2.7 GHz DDS-Based AgileRF
TM
Synthesizer
AD9956
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no 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 license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703
© 2004 Analog Devices, Inc. All rights reserved.
FEATURES
400 MSPS internal DDS clock speed
48-bit frequency tuning word
14-bit programmable phase offset
Integrated 14-bit DAC
Excellent dynamic performance
Phase noise 135 dBc/Hz @ 1 KHz offset
-80 dB SFDR @ 160 MHz (±100 KHz offset I
OUT
)
25 Mb/s write-speed serial I/O control
200 MHz phase frequency detector inputs
655 MHz programmable input dividers for the phase
frequency detector (÷M, ÷N) {M, N = 1..16} (bypassable)
Programmable RF divider (÷R) {R = 1, 2, 4, 8} (bypassable)
8 phase/frequency profiles
1.8 V supply for device operation
3.3 V supply for I/O and charge pump
Software controlled power-down
48-lead LFCSP package
Automatic linear frequency sweeping capability (in DDS)
Programmable charge pump current (up to 4 mA)
Phase modulation capability
Multichip synchronization
Dual-mode PLL lock detect
655 MHz CML-mode PECL-compliant driver
APPLICATIONS
Agile LO frequency synthesis
FM chirp source for radar and scanning systems
Automotive radars
Test and measurement equipment
Acousto-optic device drivers
FUNCTIONAL BLOCK DIAGRAM
FREQUENCY
ACCUMULATOR
PHASE
ACCUMULATOR
PHASE
OFFSET
PHASE
OFFSET
WORD
TIMING AND CONTROL LOGIC
PHASE TO
AMPLITUDE
CONVERSION
14
FTW
48
24
DAC
RF-DIVIDER
÷
R
FROM PLLOSC
3
PS<2:0> RESET I/O PORT
CHARGE
PUMP
SCALER
BUFFER
BUFFER
CP_OUT
CP_RSET
PLL_LOCK/SYNC_IN
I/O_UPDATE
SYNC_OUT
REFCLK
REFCLK
CML CLOCK DRIVER
DRV DRV DRV_RSET
DAC_RSET
IOUT
IOUT
SYNC_CLK
SYSCLK
DELTA
FREQUENCY
TUNING WORD
DELTA
FREQUENCY
RAMP RATE
SYSCLK
3
LOCK
DETECT
48
19
14
DDS CORE
SYSCLK
I/O_RESET
OSCILLATOR
16
CHARGE
PUMP
PLLREF/
PLLREF
PLLOSC/
PLLOSC
÷
N
÷
4
÷
M
04806-0-001
Figure 1.
AD9956
Rev. 0 | Page 2 of 32
TABLE OF CONTENTS
Product Overview............................................................................. 3
Specifications..................................................................................... 4
Loop Measurement Conditions.................................................. 9
Absolute Maximum Ratings.......................................................... 10
ESD Caution................................................................................ 10
Pin Configuration and Function Descriptions........................... 11
Typical Performance Characteristics ........................................... 13
Typical Application Circuits.......................................................... 16
Application Circuit Explanations ............................................. 17
General Description ....................................................................... 18
DDS Core..................................................................................... 18
PLL Circuitry .............................................................................. 18
CML Driver................................................................................. 19
Modes of Operation ....................................................................... 20
DDS Modes of Operation ......................................................... 20
Synchronization Modes for Multiple Devices.............................. 20
Serial Port Operation ..................................................................... 22
Instruction Byte .......................................................................... 23
Serial Interface Port Pin Description....................................... 23
MSB/LSB Transfers .................................................................... 23
Register Map and Description ...................................................... 24
Control Function Register Descriptions ................................. 27
Outline Dimensions ....................................................................... 32
Ordering Guide .......................................................................... 32
REVISION HISTORY
7/04--Revision: Initial Version
AD9956
Rev. 0 | Page 3 of 32
PRODUCT OVERVIEW
The AD9956 is Analog Devices' newest AgileRF synthesizer.
The device is comprised of DDS and PLL circuitry. The DDS
features a 14-bit DAC operating at up to 400 MSPS and a 48-bit
frequency tuning word (FTW). The PLL circuitry includes a
phase frequency detector with scaleable 200 MHz inputs
(divider inputs operate up to 655 MHz) and digital control over
the charge pump current. The device also includes a 655 MHz
CML-mode PECL-compliant driver with programmable slew
rates. The AD9956 uses advanced DDS technology, an internal
high speed, high performance DAC, and an advanced phase
frequency detector/charge pump combination, which, when
used with an external VCO, enables the synthesis of digitally
programmable, frequency-agile analog output sinusoidal wave-
forms up to 2.7 GHz. The AD9956 is designed to provide fast
frequency hopping and fine tuning resolution (48-bit frequency
tuning word). Information is loaded into the AD9956 via a
serial I/O port that has a device write-speed of 25 Mb/s. The
AD9956 DDS block also supports a user-defined linear sweep
mode of operation.
The AD9956 is specified to operate over the extended
automotive range of -40°C to +125°C.
AD9956
Rev. 0 | Page 4 of 32
SPECIFICATIONS
AVDD = DVDD = 1.8 V ± 5%; DVDD_I/O = CP_VDD = 3.3 V ± 5% (@ T
A
= 25°C) DAC_R
SET
= 3.92 k, CP_R
SET
= 3.09 k,
DRV_R
SET
= 4.02 k, unless otherwise noted.
Table 1.
Parameter Min
Typ
Max
Unit
Test
Conditions/Comments
RF DIVIDER (REFCLK ) INPUT SECTION (÷R)
RF Divider Input Range
1
2700
MHz
DDS SYSCLK not to exceed
400 MSPS
Input Capacitance (DC)
3
pF
Input Impedance (DC)
1500
Input Duty Cycle
42
50
58
%
Input Power/Sensitivity
-10
+4
dBm
Single-ended, into a 50 load
1
Input Voltage Level
350
1000
mV p-p
PHASE FREQUENCY DETECTOR/CHARGE PUMP
PLLREF Input
Input Frequency
2
÷M Set to Divide by at Least 4
655
MHz
÷M Bypassed
200
MHz
Input Voltage Levels
200
450
600
mV p-p
Input Capacitance
10
pF
Input Resistance
1500
PLLOSC Input
Input Frequency
÷N Set to Divide by at Least 4
655
MHz
÷N Bypassed
200
MHz
Input Voltage Levels
200
450
600
mV p-p
Input Capacitance
10
pF
Input Resistance
1500
Charge Pump Source/Sink Maximum Current
4
mA
Charge Pump Source/Sink Accuracy
-15
+5
%
Charge Pump Source/Sink Matching
-5
+5
%
Charge Pump Output Compliance Range
3
0.5
CP_VDD - 0.5
V
PLL_LOCK Drive Strength
2
mA
PHASE FREQUENCY DETECTOR NOISE FLOOR
@ 50 kHz PFD Frequency
149
dBc/Hz
@ 2 MHz PFD Frequency
133
dBc/Hz
@ 100 MHz PFD Frequency
116
dBc/Hz
@ 200 MHz PFD Frequency
113
dBc/Hz
CML OUTPUT DRIVER (DRV)
Differential Output Voltage Swing
4
720
mV
50 load to supply, both lines
Maximum Toggle Rate
655
MHz
Common-Mode Output Voltage
1.75
V
Output Duty Cycle
42
50
58
%
Output Current
Continuous
5
7.2
mA
Rising Edge Surge
20.9
mA
Falling Edge Surge
13.5
mA
Output Rise Time
250
ps
100 terminated, 5 pF load
AD9956
Rev. 0 | Page 5 of 32
Parameter Min
Typ
Max
Unit
Test
Conditions/Comments
LOGIC INPUTS (SDI/O, I/O_RESET, RESET,
I/O_UPDATE, PS0 to PS2, SYNC_IN)
V
IH
, Input High Voltage
2.0
V
V
IL
, Input Low Voltage
0.8
V
I
INH
, I
INL
Input Current
±1
±5
µA
C
IN
, Maximum Input Capacitance
3
pF
LOGIC OUTPUTS (SDO, SYNC_OUT, PLL_LOCK)
6
V
OH
, Output High Voltage
2.7
V
V
OH
, Output Low Voltage
0.4
V
I
OH
100
µA
I
OL
100
µA
POWER CONSUMPTION
Total Power Consumed, All Functions On
400
mW
IAVDD
85
mA
IDVDD
45
mA
IDVDD_I/O
20
mA
ICP_VDD
15
mA
Power-Down Mode
