSB) – pin 8
D0N is least significant data bit (LSB) – pin 43
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TERMINAL FUNCTIONS (continued)
TERMINAL
I/O
DESCRIPTION
25
I
LVDS positive input clock. Unlike the other LVDS inputs, the DCLKP/N pair is self-biased to approximately
DVDD/2 and does not have an internal termination resistor in order to optimize operation of the DLL circuit.
See the “DLL Operation” section. For proper external termination, connect a 100 Ω resistor across LVDS
clock source lines followed by series 0.01 µF capacitors connected to each of DCLKP and DCLKN pins
(see Figure 17). For best performance, the resistor and capacitors should be placed as close as possible to
these pins.
DCLKN
26
I
LVDS negative input clock. (See the DCLKP description)
DVDD
10, 39, 50,
63
I
EXTIO
56
Used as external reference input when internal reference is disabled (i.e., EXTLO connected to AVDD).
I/O Used as 1.2V internal reference output when EXTLO = GND, requires a 0.1 µF decoupling capacitor to
AGND when used as reference output.
EXTLO
58
O
Connect to GND for internal reference, or AVDD for external reference.
4, Thermal
Pad
I
Pin 4 and the Thermal Pad located on the bottom of the QFN package is ground for AVDD, DVDD and
IOVDD supplies.
IOUTA1
52
O
DAC current output. An offset binary data pattern of 0x0000 at the DAC input results in a full scale current
sink and the least positive voltage on the IOUTA1 pin. Similarly, a 0xFFFF data input results in a 0 mA
current sink and the most positive voltage on the IOUTA1 pin.
IOUTA2
53
O
DAC complementary current output. The IOUTA2 has the opposite behavior of the IOUTA1 described
above. An input data value of 0x0000 results in a 0mA sink and the most positive voltage on the IOUTA2
pin.
IOVDD
9
I
Digital I/O supply voltage (3.3V) for pins RESETB, SCLK, SDENB, SDIO, SDO.
NC
64
I
No Connect. Leave open for proper operation.
RESETB
49
I
Resets the chip when low. Internal pull-up.
SCLK
47
I
Serial interface clock. Internal pull-down.
SDENB
48
I
Active low serial data enable, always an input to the DAC5681. Internal pull-up.
SDIO
46
I/O
Bi-directional serial interface data in 3-pin mode (default). In 4-pin interface mode (CONFIG5 sif4), the
SDIO pin is an input only. Internal pull-down.
SDO
45
O
Uni-directional serial interface data in 4-pin mode (CONFIG5 sif4). The SDO pin is in high-impedance state
in 3-pin interface mode (default), but can optionally be used as a status output pin via CONFIG14
SDO_func_sel(2:0). Internal pull-down.
SYNCP
5
I
LVDS SYNC positive input data. The SYNCP/N LVDS pair has an internal 100 Ω termination resistor. By
default, the SYNCP/N input must be logic ‘1’ to enable a DAC analog output. See the LVDS SYNCP/N
Operation paragraph for a detailed description.
SYNCN
6
I
LVDS SYNC negative input data.
VFUSE
44
I
Digital supply voltage. (1.8V) Connect to DVDD pins for normal operation. This supply pin is also used
for factory fuse programming.
NAME
DCLKP
GND
4
NO.
Digital supply voltage. (1.8 V)
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www.ti.com ................................................................................................................................................. SLLS864A – AUGUST 2007 – REVISED JANUARY 2009
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range (unless otherwise noted)
Supply voltage range
(1)
VALUE
UNIT
DVDD (2)
–0.5 to 2.3
V
VFUSE (2)
–0.5 to 2.3
V
CLKVDD
(2)
–0.5 to 2.3
V
AVDD (2)
–0.5 to 4
V
IOVDD (2)
–0.5 to 4
V
AVDD to DVDD
–2 to 2.6
V
CLKVDD to DVDD
–0.5 to 0.5
V
IOVDD to AVDD
–0.5 to 0.5
V
D[15..0]P ,D[15..0]N, SYNCP, SYNCN
Terminal voltage range
(2)
–0.5 to DVDD + 0.5
V
DCLKP, DCLKN (2)
–0.3 to 2.1
V
CLKIN, CLKINC (2)
–0.5 to CLKVDD + 0.5
V
–0.5 to IOVDD + 0.5
V
–0.5 to AVDD + 0.5
V
SDO, SDIO, SCLK, SDENB, RESETB
IOUTA1, IOUTA2
(2)
(2)
EXTIO, EXTLO, BIASJ (2)
Peak input current (any input)
Peak total input current (all inputs)
–0.5 to AVDD + 0.5
V
20
mA
–30
mA
Operating free-air temperature range, TA: DAC5681
–40 To 85
°C
Storage temperature range
–65 To 150
°C
(1)
(2)
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 GND.
THERMAL CHARACTERISTICS
over operating free-air temperature range (unless otherwise noted)
THERMAL CONDUCTIVITY
TJ
Maximum junction temperature
(1)
64ld QFN
UNIT
125
°C
Theta junction-to-ambient (still air)
20
Theta junction-to-ambient (150 lfm)
16
θJC
Theta junction-to-case
7
°C/W
θJP
Theta junction-to-pad
0.2
°C/W
θJA
(1)
°C/W
Air flow or heat sinking reduces θJA and may be required for sustained operation at 85° under maximum operating conditions.
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DAC5681
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ELECTRICAL CHARACTERISTICS — DC SPECIFICATION
over operating free-air temperature range , AVDD = 3.3 V, CLKVDD = 1.8 V, IOVDD = 3.3 V, DVDD = 1.8 V, IoutFS = 20 mA
(unless otherwise noted)
PARAMETER
TEST CONDITIONS
RESOLUTION
MIN
TYP
MAX
16
UNIT
Bits
DC ACCURACY (1)
INL
Integral nonlinearity
DNL
Differential nonlinearity
1 LSB = IOUTFS/216
±4
LSB
±2
ANALOG OUTPUT
Coarse gain linearity
±0.04
LSB
Offset error
Mid code offset
0.01
%FSR
Gain error
With external reference
1
%FSR
Gain error
With internal reference
0.7
%FSR
Minimum full scale output
current (2)
2
Maximum full scale output
current (2)
20
Output Compliance range (3)
mA
IOUTFS = 20 mA
AVDD
–0.5V
Output resistance
Output capacitance
AVDD
+ 0.5V
V
300
kΩ
5
pF
REFERENCE OUTPUT
Vref
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
Small signal bandwidth
1.25
1
CONFIG6: BiasLPF_A = 0
95
CONFIG6: BiasLPF_A = 1
472
Input capacitance
V
MΩ
kHz
100
pF
±1
ppm of
FSR/°C
TEMPERATURE COEFFICIENTS
Offset drift
Gain drift
With external reference
±15
With internal reference
±30
ppm of
FSR/°C
±8
ppm/°C
Reference voltage drift
POWER SUPPLY
Analog supply voltage, AVDD
3.0
3.3
3.6
V
Digital supply voltage, DVDD
1.71
1.8
2.15
V
Clock supply voltage, CLKVDD
1.71
1.8
2.15
V
3.0
3.3
3.6
V
I/O supply voltage, IOVDD
I(AVDD)
Analog supply current
67
mA
I(DVDD)
Digital supply current
191
mA
I(CLKVDD)
Clock supply current
15
mA
I(IOVDD)
IO supply current
4
mA
(1)
(2)
(3)
(4)
6
Mode 1 (below)
Measured differential across IOUTA1 and IOUTA2 with 25 Ω each to AVDD.
Nominal full-scale current, IoutFS, equals 16 × 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 DAC5681 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.
