Low Power, 12.65 mW, 2.3 V to 5.5 V,
Programmable Waveform Generator
Data Sheet
AD9833
Rev. E Document Feedback
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rights of third parties that may result from its use. Specifications subject to change without notice. No
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Technical Support www.analog.com
FEATURES
Digitally programmable frequency and phase
12.65 mW power consumption at 3 V
0 MHz to 12.5 MHz output frequency range
28-bit resolution: 0.1 Hz at 25 MHz reference clock
Sinusoidal, triangular, and square wave outputs
2.3 V to 5.5 V power supply
No external components required
3-wire SPI interface
Extended temperature range: 40°C to +105°C
Power-down option
10-lead MSOP package
Qualified for automotive applications
APPLICATIONS
Frequency stimulus/waveform generation
Liquid and gas flow measurement
Sensory applications: proximity, motion,
and defect detection
Line loss/attenuation
Test and medical equipment
Sweep/clock generators
Time domain reflectometry (TDR) applications
GENERAL DESCRIPTION
The AD9833 is a low power, programmable waveform generator
capable of producing sine, triangular, and square wave outputs.
Waveform generation is required in various types of sensing,
actuation, and time domain reflectometry (TDR) applications.
The output frequency and phase are software programmable,
allowing easy tuning. No external components are needed. The
frequency registers are 28 bits wide: with a 25 MHz clock rate,
resolution of 0.1 Hz can be achieved; with a 1 MHz clock rate,
the AD9833 can be tuned to 0.004 Hz resolution.
The AD9833 is written to via a 3-wire serial interface. This serial
interface operates at clock rates up to 40 MHz and is compatible
with DSP and microcontroller standards. The device operates
with a power supply from 2.3 V to 5.5 V.
The AD9833 has a power-down function (SLEEP). This function
allows sections of the device that are not being used to be powered
down, thus minimizing the current consumption of the part. For
example, the DAC can be powered down when a clock output is
being generated.
The AD9833 is available in a 10-lead MSOP package.
FUNCTIONAL BLOCK DIAGRAM
SERIAL INTERFACE
AND
CONTROL LOGIC
SCLK SDATA
FSYNC
CONTROL REGISTER
PHASE 1 RE G
PHASE 0 RE G MUX
SIN
ROM 10-BIT DAC
MUX
FRE Q0 REG
FRE Q1 REG
12
ON-BOARD
REFERENCE
AGND DGND VDD
AD9833
PHASE
ACCUMULATOR
(28-BIT)
REGULATOR
CAP/2.5V
2.5V
AVDD/
DVDD
MUX
DIVIDE
BY 2
MSB
MUX
FULL-SCALE
CONTROL COMP
VOUT
R
200Ω
MCLK
02704-001
Figure 1.
AD9833* PRODUCT PAGE QUICK LINKS
Last Content Update: 12/18/2017
COMPARABLE PARTS
View a parametric search of comparable parts.
EVALUATION KITS
AD9833 Evaluation Board
DOCUMENTATION
Application Notes
AN-1044: Programming the AD5932 for Frequency Sweep
and Single Frequency Outputs
AN-1070: Programming the AD9833/AD9834
AN-1389: Recommended Rework Procedure for the Lead
Frame Chip Scale Package (LFCSP)
AN-237: Choosing DACs for Direct Digital Synthesis
AN-280: Mixed Signal Circuit Technologies
AN-342: Analog Signal-Handling for High Speed and
Accuracy
AN-345: Grounding for Low-and-High-Frequency Circuits
AN-419: A Discrete, Low Phase Noise, 125 MHz Crystal
Oscillator for the AD9850
AN-423: Amplitude Modulation of the AD9850 Direct
Digital Synthesizer
AN-543: High Quality, All-Digital RF Frequency
Modulation Generation with the ADSP-2181 and the
AD9850 DDS
AN-557: An Experimenter's Project:
AN-587: Synchronizing Multiple AD9850/AD9851 DDS-
Based Synthesizers
AN-605: Synchronizing Multiple AD9852 DDS-Based
Synthesizers
AN-621: Programming the AD9832/AD9835
AN-632: Provisionary Data Rates Using the AD9951 DDS as
an Agile Reference Clock for the ADN2812 Continuous-
Rate CDR
AN-769: Generating Multiple Clock Outputs from the
AD9540
AN-772: A Design and Manufacturing Guide for the Lead
Frame Chip Scale Package (LFCSP)
AN-823: Direct Digital Synthesizers in Clocking
Applications Time
AN-837: DDS-Based Clock Jitter Performance vs. DAC
Reconstruction Filter Performance
AN-843: Measuring a Loudspeaker Impedance Profile
Using the AD5933
AN-847: Measuring a Grounded Impedance Profile Using
the AD5933
AN-851: A WiMax Double Downconversion IF Sampling
Receiver Design
AN-927: Determining if a Spur is Related to the DDS/DAC
or to Some Other Source (For Example, Switching
Supplies)
AN-939: Super-Nyquist Operation of the AD9912 Yields a
High RF Output Signal
AN-953: Direct Digital Synthesis (DDS) with a
Programmable Modulus
SPI Interface
Data Sheet
AD9833-DSCC: Military Data Sheet
AD9833-EP: Enhanced Product Data Sheet
AD9833: Low Power 12.65 mW, 2.3 V to 5.5 V,
Programmable Waveform Generator Data Sheet
Product Highlight
Introducing Digital Up/Down Converters: VersaCOMM™
Reconfigurable Digital Converters
Technical Books
A Technical Tutorial on Digital Signal Synthesis, 1999
User Guides
UG-272: Evaluating the AD9833 Low Power 12.65 mW, 2.3
V to 5.5 V, Programmable Waveform Generator
SOFTWARE AND SYSTEMS REQUIREMENTS
AD9833 - Microcontroller No-OS Driver
AD9834 IIO Direct Digital Synthesis Linux Driver
AD9833 Evaluation Software
AD9833 FMC-SDP Interposer & Evaluation Board / Xilinx
KC705 Reference Design
BeMicro FPGA Project for AD9833 with Nios driver
TOOLS AND SIMULATIONS
ADIsimDDS (Direct Digital Synthesis)
AD9833 IBIS Model
REFERENCE MATERIALS
Technical Articles
400-MSample DDSs Run On Only +1.8 VDC
ADI Buys Korean Mobile TV Chip Maker
Basics of Designing a Digital Radio Receiver (Radio 101)
DDS Applications
DDS Circuit Generates Precise PWM Waveforms
DDS Design
DDS Device Produces Sawtooth Waveform
DDS Device Provides Amplitude Modulation
DDS IC Initiates Synchronized Signals
DDS IC Plus Frequency-To-Voltage Converter Make Low-
Cost DAC
DDS Simplifies Polar Modulation
Digital Potentiometers Vary Amplitude In DDS Devices
Digital Up/Down Converters: VersaCOMM™ White Paper
Digital Waveform Generator Provides Flexible Frequency
Tuning for Sensor Measurement
Improved DDS Devices Enable Advanced Comm Systems
Integrated DDS Chip Takes Steps To 2.7 GHz
Simple Circuit Controls Stepper Motors
Speedy A/Ds Demand Stable Clocks
Synchronized Synthesizers Aid Multichannel Systems
The Year of the Waveform Generator
Two DDS ICs Implement Amplitude-shift Keying
Video Portables and Cameras Get HDMI Outputs
DESIGN RESOURCES
AD9833 Material Declaration
PCN-PDN Information
Quality And Reliability
Symbols and Footprints
DISCUSSIONS
View all AD9833 EngineerZone Discussions.
