Gain control arrangement useful in a television signal processing system

Abstract

In a color television receiver, first and second amplifiers are respectively included in the luminance and chrominance channels to permit control of contrast and saturation. The amplifiers have gain versus control voltage characteristics including linear portions extrapolated to cut off at predetermined voltages which may or may not be the same. A first potentiometer is coupled between a source of fixed voltage equal to the extrapolated cut off voltage of the first amplifier and a gain controlling voltage source. The gain controlling voltage may be produced by a circuit including an element responsive to ambient light. The wiper of the first potentiometer is coupled to the first amplifier to couple a voltage developed at a predetermined point of the first potentiometer to the first amplifier to control its gain. A second potentiometer is coupled between a source of voltage equal to the extrapolated cut off voltage of the second amplifier and the gain controlling voltage source to receive a portion of the gain controlling voltage in accordance with the ratio of the extrapolated cut off voltages of the first and second amplifiers. The wiper of the second potentiometer is coupled to the second amplifier to couple a voltage developed at a predetermined point of the second potentiometer to the second amplifier to control its gain. In this manner, the contrast of the receiver may be varied over a relatively wide range while saturation is maintained substantially constant.