Video amplifier for a color television apparatus

Claim 2

A video amplifier for a color television apparatus for amplifying a video signal having different intensity levels, comprising: means for interposing black and white reference pulses into the former and latter halves of the horizontal retrace period respectively to be amplified by the video amplifier with the video signal, sampling means for sampling the peak amplitudes of said black and white reference pulses at the output of the video amplifier, and control means for controlling the DC level and the gain of the video amplifier according to the outputs from said sampling means.

Claim 3

A video amplifier according to claim 1, wherein said black reference pulse has a predetermined amplitude corresponding to the cut-off voltage of each electron gun of a picture tube, and said white reference pulse has a controllable amplitude which changes depending on the setting of a contrast control.

Claim 4

A video amplifier according to claim 1, wherein said means for interposing said black and white reference pulses includes: a counter for counting a clock pulse of a given frequency generated upon receiving a horizontal gate pulse, and three identical current summing circuits for interposing said black and white reference pulses into the horizontal retrace period under control of said counter.

Claim 5

A video amplifier according to claim 1, wherein said control means includes comparator means for comparing the samples from said sampling means with a controllable reference signal so as to compensate for differences in electrical characteristics of each electron gun and also of different picture tubes.

Claim 6

A video amplifier for a color television apparatus for amplifying a video signal having different intensity levels between black and white levels having brightness and contrast controls, comprising: three identical DC coupled video amplifiers for amplifying three color video signal components at a controllable gain and a fixed quiescent DC level, a white reference pulse generator for generating a white reference pulse whose amplitude varies depending on the setting of the contrast control, a black reference pulse generator for generating a black reference pulse of fixed amplitude corresponding to the cut-off voltage of the electron guns of the picture tube, current summing means for inserting said black and white reference pulses into the horizontal retrace period to apply said reference pulses together with the three video signals to said three video amplifiers, and for superimposing the three color video signals with the brightness control signal, sampling means for sampling said black and white reference pulses transmitted to the output terminl of the video amplifier, and control means for controlling the DC level and gain of each video amplifier by samples of said black and white reference pulses respectively.

Claim 7

A video amplifier for a color television apparatus for amplifying a video signal having different intensity levels between black and white levels having brightness and contrast controls, comprising: three identical DC coupled video amplifiers for amplifying three color video signal components at a controllable gain and a fixed quiescent DC level, a white reference pulse generator for generating a white reference pulse whose amplitude varies depending on the setting of the contrast control, a black reference pulse generator for generating a black reference pulse of fixed amplitude corresponding to the cut-off voltage of the electron guns of the picture tube, current summing means for inserting said black and white reference pulses into the horizontal retrace period to apply said reference pulses together with the three video signals to said three video amplifiers, and for superimposing the three color video signals with the brightness control signal, sampling means for sampling said black and white reference pulses transmitted to the output terminl of the video amplifier, and control means for controlling the DC level and gain of each video amplifier by samples of said black and white reference pulses respectively.

Claim 8

A video amplifier according to claim 5, wherein said white reference pulse generator includes a circuit for generating a DC signal corresponding to the amplitude of said white reference pulse, which is applied to the brightness control in order to eliminate the interaction between the contrast and brightness controls, controlling the brightness control range.

Claim 9

A video amplifier for a color television apparatus according to claim 5, said current summing means, comprising: a current source, first and second transistors connected in series between said current source and said white reference pulse generator, the common junction of said first and second transistors being connected to the video signal, and third transistor connected in parallel with said first and secoNd transistors.

Claim 10

A video amplifier for a color television apparatus according to claim 7 wherein said first and second transistors are turned off while said white reference pulse generator is generating the white reference pulse.

Claim 11

A brightness and contrast control circuit for a TV apparatus comprising: means for controlling the contrast of the TV apparatus, means for controlling the brightness of the TV apparatus including a pair of signal paths defining resistance means and amplifier means, and means for receiving a control signal relating to said frist mentioned means to provide the control signal to both of said signal paths in a selectable different proportion.

Claim 12

A brightness and contrast control circuit for a TV apparatus comprising: means for controlling the contrast of the TV apparatus, means for controlling the brightness of the TV apparatus including a pair of signal paths defining resistance means and amplifier means, and means for receiving a control signal relating to said frist mentioned means to provide the control signal to both of said signal paths in a selectable different proportion.

Claim 13

A brightness and contrast circuit according to claim 9 wherein said means for receiving a control signal is a potentiometer connected at a movable top thereof to said first mentioned means and at both fixed terminals to said amplifier means and resistance means.

Claim 14

A brightness and contrast circuit according to claim 10 wherein said amplifier means is an operational amplifier including input resistor means, a feedback resistor and output resistor means.

Claim 15

A brightness and contrast circuit according to claim 11 wherein said resistor means are substantially the same resistive value and said brightness control means includes second operational amplifier means whose input is connected to the input terminal of said pair of signal path.