SAMPLE AND BUY
Visit the product page to see pricing options.
TECHNICAL SUPPORT
Submit a technical question or find your regional support
number.
DOCUMENT FEEDBACK
Submit feedback for this data sheet.
This page is dynamically generated by Analog Devices, Inc., and inserted into this data sheet. A dynamic change to the content on this page will not
trigger a change to either the revision number or the content of the product data sheet. This dynamic page may be frequently modified.
AD9833* PRODUCT PAGE QUICK LINKS
Last Content Update: 02/23/2017
COMPARABLE PARTS
View a parametric search of comparable parts.
EVALUATION KITS
AD9833 Evaluation Board
DOCUMENTATION
Application Notes
AN-1044: Programming the AD5932 for Frequency Sweep
and Single Frequency Outputs
AN-1070: Programming the AD9833/AD9834
AN-1248: SPI Interface
AN-1389: Recommended Rework Procedure for the Lead
Frame Chip Scale Package (LFCSP)
AN-237: Choosing DACs for Direct Digital Synthesis
AN-280: Mixed Signal Circuit Technologies
AN-342: Analog Signal-Handling for High Speed and
Accuracy
AN-345: Grounding for Low-and-High-Frequency Circuits
AN-419: A Discrete, Low Phase Noise, 125 MHz Crystal
Oscillator for the AD9850
AN-423: Amplitude Modulation of the AD9850 Direct
Digital Synthesizer
AN-543: High Quality, All-Digital RF Frequency
Modulation Generation with the ADSP-2181 and the
AD9850 DDS
AN-557: An Experimenter's Project:
AN-587: Synchronizing Multiple AD9850/AD9851 DDS-
Based Synthesizers
AN-605: Synchronizing Multiple AD9852 DDS-Based
Synthesizers
AN-621: Programming the AD9832/AD9835
AN-632: Provisionary Data Rates Using the AD9951 DDS as
an Agile Reference Clock for the ADN2812 Continuous-
Rate CDR
AN-769: Generating Multiple Clock Outputs from the
AD9540
AN-772: A Design and Manufacturing Guide for the Lead
Frame Chip Scale Package (LFCSP)
AN-823: Direct Digital Synthesizers in Clocking
Applications Time
AN-837: DDS-Based Clock Jitter Performance vs. DAC
Reconstruction Filter Performance
AN-843: Measuring a Loudspeaker Impedance Profile
Using the AD5933
AN-847: Measuring a Grounded Impedance Profile Using
the AD5933
AN-851: A WiMax Double Downconversion IF Sampling
Receiver Design
AN-927: Determining if a Spur is Related to the DDS/DAC
or to Some Other Source (For Example, Switching
Supplies)
AN-939: Super-Nyquist Operation of the AD9912 Yields a
High RF Output Signal
AN-953: Direct Digital Synthesis (DDS) with a
Programmable Modulus
Data Sheet
AD9833-DSCC: Military Data Sheet
AD9833-EP: Enhanced Product Data Sheet
AD9833: Low Power 12.65 mW, 2.3 V to 5.5 V,
Programmable Waveform Generator Data Sheet
Product Highlight
Introducing Digital Up/Down Converters: VersaCOMM™
Reconfigurable Digital Converters
Technical Books
A Technical Tutorial on Digital Signal Synthesis, 1999
User Guides
UG-272: Evaluating the AD9833 Low Power 12.65 mW, 2.3
V to 5.5 V, Programmable Waveform Generator
SOFTWARE AND SYSTEMS REQUIREMENTS
AD9833 - Microcontroller No-OS Driver
AD9834 IIO Direct Digital Synthesis Linux Driver
AD9833 Evaluation Board Software
AD9833 FMC-SDP Interposer & Evaluation Board / Xilinx
KC705 Reference Design
BeMicro FPGA Project for AD9833 with Nios driver
TOOLS AND SIMULATIONS
ADIsimDDS (Direct Digital Synthesis)
AD9833 IBIS Model
REFERENCE MATERIALS
Technical Articles
400-MSample DDSs Run On Only +1.8 VDC
ADI Buys Korean Mobile TV Chip Maker
Basics of Designing a Digital Radio Receiver (Radio 101)
DDS Applications
DDS Circuit Generates Precise PWM Waveforms
DDS Design
DDS Device Produces Sawtooth Waveform
DDS Device Provides Amplitude Modulation
DDS IC Initiates Synchronized Signals
DDS IC Plus Frequency-To-Voltage Converter Make Low-
Cost DAC
DDS Simplifies Polar Modulation
Digital Potentiometers Vary Amplitude In DDS Devices
Digital Up/Down Converters: VersaCOMM™ White Paper
Digital Waveform Generator Provides Flexible Frequency
Tuning for Sensor Measurement
Improved DDS Devices Enable Advanced Comm Systems
Integrated DDS Chip Takes Steps To 2.7 GHz
Simple Circuit Controls Stepper Motors
Speedy A/Ds Demand Stable Clocks
Synchronized Synthesizers Aid Multichannel Systems
The Year of the Waveform Generator
Two DDS ICs Implement Amplitude-shift Keying
Video Portables and Cameras Get HDMI Outputs
DESIGN RESOURCES
AD9833 Material Declaration
PCN-PDN Information
Quality And Reliability
Symbols and Footprints
DISCUSSIONS
View all AD9833 EngineerZone Discussions.
SAMPLE AND BUY
Visit the product page to see pricing options.
TECHNICAL SUPPORT
Submit a technical question or find your regional support
number.
DOCUMENT FEEDBACK
Submit feedback for this data sheet.
