System and method for decoding a quadrature ampliture modulated signal

Abstract

A video signal decoder using a sample clock tied to a frequency that is an integer multiple of four times the color subcarrier (4*Fsc). By using a 4*Fsc rate on a given input wave, the decoder determines the phase shift between the sample clock and the original wave being sampled. Then, the decoder calculates the color based upon that shift. Circuitry for implementing the decoder contains two major circuit paths. The decoding process consists of two main phases and each path performs a different function during each phase. During the first phase, the first path calculates constants based upon a user's hue and saturation adjustments used for chroma demodulation. Also during the first phase, the second path examines the color burst signal and from that signal finds the black level of the incoming video signal. During the second phase, the first path decodes the color in the TV signal using the constants calculated during the first phase. Also during the second phase, the second path pulls the luma information out of the signal line.

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