Frequency generator with a controlled limit on frequency deviation from a synchronizing frequency

摘要

A digital counter driven by a stable high frequency source generates a periodic signal synchronized to an external signal source. Gating circuitry responsive to particular digital counts, accumulated by the counter, defines precise quantized time intervals. The external signal is examined during these quantized time intervals for the occurrence of significant cyclic events such as zero crossing. A single occurrence of cyclic event is determined during a first time interval while successive multiple occurrences of the cyclic event are searched for during a second but smaller time interval. In each instance failure of the event searched for activates corrective circuitry to inhibit synchronous oscillation with the external signal source.