| 摘要 |
PURPOSE:To automate an operation mode changeover by discriminating whether an input signal is an NTSC subcarrier signal or a PAL subcarrier signal based on a signal in response to the frequency of the input signal and using a discrimination output so as to generate a correction signal in response to the kind of the subcarrier signal. CONSTITUTION:An input signal detection circuit 1 outputs a 1st detection signal when an NTSC subcarrier signal fsc is inputted and outputs a 2nd detection signal when a PAL subcarrier signal fsc is inputted. A correction circuit 2 compares the detection signal with a reference voltage to generate a correction use difference S2 and it is fed back to the detection circuit 1 to correct the detection. A discrimination circuit 3 compares the detection signal with the reference voltage so as to discriminate whether the signal given to the input signal detection circuit 1 is an NTSC subcarrier signal fsc or a PAL subcarrier signal fsc. Thus, the cut-off frequency of the active filter 4 is adjusted or the changeover of the operating mode of the synchronization system circuit of the chroma system or the like is implemented automatically.
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