AD AD9912A/PCBZ 1 gsps direct digital synthesizer with 14-bit dac Datasheet

1 GSPS Direct Digital
Synthesizer with 14-Bit DAC
AD9912
FEATURES
APPLICATIONS
1 GSPS internal clock speed (up to 400 MHz output directly)
Integrated 1 GSPS 14-bit DAC
48-bit frequency tuning word with 4 μHz resolution
Differential HSTL comparator
Flexible system clock input accepts either crystal or external
reference clock
On-chip low noise PLL REFCLK multiplier
2 SpurKiller channels
Low jitter clock doubler for frequencies up to 750 MHz
Single-ended CMOS comparator; frequencies of <150 MHz
Programmable output divider for CMOS output
Serial I/O control
Excellent dynamic performance
Software controlled power-down
Available in two 64-lead LFCSP packages
Residual phase noise @ 250 MHz
10 Hz offset: −113 dBc/Hz
1 kHz offset: −133 dBc/Hz
100 kHz offset: −153 dBc/Hz
40 MHz offset: −161 dBc/Hz
Agile LO frequency synthesis
Low jitter, fine tune clock generation
Test and measurement equipment
Wireless base stations and controllers
Secure communications
Fast frequency hopping
GENERAL DESCRIPTION
The AD9912 is a direct digital synthesizer (DDS) that features
an integrated 14-bit digital-to-analog converter (DAC). The
AD9912 features a 48-bit frequency tuning word (FTW) that
can synthesize frequencies in step sizes no larger than 4 μHz.
Absolute frequency accuracy can be achieved by adjusting the
DAC system clock.
The AD9912 also features an integrated system clock phaselocked loop (PLL) that allows for system clock inputs as low
as 25 MHz.
The AD9912 operates over an industrial temperature range,
spanning −40°C to +85°C.
BASIC BLOCK DIAGRAM
AD9912
DAC_OUT
S1 TO S4
DIGITAL
INTERFACE
STARTUP
CONFIGURATION
LOGIC
DIRECT
DIGITAL
SYNTHESIS
CORE
FDBK_IN
CLOCK
OUTPUT
DRIVERS
SERIAL PORT,
I/O LOGIC
FILTER
OUT
OUT_CMOS
06763-001
SYSTEM CLOCK
MULTIPLIER
Figure 1.
Rev. F
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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
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Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©2007–2010 Analog Devices, Inc. All rights reserved.
AD9912
TABLE OF CONTENTS
Features .............................................................................................. 1
Default Output Frequency on Power-Up ................................ 25
Applications ....................................................................................... 1
Power Supply Partitioning............................................................. 26
General Description ......................................................................... 1
3.3 V Supplies.............................................................................. 26
Basic Block Diagram ........................................................................ 1
1.8 V Supplies.............................................................................. 26
Revision History ............................................................................... 3
Serial Control Port ......................................................................... 27
Specifications..................................................................................... 4
Serial Control Port Pin Descriptions ....................................... 27
DC Specifications ......................................................................... 4
Operation of Serial Control Port .............................................. 27
AC Specifications.......................................................................... 6
The Instruction Word (16 Bits) ................................................ 28
Absolute Maximum Ratings............................................................ 8
MSB/LSB First Transfers ........................................................... 28
Thermal Resistance ...................................................................... 8
I/O Register Map ............................................................................ 31
ESD Caution .................................................................................. 8
I/O Register Descriptions .............................................................. 33
Pin Configuration and Function Descriptions ............................. 9
Serial Port Configuration (Register 0x0000 to
Register 0x0005) ......................................................................... 33
Typical Performance Characteristics ........................................... 11
Input/Output Termination Recommendations .......................... 16
Theory of Operation ...................................................................... 17
Overview...................................................................................... 17
Direct Digital Synthesizer (DDS) ............................................. 17
Digital-to-Analog (DAC) Output ............................................ 18
Reconstruction Filter ................................................................. 18
FDBK_IN Inputs ........................................................................ 19
SYSCLK Inputs ........................................................................... 20
Output Clock Drivers and 2× Frequency Multiplier ............. 22
Harmonic Spur Reduction ........................................................ 22
Power-Down and Reset (Register 0x0010 to
Register 0x0013) ......................................................................... 33
System Clock (Register 0x0020 to Register 0x0022) ............. 34
CMOS Output Divider (S-Divider) (Register 0x0100 to
Register 0x0106) ......................................................................... 35
Frequency Tuning Word (Register 0x01A0 to
Register 0x01AD) ....................................................................... 35
Doubler and Output Drivers (Register 0x0200 to
Register 0x0201) ......................................................................... 37
Calibration (User-Accessible Trim) (Register 0x0400 to
Register 0x0410) ......................................................................... 37
Thermal Performance .................................................................... 24
Harmonic Spur Reduction (Register 0x0500 to
Register 0x0509) ......................................................................... 37
Power-Up ......................................................................................... 25
Outline Dimensions ....................................................................... 39
Power-On Reset .......................................................................... 25
Ordering Guide .......................................................................... 39
Rev. F | Page 2 of 40
AD9912
REVISION HISTORY
6/10—Rev. E to Rev. F
Changed Default Value of Register 0x003 to 0x19 (Table 12).....31
5/10—Rev. D to Rev. E
Deleted 64-Lead LFCSP (CP-64-1) .................................. Universal
Changes to SYSCLK PLL Enabled/ Maximum Input Rate of System
Clock PFD, Table 2 ............................................................................... 6
Updated Outline Dimensions ........................................................39
Changes to Ordering Guide ...........................................................39
11/09—Rev. C to Rev. D
Added 64-Lead LFCSP (CP-64-7).................................... Universal
Changes to Serial Port Timing Specifications and
Propagation Delay Parameters ........................................................ 6
Added Exposed Paddle Notation to Figure 2 ................................ 8
Changes to Power Supply Partitioning Section ...........................25
Change to Serial Control Port Section .........................................26
Changes to Figure 52 ......................................................................28
Added Exposed Paddle Notation to Outline Dimensions .........38
Changes to Ordering Guide ...........................................................39
7/09—Rev. B to Rev. C
Changes to Logic Outputs Parameter, Table 1 .............................. 3
Changes to AVDD (Pin 25, Pin 26, Pin 29, and Pin 30) ............ 25
6/09—Rev. A to Rev. B
Changes to Figure 40 and Direct Digital Synthesizer Section .. 17
Changes to Figure 48 ...................................................................... 22
Changes to Table 11 ........................................................................ 30
Changes to Table 22 and Table 23 ................................................. 34
1/08—Rev. 0 to Rev. A
Changes to Table 1 ............................................................................ 3
Changes to Table 2 ............................................................................ 5
Changes to Table 4 ............................................................................ 8
Changes to Typical Performance Characteristics ....................... 10
Changes to Functional Description Section ................................ 19
Changes to Single-Ended CMOS Output Section ...................... 21
Changes to Harmonic Spur Reduction Section .......................... 21
Changes to Power Supply Partitioning Section........................... 25
10/07—Revision 0: Initial Version
Rev. F | Page 3 of 40
AD9912
SPECIFICATIONS
DC SPECIFICATIONS
AVDD = 1.8 V ± 5%, AVDD3 = 3.3 V ± 5%, DVDD = 1.8 V ± 5%, DVDD_I/O = 3.3 V ± 5%, AVSS = 0 V, DVSS = 0 V, unless otherwise noted.
Table 1.
Parameter
SUPPLY VOLTAGE
DVDD_I/O (Pin 1)
DVDD (Pin 3, Pin 5, Pin 7)
AVDD3 (Pin 14, Pin 46, Pin 47, Pin 49)
AVDD3 (Pin 37)
AVDD (Pin 11, Pin 19, Pin 23 to Pin 26, Pin 29,
Pin 30, Pin 36, Pin 42, Pin 44, Pin 45, Pin 53)
SUPPLY CURRENT
Min
Typ
Max
Unit
3.135
1.71
3.135
1.71
1.71
3.30
1.80
3.30
3.30
1.80
3.465
1.89
3.465
3.465
1.89
V
V
V
V
V
IAVDD3 (Pin 37)
8
9.6
mA
IAVDD3 (Pin 46, Pin 47, Pin 49)
IAVDD (Pin 11, Pin 19, Pin 23 to Pin 26, Pin 29,
Pin 30, Pin 36, Pin 42, Pin 44, Pin 45)
26
113
31
136
mA
mA
40
205
2
48
246
3
mA
mA
mA
DVDD_I/O
0.8
±200
V
V
μA
pF
AVDD
0.4
−50
V
V
μA
pF
IAVDD (Pin 53)
IDVDD (Pin 3, Pin 5, Pin 7)
IDVDD_I/O (Pin 1, Pin 14 1 )
LOGIC INPUTS (Except Pin 32)
Input High Voltage (VIH)
Input Low Voltage (VIL)
Input Current (IINH, IINL)
Maximum Input Capacitance (CIN)
CLKMODESEL (Pin 32) LOGIC INPUT
Input High Voltage (VIH)
Input Low Voltage (VIL)
Input Current (IINH, IINL)
Maximum Input Capacitance (CIN)
LOGIC OUTPUTS
2.0
DVSS
Output High Voltage (VOH)
Output Low Voltage (VOL)
FDBK_IN INPUT
Input Capacitance
Input Resistance
Differential Input Voltage Swing
2.7
DVSS
±60
3
Test Conditions/Comments
Pin 37 is typically 3.3 V but can be set to 1.8 V
See also the Total Power Dissipation
specifications
CMOS output driver at 3.3 V, 50 MHz, with
5 pF load
DAC output current source, fS = 1 GSPS
Aggregate analog supply, with system
clock PLL, HSTL output driver, and S-divider
enabled
DAC power supply
Digital core (SpurKiller off )
Digital I/O (varies dynamically)
Pin 9, Pin 10, Pin 54, Pin 55, Pin 58 to Pin 61,
Pin 63, Pin 64
At VIN = 0 V and VIN = DVDD_I/O
Pin 32 only
1.4
AVSS
−18
3
18
225
3
22
DVDD_I/O
0.4
V
V
26
pF
kΩ
mV p-p
Rev. F | Page 4 of 40
At VIN = 0 V and VIN = AVDD
Pin 62 and the following bidirectional pins:
Pin 9, Pin 10, Pin 54, Pin 55, Pin 63
IOH = 1 mA
IOL = 1 mA
Pin 40, Pin 41
Differential
Equivalent to 112.5 mV swing on each leg;
must be ac-coupled
AD9912
Parameter
SYSTEM CLOCK INPUT
SYSCLK PLL Bypassed
Input Capacitance
Input Resistance
Internally Generated DC Bias Voltage 2
Differential Input Voltage Swing
SYSCLK PLL Enabled
Input Capacitance
Input Resistance
Internally Generated DC Bias Voltage2
Differential Input Voltage Swing
Crystal Resonator with SYSCLK PLL Enabled
Motional Resistance
CLOCK OUTPUT DRIVERS
HSTL Output Driver
Differential Output Voltage Swing
Common-Mode Output Voltage2
CMOS Output Driver
Output Voltage High (VOH)
Output Voltage Low (VOL)
Output Voltage High (VOH)
Output Voltage Low (VOL)
TOTAL POWER DISSIPATION
DDS Only
1
2
Min
2.4
0.93
632
2.4
0.93
632
Typ
Max
Unit
Test Conditions/Comments
System clock inputs should always be accoupled (both single-ended and differential)
1.5
2.6
1.17
2.9
1.38
pF
kΩ
V
mV p-p
Single-ended, each pin
Differential
3
2.6
1.17
2.9
1.38
Equivalent to 316 mV swing on each leg
pF
kΩ
V
mV p-p
Single-ended, each pin
Differential
Equivalent to 316 mV swing on each leg
9
100
Ω
25 MHz, 3.2 mm × 2.5 mm AT cut
1080
1280
1480
mV
Output driver static, see Figure 27 for
output swing vs. frequency
0.7
0.88
1.06
V
2.7
0.4
V
V
V
V
637
765
mW
DDS with Spur Reduction On
686
823
mW
DDS with HSTL Driver Enabled
657
788
mW
DDS with CMOS Driver Enabled
729
875
mW
DDS with HSTL and CMOS Drivers Enabled
747
897
mW
DDS with SYSCLK PLL Enabled
648
777
mW
Power-Down Mode
13
16
mW
0.4
1.4
Pin 14 is in the AVDD3 group, but it is recommended that Pin 14 be tied to Pin 1.
AVSS = 0 V.
Rev. F | Page 5 of 40
Output driver static, see Figure 28 and
Figure 29 for output swing vs. frequency
IOH = 1 mA, Pin 37 = 3.3 V
IOL = 1 mA, Pin 37 = 3.3 V
IOH = 1 mA, Pin 37 = 1.8 V
IOL = 1 mA, Pin 37 = 1.8 V
Power-on default, except SYSCLK PLL bypassed and CMOS driver off; SYSCLK = 1 GHz;
HSTL driver off; spur reduction off; fOUT =
200 MHz
Same as “DDS Only” case, except both spur
reduction channels on
Same as “DDS Only” case, except HSTL driver
enabled
Same as “DDS Only” case, except CMOS
driver and S-divider enabled and at 3.3 V;
CMOS fOUT = 50 MHz (S-divider = 4)
Same as “DDS Only” case, except both HSTL
and CMOS drivers enabled; S-divider
enabled and set to 4; CMOS fOUT = 50 MHz
Same as “DDS Only” case, except 25 MHz on
SYCLK input and PLL multiplier = 40
Using either the power-down and enable
register or the PWRDOWN pin
AD9912
AC SPECIFICATIONS
fS = 1 GHz, DAC RSET = 10 kΩ, unless otherwise noted. Power supply pins within the range specified in the DC Specifications section.
