| 摘要 |
PROBLEM TO BE SOLVED: To provide an automatic level control (ALC) circuit capable of shortening a return time after a large level input while keeping the distortion performance. SOLUTION: The ALC circuit 30 is provided with a variable attenuator 1, an amplifier 3 for amplifying a low-frequency signal Vs which has passed through the attenuator 1, two detectors 4a, 4b for detecting a low-frequency signal V1 which has been amplified, a short time constant circuit 14 charged with a low-frequency signal voltage V2 which has been detected and a long time constant circuit 15 having a charge acceleration switch 19, a level comparator 17 for comparing the charging voltage V2 on the circuit 14 side with a voltage V4 on the circuit 15 side, and a timer circuit 18 for allowing the switch 19 to conduct to discharge the electric charges of a capacitor C3 rapidly, when the duration time of a state that the voltage V4 on the circuit 15 side is larger than a prescribed potential difference compared with the voltage V2 on the circuit 14 side becomes not less than a prescribed time T1. The circuit 30 has a feedback structure in which the voltage V3 on the circuit 15 side is inputted as a control signal S of the attenuator 1. |
