Clamping circuit for color television signals

Abstract

A clamping circuit for color television signals includes a demodulator for demodulating the chrominance component of the color television signals to produce first and second color difference signals, and first and second adders for adding adjustable first and second control signals to the first and second color difference signals so as to produce modified first and second color difference signals. A matrix circuit is responsive to the outputs from the first and second adders to produce a third color difference signal. A reference signal, which represents a predetermined level of a color television signal, such as the pedestal level, is added to each of the color difference signals; and a first comparator compares the first color difference signal, with the reference signal added thereto, to the third color difference signal, with the reference signal added thereto, and a second comparator compares the second color difference signal, with the reference signal added thereto, to the third color difference signal, with the reference signal added thereto. At the times of occurrence of the pedestal level of the color television signal, the outputs from the first and second comparators are sampled, respectively, to produce the first and second control signals which are fed back and added to the first and second color difference signals. In one embodiment, the reference signal is a d.c. level proportional to the pedestal level of the color television signal. In another embodiment, the reference signal is the luminance component of the color television signal clamped to the pedestal level. This clamped luminance signal is produced by another clamp circuit.