The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 06, 1977
Filed:
Jan. 16, 1976
Judson A Hofmann, Schaumburg, IL (US);
Zenith Radio Corporation, Glenview, IL (US);
Abstract
A frequency scanning automatic phase control includes a phase detector, a local oscillator and an APC filter. A coincidence detector includes an AND gate responsive to the horizontal retrace and reference synchronizing pulses. A lock detector also responsive to the retrace and reference sync pulses produces an output signal when a predetermined interval of non-coincidence has existed. An AND gate responsive to both the lock detector and coincidence detector gates a current sink which unbalances the phase detector producing a ramp-like error voltage across the APC filter. A threshold detector coupled to the APC filter activates a discharge circuit also coupled to the filter when the filter voltage exceeds the threshold. The oscillator responds to the variations of error voltage and changes frequency accordingly. Once coincidence occurs frequency variation ceases and is resumed only if non-coincidence returns.