Patent ID: 6859095

Claim:
A method for reducing offset voltage in an operational amplifier without the need for switched-capacitors, external offset-correction resistors, precise matching between the internal components of the operational amplifier or analog characterization of the fabrication process, said method not resulting in any increase in the static current consumption of the operational amplifier and comprising the steps of: introducing a tapped resistor chain between the common connected terminals of the transistors of the input differential pair of the operational amplifier and connecting the tail current source/sink of the differential amplifier to a selected tap of the resistor chain, operating periodically or whenever desired, the operational amplifier in a calibration mode when the input terminals of the input differential amplifier are disconnected from the input terminals of the operational amplifier and connected to the same common-mode internal reference voltage point, monitoring the final output voltage and adjusting the selection of the tap in the resister chain to which the tail current source/sink is connected in the input differential amplifier in order to minimize the value of the final offset voltage, and storing the final tap selection and reconnecting the input differential amplifier inputs to the operational amplifier input terminals for resuming normal operation.