Abstract A circuit deployed in a color televison receiver for varying the brightness, contrast and color saturation of a displayed picture in accordance with variations in ambient light in the vicinity of a receiver screen is disclosed comprising a light sensing means mounted near the receiver screen and having an electrical parameter which varies in accordance with variations in the light incident on the light sensing means and means responsive to those variations in the electrical parameter for varying the gains imparted to both the luminance and chrominance signals. In the disclosed preferred embodiment the light sensing means is a light dependent resistor such as a simple cadmium sulphide cell the resistance of which varies in response to changes in the light impinging thereon. These variations in resistance are used to control the gain of both the chrominance and the luminance amplifiers of the receiver and in one preferred embodiment these resistance variations were transferred by way of a light emitting diode and second light dependent resistor to the luminance amplifier stage in order to isolate the luminance amplifier from the original light dependent resistor.
In a television receiver, picture tube means for displaying a televised signal, signal receiving means for receiving a transmitted signal and processing said signal to provide a video component, means for sensing ambient light intensity to provide an ambient modifier, means for amplifying said video component, said last means comprising an amplifying member having a load component, means for modifying said video component with said ambient modifier being in parallel with said load component, said last means comprising circuitry to provide predetermined variations in black level display on said picture tube means.
Claim 2
Dependent Claim
92 words
In a television receiver, picture tube means for displaying a televised signal, signal receiving means for receiving a transmitted signal and processing said signal to provide a video component, means for sensing ambient light intensity to provide an ambient modifier, means for amplifying said video component, said last means comprising an amplifying member having a load component, means for modifying said video component with said ambient modifier being in parallel with said load component, said last means comprising circuitry to provide predetermined variations in black level display on said picture tube means.
Claim 3
Dependent Claim
49 words
The receiver of claim 1 with said last means comprising a parallel circuit having capacitive means in one branch and resistive means in a parallel branch whereby the A.C. signal in the video component is altered in accordance with ambient light to provide said predetermined variations in black level.
Claim 4
Dependent Claim
72 words
The receiver in claim 1 with: said means for amplifying said video component comprising a transistor having an emitter, base and collector, with said collector having a load circuit, said means for modifying said video component comprising a light dependent resistor being in parallel with said load circuit, said circuitry to provide predetermined variations in black level comprising parallel circuitry having capacitive means in one branch and resistive means in another branch.