| 摘要 |
A low phase noise signal source is disclosed which incorporates a voltage controlled oscillator (VCO) and a feedback network that, in effect, demodulates the VCO output signal and supplies negative feedback representative of the VCO signal noise to the VCO frequency control terminal. The feedback network includes a frequency discriminator of the type wherein a time delay network is connected to one input port of a phase detector, with the VCO output signal being supplied to the time delay network and the second input port of the phase detector. A variable phase shifter, responsive to the signal supplied by the phase detector, is included in one of the phase detector input paths to cause a zero crossover of the frequency discriminator transfer characteristic to occur at the frequency to which the VCO is tuned. By establishing predetermined relationships between the transmission poles and zeroes of the feedback network, normal VCO tuning characteristics are preserved while simultaneously decreasing VCO phase noise. Various arrangements for operating the signal source over a wide band of output frequencies are disclosed, including a low-noise phase-locked loop frequency synthesizer.
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