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Differential Amplifier With Test and Lockout

IP.com Disclosure Number: IPCOM000081110D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Oliver, BL: AUTHOR [+2]

Abstract

This circuit comprises a differential amplifier provided with controlled clamps to enable the testing and locking out of the amplifier.

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Differential Amplifier With Test and Lockout

This circuit comprises a differential amplifier provided with controlled clamps to enable the testing and locking out of the amplifier.

Normally if the input voltage at SI is less than the reference voltage VR, transistor T2 is conducting and T1 is cut off. Under such conditions, the output signal at SO is in its "off" state. When the sensed input voltage at SI is greater than VR, T2 is cut off and T1 is conducting, and the output at SO is then in its "on" state.

The lockout function is accomplished by supplying a suitable signal to terminal SL so that transistor T3 is turned on, thereby clamping the input at S1 so that T1 cannot be turned on.

The test function is performed by supplying a suitable signal to terminal ST to turn on transistor T4, thereby causing the reference voltage VR to approach or attain ground potential, and hence cause an output signal at terminal SO.

A sensor valid indication is provided by supplying the output signal SO to one input of AND circuit 7, while the output SO from transistor T1 is supplied via inverter 9 to the other input of AND circuit 7. When SO is present and SO is present, an output will be present at SV, indicating correct operation of the circuitry.

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