Direct Digital Synthesis:- Direct digital synthesis, DDS is a frequency synthesizer technique that uses a waveform stored in ROM. It is a frequency synthesizer technique that is becoming more widespread.

DDS takes a different approach to that of the more usual indirect frequency synthesis techniques using PLLs by directly synthesizing the waveform from a digital map of the waveform stored in a memory.

Using digital techniques in this way, along with high speed logic, direct digital synthesis provides a powerful technique for creating accurate signals whose frequency can be stepped by very small increments giving virtually analogue or continuous tuning if needed.

Earlier direct digital synthesizers were limited in frequency by the speed of the logic. With speeds improving he top frequency limits for direct digital synthesizers is increasing.

A direct digital synthesizer operates by storing the points of a waveform in digital format, and then recalling them to generate the waveform. The rate at which the synthesizer completes one waveform governs the frequency.

fig: Direct digital synthesizer block diagram: