Current reference circuit

Abstract

A constant-current generator circuit includes an output circuit and a control circuit, with the control circuit producing a control voltage to define a reference current through the output circuit. An important feature is that the control circuit uses a pair of transistors having different threshold voltages in generating the control voltage. The circuit is formed using CMOS technology, and the difference in threshold voltage may be produced by doping the polysilicon gate of an N-channel or P-channel field effect transistor. The step of doping to produce the change in threshold voltage is compatible with the standard processing for the CMOS device. In a preferred embodiment, the control circuit uses two pairs of control transistors, each pair having differing thresholds. One pair is P-channel and the other N-channel. These pairs are in parallel, the P-channel pair connected to the positive supply and the N-channel pair to the negative supply or ground. Each pair is connected in a cascode arrangement, producing two control voltages for two symmetrical output transistors in the output circuit, one N-channel and one P-channel.

Dependencies are inferred from the claim text.