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Operational Amplifier

IP.com Disclosure Number: IPCOM000076348D
Original Publication Date: 1972-Feb-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Jacquart, CA: AUTHOR [+2]

Abstract

By using monolithic techniques, matched transistors are presently easier to manufacture than precision resistors. Furthermore, reduction of circuit size may be obtained by avoiding the use of resistors in the circuit design. This unconditionally stable operational amplifier with minimum offset current belongs to the above type of circuits. Only one resistor is used.

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Operational Amplifier

By using monolithic techniques, matched transistors are presently easier to manufacture than precision resistors. Furthermore, reduction of circuit size may be obtained by avoiding the use of resistors in the circuit design. This unconditionally stable operational amplifier with minimum offset current belongs to the above type of circuits. Only one resistor is used.

The circuit includes an input differential stage using NPN transistors T1-T2, respectively, loaded by diode connected PNP transistors T3 and T4. A 2 I current source T5 feeds DC current to both sides of the differential stage. Transistor T4 is used as current inverter by connecting the collector of T1 to its base electrode. The differential output signal is fed to the emitter of a PNP transistor T8 in series with a 2 I current source T6. The collector electrode of T8 is connected to an output stage comprising a Darlington T9-T10 in series with a Io current source T11.

The circuit is also provided with an additional 2 I current source T7 to provide balanced operation of the circuit during quiescent state. All these current-source transistors are base-to-emitter biased by a diode connected transistor T12 fed by a reference current Io. When the input voltage on E1 and E2 are equal, no current is fed to the Darlington input, therefore avoiding, any offset.

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