Extended Information

Direct Digital Frequency Synthesis (DDFS, generally referred to as DDS) is a frequency synthesis technology that directly generates the required waveform based on phase concepts. A direct digital frequency synthesizer typically consists of a phase accumulator, an adder, a waveform storage ROM (often holding a sine lookup table), a D/A converter, and a low-pass filter (LPF). A DDS chip mainly includes three parts: a frequency control register, a high-speed phase accumulator, and a sine lookup table. The frequency control register loads and stores the user-input frequency control word, either in serial or parallel mode. The phase accumulator, based on this frequency control word, updates the phase value by accumulating phase increments with each clock cycle. The sine lookup table (or sine calculator) retrieves the corresponding digital sine wave amplitude from the phase value. Since the DDS output is generally a digitized waveform (commonly a sine wave), it passes through a high-speed D/A converter and a low-pass filter to obtain a usable analog frequency signal.