80
mW
WAKE-UP TIME (from Power-Down Mode)
Digital Power-Down (CFR1<7>)
12
ns
DAC Power-Down (CFR2<39>)
7
µs
RF Divider Power-Down (CFR2<23>)
400
ns
Clock Driver Power-Down (CFR2<20>)
6
µs
Charge Pump Full Power-Down (CFR2<4>)
10
µs
Charge Pump Quick Power-Down (CFR2<3>)
150
ns
DAC OUTPUT CHARACTERISTICS
Resolution
14
Bits
Full-Scale Output Current
10
15
mA
Gain Error
-10
+10
% FS
Output Offset
0.6
µA
Output Capacitance
5
pF
Voltage Compliance Range
AVDD - 0.50
AVDD + 0.50
V
Wideband SFDR (DC to Nyquist)
10 MHz Analog Out
-64
dBc
40 MHz Analog Out
-62
dBc
80 MHz Analog Out
-60
dBc
120 MHz Analog Out
-55
dBc
160 MHz Analog Out
-55
dBc
Narrowband SFDR
10 MHz Analog Out (±1 MHz)
-89
dBc
10 MHz Analog Out (±250 kHz)
-91
dBc
10 MHz Analog Out (±50 kHz)
-93
dBc
40 MHz Analog Out (±1 MHz)
-87
dBc
40 MHz Analog Out (±250 kHz)
-89
dBc
40 MHz Analog Out (±50 kHz)
-91
dBc
80 MHz Analog Out (±1 MHz)
-85
dBc
80 MHz Analog Out (±250 kHz)
-87
dBc
80 MHz Analog Out (±50 kHz)
-89
dBc
120 MHz Analog Out (±1 MHz)
-83
dBc
120 MHz Analog Out (±250 kHz)
-85
dBc
120 MHz Analog Out (±50 kHz)
-87
dBc
AD9956
Rev. 0 | Page 6 of 32
Parameter Min
Typ
Max
Unit
Test
Conditions/Comments
160 MHz Analog Out (±1 MHz)
-81
dBc
160 MHz Analog Out (±250 kHz)
-83
dBc
160 MHz Analog Out (±50 kHz)
-85
dBc
DAC Residual Phase Noise
19.7 MHz F
OUT
@ 10 Hz Offset
125
dBc/Hz
@ 100 Hz Offset
135
dBc/Hz
@ 1 kHz Offset
143
dBc/Hz
@ 10 kHz Offset
152
dBc/Hz
@ 100 kHz Offset
158
dBc/Hz
>1 MHz Offset
163
dBc/Hz
51.84 MHz F
OUT
@ 10 Hz Offset
119
dBc/Hz
@ 100 Hz Offset
125
dBc/Hz
@ 1 kHz Offset
132
dBc/Hz
@ 10 kHz Offset
142
dBc/Hz
@ 100 kHz Offset
150
dBc/Hz
>1 MHz Offset
155
dBc/Hz
105.3 MHz Analog Out
@ 10 Hz Offset
105
dBc/Hz
@ 100 Hz Offset
115
dBc/Hz
@ 1 kHz Offset
122
dBc/Hz
@ 10 kHz Offset
131
dBc/Hz
@ 100 kHz Offset
139
dBc/Hz
>1 MHz Offset
142
dBc/Hz
155.52 MHz Analog Out
@ 10 Hz Offset
105
dBc/Hz
@ 100 Hz Offset
110
dBc/Hz
@ 1 kHz Offset
119
dBc/Hz
@ 10 kHz Offset
127
dBc/Hz
@ 100 kHz Offset
135
dBc/Hz
>1 MHz Offset
142
dBc/Hz
CRYSTAL OSCILLATOR (ON PLLREF INPUT)
Operating Range
20
25
30
MHz
Residual Phase Noise (@ 25 MHz)
@ 10 Hz Offset
95
dBc/Hz
@ 100 Hz Offset
120
dBc/Hz
@ 1 kHz Offset
137
dBc/Hz
@ 10 kHz Offset
156
dBc/Hz
@ 100 kHz Offset
164
dBc/Hz
>1 MHz Offset
170
dBc/Hz
DIGITAL TIMING SPECIFICATIONS
CS to SCLK Setup Time TPRE
6
ns
Period of SCLK (Write Speed) TSCLKW
40
ns
Period of SCLK (Read Speed) TSCLKR
400
ns
Serial Data Setup Time TDSU
6.5
ns
Serial Data Hold Time TDHLD
0
ns
TDV Data Valid Time TDV
40
ns
I/O Update to SYNC_CLK Setup Time TUD
7
ns
PS<2:0> to SYNC_CLK Setup Time TPS
7
ns
AD9956
Rev. 0 | Page 7 of 32
Parameter Min
Typ
Max
Unit
Test
Conditions/Comments
Latencies/Pipeline Delays
7
I/O Update to DAC Frequency Change
33
SYSCLK Cycles
I/O Update to DAC Phase Change
33
SYSCLK Cycles
PS<2:0> to DAC Frequency Change
29
SYSCLK Cycles
PS<2:0> to DAC Phase Change
29
SYSCLK Cycles
I/O Update to CP_OUT Scaler Change
4
SYSCLK Cycles
I/O Update to Frequency Accumulator
Step Size Change
4
SYSCLK
Cycles
I/O Update to Frequency Accumulator
Ramp Rate Change
4
SYSCLK
Cycles
RF DIVIDER/CML DRIVER EQUIVALENT
INTRINSIC TIME JITTER
F
IN
= 414.72 MHz, F
OUT
= 51.84 MHz
BW = 12 kHz -> 400 kHz
136
f
S
rms
OC1, RF Divider R = 8
F
IN
= 1244.16 MHz, F
OUT
= 155.52 MHz
BW = 12 kHz -> 1.3 MHz
101
f
S
rms
OC3, RF Divider R = 8
F
IN
= 2488.32 MHz, F
OUT
= 622.08 MHz
BW = 12 kHz -> 5 MHz
108
f
S
rms
OC12, RF Divider R = 4
RF DIVIDER/CML DRIVER RESIDUAL PHASE NOISE
F
IN
= 157.6 MHz, F
OUT
= 19.7 MHz
RF Divider R = 8
@ 10 Hz
-115
dBc/Hz
@ 100 Hz
-126
dBc/Hz
@ 1 kHz
-134
dBc/Hz
@ 10 kHz
-143
dBc/Hz
@ 100 kHz
-150
dBc/Hz
> 1 MHz
-151
dBc/Hz
F
IN
= 1240 MHz, F
OUT
= 155 MHz
RF Divider R = 8
@ 10 Hz
-111
dBc/Hz
@ 100 Hz
-122
dBc/Hz
@ 1 kHz
-129
dBc/Hz
@ 10 kHz
-138
dBc/Hz
@ 100 kHz
-146
dBc/Hz
@ 1 MHz
-150
dBc/Hz
>3 MHz
-153
dBc/Hz
F
IN
= 2488MHz, F
OUT
= 622 MHz
RF Divider R = 4
@ 10 Hz
-97
dBc/Hz
@ 100 Hz
-110
dBc/Hz
@ 1 kHz
-120
dBc/Hz
@ 10 kHz
-126
dBc/Hz
@ 100 kHz
-136
dBc/Hz
@ 1 MHz
-141
dBc/Hz
>3 MHz
-144
dBc/Hz
TOTAL SYSTEM TIME JITTER FOR 622 MHz CLOCK
See the Loop Measurement Condi-
tions section
12 kHz to 5 MHz Bandwidth
0.7
ps rms
AD9956
Rev. 0 | Page 8 of 32
Parameter Min
Typ
Max
Unit
Test
Conditions/Comments
TOTAL SYSTEM JITTER AND PHASE NOISE FOR
105.33 MHz ADC CLOCK GENERATION CIRCUIT
See the Loop Measurement Condi-
tions section
Converter Limiting Jitter
0.53
ps rms
Resultant SNR
67
dB
Phase Noise of Fundamental
@ 10 Hz Offset
-75
dBc/Hz
@ 100 Hz Offset
-87
dBc/Hz
@ 1 kHz Offset
-93
dBc/Hz
@ 10 kHz Offset
-105
dBc/Hz
@ 100 kHz Offset
-145
dBc/Hz
@ 1 MHz Offset
-152
dBc/Hz
1
The input impedance of the REFCLK input is 1500 . However, in order to provide matching on the clock line, an external 50 load is used.
2
Driving the PLLREF input buffer, the crystal oscillator section of this input stage performs up to only 30 MHz.
3
The charge pump output compliance range is functionally 0.2 V to (CP_VDD - 0.2 V). The value listed here is the compliance range for 5% matching.
4
Measured as peak-to-peak from DRV to DRV.
5
For a 4.02 k resistor from DRV_RSET to GND.
6
Assumes a 1 mA load.
7
I/O_UPDATE/PS<2:0> are detected by the AD9956 synchronous to the rising edge of SYNC_CLK. Each latency measurement is from the first SYNC_CLK rising edge
after the I/O_UPDATE/PS<2:0> state change.
AD9956
Rev. 0 | Page 9 of 32
LOOP MEASUREMENT CONDITIONS
622 MHz OC-12 Clock
VCO = Sirenza 190-640T
Reference = Wenzel 500-10116 (30.3 MHz)
Loop Filter = 10 kHz BW, 60° Phase Margin
C1 = 170 nF, R1 = 14.4 , C2 = 5.11 µF, R2 = 89.3 ,
C3 Omitted
CP_OUT = 4 mA (Scaler = ×8)
÷R = 2, ÷M = 1, ÷N = 1
105 MHz Converter Clock
VCO = Sirenza 190-845T
Reference = Wenzel 500-10116 (30.3 MHz)
Loop Filter = 10 kHz BW, 45° Phase Margin
C1 = 117 nF, R1 = 28 , C2 = 1.6 µF, R2 = 57.1 , C3 = 53.4 nF
CP_OUT = 4 mA (Scaler = ×8)
÷R = 8, ÷M = 1, ÷N = 1
C1
C3
INPUT
OUTPUT
C2
R1
R2
04806-0-033
Figure 2. Generic Loop Filter
AD9956
Rev. 0 | Page 10 of 32
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Analog Supply Voltage (AVDD)
2 V
Digital Supply Voltage (DVDD)
2 V
Digital I/O Supply Voltage
(DVDD_I/0)
3.6 V
Charge Pump Supply Voltage
(CPVDD)
3.6 V
Maximum Digital Input Voltage
-0.5 V to DVDD_I/O + 0.5 V
Storage Temperature
-65°C to +150°C
Operating Temperature Range
-40°C to +125°C
Lead Temperature Range
(Soldering 10 sec)
300°C
Junction Temperature
150°C
Thermal Resistance (
JA
) 26°C/W
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.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate
on the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy elec-
trostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation
or loss of functionality.
AD9956
Rev. 0 | Page 11 of 32
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
13
14
15
16
17
18
19
20
21
22
23
24
SD
O
SD
I/O
SC
LK
CS
DV
DD_
I/O
S
Y
NC_
OUT
P
LL_
LOCK/S
Y
NC_
IN
I/O_UPDATE
PS0
PS1
PS2
DGND
48
47
46
45
44
43
42
41
40
39
38
37
AV
DD
DAC_
RS
E
T
DRV
_
R
S
E
T
C
P
_R
SET
AV
DD
AGND
PLLOSC
PLLOSC
PLLREF
PLLREF
AV
DD
AGND
1
2
3
4
5
6
7
8
9
10
11
12
AGND
AVDD
AGND
AVDD
IOUT
IOUT
AVDD
AGND
I/O_RESET
RESET
DVDD
DGND
NC = NO CONNECT
CP_VDD
AGND
DRV
DRV
AVDD
AGND
REFCLK
REFCLK
AVDD
AGND
DVDD
35
CP_OUT
36
34
33
32
31
30
29
28
27
26
25
AD9956
TOP VIEW
(Not to Scale)
PIN 1
INDICATOR
04806-0-008
Figure 3. 48-Lead LFCSP Pin Configuration
Note that the exposed paddle on this package is an electrical connection (Pin 49) as well as a thermal enhancement. For the device to
function properly, the paddle MUST be attached to analog ground.
