| 摘要 |
An AGC circuit comprises a variable gain amplifier that has a gain set variably and amplifies an input signal with the gain; a detection circuit that detects an output signal amplified by the variable gain amplifier; an error amplifier that outputs an error voltage corresponding to a difference voltage between a detected voltage indicating amplitude of the detected output signal and a reference voltage for fixing the amplitude of the output signal to be at a predetermined degree; a capacitor that is charged depending on the error voltage and holds a setting voltage for fixing the gain of the variable gain amplifier to be constant that is applied to a gain setting input of the variable gain amplifier; and a charging switch circuit that is closed to permit charging the capacitor until the charged voltage of the capacitor reaches the setting voltage and is opened to forbid charging the capacitor after the charged voltage reaches the setting voltage.
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