| 摘要 |
PURPOSE:To obtain an APC circuit of a PAL system whch produces no DP by constituting of a phase comparator, a 1H delay circuit, an adder, an LPF and a variable frequency oscillator. CONSTITUTION:The phse comparison action of a phase comparator 3 is controlled by a burst gate pulse (b) sent from a terminal 2. Then the comparator 3 performs the phase comparison between a color burst signal A contained in a carrier chrominance signal (a) sent from a terminal 1 and the output of a variable frequency oscillator 7. The phase of the signal A repeats +45 deg. and -45 deg. for each line and therefore the output of the comparator 3 has a waveform (c). Thus the output of a 1H delay circuit 4 has a waveform (d) and therefore the output of an adder 5 has a waveform (e). Thus it is possible to remove the factor for generation of a frequency component of 1/2 horizontal scan frequency, i.e., DP which is due to a fact that the phase of the signal A has a shift by 90 deg. every line. This attains an APC circuit of a PAL system which is free from generation of DP. |
