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Exclusive OR Circuit

IP.com Disclosure Number: IPCOM000094006D
Original Publication Date: 1966-Apr-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Murphy, DW: AUTHOR

Abstract

This Exclusive-Or circuit utilizes current mode logic to provide the desired output function. Transistor pairs T1-T2, T3-T4, and T5-T6 are connected in the conventional current switch configuration. Their respective emitters are coupled through common emitter resistances to a potential source of -0.3 volts. Transistor T7 is connected in the emitter-follower configuration and is in a continually conductive state. Its output is taken via conductor 8 to the base of T4. The base inputs for both T2 and T7 are taken from the collector of T5. The A logic input is applied to T1 and T3. The B logic input is applied to the base of T5.

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Exclusive OR Circuit

This Exclusive-Or circuit utilizes current mode logic to provide the desired output function. Transistor pairs T1-T2, T3-T4, and T5-T6 are connected in the conventional current switch configuration. Their respective emitters are coupled through common emitter resistances to a potential source of -0.3 volts. Transistor T7 is connected in the emitter-follower configuration and is in a continually conductive state. Its output is taken via conductor 8 to the base of T4. The base inputs for both T2 and T7 are taken from the collector of T5. The A logic input is applied to T1 and T3. The B logic input is applied to the base of T5.

If it is first assumed that the B logic input is at a down logic level, T5 is nonconductive. Its collector potential is more positive than the up logic level of the A input. For this reason, T2 is rendered conductive and raises the emitter potential of T1. The rise is to a point where it is rendered unconditionally nonconductive, notwithstanding the state of the A logic input. The application of the high collector potential of T5 to T7 raises the potential across emitter resistance 10 to approximately ground level. As thus applied to the base of T4, this potential falls midway between the up and down logic levels of the A input and thus allows current switch T3-T4 to operate in the normal manner. If the A input is at the up logic level, T3 is rendered conductive and T4 nonconductive thus causing output terminal 12 to go t...