This page is dynamically generated by Analog Devices, Inc., and inserted into this data sheet. A dynamic change to the content on this page will not
trigger a change to either the revision number or the content of the product data sheet. This dynamic page may be frequently modified.
AD9833 Data Sheet
Rev. E | Page 2 of 24
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications ..................................................................................... 3
Timing Characteristics ................................................................ 4
Absolute Maximum Ratings ............................................................ 5
ESD Caution .................................................................................. 5
Pin Configuration and Function Descriptions ............................. 6
Typical Performance Characteristics ............................................. 7
Terminology .................................................................................... 10
Theory of Operation ...................................................................... 11
Circuit Description ......................................................................... 12
Numerically Controlled Oscillator Plus Phase Modulator ... 12
Sin ROM ...................................................................................... 12
Digital-to-Analog Converter (DAC) ....................................... 12
Regulator...................................................................................... 12
Functional Description .................................................................. 13
Serial Interface ............................................................................ 13
Powering Up the AD9833 ......................................................... 13
Latency Period ............................................................................ 13
Control Register ......................................................................... 13
Frequency and Phase Registers ................................................ 15
Reset Function ............................................................................ 16
Sleep Function ............................................................................ 16
VOUT Pin ................................................................................... 16
Applications Information .............................................................. 17
Grounding and Layout .............................................................. 17
Interfacing to Microprocessors ..................................................... 20
AD9833 to 68HC11/68L11 Interface ....................................... 20
AD9833 to 80C51/80L51 Interface .......................................... 20
AD9833 to DSP56002 Interface ............................................... 20
Evaluation Board ............................................................................ 21
System Demonstration Platform .............................................. 21
AD9833 to SPORT Interface ..................................................... 21
Evaluation Kit ............................................................................. 21
Crystal Oscillator vs. External Clock ....................................... 21
Power Supply ............................................................................... 21
Evaluation Board Schematics ................................................... 22
Evaluation Board Layout ........................................................... 23
Outline Dimensions ....................................................................... 24
Ordering Guide .......................................................................... 24
Automotive Products ................................................................. 24
REVISION HISTORY
9/12—Rev. D to Rev. E
Changed Input Current, IINH/IINL from 10 mA to 10 µA.............. 3
4/11—Rev. C to Rev. D
Change to Figure 13 ......................................................................... 8
Changes to Table 9 .......................................................................... 15
Deleted AD9833 to ADSP-2101/ADSP-2103 Interface
Section .............................................................................................. 20
Changes to Evaluation Board Section .......................................... 21
Added System Demonstration Platform Section, AD9833
to SPORT Interface Section, and Evaluation Kit Section .......... 21
Changes to Crystal Oscillator vs. External Clock Section
and Power Supply Section ............................................................. 21
Added Figure 32 and Figure 33; Renumbered Figures
Sequentially ..................................................................................... 21
Deleted Prototyping Area Section and Figure 33 ....................... 22
Added Evaluation Board Schematics Section, Figure 34,
and Figure 35 ................................................................................... 22
Deleted Table 16 .............................................................................. 23
Added Evaluation Board Layout Section, Figure 36,
Figure 37, and Figure 38 ................................................................ 23
Changes to Ordering Guide .......................................................... 24
9/10Rev. B to Rev. C
Changed 20 mW to 12.65 mW in Data Sheet Title
and Features List ................................................................................ 1
Changes to Figure 6 Caption and Figure 7..................................... 7
6/10Rev. A to Rev. B
Changes to Features Section ............................................................ 1
Changes to Serial Interface Section.............................................. 13
Changes to VOUT Pin Section ..................................................... 16
Changes to Grounding and Layout Section ................................ 17
Updated Outline Dimensions ....................................................... 24
Changes to Ordering Guide .......................................................... 24
Added Automotive Products Section .......................................... 24
6/03—Rev. 0 to Rev. A
Updated Ordering Guide ................................................................. 4
Data Sheet AD9833
Rev. E | Page 3 of 24
SPECIFICATIONS
VDD = 2.3 V to 5.5 V, AGND = DGND = 0 V, TA = TMIN to TMAX, RSET = 6.8 kfor VOUT, unless otherwise noted.
Table 1.
Parameter
1
Min Typ Max Unit Test Conditions/Comments
SIGNAL DAC SPECIFICATIONS
Resolution 10 Bits
Update Rate 25 MSPS
VOUT Maximum 0.65 V
VOUT Minimum 38 mV
VOUT Temperature Coefficient 200 ppm/°C
DC Accuracy
Integral Nonlinearity ±1.0 LSB
Differential Nonlinearity ±0.5 LSB
DDS SPECIFICATIONS (SFDR)
Dynamic Specifications
Signal-to-Noise Ratio (SNR) 55 60 dB f
MCLK
= 25 MHz, f
OUT
= f
MCLK
/4096
Total Harmonic Distortion (THD) 66 56 dBc f
MCLK
= 25 MHz, f
OUT
= f
MCLK
/4096
Spurious-Free Dynamic Range (SFDR)
Wideband (0 to Nyquist) 60 dBc f
MCLK
= 25 MHz, f
OUT
= f
MCLK
/50
Narrow-Band (±200 kHz) 78 dBc f
MCLK
= 25 MHz, f
OUT
= f
MCLK
/50
Clock Feedthrough 60 dBc
Wake-Up Time 1 ms
LOGIC INPUTS
Input High Voltage, V
INH
1.7 V 2.3 V to 2.7 V power supply
2.0 V 2.7 V to 3.6 V power supply
2.8 V 4.5 V to 5.5 V power supply
Input Low Voltage, V
INL
0.5 V 2.3 V to 2.7 V power supply
0.7 V 2.7 V to 3.6 V power supply
0.8 V 4.5 V to 5.5 V power supply
Input Current, I
INH
/I
INL
10 µA
Input Capacitance, C
IN
3 pF
POWER SUPPLIES f
MCLK
= 25 MHz, f
OUT
= f
MCLK
/4096
VDD 2.3 5.5 V
I
DD
4.5 5.5 mA I
DD
code dependent; see Figure 7
Low Power Sleep Mode 0.5 mA DAC powered down, MCLK running
1 Operating temperature range is −40°C to +105°C; typical specifications are at 25°C.
VOUT
COMP
12
AD9833
10-BI T DAC
SIN
ROM
20pF
10nF VDD
REGULATOR
100nF
CAP/2.5V
02704-002
Figure 2. Test Circuit Used to Test Specifications
AD9833 Data Sheet
Rev. E | Page 4 of 24
TIMING CHARACTERISTICS
VDD = 2.3 V to 5.5 V, AGND = DGND = 0 V, unless otherwise noted.1
Table 2.
