| 摘要 |
PROBLEM TO BE SOLVED: To provide a video image voice receiving circuit which functions AFT (Automatic Frequency Tuning) as much as possible even in an area where an electric wave is weak, and can clearly receive the video image and voice. SOLUTION: The circuit is provided with a limiter 42 which amplifies a voice intermediate frequency signal, a signal strength detector 46 which is connected to the limiter 42, and detects strength of the voice intermediate frequency signal, and a comparison circuit 31 in which output voltage of the signal strength detector 46 is connected to one input terminal, a reference voltage is applied to another input terminal, and its output terminal is connected to the AFT circuit 30. The comparison circuit 31 comprises a switch circuit which changes over the output voltage when strength of the voice intermediate signal is weak, and makes operation of the AFT circuit 30 stop. Since the reference voltage of the comparison circuit 31 is possible to be optimally set, the AFT function can continuously operate as long as possible even when the input signal is weak. COPYRIGHT: (C)2005,JPO&NCIPI
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