Apparatus and method for an input stage of an operational amplif

Details Apparatus and method for an input stage of an operational amplif Apparatus and method for an input stage of an operational amplif

1990-12-19

1992-08-25

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330259, 330260, 330261, H03F 345

Patent

active

051422433

ABSTRACT:
An operational amplifier input stage includes two transistors coupled as a differential amplifier to receive input signals. At least one transistor is stacked in a load circuit of each input transistor for the purpose of lowering the voltage across each transistor. In order to eliminate the effects of error currents resulting from conventional resistor self biasing of the stacked transistors, two nodes, to which the input transistors are coupled, are identified. A feedback circuit is coupled to each node and each feedback circuit maintains the coupled node at a voltage level established by the feedback apparatus of the operational amplifier. The disclosed circuit eliminates circuit drift and offset voltages resulting from changes in common mode and/or power supply voltages by eliminating the effects of resistive loading on the input stage components.

REFERENCES:
Jaeger, "High-Performance Input Stage for Integrated Operational Amplifiers," IBM Technical Disclosure Bulletin, vol. 18, No. 6, Nov. 1975, pp. 1645, 1646.

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