Television – Basic receiver with additional function – Multimode
Reexamination Certificate
1997-12-10
2001-01-09
Peng, John K. (Department: 2714)
Television
Basic receiver with additional function
Multimode
C348S021000, C348S041000, C348S454000, C348S457000, C348S500000, C348S505000, C348S506000, C348S507000, C348S508000, C348S554000, C348S555000, C348S557000, C348S558000, C348S638000, C348S640000, C348S641000, C348S912000, C386S349000, C386S349000, C386S349000
Reexamination Certificate
active
06172713
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of color television broadcasting system determination circuits (hereafter referred to as the “color system determination circuit”) in color television receivers.
BACKGROUND OF THE INVENTION
Television receivers for multiple color television broadcasting systems including PAL and NTSC incorporate a color system determination circuit for automatically determining the type of color television broadcast signal received.
The Japanese Laid-open Patent No. S63-131680 discloses one such type of color system determination circuit.
The color system determination circuit of the prior art employs two clock oscillators for determining color systems. Specifically, this color system determination circuit has two clock oscillators for producing two different color subcarrier frequencies. These two clock oscillators are switched for oscillation, and the broadcasting system of the television input signal is checked and determined based on these oscillation signals. The prior art may require a certain period of time for making a determination.
SUMMARY OF THE INVENTION
A color system determination circuit of the present invention comprises a color trap filter for attenuating a frequency component of the input video signal, and a comparator for comparing the color burst signal in the output of the color trap filter and the frequency component of the input video signal. The frequency component is preferably a color subcarrier component. In other words, the present invention employs the color trap filter for attenuating the color subcarrier component of one type of color broadcast signal in probable color television broadcast signals to be received. The color system of the input signal is determined by comparing the color burst signal of the input signal and the color burst signal output from the color trap filter.
The present invention can therefore offer a high-speed color system determination circuit which shortens the time required for determining color systems.
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Matsushita Electric - Industrial Co., Ltd.
Peng John K.
Ratner & Prestia
Yenke Brian P.
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