Table 2.
Parameter
FDBK_IN INPUT
Input Frequency Range
Minimum Differential Input Level
SYSTEM CLOCK INPUT
SYSCLK PLL Bypassed
Input Frequency Range
Duty Cycle
Minimum Differential Input Level
SYSCLK PLL Enabled
VCO Frequency Range, Low Band
VCO Frequency Range, Auto Band
VCO Frequency Range, High Band
Maximum Input Rate of System
Clock PFD
Without SYSCLK PLL Doubler
Input Frequency Range
Multiplication Range
Minimum Differential Input Level
With SYSCLK PLL Doubler
Input Frequency Range
Multiplication Range
Input Duty Cycle
Minimum Differential Input Level
Crystal Resonator with SYSCLK PLL
Enabled
Crystal Resonator Frequency Range
Maximum Crystal Motional Resistance
CLOCK DRIVERS
HSTL Output Driver
Frequency Range
Duty Cycle
Rise Time/Fall Time (20% to 80%)
Jitter (12 kHz to 20 MHz)
HSTL Output Driver with 2× Multiplier
Frequency Range
Duty Cycle
Rise Time/Fall Time (20% to 80%)
Subharmonic Spur Level
Jitter (12 kHz to 20 MHz)
CMOS Output Driver
(AVDD3/Pin 37) @ 3.3 V
Frequency Range
Duty Cycle
Rise Time/Fall Time (20% to 80%)
Min
Typ
10
225
40
Max
Unit
400
MHz
mV p-p
V/μs
Test Conditions/Comments
Pin 40, Pin 41
−12 dBm into 50 Ω; must be ac-coupled
Pin 27, Pin 28
250
45
632
1000
55
MHz
%
mV p-p
Maximum fOUT is 0.4 × fSYSCLK
700
810
900
810
900
1000
200
MHz
MHz
MHz
MHz
When in the range, use the low VCO band exclusively
When in the range, use the VCO auto band select
When in the range, use the high VCO band exclusively
11
4
200
66
MHz
632
mV p-p
6
8
100
132
50
Integer multiples of 2, maximum PFD rate and system clock
frequency must be met
Equivalent to 316 mV swing on each leg
MHz
mV p-p
Integer multiples of 8
Deviating from 50% duty cycle may adversely affect
spurious performance
Equivalent to 316 mV swing on each leg
%
632
Equivalent to 316 mV swing on each leg
10
50
100
MHz
Ω
AT cut, fundamental mode resonator
See the SYSCLK Inputs section for recommendations
20
48
725
52
165
MHz
%
ps
ps
See Figure 27 for maximum toggle rate
725
55
165
MHz
%
ps
dBc
ps
150
MHz
65
4.6
%
ns
115
1.5
400
45
115
−35
1.6
0.008
45
55
3
Rev. F | Page 6 of 40
100 Ω termination across OUT/OUTB, 2 pF load
fOUT = 155.52 MHz, 50 MHz system clock input (see Figure 12
through Figure 14 for test conditions)
100 Ω termination across OUT/OUTB, 2 pF load
Without correction
fOUT = 622.08 MHz, 50 MHz system clock input (see Figure 15
for test conditions)
See Figure 29 for maximum toggle rate; the S-divider
should be used for low frequencies because the FDBK_IN
minimum frequency is 10 MHz
With 20 pF load and up to 150 MHz
With 20 pF load
AD9912
Parameter
CMOS Output Driver
(AVDD3/Pin 37) @ 1.8 V
Frequency Range
Duty Cycle
Rise Time/Fall Time (20% to 80%)
DAC OUTPUT CHARACTERISTICS
DCO Frequency Range (1st Nyquist Zone)
Output Resistance
Output Capacitance
Full-Scale Output Current
Gain Error
Output Offset
Voltage Compliance Range
Min
0.008
45
Max
Unit
Test Conditions/Comments
55
5
40
65
6.8
MHz
%
ns
See Figure 28 for maximum toggle rate
With 20 pF load and up to 40 MHz
With 20 pF load
450
MHz
DAC lower limit is 0 Hz; however, the minimum slew rate
for FDBK_IN dictates the lower limit if using CMOS or HSTL
outputs
Single-ended (each pin internally terminated to AVSS)
0
50
5
20
−10
AVSS −
0.50
Wideband SFDR
20.1 MHz Output
98.6 MHz Output
201.1 MHz Output
398.7 MHz Output
Narrow-Band SFDR
20.1 MHz Output
98.6 MHz Output
201.1 MHz Output
398.7 MHz Output
DIGITAL TIMING SPECIFICATIONS
Time Required to Enter Power-Down
Time Required to Leave Power-Down
Reset Assert to High-Z Time
for S1 to S4 Configuration Pins
SERIAL PORT TIMING SPECIFICATIONS
SCLK Clock Rate (1/tCLK )
SCLK Pulse Width High, tHIGH
SCLK Pulse Width Low, tLOW
SDO/SDIO to SCLK Setup Time, tDS
SDO/SDIO to SCLK Hold Time, tDH
SCLK Falling Edge to Valid Data on
SDIO/SDO, tDV
CSB to SCLK Setup Time, tS
CSB to SCLK Hold Time, tH
CSB Minimum Pulse Width High, tPWH
IO_UPDATE Pin Setup Time
(from SCLK Rising Edge of the Final Bit)
IO_UPDATE Pin Hold Time
PROPAGATION DELAY
FDBK_IN to HSTL Output Driver
FDBK_IN to HSTL Output Driver with 2×
Frequency Multiplier Enabled
FDBK_IN to CMOS Output Driver
FDBK_IN Through S-Divider to CMOS
Output Driver
Frequency Tuning Word Update:
IO_UPDATE Pin Rising Edge to DAC
Output
Typ
+0.5
31.7
+10
0.6
AVSS +
0.50
Ω
pF
mA
% FS
μA
V
−79
−67
−61
−59
dBc
dBc
dBc
dBc
−95
−96
−91
−86
dBc
dBc
dBc
dBc
15
18
60
μs
μs
ns
25
Range depends on DAC RSET resistor
Outputs connected to a transformer whose center tap is
grounded
See the Typical Performance Characteristics section
0 MHz to 500 MHz
0 MHz to 500 MHz
0 MHz to 500 MHz
0 MHz to 500 MHz
See the Typical Performance Characteristics section
±250 kHz
±250 kHz
±250 kHz
±250 kHz
Time from rising edge of RESET to high-Z on the S1, S2, S3,
S4 configuration pins
50
MHz
11
ns
ns
ns
ns
ns
Refer to Figure 54
1.34
−0.4
3
tCLK
ns
ns
ns
sec
tCLK = period of SCLK in Hz
tCLK
sec
tCLK = period of SCLK in Hz
8
8
1.93
1.9
Refer to Figure 56 for all write-related serial port parameters;
maximum SCLK rate for readback is governed by tDV
2.8
7.3
ns
ns
8.0
8.6
ns
ns
S-divider bypassed
60/fS
ns
fS = system clock frequency in GHz
Rev. F | Page 7 of 40
AD9912
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter
Analog Supply Voltage (AVDD)
Digital Supply Voltage (DVDD)
Digital I/O Supply Voltage
(DVDD_I/O)
DAC Supply Voltage (AVDD3 Pins)
Maximum Digital Input Voltage
Storage Temperature
Operating Temperature Range
Lead Temperature
(Soldering, 10 sec)
Junction Temperature
THERMAL RESISTANCE
Rating
2V
2V
3.6 V
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 4. Thermal Resistance
3.6 V
−0.5 V to DVDD_I/O + 0.5 V
−65°C to +150°C
−40°C to +85°C
300°C
Package Type
64-Lead LFCSP
θJB
13.9
θJC
1.7
Unit
°C/W typical
Note that the exposed pad on the bottom of package must be
soldered to ground to achieve the specified thermal performance.
See the Typical Performance Characteristics section for more
information.
150°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
θJA
25.2
ESD CAUTION
Rev. F | Page 8 of 40
AD9912
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
SCLK
SDIO
SDO
CSB
IO_UPDATE
RESET
PWRDOWN
DVSS
DVSS
S4
S3
AVDD
AVSS
DAC_OUTB
DAC_OUT
AVDD3
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
PIN 1
INDICATOR
AD9912
TOP VIEW
(Not to Scale)
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
DAC_RSET
AVDD3
AVDD3
AVDD
AVDD
AVSS
AVDD
FDBK_IN
FDBK_INB
AVSS
OUT_CMOS
AVDD3
AVDD
OUT
OUTB
AVSS
NOTES
1. NC = NO CONNECT.
2. THE EXPOSED PAD MUST BE CONNECTED TO GROUND FOR PROPER OPERATION.
06763-002
NC
NC
AVDD
NC
NC
NC
AVDD
AVDD
AVDD
AVDD
SYSCLK
SYSCLKB
AVDD
AVDD
LOOP_FILTER
CLKMODESEL
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
DVDD_I/O
DVSS
DVDD
DVSS
DVDD
DVSS
DVDD
DVSS
S1
S2
AVDD
NC
NC
AVDD3
NC
NC
Figure 2. Pin Configuration
Table 5. Pin Function Descriptions
Pin No.
1
2, 4, 6, 8
3, 5, 7
9, 10, 54, 55
Input/
Output
I
I
I
I/O
Pin Type
Power
Power
Power
3.3 V CMOS
Mnemonic
DVDD_I/O
DVSS
DVDD
S1, S2, S3, S4
I
Power
AVDD
Description
I/O Digital Supply.
Digital Ground. Connect to ground.
Digital Supply.
Start-Up Configuration Pins. These pins are configured under program
control and do not have internal pull-up/pull-down resistors.
Analog Supply. Connect to a nominal 1.8 V supply.
NC
No Connect. These unused pins can be left unconnected.
Analog Supply. Connect to a nominal 3.3 V supply.
System Clock Input. The system clock input has internal dc biasing and
should always be ac-coupled, except when using a crystal. Single-ended
1.8 V CMOS can also be used, but it may introduce a spur caused by an input
duty cycle that is not 50%. When using a crystal, tie the CLKMODESEL pin
to AVSS, and connect crystal directly to this pin and Pin 28.
Complementary System Clock. Complementary signal to the input
provided on Pin 27. Use a 0.01 μF capacitor to ground on this pin if the
signal provided on Pin 27 is single-ended.
System Clock Multiplier Loop Filter. When using the frequency multiplier to
drive the system clock, an external loop filter must be constructed and
attached to this pin. This pin should be pulled down to ground with 1 kΩ
resistor when the system clock PLL is bypassed. See Figure 46 for a diagram
of the system clock PLL loop filter.
11, 19, 23 to 26,
29, 30, 36, 42, 44,
45, 53
12, 13, 15, 16, 17,
18, 20, 21, 22
14, 46, 47, 49
27
I
I
Power
Differential
input
AVDD3
SYSCLK
28
I
Differential
input
SYSCLKB
31
O
LOOP_FILTER
Rev. F | Page 9 of 40
AD9912
Pin No.
32
Input/
Output
I
Pin Type
1.8 V CMOS
Mnemonic
CLKMODESEL
33, 39, 43, 52
34
O
O
GND
1.8 V HSTL
AVSS
OUTB
35
O
1.8 V HSTL
OUT
37
I
Power
AVDD3
38
O
3.3 V CMOS
OUT_CMOS
40
I
Differential
input
FDBK_INB
41
I
FDBK_IN
48
O
50
O
51
O
Differential
input
Current set
resistor
Differential
output
Differential
output
56, 57
58
I
Power
3.3 V CMOS
DVSS
PWRDOWN
59
I
3.3 V CMOS
RESET
60
I
3.3 V CMOS
IO_UPDATE
61
I
3.3 V CMOS
CSB
62
O
3.3 V CMOS
SDO
63
I/O
3.3 V CMOS
SDIO
64
I
3.3 V CMOS
SCLK
Exposed Die Pad
O
GND
EPAD
DAC_RSET
DAC_OUT
DAC_OUTB
Description
Clock Mode Select. Set to GND when connecting a crystal to the system
clock input (Pin 27 and Pin 28). Pull up to 1.8 V when using either an
oscillator or an external clock source. This pin can be left unconnected
when the system clock PLL is bypassed. (See the SYSCLK Inputs section for
details on the use of this pin.)
Analog Ground. Connect to ground.
Complementary HSTL Output. See the Specifications and Primary 1.8 V
Differential HSTL Driver sections for details.
HSTL Output. See the Specifications and Primary 1.8 V Differential HSTL
Driver sections for details.
Analog Supply for CMOS Output Driver. This pin is normally 3.3 V but can
be 1.8 V. This pin should be powered even if the CMOS driver is not used.
See the Power Supply Partitioning section for power supply partitioning.
CMOS Output. See the Specifications section and the Output Clock Drivers
and 2× Frequency Multiplier section. This pin is 1.8 V CMOS if Pin 37 is set
to 1.8 V.
Complementary Feedback Input. When using the HSTL and CMOS outputs,
this pin is connected to the filtered DAC_OUTB output. This internally
biased input is typically ac-coupled, and when configured as such, can
accept any differential signal whose single-ended swing is at least 400 mV.
Feedback Input. In standard operating mode, this pin is connected to the
filtered DAC_OUT output.
DAC Output Current Setting Resistor. Connect a resistor (usually 10 kΩ)
from this pin to GND. See the Digital-To-Analog (DAC) Output section.
DAC Output. This signal should be filtered and sent back on-chip through
the FDBK_IN input. This pin has an internal 50 Ω pull-down resistor.
Complementary DAC Output. This signal should be filtered and sent back
on-chip through the FDBK_INB input. This pin has an internal 50 Ω pulldown resistor.
Digital Ground. Connect to ground.
