| 摘要 |
PURPOSE:To perform excellent conversion when the sampling frequency of an AD converting circuit is varied by controlling the cutoff frequency of a variable filter corresponding to the sampling frequency of the AD converting circuit and reducing the generation of return distortion caused by the AD converting circuit. CONSTITUTION:A video signal supplied to an input terminal 1 is supplied to a voltage-controlled variable filter(VCF) 4 through a synchronous separating circuit 2 and a switch 3 and a signal from this VCF 4 is supplied to the AD converting circuit 6 through a switch 5. A digital signal from this circuit 6 is supplied to a digital signal processing circuit 7. Further, the processed signal is supplied to a DA converting circuit 8, whose analog signal is supplied to an image receiving tube 11 through an LPF 9 and a driving amplifier 10. Then horizontal synchronizing pulses which are separated by the circuit 2 are supplied to a pulse multiplying circuit 12 to generate a clock signal which is a multiple of the number of samples in one horizontal period, and this signal is supplied to the circuits 6 and 7.
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