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www.ti.com ................................................................................................................................................. SLLS864A – AUGUST 2007 – REVISED JANUARY 2009
ELECTRICAL CHARACTERISTICS — DC SPECIFICATION (continued)
over operating free-air temperature range , AVDD = 3.3 V, CLKVDD = 1.8 V, IOVDD = 3.3 V, DVDD = 1.8 V, IoutFS = 20 mA
(unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
I(AVDD)
Sleep mode, AVDD supply current
1.5
mA
I(DVDD)
Sleep mode, DVDD supply current
91
mA
I(CLKVDD)
Sleep mode, CLKVDD supply
current
15
mA
I(IOVDD)
Sleep mode, IOVDD supply
current
AVDD + IOVDD current, 3.3V
DVDD + CLKVDD current, 1.8V
Mode 3 (below)
Mode 1: CLKIN = 1000 MHz
IF = 40 MHz
Single Tone, 0 dBFS
71
DVDD + CLKVDD current, 1.8V
P
605
Mode 2: CLKIN = 500 MHz
IF = 40 MHz
Single Tone, 0 dBFS
DVDD + CLKVDD current, 1.8V
Mode 3: CLKIN = 1000 MHz
DAC on SLEEP, Static Data Pattern
Power Dissipation
AVDD + IOVDD current, 3.3V
DVDD + CLKVDD current, 1.8V
Mode 4: CLKIN = OFF
DAC on SLEEP, Static Data Pattern
Power supply rejection ratio
T
Operating range
mA
111
mA
435
mW
3
mA
106
mA
200
mW
3
mA
20
DC tested
mW
6
Power Dissipation
PSRR
mA
650
71
Power Dissipation
AVDD + IOVDD current, 3.3V
mA
206
Power Dissipation
AVDD + IOVDD current, 3.3V
mA
1.5
mA
30
mW
–0.2
0.2
%FSR/V
–40
85
°C
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ELECTRICAL CHARACTERISTICS — AC SPECIFICATION (1)
Over recommended operating free-air temperature range, AVDD, IOVDD = 3.3 V, CLKVDD, DVDD = 1.8 V, IOUTFS = 20 mA,
4:1 transformer output termination, 50Ω doubly terminated load (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP MAX
UNIT
ANALOG OUTPUT
fCLK
Maximum output update rate
ts(DAC)
Output settling time to 0.1%
Transition: Code 0x0000 to 0xFFFF
1000
tpd
Output propagation delay
DAC output is updated on falling edge of DAC clock.
Does not include Digital Latency (see below).
tr(IOUT)
tf(IOUT)
MSPS
10.4
ns
2.5
ns
Output rise time 10% to 90%
220
ps
Output fall time 90% to 10%
220
ps
76
DAC
clock
cycles
BiasLPF_A enabled; register 0x06, Bit 3 set to 1.
8
µs
BiasLPF_A disabled; register 0x06, Bit 3 set to 0.
80
µs
BiasLPF_A enabled; register 0x06, Bit 3 set to 1.
8
µs
BiasLPF_A disabled; register 0x06, Bit 3 set to 0.
80
µs
CLKIN = 500 MHz, IF = 5.1 MHz,
First Nyquist Zone < fDATA/2
81
CLKIN = 1000 MHz, IF = 5.1 MHz,
First Nyquist Zone < fDATA/2
80
CLKIN = 1000 MHz, IF = 20.1 MHz,
First Nyquist Zone < fDATA/2
77
CLKIN = 500 MHZ, Single tone, 0 dBFS,
IF = 20.1 MHz
75
CLKIN = 1000 MHZ, Single tone, 0 dBFS,
IF = 20.1 MHz
70
CLKIN = 1000 MHZ, Single tone, 0 dBFS,
IF = 70.1 MHz
66
CLKIN = 1000 MHZ, Single tone, 0 dBFS,
IF = 180 MHz
60
CLKIN = 1000 MHZ, Single tone, 0 dBFS,
IF = 300.2 MHz
60
CLKIN = 1000 MHZ, Four tone, each -12 dBFS,
IF = 24.7, 24.9, 25.1 and 25.3 MHz
73
CLKIN = 1000 MHZ, IF = 20.1 and 21.1 MHz
88
CLKIN = 1000 MHZ, IF = 70.1 and 71.1 MHz
75
CLKIN = 1000 MHZ, IF = 150.1 and 151.1 MHz
67
CLKIN = 1000 MHz, IF = 298.4, 299.2, 300.8 and 301.6 MHz
64
Digital Latency
DAC Wake-up Time (2)
Power-up
Time
DAC Sleep Time
(3)
AC PERFORMANCE
SFDR
SNR
IMD3
Spurious free dynamic range
Signal-to-noise ratio
Third-order two-tone
intermodulation
(each tone at –6 dBFS)
Four-tone intermodulation
(each tone at –12 dBFS)
IMD
dBc
Single carrier, baseband, CLKIN = 983.04 MHz
ACLR (4)
Adjacent channel leakage ratio
Noise floor (5)
(1)
(2)
(3)
(4)
(5)
8
dBc
80
dBc
dBc
83
Single carrier, IF = 180 MHz, CLKIN = 983.04 MHz
73
Four carrier, IF = 180 MHz, CLKIN = 983.04 MHz
68
Four carrier, IF = 275 MHz, CLKIN = 983.04 MHz
66
50-MHz offset, 1-MHz BW, Single Carrier, baseband,
CLKIN = 983.04
93
50-MHz offset, 1-MHz BW, Four Carrier, baseband,
CLKIN = 983.04
85
dBc
dBc
Measured single-ended into 50 Ω load.
IOUT current settling to 1% of IOUTFS. Measured from SDENB rising edge; Register 0x06, toggle Bit 4 from 1 to 0.
IOUT current settling to less than 1% of IOUTFS. Measured from SDENB rising edge; Register 0x06, toggle Bit 4 from 0 to 1.
W-CDMA with 3.84 MHz BW, 5-MHz spacing, centered at IF. TESTMODEL 1, 10 ms
Carrier power measured in 3.84 MHz BW.
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ELECTRICAL CHARACTERISTICS (DIGITAL SPECIFICATIONS)
over recommended operating free-air temperature range, AVDD, IOVDD = 3.3V, CLKVDD, DVDD = 1.8V.
PARAMETER
TEST CONDITIONS
LVDS INTERFACE: D[15:0]P/N, SYNCP/N, DCLKP/N
MIN
TYP MAX
UNIT
(1)
VA,B+
Logic high differential
input voltage threshold
175
mV
VA,B–
Logic low differential
input voltage threshold
–175
mV
VCOM1
Input Common Mode
VCOM2
Input Common Mode
ZT
Internal termination
CL
LVDS Input
capacitance
tS, tH
DCLK to Data
SYNCP/N, D[15:0]P/N only
1.0
DCLKP/N only
SYNCP/N, D[15:0]P/N only
85
DCLKP/N: 0 to 125MHz (see Figure 20) DLL
Disabled, CONFIG5 DLL_bypass = 1, CONFIG10
= '00000000'
DCLKP/N = 200 MHz
DCLKP/N = 250 MHz
DCLK to Data Skew (2)
DLL Enabled,
CONFIG5 DLL_bypass =
0,
DDR format
DCLKP/N = 300 MHz
DCLKP/N = 350 MHz
DCLKP/N = 400 MHz
DCLKP/N = 450 MHz
DCLKP/N = 500 MHz
fDATA
Input data rate
supported
DLL Operating
Frequency (DCLKP/N
Frequency)
(1)
(2)
110
V
135
2
DCLKP/N = 150 MHz
tSKEW(A),
tSKEW(B)
V
DVDD
÷2
Setup_min
1100
Hold_min
–600
Positive
1000
Negative
–1800
Positive
pF
ps
800
Negative
–1300
Positive
600
Negative
–1000
Positive
450
Negative
–800
Positive
400
Negative
–700
Positive
300
Negative
–600
Positive
300
Negative
–500
Positive
350
Negative
–300
DLL Disabled, CONFIG5 DLL_bypass = 1, DDR format,
DCLKP frequency: <125 MHz
ps
250
MSPS
DLL Enabled, CONFIG5 DLL_bypass = 0, DDR format,
DCLKP frequency: 125 to 500 MHz
DLL Enabled, CONFIG5
DLL_bypass = 0, DDR
format
Ω
250
1000
CONFIG10 = '11001101' = 0xCD
125-150
CONFIG10 = '11001110' = 0xCE
150-175
CONFIG10 = '11001111' = 0xCF
175-200
CONFIG10 = '11001000' = 0xC8
200-325
CONFIG10 = '11000000' = 0xC0
325-500
MHz
See LVDS INPUTS section for terminology.
Positive skew: Clock ahead of data.
Negative skew: Data ahead of clock.
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ELECTRICAL CHARACTERISTICS (DIGITAL SPECIFICATIONS) (continued)
over recommended operating free-air temperature range, AVDD, IOVDD = 3.3V, CLKVDD, DVDD = 1.8V.
PARAMETER
TEST CONDITIONS
MIN
TYP MAX
UNIT
CMOS INTERFACE: SDO, SDIO, SCLK, SDENB, RESETB
VIH
High-level input voltage
2
VIL
Low-level input voltage
0
IIH
High-level input current
±20
µA
IIL
Low-level input current
±20
µA
CI
CMOS Input
capacitance
0
5
V
0.8
V
pF
IOVDD
–0.2
V
0.8
x IOVDD
V
Iload = 100 µA
0.2
V
Iload = 2 mA
0.5
V
Iload = –100 µA
VOH
3
SDO, SDIO
Iload = –2mA
VOL
SDO, SDIO
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
t(SCLK)
Period of SCLK
100
ns
t(SCLKH)
High time of SCLK
40
ns
t(SCLKL)
Low time of SCLK
40
ns
td(Data)
Data output delay after
falling edge of SCLK
10
ns
tRESET
Minimum RESETB
pulse width
25
ns
CLOCK INPUT (CLKIN/CLKINC)
Duty cycle
50%
Differential voltage (3)
0.4
CLKIN/CLKINC input
common mode
(3)
10
1
V
CLKVDD
÷2
V
Driving the clock input with a differential voltage lower than 1V will result in degraded performance.
