Patent ID: 7135849

Claim:
An extremal voltage detector for receiving a plurality of input voltages and producing an output voltage equal to an extremal one of the input voltages, comprising: a first power supply terminal supplying a first potential; a second power supply terminal supplying a second potential different from the first potential; a first node; a second node; a plurality of first metal-oxide-semiconductor field-effect transistors (MOSFETs) connected in parallel between the first power supply terminal and the first node, the first MOSFETs having identical electrical characteristics, each first MOSFET having a gate, receiving one of the input voltages at said gate, and conducting current responsive to the received input voltage; a second MOSFET having the same electrical characteristics as the first MOSFETs, connected between the first power supply terminal and the second node, the second MOSFET having a gate, receiving the output voltage at said gate, and conducting current responsive to the output voltage; a first constant-current circuit conducting a first constant current between the first node and the second power supply terminal; a second constant-current circuit conducting a second constant current, equal to the first constant current, between the second node and the second power supply terminal; and an operational amplifier having a non-inverting input terminal connected to the first node, an inverting input terminal connected to the second node, and an output terminal at which the output voltage is produced.