CHROMINANCE CONTROL CIRCUIT FOR A DIGITAL TELEVISION RECEIVER

摘要

In a chroma control circuit for a digital television receiver, the system clock lies in the range of four-times the chrominance-subcarrier frequency. The originally received color-burst signal is locked in frequency and phase to the system clock by means of an all-digital phase-locked loop. The phase-difference angle between the color-burst signal and the system clock appears as a sine or cosine value in the two standard color-difference signals of the chrominance demodulator during the reception of the color-burst signal. One of the standard color-difference signals, the B-Y signal, is fed through a horizontal-frequency-suppressing loop filter to a digital oscillator. The latter determines the speed of rotation of a hue adjustment angle rotating at approximately constant angular speed. The respective sine and cosine values of the hue adjustment angle are read as data values from first and second read-only memories, respectively, and are fed to the sine and cosine inputs of a hue adjuster in a calculating stage which derives the color-burst signal and the chrominance signal.