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Multipurpose Operational Amplifier Structure

IP.com Disclosure Number: IPCOM000088058D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Maillet, JC: AUTHOR

Abstract

With large scale integration techniques, structures allowing several functions to be performed present advantages since the same structure can be extensively used.

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Multipurpose Operational Amplifier Structure

With large scale integration techniques, structures allowing several functions to be performed present advantages since the same structure can be extensively used.

Shown on the drawing is an arrangement comprising a plurality of N similar differential amplifiers and a common output stage. Only two amplifiers, the output stage and the biasing circuit are represented. Depending upon the connections and the values of the currents, this arrangement acts as multiplexed sample-and-hold devices or operational amplifiers.

Each amplifier comprises differential amplifier T1, T2 associated with current source T5, T6 and loaded by current mirror T11, T12. Cascode stage T7, T8 prevents transistors T1, T2 from entering into the saturation region with large negative input voltage, and increases output impedance. Emitter followers T3, T4 associated with current sources T9, T10 allow low impedance drive of the PNP input transistors T1, T2 while giving low input current.

Current source T6 of each amplifier can be switched ON or OFF by controlling the terminal CHANNEL SELECTION.

The output stage is composed of a common emitter amplifier T16, T17 loaded by current source T18. The output is buffered by a complementary emitter follower stage T19 to T23.

Outputs S1 to SN of the differential amplifiers are connected to input I of the output stage at the base of transistor T16. Capacitor C connected between the output terminal and terminal I i...