Voltage to current converter having feedback for providing an

Abstract

A voltage to current converter which exhibits a well-defined substantially exponential voltage-current characteristic. First and second input bipolar transistors of the voltage to current converter each have an emitter, a base, and a collector. The first and second input bipolar transistors are coupled at their emitters, and may be biased with a pre-determined constant current source, and they accept a selectable differential input voltage at their bases. A reference current source is connected to the collector of the first input bipolar transistor, and all output current source is connected to the collector of the second input bipolar transistor. A feedback element, having a gain, is connected between the coupled emitters and the collector of the first input bipolar transistor. The feedback element senses a voltage at the collector of the first input bipolar transistor and regulates a voltage at the coupled emitters to maintain a constant current through said first input bipolar transistor. As a result, an output current at the collector of the second input bipolar transistor varies substantially exponentially with the differential input voltage accepted at the bases of the first and second input bipolar transistors.