DIRECT DIGITAL FREQUENCY SYNTHESIZER AND A HYBRID FREQUENCY SYNTHESIZER COMBINING A DIRECT DIGITAL FREQUENCY SYNTHESIZER AND A PHASE LOCKED LOOP

摘要

A direct digital frequency synthesizer and a hybrid frequency synthesiz er combining the direct digital frequency synthesizer and a phase locked loop i s provided. The direct digital frequency synthesizer includes a phase accumulator that is configured to generate a discrete phase signal. Spurious phase modulation in the discrete phase signal is reduced by a noise shaper, and the output of the noise shaper is then used to address a phase-to-amplitude translator. The phase-to-amplitude translator generates a discrete waveform which is convert ed to a continuous waveform by a digital to analog converter. The hybrid frequency synthesizer uses a mixer to combine a reference frequency generated by a reference source and a DDFS output signal generated by a direct digital frequency synthesizer. The output from the mixer is then coupled to the input of a pha se locked loop which multiplies the mixer output to generate the frequency synthesizer output.