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Three Transistor Exclusive Or Circuit

IP.com Disclosure Number: IPCOM000096156D
Original Publication Date: 1963-Jan-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Patterson, LJ: AUTHOR

Abstract

The Exclusive Or employs only three transistors and two diodes. The input voltages at A and B and the corresponding output voltages at O1 an and O2 are shown in the waveform diagram.

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Three Transistor Exclusive Or Circuit

The Exclusive Or employs only three transistors and two diodes. The input voltages at A and B and the corresponding output voltages at O1 an and O2 are shown in the waveform diagram.

Initially with negative inputs at A and B, input transistors T1 and T2 are nonconductive, transistor T3 is conductive and diodes D1 and D2 are biased for conduction. Under these conditions, output O1 is up and output O2 is down. When either input A or B comes up to a positive voltage, either T1 or T2 becomes conductive causing the output voltage O1 to fall. Simultaneously, the conduction of one of the input transistors causes the emitter voltage of T3 to rise, causing it to cease conduction and provide an up output voltage O2. A positive input potential at either A or B does not effect the base voltage of T3. This is because, while one of the diodes is back biased by the positive voltage input, the other remains conductive to clamp the base voltage at the most negative level.

When both inputs A and B become positive, D1 and D2 are rendered nonconductive, raising the potential at the base of T3 and causing it to become conductive. This results in the emitter-base junctions of T1 and T2 being back- biased so that they are prevented from becoming conductive. At such time, the positive voltages at O1 and O2 are, respectively, up and down.

The Esaki diode pairs connected to outputs Ol and O2 are for the purpose of wave shaping and do not perform any l...