| 摘要 |
PROBLEM TO BE SOLVED: To obtain a sufficient reception level in the case of channel selection and to keep a selected channel in a good state in the case of usual reception. SOLUTION: An input signal is fed to a gain control(GC) amplifier 41, from which an output signal is fetched, this output signal is fed to a level comparator circuit 42, where the level is compared with, e.g. a level of the signal at a position of a horizontal synchronizing signal. Then the comparison output is fed to a control terminal of a gain control amplifier 41 through a low pass filter circuit 43 and an amplifier 44. Thus, automatic gain control(AGC) is conducted and this response speed is controlled by a cut-off frequency of the lower pass filter circuit 44 and a gain of the amplifier 44. Then the cur-off frequency and the gain are set by a setting value (digital value) of a register 45 controlled by, e.g. a controlling microcomputer.
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