Parameter Limit at T
MIN
to T
MAX
Unit Description
t
1
40 ns min MCLK period
t
2
16 ns min MCLK high duration
t
3
16 ns min MCLK low duration
t
4
25 ns min SCLK period
t
5
10 ns min SCLK high duration
t
6
10 ns min SCLK low duration
t
7
5 ns min FSYNC to SCLK falling edge setup time
t
8
min
10 ns min FSYNC to SCLK hold time
t
8
max
t
4
− 5 ns max
t
9
5 ns min Data setup time
t
10
3 ns min Data hold time
t
11
5 ns min SCLK high to FSYNC falling edge setup time
1 Guaranteed by design, not production tested.
Timing Diagrams
t
2
t
1
MCLK
t
3
02704-003
Figure 3. Master Clock
t
5
t
4
t
6
t
7
t
8
t
10
t
9
41D
51DD0
D1D2D14
SCLK
FSYNC
SDATA D15
t11
02704-004
Figure 4. Serial Timing
Data Sheet AD9833
Rev. E | Page 5 of 24
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 3.
Parameter Rating
VDD to AGND 0.3 V to +6 V
VDD to DGND 0.3 V to +6 V
AGND to DGND 0.3 V to +0.3 V
CAP/2.5V 2.75 V
Digital I/O Voltage to DGND 0.3 V to VDD + 0.3 V
Analog I/O Voltage to AGND 0.3 V to VDD + 0.3 V
Operating Temperature Range
Industrial (B Version) 40°C to +105°C
Storage Temperature Range 65°C to +150°C
Maximum Junction Temperature 150°C
MSOP Package
θ
JA
Thermal Impedance 206°C/W
θ
JC
Thermal Impedance 44°C/W
Lead Temperature, Soldering (10 sec) 300°C
IR Reflow, Peak Temperature 220°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.
ESD CAUTION
AD9833 Data Sheet
Rev. E | Page 6 of 24
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
COMP
1
VDD
2
CAP/2.5V
3
DGND
4
MCLK
5
VOUT
10
AGND
9
FSYNC
8
SCLK
7
SDATA
6
AD9833
TOP VIEW
(Not t o Scale)
02704-005
Figure 5. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 COMP DAC Bias Pin. This pin is used for decoupling the DAC bias voltage.
2 VDD Positive Power Supply for the Analog and Digital Interface Sections. The on-board 2.5 V regulator is also supplied
from VDD. VDD can have a value from 2.3 V to 5.5 V. A 0.1 µF and a 10 µF decoupling capacitor should be connected
between VDD and AGND.
3 CAP/2.5V The digital circuitry operates from a 2.5 V power supply. This 2.5 V is generated from VDD using an on-board
regulator when VDD exceeds 2.7 V. The regulator requires a decoupling capacitor of 100 nF typical, which is
connected from CAP/2.5V to DGND. If VDD is less than or equal to 2.7 V, CAP/2.5V should be tied directly to VDD.
4 DGND Digital Ground.
5 MCLK Digital Clock Input. DDS output frequencies are expressed as a binary fraction of the frequency of MCLK. The
output frequency accuracy and phase noise are determined by this clock.
6 SDATA Serial Data Input. The 16-bit serial data-word is applied to this input.
7 SCLK Serial Clock Input. Data is clocked into the AD9833 on each falling edge of SCLK.
8 FSYNC Active Low Control Input. FSYNC
is the frame synchronization signal for the input data. When FSYNC is taken low,
the internal logic is informed that a new word is being loaded into the device.
9 AGND Analog Ground.
10 VOUT Voltage Output. The analog and digital output from the AD9833 is available at this pin. An external load resistor
is not required because the device has a 200 resistor on board.
Data Sheet AD9833
Rev. E | Page 7 of 24
TYPICAL PERFORMANCE CHARACTERISTICS
MCL K FREQ UE NCY ( M Hz )
I
DD
(mA)
5.5
5.0
3.0
3.5
4.0
4.5
0 5 10 15 20 25
T
A
= 25° C
02704-006
VDD = 5V
VDD = 3V
Figure 6. Typical Current Consumption (IDD) vs. MCLK Frequency
for fOUT = MCLK/10
0
1
2
3
4
5
6
100 1k 10k 100k 1M 10M
I
DD
(mA)
fOUT
(Hz)
VDD = 5V
VDD = 3V
02704-007
Figure 7. Typical IDD vs. fOUT for fMCLK = 25 MHz
0 5 10 15 20 25
MCL K FREQUENCY (MHz)
SF DR ( dBc)
–65
–60
–90
–70
–75
–80
–85
MCLK/7 MCLK/50
VDD = 3V
TA= 25° C
02704-008
Figure 8. Narrow-Band SFDR vs. MCLK Frequency
–45
–40
–70 57911 13 15 17 19 21 23 25
–50
–55
–60
–65
MCL K FREQUENCY (MHz)
SF DR ( dBc)
MCLK/7
MCLK/50
VDD = 3V
TA= 25° C
02704-009
Figure 9. Wideband SFDR vs. MCLK Frequency
f
OUT
/
f
MCLK
–30
–90
–80
–70
–60
–50
–40
SF DR ( dB)
0
–20
–10
f
MCLK
= 1MHz
f
MCLK
= 10MHz
0.001 0.01 0.1 110 100
f
MCLK
= 25MHz
VDD = 3V
TA= 25° C
02704-010
fMCLK = 18MHz
Figure 10. Wideband SFDR vs. fOUT/fMCLK for Various MCLK Frequencies
MCL K FREQUENCY (MHz)
1.0 5.0 10.0 12.5 25.0
SNR (dB)
–60
–65
–70
–50
–55
–40
–45 VDD = 3V
T
A
= 25° C
fOUT
= MCL K/4096
02704-011
Figure 11. SNR vs. MCLK Frequency
AD9833 Data Sheet
Rev. E | Page 8 of 24
500
1000
700
650
600
550
850
750
800
900
950
–40 25 105
TEMPERATURE (°C)
WAKE-UP TI ME (µs)
VDD = 5. 5V
02704-012
VDD = 2. 3V
Figure 12. Wake-Up Time vs. Temperature
–40 25 105
TEMPERATURE (°C)
V
REF
(V)
LOWER RANGE
UPPE R RANGE
1.150
1.125
1.100
1.175
1.200
1.250
1.225
02704-013
Figure 13. VREF vs. Temperature
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
0100k
RWB 100 ST 100 S E C
VW B 30
02704-014
Figure 14. Power vs. Frequency, fMCLK = 10 MHz, fOUT = 2.4 kHz,
Frequency Word = 0x000FBA9
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
05M
RWB 1k ST 50 SEC
VW B 300
02704-015
Figure 15. Power vs. Frequency, fMCLK = 10 MHz, fOUT = 1.43 MHz = fMCLK/7,
Frequency Word = 0x2492492
FREQUENCY (Hz)
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
05M
RWB 1k ST 50 SEC
VW B 300
02704-016
Figure 16. Power vs. Frequency, fMCLK = 10 MHz, fOUT = 3.33 MHz = fMCLK/3,
Frequency Word = 0x5555555
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
0100k
RWB 100 ST 100 S E C
VW B 30
02704-017
Figure 17. Power vs. Frequency, fMCLK = 25 MHz, fOUT = 6 kHz,
Frequency Word = 0x000FBA9
Data Sheet AD9833
Rev. E | Page 9 of 24
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
01M
RWB 300 ST 100 S E C
VW B 100
02704-018
Figure 18. Power vs. Frequency, fMCLK = 25 MHz, fOUT = 60 kHz,
Frequency Word = 0x009D495