AD9956
Rev. 0 | Page 12 of 32
Table 3. 48-Lead LFCSP Pin Function Description
Pin No.
Mnemonic
Description
1, 3, 8, 26, 30,
34, 37, 43, 49
AGND Analog
Ground.
2, 4, 7, 27, 31,
38, 44, 48
AVDD
Analog Core Supply (1.8 V).
5
IOUT
DAC Analog Output.
6
IOUT
DAC Analog Complementary Output.
9 I/O_RESET
Resets the serial port when synchronization is lost in communications but does not reset the de-
vice itself (ACTIVE HIGH). When not being used, this pin should be forced low, because it floats to
the threshold value.
10 RESET Master RESET. Clears all accumulators and returns all registers to their default values (ACTIVE
HIGH).
11, 25
DVDD
Digital Core Supply (1.8 V).
12, 24
DGND
Digital Ground.
13
SDO
Serial Data Output. Used only when device is programmed for 3-wire serial data mode.
14 SDI/O Serial Data I/O. When the part is programmed for 3-wire serial data mode, this is input only; in
2-wire mode, it serves as both the input and output.
15
SCLK
Serial Data Clock. Provides the clock signal for the serial data port.
16
CS
Active Low Signal That Enables Shared Serial Busses. When brought high, the serial port ignores
the serial data clocks.
17
DVDD_I/O
Digital Interface Supply (3.3 V).
18
SYNC_OUT
Synchronization Clock Output.
19 PLL_LOCK/SYNC_IN
Bidirectional Dual Function Pin. Depending on device programming, it is either the DDS' synchro-
nization input (allows alignment of multiple subclocks) or the PLL lock detect output signal.
20 I/O_UPDATE
This input pin, when set high, transfers the data from the I/O buffers to the internal registers on the
rising edge of the internal SYNC_CLK, which can be observed on SYNC_OUT.
21 to 23
PS0 to PS2
Profile Select Pins. Specify one of eight frequency tuning word/phase offset word profiles. In linear
sweep mode, PS0 determines the state of the sweep. In linear sweep no dwell mode, PS0 is a trig-
ger that initiates the sweep. PS1 and PS2 have no function during linear sweep mode or linear
sweep no dwell mode.
28
REFCLK
RF Divider and DDS REFCLK Complementary Input.
29
REFCLK
RF Divider and DDS REFCLK Input.
32
DRV
CML Driver Complementary Output.
33
DRV
CML Driver Output.
35 CP_VDD
Charge Pump Supply Pin (3.3 V). To minimize noise on the charge pump, isolate this supply from
DVDD_I/O.
36
CP_OUT
Charge Pump Output.
39
PLLREF
Phase Frequency Detector Reference Input.
40
PLLREF
Phase Frequency Detector Reference Complementary Input.
41
PLLOSC
Phase Frequency Detector Oscillator (Feedback) Complementary Input.
42
PLLOSC
Phase Frequency Detector Oscillator (Feedback) Input.
45
CP_RSET
Charge Pump Current Set (Program Charge Pump Current with a Resistor to AGND).
46
DRV_RSET
CML Driver Output Current Set (Program CML Output Current with a Resistor to AGND).
47
DAC_RSET
DAC Output Current Set (Program DAC Output Current with a Resistor to AGND).
Note that the exposed paddle on this package is an electrical connection (Pin 49) as well as a thermal enhancement. In order for the
device to function properly, the paddle MUST be attached to analog ground.
AD9956
Rev. 0 | Page 13 of 32
TYPICAL PERFORMANCE CHARACTERISTICS
04806-0-015
CENTER 10.1MHz
100kHz/
SPAN 1MHz
REF LVL
0dBm
DELTA 1 [T1]
84.82dB
404.80961924kHz
RBW
VBW
SWT
RF ATT
UNIT
500Hz
500Hz
20s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 4. AD9956 DAC Performance: 400 MSPS Clock,
10 MHz F
OUT
, 1 MHz Span
04806-0-016
CENTER 40.1MHz
100kHz/
SPAN 1MHz
REF LVL
0dBm
DELTA 1 [T1]
78.67dB
100.20040080kHz
RBW
VBW
SWT
RF ATT
UNIT
500Hz
500Hz
20s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 5. AD9956 DAC Performance: 400 MSPS Clock,
40 MHz F
OUT
, 1 MHz Span
04806-0-017
CENTER 100.1MHz
100kHz/
SPAN 1MHz
REF LVL
0dBm
DELTA 1 [T1]
57.74dB
400.80160321kHz
RBW
VBW
SWT
RF ATT
UNIT
500Hz
500Hz
20s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 6. AD9956 DAC Performance: 400 MSPS Clock,
100 MHz F
OUT
, 1 MHz Span
04806-0-018
START 0Hz
16.9MHz/
STOP 169MHz
REF LVL
0dBm
DELTA 1 [T1]
67.45dB
74.50901804MHz
RBW
VBW
SWT
RF ATT
UNIT
10kHz
10kHz
4.3s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 7. AD9956 DAC Performance: 400 MSPS Clock,
10 MHz F
OUT
, 200 MHz Span
04806-0-019
START 0Hz
20MHz/
STOP 200MHz
REF LVL
0dBm
DELTA 1 [T1]
62.65dB
100.20040080MHz
RBW
VBW
SWT
RF ATT
UNIT
10kHz
10kHz
5s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 8. AD9956 DAC Performance: 400 MSPS Clock,
40 MHz F
OUT
, 200 MHz Span
04806-0-020
START 0Hz
20MHz/
STOP 200MHz
REF LVL
0dBm
DELTA 1 [T1]
48.78dB
400.80160321kHz
RBW
VBW
SWT
RF ATT
UNIT
10kHz
10kHz
5s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 9. AD9956 DAC Performance: 400 MSPS Clock,
100 MHz F
OUT
, 200 MHz Span
AD9956
Rev. 0 | Page 14 of 32
04806-0-021
CENTER 159.5MHz
100kHz/
SPAN 1MHz
REF LVL
0dBm
DELTA 1 [T1]
78.13dB
100.20040080kHz
RBW
VBW
SWT
RF ATT
UNIT
500kHz
500kHz
20s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 10. AD9956 DAC Performance: 400 MSPS Clock,
160 MHz F
OUT
, 1 MHz Span
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
1M
04806-0-023
Figure 11. AD9956 DDS/DAC Residual Phase Noise
400 MHz Clock, 10 MHz Output
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
1M
04806-0-024
Figure 12. AD9956 DDS/DAC Residual Phase Noise
400 MHz Clock, 40 MHz Output
04806-0-022
START 0Hz
20MHz/
STOP 200MHz
REF LVL
0dBm
DELTA 1 [T1]
56.33dB
80.96192385MHz
RBW
VBW
SWT
RF ATT
UNIT
10kHz
10kHz
5s
20dB
dB
1 AP
A
20
40
0
60
30
50
10
70
80
90
100
1
1
Figure 13. AD9956 DAC Performance: 400 MSPS Clock,
160 MHz F
OUT
, 200 MHz Span
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
10M
1M
04806-0-025
Figure 14. AD9956 DDS/DAC Residual Phase Noise
400 MHz Clock, 103 MHz Output
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
10M
1M
04806-0-026
Figure 15. AD9956 DDS/DAC Residual Phase Noise
400 MHz Clock, 159 MHz Output
AD9956
Rev. 0 | Page 15 of 32
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
10M
1M
04806-0-027
Figure 16. RF Divider and CML Driver Residual
Phase Noise (840 MHz In, 105 MHz Out)
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
10M
1M
04806-0-028
Figure 17. RF Divider and CML Driver Residual
Phase Noise (1240 MHz In, 155 MHz Out)
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
10M
1M
04806-0-029
Figure 18. RF Divider and CML Driver Residual
Phase Noise (1680 MHz In, 210 MHz Out)
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
170
10
1k
100
10k
100k
100M
10M
1M
04806-0-030
Figure 19. RF Divider and CML Driver Residual
Phase Noise (2488 MHz In, 622 MHz Out)
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
180
170
10
1k
100
10k
100k
10M
1M
04806-0-031
Figure 20. Total System Phase Noise for 105 MHz Converter Clock
FREQUENCY (Hz)
L(f) (dBc
/
H
z)
0
10
20
30
40
60
50
70
80
90
100
110
130
120
140
160
150
180
170
10
1k
100
10k
100k
10M
1M
04806-0-032
Figure 21. Total System Phase Noise for 622 MHz OC-12 Clock
AD9956
Rev. 0 | Page 16 of 32
TYPICAL APPLICATION CIRCUITS
DAC
PLLREF
PLLOSC
CP_OUT
DDS
÷
N
÷
M
÷
R
LPF
VCO
CML
DRIVER
PHASE FREQUENCY
DETECTOR/CHARGE PUMP
25MHz
CRYSTAL
400MHz
CLOCK1
CLOCK1
AD9956
04806-0-010
LPF
Figure 22. Dual-Clock Configuration
PLLREF
PLLOSC
CP_OUT
DDS
÷
R
VCO
AD9956
04806-0-011
LPF
LPF
DAC
Figure 23. Fractional-Divider Loop
PLLREF
PLLOSC
CP_OUT
DDS
÷
R
VCO
AD9956
04806-0-012
LPF
DAC
÷
N
CML
DRIVER
2.5GHz
TONE
8-LEVEL FSK
(FC = 100MHz)
BPF
BPF
25MHz
CRYSTAL
Figure 24. LO and Baseband Modulation Generation
AD9956
Rev. 0 | Page 17 of 32
DAC
CHARGE
PUMP
REF
OSC
DDS
÷
N
÷
M
÷
R
LPF
VCO
CML
DRIVER
PHASE FREQUENCY
DETECTOR
EXTERNAL
REFERENCE
622MHz
CLOCK1
CLOCK2
AD9956
04806-0-013
Figure 25. Optical Networking Clock
CHARGE
PUMP
PLLREF
PLLOSC
÷
N
VCO
DAC
DDS
PHASE
FREQUENCY
DETECTOR
650MHz
04806-0-014
LPF
LPF
Figure 26. Direct Upconversion
APPLICATION CIRCUIT EXPLANATIONS
Dual-Clock Configuration
In this loop, M = 1, N = 16, and R = 4. The DDS tuning word is
also equal to ¼ so that the frequency of CLOCK 1' equals the
frequency of CLOCK 1. Phase adjustments in the DDS provide
a 14-bit programmable rising edge skew capability of CLOCK 1'
with respect to CLOCK 1 (see Figure 22).
