H - Electricity – 03 – J
Patent
H - Electricity
03
J
331/40
H03J 7/04 (2006.01) H03L 7/10 (2006.01) H04N 5/50 (2006.01)
Patent
CA 1202092
AUTO TUNING FOR AN OSCILLATOR ABSTRACT OF THE DISCLOSURE To adjust the free running frequency of a voltage controlled oscillator so that it is close enough to a target frequency for a phase locked loop to lock the frequency, a reference signal is derived from a stable external source. A derived signal is generated from the oscillator. The derived signal and the reference signal are applied to a comparison circuit which examines the relationship of a specific edge of the reference signal at times determined by the signal derived from the oscillator. If the oscillator is within its proper frequency range, the edge of the reference signal will have a certain relationship to the times determined by the derived signal. If this relation- ship is found to be improper, correction signals are applied to the oscillator. In the preferred embodiment, this occurs in a television receiver where the reference signal is based on a 3,58 megahertz signal. The examination which is made takes an output from a counter which divides by 455, specifically, the 160 count. Times T1 and T2 are developed based on the output of the oscillator, At time T1, the counter output should be low, but at time T2, the counter output should be high. Approximately a 1 microsecond tolerance is provided in both directions, Error is permitted to accumulate during a part of the vertical retrace time. If the error becomes too great, corrective action is taken.
448426
Lee Ronald B.
Srivastava Gopal K.
Macrae & Co.
Zenith Radio Corporation
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