Direct digital synthesizers (DDS), or numerically controlled oscillators (NCO), are important components in many digital communication systems. Quadrature synthesizers are used for constructing digital down and up converters, demodulators, and implementing various
types of modulation schemes, including PSK (phase shift keying), FSK (frequency shift keying), and MSK (minimum shift keying). A common method for digitally
generating a complex or real valued sinusoid
employs a look-up table scheme. The look-up table
stores samples of a sinusoid. A digital integrator is used
to generate a suitable phase argument that is mapped
by the look-up table to the desired output waveform. A
simple user interface accepts system-level parameters such as the desired output frequency and spur suppression of the generated waveforms. A high-level view of the DDS core is presented in Figure 1.