Fractional-Divider Loop
This loop offers the precise frequency division (48-bit) of the
DDS in the feedback path as well as the frequency sweeping
capability of the DDS. Programming the DDS to sweep from
24 MHz to 25 MHz sweeps the output of the VCO from
2.7 GHz to 2.6 GHz. The reference in this case is a simple
crystal (see Figure 23).
LO and Baseband Modulation Generation
Using the AD9956's PLL section to generate an LO and the
DDS portion to generate a modulated baseband, this circuit
uses an external mixer to perform some simple modulation at
RF frequencies (see Figure 24).
Optical Networking Clock
This is the AD9956 configured as an optical networking clock.
The loop can be used to generate a 622 MHz clock for OC12.
The DDS can be programmed to output 8 kHz to serve as a base
reference for other circuits in the subsystem (see Figure 25).
Direct Upconversion
The AD9956 is configured to use the DDS as a precision refer-
ence to the PLL loop. Since the VCO is < 655 MHz, it can be fed
straight into the phase frequency detector feedback input (with
the divider enabled), as seen in Figure 26.
AD9956
Rev. 0 | Page 18 of 32
GENERAL DESCRIPTION
DDS CORE
The DDS can create digital phase relationships by clocking a
48-bit accumulator. The incremental value loaded into the
accumulator, known as the frequency tuning word, controls the
overflow rate of the accumulator. Similar to a sine wave com-
pleting a 2 radian revolution, the overflow of the accumulator
is cyclical in nature and generates a base frequency according to
the following equation.
48
2
)
(
s
o
f
FTW
f
×
=
}
2
0
{
47
FTW
The instantaneous phase of the sine wave is, therefore, the out-
put of the phase accumulator block. This signal can be phase-
offset by programming an additive digital phase added to each
and every phase sample coming out of the accumulator.
These instantaneous phase values are then piped through a
phase-to-amplitude conversion (sometimes called an angle-
to-amplitude conversion or AAC) block. This algorithm follows
a COS(x) relationship where x is the phase coming out of the
phase offset block, normalized to 2.
Finally, the amplitude words are piped to a 14-bit DAC. Because
the DAC is a sampled data system, the output is a reconstructed
sine wave that needs to be filtered to take high frequency
images out of the spectrum. The DAC is a current-steering
DAC that is AVDD referenced. To get a measurable voltage
output, the DAC outputs must terminate through a load resistor
to AVDD, typically 50 . At positive full scale, IOUT sinks no
current and the voltage drop across the load resistor is zero.
However, the IOUT output sinks the DAC's programmed full-
scale output current, causing the maximum output voltage to
drop across the load resistor. At negative full-scale, the situation
is reversed and IOUT sinks the full-scale current (and generates
the maximum drop across the load resistor). At the same time,
IOUT sinks no current (and generates no voltage drop). At
midscale, the outputs sink equal amounts of current, generating
equal voltage drops.
PLL CIRCUITRY
The AD9956 includes an RF divider (divide-by-R), a phase
frequency detector, and a programmable output current charge
pump. Incorporating these blocks together, users can generate
many useful circuits for frequency synthesis. A few simple
examples are shown in the Typical Application Circuits.
The RF divider accepts differential or single-ended signals up to
2.7 GHz. The RF divider also supplies the SYSCLK input to the
DDS. Because the DDS operates up to only 400 MSPS, device
function requires that for any RF input signal > 400 MHz, the
RF divider be engaged. The RF divider can be programmed to
take values of 1, 2, 4, or 8. The ratio for the divider is pro-
grammed in the control register. The output of the divider can
be routed to the input of the on-chip CML driver. For lower
frequency input signals, it is possible to use the divider to divide
the input signal to the CML driver and use the undivided input
of the divider as the SYSCLK input to the DDS, or vice versa. In
all cases, the clock to the DDS should not exceed 400 MSPS.
The on-chip phase frequency detector has two differential
inputs, PLLREF (the reference input) and PLLOSC (the feed-
back or oscillator input). These differential inputs can be driven
by single-ended signals; however, when doing so, tie the unused
input through a 100 pF capacitor to the analog supply (AVDD).
The maximum speed of the phase frequency detector inputs is
200 MHz. Each of the inputs has a buffer and a divider (÷M on
PLLREF and ÷N on PLLOSC) that operates at up to 655 MHz.
If the signal exceeds 200 MHz, however, the divider must be
used. The dividers are programmed through the control registers
and take any integer value between 1 and 16.
The PLLREF input also has the option of engaging an in-line
oscillator circuit. Engaging this circuit means that the PLLREF
input can be driven with a crystal in the of 20 MHz PLLREF
30 MHz range.
The charge pump outputs a current in response to an error
signal generated in the phase frequency detector. The output
current is programmed through by placing a resistor (CP_R
SET
)
from the CP_RSET pin to ground. The value is dictated by the
following equation:
SET
CP_R
CP_OUT
1.55
=
This sets the charge pump's reference output current. Also, a
programmable scaler multiplies this base value by any integer
from 1 to 8, programmable through the CP current scale bits in
the Control Function Register 2, CFR2<2:0>.
AD9956
Rev. 0 | Page 19 of 32
CML DRIVER
For clocking applications, an on-chip current mode logic
(CML) driver is included. This CML driver generates very low
jitter clock edges. The outputs of the CML driver are current
outputs and drives PECL levels when terminated into a 100
load. The base output current of the driver is programmed by
attaching a resistor from the DRV_RSET pin to ground (nomi-
nally 4.02 k for a continuous current of 7.2 mA). An optional
on-chip current programming resistor is enabled by setting a bit
in the control register. The rising edge and falling edge slew
rates are independently programmable to help control over-
shoot and ringing through the application of surge current
during rising edge transitions and falling edge transitions (see
Figure 27). There is a default surge current of 7.6 mA on the
rising edge and 4.05 mA on the falling edge. Bits in the control
register enable additional rising edge and falling edge surge
current, as well disable the default surge current (see the
Control Function Register Descriptions section for details). The
CML driver can be driven by the
·
RF divider input
·
RF divider output
·
PLLOSC input
I(t)
t
~250ps
~250ps
RISING EDGE SURGE
CONTINUOUS
FALLING EDGE SURGE
CONTINUOUS
04806-0-002
Figure 27. Rising Edge and Falling Edge Surge Current Output of the
CML Clock Driver, as Opposed to the Steady State Continuous Current
AD9956
Rev. 0 | Page 20 of 32
MODES OF OPERATION
DDS MODES OF OPERATION
Single-Tone Mode
This is the default mode of operation for the DDS core. The
phase accumulator runs at a fixed frequency, as per the active
profile's tuning word. Likewise, any phase offset applied to the
signal is a static value, which comes from the phase offset word
of the active profile. The device has eight different phase/fre-
quency profiles, each with its own 48-bit frequency tuning word
and 14-bit phase offset word. Profiles are selected by applying
their digital value on the profile-select pins (PS2, PS1, and PS0).
It is impossible to use the phase offset of one profile and the
frequency tuning word of another.
Linear Sweep Mode
This mode is entered by setting the linear sweep enable bit in
the control register (CFR1<17> = 1) but leaving the linear
sweep no dwell bit clear (CFR1<16> = 0). When the part is in
linear sweep mode, the frequency accumulator ramps the
output frequency of the device from a programmed lower
frequency to a programmed upper frequency or from the upper
frequency to the lower frequency. The lower frequency is set by the
frequency tuning word stored in Profile 0, and the upper frequency
is set by the frequency tuning word stored in Profile 1.
The combinational logic within the frequency accumulator
requires that the value stored at FTW0 must always be less than
the value stored in FTW. The direction of the sweep (sweep up
to FTW1, sweep down to FTW0) is controlled by the PS0 pin. A
high state on this pin tells the part to sweep up to FTW1. A low
state on this pin tells the part to sweep down to FTW0. The
frequency accumulator requires four values, which are stored in
the register map. First, it requires an incremental frequency
value that tells the frequency accumulator how big of a fre-
quency step to take each time it takes a step when ramping up.
This value is stored in the rising delta frequency tuning word
(RDFTW). The second value required is the rate at which the
frequency accumulator should increment, that is, how often it
should take a step. This value is stored in the rising sweep ramp
rate word (RSRR). The RSRR value specifies the number of
SYNC_CLK cycles the frequency accumulator should count
between steps. The third and fourth values are the falling ramp
equivalents, the falling delta frequency tuning word (FDFTW)
and the falling sweep ramp rate (FSRR).
When operating in the linear sweep default mode, combina-
tional logic ensures that the part never ramps up past FTW1,
even if the next RDFTW increments the frequency past FTW1.
Once it reaches FTW1, as long as the PS0 pin stays high, the
frequency remains at FTW1. Likewise, the internal logic ensures
that the part never ramps down past FTW0, even if the next
RDFTW increments the frequency past FTW0. During a sweep
down (PS0 = 0), once the part reaches FTW0, as long as the PS0
pin stays low, the frequency remains at FTW0.
If a sweep is interrupted and the state of the PS0 pin is changed
during the midst of a sweep, the part begins sweeping in the
new direction at the rate dictated by the relevant delta fre-
quency tuning word and sweep ramp rate word. For example, if
the part is programmed to sweep from 100 MHz to 140 MHz
and to take 1 kHz steps every 1000 sync clock cycles (rising and
falling sweep words are the same), it would take four seconds to
complete a sweep. If the PS0 has been low for a very long time
(more than four seconds), changing the PS0 pin to high starts a
sweep up to 140 MHz. If after two seconds (not enough time for
a full sweep in this example) the PS0 pin is brought low again,
the part begins sweeping down from the current value, roughly
120 MHz.
Linear Sweep No Dwell Mode
This mode is entered by setting the linear sweep enable bit and
the linear sweep no dwell bit in the control register
(CFR<17:16> =1). When the part is in linear sweep no dwell
mode, the frequency accumulator ramps the output frequency
of the device from a programmed lower frequency to a pro-
grammed upper frequency. Upon reaching the upper frequency,
the accumulator returns to the lower frequency directly, without
ramping back down. Unlike the default mode of the linear
sweep, this mode uses only the rising delta frequency tuning
word (RDFTW) and the rising sweep ramp rate (RSRR). The
operation is still controlled by the PS0 pin. In this mode, how-
ever, it acts as a trigger for the sweep, not a direction bit. Once a
PS0 low-to-high transition is detected, the part completes the
entire sweep, regardless of whether or not the PS0 pin is
changed back to low during the sweep. After the sweep is com-
pleted, another sweep may be initiated by applying another
rising edge on the PS0 pin. This means that the PS0 pin needs to
be brought low prior to the next sweep.