Power-Down. When this active high pin is asserted, the device becomes
inactive and enters the full power-down state. This pin has an internal
50 kΩ pull-down resistor.
Chip Reset. When this active high pin is asserted, the chip goes into reset.
Note that on power-up, a 10 μs reset pulse is internally generated when
the power supplies reach a threshold and stabilize. This pin should be
grounded with a 10 kΩ resistor if not used.
I/O Update. A logic transition from 0 to 1 on this pin transfers data from the
I/O port registers to the control registers (see the Write section). This pin
has an internal 50 kΩ pull-down resistor.
Chip Select. Active low. When programming a device, this pin must be held
low. In systems where more than one AD9912 is present, this pin enables
individual programming of each AD9912. This pin has an internal 100 kΩ
pull-up resistor.
Serial Data Output. When the device is in 3-wire mode, data is read on this
pin. There is no internal pull-up/pull-down resistor on this pin.
Serial Data Input/Output. When the device is in 3-wire mode, data is
written via this pin. In 2-wire mode, data reads and writes both occur on
this pin. There is no internal pull-up/pull-down resistor on this pin.
Serial Programming Clock. Data clock for serial programming. This pin has
an internal 50 kΩ pull-down resistor.
Analog Ground. The exposed die pad on the bottom of the package
provides the analog ground for the part; this exposed pad must be
connected to ground for proper operation.
Rev. F | Page 10 of 40
AD9912
TYPICAL PERFORMANCE CHARACTERISTICS
AVDD, AVDD3, and DVDD at nominal supply voltage; DAC RSET = 10 kΩ, unless otherwise noted. See Figure 26 for 1 GHz reference
phase noise used for generating these plots.
–50
10
CARRIER:
SFDR:
FREQ. SPAN:
RESOLUTION BW:
VIDEO BW:
0
–55
SIGNAL POWER (dBm)
–10
–65
–70
+25°C
–40°C
+85°C
200
300
OUTPUT FREQUENCY (MHz)
400
–50
–60
–70
500
–100
0
Figure 3. Wideband SFDR vs. Output Frequency at −40°C, +25°C, and +85°C,
SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
100
500
10
CARRIER:
SFDR:
FREQ. SPAN:
RESOLUTION BW:
VIDEO BW:
0
–55
SIGNAL POWER (dBm)
–10
–60
–65
–70
HIGH VDD
NORMAL VDD
LOW VDD
100
200
300
OUTPUT FREQUENCY (MHz)
400
–40
–50
–60
–70
–90
–80
0
–30
–80
500
–100
06763-004
–75
–20
201.1MHz
–61dBc
500MHz
3kHz
10kHz
0
Figure 4. Variation of Wideband SFDR vs. Frequency over DAC Power Supply
Voltage, SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
100
200
300
FREQUENCY (MHz)
400
500
06763-007
SFDR (dBc)
400
Figure 6. Wideband SFDR at 98.6 MHz,
SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
–50
500
Figure 7. Wideband SFDR at 201.1 MHz,
SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
10
10
–10
–20
20.1MHz
–79dBc
500MHz
3kHz
10kHz
CARRIER:
SFDR:
FREQ. SPAN:
RESOLUTION BW:
VIDEO BW:
0
–10
SIGNAL POWER (dBm)
CARRIER:
SFDR:
FREQ. SPAN:
RESOLUTION BW:
VIDEO BW:
0
–30
–40
–50
–60
–70
–80
–20
398.7MHz
–59dBc
500MHz
3kHz
10kHz
–30
–40
–50
–60
–70
–80
–90
–90
–100
–100
0
100
200
300
FREQUENCY (MHz)
400
500
06763-005
SIGNAL POWER (dBm)
200
300
FREQUENCY (MHz)
06763-006
100
–40
–90
–80
0
–30
–80
06763-003
–75
–20
06763-008
SFDR (dBc)
–60
98.6MHz
–67dBc
500MHz
3kHz
10kHz
Figure 5. Wideband SFDR at 20.1 MHz,
SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
0
100
200
300
FREQUENCY (MHz)
400
Figure 8. Wideband SFDR at 398.7 MHz,
SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
Rev. F | Page 11 of 40
AD9912
10
–80
CARRIER:
20.1MHz
SFDR:
–95dBc
FREQ. SPAN:
500kHz
RESOLUTION BW: 300Hz
VIDEO BW:
1kHz
0
–10
PHASE NOISE (dBc/Hz)
SIGNAL POWER (dBm)
–20
RMS JITTER (100Hz TO 40MHz):
99MHz: 413fs
399MHz: 222fs
–90
–30
–40
–50
–60
–70
–80
–100
–110
–120
–130
399MHz
–140
–90
–150
–100
20.05
20.15
FREQUENCY (MHz)
20.25
20.35
–160
100
Figure 9. Narrow-Band SFDR at 20.1 MHz,
SYSCLK = 1 GHz (SYSCLK PLL Bypassed)
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
Figure 12. Absolute Phase Noise Using HSTL Driver,
SYSCLK = 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
10
–80
CARRIER:
201.1MHz
SFDR:
–91dBc
FREQ. SPAN:
500kHz
RESOLUTION BW: 300Hz
VIDEO BW:
1kHz
0
–10
RMS JITTER (12kHz TO 20MHz):
99MHz: 0.98ps
399MHz: 0.99ps
–90
PHASE NOISE (dBc/Hz)
–20
SIGNAL POWER (dBm)
1k
06763-012
99MHz
19.95
06763-009
–110
19.85
–30
–40
–50
–60
–70
–80
–100
–110
–120
399MHz
–130
–140
99MHz
–90
–150
200.95
201.05
201.15
FREQUENCY (MHz)
201.25
201.35
–160
10
06763-010
Figure 10. Narrow-Band SFDR at 201.1 MHz,
SYSCLK = 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
PHASE NOISE (dBc/Hz)
–30
–40
–50
–60
–70
–80
–100
–110
–120
–130
399MHz
–140
99MHz
–90
–150
–100
–110
398.45
100M
RMS JITTER (12kHz TO 20MHz):
99MHz: 1.41ps
399MHz: 1.46ps
–90
398.55
398.65
398.75
FREQUENCY (MHz)
398.85
398.95
Figure 11. Narrow-Band SFDR at 398.7 MHz,
SYSCLK = 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
–160
10
06763-011
SIGNAL POWER (dBm)
–20
10M
–80
CARRIER:
398.7MHz
SFDR:
–86dBc
FREQ. SPAN:
500kHz
RESOLUTION BW: 300Hz
VIDEO BW:
1kHz
–10
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
Figure 13. Absolute Phase Noise Using HSTL Driver,
SYSCLK = 1 GHz (SYSCLK PLL Driven by Rohde & Schwarz SMA100 Signal
Generator at 83.33 MHz )
10
0
100
100
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
06763-014
–110
200.85
06763-013
–100
Figure 14. Absolute Phase Noise Using HSTL Driver,
SYSCLK = 1 GHz (SYSCLK PLL Driven by Rohde & Schwarz SMA100 Signal
Generator at 25 MHz )
Rev. F | Page 12 of 40
AD9912
800
–100
RMS JITTER (100Hz TO 100MHz):
600MHz: 585fs
800MHz: 406fs
POWER DISSIPATION (mW)
PHASE NOISE (dBc/Hz)
–110
–120
800MHz
–130
TOTAL
3.3V
1.8V
700
600MHz
600
500
400
300
200
–140
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
0
250
06763-015
–150
100
Figure 15. Absolute Phase Noise Using HSTL Driver,
SYSCLK = 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed),
HSTL Output Doubler Enabled
500
625
750
875
SYSTEM CLOCK FREQUENCY (MHz)
1000
Figure 18. Power Dissipation vs. System Clock Frequency
(SYSCLK PLL Bypassed), fOUT = fSYSCLK/5, HSTL Driver On, CMOS Driver On,
SpurKiller Off
800
–110
RMS JITTER (100Hz TO 20MHz):
150MHz: 308fs
50MHz: 737fs
700
POWER DISSIPATION (mW)
–120
PHASE NOISE (dBc/Hz)
375
06763-018
100
–130
–140
150MHz
–150
600
500
400
TOTAL
3.3V
1.8V
300
200
50MHz
100
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
0
06763-016
400
10
–110
RMS JITTER (100Hz TO 20MHz):
50MHz: 790fs
CARRIER:
SFDR W/O SPURKILLER:
SFDR WITH SPURKILLER:
FREQUENCY SPAN:
RESOLUTION BW:
VIDEO BW:
0
–10
SIGNAL POWER (dBm)
–120
–130
–140
50MHz
–150
–20
399MHz
–63.7dBc
–69.3dBc
500MHz
3kHz
30kHz
–30
–40
THESE TWO SPURS
ELIMINATED WITH
SPURKILLER
–50
–60
–70
–80
–90
10MHz
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
06763-017
PHASE NOISE (dBc/Hz)
100
200
300
OUTPUT FREQUENCY (MHz)
Figure 19. Power Dissipation vs. Output Frequency
SYSCLK = 1 GHz (SYSCLK PLL Bypassed), HSTL Driver On,
CMOS Driver On, SpurKiller Off
Figure 16. Absolute Phase Noise Using CMOS Driver at 3.3 V,
SYSCLK = 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
DDS Run at 200 MSPS for 10 MHz Plot
–160
100
0
–100
0
100
200
300
FREQUENCY (MHz)
400
500
Figure 20. SFDR Comparison With and Without SpurKiller,
SYSCLK = 1 GHz, fOUT = 400 MHz
Figure 17. Absolute Phase Noise Using CMOS Driver at 1.8 V,
SYSCLK = 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
Rev. F | Page 13 of 40
06763-020
–160
100
06763-019
10MHz
AD9912
–115
RMS JITTER (100Hz TO 100MHz): 83fs
–125
PHASE NOISE (dBc/Hz)
–125
–135
–145
–155
400MHz
–165
–145
–155
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
–175
100
Figure 21. Absolute Phase Noise of Unfiltered DAC Output,
fOUT = 50 MHz, 200 MHz, and 400 MHz, SYSCLK Driven by
a 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
1k
RMS JITTER (100Hz TO 100MHz): 82fs
–125
PHASE NOISE (dBc/Hz)
–135
–145
–155
–135
–145
–155
–165
–165
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
–175
100
06763-052
1k
Figure 22. Absolute Phase Noise of Unfiltered DAC Output, fOUT = 63 MHz,
SYSCLK Driven by a 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
06763-055
PHASE NOISE (dBc/Hz)
–125
Figure 25. Absolute Phase Noise of Unfiltered DAC Output, fOUT = 311.6 MHz,
SYSCLK Driven by a 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
–110
–115
RMS JITTER (100Hz TO 100MHz): 22fs
RMS JITTER (100Hz TO 40MHz): 61fs
–120
PHASE NOISE (dBc/Hz)
–125
PHASE NOISE (dBc/Hz)
100M
–115
RMS JITTER (100Hz TO 20MHz): 69fs
–135
–145
–155
–130
–140
–150
–160
–165
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
–170
100
06763-053
–175
100
10M
Figure 24. Absolute Phase Noise of Unfiltered DAC Output, fOUT = 258.3 MHz,
SYSCLK Driven by a 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
–115
–175
100
10k
100k
1M
FREQUENCY OFFSET (Hz)
06763-054
50MHz
1k
Figure 23. Absolute Phase Noise of Unfiltered DAC Output, fOUT = 171 MHz,
SYSCLK Driven by a 1 GHz Wenzel Oscillator (SYSCLK PLL Bypassed)
1k
10k
100k
1M
FREQUENCY OFFSET (Hz)
10M
100M
06763-056
–175
100
–135
–165
200MHz
06763-051
PHASE NOISE (dBc/Hz)
–115
RMS JITTER (100Hz TO 20MHz):
50MHz: 62fs
200MHz: 37fs
400MHz: 31fs
Figure 26. Absolute Phase Noise of 1 GHz Reference Used for Performance
Plots; Wenzel Components Used: 100 MHz Oscillator, LNBA-13-24 Amp,
LNOM 100-5 Multiplier, LNDD 500-14 Diode Doubler
Rev. F | Page 14 of 40
AD9912
650
0.6
0.4
550
0.2
0
FREQUENCY = 600MHz
tRISE (20%→80%) = 104ps
tFALL (80%→20%) = 107ps
V p-p = 1.17V DIFF.
DUTY CYCLE = 50%
–0.2
500
NOM SKEW 25°C, 1.8V SUPPLY
WORST CASE (SLOW SKEW 90°C, 1.7V SUPPLY)
–0.4
0
200
400
FREQUENCY (MHz)
600
800
–0.6
06763-021
450
0
Figure 27. HSTL Output Driver Single-Ended Peak-to-Peak Amplitude vs.
