VARIABLE GAIN AMPLIFIER CIRCUIT

摘要

PURPOSE:To attain automatic gain control without distortion by giving a gain control voltage corresponding to the amplified output via a diode to a connecting point between the 1st and 2nd transistors (TR) so as to employ conventional TRs. CONSTITUTION:A collector of the 1st TR2 of common emitter and an emitter of the 2nd TR3 of common base are connected, a signal is outputted from a collector of the 2nd TR3 and an AGC voltage corresponding to the output is given to a connecting point between the collector of the 1st TR2 and the emitter of the 2nd TR3. Thus, the control gain depends only on the current amplification factor of the 1st and 2nd TRs and it is possible to vary it in a wide range.