70_dB_VOLTAGECONTROLLED_GAIN

Published:2009/6/25 22:24:00 Author:May | From:SeekIC

Amplifier Q1 uses current source Q2 as emitter resistor to provide correct current bias for class A operation. Coupling through 150-μF capacitor to silicon diode string D1-D8 provides variable re-sistance needed to achieve variable gain. Sim-ple differential amplifier Q3-Q4 adjusts forward bias of diodes to change their forward resis-tanco. Increasing positive control voltage from 0 to 4.5 V changes voltage gain from -74 dBm to about -4 dBm with respect to 0-dBm input signaL-N.A Steiner, Voltage-Controlled Am-plifier Covers 70 dB Range, EDN Magazine, March 5, 1975, p 72 and 74.



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