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TYPICAL CHARACTERISTICS
DNL
10
10
8
6
8
6
4
2
4
2
DNL- LSBs
INL - LSBs
INL
0
-2
0
-2
-4
-4
-6
-8
-10
0
-6
-8
-10
0
10000
20000
30000
Code
40000
50000
60000
10000
10
85
0
80
-10
75
-20
70
-12 dBFS
65
-6 dBFS
60
55
40000
50000
60000
Fdata = 1000 MSPS,
FOUT = 20 MHz
-30
-40
-50
-60
50
0 dBFS
-70
45
-80
40
0
-90
50
100 150 200 250 300 350 400 450
IF - Intermediate Frequency - MHz
0
50
Figure 3. SFDR vs IF
100 150 200 250 300 350 400 450 500
f - Frequency - MHz
Figure 4. Single-Tone Spectral Plot
10
10
Fdata = 1000 MSPS,
FOUT = 170 MHz
0
-10
-10
-20
-20
-30
-40
-50
-30
-40
-50
-60
-60
-70
-70
-80
-80
-90
-90
0
50
100 150 200 250 300 350 400 450 500
f - Frequency - MHz
Fdata = 1000 MSPS,
FOUT = 270 MHz
0
Power - dBm
Power - dBm
30000
Code
Figure 2. Differential Nonlinearity
90
Power - dBm
SFDR - Spurious Free Dynamic Range - dBc
Figure 1. Integral Nonlinearity
20000
0
50
Figure 5. Single-Tone Spectral Plot
100 150 200 250 300 350 400 450 500
f - Frequency - MHz
Figure 6. Single-Tone Spectral Plot
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TYPICAL CHARACTERISTICS (continued)
0
100
95
-20
90
-12 dBFS
85
IMD - dBc
Power - dBm
-40
80
-6 dBFS
75
70
65
-60
-80
0 dBFS
60
-100
Fdata = 1000 MSPS,
FOUT = 40 ±0.5 MHz
55
50
0
50
-120
38
100 150 200 250 300 350 400 450
IF - Intermediate Frequency - MHz
38.5
Figure 7. Two-Tone IMD vs Output Frequency
39
39.5 40
40.5 41
f - Frequency - MHz
41.5
42
Figure 8. Two-Tone IMD Spectral Plot
85
0
Fdata = 491.52 MSPS
-20
80
ACLR - dBc
Power - dBm
-40
-60
75
-80
70
-100
Fdata = 1000 MSPS,
FOUT = 250 MHz, ±0.5 MHz
-120
248
249
249.5
250
250.5 251
f - Frequency - MHz
251.5
252
252.5
65
0
Figure 9. Two-Tone IMD Spectral Plot
12
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61.44
122.88
184.32
IF - Intermediate Frequency - MHz
245.76
Figure 10. Single Carrier W-CDMA
Test Model 1 - ACLR vs IF
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TYPICAL CHARACTERISTICS (continued)
-20
-20
-30
-40
-40
-50
-50
Power - dBm
Power - dBm
-30
Fdata = 983.04 MSPS,
FOUT = 61.44 MHz
-60
-70
-80
-60
-70
-80
-90
-90
-100
-100
-110
-110
-120
48.7
53.7
58.7
63.7
f - Frequency - MHz
68.7
Fdata = 983.04 MSPS,
FOUT = 184.32 MHz
-120
171.5
73.7
Figure 11. Single Carrier W-CDMA Test Model 1
Carrier Power: -8.2 dBm, ACLR 79.7 dB
-40
-50
-50
Power - dBm
Power - dBm
Fdata = 983.04 MSPS,
-30 FOUT = 184.32 MHz
-40
-60
-70
-80
-60
-70
-80
-90
-90
-100
-100
-110
-110
179
184
189
f - Frequency - MHz
196.5
-20
Fdata = 983.04 MSPS,
-30 FOUT = 184.32 MHz
174
181.5
186.5
191.5
f - Frequency - MHz
Figure 12. Single Carrier W-CDMA Test Model 1
Carrier Power: -9 dBm, ACLR 73.3 dB
-20
-120
169
176.5
194
199
Figure 13. Two Carrier W-CDMA Test Model 1
Carrier Power: -12 dBm, ACLR 70.6 dB
-120
164
169
174
179 184 189 194
f - Frequency - MHz
199
204
Figure 14. Four Carrier W-CDMA Test Model 1
Carrier Power: -16.8 dBm, ACLR 68.3 dB
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TYPICAL CHARACTERISTICS (continued)
-20
Fdata = 983.04 MSPS,
-30 FOUT = 184.32 MHz
-40
Power - dBm
-50
-60
-70
-80
-90
-100
-110
-120
164
169
174
179 184 189 194
f - Frequency - MHz
199
204
Figure 15. Three Carrier W-CDMA Test Model 1 with GAP
Carrier Power: -14.8 dBm, ACLR 70.1 dB
14
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TEST METHODOLOGY
Typical AC specifications were characterized with the DAC5681EVM using the test configuration shown in
Figure 16. A sinusoidal master clock frequency is generated by an HP8665B signal generator and into a splitter.
One output drives an Agilent 8133A pulse generator, and the other drives the CDCM7005 clock driver. The
8133A converts the sinusoidal frequency into a square wave output clock and drives an Agilent ParBERT
81250A pattern-generator clock. On the EVM, the DAC5681 CLKIN/C input clock is driven by an CDCM7005
clock distribution chip that is configured to simply buffer the external 8665B clock.
The DAC5681 output is characterized with a Rohde and Schwarz FSU 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.
DAC5681EVM SMA Adapter Board
DAC5681 DAC
P
N
D0
P
N
Pattern
Memory
SYNC
P
N
DCLK
P
N
100
100
3.3 V
FIFO & Demux
Stacking Interface Connector
D15
100
DLL
Opt.
Clock
Divider
Splitter
100
Rohde &
Schwartz
FSU
Spectrum
Analyzer
3.3 V
CDCM7005
Agilent 8133A
Pulse Generator
3.3 V
DAC
100
36 each
SMA-SMA cables
Optional
Divider
100
CLKIN
CLKINC
Agilent 81205A
ParBERT
100
DAC5681EVM
HP8665B
Synthesized
Signal
Generator
Figure 16. DAC5681 Test Configuration
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DEFINITION OF SPECIFICATIONS
Adjacent Carrier Leakage Ratio (ACLR): Defined for a 3.84Mcps 3GPP W-CDMA input signal measured in a
3.84MHz bandwidth at a 5MHz offset from the carrier with a 12dB peak-to-average ratio.
Analog and Digital Power Supply Rejection Ratio (APSSR, DPSSR): Defined as the percentage error in the
ratio of the delta IOUT and delta supply voltage normalized with respect to the ideal IOUT current.
Differential Nonlinearity (DNL): Defined as the variation in analog output associated with an ideal 1 LSB
change in the digital input code.
Gain Drift: Defined as the maximum change in gain, in terms of ppm of full-scale range (FSR) per °C, from the
value at ambient (25°C) to values over the full operating temperature range.
Gain Error: Defined as the percentage error (in FSR%) for the ratio between the measured full-scale output
current and the ideal full-scale output current.
Integral Nonlinearity (INL): Defined as the maximum deviation of the actual analog output from the ideal output,
determined by a straight line drawn from zero scale to full scale.
Intermodulation Distortion (IMD3, IMD): The two-tone IMD3 or four-tone IMD is defined as the ratio (in dBc) of
the worst 3rd-order (or higher) intermodulation distortion product to either fundamental output tone.
Offset Drift: Defined as the maximum change in DC offset, in terms of ppm of full-scale range (FSR) per °C,
from the value at ambient (25°C) to values over the full operating temperature range.
Offset Error: Defined as the percentage error (in FSR%) for the ratio of the differential output current
(IOUT1–IOUT2) and the mid-scale output current.
Output Compliance Range: Defined as the minimum and maximum allowable voltage at the output of the
current-output DAC. Exceeding this limit may result reduced reliability of the device or adversely affecting
distortion performance.
Reference Voltage Drift: Defined as the maximum change of the reference voltage in ppm per degree Celsius
from value at ambient (25°C) to values over the full operating temperature range.
