Current compensation circuit for improved open-loop gain in an amplifier

In contemporary operational amplifiers, isolation of the voltage of the input signals applied to the input ports from the load at the output port is a common goal, as is the goal of optimal gain. With reference to the example of Prior Art , first and second input signals are provided at input nodes inp, inm at the bases of first and second input transistors q , q respectively. Current sources i , i are coupled between a positive supply voltage VPLUS and the collectors of transistors q , q respectively. The emitters of transistors q , q are jointly coupled to a current source i , in turn coupled to a negative supply voltage VMINUS. Collectively, the transistors q , q and current sources i , i , and i comprise a transconductance stage for the amplifier for converting voltage signals applied at the input nodes inp, inm to current signals at nodes N , N . A current compensation circuit for an amplifier, for example an operational amplifier, having input and output stages coupled at a high-impedance node, compensates for any modulation of current occurring at the high-impedance node. Particularly, the compensation circuit of the present invention reduces the error current at the high-impedance node resulting from a mismatch in beta between PNP and NPN transistors in the output stage, and reduces any error current resulting from the Early voltage effects of transistors in the output stage. In this manner, the present invention serves to substantially isolate the amplifier input stage from the output load, and from any beta mismatch or Early voltage effects in the transistors of the output stage, resulting in greatly improved open-loop gain.