Oscillators – Automatic frequency stabilization using a phase or frequency... – Plural a.f.s. for a single oscillator
Patent
1991-06-04
1993-02-02
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
Plural a.f.s. for a single oscillator
331 20, 331 25, 358158, H03L 706, H04N 505
Patent
active
051840910
ABSTRACT:
An adaptive oscillator control system for use in television receivers or monitors includes a phase locked loop together with a static phase error correction system which responds to long term error signals of significant magnitude within the phase locked loop to adjust the free-running frequency of the oscillator. An oscillator range control includes a processor having a plurality of established oscillator frequency ranges which are identified by oscillator range code numbers. A measuring counter and clock circuit cooperate to count the number of clock signals occurring during the horizontal sync reference signal period to establish a frequency reference number. A first frequency approximation is provided based upon the oscillator range code number or a known standard scan frequency. A frequency detector examines the oscillator output and provides a second frequency approximation to adjust the oscillator frequency until it falls within the appropriate frequency range. A confidence circuit examines the consistency of oscillator frequency maintenance within the appropriate frequency range and upon establishing the desired confidence level enables the phase locked loop to provide synchronization. Thereafter, a lock detector responds to the occurrence of frequency and phase lock by the phase lock loop to enable the static phase error corrector and deactivate the oscillator range control system. The lock detector upon detecting horizontal synchronization, for broadcast type video, increases the second frequency approximation range.
REFERENCES:
patent: 4680555 (1987-07-01), Waldeck
patent: 4761587 (1988-08-01), Wharton
patent: 4991023 (1991-02-01), Nicols
patent: 4996596 (1991-02-01), Hirao et al.
Grimm Siegfried H.
Zenith Electronics Corporation
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