Offset trim using hot-electron induced vt-shifts

Abstract

A method and apparatus are provided for adjusting an offset in an electronic circuit by shifting at least one threshold voltage of a MOS transistor in an electronic circuit. By biasing a transistor into hard saturation, with sufficient supply voltage, charge carriers will be injected into the oxide layer of the MOS transistor over a predetermined time interval. Injection of charge carriers into the oxide layer of a MOS transistor causes the absolute value of the MOS transistor threshold voltage to increase. The injection of charge carriers is used to either intentionally increase or decrease the offset voltage in an electronic circuit due to mismatched components, process variations or to improve overall system accuracy or performance. In an operational amplifier or comparator, systematic offset voltage is measured at the output of the amplifier, and the threshold voltages of the differential input stage transistors are adjusted accordingly. In a digital to analog converter using precision current sources, the output voltage is measured for various code bits and the current levels for each current source are adjusted by shifting the threshold voltages as required. Offset voltage or mismatches in currents may be shifted in packaged electronic parts. The hot carrier injection method and apparatus, does not alter the temperature coefficient of the electronic part, requires minimal additional circuitry in electronic circuits, and greatly improves the precision with which electronic circuits may be manufactured.