| 摘要 |
A synthesizer produces step frequencies by multiplying the frequency of a reference oscillator and stimulating an SRD comb frequency generator, then adding or subtracting a reference frequency. The selected step frequency can be placed on either side of each picket of the comb's spectrum. A fine adjustment frequency is then added in a translation oscillator. The fine frequency component can also be placed on either side of the selected step frequency. Frequency dividers, which would result in noisy final outputs, are not employed. Instead, the frequency of a reference signal is multiplied up in a narrowband channel to serve as a local oscillator, and the VCO signal frequency is reduced by heterodyning it down from its ultra-high frequency. The down-converted difference frequency is compared as to phase with the reference oscillator. The loop gain and bandwidth are so high in the phase lock loops that output noise is low and switching time is fast.
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