Toggle Rate (100 Ω Across Differential Pair)
0.5
1.0
1.5
TIME (ns)
2.0
2.5
06763-024
AMPLITUDE (V)
AMPLITUDE (mV)
600
Figure 30. Typical HSTL Output Waveform, Nominal Conditions,
DC-Coupled, Differential Probe Across 100 Ω load
2.5
1.8
1.6
2.0
1.4
AMPLITUDE (V)
1.0
1.0
0.8
0.6
FREQUENCY = 20MHz
tRISE (20%→80%) = 5.5ns
tFALL (80%→20%) = 5.9ns
V p-p = 1.8V
DUTY CYCLE = 53%
0.4
NOM SKEW 25°C, 1.8V SUPPLY (20pF)
WORST CASE (SLOW SKEW 90°C,
1.7V SUPPLY (20pF))
0.2
0
0
0
10
20
FREQUENCY (MHz)
30
40
–0.2
06763-022
0.5
0
20
40
60
80
100
TIME (ns)
06763-025
AMPLITUDE (V)
1.2
1.5
Figure 31. Typical CMOS Output Driver Waveform (@ 1.8 V),
Nominal Conditions, Estimated Capacitance = 5 pF
Figure 28. CMOS Output Driver Peak-to-Peak Amplitude vs. Toggle Rate
(AVDD3 = 1.8 V) with 20 pF Load
3.5
3.3
3.0
2.8
AMPLITUDE (V)
2.0
1.5
NOM SKEW 25°C, 1.8V SUPPLY (20pF)
WORST CASE (SLOW SKEW 90°C,
3.0V SUPPLY (20pF))
1.0
2.3
1.8
FREQUENCY = 40MHz
tRISE (20%→80%) = 2.25ns
tFALL (80%→20%) = 2.6ns
V p-p = 3.3V
DUTY CYCLE = 52%
1.3
0.8
0.3
0.5
0
50
100
FREQUENCY (MHz)
150
–0.2
06763-023
0
0
10
20
30
40
TIME (ns)
Figure 29. CMOS Output Driver Peak-to-Peak Amplitude vs. Toggle Rate
(AVDD3 = 3.3 V) with 20 pF Load
Rev. F | Page 15 of 40
Figure 32. CMOS Output Driver Waveform (@ 3.3 V),
Nominal Conditions, Estimated Capacitance = 5 pF
50
06763-026
AMPLITUDE (V)
2.5
AD9912
INPUT/OUTPUT TERMINATION RECOMMENDATIONS
0.1µF
0.01µF
AD9912
1.8V
HSTL
OUTPUT
100Ω
AD9912
CLOCK
SOURCE
WITH DIFF.
OUTPUT
DOWNSTREAM
DEVICE
(HIGH-Z)
SELF-BIASING
SYSCLK
INPUT
100Ω
0.01µF
06763-030
06763-027
0.1µF
Figure 33. AC-Coupled HSTL Output Driver
Figure 36. SYSCLK Differential Input, Non-Xtal
0.01µF
50Ω
AD9912
1.8V
HSTL
OUTPUT
CLOCK SOURCE
WITH
SINGLE-ENDED
1.8V CMOS
OUTPUT
DOWNSTREAM
DEVICE
(HIGH-Z)
AVDD/2
0.01µF
06763-049
06763-028
50Ω
AD9912
SELF-BIASING
SYSCLK
INPUT
Figure 34. DC-Coupled HSTL Output Driver
Figure 37. SYSCLK Single-Ended Input, Non-Xtal
10pF*
0.1µF
AD9912
10pF*
SELF-BIASING
SYSCLK
INPUT
(CRYSTAL
MODE)
100Ω
(OPTIONAL)
AD9912
SELF-BIASING
FDBK INPUT
06763-029
*REFER TO CRYSTAL
DATA SHEET.
06763-050
0.1µF
Figure 38. FDBK_IN Input
Figure 35. SYSCLK Input, Xtal
Rev. F | Page 16 of 40
AD9912
THEORY OF OPERATION
OUT_CMOS
OUT
2×
OUTB
÷S
FDBK_IN
FDBK_INB
DIGITAL SYNTHESIS CORE
FREQUENCY
TUNING WORD
DAC_OUT
CONTROL
LOGIC
DDS/DAC
DAC_OUTB
LOW NOISE
CLOCK
MULTIPLIER
CONFIGURATION
LOGIC
EXTERNAL
ANALOG
LOW-PASS
FILTER
EXTERNAL
LOOP
FILTER
AMP
S1 TO S4
DIGITAL
INTERFACE
SYSCLK SYSCLKB
06763-031
SYSCLK PORT
Figure 39. Detailed Block Diagram
OVERVIEW
The AD9912 is a high performance, low noise, 14-bit DDS
clock synthesizer with integrated comparators for applications
desiring an agile, finely tuned square or sinusoidal output signal.
A digitally controlled oscillator (DCO) is implemented using a
direct digital synthesizer (DDS) with an integrated output DAC,
clocked by the system clock.
A bypassable PLL-based frequency multiplier is present,
enabling use of an inexpensive, low frequency source for the
system clock. For best jitter performance, the system clock PLL
should be bypassed, and a low noise, high frequency system
clock should be provided directly. Sampling theory sets an upper
bound for the DDS output frequency at 50% of fS (where fS is
the DAC sample rate), but a practical limitation of 40% of
fS is generally recommended to allow for the selectivity of the
required off-chip reconstruction filter.
The output signal from the reconstruction filter can be fed back
to the AD9912 to be processed through the output circuitry.
The output circuitry includes HSTL and CMOS output buffers,
as well as a frequency doubler for applications that need
frequencies above the Nyquist level of the DDS.
The AD9912 also offers preprogrammed frequency profiles that
allow the user to generate frequencies without programming
the part. The individual functional blocks are described in the
following sections.
DIRECT DIGITAL SYNTHESIZER (DDS)
The frequency of the sinusoid generated by the DDS is
determined by a frequency tuning word (FTW), which is a
digital (that is, numeric) value. Unlike an analog sinusoidal
generator, a DDS uses digital building blocks and operates as
a sampled system. Thus, it requires a sampling clock (fS) that
serves as the fundamental timing source of the DDS. The
accumulator behaves as a modulo-248 counter with a programmable step size that is determined by the frequency tuning word
(FTW). A block diagram of the DDS is shown in Figure 40.
Rev. F | Page 17 of 40
AD9912
PHASE
OFFSET
48-BIT ACCUMULATOR
48
48
48
DAC_RSET
DAC
(14-BIT)
DAC_OUT
14
D Q
19
19
ANGLE TO
14
AMPLITUDE
CONVERSION
DAC_OUTB
06763-032
FREQUENCY
TUNING WORD
(FTW)
DAC I-SET
REGISTERS
AND LOGIC
fS
Figure 40. DDS Block Diagram
The input to the DDS is a 48-bit FTW that provides the accumulator with a seed value. On each cycle of fS, the accumulator
adds the value of the FTW to the running total of its output.
For example, given an FTW = 5, the accumulator increments
the count by 5 sec on each fS cycle. Over time, the accumulator
reaches the upper end of its capacity (248 in this case) and then
rolls over, retaining the excess. The average rate at which the
accumulator rolls over establishes the frequency of the output
sinusoid. The following equation defines the average rollover
rate of the accumulator and establishes the output frequency
(fDDS) of the DDS:
is internally connected to a virtual voltage reference of 1.2 V
nominal, so the reference current can be calculated by
I DAC _ REF =
R DAC _ REF
Note that the recommended value of IDAC_REF is 120 μA, which
leads to a recommended value for RDAC_REF of 10 kΩ.
The scale factor consists of a 10-bit binary number (FSC)
programmed into the DAC full-scale current register in the
I/O register map. The full-scale DAC output current (IDAC_FS)
is given by
⎛ FTW ⎞
f DDS = ⎜ 48 ⎟ f S
⎝ 2 ⎠
192 FSC ⎞
⎛
I DAC _ FS = I DAC _ REF ⎜ 72 +
⎟
1024 ⎠
⎝
Solving this equation for FTW yields
Using the recommended value of RDAC_REF, the full-scale DAC
output current can be set with 10-bit granularity over a range of
approximately 8.6 mA to 31.7 mA. 20 mA is the default value.
⎞⎤
⎟⎥
⎟⎥
⎠⎦
AVDD3
49
For example, given that fS = 1 GHz and fDDS = 19.44 MHz, then
FTW = 5,471,873,547,255 (0x04FA05143BF7).
The relative phase of the sinusoid can be controlled numerically,
as well. This is accomplished using the phase offset function of
the DDS (a programmable 14-bit value (Δphase); see the I/O
Register Map section). The resulting phase offset, ΔΦ (radians),
is given by
⎛ Δphase ⎞
ΔΦ = 2π⎜ 14 ⎟
⎠
⎝ 2
IFS
IFS/2
CURRENT
SWITCH
ARRAY
SWITCH
CONTROL
IFS/2
CURRENT
SWITCH
ARRAY
IFS/2 + ICODE
IFS/2 – ICODE
CODE
DAC_OUT 50
51 DAC_OUTB
INTERNAL
50Ω
DIGITAL-TO-ANALOG (DAC) OUTPUT
INTERNAL
50Ω
52
The output of the digital core of the DDS is a time series of
numbers representing a sinusoidal waveform. This series is
translated to an analog signal by means of a digital-to-analog
converter (DAC).
The DAC outputs its signal to two pins driven by a balanced
current source architecture (see the DAC output diagram in
Figure 41). The peak output current derives from a combination
of two factors. The first is a reference current (IDAC_REF) that is
established at the DAC_RSET pin, and the second is a scale
factor that is programmed into the I/O register map.
The value of IDAC_REF is set by connecting a resistor (RDAC_REF)
between the DAC_RSET pin and ground. The DAC_RSET pin
AVSS
06763-033
⎡ ⎛f
FTW = round ⎢2 48 ⎜ DDS
⎢⎣ ⎜⎝ f S
1 .2
Figure 41. DAC Output
RECONSTRUCTION FILTER
The origin of the output clock signal produced by the AD9912
is the combined DDS and DAC. The DAC output signal appears
as a sinusoid sampled at fS. The frequency of the sinusoid is
determined by the frequency tuning word (FTW) that appears
at the input to the DDS. The DAC output is typically passed
through an external reconstruction filter that serves to remove
the artifacts of the sampling process and other spurs outside the
filter bandwidth. If desired, the signal can then be brought back
on-chip to be converted to a square wave that is routed internally
to the output clock driver or the 2× DLL multiplier.
Rev. F | Page 18 of 40
AD9912
MAGNITUDE
(dB)
IMAGE 0
IMAGE 1
IMAGE 2
IMAGE 3
IMAGE 4
0
–20
PRIMARY
SIGNAL
FILTER
RESPONSE
SIN(x)/x
ENVELOPE
–60
–80
SPURS
f
–100
fs/2
fs
3fs/2
2fs
5fs/2
BASE BAND
06763-034
–40
Figure 42. DAC Spectrum vs. Reconstruction Filter Response
For applications using the fundamental frequency of the DAC
output, the response of the reconstruction filter should preserve
the baseband signal (Image 0), while completely rejecting all
other images. However, a practical filter implementation
typically exhibits a relatively flat pass band that covers the
desired output frequency plus 20%, rolls off as steeply as
possible, and then maintains significant (though not complete)
rejection of the remaining images. Depending on how close
unwanted spurs are to the desired signal, a third-, fifth-, or
seventh-order elliptic low-pass filter is common.
FDBK_IN INPUTS
The FDBK_IN pins serve as the input to the comparators and
output drivers of the AD9912. Typically, these pins are used to
receive the signal generated by the DDS after it has been bandlimited by the external reconstruction filter.
A diagram of the FDBK_IN input pins is provided in Figure 43,
which includes some of the internal components used to bias
the input circuitry. Note that the FDBK_IN input pins are
internally biased to a dc level of ~1 V. Care should be taken to
ensure that any external connections do not disturb the dc bias
because this may significantly degrade performance.
Some applications operate off an image above the Nyquist
frequency, and those applications use a band-pass filter instead
of a low-pass filter.
The design of the reconstruction filter has a significant impact
on the overall signal performance. Therefore, good filter design
and implementation techniques are important for obtaining the
best possible jitter results.
Rev. F | Page 19 of 40
FDBK_IN
~1pF
15kΩ
~1pF
15kΩ
TO S-DIVIDER
AND CLOCK
OUTPUT SECTION
AVSS
FDBK_INB
+
~1V
~2pF
AVSS
Figure 43. Differential FDBK_IN Inputs
06763-035
Because the DAC constitutes a sampled system, its output must
be filtered so that the analog waveform accurately represents the
digital samples supplied to the DAC input. The unfiltered DAC
output contains the (typically) desired baseband signal, which
extends from dc to the Nyquist frequency (fS/2). It also contains
images of the baseband signal that theoretically extend to infinity.
Notice that the odd images (shown in Figure 42) are mirror
images of the baseband signal. Furthermore, the entire DAC
output spectrum is affected by a sin(x)/x response, which is
caused by the sample-and-hold nature of the DAC output signal.
AD9912
Note that although these crystals meet the preceding criteria
according to their data sheets, Analog Devices, Inc., does not
guarantee their operation with the AD9912, nor does Analog
Devices endorse one supplier of crystals over another.
SYSCLK INPUTS
Functional Description
An external time base connects to the AD9912 at the SYSCLK
pins to generate the internal high frequency system clock (fS).
When the SYSCLK PLL multiplier path is disabled, the AD9912
must be driven by a high frequency signal source (250 MHz to
1 GHz). The signal thus applied to the SYSCLK input pins becomes
the internal DAC sampling clock (fS) after passing through an
internal buffer.
The SYSCLK inputs can be operated in one of the following
three modes:
SYSCLK PLL bypassed
SYSCLK PLL enabled with input signal generated externally
Crystal resonator with SYSCLK PLL enabled
It is important to note that when bypassing the system clock
PLL, the LOOP_FILTER pin (Pin 31) should be pulled down to
the analog ground with a 1 kΩ resistor.
A functional diagram of the system clock generator is shown in
Figure 44.
SYSCLK PLL Doubler
The SYSCLK PLL multiplier path is enabled by a Logic 0 (default)
in the PD SYSCLK PLL bit (Register 0x0010, Bit 4) of the I/O
register map. The SYSCLK PLL multiplier can be driven from
the SYSCLK input pins by one of two means, depending on the
logic level applied to the 1.8 V CMOS CLKMODESEL pin.
When CLKMODESEL = 0, a crystal can be connected directly
across the SYSCLK pins. When CLKMODESEL = 1, the
maintaining amp is disabled, and an external frequency source
(such as an oscillator or signal generator) can be connected
directly to the SYSCLK input pins. Note that CLKMODESEL = 1
does not disable the system clock PLL.
