Bias current modulation for differentially coupled transistor circuit

Abstract

Improved operation of a differentially coupled transistor circuit is achieved by modulating the circuit's bias current as a function of the input differential voltage. The bias current-modulated, differentially coupled transistor circuit includes first and second differentially transistor pairs, the bases of which are coupled across input terminals to which the differential voltage is applied. The emitters of the first transistor pair are coupled in common to a first constant bias current source, and the emitters of the second transistor pair are coupled in common to a second constant bias current source. The collector of one of the transistors of the first pair is coupled to the collector of the differentially coupled transistor of the second pair, so as to provide a first summation collector current. Similarly, the collector of one of the transistors of the second pair is coupled to the collector of the differentially coupled transistor of the first pair, so as to provide a second summation collector current. The emitters of transistors of a third differentially coupled pair are coupled in common to a modulated bias current source, the output of which is a function of the sum of one of the second collector currents. Output current is derived from one or both collectors of the third pair.