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Exclusive OR Circuit

IP.com Disclosure Number: IPCOM000098662D
Original Publication Date: 1959-Aug-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Walsh, JL: AUTHOR

Abstract

This circuit performs the exclusive OR function with two transistors and four diodes and does not require complemented inputs. Transistors T(1) and T(2) have their emitters tied to a constant current source consisting of a high resistance and a D.C. supply. The upper pair of diodes forms an AND circuit coupled to the base of T(1) and the lower pair of diodes forms an OR circuit connected to the base of T(2). If both inputs, A and B, are up or if both are down, the base of T(2) is negative with respect to the base of T(1) by twice the voltage drop across the input diodes. T(2) therefore conducts and the negative of the exclusive OR function is indicated at its output line.

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Exclusive OR Circuit

This circuit performs the exclusive OR function with two transistors and four diodes and does not require complemented inputs. Transistors T(1) and T(2) have their emitters tied to a constant current source consisting of a high resistance and a D.C. supply. The upper pair of diodes forms an AND circuit coupled to the base of T(1) and the lower pair of diodes forms an OR circuit connected to the base of T(2). If both inputs, A and B, are up or if both are down, the base of T(2) is negative with respect to the base of T(1) by twice the voltage drop across the input diodes. T(2) therefore conducts and the negative of the exclusive OR function is indicated at its output line. When inputs A and B are different, the base of T(1) becomes more negative than that of T(2), and T(1) conducts, indicating the exclusive OR condition at its output.

By substituting emitter follower transistor logic for the diode inputs and providing a latching feedback path, the circuit may be used to perform more complicated logical functions.

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