ad9850.pdf

CMOS, 125 MHz Complete DDS Synthesizer The AD9850 is a highly integrated device that uses advancedDDS technology coupled with an internal high speed, highperformance, D/A converter and comparator, to form a completedigitally programmable frequency synthesizer and clockgenerator funcTIon. When referenced to an accurate clocksource, the AD9850 generates a spectrally pure, frequency/phase-programmable, analog output sine wave. This sine wavecan be used directly as a frequency source or converted to asquare wave for agile-clock generator applicaTIons. The AD9850’sinnovaTIve high speed DDS core provides a 32-bit frequencytuning word, which results in an output tuning resoluTIon of0.0291 Hz, for a 125 MHz reference clock input. TheAD9850’s circuit architecture allows the generation of outputfrequencies of up to one-half the reference clock frequency (or62.5 MHz), and the output frequency can be digitally changed(asynchronously) at a rate of up to 23 million new frequenciesper second. The device also provides five bits of digitallycontrolled phase modulation, which enables phase shifting of itsoutput in increments of 180°, 90°, 45°, 22.5°, 11.25° and anycombination thereof. The AD9850 also contains a high speedcomparator that can be configured to accept the (externally)filtered output of the DAC to generate a low jitter square waveoutput. This facilitates the device’s use as an agile clock generatorfunction.The frequency tuning, control, and phase modulation words areloaded into the AD9850 via a parallel byte or serial loadingformat. The parallel load format consists of five iterative loadsof an 8-bit control word (byte). The first byte controls phasemodulation, power-down enable, and loading format; bytes 2–5comprise the 32-bit frequency tuning word. Serial loading isaccomplished via a 40-bit serial data stream on a single pin. TheAD9850 Complete-DDS uses advanced CMOS technology toprovide this breakthrough level of functionality and performanceon just 155 mW of power dissipation (+3.3 V supply).The AD9850 is available in a space saving 28-lead SSOP, surfacemount package. It is specified to operate over the extendedindustrial temperature range of –40°C to +85°C.