SYNCHRONIZATION MODES FOR MULTIPLE DEVICES
In a DDS system, the SYNC_CLK is derived internally off the
master system clock, SYSCLK, with a ÷4 divider. Because the
divider does not power up to a known state, it is possible for
multiple devices in a system to have staggered clock-phase
relationships. This is because each device could potentially gen-
erate the SYNC_CLK rising edge from any one of four rising
edges of SYSCLK. This ambiguity can be resolved by employing
digital synchronization logic to control the phase relationships
of the derived clocks among different devices in the system. It is
important to note that the synchronization functions included
on the AD9956 control only the timing relationships among
different digital clocks. They do not compensate for the analog
timing skew on the system clock due to mismatched phase
relationships on the input clock, REFCLK. Figure 28 illustrates
this concept.
AD9956
Rev. 0 | Page 21 of 32
Automatic Synchronization
In automatic synchronization mode, the device is placed into
slave mode and automatically aligns the internal SYNC_CLK to
a master SYNC_CLK signal, supplied on the SYNC_IN input.
When this bit is enabled, the PLL_LOCK is not available as an
output, however, an out-of-lock condition can be detected by
reading Control Function Register 1 and checking the status of
the PLL_LOCK_ERROR bit, CFR1<24>. The automatic
synchronization function is enabled by setting the Control
Function Register 1 automatic synchronization bit, CFR1<3>.
To employ this function at higher clock rates (SYNC_CLK >
62.5 MHz and SYSCLK > 250 MHz), the high speed sync
enable bit (CFR1<0>) should be set as well.
Manual Synchronization, Hardware Controlled
In this mode, the user controls the timing relationship of the
SYNC_CLK with respect to SYSCLK. When hardware manual
synchronization is enabled, the PLL_LOCK/ SYNC_IN pin
becomes a digital input. For each and every rising edge detected
on the SYNC_IN input, the device advances the SYNC_IN
rising edge by one SYSCLK period. When this bit is enabled, the
PLL_LOCK is not available as an output. However, an out-of-
lock condition can be detected by reading Control Function
Register 1 and checking the status of the PLL Lock Error bit,
CFR1<24>. This synchronization function is enabled by setting
the hardware manual synchronization enable bit, CFR1<1>.
Manual Synchronization, Software Controlled
In this mode, the user controls the timing relationship between
SYNC_CLK and SYSCLK through software programming.
When the software manual synchronization bit (CFR1<2>) is
set high, the SYNC_CLK is advanced by one SYSCLK cycle.
Once this operation is complete, the bit is cleared. The user can
set this bit repeatedly to advance the SYNC_CLK rising edge
multiple times. Because the operation does not use the
PLL_LOCK/ SYNC_IN pin as a SYNC_IN input, the
PLL_LOCK signal can be monitored on the PLL_LOCK pin
during this operation.
SYSCLK DUT 1
SYNC CLK
DUT1
SYNC CLK DUT2 WITHOUT
SYNC_CLK ALIGNED
SYSCLK DUT 2
SYNCHRONIZATION FUNCTIONS CAN ALIGN DIGITAL CLOCK
RELATIONSHIPS, THEY CANNOT DESKEW THE EDGES OF CLOCKS
SYNC CLK DUT2 WITH
SYNC_CLK ALIGNED
0
1
2
3
0
0
1
2
3
3
04806-0-003
Figure 28. Synchronization Functions: Capabilities and Limitations
AD9956
Rev. 0 | Page 22 of 32
SERIAL PORT OPERATION
An AD9956 serial data-port communication cycle has two
phases. Phase 1 is the instruction cycle, which is the writing of
an instruction byte to the AD9956, coincident with the first
eight SCLK rising edges. The instruction byte provides the
AD9956 serial port controller with information regarding the
data transfer cycle, which is Phase 2 of the communication cycle.
The Phase 1 instruction byte defines whether the upcoming data
transfer is read or write and the serial address of the
register being accessed.
The first eight SCLK rising edges of each communication cycle
are used to write the instruction byte into the AD9956. The
remaining SCLK edges are for Phase 2 of the communication
cycle. Phase 2 is the actual data transfer between the AD9956
and the system controller. The number of bytes transferred
during Phase 2 of the communication cycle is a function of the
register being accessed. For example, when accessing Control
Function Register 2, which is four bytes wide, Phase 2 requires that
four bytes be transferred. If accessing a frequency tuning word,
which is six bytes wide, Phase 2 requires that six bytes be
transferred. After transferring all data bytes per the instruction,
the communication cycle is completed.
At the completion of any communication cycle, the AD9956
serial port controller expects the next eight rising SCLK edges
to be the instruction byte of the next communication cycle. All
data input to the AD9956 is registered on the rising edge of
SCLK. All data is driven out of the AD9956 on the falling edge
of SCLK. Figure 29 through Figure 32 are useful in understand-
ing the general operation of the AD9956 serial port.
04806-0-004
I
6
I
5
I
4
I
3
I
2
I
1
D
5
D
4
D
3
D
2
D
1
D
0
I
0
D
7
D
6
I
7
INSTRUCTION CYCLE
SCLK
SDI/O
DATA TRANSFER CYCLE
CS
Figure 29. Serial Port Write Timing--Clock Stall Low
04806-0-005
I
6
I
5
I
4
I
3
I
2
I
1
I
0
DON'T CARE
I
7
INSTRUCTION CYCLE
SCLK
SDI/O
DATA TRANSFER CYCLE
D
O 5
D
O 4
D
O 3
D
O 2
D
O 1
D
O 0
D
O 7
D
O 6
SDO
CS
Figure 30. 3-Wire Serial Port Read Timing--Clock Stall Low
04806-0-006
I
6
I
5
I
4
I
3
I
2
I
1
D
5
D
4
D
3
D
2
D
1
D
0
I
0
D
7
D
6
I
7
INSTRUCTION CYCLE
SCLK
SDI/O
DATA TRANSFER CYCLE
CS
Figure 31. Serial Port Write Timing--Clock Stall High
04806-0-007
I
6
I
5
I
4
I
3
I
2
I
1
D
O 5
D
O 4
D
O 3
D
O 2
D
O 1
D
O 0
I
0
D
O 7
D
O 6
I
7
INSTRUCTION CYCLE
SCLK
SDI/O
DATA TRANSFER CYCLE
CS
Figure 32. 2-Wire Serial Port Read Timing--Clock Stall High
AD9956
Rev. 0 | Page 23 of 32
INSTRUCTION BYTE
The instruction byte contains the following information:
Table 4.
D7 D6 D5 D4 D3 D2 D1 D0
R/Wb X X A4 A3 A2 A1 A0
R/Wb--Bit 7 of the instruction byte determines whether a read
or write data transfer occurs after the instruction byte write.
Logic 1 indicates a read operation. Logic 0 indicates a write
operation.
X, X--Bits 6 and 5 of the instruction byte are Don't Care.
A4 to A0--Bits 4 to 0 of the instruction byte determine which
register is accessed during the data transfer portion of the
communications cycle.
SERIAL INTERFACE PORT PIN DESCRIPTION
SCLK--Serial Clock. The serial clock pin is used to synchronize
data to and from the AD9956 and to run the internal state
machines. The SCLK maximum frequency is 25 MHz.
CS--Chip Select Bar. CS is an active low input that allows more
than one device on the same serial communications line. The
SDO and SDI/O pins go to a high impedance state when this
input is high. If driven high during any communications cycle,
that cycle is suspended until CS is reactivated low. Chip select
can be tied low in systems that maintain control of SCLK.
SDI/O--Serial Data Input/Output. Data is always written to the
AD9956 on this pin. However, this pin can be used as a bidirec-
tional data line. CFR1<7> controls the configuration of this pin.
The default value (0) configures the SDI/O pin as bidirectional.
SDO--Serial Data Out. Data is read from this pin for protocols
that use separate lines for transmitting and receiving data. When
the AD9956 operates in a single bidirectional I/O mode, this pin
does not output data and is set to a high impedance state.
I/O_RESET--A high signal on this pin resets the I/O port state
machines without affecting the addressable registers' contents.
An active high input on the I/O_RESET pin causes the current
communication cycle to abort. After I/O_RESET returns low
(0), another communication cycle can begin, starting with the
instruction byte write. Note that when not in use, this pin
should be forced low, because it floats to the threshold value.
MSB/LSB TRANSFERS
The AD9956 serial port can support both most significant bit
(MSB) first or least significant bit (LSB) first data formats. This
functionality is controlled by the LSB first bit in Control
Register 1 (CFR1<15>). The default value of this bit is low
(MSB first). When CFR1 <15> is set high, the AD9956 serial
port is in LSB first format. The instruction byte must be written
in the format indicated by CFR1 <15>. If the AD9956 is in LSB
first mode, the instruction byte must be written from least
significant bit to most significant bit. However, the instruction
byte phase of the communications cycle still precedes the data
transfer cycle.
For MSB first operation, all data written to (read from) the
AD9956 are in MSB first order. If the LSB mode is active, all
data written to (read from) the AD9956 are in LSB first order.
CS
SCLK
SDI/O
T
PRE
T
DSU
T
SCLKW
T
DHLD
SECOND BIT
FIRST BIT
SYMBOL
T
PRE
T
SCLKW
T
DSU
T
DHLD
MIN
6ns
40ns
6.5ns
0ns
DEFINITION
CS SETUP TIME
PERIOD OF SERIAL DATA CLOCK (WRITE)
SERIAL DATA SETUP TIME
SERIAL DATA HOLD TIME
04806-0-034
Figure 33. Timing Diagram for Data Write to AD9956
T
DV
FIRST BIT
SECOND BIT
SDI/O
SDO
SCLK
CS
SYMBOL
T
DV
T
SCLKR
MAX
40ns
400ns
DEFINITION
DATA VALID TIME
PERIOD OF SERIAL DATA CLOCK (READ)
04806-0-035
T
SCLKR
Figure 34. Timing Diagram for Data Read to AD9956
AD9956
Rev. 0 | Page 24 of 32
REGISTER MAP AND DESCRIPTION
Table 5.
