DC AMPLIFIER WITH AUTOMATIC GAIN CONTROL

摘要

PURPOSE:To simplify a circuit and to improve control accuracy by providing a DC offset voltage detection circuit so as to make control of the gain and DC offset possible by detecting only a positive peak value of an output signal in case detecting the peak value of an output signal. CONSTITUTION:A DC offset voltage detection circuit 17 is provided. The circuit 17 extracts a DC offset voltage from an output signal voltage of a main amplifier circuit 5. A level shift circuit 18 boosts the DC level by a half of the specified amplitude of the circuit 5 to obtain a potential 22. The potential 22 is made always constant even when the DC bias of the output is fluctuated. Since the LOW level of a negative signal of the circuit 5 is detected by a positive peak detection circuit 7a and its output voltage is a value lower by the base- emitter voltage of a transistor from the actual peak voltage. Thus, the output of the detection circuit 7a is controlled to be equal to the output voltage 23 to realize the stable state.