| 摘要 |
A VCO control circuit features a first exclusive-OR gate to the inputs of which are applied signals derived from the VCO to provide an output signal that has a 90 DEG phase shift with respect to a reference signal. A second exclusive-OR gate serves as a phase detector for the output and reference signals and provides, after filtering, a frequency control voltage for the VCO. The control voltage has about the same amplitude regardless of the presence or absence of the reference signal.
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