Register
Name
(Serial
Address)
Bit
Range
(MSB) Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Default
Value/
Profile
<31:24> Open
1
Open
1
Open
1
Open
1
Open
1
Open
1
Open
1
PLL Lock
Error
0x00
<23:16>
LOAD SRR @
I/O_UPDATE
Auto-Clr
Frequency
Accum.
Auto-
Clr
Phase
Accum.
Enable
Sine
Output
Clear
Frequency
Accum.
Clear
Phase
Accum.
Linear
Sweep
Enable
Linear
Sweep
No Dwell
0x00
<15:8> LSB
First
SDI/O
Input
Only
Open
1
Open
1
Open
1
Open
1
Open
1
Open
1
0x00
Control
Function
Register 1
(CFR1)
(0x00)
<7:0>
Digital
Power-
Down
PFD Input
Power-
Down
PLLREF
Crystal
Enable
SYNC_CLK
Disable
Auto Sync
Multiple
AD9956s
Software
Manual
Sync
Hardware
Manual
Sync
High
Speed
Sync
Enable
0x00
<39:32>
DAC
Power-
Down
Open
1
Open
1
Open
1
Open
1
Open
1
Internal
Band Gap
Power-
Down
Internal
CML
Driver
DRV_RSET
0x00
<31:24>
Clock Driver Rising Edge <31:29>
Clock Driver Falling Edge Control
<28:26>
PLL Lock
Detect
Enable
PLL Lock
Detect
Mode
0x00
<23:16>
RF Divider
Power-
Down
RF Divider Ratio
<22:21>
Clock
Driver
Power-
Down
Clock Driver Input
Select <19:18>
Slew Rate
Control
RF Div
REFCLK
Mux Bit
0x78
<15:8>
Divider M Control <15:12>
Divider N Control <11:8>
0x00
Control
Function
Register 2
(CFR2)
(0x01)
<7:0> Open
1
Open
1
CP
Polarity
CP
Full PD
CP
Quick PD
CP Current Scale <2:0>
0x07
<23:16>
Rising Delta Frequency Tuning Word <23:16>
0x00
<15:8>
Rising Delta Frequency Tuning Word <15:8>
0x00
Rising Delta
Frequency
Tuning
Word
(RDFTW)
(0x02)
<7:0>
Rising Delta Frequency Tuning Word <7:0>
0x00
<23:16>
Falling Delta Frequency Tuning Word <23:16>
0x00
<15:8>
Falling Delta Frequency Tuning Word <15:8>
0x00
Falling Delta
Frequency
Tuning
Word
(FDFTW)
(0x03)
<7:0>
Falling Delta Frequency Tuning Word <7:0>
0x00
<15:8>
Rising Sweep Ramp Rate <15:8>
0x00
Rising
Sweep
Ramp Rate
(RSRR)
(0x04)
<7:0>
Rising Sweep Ramp Rate <7:0>
0x00
<15:8>
Rising Sweep Ramp Rate <15:8>
0x00
Falling
Sweep
Ramp Rate
(FSRR)
(0x05)
<7:0>
Rising Sweep Ramp Rate <7:0>
0x00
1
In all cases, open bits must be written to 0.
AD9956
Rev. 0 | Page 25 of 32
Register Name
(Serial Address)
Bit Range
(MSB) Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Default Value/
Profile
<63:56> Open
1
Phase Offset Word 0 (POW0) <13:8>
0x00
<55:48>
Phase Offset Word 0 (POW0) <7:0>
0x00
<47:40>
Frequency Tuning Word 0 (FTW0) <47:40>
0x00
<39:32>
Frequency Tuning Word 0 (FTW0) <39:32>
0x00
<31:24>
Frequency Tuning Word 0 (FTW0) <31:24>
0x00
<23:16>
Frequency Tuning Word 0 (FTW0) <23:16>
0x00
<15:8>
Frequency Tuning Word 0 (FTW0) <15:8>
0x00
Profile Control Register
No. 0 (PCR0) (0x06)
<7:0>
Frequency Tuning Word 0 (FTW0) <7:0>
0x00
<63:56> Open
1
Phase Offset Word 1 (POW1) <13:8>
0x00
<55:48>
Phase Offset Word 1 (POW1) <7:0>
0x00
<47:40>
Frequency Tuning Word 1 (FTW1) <47:40>
0x00
<39:32>
Frequency Tuning Word 1 (FTW1) <39:32>
0x00
<31:24>
Frequency Tuning Word 1 (FTW1) <31:24>
0x00
<23:16>
Frequency Tuning Word 1 (FTW1) <23:16>
0x00
<15:8>
Frequency Tuning Word 1 (FTW1) <15:8>
0x00
Profile Control Register
No. 1 (PCR1) (0x07)
<7:0>
Frequency Tuning Word 1 (FTW1) <7:0>
0x00
<63:56> Open
1
Phase Offset Word 2 (POW2) <13:8>
0x00
<55:48>
Phase Offset Word 2 (POW2) <7:0>
0x00
<47:40>
Frequency Tuning Word 2 (FTW1) <47:40>
0x00
<39:32>
Frequency Tuning Word 2 (FTW2) <39:32>
0x00
<31:24>
Frequency Tuning Word 2 (FTW2) <31:24>
0x00
<23:16>
Frequency Tuning Word 2 (FTW2) <23:16>
0x00
<15:8>
Frequency Tuning Word 2 (FTW2) <15:8>
0x00
Profile Control Register
No. 2 (PCR2) (0x08)
<7:0>
Frequency Tuning Word 2 (FTW2) <7:0>
0x00
<63:56> Open
1
Phase Offset Word 3 (POW3) <13:8>
0x00
<55:48>
Phase Offset Word 3 (POW3) <7:0>
0x00
<47:40>
Frequency Tuning Word 3 (FTW3) <47:40>
0x00
<39:32>
Frequency Tuning Word 3 (FTW3) <39:32>
0x00
<31:24>
Frequency Tuning Word 3 (FTW3) <31:24>
0x00
<23:16>
Frequency Tuning Word. 3 (FTW3) <23:16>
0x00
<15:8>
Frequency Tuning Word 3 (FTW3) <15:8>
0x00
Profile Control Register
No. 3 (PCR3) (0x09)
<7:0>
Frequency Tuning Word 3 (FTW3) <7:0>
0x00
1
In all cases, open bits must be written to 0.
AD9956
Rev. 0 | Page 26 of 32
Register Name
(Serial Address)
Bit
Range
(MSB)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
(LSB)
Default
Value/
Profile
<63:56> Open
1
Phase Offset Word 4 (POW4) <13:8>
0x00
<55:48>
Phase Offset Word 4 (POW4) <7:0>
0x00
<47:40>
Frequency Tuning Word 4 (FTW4) <47:40>
0x00
<39:32>
Frequency Tuning Word 4 (FTW4) <39:32>
0x00
<31:24>
Frequency Tuning Word 4 (FTW4) <31:24>
0x00
<23:16>
Frequency Tuning Word 4 (FTW4) <23:16>
0x00
<15:8>
Frequency Tuning Word 4 (FTW4) <15:8>
0x00
Profile Control
Register
No. 4 (PCR4) (0x0A)
<7:0>
Frequency Tuning Word 4 (FTW4) <7:0>
0x00
<63:56> Open
1
Phase Offset Word 5 (POW5) <13:8>
0x00
<55:48>
Phase Offset Word 5 (POW5) <7:0>
0x00
<47:40>
Frequency Tuning Word 5 (FTW5) <47:40>
0x00
<39:32>
Frequency Tuning Word 5 (FTW5) <39:32>
0x00
<31:24>
Frequency Tuning Word 5 (FTW5) <31:24>
0x00
<23:16>
Frequency Tuning Word 5 (FTW5) <23:16>
0x00
<15:8>
Frequency Tuning Word 5 (FTW5) <15:8>
0x00
Profile Control
Register
No. 5 (PCR5) (0x0B)
<7:0>
Frequency Tuning Word 5 (FTW5) <7:0>
0x00
<63:56> Open
1
Phase Offset Word 6 (POW6) <13:8>
0x00
<55:48>
Phase Offset Word 6 (POW6) <7:0>
0x00
<47:40>
Frequency Tuning Word 6 (FTW6) <47:40>
0x00
<39:32>
Frequency Tuning Word 6 (FTW6) <39:32>
0x00
<31:24>
Frequency Tuning Word 6 (FTW6) <31:24>
0x00
<23:16>
Frequency Tuning Word 6 (FTW6) <23:16>
0x00
<15:8>
Frequency Tuning Word 6 (FTW6) <15:8>
0x00
Profile Control
Register
No. 6 (PCR6) (0x0C)
<7:0>
Frequency Tuning Word 6 (FTW6) <7:0>
0x00
<63:56> Open
1
Phase Offset Word 7 (POW7) <13:8>
0x00
<55:48>
Phase Offset Word 7 (POW7) <7:0>
0x00
<47:40>
Frequency Tuning Word 7 (FTW7) <47:40>
0x00
<39:32>
Frequency Tuning Word 7 (FTW7) <39:32>
0x00
<31:24>
Frequency Tuning Word 7 (FTW7) <31:24>
0x00
<23:16>
Frequency Tuning Word 7 (FTW7) <23:16>
0x00
<15:8>
Frequency Tuning Word 7 (FTW7) <15:8>
0x00
Profile Control
Register
No. 7 (PCR7) (0x0D)
<7:0>
Frequency Tuning Word 7 (FTW7) <7:0>
0x00
1
In all cases, open bits must be written to 0.
AD9956
Rev. 0 | Page 27 of 32
CONTROL FUNCTION REGISTER DESCRIPTIONS
Control Function Register 1 (CFR1)
This control register is comprised of four bytes, all of which
must be written during a write operation involving CFR1. CFR1
is used to control various functions, features, and operating
modes of the AD9956. The functionality of each bit(s) is
described below. In general, the bit is named for the function it
serves when the bit is set.
