| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic gain control circuit capable of being normally operated even in the case of low power source voltage. SOLUTION: The automatic gain control circuit is constituted of a noninverted amplifier circuit 12 formed by inputting an input signal V11 in a noninverted input terminal (+) and performing negative feedback to an inverted input terminal (-) of the noninverted input terminal (+), a half-wave rectifier circuit 13 connected with output of the noninverted amplifier circuit 12, a level shift circuit 14 connected with the output of the half-wave rectifier circuit 13, a low-pass filter 18 connected with the output of the level shift circuit 14 and a third P channel type MOS transistor 19 whose gate electrode G3 is connected with the output of the low-pass filter 18 and whose source electrode S3 is connected with the input side of the noninverted amplifier circuit 12. Thus, normal operation is enabled even inn the case of low power source voltage by shifting output V13 of the half-wave rectifier circuit down by threshold voltage (|Vtp2|) of the second P channel type MOS transistor constituting the level shift circuit 14.
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