Spurious Free Dynamic Range (SFDR): Defined as the difference (in dBc) between the peak amplitude of the
output signal and the peak spurious signal.
Signal to Noise Ratio (SNR): Defined as the ratio of the RMS value of the fundamental output signal to the
RMS sum of all other spectral components below the Nyquist frequency, including noise, but excluding the first
six harmonics and dc.
16
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TYPICAL APPLICATION SCHEMATIC
(1)
Power supply decoupling capacitors not shown.
(2)
Internal Reference configuration shown.
Figure 17. Schematic
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DETAILED DESCRIPTION
Table 1. Register Map
Name
Address
Default
(MSB)
Bit 7
STATUS0
0x00
0x1F
Reserved
CONFIG1
0x01
0x10
CONFIG2
0x02
0xC0
Bit 6
Bit 5
DLL_lock
Unused
DAC_delay(1:0)
Unused
Twos_ comp
Reserved
Bit 4
Bit 3
Reserved
SLFTST _ena
Bit 2
device_ID(2:0)
Reserved
Unused
FIFO_err_ mask
Pattern_err
_mask
(LSB)
Bit 0
Bit 1
version(1:0)
FIFO_offset(2:0)
Reserved
CONFIG3
0x03
0x70
DAC_offset _ena
SLFTST_err
_mask
STATUS4
0x04
0x00
Unused
SLFTST_err
FIFO_err
Pattern_ err
Unused
Unused
Unused
Unused
CONFIG5
0x05
0x00
SIF4
rev_bus
clkdiv_ sync_dis
FIFO_
sync_dis
Reserved
DLL_ bypass
Reserved
Reserved
CONFIG6
0x06
0x0C
Hold_sync _dis
Unused
Reserved
Sleep_A
BiasLPF_A
Reserved
Reserved
DLL_ sleep
CONFIG7
0x07
0xFF
CONFIG8
0x08
0x00
CONFIG9
0x09
0x00
CONFIG10
0x0A
0x00
CONFIG11
0x0B
0x00
CONFIG12
0x0C
0x00
CONFIG13
0x0D
0x00
CONFIG14
0x0E
0x00
CONFIG15
0x0F
0x00
18
Reserved
DACA_gain(3:0)
Reserved
SW_sync
SW_sync _sel
Reserved
Reserved
DLL_ restart
Reserved
Reserved
DLL_delay(3:0)
DLL_invclk
DLL_ifixed(2:0)
Reserved
Reserved
Offset_sync
OffsetA(12:8)
OffsetA(7:0)
SDO_func_sel(2:0)
Reserved
Reserved
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Register name: STATUS0 – Address: 0x00, Default = 0x1F
Bit 7
Bit 6
Bit 5
Reserved
0
DLL_lock
0
Unused
0
Bit 4
Bit 3
1
device_ID(2:0)
1
Bit 2
Bit 1
Bit 0
version(1:0)
1
1
1
Reserved (Bit 7):
Set to '0' by default. (Read Only)
DLL_lock:
Asserted when the internal DLL is locked. Once the DLL is locked, this bit should remain a
‘1’ unless the DCLK input clock is removed or abruptly changes frequency causing the
DLL to fall out of lock. (Read Only)
device_ID(2:0):
Returns ‘111’ for DAC5681 Device_ID code. (ReadOnly)
version(1:0):
A hardwired register that contains the register set version of the chip. (ReadOnly)
version (1:0)
Identification
‘01’
‘10’
‘11'
PG1.0 Initial Register Set
PG1.1 Register Set
Production Register Set
Register name: CONFIG1 – Address: 0x01, Default = 0x10
Bit 7
Bit 6
DAC_delay(1:0)
0
0
Bit 5
Bit 4
Bit 3
Unused
0
Reserved
1
SLFTST_ena
0
Bit 2
Bit 1
Bit 0
0
FIFO_offset(2:0)
0
0
DAC_delay(1:0):
DAC data delay adjustment. (0–3 periods of the DAC clock) This can be used to adjust
system level output timing. The same delay is applied to DACA data paths.
Reserved (Bit 4):
Set to '1' for proper operation.
SLFTST_ena:
When set, a Digital Self Test (SLFTST) of the core logic is enabled. Refer to Digital Self
Test Mode section for details on SLFTST operation.
FIFO_offset(2:0):
Programs the FIFO’s output pointer location, allowing the input pointer to be shifted –4 to
+3 positions upon SYNC. Default offset is 0 and is updated upon each sync event – unless
disabled via FIFO_sync_dis in CONFIG5 register.
FIFO_offset(2:0)
Offset
011
+3
010
+2
001
+1
000
0
111
–1
110
–2
101
–3
100
–4
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Register name: CONFIG2 – Address: 0x02, Default = 0xC0
Bit 7
Bit 6
Bit 5
Bit 4
Twos_comp
1
Reserved
1
Reserved
0
Unused
0
Bit 3
Bit 2
Bit 1
Bit 0
0
0
Reserved
0
0
Twos_comp:
When set (default) the input data format is expected to be 2s complement, otherwise
offset binary format is expected.
Reserved (Bit 6):
Set to '1' for proper operation.
Reserved (Bit 5):
Set to '0' for proper operation.
Reserved (3:0):
Set to '0000' for proper operation.
Register name: CONFIG3 – Address: 0x03, Default = 0x70
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DAC_offset
_ena
0
SLFTST_err
_mask
FIFO_err_
mask
Pattern_err_
mask
Reserved
Reserved
SW_sync
SW_sync_sel
1
1
1
0
0
0
0
DAC_offset_ena:
When set, the values of OffsetA(12:0) in CONFIG12 through CONFIG13 registers are
summed into the DAC-A data path. This provides a system-level offset adjustment
capability that is independent of the input data.
SLFTST_err_mask:
When set, masks out the SLFTST_err bit in STATUS4 register. Refer to Digital Self
Test Mode section for details on SLFTST operation.
FIFO_err_mask:
When set, masks out the FIFO_err bit in STATUS4 register.
Pattern_err_mask:
When set, masks out the Pattern err bit in STATUS4 register.
Reserved (Bit 3):
Set to '0' for proper operation.
Reserved (Bit 2):
Set to '0' for proper operation.
SW_sync:
This bit can be used as a substitute for the LVDS external SYNC input pins for both
synchronization and transmit enable control.
SW_sync_sel:
When set, the SW_sync bit is used as the only synchronization input and the LVDS
external SYNC input pins are ignored.
20
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Register name: STATUS4 – Address: 0x04, Default = 0x00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Unused
0
SLFTST_err
0
FIFO_err
0
Pattern_err
0
Unused
0
Unused
0
Unused
0
Unused
0
SLFTST_err:
Asserted when the Digital Self Test (SLFTST) fails. To clear the error, write a ‘0’ to this
register bit. This bit is also output on the SDO pin when the Self Test is enabled via
SLFTST_ena control bit in CONFIG1. Refer to Digital Self Test Mode section for details on
SLFTST operation.
FIFO_err:
Asserted when the FIFO pointers over run each other causing a sample to be missed. To
clear the error, write a ‘0’ to this register bit.
Pattern_err:
A digital checkerboard pattern compare function is provided for board level confidence
testing and DLL limit checks. If the Pattern_err_mask bit via CONFIG3 is cleared, logic is
enabled to continuously monitor input FIFO data. Any received data pattern other than
0xAAAA or 0x5555 causes this bit to be set. To clear the error, flush out the previous
pattern error by inputting at least 8 samples of the 0xAAAA and/or 0x5555, then write a ‘0’
to this register bit.
Register name: CONFIG5 – Address: 0x05, Default = 0x00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
SIF4
rev_bus
FIFO_sync _dis
Reserved
DLL_bypass
Reserved
Reserved
0
0
clkdiv_sync
_dis
0
0
0
0
0
0
SIF4:
When set, the serial interface is in 4 pin mode, otherwise it is in 3 pin mode. Refer to
SDO_func_sel(2:0) bits in CONFIG14 register for options available to output status
indicator data on the SDO pin.
rev_bus:
Reverses the LVDS input data bus so that the MSB to LSB order is swapped. This
function is provided to ease board level layout and avoid wire crossovers in case the
LVDS data source output bus is mirrored with respect to the DAC’s input data bus.
clkdiv_sync_dis:
Disables the clock divider sync when this bit is set.
FIFO_sync_dis:
Disables the FIFO offset sync when this bit is set. See FIFO_offset(2:0) bits in CONFIG1
register
Reserved (Bit 3):
Set to '0' for proper operation.
DLL_bypass:
When set, the DLL is bypassed and the LVDS data source is responsible for providing
correct setup and hold timing.
Reserved (Bit 1):
Set to '0' for proper operation.