FREQUENCY (Hz)
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
012.5M
RWB 1k ST 100 S E C
VW B 300
02704-019
Figure 19. Power vs. Frequency, fMCLK = 25 MHz, fOUT = 600 kHz,
Frequency Word = 0x0624DD3
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
012.5M
RWB 1k ST 100 S E C
VW B 300
02704-020
Figure 20. Power vs. Frequency, fMCLK = 25 MHz, fOUT = 2.4 MHz,
Frequency Word = 0x189374D
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
012.5M
RWB 1k ST 100 S E C
VW B 300
02704-021
Figure 21. Power vs. Frequency, fMCLK = 25 MHz, fOUT = 3.857 MHz = fMCLK/7,
Frequency Word = 0x2492492
FREQUENCY ( Hz )
POWER (dB)
0
–20
–50
–90
–100
–80
–70
–60
–40
–30
–10
012.5M
RWB 1k ST 100 SE C
VW B 300
02704-022
Figure 22. Power vs. Frequency, fMCLK = 25 MHz, fOUT = 8.333 MHz = fMCLK/3,
Frequency Word = 0x5555555
AD9833 Data Sheet
Rev. E | Page 10 of 24
TERMINOLOGY
Integral Nonlinearity (INL)
INL is the maximum deviation of any code from a straight line
passing through the endpoints of the transfer function. The end-
points of the transfer function are zero scale, a point 0.5 LSB
below the first code transition (000 00 to 000 … 01), and full
scale, a point 0.5 LSB above the last code transition (111 10
to 111 11). The error is expressed in LSBs.
Differential Nonlinearity (DNL)
DNL is the difference between the measured and ideal 1 LSB
change between two adjacent codes in the DAC. A specified
DNL of ±1 LSB maximum ensures monotonicity.
Output Compliance
Output compliance refers to the maximum voltage that can be
generated at the output of the DAC to meet the specifications.
When voltages greater than that specified for the output compli-
ance are generated, the AD9833 may not meet the specifications
listed in the data sheet.
Spurious-Free Dynamic Range (SFDR)
Along with the frequency of interest, harmonics of the funda-
mental frequency and images of these frequencies are present at
the output of a DDS device. SFDR refers to the largest spur or
harmonic present in the band of interest. The wideband SFDR
gives the magnitude of the largest spur or harmonic relative to
the magnitude of the fundamental frequency in the zero to Nyquist
bandwidth. The narrow-band SFDR gives the attenuation of the
largest spur or harmonic in a bandwidth of ±200 kHz about the
fundamental frequency.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the rms value
of the fundamental. For the AD9833, THD is defined as
1
2
6
2
5
2
4
2
3
2
2
log20THD V
VVVVV ++++
=
where:
V1 is the rms amplitude of the fundamental.
V2, V3, V4, V5, and V6 are the rms amplitudes of the second
through sixth harmonics.
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the measured output signal
to the rms sum of all other spectral components below the
Nyquist frequency. The value for SNR is expressed in decibels.
Clock Feedthrough
There is feedthrough from the MCLK input to the analog
output. Clock feedthrough refers to the magnitude of the
MCLK signal relative to the fundamental frequency in the
output spectrum of the AD9833.
Data Sheet AD9833
Rev. E | Page 11 of 24
THEORY OF OPERATION
Sine waves are typically thought of in terms of their magnitude
form: a(t) = sin(ωt). However, these sine waves are nonlinear and
not easy to generate except through piecewise construction. On
the other hand, the angular information is linear in nature. That
is, the phase angle rotates through a fixed angle for each unit of
time. The angular rate depends on the frequency of the signal
by the traditional rate of ω = 2πf.
MAGNITUDE
PHASE
+1
0
–1
2p
0
2π4π
6π
2π4π6π
0
2704-023
Figure 23. Sine Wave
Knowing that the phase of a sine wave is linear and given a
reference interval (clock period), the phase rotation for that
period can be determined.
ΔPhase = ωΔt
Solving for ω,
ω = ΔPhase/Δt = f
Solving for f and substituting the reference clock frequency for
the reference period (1/fMCLK = Δt)
f = ΔPhase × fMCLK∕2π
The AD9833 builds the output based on this simple equation. A
simple DDS chip can implement this equation with three major
subcircuits: numerically controlled oscillator (NCO) and phase
modulator, SIN ROM, and digital-to-analog converter (DAC).
Each subcircuit is described in the Circuit Description section.
AD9833 Data Sheet
Rev. E | Page 12 of 24
CIRCUIT DESCRIPTION
The AD9833 is a fully integrated direct digital synthesis (DDS)
chip. The chip requires one reference clock, one low precision
resistor, and decoupling capacitors to provide digitally created
sine waves up to 12.5 MHz. In addition to the generation of this
RF signal, the chip is fully capable of a broad range of simple
and complex modulation schemes. These modulation schemes
are fully implemented in the digital domain, allowing accurate
and simple realization of complex modulation algorithms using
DSP techniques.
The internal circuitry of the AD9833 consists of the following
main sections: a numerically controlled oscillator (NCO),
frequency and phase modulators, SIN ROM, a DAC, and a
regulator.
NUMERICALLY CONTROLLED OSCILLATOR PLUS
PHASE MODULATOR
This consists of two frequency select registers, a phase accumulator,
two phase offset registers, and a phase offset adder. The main
component of the NCO is a 28-bit phase accumulator. Continuous
time signals have a phase range of 0 to 2π. Outside this range of
numbers, the sinusoid functions repeat themselves in a periodic
manner. The digital implementation is no different. The
accumulator simply scales the range of phase numbers into a
multibit digital word. The phase accumulator in the AD9833 is
implemented with 28 bits. Therefore, in the AD9833, 2π = 228.
