ad9850.pdf

CMOS, 125 MHz Complete DDS Synthesizer

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 complete

digitally programmable frequency synthesizer and clock

generator funcTIon. When referenced to an accurate clock

source, the AD9850 generates a spectrally pure, frequency/

phase-programmable, analog output sine wave. This sine wave

can be used directly as a frequency source or converted to a

square wave for agile-clock generator applicaTIons. 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 digitally 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 2–5

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.