| 摘要 |
PURPOSE:To make the cut-off frequency constant even when a gain for a prescribed frequency band is varied, to reduce the cost and to improve the characteristic in the vicinity of the cut-off frequency more stably with respect to the amplifier circuit in which the gain at a prescribed frequency band is made variable. CONSTITUTION:In the amplifier circuit 1 provided with a differential amplifier 2 amplifying an input signal VIN to provide an output of the amplified signal and a feedback circuit 6 feeding back an output signal VOUT from the differential amplifier 2 to an input terminal of the differential amplifier 2 to provide a prescribed frequency characteristic to the output signal VOUT, a variable impedance circuit 5 detects a voltage between terminals 3, 4 of the feedback circuit 6 and feeds back a current corresponding to the detected voltage and a current of a built-in current source to a terminal 9 in the feedback circuit. |
