Frequency Interleaved Sampling of a Color Television Signal

Abstract

In the transmission of color television signals over a digital communications system, the analog TV signal must first be converted to digital form. This paper treats the first step in this conversion, sampling of the analog waveform. A significant reduction in sampling rate can be achieved by using several properties of the television signal. The spectrum of the TV signal has the energy concentrated at harmonics of the line and field rates. By choosing a sampling rate that is less than twice the bandwidth and a frequency that is an odd multiple of one-half the line rate, the aliased energy resulting from the sampling process falls in the gaps of the video signal energy. A comb filter is then used to remove most of the aliased energy. The resulting signal shows no appreciable deterioration. The subjective effects of noise added between harmonics of the line rate are discussed. These results are used to determine the requirements of the comb filter. The key parameters of one form of a comb filter are developed. A quantitative evaluation of the comb filter parameters shows that adequate suppression of the aliased energy can be achieved.