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Optical Isolation Operational Amplifier

IP.com Disclosure Number: IPCOM000086576D
Original Publication Date: 1976-Sep-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Castellano, AJ: AUTHOR [+2]

Abstract

In many electrical measurements such as the determination of electrical conductivity of thick insulating films and characterization of ion or electron-induced secondary emission in various materials, it is often advantageous to use an isolation operational amplifier which can be floated off the ground at large applied voltages. The employment of a floating operational amplifier in the measuring circuit not only minimizes the noise associated with the high-voltage supply, shortens the leakage path and simplifies the problem involving the polarity reversal of the applied potential, but also permits direct interfacing with sensor-based computers and conventional recording devices.

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Optical Isolation Operational Amplifier

In many electrical measurements such as the determination of electrical conductivity of thick insulating films and characterization of ion or electron- induced secondary emission in various materials, it is often advantageous to use an isolation operational amplifier which can be floated off the ground at large applied voltages. The employment of a floating operational amplifier in the measuring circuit not only minimizes the noise associated with the high-voltage supply, shortens the leakage path and simplifies the problem involving the polarity reversal of the applied potential, but also permits direct interfacing with sensor-based computers and conventional recording devices.

As shown in the figure, an optically isolated operational amplifier used in secondary emission measurements consists of an input amplifier 1 followed by an isolation stage having two optically coupled isolators 2 and 3. The source signal flowing between lines 4 and 5 is differentially amplified by the amplifier 1, which includes an inverter stage so that the inverted and noninverted signal can be differentially applied on lines 6 and 7 to the optical isolators 2 and 3. Optical isolators 2 and 3 have low gain and their outputs are summed in an output operational amplifier 8 to provide the final output signal.

The isolation stage is powered by a rectified AC supply 9 while the input stage is powered by rechargeable Ni-Cd batteries. This separate power...