The SYSCLK PLL multiplier path offers an optional SYSCLK
PLL doubler. This block comes before the SYSCLK PLL
multiplier and acts as a frequency doubler by generating a pulse
on each edge of the SYSCLK input signal. The SYSCLK PLL
multiplier locks to the falling edges of this regenerated signal.
The impetus for doubling the frequency at the input of the
SYSCLK PLL multiplier is that an improvement in overall phase
noise performance can be realized. The main drawback is that
the doubler output is not a rectangular pulse with a constant
duty cycle even for a perfectly symmetric SYSCLK input signal.
This results in a subharmonic appearing at the same frequency
as the SYSCLK input signal, and the magnitude of the subharmonic
can be quite large. When employing the doubler, care must be
taken to ensure that the loop bandwidth of the SYSCLK PLL
multiplier adequately suppresses the subharmonic.
The maintaining amp on the AD9912 SYSCLK pins is intended
for 25 MHz, 3.2 mm × 2.5 mm AT cut fundamental mode crystals
with a maximum motional resistance of 100 Ω. The following
crystals, listed in alphabetical order, meet these criteria (as of
the revision date of this data sheet):
•
•
•
•
•
The benefit offered by the doubler depends on the magnitude
of the subharmonic, the loop bandwidth of the SYSCLK PLL
multiplier, and the overall phase noise requirements of the
specific application. In many applications, the AD9912 clock
output is applied to the input of another PLL, and the subharmonic is often suppressed by the relatively narrow bandwidth of
the downstream PLL.
AVX/Kyocera CX3225SB
ECS ECX-32
Epson/Toyocom TSX-3225
Fox FX3225BS
NDK NX3225SA
Note that generally, the benefits of the SYSCLK PLL doubler are
realized for SYSCLK input frequencies of 25 MHz and above.
PD SYSCLK PLL
(I/O REGISTER BIT)
BIPOLAR EDGE DETECTOR
(I/O REGISTER BIT)
SYSCLK PLL BYPASSED
SYSCLK
SYSCLKB
2
1
0
2
WITH EXTERNAL DRIVE
2
1
SYSCLK
PLL
ENABLED
2
0
0
1
WITH CRYSTAL
RESONATOR
CLKMODESEL
2
1
0 2
SYSCLK
PLL
MULTIPLIER
2
1
0
2
DAC
SAMPLE
CLOCK
BIPOLAR
EDGE
DETECTOR
LOOP_FILTER
Figure 44. System Clock Generator Block Diagram
Rev. F | Page 20 of 40
06763-036
•
•
•
AD9912
EXTERNAL
LOOP FILTER
SYSCLK PLL Multiplier
When the SYSCLK PLL multiplier path is employed, the
frequency applied to the SYSCLK input pins must be limited so
as not to exceed the maximum input frequency of the SYSCLK
PLL phase detector. A block diagram of the SYSCLK generator
appears in Figure 45.
AVDD
C2
C1
LOOP_FILTER
29
ICP
(125µA, 250µA, 375µA)
CHARGE
PUMP
26
31
~2pF
KVCO
(HIGH/LOW RANGE)
VCO
06763-038
SYSCLK PLL MULTIPLIER
2
R1
FERRITE
BEAD
AD9912
Figure 46. External Loop Filter for SYSCLK PLL
PHASE
FREQUENCY
DETECTOR
CHARGE
PUMP
VCO
DAC
SAMPLE
CLOCK
Table 6. Recommended Loop Filter Values for a Nominal
1.5 MHz SYSCLK PLL Loop Bandwidth
1GHz
~2pF
÷N
÷2
06763-037
(N = 2 TO 33)
LOOP_FILTER
Figure 45. Block Diagram of the SYSCLK PLL
The SYSCLK PLL multiplier has a 1 GHz VCO at its core.
A phase/frequency detector (PFD) and charge pump provide
the steering signal to the VCO in typical PLL fashion. The PFD
operates on the falling edge transitions of the input signal, which
means that the loop locks on the negative edges of the reference
signal. The charge pump gain is controlled via the I/O register
map by selecting one of three possible constant current sources
ranging from 125 μA to 375 μA in 125 μA steps. The center
frequency of the VCO is also adjustable via the I/O register map
and provides high/low gain selection. The feedback path from
VCO to PFD consists of a fixed divide-by-2 prescaler followed
by a programmable divide-by-N block, where 2 ≤ N ≤ 33. This
limits the overall divider range to any even integer from 4 to 66,
inclusive. The value of N is programmed via the I/O register map
via a 5-bit word that spans a range of 0 to 31, but the internal
logic automatically adds a bias of 2 to the value entered, extending
the range to 33. Care should be taken when choosing these
values so as not to exceed the maximum input frequency of the
SYSCLK PLL phase detector or SYSCLK PLL doubler. These
values can be found in the AC Specifications section.
Multiplier
<8
10
20
40 (default)
60
R1
390 Ω
470 Ω
1 kΩ
2.2 kΩ
2.7 kΩ
Series C1
1 nF
820 pF
390 pF
180 pF
120 pF
Shunt C2
82 pF
56 pF
27 pF
10 pF
5 pF
Detail of SYSCLK Differential Inputs
A diagram of the SYSCLK input pins is provided in Figure 47.
Included are details of the internal components used to bias the
input circuitry. These components have a direct effect on the
static levels at the SYSCLK input pins. This information is
intended to aid in determining how best to interface to the
device for a given application.
CRYSTAL RESONATOR WITH
SYSCLK PLL ENABLED
MUX
SYSCLK
INTERNAL
CLOCK
AMP
SYSCLKB
SYSCLK PLL ENABLED
~3pF
1kΩ
~3pF
1kΩ
INTERNAL
CLOCK
VSS
+
~1V
~2pF
External Loop Filter (SYSCLK PLL)
VSS
The loop bandwidth of the SYSCLK PLL multiplier can be
adjusted by means of three external components as shown in
Figure 46. The nominal gain of the VCO is 800 MHz/V. The
recommended component values (shown in Table 6) establish
a loop bandwidth of approximately 1.6 MHz with the charge
pump current set to 250 μA. The default case is N = 40, and
it assumes a 25 MHz SYSCLK input frequency and generates
an internal DAC sampling frequency (fS) of 1 GHz.
SYSCLK PLL BYPASSED
~1.5pF
500Ω
INTERNAL
CLOCK
VSS
~1.5pF
500Ω
+
~1V
~2pF
VSS
Figure 47. Differential SYSCLK Inputs
Rev. F | Page 21 of 40
06763-039
FROM
SYSCLK
INPUT
AD9912
Note that the SYSCLK PLL bypassed and SYSCLK PLL enabled
input paths are internally biased to a dc level of ~1 V. Care should
be taken to ensure that any external connections do not disturb
the dc bias because this may significantly degrade performance.
Generally, it is recommended that the SYSCLK inputs be
ac-coupled, except when using a crystal resonator.
OUTPUT CLOCK DRIVERS AND 2× FREQUENCY
MULTIPLIER
There are two output drivers provided by the AD9912. The
primary output driver supports differential 1.8 V HSTL output
levels, while the secondary supports either 1.8 V or 3.3 V CMOS
levels, depending on whether Pin 37 is driven at 1.8 V or 3.3 V.
The primary differential driver nominally provides an output
voltage with 100 Ω load applied differentially. The source
impedance of the driver is approximately 100 Ω for most of
the output clock period; during transition between levels, the
source impedance reaches a maximum of about 500 Ω. The
driver is designed to support output frequencies of up to and
beyond the OC-12 network rate of 622.08 MHz.
The output clock can also be powered down by a control bit in
the I/O register map.
Primary 1.8 V Differential HSTL Driver
The DDS produces a sinusoidal clock signal that is sampled at
the system clock rate. This DDS output signal is routed off chip
where it is passed through an analog filter and brought back on
chip for buffering and, if necessary, frequency doubling. Where
possible, for the best jitter performance, it is recommended that
the frequency doubler be bypassed.
The 1.8 V HSTL output should be ac-coupled, with 100 Ω termination at the destination. The driver design has low jitter injection
for frequencies in the range of 50 MHz to 750 MHz. Refer to the
AC Specifications section for the exact frequency limits.
2× Frequency Multiplier
The AD9912 can be configured (via the I/O register map) with
an internal 2× delay-locked loop (DLL) multiplier at the input
of the primary clock driver. The extra octave of frequency gain
allows the AD9912 to provide output clock frequencies that
exceed the range available from the DDS alone. These settings
are found in Register 0x0010 and Register 0x0200.
The input to the DLL consists of the filtered DDS output signal
after it has been squared up by an integrated clock receiver
circuit. The DLL can accept input frequencies in the range of
200 MHz to 400 MHz.
Single-Ended CMOS Output
In addition to the high-speed differential output clock driver,
the AD9912 provides an independent, single-ended output,
CMOS clock driver that is very good for frequencies up to
150 MHz. The signal path for the CMOS clock driver can either
include or bypass the CMOS output divider.
If the CMOS output divider is bypassed, the HSTL and CMOS
drivers are the same frequency as the signal presented at the
FDBK_IN pins. When using the CMOS output in this configuration, the DDS output frequency should be in the range of
30 MHz to 150 MHz. At low output frequencies (<30 MHz), the
low slew rate of the DAC results in a higher noise floor. This can
be remedied by running the DDS at 100 MHz or greater and
using the CMOS divider. At an output frequency of 50 MHz,
the best technique depends on the user’s application. Running
the DDS at 200 MHz, and using a CMOS divider of 4, results in
a lower noise floor, but at the expense of close-in phase noise.
At frequencies greater than 150 MHz, the HSTL output should
be used.
CMOS Output Divider (S-Divider)
The CMOS output divider is 16 bits cascaded with an additional
divide-by-two. The divider is therefore capable of integer division
from 1 to 65,535 (index of 1) or from 2 to 131,070 (index of 2).
The divider is programmed via the I/O register map to trigger
on either the rising (default) or falling edge of the feedback
signal.
The CMOS output divider is an integer divider capable of
handling frequencies well above the Nyquist limit of the DDS.
The S-divider/2 bit (Register 0x0106, Bit 0) must be set when
FDBK_IN is greater than 400 MHz.
Note that the actual output divider values equal the value stored
in the output divider register minus one. Therefore, to have an
output divider of one, the user writes zeros to the output divider
register.
HARMONIC SPUR REDUCTION
The most significant spurious signals produced by the DDS are
harmonically related to the desired output frequency of the DDS.
The source of these harmonic spurs can usually be traced to the
DAC, and the spur level is in the −60 dBc range. This ratio
represents a level that is about 10 bits below the full-scale
output of the DAC (10 bits down is 2−10, or 1/1024).
Such a spur can be reduced by combining the original signal
with a replica of the spur, but offset in phase by 180°. This idea
is the foundation of the technique used to reduce harmonic
spurs in the AD9912. Because the DAC has 14-bit resolution,
a −60 dBc spur can be synthesized using only the lower 4 bits of
the DAC full-scale range. That is, the 4 LSBs can create an output
level that is approximately 60 dB below the full-scale level of the
DAC (commensurate with a −60 dBc spur). This fact gives rise
to a means of digitally reducing harmonic spurs or their aliased
images in the DAC output spectrum by digitally adding a sinusoid
at the input of the DAC with a similar magnitude as the offending
spur, but shifted in phase to produce destructive interference.
Rev. F | Page 22 of 40
AD9912
The procedure for tuning the spur reduction is as follows:
Although the worst spurs tend to be harmonic in origin, the fact
that the DAC is part of a sampled system results in the possibility
of spurs appearing in the output spectrum that are not harmonically related to the fundamental. For example, if the DAC is
sampled at 1 GHz and generates an output sinusoid of 170 MHz,
the fifth harmonic would normally be at 850 MHz. However,
because of the sampling process, this spur appears at 150 MHz,
only 20 MHz away from the fundamental. Therefore, when
attempting to reduce DAC spurs it is important to know the
actual location of the harmonic spur in the DAC output
spectrum based on the DAC sample rate so that its harmonic
number can be reduced.
The mechanics of performing harmonic spur reduction is shown
in Figure 48. It essentially consists of two additional DDS cores
operating in parallel with the original DDS. This enables the user
to reduce two different harmonic spurs from the second to the
15th with nine bits of phase offset control (±π) and eight bits of
amplitude control.
1.
Determine which offending harmonic spur to reduce and
its amplitude. Enter that harmonic number into Bit 0 to
Bit 3 of Register 0x0500/Register 0x0505.
2.
Turn off the fundamental by setting Bit 7 of Register 0x0013
and enable the SpurKiller channel by setting Bit 7 of
Register 0x0500/Register 0x0505.
3.
Adjust the amplitude of the SpurKiller channel so that it
matches the amplitude of the offending spur.
4.
Turn the fundamental on by clearing Bit 7 of Register 0x0013.
5.
Adjust the phase of the SpurKiller channel so that
maximum interference is achieved.
Note that the SpurKiller setting is sensitive to the loading of the
DAC output pins, and that a DDS reset is required if a SpurKiller
channel is turned off. The DDS can be reset by setting Bit 0 of
Register 0x0012, and resetting the part is not necessary.
The performance improvement offered by this technique varies
widely and depends on the conditions used. Given this extreme
variability, it is impossible to define a meaningful specification
to guarantee SpurKiller performance. Current data indicate that
a 6 dB to 8 dB improvement is possible for a given output
frequency using a common setting over process, temperature,
and voltage. There are frequencies, however, where a common
setting can result in much greater improvement. Manually
adjusting the SpurKiller settings on individual parts can result
in more than 30 dB of spurious performance improvement.
