| 摘要 |
PURPOSE:To stabilize an output with respect to the fluctuation throughout the wide range of an input signal level and to obtain an even picture quality by adjusting a tuning frequency in the vicinity of the instantaneous value of a receiving frequency in response to the output of a demodulation circuit and making a pass band width smaller than an occupying frequency width as the input signal level is lowered. CONSTITUTION:The first control circuit 17 consists of a transistor Q3 inserted into the emitter side of a differential amplifier circuit constituting the second control circuit 18 and the output of a channel selection circuit 15 and the output of a low pass filter 16 are inputted to the base of the transistor Q3. The first control circuit 17 controls both narrow band variable tuning filters 5b, 5c in phase and the second control circuit 18 controls both the narrow band variable tuning filters 5b, 5c in differential manner. Thereby, when the input signal level is high, the pass band width of the variable band width variable tuning filter is widened and when the input signal level is low, the pass band width is controlled to be narrow.
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