Direct digital synthesis
Frequency synthesis

The principle of the digital direct synthesizer (DDS) is shown in figure 15.

The output of the R-bit phase accumulator addresses a ROM (read-only memory) containing an M-bit tabulated representation of the sine function. This ROM converts the phase information produced by the accumulator into a digital value representing the signal amplitude. An S-bit digital-to-analog converter (DAC) then translates this digital value to deliver the analog signal of frequency ν_S = (n/d)ν_E with d = 2^R. The signal obtained corresponds to the sampling of the ideal function sin 2πν_S. In accordance with the sampling theorem, the maximum frequency that can be synthesized is ν_E/2.