Likewise, the ΔPhase term is scaled into this range of numbers:
0 < ΔPhase < 228 − 1
With these substitutions, the previous equation becomes
f = ΔPhase × fMCLK∕228
where 0 < ΔPhase < 228 − 1.
The input to the phase accumulator can be selected from either
the FREQ0 register or the FREQ1 register and is controlled by
the FSELECT bit. NCOs inherently generate continuous phase
signals, thus avoiding any output discontinuity when switching
between frequencies.
Following the NCO, a phase offset can be added to perform
phase modulation using the 12-bit phase registers. The contents
of one of these phase registers are added to the most significant
bits of the NCO. The AD9833 has two phase registers; their
resolution is 2π/4096.
SIN ROM
To make the output from the NCO useful, it must be converted
from phase information into a sinusoidal value. Because phase
information maps directly into amplitude, the SIN ROM uses the
digital phase information as an address to a lookup table and
converts the phase information into amplitude. Although the NCO
contains a 28-bit phase accumulator, the output of the NCO is
truncated to 12 bits. Using the full resolution of the phase
accumulator is impractical and unnecessary, because this would
require a lookup table of 228 entries. It is necessary only to have
sufficient phase resolution such that the errors due to truncation
are smaller than the resolution of the 10-bit DAC. This requires
that the SIN ROM have two bits of phase resolution more than
the 10-bit DAC.
The SIN ROM is enabled using the mode bit (D1) in the control
register (see Table 15).
DIGITAL-TO-ANALOG CONVERTER (DAC)
The AD9833 includes a high impedance, current source 10-bit
DAC. The DAC receives the digital words from the SIN ROM
and converts them into the corresponding analog voltages.
The DAC is configured for single-ended operation. An external
load resistor is not required because the device has a 200
resistor on board. The DAC generates an output voltage of
typically 0.6 V p-p.
REGULATOR
VDD provides the power supply required for the analog section
and the digital section of the AD9833. This supply can have a
value of 2.3 V to 5.5 V.
The internal digital section of the AD9833 is operated at 2.5 V.
An on-board regulator steps down the voltage applied at VDD
to 2.5 V. When the applied voltage at the VDD pin of the AD9833
is less than or equal to 2.7 V, the CAP/2.5V and VDD pins
should be tied together, thus bypassing the on-board regulator.
Data Sheet AD9833
Rev. E | Page 13 of 24
FUNCTIONAL DESCRIPTION
SERIAL INTERFACE
The AD9833 has a standard 3-wire serial interface that is
compatible with the SPI, QSPI™, MICROWIRE®, and DSP
interface standards.
Data is loaded into the device as a 16-bit word under the
control of a serial clock input, SCLK. The timing diagram for
this operation is given in .
The FSYNC input is a level-triggered input that acts as a frame
synchronization and chip enable. Data can be transferred into the
device only when FSYNC is low. To start the serial data transfer,
FSYNC should be taken low, observing the minimum FSYNC-
to-SCLK falling edge setup time, t7. After FSYNC goes low, serial
data is shifted into the input shift register of the device on the
falling edges of SCLK for 16 clock pulses. FSYNC may be taken
high after the 16th falling edge of SCLK, observing the minimum
SCLK falling edge to FSYNC rising edge time, t8. Alternatively,
FSYNC can be kept low for a multiple of 16 SCLK pulses and
then brought high at the end of the data transfer. In this way, a
continuous stream of 16-bit words can be loaded while FSYNC
is held low; FSYNC goes high only after the 16th SCLK falling
edge of the last word loaded.
The SCLK can be continuous, or it can idle high or low between
write operations. In either case, it must be high when FSYNC
goes low (t11).
For an example of how to program the AD9833, see the AN-1070
Application Note on the Analog Devices, Inc., website.
POWERING UP THE AD9833
The flowchart in Figure 26 shows the operating routine for the
AD9833. When the AD9833 is powered up, the part should be
reset. This resets the appropriate internal registers to 0 to provide
an analog output of midscale.
To avoid spurious DAC outputs during AD9833 initialization,
the reset bit should be set to 1 until the part is ready to begin
generating an output. A reset does not reset the phase, frequency,
or control registers. These registers will contain invalid data and,
therefore, should be set to known values by the user. The reset
bit should then be set to 0 to begin generating an output. The
data appears on the DAC output seven or eight MCLK cycles
after the reset bit is set to 0.
LATENCY PERIOD
A latency period is associated with each asynchronous write
operation in the AD9833. If a selected frequency or phase
register is loaded with a new word, there is a delay of seven
or eight MCLK cycles before the analog output changes. The
delay can be seven or eight cycles, depending on the position
of the MCLK rising edge when the data is loaded into the
destination register.
CONTROL REGISTER
The AD9833 contains a 16-bit control register that allows the
user to configure the operation of the AD9833. All control bits
other than the mode bit are sampled on the internal falling edge
of MCLK.
Table 6 describes the individual bits of the control register.
The different functions and the various output options of
the AD9833 are described in more detail in the Frequency and
Phase Registers section.
To inform the AD9833 that the contents of the control register
will be altered, D15 and D14 must be set to 0, as shown in Table 5.
Table 5. Control Register Bits
D15 D14 D13 D0
0 0 Control Bits
SIN
ROM
PHASE
ACCUMULATOR
(28-BIT)
AD9833
(LOW PO W ER)
10-BI T DAC
0
MUX
1
SLEEP12
SLEEP1
RESET
MODE + OPBITEN
DIV2
OPBITEN
VOUT
1
MUX
0
DIGITAL
OUTPUT
(ENABLE)
DIVIDE
BY 2
DB15
0DB14
0DB13
B28 DB12
HLB DB11
FSELECT DB10
PSELECT DB9
0DB8
RESET DB7
SLEEP1 DB6
SLEEP12 DB5
OPBITEN DB4
0DB3
DIV2 DB2
0DB1
MODE DB0
0
02704-024
Figure 24. Function of Control Bits
AD9833 Data Sheet
Rev. E | Page 14 of 24
Table 6. Description of Bits in the Control Register
Bit Name Function
D13 B28 Two write operations are required to load a complete word into either of the frequency registers. B28 = 1 allows a
complete word to be loaded into a frequency register in two consecutive writes. The first write contains the 14 LSBs of
the frequency word, and the next write contains the 14 MSBs. The first two bits of each 16-bit word define the
frequency register to which the word is loaded and should, therefore, be the same for both of the consecutive writes.
