Satellite television broadcasting receiver including improved clamping circuit
First Claim
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1. A satellite television broadcasting receiver comprising:
- a channel selecting circuit for receiving, as an input signal, a first intermediate frequency signal obtained by frequency converting a plural channel of radio waves received from a satellite and for frequency converting said first intermediate frequency signal into a second intermediate frequency signal such that a selected channel of the second intermediate frequency signal has a predetermined frequency;
a band-pass filter for receiving said second intermediate frequency signal and for passing therethrough only a desired FM signal of said selected channel of said second intermediate frequency signal;
an FM demodulator for demodulating the desired FM signal so as to obtain a pre-emphasized video signal which has been pre-emphasized at a transmitter;
a de-emphasis circuit for de-emphasizing the pre-emphasized video signal;
a low-pass filter, receiving an output signal of said de-emphasis circuit, for passing therethrough only a video signal;
a first amplifier for amplifying said video signal from said low-pass filter and outputting an amplified video signal;
a first clamping circuit for clamping the amplified video signal and outputting a clamped video signal;
a second amplifier for amplifying the clamped video signal and outputting a second amplified video signal; and
a second clamping circuit for clamping the second amplified video signal and outputting a second clamped video signal,wherein each of said first clamping circuit and said second clamping circuit has an input terminal and an output terminal and each comprises;
a capacitor connected at a first end to said input terminal and connected at a second end to said output terminal;
a DC power source; and
a transistor having an emitter connected to said output terminal and a base connected to said DC power source.
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Abstract
The present invention relates to a satellite television broadcasting receiver which receives waves from a satellite, selects a broadcasting channel and obtains an FM demodulated video signal by passing a selected signal through the band-pass filter. In this satellite television broadcasting receiver, the video signal superposed with a large energy dispersion signal is inputted to the first clamping circuit at a low level, to eliminate the energy dispersion signal. Thus, a room is provided in the dynamic range of the amplifier at the later stage and the DG and DP of the amplifier at the later stage are maintained at a satisfactory level by the second clamping circuit. As a result, even in the case of a satellite television broadcasting in which the level of the energy dispersion signal superposed on the video signal is large, distortion which occurs due to the nonlinearity of the amplifier can be reduced substantially so that the image can be reproduced on the screen in a satisfactory condition without an interference of flickering.
12 Citations
2 Claims
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1. A satellite television broadcasting receiver comprising:
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a channel selecting circuit for receiving, as an input signal, a first intermediate frequency signal obtained by frequency converting a plural channel of radio waves received from a satellite and for frequency converting said first intermediate frequency signal into a second intermediate frequency signal such that a selected channel of the second intermediate frequency signal has a predetermined frequency; a band-pass filter for receiving said second intermediate frequency signal and for passing therethrough only a desired FM signal of said selected channel of said second intermediate frequency signal; an FM demodulator for demodulating the desired FM signal so as to obtain a pre-emphasized video signal which has been pre-emphasized at a transmitter; a de-emphasis circuit for de-emphasizing the pre-emphasized video signal; a low-pass filter, receiving an output signal of said de-emphasis circuit, for passing therethrough only a video signal; a first amplifier for amplifying said video signal from said low-pass filter and outputting an amplified video signal; a first clamping circuit for clamping the amplified video signal and outputting a clamped video signal; a second amplifier for amplifying the clamped video signal and outputting a second amplified video signal; and a second clamping circuit for clamping the second amplified video signal and outputting a second clamped video signal, wherein each of said first clamping circuit and said second clamping circuit has an input terminal and an output terminal and each comprises; a capacitor connected at a first end to said input terminal and connected at a second end to said output terminal; a DC power source; and a transistor having an emitter connected to said output terminal and a base connected to said DC power source.
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2. A satellite television broadcasting receiver comprising:
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a channel selecting circuit for receiving, as an input signal, a first intermediate frequency signal obtained by frequency converting a plural channel of radio waves received from a satellite and for frequency converting said first intermediate frequency signal into a second intermediate frequency signal such that a selected channel of the second intermediate frequency signal has a predetermined frequency; a band-pass filter for receiving said second intermediate frequency signal and for passing therethrough only a desired FM signal of said selected channel of said second intermediate frequency signal; an FM demodulator for demodulating the desired FM signal so as to obtain a pre-emphasized video signal which has been pre-emphasized at a transmitter; a de-emphasis circuit for de-emphasizing the pre-emphasized video signal; a low-pass filter, receiving an output signal of said de-emphasis circuit, for passing therethrough only a video signal; a first amplifier for amplifying said video signal from said low-pass filter and outputting an amplified video signal; a pulse clamping circuit comprising; an input terminal receiving said amplified video signal from said first amplifier and an output terminal, a switching circuit connected to said input terminal and selectively providing a constant voltage to said amplified video signal that is input to said input terminal, in accordance with a control signal, an inversion amplifier receiving said amplified video signal and providing an output based on inversion amplifying the amplified video signal, a peak holder circuit for receiving said output of said inversion amplifier and providing an output representing a peak of said output of said inversion amplifier, a level shifter circuit for receiving said output of said peak holder circuit and shifting a level thereof by a given amount to obtain a level shifted output, and a comparator for comparing said level shifted output of said level shifter circuit to the output of said inversion amplifier and generating said control signal in response thereto; a second amplifier for amplifying the video signal clamped by said switching circuit and outputting a second amplified video signal; and a clamping circuit for clamping the second amplified video signal output from said second amplifier so as to output a clamped video signal.
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Specification
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Current AssigneeMatsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
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Original AssigneeMatsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
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InventorsShogaki, Toshihiro, Kawakami, Shigeru, Omoto, Noriaki
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Primary Examiner(s)Groody, James J.
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Assistant Examiner(s)HSIA, SHERRIE Y
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Application NumberUS08/424,568Time in Patent Office372 DaysField of Search348/725, 348/729, 348/726, 348/731-735, 348/737, 348/738, 358/695, 358/188, 358/189, 358/191.1, 358/195.1, 358/198, 358/197, 358/172, 455/43, 455/3.2, 455/205, 455/214, 455/311US Class Current348/695CPC Class CodesH04N 5/60 for the sound signalsH04N 7/045 the carrier being frequency...H04N 7/20 Adaptations for transmissio...