The dynamic range of the cancellation signal is further augmented by a gain bit associated with each channel. When this
bit is set, the magnitude of the cancellation signal is doubled by
employing a 1-bit left-shift of the data. However, the shift
operation reduces the granularity of the cancellation signal
magnitude. The full-scale amplitude of a cancellation spur is
approximately −60 dBc when the gain bit is a Logic 0 and
approximately −54 dBc when the gain bit is a Logic 1.
DDS
DDS
PHASE
OFFSET
48-BIT ACCUMULATOR
48
48-BIT
FREQUENCY
TURNING WORD
(FTW)
14
48
D Q
SPUR
CANCELLATION
ENABLE
14
19
19
ANGLE TO
AMPLITUDE
CONVERSION
14
0
14
1
DAC I-SET
REGISTERS
AND LOGIC
DAC_RSET
DAC
(14-BIT)
DAC_OUT
DAC_OUTB
SYSCLK
CH1 CANCELLATION PHASE OFFSET
4
9
2-CHANNEL
HARMONIC
FREQUENCY
GENERATOR
0
CH1
CH2 HARMONIC NUMBER
CH2 CANCELLATION PHASE OFFSET
CH2 CANCELLATION MAGNITUDE
1
SHIFT
4
CH1 GAIN
9
0
CH2
CH1 CANCELLATION MAGNITUDE
HEADROOM
CORRECTION
SHIFT
1
8
CH2 GAIN
8
HARMONIC SPUR CANCELLATION
Figure 48. Spur Reduction Circuit Diagram
Rev. F | Page 23 of 40
06763-040
CH1 HARMONIC NUMBER
AD9912
THERMAL PERFORMANCE
Table 7. Thermal Parameters
Symbol
θJA
θJMA
θJMA
θJB
θJC
ΨJT
Thermal Characteristic Using a JEDEC51-7 Plus JEDEC51-5 2S2P Test Board
Junction-to-ambient thermal resistance, 0.0 m/sec air flow per JEDEC JESD51-2 (still air)
Junction-to-ambient thermal resistance, 1.0 m/sec air flow per JEDEC JESD51-6 (moving air)
Junction-to-ambient thermal resistance, 2.0 m/sec air flow per JEDEC JESD51-6 (moving air)
Junction-to-board thermal resistance, 1.0 m/sec air flow per JEDEC JESD51-8 (moving air)
Junction-to-case thermal resistance (die-to-heat sink) per MIL-Std 883, Method 1012.1
Junction-to-top-of-package characterization parameter, 0 m/sec air flow per JEDEC JESD51-2 (still air)
The AD9912 is specified for a case temperature (TCASE). To
ensure that TCASE is not exceeded, an airflow source can be used.
Use the following equation to determine the junction temperature on the application PCB:
Value
25.2
22.0
19.8
13.9
1.7
0.1
Unit
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
Values of θJA are provided for package comparison and PCB
design considerations. θJA can be used for a first-order
approximation of TJ by the equation
TJ = TA + (θJA × PD)
where TA is the ambient temperature (°C).
TJ = TCASE + (ΨJT × PD)
where:
TJ is the junction temperature (°C).
TCASE is the case temperature (°C) measured by customer at top
center of package.
ΨJT is the value from Table 7.
PD is the power dissipation (see the Total Power Dissipation
section in the Specifications section).
Values of θJC are provided for package comparison and PCB
design considerations when an external heat sink is required.
Values of θJB are provided for package comparison and PCB
design considerations.
The values in Table 7 apply to both 64-lead package options.
Rev. F | Page 24 of 40
AD9912
POWER-UP
POWER-ON RESET
On initial power-up, the AD9912 internally generates a 75 ns
RESET pulse. The pulse is initiated when both of the following
two conditions are met:
•
•
The DDS output frequency listed in Table 8 assumes that
the internal DAC sampling frequency (fS) is 1 GHz. These
frequencies scale 1:1 with fS, meaning that other start-up
frequencies are available by varying the SYSCLK frequency.
At startup, the internal frequency multiplier defaults to 40×
when the Xtal/PLL mode is selected via the status pins.
The 3.3 V supply is greater than 2.35 V ± 0.1 V.
The 1.8 V supply is greater than 1.4 V ± 0.05 V.
Less than 1 ns after RESET goes high, the S1 to S4 configuration
pins go high impedance and remain high impedance until
RESET is deactivated. This allows strapping and configuration
during RESET.
Because of this reset sequence, external power supply sequencing is not critical.
DEFAULT OUTPUT FREQUENCY ON POWER-UP
The four status pins (S1 to S4) are used to define the output
frequency of the DDS at power-up even though the I/O registers
have not yet been programmed. At power-up, internal logic
initiates a reset pulse of about 10 ns. During this time, S1 to S4
briefly function as input pins and can be driven externally. Any
logic levels thus applied are transferred to a 4-bit register on the
falling edge of the internally initiated pulse. The same behavior
occurs when the RESET pin is asserted manually.
Setting up S1 to S4 for default DDS startup is accomplished by
connecting a resistor to each pin (either pull-up or pull-down)
to produce the desired bit pattern, yielding 16 possible states
that are used both to address an internal 8 × 16 ROM and to
select the SYSCLK mode (see Table 8). The ROM contains eight
16-bit DDS frequency tuning words (FTWs), one of which is
selected by the state of the S1 to S3 pins. The selected FTW is
transferred to the FTW0 register in the I/O register map
without the need for an I/O update. This ensures that the DDS
generates the selected frequency even if the I/O registers have
not been programmed. The state of the S4 pin selects whether
the internal system clock is generated by means of the internal
SYSCLK PLL multiplier or not (see the SYSCLK Inputs section
for details).
Table 8. Default Power-Up Frequency Options for 1 GHz
System Clock
S4
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Rev. F | Page 25 of 40
Status Pin
S3
S2
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
S1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
SYSCLK
Input Mode
Xtal/PLL
Xtal/PLL
Xtal/PLL
Xtal/PLL
Xtal/PLL
Xtal/PLL
Xtal/PLL
Xtal/PLL
Direct
Direct
Direct
Direct
Direct
Direct
Direct
Direct
Output Frequency
(MHz)
0
38.87939
51.83411
61.43188
77.75879
92.14783
122.87903
155.51758
0
38.87939
51.83411
61.43188
77.75879
92.14783
122.87903
155.51758
AD9912
POWER SUPPLY PARTITIONING
The AD9912 features multiple power supplies, and their power
consumption varies with its configuration. This section covers
which power supplies can be grouped together and how the
power consumption of each block varies with frequency.
1.8 V SUPPLIES
DVDD (Pin 3, Pin 5, and Pin 7)
The recommendations here are for typical applications, and for
these applications, there are four groups of power supplies:
3.3 V digital, 3.3 V analog, 1.8 V digital, and 1.8 V analog.
These pins should be grouped together and isolated from the
1.8 V AVDD supplies. For most applications, a ferrite bead
provides sufficient isolation, but a separate regulator may be
necessary for applications demanding the highest performance.
The current consumption of this group increases from about
160 mA at a system clock of 700 MHz to about 205 mA at a
system clock of 1 GHz. There is also a slight (~5%) increase as
fOUT increases from 50 MHz to 400 MHz.
Applications demanding the highest performance may require
additional power supply isolation.
AVDD (Pin 11, Pin 19, Pin 23, Pin 24, Pin 36, Pin 42,
Pin 44, and Pin 45)
Important: All power supply pins must receive power regardless
of whether that block is used.
These pins can be grouped together and should be isolated from
other 1.8 V supplies. A separate regulator is recommended. At
a minimum, a ferrite bead should be used for isolation.
The numbers quoted here are for comparison only. Refer to the
Specifications section for exact numbers. With each group, use
bypass capacitors of 1 μF in parallel with a 10 μF.
3.3 V SUPPLIES
AVDD (Pin 53)
DVDD_I/O (Pin 1) and AVDD3 (Pin 14)
Although one of these pins is analog and the other is digital,
these two 3.3 V supplies can be grouped together. The power
consumption on Pin 1 varies dynamically with serial port
activity.
AVDD3 (Pin 37)
This 1.8 V supply consumes about 40 mA. The supply can be
run off the same regulator as the 1.8 V AVDD group, with a
ferrite bead to isolate Pin 53 from the rest of the 1.8 V AVDD
group. However, for applications demanding the highest
performance, a separate regulator is recommended.
AVDD (Pin 25, Pin 26, Pin 29, and Pin 30)
This is the CMOS driver supply. It can be either 1.8 V or 3.3 V,
and its power consumption is a function of the output frequency
and loading of OUT_CMOS (Pin 38).
If the CMOS driver is used at 3.3 V, this supply should be
isolated from other 3.3 V supplies with a ferrite bead to avoid
a spur at the output frequency. If the HSTL driver is not used,
AVDD3 (Pin 37) can be connected (using a ferrite bead) to
AVDD3 (Pin 46, Pin 47, and Pin 49). If the HSTL driver is used,
connect AVDD3 (Pin 37) to Pin 1 and Pin 14, using a ferrite bead.
These system clock PLL power pins should be grouped together
and isolated from other 1.8 V AVDD supplies.
At a minimum, it is recommended that Pin 25 and Pin 30 be
tied together and isolated from the aggregate AVDD 1.8 V
supply with a ferrite bead. Likewise, Pin 26 and Pin 29 can also
be tied together, with a ferrite bead isolating them from the same
aggregate 1.8 V supply. The loop filter for the system clock PLL
should directly connect to Pin 26 and Pin 29 (see Figure 46).
Applications demanding the highest performance may need to
have these four pins powered by their on their own LDO.
If the CMOS driver is used at 1.8 V, AVDD3 (Pin 37) can be
connected to AVDD (Pin 36).
If the system clock PLL is bypassed, the loop filter pin (Pin 31)
should be pulled down to analog ground using a 1 kΩ resistor.
Pin 25, Pin 26, Pin 29, and Pin 30 should be included in the large
1.8 V AVDD power supply group. In this mode, isolation of these
pins is not critical, and these pins consume almost no power.
If the CMOS driver is not used, AVDD3 (Pin 37) can be tied
directly to the 1.8 V AVDD (Pin 36) and the CMOS driver
powered down using Register 0x0010.
AVDD3 (Pin 46, Pin 47, and Pin 49)
These are 3.3 V DAC power supplies that typically consume
about 25 mA. At a minimum, a ferrite bead should be used to
isolate these from other 3.3 V supplies, with a separate regulator
being ideal.
Rev. F | Page 26 of 40
AD9912
SERIAL CONTROL PORT
The AD9912 serial control port is a flexible, synchronous, serial
communications port that allows an easy interface with many
industry-standard microcontrollers and microprocessors. Single
or multiple byte transfers are supported, as well as MSB first or
LSB first transfer formats. The AD9912 serial control port can
be configured for a single bidirectional I/O pin (SDIO only) or
for two unidirectional I/O pins (SDIO and SDO).
Note that all serial port operations (such as the frequency
tuning word update) depend on the presence of the DAC
system clock.
SERIAL CONTROL PORT PIN DESCRIPTIONS
SCLK (serial clock) is the serial shift clock. This pin is an input.
SCLK is used to synchronize serial control port reads and writes.
Write data bits are registered on the rising edge of this clock,
and read data bits are registered on the falling edge. This pin
has an internal pull-down resistor.
SDIO (serial data input/output) is a dual-purpose pin and
acts as input only or input/output. The AD9912 defaults to
bidirectional pins for I/O. Alternatively, SDIO can be used
as a unidirectional I/O pin by writing to the SDO active bit
(Register 0x0000, Bit 0 = 1). In this case, SDIO is the input,
and SDO is the output.
SDO (serial data out) is used only in the unidirectional I/O mode
(Register 0x0000, Bit 0 = 1) as a separate output pin for reading
back data. Bidirectional I/O mode (using SDIO as both input
and output) is active by default (SDO active bit: Register 0x0000,
Bit 0 = 0).
CSB (chip select bar) is an active low control that gates the read
and write cycles. When CSB is high, SDO and SDIO are in a high
impedance state. This pin is internally pulled up by a 100 kΩ
resistor to 3.3 V. It should not be left floating. See the Operation
of Serial Control Port section on the use of the CSB in a
communication cycle.
SDIO (PIN 63)
SDO (PIN 62)
CSB (PIN 61)
AD9912
SERIAL
CONTROL
PORT
06763-041
SCLK (PIN 64)
Figure 49. Serial Control Port
OPERATION OF SERIAL CONTROL PORT
Framing a Communication Cycle with CSB
A communication cycle (a write or a read operation) is gated by
the CSB line. CSB must be brought low to initiate a communication cycle.
CSB stall high is supported in modes where three or fewer bytes
of data (plus the instruction data) are transferred ([W1:W0]
must be set to 00, 01, or 10; see Table 9). In these modes, CSB
can temporarily return high on any byte boundary, allowing
time for the system controller to process the next byte. CSB can
go high on byte boundaries only and can go high during either
part (instruction or data) of the transfer. During this period, the
serial control port state machine enters a wait state until all data
has been sent. If the system controller decides to abort the transfer
before all of the data is sent, the state machine must be reset by
either completing the remaining transfer or by returning the CSB
low for at least one complete SCLK cycle (but fewer than eight
SCLK cycles). Raising the CSB on a nonbyte boundary terminates
the serial transfer and flushes the buffer.
In the streaming mode ([W1:W0] = 11), any number of data
bytes can be transferred in a continuous stream. The register
address is automatically incremented or decremented (see the
MSB/LSB First Transfers section). CSB must be raised at the end
of the last byte to be transferred, thereby ending the stream mode.
Communication Cycle—Instruction Plus Data
There are two parts to a communication cycle with the AD9912.
