US Patent 7154563 Automatic brightness limitation for avoiding video signal clipping

A brightness limitation system is employed in a television circuit to prevent the black reference voltage level and the video signal from entering a minimum signal clipping zone, to provide precise correction signal, limiting the brightness, to maintain a constant black reference voltage level, and maintain a video signal with dynamic amplitude. The brightness limitation circuit detects a minimum signal level amongst the black reference signals from each color channel and compares the minimum signal with a fixed voltage level to generate a brightness feedback signal. The brightness feedback signal is then used to modify the black reference signal level for each color channel.