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:
Feb. 11, 2003
Filed:
May. 12, 1999
Axel Kattner, Seevetal, DE;
Joachim Brilka, Hamburg, DE;
Koninklijke Philips Electronics N.V., Eindhoven, NL;
Abstract
For an optimal adjustment of the filter frequency of a signal filter, independently of external influences, process spreads and temperature fluctuations, a filter circuit for filtering at least one sound carrier in a composite video signal by at least one signal filter ( ) having at least one filter frequency which is adjustable in dependence upon a control signal, is characterized in that the filter circuit ( ) includes a reference filter ( ) whose filter frequency is adjustable in dependence upon the control signal and which shifts the phase of a reference signal applied thereto by a defined value when tuning the filter frequency to the frequency of said reference signal, in that a phase comparator ( ) is provided which receives the output signal of the reference filter ( ) and the reference signal, in that the control signal is derived from the output signal of the phase comparator ( ) in such a way that the reference filter ( ) is tuned to the frequency of the reference signal, and in that an output signal of a controlled oscillator ( ) of a phase-locked loop ( ) is used as a reference signal which serves for demodulating a sound signal modulated on the sound carrier and whose controlled oscillator ( ) supplies an output signal at the frequency of the sound carrier in the locked state of the phase-locked loop ( ).