The first writes a 16-bit instruction word into the AD9912, coincident with the first 16 SCLK rising edges. The instruction word
provides the AD9912 serial control port with information
regarding the data transfer, which is the second part of the
communication cycle. The instruction word defines whether
the upcoming data transfer is a read or a write, the number of
bytes in the data transfer, and the starting register address for
the first byte of the data transfer.
Write
If the instruction word is for a write operation (I15 = 0), the
second part is the transfer of data into the serial control port
buffer of the AD9912. The length of the transfer (1, 2, or 3 bytes,
or streaming mode) is indicated by two bits ([W1:W0]) in the
instruction byte. The length of the transfer indicated by [W1:W0]
does not include the 2-byte instruction. CSB can be raised after
each sequence of eight bits to stall the bus (except after the last
byte, where it ends the cycle). When the bus is stalled, the serial
transfer resumes when CSB is lowered. Stalling on nonbyte
boundaries resets the serial control port.
There are three types of registers on the AD9912: buffered, live,
and read only. Buffered (also referred to as mirrored) registers
require an I/O update to transfer the new values from a
temporary buffer on the chip to the actual register and are
marked with an M in the Type column of the register map.
Toggling the IO_UPDATE pin or writing a 1 to the register
update bit (Register 0x0005, Bit 0) causes the update to occur.
Because any number of bytes of data can be changed before
issuing an update command, the update simultaneously enables
all register changes that have occurred since any previous update.
Live registers do not require I/O update; they update immediately
after being written. Read-only registers ignore write commands
and are marked RO in the Type column of the register map. An
AC in this column indicates that the register is autoclearing.
Rev. F | Page 27 of 40
AD9912
Read
If the instruction word is for a read operation (I15 = 1), the next
N × 8 SCLK cycles clock out the data from the address specified
in the instruction word, where N is 1, 2, 3, or 4, as determined
by [W1:W0]. In this case, 4 is used for streaming mode where
four or more words are transferred per read. The data readback
is valid on the falling edge of SCLK.
The default mode of the AD9912 serial control port is bidirectional mode, and the data readback appears on the SDIO pin. It
is possible to set the AD9912 to unidirectional mode by writing
to the SDO active bit (Register 0x0000, Bit 0 = 1), and in that
mode, the requested data appears on the SDO pin.
SDO
CSB
SERIAL
CONTROL
PORT
UPDATE
REGISTERS
TOGGLE
IO_UPDATE
PIN
AD9912
CORE
06763-042
SDIO
CONTROL REGISTERS
SCLK
REGISTER BUFFERS
By default, a read request reads the register value that is currently in use by the AD9912. However, setting Register 0x0004,
Bit 0 = 1 causes the buffered registers to be read instead. The
buffered registers are the ones that take effect during the next
I/O update.
Figure 50. Relationship Between Serial Control Port Register Buffers and
Control Registers of the AD9912
The AD9912 uses Register 0x0000 to Register 0x0509. Although
the AD9912 serial control port allows both 8-bit and 16-bit
instructions, the 8-bit instruction mode provides access to five
address bits (A4 to A0) only, which restricts its use to Address
Space 0x00 to Address Space 0x31. The AD9912 defaults to 16-bit
instruction mode on power-up, and the 8-bit instruction mode
is not supported.
THE INSTRUCTION WORD (16 BITS)
The MSB of the instruction word is R/W, which indicates
whether the instruction is a read or a write. The next two bits,
[W1:W0], are the transfer length in bytes. The final 13 bits are
the address ([A12:A0]) at which to begin the read or write
operation.
For a write, the instruction word is followed by the number of
bytes of data indicated by Bits[W1:W0], which is interpreted
according to Table 9.
Bits[A12:A0] select the address within the register map that is
written to or read from during the data transfer portion of the
communications cycle. The AD9912 uses all of the 13-bit
address space. For multibyte transfers, this address is the
starting byte address.
Table 9. Byte Transfer Count
W1
0
0
1
1
W0
0
1
0
1
Bytes to Transfer
(Excluding the 2-Byte Instruction)
1
2
3
Streaming mode
MSB/LSB FIRST TRANSFERS
The AD9912 instruction word and byte data can be MSB first or
LSB first. The default for the AD9912 is MSB first. The LSB first
mode can be enabled by writing a 1 to the LSB first bit in the
serial configuration register and then issuing an I/O update.
Immediately after the LSB first bit is set, all serial control port
operations are changed to LSB first order.
When MSB first mode is active, the instruction and data bytes
must be written from MSB to LSB. Multibyte data transfers in
MSB first format start with an instruction byte that includes the
register address of the most significant data byte. Subsequent
data bytes must follow in order from high address to low address.
In MSB first mode, the serial control port internal address
generator decrements for each data byte of the multibyte
transfer cycle.
When LSB first = 1 (LSB first), the instruction and data bytes
must be written from LSB to MSB. Multibyte data transfers in
LSB first format start with an instruction byte that includes the
register address of the least significant data byte followed by
multiple data bytes. The serial control port internal byte address
generator increments for each byte of the multibyte transfer cycle.
The AD9912 serial control port register address decrements from
the register address just written toward 0x0000 for multibyte
I/O operations if the MSB first mode is active (default). If the
LSB first mode is active, the serial control port register address
increments from the address just written toward 0x1FFF for
multibyte I/O operations.
Unused addresses are not skipped during multibyte I/O operations.
The user should write the default value to a reserved register and
should write only zeros to unmapped registers. Note that it is
more efficient to issue a new write command than to write the
default value to more than two consecutive reserved (or
unmapped) registers.
Rev. F | Page 28 of 40
AD9912
Table 10. Serial Control Port, 16-Bit Instruction Word, MSB First
MSB
I15
R/W
I14
W1
I13
W0
I12
A12
I11
A11
I10
A10
I9
A9
I8
A8
I7
A7
I6
A6
I5
A5
I4
A4
I3
A3
I2
A2
LSB
I0
A0
I1
A1
CSB
SCLK DON'T CARE
SDIO DON'T CARE
R/W W1 W0 A12 A11 A10 A9
A8
A7
A6 A5
A4 A3 A2
A1 A0
D7 D6 D5
16-BIT INSTRUCTION HEADER
D4 D3
D2 D1
D0
D7
REGISTER (N) DATA
D6 D5
D4 D3 D2
D1 D0
DON'T CARE
REGISTER (N – 1) DATA
06763-043
DON'T CARE
Figure 51. Serial Control Port Write—MSB First, 16-Bit Instruction, Two Bytes Data
CS
SCLK
DON'T CARE
SDIO
DON'T CARE
R/W W1 W0 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
SDO DON'T CARE
REGISTER (N) DATA
REGISTER (N – 1) DATA
REGISTER (N – 2) DATA
REGISTER (N – 3) DATA
DON'T
CARE
06763-057
D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
16-BIT INSTRUCTION HEADER
Figure 52. Serial Control Port Read—MSB First, 16-Bit Instruction, Four Bytes Data
tDS
tHI
tS
tDH
CSB
DON'T CARE
SDIO
DON'T CARE
DON'T CARE
R/W
W1
W0
A12
A11
A10
A9
A8
A7
A6
A5
D4
D3
D2
D1
D0
DON'T CARE
06763-045
SCLK
tH
tCLK
tLO
Figure 53. Serial Control Port Write—MSB First, 16-Bit Instruction, Timing Measurements
CSB
SCLK
DATA BIT N
06763-046
tDV
SDIO
SDO
DATA BIT N – 1
Figure 54. Timing Diagram for Serial Control Port Register Read
CSB
SCLK DON'T CARE
A0 A1 A2 A3
A4
A5 A6
A7
A8
A9 A10 A11 A12 W0 W1 R/W D0 D1 D2 D3 D4
16-BIT INSTRUCTION HEADER
D5 D6
REGISTER (N) DATA
D7
D0
D1 D2
D6
REGISTER (N + 1) DATA
Figure 55. Serial Control Port Write—LSB First, 16-Bit Instruction, Two Bytes Data
Rev. F | Page 29 of 40
D3 D4 D5
D7
DON'T CARE
06763-047
SDIO DON'T CARE
DON'T CARE
AD9912
tS
tH
CSB
tCLK
tHIGH
SCLK
tLOW
tDS
SDIO
BIT N
BIT N + 1
Figure 56. Serial Control Port Timing—Write
Table 11. Definitions of Terms Used in Serial Control Port Timing Diagrams
Parameter
tCLK
tDV
tDS
tDH
tS
tH
tHI
tLO
Description
Period of SCLK
Read data valid time (time from falling edge of SCLK to valid data on SDIO/SDO)
Setup time between data and rising edge of SCLK
Hold time between data and rising edge of SCLK
Setup time between CSB and SCLK
Hold time between CSB and SCLK
Minimum period that SCLK should be in a logic high state
Minimum period that SCLK should be in a logic low state
Rev. F | Page 30 of 40
06763-048
tDH
AD9912
I/O REGISTER MAP
All address and bit locations that are left blank in Table 12 are unused.
Table 12.
Addr
(Hex)
Bit 7
Type 1 Name
Serial port configuration and part identification
0x0000
Serial
SDO
config.
active
0x0001
Reserved
0x0002
RO
Part ID
0x0003
RO
0x0004
Serial
options
0x0005
AC
Power-down and reset
0x0010
Powerdown and
enable
0x0011
Reserved
0x0012
M, AC
Reset
0x0013
M
System clock
0x0020
0x0021
0x0022
N-divider
Reserved
PLL
parameters
PD HSTL
driver
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
LSB first
(buffered)
Soft
reset
Long
instruction
Long
instruction
Soft reset
LSB first
(buffered)
SDO
active
Part ID
Read buffer
register
Register
update
Enable
CMOS
driver
Enable
output
doubler
PD
SYSCLK
PLL
Full PD
Digital PD
DDS reset
PD fund
DDS
S-div/2
reset
S-divider
reset
N-divider, Bits[4:0]
0x01AB
0x0201
0x00
0xC0 or
0xD0
0x00
0x00
0x00
VCO range
Charge pump current,
Bits[1:0]
0x04
0x30
0x00
S-divider, Bits[15:0]
LSB: Register 0x0104
S-divider
0x00
S-divider/2
Falling
edge
triggered
0x01
0x00
FTW0, Bits[47:0]
LSB: Register 0x01A6
0x00
0x00
0x00
0x00
Start-up
cond.
Start-up
cond.
0x00
0x00
M
0x01AC M
Phase
0x01AD M
Doubler and output drivers
0x0200
HSTL driver
0x00
0x02
0x19
0x00
0x00
2× reference
VCO auto
range
Reserved
Frequency tuning word
0x01A0
Reserved
to
0x01A5
0x01A6
M
FTW0
(frequency
0x01A7
M
tuning
0x01A8
M
word)
0x01A9
M
0x01AA M
0x18
0x12
CMOS output divider (S-divider)
0x0100
Reserved
0x0101
to
0x0103
0x0104
and
0x0105
0x0106
Default
(Hex)
DDS phase word, Bits[7:0]
DDS phase word, Bits[13:8]
OPOL
(polarity)
CMOS driver
Rev. F | Page 31 of 40
HSTL output doubler,
Bits[1:0]
CMOS mux
0x05
0x00
AD9912
Addr
(Hex)
Type 1 Name
Calibration (user-accessible trim)
0x0400
Reserved
to
0x040A
0x040B
DAC fullscale
0x040C
current
0x040D
Reserved
0x040E
Reserved
0x040F
Reserved
and
0x0410
Harmonic spur reduction
0x0500
M
Spur A
0x0501
0x0503
0x0504
M
M
M
0x0505
M
0x0506
0x0508
0x0509
M
M
M
1
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x00
DAC full-scale current, Bits[7:0]
DAC full-scale current,
Bits[9:8]
0xFF
0x01
0x00
0x10
0x00
HSR-A
enable
Amplitude
gain × 2
Spur A harmonic, Bits[3:0]
0x00
Spur A magnitude, Bits[7:0]
Spur A phase, Bits[7:0]
Spur A
phase, Bit 8
Spur B
Default
(Hex)
HSR-B
enable
Amplitude
gain × 2
Spur B harmonic, Bits[3:0]
0x00
0x00
0x00
0x00
Spur B magnitude, Bits[7:0]
Spur B phase, Bits[7:0]
Spur B
phase, Bit 8
0x00
0x00
0x00
Types of registers: M = mirrored (also called buffered). This type of register needs an I/O update for the new value to take effect; RO = read-only; AC = autoclear.
Rev. F | Page 32 of 40
AD9912
I/O REGISTER DESCRIPTIONS
SERIAL PORT CONFIGURATION (REGISTER 0x0000 TO REGISTER 0x0005)
Register 0x0000—Serial Port Configuration
Table 13.
Bits
[7:4]
3
2
Bit Name
Long instruction
Soft reset
1
LSB first
0
SDO active
Description
These bits are the mirror image of Bits[3:0].
Read-only; the AD9912 supports only long instructions.
Resets register map, except for Register 0x0000. Setting this bit forces a soft reset, meaning that S1 to
S4 are not tristated, nor is their state read when this bit is cleared. The AD9912 assumes the values of
S1 to S4 that were present during the last hard reset. This bit is not self-clearing, and all other registers
are restored to their default values after a soft reset.
Sets bit order for serial port.
1 = LSB first.
0 = MSB first. I/O update must occur for the MSB first to take effect.
Enables SDO pin.
1 = SDO pin enabled (4-wire serial port mode).
0 = 3-wire mode.
Register 0x0001—Reserved
Register 0x0002 and Register 0x0003—Part ID (Read-Only)
Register 0x0004—Serial Options
Table 14.
Bits
0
Bit Name
Read buffer register
Description
For buffered registers, serial port readback reads from actual (active) registers instead of the buffer.
1 = reads the buffered values that take effect during the next I/O update.
