AMPLIFIER CIRCUIT

摘要

PURPOSE:To vary the amplification gain by the current control by comparing a feedback current of an operational amplifier with a reference current of a voltage follower so as to vary the resistance value of the voltage follower thereby varying the gain of the operational amplifier corresponding to the varied resistor. CONSTITUTION:The relation expressed in equation 1 exists between an input signal Vin and an output signal Vout of an amplifier A1 and a gain Gv is decided by equation (2). A resistor R4 consists of the voltage follower and when the input signal Vin rises and the resistance value is regarded as a infinite value, the gain is varied with Gv 1 from the equation (2). That is, the output voltage is limited in the amplifier A1 according to the level change of the input signal Vin. When the output impedance of the voltage follower 1 is regarded nearly as re (emitter resistor of a transistor Q1 or Q2) when the relation of Ix<=Io exists in the feedback current Ix of the amplifier.