AUTOMATIC GAIN CONTROL CIRCUIT AND SINE WAVE OSCILLATION CIRCUIT EMPLOYING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide an automatic gain control circuit for extending a dynamic range by increasing a gain variable width.;SOLUTION: The automatic gain control (AGC) circuit includes: an input terminal 1 for receiving an input signal IN; an output terminal 3 for outputting an output signal OUT; an operational amplifier 2; an inverting circuit 10; and control circuits 13, 14, 15. There are provided a depletion MOS transistor (DMOS) 4 connected between an inverting input terminal of the operational amplifier 2 and ground and whose resistance changes with a control signal S1; and a DMOS 7 connected between an output terminal and the inverting input terminal of the operational amplifier 2 and whose resistance varies with a control signal S2. The inverting circuit 10 receives the control signal S1, inverts the received control signal S1 to produce the control signal S2 and gives the control signal S2 to the DMOS 7. The control circuits 13, 14, 15 obtain an error between the output signal OUT and a reference signal VT, generates the control signal S1 corresponding to the error and gives the control signal S1 to the inverting circuit 10.;COPYRIGHT: (C)2007,JPO&INPIT