Abstract: An analog-to-digital conversion system of the incremental pulse-width modulation type for generating a digital representation of the amplitude of an input analog current to be converted comprising a current integrator, a precision unipolar current source, means for switching current from that source in opposite directions to and from a current summing terminal at the input to the integrator, a timing source, and pulse-width control circuit which controls the means for switching current and which controls a clock signal gating circuit on and off to obtain the output digital representation.