Reserved (Bit 0):
Set to '0' for proper operation.
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Register name: CONFIG6 – Address: 0x06, Default = 0x0C
Bit 7
Hold_sync _dis
0
Bit 6
Unused
0
Bit 5
Reserved
0
Bit 4
Sleep_A
0
Bit 3
Bit 2
Bit 1
Bit 0
BiasLPF_A
1
Reserved
1
Reserved
0
DLL_sleep
0
Hold_sync_dis:
When set, disables the sync to the FIFO output HOLD block. Typically this bit should be
cleared to ‘0’ for normal operation and also follow the same value as the FIFO_sync_dis
control bit in CONFIG5.
Reserved (Bit 5):
Set to '0' for proper operation.
Sleep_A:
When set, DACA is put into sleep mode.
BiasLPF_A:
Enables a 95 kHz low pass filter corner on the DACA current source bias when cleared. If
this bit is set, a 472 kHz filter corner is used.
Reserved (Bit 2):
Set to '1' for proper operation.
Reserved (Bit 1):
Set to '0' for proper operation.
DLL_sleep:
When set, the DLL is put into sleep mode.
Register name: CONFIG7 – Address: 0x07, Default = 0xFF
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
1
1
Bit 3
Bit 2
Bit 1
0
DLL_restart
0
DACA_gain(3:0)
1
1
Reserved
1
1
1
DACA_gain(3:0):
Scales DACA output current in 16 equal steps.
VEXTIO
x (DACA_gain + 1)
Rbias
Reserved (3:0):
Set to '1111' for proper operation.
Register name: CONFIG8 – Address: 0x08, Default = 0x00
Bit 7
0
Bit 6
Bit 5
0
Reserved
0
Bit 4
0
Bit 0
Reserved
0
0
Reserved (7:3):
Set to ‘00000’ for proper operation.
DLL_restart:
This bit is used to restart the DLL. When this bit is set, the internal DLL loop filter is reset to
zero volts, and the DLL delay line is held at the center of its bias range. When cleared, the
DLL will acquire lock to the DCLK signal. A DLL restart is accomplished by setting this bit
with a serial interface write, and then clearing this bit with another serial interface write. Any
interruption in the DCLK signal or changes to the DLL programming in the CONFIG10
register must be followed by this DLL restart sequence. Also, when this bit is set, the
DLL_lock indicator in the STATUS0 register is cleared.
Reserved (1:0):
Set to ‘00’ for proper operation
22
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Register name: CONFIG9 – Address: 0x09, Default = 0x00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
0
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
DLL_invclk
0
0
DLL_ifixed(2:0)
0
0
Reserved
0
Reserved (7:0):
0
0
0
Set to '0x00' for proper operation
Register name: CONFIG10 – Address: 0x0A, Default = 0x00
Bit 7
Bit 6
0
0
Bit 5
DLL_delay(3:0)
DLL_delay(3:0):
0
The DCLKP/N LVDS input data clock has a DLL to automatically skew the clock to LVDS
data timing relationship, providing proper setup and hold times. DLL_delay(3:0) is used to
manually adjust the DLL delay ± from the fixed delay set by DLL_ifixed(2:0). Adjustment
amounts are approximate.
DLL_delay(3:0)
Delay Adjust (degrees)
1000
50°
1001
55°
1010
60°
1011
65°
1100
70°
1101
75°
1110
80°
1111
85°
0000
90° (Default)
0001
95°
0010
100°
0011
105°
0100
110°
0101
115°
0110
120°
0111
125°
DLL_invclk:
When set, used to invert an internal DLL clock to force convergence to a different solution.
This can be used in the case where the DLL delay adjustment has exceeded the limits of
its range.
DLL_ifixed(2:0):
Adjusts the DLL delay line bias current. Refer to the Electrical Characteristics table. Used
in conjunction with the DLL_invclk bit to select appropriate delay range for a given DCLK
frequency:
'011' – maximum bias current and minimum delay range
'000' – mid scale bias current
'101' – minimum bias current and maximum delay range
'100' – do not use.
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Register name: CONFIG11 – Address: 0x0B, Default = 0x00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
0
Bit 3
Bit 2
Bit 1
Bit 0
0
OffsetA(12:8)
0
0
0
Reserved
0
0
Reserved (7:0):
0
0
Set to '0x00' for proper operation.
Register name: CONFIG12 – Address: 0x0C, Default = 0x00
Bit 7
Bit 6
Bit 5
0
Offset_sync
0
Reserved
0
Bit 4
0
Reserved (1:0):
Set to ‘00’ for proper operation.
Offset_sync:
On a change from ‘0’ to ‘1’ the values of the OffsetA(12:0) and OffsetB(12:0) control
registers are transferred to the registers used in the DAC-A and DAC-B offset calculations.
This double buffering allows complete control by the user as to when the change in the
offset value occurs. This bit does not auto-clear. Prior to updating new offset values, it is
recommended that the user clear this bit.
OffsetA(12:8):
Upper 5 bits of the offset adjustment value for the A data path. (SYNCED via Offset_sync)
Register name: CONFIG13 – Address: 0x0D, Default = 0x00
Bit 7
Bit 6
Bit 5
Bit 4
0
0
0
0
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
0
OffsetA(7:0)
OffsetA(7:0):
24
Lower 8 bits of the offset adjustment value for the A data path. (SYNCED via Offset_sync)
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Register name: CONFIG14 – Address: 0x0E, Default = 0x00
Bit 7
Bit 6
0
SDO_func_sel(2:0)
0
SDO_func_sel(2:0):
Reserved (4:0):
Bit 5
Bit 4
0
0
Bit 3
Bit 2
Bit 1
Bit 0
0
Reserved
0
0
0
Selects the signal for output on the SDO pin. When using the 3 pin serial interface
mode, this allows the user to multiplex several status indicators onto the SDO pin. In 4
pin serial interface mode, programming this register to view one of the 5 available status
indicators will override normal SDO serial interface operation.
SDO_func_sel
(2:0)
Output to SDO
000, 110, 111
Normal SDO function
001
Not defined
010
DLL_lock
011
Pattern_err
100
FIFO_err
101
SLFTST_err
Set to '00000' for proper operation.
Register name: CONFIG15 – Address: 0x0F, Default = 0x00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
0
Reserved
0
Reserved (7:0):
0
0
0
Set to '0x00' for proper operation.
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SERIAL INTERFACE
The serial port of the DAC5681 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 DAC5681. It is compatible with most synchronous transfer formats and can be configured as
a 3 or 4 pin interface by SIF4 in register CONFIG5. 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. Data is input into the device
with the rising edge of SCLK.Data is output from the device on the falling edge of SCLK.
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 2 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 2. Instruction Byte of the Serial Interface
MSB
Bit
Description
7
R/W
LSB
6
N1
5
N0
4
A4
3
A3
2
A2
1
A1
0
A0
R/W
Identifies the following data transfer cycle as a read or write operation. A high indicates a read
operation from DAC5681 and a low indicates a write operation to DAC5681.
[N1 : N0]
Identifies the number of data bytes to be transferred per Table 5 below. Data is transferred MSB
first.
Table 3. Number of Transferred Bytes Within One
Communication Frame
[A4 : A0]
N1
N0
Description
0
0
Transfer 1 Byte
0
1
Transfer 2 Bytes
1
0
Transfer 3 Bytes
1
1
Transfer 4 Bytes
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
DAC5681 MSB first and counts down for each byte.
Figure 18 shows the serial interface timing diagram for a DAC5681 write operation. SCLK is the serial interface
clock input to DAC5681. Serial data enable SDENB is an active low input to DAC5681. SDIO is serial data in.
Input data to DAC5681 is clocked on the rising edges of SCLK.
26
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Instruction Cycle
Data Transfer Cycle (s)
SDENB
SCLK
SDIO
r/w
N1
N0
A4
A3
A2
A1
A0
D7
D6
tS (SDENB)
D5
D4
D3
D2
D1
D0
tSCLK
SDENB
SCLK
SDIO
tSCLKL
th (SDIO)
tSCLKH
tS (SDIO)
Figure 18. Serial Interface Write Timing Diagram
Figure 19 shows the serial interface timing diagram for a DAC5681 read operation. SCLK is the serial interface
clock input to DAC5681. Serial data enable SDENB is an active low input to DAC5681. SDIO is serial data in
during the instruction cycle. In 3 pin configuration, SDIO is data out from DAC5681 during the data transfer
cycle(s), while SDO is in a high-impedance state. In 4 pin configuration, SDO is data out from DAC5681 during
the data transfer cycle(s). At the end of the data transfer, SDO will output low on the final falling edge of SCLK
until the rising edge of SDENB when it will 3-state.