See Table 8 for the appropriate addresses. The write to the frequency register occurs after both words have been
loaded; therefore, the register never holds an intermediate value. An example of a complete 28-bit write is shown in
Table 9. When B28 = 0, the 28-bit frequency register operates as two 14-bit registers, one containing the 14 MSBs and
the other containing the 14 LSBs. This means that the 14 MSBs of the frequency word can be altered independent of
the 14 LSBs, and vice versa. To alter the 14 MSBs or the 14 LSBs, a single write is made to the appropriate frequency
address. The control bit D12 (HLB) informs the AD9833 whether the bits to be altered are the 14 MSBs or 14 LSBs.
D12 HLB This control bit allows the user to continuously load the MSBs or LSBs of a frequency register while ignoring the
remaining 14 bits. This is useful if the complete 28-bit resolution is not required. HLB is used in conjunction with D13
(B28). This control bit indicates whether the 14 bits being loaded are being transferred to the 14 MSBs or 14 LSBs of the
addressed frequency register. D13 (B28) must be set to 0 to be able to change the MSBs and LSBs of a frequency word
separately. When D13 (B28) = 1, this control bit is ignored. HLB = 1 allows a write to the 14 MSBs of the addressed
frequency register. HLB = 0 allows a write to the 14 LSBs of the addressed frequency register.
D11 FSELECT The FSELECT bit defines whether the FREQ0 register or the FREQ1 register is used in the phase accumulator.
D10 PSELECT The PSELECT bit defines whether the PHASE0 register or the PHASE1 register data is added to the output of the phase
accumulator.
D9 Reserved This bit should be set to 0.
D8 Reset Reset = 1 resets internal registers to 0, which corresponds to an analog output of midscale. Reset = 0 disables reset.
This function is explained further in Table 13.
D7 SLEEP1 When SLEEP1 = 1, the internal MCLK clock is disabled, and the DAC output remains at its present value because the
NCO is no longer accumulating. When SLEEP1 = 0, MCLK is enabled. This function is explained further in Table 14.
D6 SLEEP12 SLEEP12 = 1 powers down the on-chip DAC. This is useful when the AD9833 is used to output the MSB of the DAC data.
SLEEP12 = 0 implies that the DAC is active. This function is explained further in Table 14.
D5
OPBITEN
The function of this bit, in association with D1 (mode), is to control what is output at the VOUT pin. This is explained
further in Table 15. When OPBITEN = 1, the output of the DAC is no longer available at the VOUT pin. Instead, the MSB
(or MSB/2) of the DAC data is connected to the VOUT pin. This is useful as a coarse clock source. The DIV2 bit controls
whether it is the MSB or MSB/2 that is output. When OPBITEN = 0, the DAC is connected to VOUT. The mode bit
determines whether it is a sinusoidal or a ramp output that is available.
D4 Reserved This bit must be set to 0.
D3 DIV2 DIV2 is used in association with D5 (OPBITEN). This is explained further in Table 15. When DIV2 = 1, the MSB of the DAC
data is passed directly to the VOUT pin. When DIV2 = 0, the MSB/2 of the DAC data is output at the VOUT pin.
D2 Reserved This bit must be set to 0.
D1 Mode This bit is used in association with OPBITEN (D5). The function of this bit is to control what is output at the VOUT pin
when the on-chip DAC is connected to VOUT. This bit should be set to 0 if the control bit OPBITEN = 1. This is explained
further in Table 15. When mode = 1, the SIN ROM is bypassed, resulting in a triangle output from the DAC. When mode = 0,
the SIN ROM is used to convert the phase information into amplitude information, which results in a sinusoidal signal
at the output.
D0 Reserved This bit must be set to 0.
Data Sheet AD9833
Rev. E | Page 15 of 24
FREQUENCY AND PHASE REGISTERS
The AD9833 contains two frequency registers and two phase
registers, which are described in Table 7.
Table 7. Frequency and Phase Registers
Register Size Description
FREQ0 28 bits Frequency Register 0. When the FSELECT
bit = 0, this register defines the output
frequency as a fraction of the MCLK
frequency.
FREQ1 28 bits Frequency Register 1. When the FSELECT
bit = 1, this register defines the output
frequency as a fraction of the MCLK
frequency.
PHASE0 12 bits Phase Offset Register 0. When the PSELECT
bit = 0, the contents of this register are
added to the output of the phase
accumulator.
PHASE1 12 bits Phase Offset Register 1. When the PSELECT
bit = 1, the contents of this register are
added to the output of the phase
accumulator.
The analog output from the AD9833 is
fMCLK/228 × FREQREG
where FREQREG is the value loaded into the selected frequency
register. This signal is phase shifted by
/4096 × PHASEREG
where PHASEREG is the value contained in the selected phase
register. Consideration must be given to the relationship of the
selected output frequency and the reference clock frequency to
avoid unwanted output anomalies.
The flowchart in Figure 28 shows the routine for writing to the
frequency and phase registers of the AD9833.
Writing to a Frequency Register
When writing to a frequency register, Bit D15 and Bit D14 give
the address of the frequency register.
Table 8. Frequency Register Bits
D15 D14 D13 D0
0 1 MSB 14 FREQ0 REG bits LSB
1 0 MSB 14 FREQ1 REG bits LSB
If the user wants to change the entire contents of a frequency
register, two consecutive writes to the same address must be
performed because the frequency registers are 28 bits wide. The
first write contains the 14 LSBs, and the second write contains
the 14 MSBs. For this mode of operation, the B28 (D13) control
bit should be set to 1. An example of a 28-bit write is shown in
Table 9.
Table 9. Writing 0xFFFC000 to the FREQ0 Register
SDATA Input Result of Input Word
0010 0000 0000 0000 Control word write
(D15, D14 = 00), B28 (D13) = 1,
HLB (D12) = X
0100 0000 0000 0000 FREQ0 register write
(D15, D14 = 01), 14 LSBs = 0x0000
0111 1111 1111 1111 FREQ0 register write
(D15, D14 = 01), 14 MSBs = 0x3FFF
In some applications, the user does not need to alter all 28 bits
of the frequency register. With coarse tuning, only the 14 MSBs
are altered, while with fine tuning, only the 14 LSBs are altered.
By setting the B28 (D13) control bit to 0, the 28-bit frequency
register operates as two, 14-bit registers, one containing the 14 MSBs
and the other containing the 14 LSBs. This means that the 14 MSBs
of the frequency word can be altered independent of the 14 LSBs,
and vice versa. Bit HLB (D12) in the control register identifies
which 14 bits are being altered. Examples of this are shown in
Table 10 an d Table 11.
