Enhanced transconductance circuit

Abstract

A transconductance circuit that improves linearity and output current over a wider range of input voltages than prior designs. The transconductance circuit may include first and second sets of paired differential transistors. In each set, emitters of the paired transistors may be commonly coupled to corresponding nodes of a common impedance, and collectors may be coupled to output terminals of the transconductance circuit. The circuit may further include first and second sets of doublet differential transistor pairs, each doublet pair having transistors of different sizes. Each doublet pair may have current sources coupled between commonly coupled emitters and a source potential. Respective collectors for each doublet pair may be coupled to the output terminals of the transconductance circuit. A pair of voltage followers may be provided to replicate corresponding input voltages across corresponding bases of the differential transistor pairs and the doublet transistor pairs.

What is claimed is: 
     
         1 . A transconductance circuit, comprising:
 first and second sets of differential transistor pairs, wherein within the first set, emitters of the transistors are coupled to a first common node and collectors of the transistors are coupled to a first pair of output terminals of the transconductance circuit, and wherein within the second set, emitters of the transistors are coupled to a second common node, and collectors of the transistors are coupled to a second pair of output terminals of the transconductance circuit, and wherein each set has a first transistor to receive a first input voltage at its base, and a second transistor to receive a second input voltage at its base; and   an impedance coupled between the first and second common nodes.   
     
     
         2 . The transconductance circuit of  claim 1 , further comprising:
 a first voltage follower to receive the first input voltage at a first input terminal and replicate the first input voltages across the bases of the first transistors of each set; and   a second voltage follower to receive the second input voltage at a second input terminal and replicate the second input voltage across the bases of the second transistors of each set.   
     
     
         3 . The transconductance circuit of  claim 2 , wherein the circuit is configured to generate output currents from each output terminal that track changes for the first and second input voltages across a predetermined voltage range.