0 = reads values that are currently in effect.
Register 0x0005—Serial Options (Self Clearing)
Table 15.
Bits
0
Bit Name
Register update
Description
Software access to the register update pin function. Writing a 1 to this bit is identical to performing
an I/O update.
POWER-DOWN AND RESET (REGISTER 0x0010 TO REGISTER 0x0013)
Register 0x0010—Power-Down and Enable
Power-up default is defined by the start-up pins.
Table 16.
Bits
7
Bit Name
PD HSTL driver
6
Enable CMOS driver
5
4
Enable output doubler
PD SYSCLK PLL
1
Full PD
0
Digital PD
Description
Powers down HSTL output driver.
1 = HSTL driver powered down.
Powers up CMOS output driver.
1 = CMOS driver on.
Powers up output clock generator doubler. Output doubler must still be enabled in Register 0x0200.
System clock multiplier power-down.
1 = system clock multiplier powered down.
If the S4 pin is tied high at power-up or reset, this bit is set, and the default value for Register 0x0010
is D0, not C0.
Setting this bit is identical to activating the PD pin and puts all blocks (except serial port) into powerdown mode. SYSCLK is turned off.
Removes clock from most of digital section; leave serial port usable. In contrast to full PD, setting this
bit does not debias inputs, allowing for quick wake-up.
Rev. F | Page 33 of 40
AD9912
Register 0x0011—Reserved
Register 0x0012—Reset (Autoclearing)
To reset the entire chip, the user can use the (non-autoclearing) soft reset bit in Register 0x0000.
Table 17.
Bits
0
Bit Name
DDS reset
Description
Reset of the direct digital synthesis block. Reset of this block is very seldom needed.
Register 0x0013—Reset (Continued) (Not Autoclearing)
Table 18.
Bits
7
Bit Name
PD fund DDS
3
1
S-div/2 reset
S-divider reset
Description
Setting this bit powers down the DDS fundamental output but not the spurs. It is used during tuning
of the SpurKiller circuit.
Asynchronous reset for S prescaler.
Synchronous (to S-divider prescaler output) reset for integer divider.
SYSTEM CLOCK (REGISTER 0x0020 TO REGISTER 0x0022)
Register 0x0020—N-Divider
Table 19.
Bits
[4:0]
Bit Name
N-divider
Description
These bits set the feedback divider for system clock PLL. There is a fixed divide-by-2 preceding this
block, as well as an offset of 2 added to this value. Therefore, setting this register to 00000 translates to
an overall feedback divider ratio of 4. See Figure 45.
Register 0x0021—Reserved
Register 0x0022—PLL Parameters
Table 20.
Bits
7
[6:4]
3
Bit Name
VCO auto range
Reserved
2× reference
2
VCO range
[1:0]
Charge pump current
Description
Automatic VCO range selection. Enabling this bit allows Bit 2 of this register to be set automatically.
Reserved.
Enables a frequency doubler prior to the SYSCLK PLL and can be useful in reducing jitter induced by
the SYSCLK PLL. See Figure 44.
Selects low range or high range VCO.
0 = low range (700 MHz to 810 MHz).
1 = high range (900 MHz to 1000 MHz). For system clock settings between 810 MHz and 900 MHz, use
the VCO auto range (Bit 7) to set the correct VCO range automatically.
Charge pump current.
00 = 250 μA.
01 = 375 μA.
10 = off.
11= 125 μA.
Rev. F | Page 34 of 40
AD9912
CMOS OUTPUT DIVIDER (S-DIVIDER) (REGISTER 0x0100 TO REGISTER 0x0106)
Register 0x0100 to Register 0x0103—Reserved
Register 0x0104—S-Divider
Table 21.
Bits
[7:0]
Bit Name
S-divider
Description
CMOS output divider. Divide ratio = 1 − 65,536. If the desired S-divider setting is greater than 65,536,
or if the signal on FDBK_IN is greater than 400 MHz, then Bit 0 in Register 0x0106 must be set. Note that
the actual S-divider is the value in this register plus 1; so to have an S-divider of 1, Register 0x0104 and
Register 0x0105 must both be 0x00. Register 0x0104 is the least significant byte.
Register 0x0105—S-Divider (Continued)
Table 22.
Bits
[15:8]
Bit Name
S-divider
Description
CMOS output divider. Divide ratio = 1 − 65,536. If the desired S-divider setting is greater than 65,536,
or if the signal on FDBK_IN is greater than 400 MHz, then Bit 0 in Register 0x0106 must be set. Note that
the actual S-divider is the value in this register plus 1; so to have an S-divider of 1, Register 0x0104 and
Register 0x0105 must both be 0x00. Register 0x104 is the least significant byte.
Register 0x0106—S-Divider (Continued)
Table 23.
Bits
7
[6:1]
0
Bit Name
Falling edge triggered
Reserved
S-divider/2
Description
Setting this bit inverts the reference clock before S-divider.
Reserved.
Setting this bit enables an additional /2 prescaler. See the CMOS Output Divider (S-Divider) section.
If the desired S-divider setting is greater than 65,536, or if the signal on FDBK_IN is greater than 400 MHz,
this bit must be set.
FREQUENCY TUNING WORD (REGISTER 0x01A0 TO REGISTER 0x01AD)
Register 0x01A0 to Register 0x01A5—Reserved
Register 0x01A6—FTW0 (Frequency Tuning Word)
Table 24.
Bits
[7:0]
Bit Name
FTW0
Description
These registers contain the FTW (frequency tuning word) for the DDS. The FTW determines the ratio
of the AD9912 output frequency to its DAC system clock. Register 0x01A6 is the least significant byte
of the FTW. Note that the power-up default is defined by start-up Pin S1 to Pin S4. Updates to the FTW
results in an instantaneous frequency jump but no phase discontinuity.
Register 0x01A7—FTW0 (Frequency Tuning Word) (Continued)
Table 25.
Bits
[15:8]
Bit Name
FTW0
Description
These registers contain the FTW (frequency tuning word) for the DDS. The FTW determines the ratio
of the AD9912 output frequency to its DAC system clock. Register 0x01A6 is the least significant byte
of the FTW. Note that the power-up default is defined by start-up Pin S1 to Pin S4. Updates to the FTW
results in an instantaneous frequency jump but no phase discontinuity.
Register 0x01A8—FTW0 (Frequency Tuning Word) (Continued)
Table 26.
Bits
[23:16]
Bit Name
FTW0
Description
These registers contain the FTW (frequency tuning word) for the DDS. The FTW determines the ratio
of the AD9912 output frequency to its DAC system clock. Register 0x01A6 is the least significant byte
of the FTW. Note that the power-up default is defined by start-up Pin S1 to Pin S4. Updates to the FTW
results in an instantaneous frequency jump but no phase discontinuity.
Rev. F | Page 35 of 40
AD9912
Register 0x01A9—FTW0 (Frequency Tuning Word) (Continued)
Table 27.
Bits
[31:24]
Bit Name
FTW0
Description
These registers contain the FTW (frequency tuning word) for the DDS. The FTW determines the ratio
of the AD9912 output frequency to its DAC system clock. Register 0x01A6 is the least significant
byte of the FTW. Note that the power-up default is defined by start-up Pin S1 to Pin S4. Updates to
the FTW results in an instantaneous frequency jump but no phase discontinuity.
Register 0x01AA—FTW0 (Frequency Tuning Word) (Continued)
Table 28.
Bits
[39:32]
Bit Name
FTW0
Description
These registers contain the FTW (frequency tuning word) for the DDS. The FTW determines the ratio
of the AD9912 output frequency to its DAC system clock. Register 0x01A6 is the least significant
byte of the FTW. Note that the power-up default is defined by start-up Pin S1 to Pin S4. Updates to
the FTW results in an instantaneous frequency jump but no phase discontinuity.
Register 0x01AB—FTW0 (Frequency Tuning Word) (Continued)
Table 29.
Bits
[47:40]
Bit Name
FTW0
Description
These registers contain the FTW (frequency tuning word) for the DDS. The FTW determines the ratio
of the AD9912 output frequency to its DAC system clock. Register 0x01A6 is the least significant
byte of the FTW. Note that the power-up default is defined by start-up Pin S1 to Pin S4. Updates to
the FTW results in an instantaneous frequency jump but no phase discontinuity.
Register 0x01AC—Phase
Table 30.
Bits
[7:0]
Bit Name
DDS phase word
Description
Allows the user to vary the phase of the DDS output. See the Direct Digital Synthesizer section.
Register 0x01AC is the least significant byte of the phase offset word (POW). Note that a momentary
phase discontinuity may occur as the phase passes through 45° intervals.
Register 0x01AD—Phase (Continued)
Table 31.
Bits
[13:8]
Bit Name
DDS phase word
Description
Allows the user to vary the phase of the DDS output. See the Direct Digital Synthesizer section.
Register 0x01AC is the least significant byte of the phase offset word (POW). Note that a momentary
phase discontinuity may occur as the phase passes through 45° intervals.
Rev. F | Page 36 of 40
AD9912
DOUBLER AND OUTPUT DRIVERS (REGISTER 0x0200 TO REGISTER 0x0201)
Register 0x0200—HSTL Driver
Table 32.
Bits
4
[3:2]
[1:0]
Bit Name
OPOL
Reserved
HSTL output doubler
Description
Output polarity. Setting this bit inverts the HSTL driver output polarity.
Reserved.
HSTL output doubler.
01 = doubler disabled.
10 = doubler enabled. When using doubler, Bit 5 in Register 0x0010 must also be set to 1.
Register 0x0201—CMOS Driver
Table 33.
Bits
0
Bit Name
CMOS mux
Description
This bit allows the user to select whether the CMOS driver output is divided by the S-divider.
0 = S-divider input sent to CMOS driver.
1 = S-divider output sent to CMOS driver. See Figure 39.
CALIBRATION (USER-ACCESSIBLE TRIM) (REGISTER 0x0400 TO REGISTER 0x0410)
Register 0x0400 to Register 0x040A—Reserved
Register 0x040B—DAC Full-Scale Current
Table 34.
Bits
[7:0]
Bit Name
DAC full-scale current
Description
DAC full-scale current, Bits[7:0]. See the Digital-to-Analog (DAC) Output section.
Register 0x040C—DAC Full-Scale Current (Continued)
Table 35.
Bits
[9:8]
Bit Name
DAC full-scale current
Description
DAC full-scale current, Bits[9:8]. See Register 0x040B.
Register 0x040D to Register 0x0410—Reserved
HARMONIC SPUR REDUCTION (REGISTER 0x0500 TO REGISTER 0x0509)
See the Harmonic Spur Reduction section.
Register 0x0500—Spur A
Table 36.
Bits
7
6
[5:4]
[3:0]
Bit Name
HSR-A enable
Amplitude gain × 2
Reserved
Spur A harmonic
Description
Harmonic Spur Reduction A enable.
Setting this bit doubles the gain of the cancelling circuit and also doubles the minimum step size.
Reserved.
Spur A Harmonic 1 to Spur A Harmonic 15. Allows user to choose which harmonic to eliminate.
Register 0x0501—Spur A (Continued)
Table 37.
Bits
[7:0]
Bit Name
Spur A magnitude
Description
Linear multiplier for Spur A magnitude.
Rev. F | Page 37 of 40
AD9912
Register 0x0503—Spur A (Continued)
Table 38.
Bits
[7:0]
Bit Name
Spur A phase
Description
Linear offset for Spur B phase.
Register 0x0504—Spur A (Continued)
Table 39.
Bits
[8]
Bit Name
Spur A phase
Description
Linear offset for Spur A phase.
Register 0x0505—Spur B
Table 40.
Bits
7
6
[5:4]
[3:0]
Bit Name
HSR-B enable
Amplitude gain × 2
Reserved
Spur B harmonic
Description
Harmonic Spur Reduction B enable.
Setting this bit doubles the gain of the cancelling circuit and also doubles the minimum step size.
Reserved.
Spur B Harmonic 1 to Spur B Harmonic 15. Allows user to choose which harmonic to eliminate.
Register 0x0506—Spur B (Continued)
Table 41.
Bits
[7:0]
Bit Name
Spur B magnitude
Description
Linear multiplier for Spur B magnitude.
Register 0x0508—Spur B (Continued)
Table 42.
Bits
[7:0]
Bit Name
Spur B phase
Description
Linear offset for Spur B phase.
Register 0x0509—Spur B (Continued)
Table 43.
Bits
8
Bit Name
Spur B phase
Description
Linear offset for Spur B phase.
Rev. F | Page 38 of 40
AD9912
OUTLINE DIMENSIONS
9.10
9.00 SQ
8.90
0.60 MAX
0.60
MAX
48
64
49
1
PIN 1
INDICATOR
PIN 1
INDICATOR
8.85
8.75 SQ
8.65
0.50
BSC
0.50
0.40
0.30
33
32
0.05 MAX
0.02 NOM
0.30
0.23
0.18
0.25 MIN
0.20 REF
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-VMMD-4
062209-A
SEATING
PLANE
16
7.50 REF
0.80 MAX
0.65 TYP
12° MAX
17
BOTTOM VIEW
TOP VIEW
1.00
0.85
0.80
5.36
5.21 SQ
5.06
EXPOSED
PAD
Figure 57. 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
9 mm × 9 mm Body, Very Thin Quad
(CP-64-7)
Dimensions shown in millimeters
ORDERING GUIDE
Model 1
AD9912ABCPZ
AD9912ABCPZ-REEL7
AD9912A/PCBZ
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
Package Description
64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
Evaluation Board
Z = RoHS Compliant Part.
Rev. F | Page 39 of 40
Package Option
CP-64-7
CP-64-7
AD9912
NOTES
©2007–2010 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D06763-0-6/10(F)
Rev. F | Page 40 of 40