Table 10. Writing 0x3FFF to the 14 LSBs of the FREQ1 Register
SDATA Input Result of Input Word
0000 0000 0000 0000 Control word write (D15, D14 = 00),
B28 (D13) = 0; HLB (D12) = 0, that is, LSBs
1011 1111 1111 1111 FREQ1 REG write (D15, D14 = 10),
14 LSBs = 0x3FFF
Table 11. Writing 0x00FF to the 14 MSBs of the FREQ0 Register
SDATA Input Result of Input Word
0001 0000 0000 0000 Control word write (D15, D14 = 00),
B28 (D13) = 0, HLB (D12) = 1, that is, MSBs
0100 0000 1111 1111 FREQ0 REG write (D15, D14 = 01),
14 MSBs = 0x00FF
Writing to a Phase Register
When writing to a phase register, Bit D15 and Bit D14 are set to 11.
Bit D13 identifies which phase register is being loaded.
Table 12. Phase Register Bits
D15 D14 D13 D12 D11 D0
1 1 0 X MSB 12 PHASE0 bits LSB
1 1 1 X MSB 12 PHASE1 bits LSB
AD9833 Data Sheet
Rev. E | Page 16 of 24
RESET FUNCTION
The reset function resets appropriate internal registers to 0 to
provide an analog output of midscale. Reset does not reset the
phase, frequency, or control registers. When the AD9833 is
powered up, the part should be reset. To reset the AD9833, set
the reset bit to 1. To take the part out of reset, set the bit to 0. A
signal appears at the DAC to output eight MCLK cycles after
reset is set to 0.
Table 13. Applying the Reset Function
Reset Bit Result
0 No reset applied
1 Internal registers reset
SLEEP FUNCTION
Sections of the AD9833 that are not in use can be powered
down to minimize power consumption. This is done using the
sleep function. The parts of the chip that can be powered down
are the internal clock and the DAC. The bits required for the
sleep function are outlined in Table 14.
Table 14. Applying the Sleep Function
SLEEP1 Bit SLEEP12 Bit Result
0 0 No power-down
0 1 DAC powered down
1 0 Internal clock disabled
1
1
Both the DAC powered down
and the internal clock disabled
DAC Powered Down
This is useful when the AD9833 is used to output the MSB
of the DAC data only. In this case, the DAC is not required;
therefore, it can be powered down to reduce power
consumption.
Internal Clock Disabled
When the internal clock of the AD9833 is disabled, the DAC
output remains at its present value because the NCO is no
longer accumulating. New frequency, phase, and control words
can be written to the part when the SLEEP1 control bit is active.
The synchronizing clock is still active, which means that the
selected frequency and phase registers can also be changed
using the control bits. Setting the SLEEP1 bit to 0 enables the
MCLK. Any changes made to the registers while SLEEP1 is
active will be seen at the output after a latency period.
VOUT PIN
The AD9833 offers a variety of outputs from the chip, all of which
are available from the VOUT pin. The choice of outputs is the
MSB of the DAC data, a sinusoidal output, or a triangle output.
The OPBITEN (D5) and mode (D1) bits in the control register
are used to decide which output is available from the AD9833.
MSB of the DAC Data
The MSB of the DAC data can be output from the AD9833. By
setting the OPBITEN (D5) control bit to 1, the MSB of the DAC
data is available at the VOUT pin. This is useful as a coarse clock
source. This square wave can also be divided by 2 before being
output. The DIV2 (D3) bit in the control register controls the
frequency of this output from the VOUT pin.
Sinusoidal Output
The SIN ROM is used to convert the phase information from
the frequency and phase registers into amplitude information
that results in a sinusoidal signal at the output. To have a sinusoidal
output from the VOUT pin, set the mode (D1) bit to 0 and the
OPBITEN (D5) bit to 0.
Triangle Output
The SIN ROM can be bypassed so that the truncated digital
output from the NCO is sent to the DAC. In this case, the
output is no longer sinusoidal. The DAC will produce a 10-bit
linear triangular function. To have a triangle output from the
VOUT pin, set the mode (D1) bit = 1.
Note that the SLEEP12 bit must be 0 (that is, the DAC is enabled)
when using this pin.
Table 15. Outputs from the VOUT Pin
OPBITEN Bit Mode Bit DIV2 Bit VOUT Pin
0 0 X
1
Sinusoid
0 1 X
1
Triangle
1 0 0 DAC data MSB/2
1 0 1 DAC data MSB
1 1 X1 Reserved
1 X = don’t care.
VOUT MIN
VOUT MAX
02704-025
Figure 25. Triangle Output
Data Sheet AD9833
Rev. E | Page 17 of 24
APPLICATIONS INFORMATION
Because of the various output options available from the part,
the AD9833 can be configured to suit a wide variety of applications.
One of the areas where the AD9833 is suitable is in modulation
applications. The part can be used to perform simple modulation,
such as FSK. More complex modulation schemes, such as
GMSK and QPSK, can also be implemented using the AD9833.
In an FSK application, the two frequency registers of the AD9833
are loaded with different values. One frequency represents the
space frequency, while the other represents the mark frequency.
Using the FSELECT bit in the control register of the AD9833, the
user can modulate the carrier frequency between the two values.
The AD9833 has two phase registers, which enables the part to
perform PSK. With phase-shift keying, the carrier frequency is
phase shifted, the phase being altered by an amount that is
related to the bit stream being input to the modulator.
The AD9833 is also suitable for signal generator applications.
Because the MSB of the DAC data is available at the VOUT pin,
the device can be used to generate a square wave.
With its low current consumption, the part is suitable for
applications in which it can be used as a local oscillator.
GROUNDING AND LAYOUT
The printed circuit board (PCB) that houses the AD9833 should be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes that can be separated easily. A minimum
etch technique is generally best for ground planes because it gives
the best shielding. Digital and analog ground planes should be
joined in one place only. If the AD9833 is the only device requiring
an AGND-to-DGND connection, then the ground planes should
be connected at the AGND and DGND pins of the AD9833. If
the AD9833 is in a system where multiple devices require AGND-
to-DGND connections, the connection should be made at one
point only, a star ground point that should be established as
close as possible to the AD9833.
Avoid running digital lines under the device as these couple noise
onto the die. The analog ground plane should be allowed to run
under the AD9833 to avoid noise coupling. The power supply
lines to the AD9833 should use as large a track as possible to
provide low impedance paths and reduce the effects of glitches
on the power supply line. Fast switching signals, such as clocks,
should be shielded with digital ground to avoid radiating noise
to other sections of the board.
Avoid crossover of digital and analog signals. Traces on opposite