Frequency tracking arrangements

摘要

A frequency tracking arrangement in which a frequency tracking circuit utilises a continuously variable analogue first order all-pass filter circuit as a controllable phase-shift element in a closed-loop system which produces a control signal to control the phase shift circuit to introduce a 90 DEG phase shift of a received reference frequency signal when the circuit is tracking that reference frequency. The control signal may then be utilised to slave the cut-off frequency of a filter and/or the delay time introduced by a delay line. <IMAGE>