VOLTAGE-CONTROLLED AMPLIFIER

PURPOSE:To make an input dynamic range wider with low distortion, by applying an input signal to the 1st differential amplifier, compressing logarithmically its output, using the 2nd differential amplifier having an expanding characteristic opposite to the compression and amplifying the output of the 1st differential amplifier. CONSTITUTION:A non-inverting output and an inverting output are obtained by a collector of transistors(TRs) Q4, Q5 from an input signal Vi applied to the 1st differential amplifier 30, and the outputs are compressed logarithmically by diodes D1, D2. The signal compressed logarithmically is applied to the 2nd differential amplifier 40, where the signal is expanded logarithmically, then a linear output waveform VO similar to the input signal Vi is obtained by the collector of TRsQ1, Q2. The operation serving as a voltage controlled amplifier is obtained by applying a control voltage Vc to a base of a TRQ3 and changing a current I1 of the differential amplifier 40.