Patent ID: 6844780

Claim:
An automatic gain control circuit connected to an amplifier capable of adjusting a gain with a control signal and having a time-constant circuit for smoothing an output voltage of said amplifier with a predetermined time constant and a control signal generation circuit for generating said control signal based on the output voltage of said time-constant circuit, characterized in that said time-constant circuit comprises: a capacitor; a voltage comparator for comparing a terminal voltage of said capacitor to an input voltage; a charging circuit for intermittently charging said capacitor in the case where said input voltage is relatively higher than said terminal voltage; a discharging circuit for intermittently emitting a discharging current from said capacitor in the case where said terminal voltage is relatively higher than said input voltage; and a charging and discharging speed setting unit for differentiating a charging speed of said charging circuit from a discharging speed of said discharging circuit.