Digitally trimmable input current cancellation circuit for analog-to-digital converter

Abstract

An analog-to-digital converter circuit usable for measuring a voltage having a large common-mode voltage includes two input voltage nodes, a voltage sensing circuit (that includes a sigma-delta modulator) that senses a voltage between the nodes, a digital filter that outputs a multi-bit digital value, and an input current cancellation circuit. The input current cancellation circuit supplies/draws cancellation currents to/from the nodes to compensate for currents drawn from/supplied to the nodes by the voltage sensing circuit. The input current cancellation circuit includes a digitally-programmable digital processing circuit and a current canceling circuit. In one example, the digital processing circuit includes a sigma-delta modulator that transforms a single-bit digital signal output by the voltage sensing circuit into a single-bit digital signal that drives the current canceling circuit. The transfer function of the current compensation loop is programmable and adjustable by loading digital trim values into the circuit.