Processing of analog video signals in digital transmission systems

Abstract

A system (FIGS. 1A-1C) for transmitting analog component video signals (Y, (R-Y), B-Y)) in digital form uses sharp cut-off low-pass filters (104-106) to bandlimit the signals. Chrominance signals are limted to one-half of the 4.2 MHz bandwidth of the luminance signal. Phase equalizers (107-109) are used to compensate for distortion caused by the sharp cut-off filters. Prior to sampling, the chrominance signals are comb-filtered by sharp cut-off comb filters (110-111) in the region where weighted sub-Nyquist sampling will cause spectral interleaving between the baseband spectrum and its replica. The luminance signals are sampled using a sampler (116) that uses a super-Nyquist sampling frequency, while the chrominance signals are sampled using samplers (117-118) that use a weighted sub-Nyquist sampling frequency. The signal samples are passed through digitizers (125, 127, 129), DPCM encoders (126, 128, 130), and a multiplexer (131) prior to being transmitted by a transmitter (132) on a 90 Mbps telephony trunk (150). Signals received at a receiver (200) are passed through a demultiplexer (201) and DPCM decoders (205, 207, 209), and are reconverted to analog form by D/A converters (211-213). The analog signals are filtered by gentle cut-off comb filters (214-216) and low-pass filters (217-219) to remove therefrom replicas of the baseband spectra. Since gentle cut-off filters introduce little phase distortion, no phase equalizers are needed at the receiver.