Automatic brightness-contrast control using photoresistive element to control brightness and agc voltages in response to ambinent light

Claim 1

AN AUTOMATIC CONTRAST CONTROL CIRCUIT FOR A TELEVISION RECEIVER HAVING A PICTURE TUBE INCLUDING A VIEWING FACE WHICH IS STRUCK BY LIGHT FROM A SOURCE EXTERNAL TO SAID PICTURE TUBE COMPRISING: A KEYED AUTOMATIC GAIN CONTROL CIRCUIT HAVING AN ELECTRON DISCHARGE DEVICE INCLUDING A CATHODE AND CONTROL ELECTRODE, MEANS FOR ESTABLISHING A BIAS VOLTAGE BETWEEN SAID CATHODE AND CONTROL ELECTRODE, A VOLTAGE DIVIDER INCLUDING A PHOTO-CONDUCTIVE CELL AND AT LEAST ONE RESISTIVE ELEMENT CONNECTED SERIALLY, SAID CELL POSITIONED RELATIVE TO THE TELEVISION RECEIVER IN A MANNER SO AS TO BE STRUCK BY LIGHT OF THE SAME INTENSITY WHICH STRIKES THE VIEWING FACE OF SAID PICTURE TUBE, MEANS CONNECTING A VOLTAGE ACROSS SAID VOLTAGE DIVIDER, AND MEANS CONNECTING A POINT ON SAID VOLTAGE DIVIDER TO SAID BIAS MEANS WHEREBY THE CONTRAST LEVEL OF SAID RECEIVER INCREASES WITH AN INCREASE IN THE INTENSITY OF THE LIGHT STRIKING SAID VIEWING FACE AND DECREASES WITH A DECREASE IN THE INTENSITY OF THE LIGHT STRIKING SAID VIEWING FACE.