CFR1<31:25> Open. Unused locations. Write a Logic 0
CFR1<24> PLL Lock Error (Read-Only)
When the device is operating in automatic synchronization
mode or hardware manual synchronization mode (see below),
the PLL_LOCK/ SYNC_IN pin behaves as the SYNC_IN. To
determine whether or not the PLL has become unlocked while
in synchronization mode, this bit serves as a flag to indicate that
an unlocked condition has occurred within the phase frequency
detector. Once set, the flag stays high until it is cleared by a
readback of the value even though the loop might have
relocked. Readback of the CFR1 register clears this bit.
CFR1<24> = 0 indicates that the loop has maintained lock since
the last readback.
CFR1<24> = 1 indicates that the loop became unlocked at some
point since the last readback of this bit.
CFR1<23> Load Sweep Ramp Rate at I/O_UPDATE, also
known as Load SRR @ I/O_UPDATE
The sweep ramp rate is set by entering a value to a down
counter that is clocked by the SYNC_CLK. Each time a new step
is taken in the linear sweep algorithm, the ramp rate value is
passed from the linear sweep ramp rate register to this down
counter. When set, CFR1<23>, enables the user to force the part
to restart the countdown sequence for the current linear sweep
step by toggling the I/O_UPDATE pin.
CFR1<23> = 0 (default). The linear sweep ramp rate countdown
value is loaded only upon completion of a countdown sequence.
CFR1<23> = 1. The linear sweep ramp rate countdown value is
reloaded, if an I/O_UPDATE signal is sent to the part during a
sweep.
CFR1<22> Auto-Clear Frequency Accumulator
This bit enables the auto-clear function for the frequency accu-
mulator. The auto-clear function serves as a clear and release func-
tion for the frequency accumulator (which performs the linear
sweep operation), which then begins sweeping from a known value
of FTW0.
CFR1 <22> = 0 (default). Issuing an I/O_UPDATE has no effect
on the current state of the frequency accumulator.
CFR1 <22> = 1. Issuing an I/O_UPDATE signal to the part
clears the current contents of the frequency accumulator for
one sync-clock period.
CFR1 <21> Auto-Clear Phase Accumulator
This bit enables the auto-clear function for the phase accumula-
tor. The auto-clear function serves as a reset function for the
phase accumulator, which then begins accumulating from a
known phase value of 0.
CFR1<21> = 0 (default). Issuing an I/O_UPDATE has no effect
on the current state of the phase accumulator.
CFR1<21> = 1. Issuing an I/O_UPDATE clears the current con-
tents of the phase accumulator for one SYNC_CLK period.
CFR1 <20> Enable Sine Output
Two different trigonometric functions can be used to convert
the phase angle to an amplitude value, cosine or sine. This bit
selects the function used.
CFR1<20> = 0 (default). The phase-to-amplitude conversion
block uses a cosine function.
CFR1<20> = 1. The phase-to-amplitude conversion block uses a
sine function.
CFR1 <19> Clear Frequency Accumulator
This bit serves as a static-clear or a clear-and-hold bit for the
frequency accumulator. It prevents the frequency accumulator
from incrementing the value as long as it is set.
CFR1 <19> = 0 (default). The frequency accumulator operates
normally.
CFR1 <19> = 1. The frequency accumulator is cleared and held
at a value of 0.
CFR1 <18> Clear Phase Accumulator
This bit serves as a static-clear or a clear-and-hold it for the
phase accumulator. It prevents the phase accumulator from
incrementing the value as long as it is set.
CFR1 <18> = 0 (default). The phase accumulator operates
normally.
CFR1 <18> = 1. The phase accumulator is cleared and held at a
value of 0.
AD9956
Rev. 0 | Page 28 of 32
CFR1 <17> Linear Sweep Enable
This bit turns on the frequency accumulator, which enables the
DDS to perform linear sweeping.
CFR1<17> = 0 (default). The DDS generates frequencies in
single-tone mode.
CFR1<17> = 1. The DDS uses the frequency accumulator to
sweep the frequency tuning word being sent to the phase
accumulator according to the values set in the delta frequency
tuning word and delta frequency ramp rate registers. For a
detailed explanation of this mode, see the linear sweep mode of
operation section.
CFR1 <16> Linear Sweep No Dwell
This bit dictates the behavior of the DDS core upon completion
of a linear sweep.
CFR1<16> = 0 (default). Upon reaching the upper value of the
sweep (FTW1), the DDS holds at the frequency value stored in
FTW1.
CFR1<16> = 1. Upon reaching the upper value of the sweep
(FTW1), the DDS returns to the initial value in the sweep
(FTW0) and continues to output that frequency until a new
sweep is initiated (by bringing PS0 low and then high).
CFR1 <15> LSB First Serial Data Mode
The serial data transfer to the device can be either MSB first or
LSB first. This bit controls that operation.
CFR1<15> = 0 (default). Serial data transfer to the device is in
MSB first mode.
CFR1<15> = 1. Serial data transfer to the device is in LSB first
mode.
CFR1<14> SDI/O Input Only (3-Wire Serial Data Mode)
The serial port on the AD9956 can act in 2-wire mode (SCLK
and SDI/O) or 3-wire mode (SCLK, SDI/O, and SDO). This bit
toggles the serial port between these two modes.
CFR1<14> = 0 (default). Serial data transfer to the device is in
2-wire mode. The SDI/O pin is bidirectional.
CFR1<14> = 1. Serial data transfer to the device is in 3-wire
mode. The SDI/O pin is input only.
CFR1<13:8> Open
Unused locations. Write a Logic 0.
CFR1<7> Digital Power-Down
This bit powers down the digital circuitry not directly related to
the I/O port. The I/O port functionality is not suspended, re-
gardless of the state of this bit.
CFR1<7> = 0 (default). Digital logic operating as normal.
CFR1<7> = 1. All digital logic not directly related to the I/O
port is powered down. Internal digital clocks are suspended.
CFR1<6> Phase Frequency Detector Input Power-Down
This bit controls the input buffers on the phase frequency detec-
tor. It provides a way to gate external signals from the phase
frequency detector itself.
CFR1<6> = 0 (default). Phase frequency detector input buffers
are functioning normally.
CFR1<6> = 1. Phase frequency detector input buffers are pow-
ered down, isolating the phase frequency detector from the
outside world.
CFR1<5> PLLREF Crystal Enable
The AD9956 phase frequency detector has an on-chip oscillator
circuit. When enabled, the reference input to the phase fre-
quency detector (PLLREF/PLLREF) can be driven by a crystal.
CFR1<5> = 0 (default). Phase frequency detector reference
input operates as a standard analog input.
CFR1<5> = 1. Reference input oscillator circuit is enabled,
allowing the use of a crystal for the reference of the phase
frequency detector.
CFR1<4> SYNC_CLK Disable
If synchronization of multiple devices is not required, the spec-
tral energy resulting from this signal can be reduced by gating
the output buffer off. This function gates the internal clock ref-
erence SYNC_CLK (SYSCLK/4) off of the SYNC_OUT pin.
CFR1<4> = 0 (default). SYNC_CLK signal is present on the
SYNC_OUT pin and is ready to be ported to other devices.
CFR1<4> = 1. SYNC_CLK signal is gated off, putting the
SYNC_OUT pin into a high impedance state.
CFR1<3> Automatic Synchronization
One of the synchronization modes of the AD9956 forces the
DDS core to derive the internal reference from an external ref-
erence supplied on the SYNC_IN pin. For details on synchroni-
zation modes for the DDS core, see the Synchronization Modes
for Multiple Devices section.
AD9956
Rev. 0 | Page 29 of 32
CFR1<3> = 0 (default). The automatic synchronization function
of the DDS core is disabled.
CFR1<3> = 1. The automatic synchronization function is on.
The device is slaved to an external reference and adjusts the
internal SYNC_CLK to match the external reference, which is
supplied on the SYNC_IN input.
CFR1<2> Software Manual Synchronization
Rather than relying on the part to automatically synchronize the
internal clocks, the user can program the part to advance the
internal SYNC_CLK one system clock cycle. This bit is self
clearing and can be set multiple times.
CFR1<2> = 0 (default). The SYNC_CLK stays in the current
timing relationship to SYSCLK.
CFR1<2> = 1. The SYNC_CLK advances the rising and falling
edges by one SYSCLK cycle. This bit is then self-cleared.
CFR1<1> Hardware Manual Synchronization
Similar to the software manual synchronization (CFR1<2>),
this function enables the user to advance the SYNC_CLK rising
edge by one system clock period. This bit enables the
PLL_LOCK/SYNC_IN pin as a digital input. Once enabled,
every rising edge on the SYNC_IN input advances the
SYNC_CLK by one SYSCLK period. While enabled, the
PLL_LOCK signal is not available on an external pin. However,
loop out-of-lock events trigger a flag in the control register
(CFR1<24>).
CFR1<1> = 0 (default). The hardware manual synchronization
function is disabled. Either the part is outputting the
PLL_LOCK (CFR1<3> = 0), or it is using the SYNC_IN to slave
the SYNC_CLK signal to an external reference provided on
SYNC_IN (CFR1<3> = 1).
CFR1<1> = 1. PLL_LOCK/SYNC_IN is set as a digital input.
Each subsequent rising edge on this pin advances the
SYNC_CLK rising edge by one SYSCLK period.
CFR1<0> High Speed Synchronization Enable Bit
This bit enables extra functionality in the auto synchronization
algorithm, which enables the device to synchronize high speed
clocks (SYNC_CLK > 62.5 MHz).
CFR1<0> = 0 (default). High speed synchronization is disabled.
CFR1<0> = 1. High speed synchronization is enabled.
Control Function Register 2 (CFR2)
This control register is comprised of five bytes, which must be
written during a write operation involving CFR2. With some
minor exceptions, the CFR2 primarily controls analog and tim-
ing functions on the AD9956.
CFR2<39> DAC Power-Down Bit
This bit powers down the DAC portion of the AD9956 and puts
it into the lowest power dissipation state.
CFR2<39> = 0 (default). DAC is powered on and operating.
CFR2<39> = 1. DAC is powered down and the output is in a
high impedance state.
CFR2<38> to CFR2<34> Open
Unused locations. Write a Logic 0.