Instruction Cycle
Data Transfer Cycle(s)
SDENB
SCLK
SDIO
r/w
N1
N0
-
A3
A2
A1
SDO
A0
D7
D6
D5
D4
D3
D2
D1
D0
0
D7
D6
D5
D4
D3
D2
D1
D0
0
3 pin Configuration Output
4 pin Configuration Output
SDENB
SCLK
SDIO
SDO
Data n
Data n-1
td (Data)
Figure 19. Serial Interface Read Timing Diagram
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CLOCK AND DATA MODES
The timing diagram for the DAC5681 is shown in Figure 20. The DAC5681 accepts an external full-rate clock
input on the CLKIN/CLKINC pins to drive the DAC and final logic stages. An LVDS half-rate data clock
(DCLKP/DCLKN) is provided by the user and is typically generated by a toggling data bit to maintain LVDS data
to DCLK timing alignment. LVDS data relative to DCLK is input using Double Data Rate (DDR) switching using
both rising and falling edges as shown in the both figures below. The CONFIG10 register contains user
controlled settings for the DLL to adjust for the DCLK input frequency and various tSKEW timing offsets between
the LVDS data and DCLK. The CDCM7005 and CDCE62005 from Texas Instruments are recommended for
providing phase aligned clocks at different frequencies for device-to-device clock distribution and multiple DAC
synchronization.
CLKIN
CLKINC
DACCLK
(Internal)
DCLKN
DCLKP
tSKEW(A)
tSKEW(B)
Valid Data (A)
tH
tS
Valid Data (B)
SYNCN
Transmit Enable / Synchronization Event
SYNCP
D[15:0]N
D[15:0]P
Single DAC Mode (1X1)
A1
A0
A2
A3
AN
AN+1
Figure 20. Clock and Data Timing Diagram
28
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CLOCK INPUTS
Figure 21 shows an equivalent circuit for the LVDS data input clock (DCLKP/N).
27 kW
DVDD
DCLKP
Note: Input and output common mode
level self-biases to approximately DVDD/2,
or 0.9 V normal.
DVDD
GND
DCLKN
GND
27 kW
Figure 21. DCLKP/N Equivalent Input Circuit
Figure 22 shows an equivalent circuit for the DAC input clock (CLKIN/C).
6 kW
CLKVDD
CLKIN
Note: Input and output common mode
level self-biases to approximately CLKVDD/2,
or 0.9 V normal.
CLKVDD
GND
CLKINC
GND
6 kW
Figure 22. CLKIN/C Equivalent Input Circuit
Figure 23 shows the preferred configuration for driving the CLKIN/CLKINC input clock with a differential
ECL/PECL source.
0.01 mF
Differential
ECL
or
(LV)PECL
Source
CLKIN
+
CAC
100 W
CLKINC
82.5 W
130 W
RT
0.01 mF
RT
130 W
82.5 W
VTT
Figure 23. Preferred Clock Input configuration With a Differential ECL/PECL Clock Source
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LVDS DATA INTERFACING
Interfacing very high-speed LVDS data and clocks presents a big challenge to system designers as they have
unique constraints and are often implemented with specialized circuits to increase bandwidth. One such
specialized LVDS circuit used in many FPGAs and ASICs is a SERializer-DESerializer (SERDES) block. For
interfacing to the DAC5681, only the SERializer functionality of the SERDES block is required. SERDES drivers
accept lower rate parallel input data and output a serial stream using a shift register at a frequency multiple of
the data bit width. For example, a 4-bit SERDES block can accept parallel 4-bit input data at 250 MSPS and
output serial data 1000 MSPS.
External clock distribution for FPGA and ASIC SERDES drivers often have a chip-to-chip system constraint of a
limited input clock frequency compared to the desired LVDS data rate. In this case, an internal clock multiplying
PLL is often used in the FPGA or ASIC to drive the high-rate SERDES outputs. Due to this possible system
clocking constraint, the DAC5681 accommodates a scheme where a toggling LVDS SERDES data bit can
provide a “data driven” half-rate clock (DCLK) from the data source. A DLL on-board the DAC is used to shift the
DCLK edges relative to LVDS data to maintain internal setup and hold timing.
To increase bandwidth of a single 16-bit input bus, the DAC5681 assumes Double Data Rate (DDR) style
interfacing of data relative to the half-rate DCLK. Refer to Figure 24 and Figure 25 providing an example
implementation using FPGA-based LVDS data and clock interfaces to drive the DAC5681. In this example, an
assumed system constraint is that the FPGA can only receive a 250 MHz maximum input clock while the desired
DAC clock is 1000 MHz. A clock distribution chip such as the CDCM7005 or the CDCE62005 is useful in this
case to provide frequency and phase locked clocks at 250 MHz and 1000 MHz.
FPGA / ASIC
DAC5681 DAC
100
1.0 GHz
CDCM7005
÷1
Clock Divider /
Distribution
PLL_LOCK
PD#
LE
DATA
CLK
RESET#
CDCM7005
Control
Status &
Control
PLL
Synth
VCTRL_IN
Loop
Filter
REF_IN
PFD
RDiv
Loop
Filter
Charge
Pump
CPOUT
Status & Control
VCXO
1000 MHz
STRB
÷4
VCXO_STATUS
REF_STATUS
10 MHz
REF
OSC
Term
VCO
NDivider
CHIP_EN
100
TRF3761-X PLL/VCO
Div
1/2/4
1.0 GHz
Term
DLL
Freq/Phase Locked
~ 2.1 GHz
CLK
DAC5681
Control
250 MHz
To RX
Path
Control
DATA
250 MHz
DLL
100
500 MHz
Toggling
Data Bit
CLKP
CLKP
DCLK
4x Clock
Multiplier
To TX
Feedback
3.3V
100
SERDES
Duplexer
SYNC
PA
DAC
LOCK_DET
SERDES
3.3V
PD_BUF
D0
100
100
SERDES
3.3V
100
100
FIFO & Demux
Q
D15
1.0 GBPS
(DDR)
SDIO
SDO
SDENB
SCLK
RESETB
I
Parallel to SERDES
Formatter
TX
Data Source
Antenna
SERDES
TRF3761-X
Control
Figure 24. Example Direct Conversion System Diagram
From the example provided by Figure 25, driving LVDS data into the DAC using SERDES blocks requires a
parallel load of 4 consecutive data samples to shift registers. Color is used in the figure to indicate how data and
clocks flow from the FPGA to the DAC5681. The figure also shows the use of the SYNCP/N input, which along
with DCLK, requires 18 individual SERDES data blocks to drive the DAC’s input data FIFO that provides an
elastic buffer to the DAC5681 digital processing chain.
30
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4x Clock
Multiplier PLL
Ref CLK
Gen &
Sync
250MHz
Clock
DCLKP
4b SERDES
(CLKOUT)
4
4b SERDES
(SYNC)
LVDS
4b SERDES
(bit 15)
LVDS
1,0,1,0...
DAC
LVDS
500MHz
(½ Rate)
DCLK
Delay Lock Loop
DCLKN
CLKA
(500MHz)
SYNC
16
16
1000MSPS DDR
(2 bits/CLKIN cycle)
4
16
D15N
4b SERDES
(bit 0)
LVDS
100
16
Serializer
Format
D15P
4
D0P
D0N
1
0
CLKB
(500MHz)
8 Sample
Input FIFO
1111
1101
1111
“
SYNCN
100
SYNCP
250MHz
Data Source
(4 phases)
x4
4
1010
1010
1010
“
System
SYNC
1000MHz
÷1
100
250MHz
Using common “data driven”
SERDES blocks, relative
delays from CLK, SYNC and
DATA are matched. (200pS)
100
FPGA
To DAC
250 MHz (FPGA)
1000 MHz (FPGA)
DCLK Data Nibble
Repeating 4 bit
Sequence “1010” …
DCLKP/N
0101
DDR Clock Gen
1
0
1
0
1
0
1
0
1
0
500 MHz
CLKIN to DLL
CLKA F
500 MHz
CLKA (DAC)
DLL Phase Offset control
determines CLKA/B skew.
CLKB F
Normally = “1111”
Ocassional = “1101”
for SYNC event
Sample “S1”
S1[15:0]
Sample “S2”
S2[15:0]
Sample “S3”
S3[15:0]
Sample “S4”
S4[15:0]
SYNC Data Nibble
1011
SYNC Generator
500 MHz
CLKB (DAC)
SYNCP/N
SERDES
1
1
0
1
1
1
1
SYNC input combines TXENABLE
function (normally “1”) and SYNChronizer
function (“0” to “1” transition)
1
Bit 15 Data Nibble
S1[15:0]
S2[15:0]
S4[15:0]
S3[15:0]
S4[15] S3[15] S2[15] S1[15]
D15P/N
SERDES
Bit 0 Data Nibble
S4[0]
S3[0]
S2[0]
S1[0]
D0P/N
SERDES
Figure 25. Example FPGA-Based LVDS Data Flow to DAC
LVDS INPUTS
The D[15:0]P/N and SYNCP/N LVDS pairs have the input configuration shown in Figure 26. Figure 27 shows the
typical input levels and common-mode voltage used to drive these inputs.
