Operational amplifier compensation circuit for preventing phase

Details Operational amplifier compensation circuit for preventing phase Operational amplifier compensation circuit for preventing phase

1994-07-07

1995-05-23

Mottola, Steven

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330261, H03F 345

Patent

active

054184916

ABSTRACT:
An operational amplifier input circuit for preventing phase reversal and maintaining performance for inputs outside the common mode range includes a pair of differentially connected transistors for receiving respective differential inputs, and a folded cascode pair of transistors that are coupled to the differential transistors. A pair of resistors are connected between a reference potential and the current circuits of the differential and cascode transistors to produce resistor voltages that control the respective cascode transistors' currents. The differential transistors respond to an input by producing a forward biased parasitic diode in one of the differential transistors. A phase compensation circuit responds to the input by shifting the resistor voltage for the other differential transistor to prevent a phase reversal of the resistor voltages. A current compensation circuit responds to the input by shifting the cascode transistors' base-emitter voltages to decrease their bias currents, and thereby limit their currents to a range within which the operational amplifier does not latch up.

REFERENCES:
patent: 5091701 (1992-02-01), Butler
patent: 5361040 (1994-11-01), Barrett
Bowers, "A 20-.mu.W Precision Operational Amplifier", IEEE Journal of Solid-State Circuits, vol. SC-22, No. 3, Jun. 1987, pp. 322-329.
"Amplifier Reference Manual", Analog Devices, Inc., Norwood, Mass., 1992, pp. 2-761 to 2-764.

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