| 摘要 |
An NTSC/PAL signal discriminating circuit automatically adjusts the trap center frequency of an active filter in accordance with the frequency of an input signal. The discriminating circuit operates to generate a signal of an amplitude corresponding to the frequency of an input signal and discriminating, in accordance with the amplitude of the signal thus generated, whether the input signal is a subcarrier signal of the NTSC format or that of the PAL format. The trap center frequency of the active filter is then adjusted in accordance with such discrimination output, and the value of a correction signal for switching the operation mode of a chrominance synchronizing circuit and so forth; wherein automatic adjustment is executed to perform a predetermined operation in each mode of the NTSC and PAL signals without the necessity of inputting any external NTSC/PAL switching signal.
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