Patent Document ID: 4020490
Application ID: 05525477
Patent Flag: 1

Claim One:
1. Apparatus for synthesizing the frequency of an unknown periodic input signal which may be accompanied by noise comprising source means providing a periodic signal of variable frequency adapted for locked operation at a sample frequency which is a predetermined multiple of said input signal, first sample means responsive to said source means for providing a first sample of said input signal for a known time interval less than one half of the period of said input signal, control means generating a control signal having a level related to the magnitude and polarity of said first sample for relatively rapidly altering the frequency of said source means in response to said control signal, second sample means responsive to said source means for providing a second sample of said input signal for a predetermined time interval less than one half of the period of said input signal, sweep means generating a sweep signal which relatively slowly alters the frequency of said source means, and means responsive to an output of said second sample means to disable said sweep means when said output of said second sample means has a predetermined polarity.