Phase locked loop tuning control system including a timed sync a

Details Phase locked loop tuning control system including a timed sync a Phase locked loop tuning control system including a timed sync a

1981-05-08

1983-05-24

Murray, Richard

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

3581951, 455182, H04N 544

Patent

active

043853153

ABSTRACT:
In a phase locked loop PLL tuning control system for a voltage controlled oscillator of the type wherein an automatic fine tuning (AFT) voltage is selectively applied to the local oscillator after a PLL configuration has obtained lock at the nominal frequency value for the selected channel so as to accommodate frequency translated RF carriers, an AFT control circuit selectively activated by the average level of composite synchronization pulses indicative of an improper tuning condition caused by certain translated carriers clamps the AFT voltage at a predetermined level. The predetermined level is selected to force the local oscillator frequency to be driven to an offset value at which an offset detector causes reinitiation of PLL control at discrete frequency step from the nominal value for the selected channel so as to properly tune the translated carrier. A timed switching arrangement only allows the AFT control circuit to operate for a predetermined time after a new channel is selected so that channels, such as music channels, which do not provide synchronization pulses, can be tuned.

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U.S. Patent Application S.N. 211,704 entitled "Phase Locked Loop Tuning Control System Including a Sync Activated AFT Signal Seeking Arrangement", filed in the name of M. P. French on 12-1-80.
U.S. Patent Application S.N. 261,450 entitled "Dual Search Mode Type Tuning System", filed in the names of J. Tults and M. P. French on 5-8-81.

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