D[15:0]P,
SYNCP
50 W
To Adjacent
LVDS Input
D[15:0]N,
SYNCN
100 pF
Total
50 W
Ref Note (1)
To Adjacent
LVDS Input
LVDS
Receiver
Note (1): RCENTER node common
to all D[15:0]P/N and SYNCP/N
receiver inputs
Figure 26. D[15:0]P/N and SYNCP/N LVDS Input Configuration
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Example
D[15:0]P,
SYNCP
VCOM1 =
(VA +VB )/2
LVDS
Receiver
100 W
VA,B
VA
VA
1.40 V
VB
1.00 V
VA,B
400 mV
DAC5681
0V
D[15:0]N,
SYNCN
VB
-400 mV
GND
1
Logical Bit
Equivalent
0
Figure 27. LVDS Data (D[15:0]P/N, SYNCP/N Pairs) Input Levels
Example LVDS Data Input Levels
APPLIED VOLTAGES
RESULTING
DEFERENTIAL
VOLTAGE
RESULTING
COMMON-MODE
VOLTAGE
VA
VB
VA,B
VCOM1
1.4 V
1.0 V
400 mV
1.2 V
1.0 V
1.4 V
–400 mV
1.2 V
0.8 V
400 mV
0.8 V
1.2 V
–400 mV
LOGICAL BIT BINARY
EQUIVALENT
1
0
1.0 V
1
0
Figure 28 shows the DCLKP/N LVDS clock input levels. Unlike the D[15:0]P/N and SYNCP/N LVDS pairs, the
DCLKP/N pair does not have an internal resistor and the common-mode voltage is self-biased to approximately
DVDD/2 in order to optimize the operation of the DLL circuit. For proper external termination a 100 Ω resistor
needs to be connected across the LVDS clock source lines followed by series 0.01 µF capacitors connected to
each of the DCLKP and DCLKN pins. For best performance, the resistor and capacitors should be placed as
close as possible to these pins.
Note: AC Coupled
DAC5681
Self-bias (VBIAS)
0.01 mF
100 W
DCLKP
VA,B
DLL
Circuit
VA
0.01 mF
DCLKN
VB
GND
VCOM2 =~ DVDD/2
Figure 28. LVDS Clock (DCLKP/N) Input Levels
LVDS SYNCP/N Operation
The SYNCP/N LVDS input control functions as a combination of Transmit Enable (TXENABLE) and
Synchronization trigger. If SYNCP is low, the transmit chain is disabled so input data from the FIFO is ignored
while zeros are inserted into the data path. If SYNCP is raised from low to high, a synchronization event occurs
with behavior defined by individual control bits in registers CONFIG1, CONFIG5 and CONFIG6. The SYNCP/N
control is sampled and input into the FIFO along with the other LVDS data to maintain timing alignment with the
data bus. See Figure 25.
The software_sync_sel and software_sync controls in CONFIG3 provide a substitute for external SYNCP/N
control; however, since the serial interface is used no timing control is provided with respect to the DAC clock.
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DLL OPERATION
The DAC5681 provides a digital Delay Lock Loop (DLL) to skew the LVDS data clock (DCLK) relative to the data
bits, D[15:0] and SYNC, in order to maintain proper setup and hold timing. Since the DLL operates closed-loop, it
requires a stable DCLK to maintain delay lock. Refer to the description of DLL_ifixed(2:0) and DLL_delay(3:0)
control bits in the CONFIG10 register. Prior to initializing the DLL, the DLL_ifixed value should be programmed
to match the expected DCLK frequency range. To initialize the DLL, refer to the DLL_Restart programming bit in
the CONFIG8 register. After initialization, the status of the DLL can be verified by reading the DLL_Lock bit from
STATUS0. See Startup Sequence below.
RECOMMENDED STARTUP SEQUENCE
The following startup sequence is recommended to initialize the DAC5681:
1. Supply all 1.8V (CLKVDD, DVDD, VFUSE) voltages simultaneously followed by all 3.3V (AVDD and IOVDD)
voltages.
2. Provide stable CLKIN/C clock.
3. Toggle RESETB pin for a minimum 25 nSec active low pulse width.
4. Program all desired SIF registers. Set DLL_Restart bit during this write cycle. The CONFIG10 register value
should match the corresponding DCLKP/N frequency range in the Electrical Characteristics table.
5. Provide stable DCLKP/N clock. (This can also be provided earlier in the sequence)
6. Clear the DLL_Restart bit when the DCLKP/N clock is expected to be stable.
7. Verify the status of DLL_Lock and repeat until set to ‘1’. DLL_Lock can be monitored by reading the
STATUS0 register or by monitoring the SDO pin in 3-wire SIF mode. (See description for CONFIG14
SDO_func_sel.)
8. Enable transmit of data by asserting the LVDS SYNCP/N input or setting CONFIG3 SW_sync bit. (See
description for CONFIG3 SW_sync and SW_sync_sel) The SYNC source must be held at a logic ‘1’ to
enable data flow through the DAC. If multiple DAC devices require synchronization, refer to the
"Recommended Multi-DAC Synchronization Procedure" below.
9. Provide data flow to LVDS D[15:0]P/N pins. If using the LVDS SYNCP/N input, data can be input
simultaneous with the logic ‘1’ transition of SYNCP/N.
RECOMMENDED MULTI-DAC SYNCHRONIZATION PROCEDURE
The DAC5681 provides a mechanism to synchronize multiple DAC devices in a system. The procedure has two
steps involving control of the CONFIG5 clkdiv_sync_dis and FIFO_sync_dis bits as well as external control of
the LVDS SYNCP/N input. (All DACs involved need to be configured to accept the external SYNCP/N input and
not "software" sync mode).
1. Synchronize Clock Dividers (for each DAC):
a. Set CONFIG5 clkdiv_sync_dis = 0.
b. Set CONFIG5 FIFO_sync_dis = 0.
c. Toggle SYNCP/N input to all DACs simultaneously (same input to all DACs).
2. Synchronize FIFO pointers (for each DAC):
a. Set CONFIG5 clkdiv_sync_dis = 1 (Disable clock divider re-sync).
b. Set CONFIG5 FIFO_sync_dis = 0 (Keep same as step 1).
c. Wait a minimum of 50 CLKIN cycles from previous SYNCP/N toggle. In practice, the time required to
write the above register value will typically occupy more than 50 cycles.
d. Assert SYNCP/N input and hold at '1' to all DACs simultaneously. Holding this at '1' is effectively the
TXENABLE for the chip so data will be output on the analog pins.
3. After the normal pipeline delay of the device, the outputs of all DACs will be synchronized to within ±1 DAC
clock cycle.
CMOS DIGITAL INPUTS
Figure 29 shows a schematic of the equivalent CMOS digital inputs of the DAC5681. SDIO and SCLK have
pull-down resistors while RESETB and SDENB have pull-up resistors internal the DAC5681. See the
specification table for logic thresholds. The pull-up and pull-down circuitry is approximately equivalent to 100kΩ.
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IOVDD
IOVDD
internal
digital in
SDIO
SCLK
internal
digital in
RESETB
SDENB
IOGND
IOGND
Figure 29. CMOS/TTL Digital Equivalent Input
DIGITAL SELF TEST MODE
The DAC5681 has a Digital Self Test (SLFTST) mode to designed to enable board level testing without requiring
specific input data test patterns. The SLFTST mode is enabled via the CONFIG1 SLFTST_ena bit and results
are only valid when CONFIG3 SLFTST_err_mask bit is cleared. An internal Linear Feedback Shift Register
(LFSR) is used to generate the input test patterns for the full test cycle while a checksum result is computed on
the digital signal chain outputs. The LVDS input data bus is ignored in SLFTST mode. After the test cycle
completes, if the checksum result does not match a hardwired comparison value, the STATUS4 SLFTST_err bit
is set and will remain set until cleared by writing a ‘0’ to the SLFTST_err bit. A full self test cycle requires no
more than 400,000 CLKIN/C clock cycles to complete and will automatically repeat until the SLFTEST_ena bit is
cleared.
