Browse Prior Art Database

Exclusive Or Input Decoders for PLA

IP.com Disclosure Number: IPCOM000089547D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Balasubramanian, PS: AUTHOR [+2]

Abstract

This circuit enables the exclusive OR (XOR) logic function to be generated by the addition of a single transistor to the standard 2-bit input decoder used in programmable logic arrays (PLAs) as described in U. S. Patents 3,593,317 and 3,761,902. With this technique, the XOR function can be generated from only two AND array lines instead of four, thus reducing the AND array utilization.

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Exclusive Or Input Decoders for PLA

This circuit enables the exclusive OR (XOR) logic function to be generated by the addition of a single transistor to the standard 2-bit input decoder used in programmable logic arrays (PLAs) as described in U. S. Patents 3,593,317 and 3,761,902. With this technique, the XOR function can be generated from only two AND array lines instead of four, thus reducing the AND array utilization.

The standard 2-bit decoder block diagram is shown in Fig. 1.

From the block diagram of Fig. 1 it can be seen that the XOR function is generated by personalization of the :AB and :AB lines while the "equal" function is produced by personalizing the :AB and :AB lines.

This invention relates to modification of the standard 2-bit decoder such that the logic function shown in the block diagram of Fig. 2 will be produced.

Fig.3 is the circuit diagram of a standard 2-bit decoder. Fig.4 is the same circuit modified to produce the exclusive OR function. Transistors 1 and 2 were added to the input inverters. Transistors 3 and 4 were moved from the second NOR circuits via a metal level personalization. All remaining changes to the circuit would also occur by changing the D-level personalization. Via this technique it can be shown that the XOR function can be generated in essentially one-half the silicon area while reducing the required AND array lines from 4 to 2.

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