High voltage supply sensing high input resistance operational amplifier input stage

摘要

A high voltage operational amplifier input stage utilizes a pair of low voltage p-type MOSFET input devices configured to operate at a common mode voltage. The input stage operates between positive and negative voltage supply rails. Common mode bipolar transistor feedback loops force drains of the MOSFETs to track corresponding source potentials. MOSFET substrate connections are maintained at a predetermined level above (or below, depending on the power supply sensing arrangement) the common mode voltage of the input stage to ensure power supply sensing capability. The input stage has a common mode range which includes the supply rail potential, and which tolerates a total supply voltage that exceeds the MOSFET breakdown voltage. The effective threshold voltage of the input devices is increased above the nominal threshold value to sustain the linear operation of the input stage.