Subcarrier regeneration circuit for color television receivers

摘要

In a subcarrier regeneration circuit for color television receivers, a phase detector output is sampled by a signal sample-and-hold circuit and a bias sample-and-hold circuit to develop a voltage between the outputs of the two sample-and-hold circuits to control the frequency of a 3.58 MHz subcarrier generated by a voltage controlled oscillator. The oscillator output is phase shifted by 90 DEG and applied to one input of the phase detector for comparison with a gated color burst. The signal sample-and-hold circuit samples the phase detector output during the interval of the color burst, while the bias sample-and-hold circuit samples the phase detector output during an interval which is substantially equal to the flyback interval minus the color burst interval.