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To initiate the Digital Self Test:
1. Provide a normal CLKIN/C input clock.
2. Provide a RESETB pulse to perform a hardware reset on device.
3. Program the registers with the values shown in Table 4. These register values contain the settings to
properly configure the SLFTST including SLFTST_ena and SLFTST_err_mask bits
4. Provide a ‘1’ on the SYNCP/N input to initiate TXENABLE.
5. Wait at a minimum of 400,000 CLKIN/C cycles for the SLFTST to complete. Example: If CLKIN = 1GHz, then
the wait period is 400,000 × 1 / 1GHz = 400 µSec.
6. Read STATUS4 SLFTST_err bit. If set, a self test error has occurred. The SLFTST_err status may
optionally be programmed to output on the SDO pin if using the 3-bit SIF interface. See Table 4 Note (1).
7. (Optional) The SLFTST function automatically repeats until SLFTST_ena bit is cleared. To loop the test,
write a ‘0’ to STATUS4 SLFTST_err to clear previous errors and continue at step 5 above.
8. To continue normal operating mode, provide another RESETB pulse and reprogram registers to the desired
normal settings.
Table 4. Digital Self Test (SLFTST) Register Values
(1)
REGISTER
ADDRESS (hex)
VALUE (Binary)
CONFIG1
01
00011000
VALUE (Hex)
18
CONFIG2
02
11101010
EA
CONFIG3
03
10110000
B0
STATUS4
04
00000000
00
CONFIG5
05
00000110
06
CONFIG6
06
00001111
0F
CONFIG12
0C
00001010
0A
CONFIG13
0D
01010101
55
CONFIG14 (1)
0E
00001010
0A
CONFIG15
0F
10101010
AA
All others
–
Default
Default
If using a 3-bit SIF interface, the SDO pin can be programmed to report SLFTST_err status via the SDO_fun_sel(2:0) bits. In this case,
set CONFIG14 = ‘10101010’ or AA hex.
REFERENCE OPERATION
The DAC5681 uses 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 default full-scale
output current equals 16 times this bias current and can thus be expressed as:
IOUTFS = 16 × IBIAS = 16 × VEXTIO / RBIAS
The DAC has a 4-bit coarse gain control via DACA_gain(3:0) in the CONFIG7 register so the IOUTFS can
expressed as:
IOUTAFS = (DACA_gain + 1) × IBIAS = (DACA_gain + 1) × 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.
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 dB.
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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 to 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 maximum full-scale output current equal to 16 times IBIAS.
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. The output
current flow in each pin driving a resistive load can be expressed as:
IOUT1 = IOUTFS × (65536 – CODE) / 65536
IOUT2 = IOUTFS × 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 – | IOUT1 | × RL
VOUT2 = AVDD – | IOUT2 | × RL
Assuming that the data is full scale (65536 in offset binary notation) and the RL is 25 Ω, the differential voltage
between pins IOUT1 and IOUT2 can be expressed as:
VOUT1 = AVDD – | –0 mA | × 25 Ω = 3.3 V
VOUT2 = AVDD – | –20 mA | × 25 Ω = 2.8 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.
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DAC OUTPUT SINC RESPONSE
Due to the sampled nature of a high-speed DAC, the well known sin(x)/x (or SINC) response can significantly
attenuate higher frequency output signals. Figure 30 shows the unitized SINC attenuation roll-off with respect to
the final DAC sample rate in 4 Nyquist zones. For example, if the final DAC sample rate FS = 1.0 GSPS, then a
tone at 440MHz is attenuated by 3.0dB. Although the SINC response can create challenges in frequency
planning, one side benefit is the natural attenuation of Nyquist images.
Figure 30. Unitized DAC sin(x)/x (SINC) Response
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ANALOG CURRENT OUTPUTS
Figure 31 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 referenced 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 DAC5681 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.
AVDD
R LOAD
IOUT1
R LOAD
IOUT2
S(1)
S(N)
S(2)
S(1)C
S(2)C
...
S(N)C
Figure 31. Equivalent Analog Current Output
The DAC5681 can be easily configured to drive a doubly terminated 50Ω cable using a properly selected RF
transformer. Figure 32 and Figure 33 show the 50Ω 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 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.
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AVDD
(3.3 V)
50 W
1:1
IOUT1
RLOAD
100 W
50 W
IOUT2
50 W
AVDD (3.3 V)
Figure 32. Driving a Doubly-Terminated 50-Ω Cable Using a 1:1 Impedance Ratio Transformer
AVDD (3.3 V)
100 W
4:1
IOUT1
RLOAD
50 W
IOUT2
100 W
AVDD (3.3 V)
Figure 33. Driving a Doubly-Terminated 50-Ω Cable Using a 4:1 Impedance Ratio Transformer
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APPLICATIONS EXAMPLES
DIGITAL INTERFACE AND CLOCKING CONSIDERATIONS FOR APPLICATION EXAMPLES
The DAC5681’s LVDS digital input bus can be driven by an FPGA or digital ASIC. This input signal can be
generated directly by the FPGA, or fed by a Texas Instruments Digital Up Converter (DUC) such as the GC5016
or GC5316. Optionally, a GC1115 Crest Factor Reduction (CFR) or Digital Pre-Distortion (DPD) processor may
be inserted in the digital signal chain for improving the efficiency of high-power RF amplifiers. For the details on
the DAC’s high-rate digital interface, refer to the LVDS Data Interfacing section.
A low phase noise clock for the DAC at the final sample rate can be generated by a VCXO and a Clock
Synchronizer/PLL such as the Texas Instruments CDCM7005 or CDCE62005, which can also provide other
system clocks.
DIGITAL IF OUTPUT RADIO
Refer to Figure 34 for an example Digital IF Output Radio. The high data rate of the DAC5681 (up to 1.0GSPS)
allows for extremely wide bandwidth signals. The DAC output signal would typically be terminated with a
transformer (see the Analog Current Outputs 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. The TRF3671
Frequency Synthesizer, with integrated VCO, may be used to drive a common LO input of the mixers for
frequencies between 375 and 2380 MHz.
DAC5681 DAC
D0P/N
100
SYNCP/N
100
3.3V
100
100
3.3V
RF
Processing
DAC
100
D15P/N
FIFO & Demux
LVDS Data Interface
3.3V
DCLKP/N
PLL/
DLL
DLL
1000 MHz
100
250 MHz
375 MHz Min to 2380 MHz Max
(Depends on divider and
“dash #” of TRF3761)
100
100
CLKIN/C
GC5016 or GC5316 DUC,
With GC1115 CFR and/or
DPD Processor
FPGA
Div
1/2/4
VCXO
÷4
÷1
Clock Divider /
Distribution
VCO
NDivider
PLL
Loop
Filter
Loop
Filter
PFD
RDiv
CDCM7005
Note : For clarity, only signal paths are shown.
VCTRL_IN
10 MHz
OSC
CPOUT
TRF3761-X PLL/VCO
Figure 34. System Diagram of a Dual Channel Real IF Output Radio
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APPLICATIONS EXAMPLES (continued)
CMTS/VOD TRANSMITTER
The exceptional SNR of the DAC5681 enables a 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.
See Figure 34 for an example IF Output Radio – this signal chain is nearly identical to a typical system using the
DAC5681 for a cost optimized two QAM transmitter. A GC5016 would accept two separate symbol rate inputs
and provide pulse shaping and interpolation to ~ 128 MSPS. The two 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 data to the DAC5681 through an FPGA for CMOS to LVDS translation. The signal is output through
a transformer and to an RF upconverter.
HIGH-SPEED ARBITRARY WAVEFORM GENERATOR
The 1GSPS bandwidth input data bus combined with the 16-bit DAC resolution of the DAC5681 allows wideband
signal generation for test and measurement applications. The FPGA-based waveform generator can make use of
the full Nyquist bandwidth of up to 500MHz.
DAC5681 DAC
D15P/N
100
D0P/N
100
SYNCP/N
100
FIFO
LVDS Data Interface
FPGA
DAC
DCLKP/N
100
DLL
Figure 35. System Diagram of Arbitrary Waveform Generator
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PACKAGE MATERIALS INFORMATION
www.ti.com
21-Apr-2009
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
Diameter Width
(mm) W1 (mm)
A0 (mm)
B0 (mm)
K0 (mm)
P1
(mm)
W
Pin1
(mm) Quadrant
DAC5681IRGCR
VQFN
RGC
64
2000
330.0
16.4
9.3
9.3
1.5
12.0
16.0
Q2
DAC5681IRGCT
VQFN
RGC
64
250
330.0
16.4
9.3
9.3
1.5
12.0
16.0
Q2
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
21-Apr-2009
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
DAC5681IRGCR
VQFN
RGC
64
2000
333.2
345.9
28.6
DAC5681IRGCT
VQFN
RGC
64
250
333.2
345.9
28.6
Pack Materials-Page 2
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