Adaptive oscillator apparatus for use in a phase-lock loop

摘要

A phase-lock loop system incorporates a normally "transparent" oscillator used in detecting whether or not the system is in a locked condition. It is essential that the oscillator, a portion of which is serially involved in the phase-lock loop, have a long time constant, so as to minimally affect the closed loop's transfer function during phase-locked conditions. It is desirable, however, that when the phase-lock loop loses lock that the time constants of the transparent oscillator change to much smaller values for quick response of the oscillator and operation at a high frequency for detection purposes and quick extinction when phase-lock is acquired. The detection of oscillation of the transparent oscillator initiates the application of a low speed sweep signal being applied to the voltage controlled oscillator portion of the phase-lock loop to reestablish phase-locked conditions and eventually return of the transparent oscillator to its long time constant values.