CFR2<33> Internal Band Gap Power-Down
To shut off all internal quiescent current, the band gap needs to
be powered down. This is normally not done because it takes a
long time (~10 ms) for the band gap to power up and settle to
its final value.
CFR2<33> = 0. Even when all other sections are powered down,
the band gap is powered up and is providing a regulated voltage.
CFR2<33> = 1. The band gap is powered down.
CFR2<32> Internal CML Driver DRV_RSET
To program the CML driver's output current, a resistor
must be placed between the DRV_RSET pin and ground. This
bit enables an internal resistor to program the output current of
the driver.
CFR2<32> = 0 (default). The DRV_RSET pin is enabled,
and an external resistor must be attached to the CP_RSET pin
to program the output current.
CFR2<32> = 1. The CML current is programmed by the inter-
nal resistor and ignores the resistor on the DRV_REST pin.
CFR2<31:29> Clock Driver Rising Edge
These bits control the slew rate of the CML clock driver output's
rising edge. When these bits are on, additional current is sent to
the output driver to increase the rising edge slew rate capability;
the contributions of each bit are cumulative. Table 6 describes
how the bits increase the current. Note that the additional cur-
rent is on only during the rising edge of the waveform for ap-
proximately 250 ps, but not on during the entire transition.
Table 6. CML Clock Driver Rising Edge Slew Rate
Control Bits and Associated Surge Current
CFR2<31> = 1
7.6 mA
CFR2<30> = 1
3.8 mA
CFR2<29> = 1
1.9 mA
AD9956
Rev. 0 | Page 30 of 32
CFR2<28:26> Clock Driver Falling Edge Control
These bits control the slew rate of the CML clock driver output's
falling edge. When these bits are on, additional current is sent to
the output driver to increase the rising edge slew rate capability.
Table 7 describes how the bits increase the current; the contri-
butions of each bit are cumulative. Note that the additional cur-
rent is on only during the rising edge of the waveform, for ap-
proximately 250 ps, but not on during the entire transition.
Table 7. CML Clock Drive Falling Edge Slew Rate
Control Bits and Associated Surge Current
CFR2<28> = 1
5.4 mA
CFR2<30> = 1
2.7 mA
CFR2<29> = 1
1.35 mA
CFR2<25> PLL_LOCK_DETECT Enable
This bit enables the PLL_LOCK/SYNC_IN pin as a lock detect
output for the PLL.
CFR2<25> = 0 (default).The PLL_LOCK_DETECT signal is
disabled.
CFR2<25> = 1. The PLL_LOCK_DETECT signal is enabled.
CFR2<24> PLL_LOCK_DETECT Mode
This bit toggles the modes of the PLL_LOCK_DETECT func-
tion. The lock detect can either be a status indicator (locked or
unlocked), or it can indicate a lead-lag relationship between the
two phase frequency detector inputs.
CFR2<24> = 0 (default). The lock detect acts as a status indica-
tor (PLL is locked 0 or unlocked 1).
CFR2<24> = 1. The lock detect acts as a lead/lag indicator. A
1 on the PLL_LOCK pin means that the PLLOSC pin lags the
reference. A 0 means that the PLLOSC pin leads the reference.
CFR2<23> RF Divider Power-Down
This bit powers the RF divider down to save power when not in
used.
CFR2<23> = 0 (default). RF divider is on.
CFR2<23> = 1. RF divider is powered down and an alternate
path between the REFCLK inputs and SYSCLK is enabled.
CFR2<22:21> RF Divider Ratio
These two bits control the RF divider ratio (÷R).
CFR2<22:21> = 11 (default). RF Divider R = 8.
CFR2<22:21> = 10. RF Divider R= 4.
CFR2<22:21> = 01. RF Divider R = 2.
CFR2<22:21> = 00. RF Divider R = 1. Note that this is not the
same as bypassing the RF divider.
CFR2<20> Clock Driver Power-Down
This bit powers down the CML clock driver circuit.
CFR2<20> =1 (default). CML clock driver circuit is powered down.
CFR2<20> = 0. CML clock driver is powered up.
CFR2<19:18> Clock Driver Input Select
These bits control the mux on the input for the CML clock driver.
CFR2<19:18> = 00. The CML clock driver is disconnected from
all inputs (and does not toggle).
CFR2<19:18> = 01. The CML clock driver is driven by the
PLLOSC input pin.
CFR2<19:18> = 10 (default). The CML clock driver is driven by
the output of the RF divider.
CFR2<19:18> = 11. The CML clock driver is driven by the input
of the RF divider
CFR2<17> Slew Rate Control Bit
Even without the additional surge current supplied by the rising
edge slew rate control bits and the falling edge slew rate control
bits, the device applies a default 7.6 mA surge current to the
rising edge and a 4.05 mA surge current to the falling edge. This
bit disables all slew rate enhancement surge current, including
the default values.
CFR2<17> = 0 (default). The CML driver applies default surge
current to rising and falling edges.
CFR2<17> = 1. Driver applies no surge current during transi-
tions. The only current is the continuous current.
CFR2<16> RF Divider SYSCLK Mux Bit
This bit toggles the mux to control whether the RF divider out-
put or input is supplying SYSCLK to the device.
CFR2<16> = 0 (default). The RF divider output supplies the
DDS SYSCLK.
CFR2<16> = 1. The RF divider input supplies the DDS SYSCLK
(bypass the divider). Note that regardless of the condition of the
configuration of the clock input, the DDS SYSCLK must not
exceed the maximum rated clock speed.
AD9956
Rev. 0 | Page 31 of 32
CFR2<15:12> PLLREF Divider Control Bits (÷M)
These 4 bits set the PLLREF divider (÷M) ratio where M is a
value equal to 1 to 16. CFR2<15:12> = 0000 means that M = 1
and CFR2<15:12> = 1111 means that M = 16, or simply, M =
CFR2<15:12> + 1.
CFR2<15:12> =
M =
CFR2<15:12> =
M =
0000 1
1000 9
0001 2
1001 10
0010 3
1010 11
0011 4
1011 12
0100 5
1100 13
0101 6
1101 14
0110 7
1110 15
0111 8
1111 16
CFR2<11:8> PLLREF Divider Control Bits (÷N)
These 4 bits set the PLLOSC divider (÷N) ratio where N is a
value equal to 1 to 16. CFR2<11:8> = 0000 means that N = 1
and CFR2<11:8> = 1111 means that N = 16, or N =
CFR2<11:8> + 1.
CFR2<15:12> =
N =
CFR2<11:8> =
N =
0000 1
1000
9
0001 2
1001
10
0010 3
1010
11
0011 4
1011
12
0100 5
1100
13
0101 6
1101
14
0110 7
1110
15
0111 8
1111
16
CFR2<7:6> Open
Unused locations. Write a Logic 0.
CFR2<5> CP Polarity
This bit sets the polarity of the charge pump, in response to a
ground referenced or a supply referenced VCO.
CFR2<5> = 0 (default). The charge pump is configured to
operate with a supply referenced VCO. If PLLOSC lags PLLREF,
the charge pump will attempt to drive the VCO control node
voltage higher. If PLLOSC leads PLLREF, the charge pump will
attempt to drive the VCO control node voltage lower.
CFR2<5> = 1. The charge pump is configured to operate with a
ground referenced VCO. If PLLOSC lags PLLREF, the charge
pump will attempt to drive the VCO control node voltage lower.
If PLLOSC leads PLLREF, the charge pump will attempt to drive
the VCO control node voltage higher.
CFR2<4> Charge Pump Full Power-Down
This bit, when set, will put the charge pump into a full power-
down mode.
CFR2<4> = 0 (default). The charge pump is powered on and
operating normally.
CFR2<4> = 1. The charge pump is completely powered down.
CFR2<3> Charge Pump Quick Power-Down
Rather than power down the charge pump, which can take a
long time to recover from, a quick power-down mode, which
powers down only the charge pump output buffer, is included.
While this doesn't reduce the power consumption significantly,
it does shut off the output to the charge pump and allows it to
come back on in a rapidly.
CFR2<3> = 0 (default). The charge pump is powered on and
operating normally.
CFR2<3> = 1. The charge pump is on and running, but the
output buffer is powered down.
CFR2<2:0> Charge Pump Current Scale.
A base output current from the charge pump is determined by a
resistor connected from the CP_RSET pin to ground (see the
PLL Circuitry section). However, it is possible to multiply the
charge pump output current by a value from 1:8 by programming
these bits. The charge pump output current are scaled by
CFR2<2:0> +1.
CFR2<2:0> = 000 (default). Scale factor = 1 to CFR2<2:0> = 111 (8).
CFR2<2:0> Scale
Factor
000 1
001 2
010 3
011 4
100 5
101 6
110 7
111 8
AD9956
Rev. 0 | Page 32 of 32
OUTLINE DIMENSIONS
PIN 1
INDICATOR
TOP
VIEW
6.75
BSC SQ
7.00
BSC SQ
1
48
12
13
37
36
24
25
5.25
5.10 SQ
4.95
0.50
0.40
0.30
0.30
0.23
0.18
0.50 BSC
12° MAX
0.20 REF
0.80 MAX
0.65 TYP
1.00
0.85
0.80
5.50
REF
0.05 MAX
0.02 NOM
0.60 MAX
0.60 MAX
PIN 1
INDICATOR
COPLANARITY
0.08
SEATING
PLANE
0.25 MIN
EXPOSED
PAD
(BOTTOM VIEW)
COMPLIANT TO JEDEC STANDARDS MO-220-VKKD-2
Figure 35. 48-Lead Lead Frame Chip Scale Package [LFCSP]
7 mm × 7 mm Body (CP-48)
Dimensions shown in millimeters
ORDERING GUIDE
Model
Temperature Range
Package Description
Package Option
AD9956YCPZ
1
40°C to +125°C
48-Lead Lead Frame Chip Scale Package (LFCSP)
CP-48
AD9956YCPZ-REEL
1
40°C to +125°C
48-Lead Lead Frame Chip Scale Package (LFCSP), Tape and Reel
CP-48
AD9956/PCB
Evaluation
Board
1
Z = Pb-free part.
© 2004 Analog Devices, Inc. All rights reserved. Trademarks and
regis-
tered trademarks are the property of their respective owners.
D0480607/04(0)
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