REV. H
a
CMOS, 125 MHz
Complete DDS Synthesizer
AD9850
FUNCTIONAL BLOCK DIAGRAM
CLOCK OUT
CLOCK OUT
ANALOG
IN
ANALOG
OUT
DAC R
SET
+V
S
GND
COMPARATOR
PHASE
AND
CONTROL
WORDS
SERIAL
LOAD
32-BIT
TUNING
WORD
HIGH SPEED
DDS
FREQUENCY/PHASE
DATA REGISTER
PARALLEL
LOAD
DATA INPUT REGISTER
AD9850
10-BIT
DAC
REF
CLOCK IN
MASTER
RESET
WORD LOAD
CLOCK
FREQUENCY
UPDATE/
DATA REGISTER
RESET
1-BIT
40 LOADS
8-BITS
5 LOADS
FREQUENCY, PHASE, AND CONTROL
DATA INPUT
GENERAL DESCRIPTION
The AD9850 is a highly integrated device that uses advanced
DDS technology coupled with an internal high speed, high
performance D/A converter and comparator to form a com-
plete, digitally programmable frequency synthesizer and
clock generator function. When referenced to an accurate
clock source, the AD9850 generates a spectrally pure, fre-
quency/phase programmable, analog output sine wave. This
sine wave can be used directly as a frequency source, or it can
be converted to a square wave for agile-clock generator applica-
tions. The AD9850’s innovative high speed DDS core provides
a 32-bit frequency tuning word, which results in an output
tuning resolution of 0.0291 Hz for a 125 MHz reference clock
input. The AD9850’s circuit architecture allows the generation
of output frequencies of up to one-half the reference clock
frequency (or 62.5 MHz), and the output frequency can be digi-
tally changed (asynchronously) at a rate of up to 23 million new
frequencies per second. The device also provides five bits of
digitally controlled phase modulation, which enables phase
shifting of its output in increments of 180°, 90°, 45°, 22.5°,
11.25°, and any combination thereof. The AD9850 also contains
a high speed comparator that can be configured to accept the
(externally) filtered output of the DAC to generate a low jitter
square wave output. This facilitates the device’s use as an
agile clock generator function.
The frequency tuning, control, and phase modulation words are
loaded into the AD9850 via a parallel byte or serial loading
format. The parallel load format consists of five iterative loads
of an 8-bit control word (byte). The first byte controls phase
modulation, power-down enable, and loading format; Bytes 2 to
5 comprise the 32-bit frequency tuning word. Serial loading is
accomplished via a 40-bit serial data stream on a single pin. The
AD9850 Complete DDS uses advanced CMOS technology to
provide this breakthrough level of functionality and performance
on just 155 mW of power dissipation (3.3 V supply).
The AD9850 is available in a space-saving 28-lead SSOP,
surface-mount package. It is specified to operate over the
extended industrial temperature range of –40°C to +85°C.
FEATURES
125 MHz Clock Rate
On-Chip High Performance DAC and High Speed
Comparator
DAC SFDR > 50 dB @ 40 MHz A
OUT
32-Bit Frequency Tuning Word
Simplified Control Interface: Parallel Byte or Serial
Loading Format
Phase Modulation Capability
3.3 V or 5 V Single-Supply Operation
Low Power: 380 mW @ 125 MHz (5 V)
Low Power: 155 mW @ 110 MHz (3.3 V)
Power-Down Function
Ultrasmall 28-Lead SSOP Packaging
APPLICATIONS
Frequency/Phase—Agile Sine Wave Synthesis
Clock Recovery and Locking Circuitry for Digital
Communications
Digitally Controlled ADC Encode Generator
Agile Local Oscillator Applications
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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. 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.
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