Satellite television broadcasting receiver including improved clamping circuit

Claim 2

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.

Claim 3

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 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.

Claim 4

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 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.