A high precision component-tolerant A/D convertor

A pulse transformer is used to double and sum voltages in an A/D encoder that is based on the recursive algorithm V/SUB i+1/=V/SUB REF/-s|V/SUB i/|. As a result of isolating the transformer from the input signal d.c. component, independence of circuit zero drift is achieved. Resistor and V/SUB BE/ mismatch do not affect the encoder accuracy. Automatic zero and gain correction are employed to provide stable adjustment-free operation. A custom analog processor chip carrying both MOS and bipolar transistors was fabricated to implement the algorithm. The 12-bit resolution with a maximum encoder error of 250 /spl mu/V in a temperature range from 0-70/spl deg/C was achieved at 20-kHz sampling rate.