Frequency synthesizer having overtone crystal oscillator

摘要

A frequency synthesizer which is capable of providing very high output frequencies of the order of 500 MHz is designed to produce a very pure signal having very low noise. An overtone crystal oscillator which is constrained to oscillate at a harmonic frequency of the fundamental frequency determined by the physical dimensions of the crystal is mixed with a variable low frequency signal which is varied to provide the necessary output frequency steps. It is not possible to adjust the frequency of the overtone crystal oscillator without degrading its stability and introducing noise, and any departure of the frequency to the overtone crystal oscillator from its nominal value is compensated by adjusting the low frequency oscillator.