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 synthesizercombining the direct digital frequency synthesizer and a phase locked loop isprovided. The direct digital frequency synthesizer includes a phaseaccumulatorthat is configured to generate a discrete phase signal. Spurious phasemodulationin the discrete phase signal is reduced by a noise shaper, and the output ofthenoise shaper is then used to address a phase-to-amplitude translator. Thephase-to-amplitude translator generates a discrete waveform which is convertedto acontinuous waveform by a digital to analog converter. The hybrid frequencysynthesizer uses a mixer to combine a reference frequency generated by areference source and a DDFS output signal generated by a direct digitalfrequencysynthesizer. The output from the mixer is then coupled to the input of a phaselocked loop which multiplies the mixer output to generate the frequencysynthesizer output.