Differential amplifier input stage capable of operating in excess of power supply voltage

Claim 1

A monolithic semiconductor integrated circuit differential amplifier input stage having first and second differential input terminals capable of supporting a common mode input voltage range that substantially exceeds the voltage span of a single two terminal power supply used to operate said circuit in which p n junction isolated transistors must have their collectors located in semiconductor regions that are reverse biased with respect to the semiconductor substrate that contains said circuit, said input stage comprising: first and second terminals of a single power supply connectable to a unitary source of operating voltage; first and second input transistors connected in a common base configuration, said first and second input transistors each having emitter, base and collector electrodes; means for connecting said emitter electrodes of said first and second transistors respectively directly to said first and second input terminals; means for reducing the base to collector current gain of said first and second transistors to a value close to unity; means for coupling said bases of said first and second transistors together and to means coupled to said second power supply terminal for providing a high resistance path for base current bias; and current mirror means coupled between said collectors of said first and second transistors and said second power supply terminal to provide a collector biasing current and to obtain a signal related to the differential voltage between said first and second input terminals.