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AND/OR Logic Circuit

IP.com Disclosure Number: IPCOM000073745D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Rajan, HD: AUTHOR

Abstract

The logic block disclosed acts as an AND gate or as an OR gate instantly. The principle adopted is shown in Figure A in terms of single pole switches. If Q1 and Q2 are open, the output is an AND function A, B AND C. If Q1 and Q2 are closed, A, B, OR C will give an output = 1. Thus Q1 and Q2 together comprise a gate which converts the AND function to an OR function. This mode of operation can be extended to any number (n) of switches of types A, B and C, the only requirement being that (n - 1) gates of the type Q1 and Q2 are needed to put the functional change into effect.

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AND/OR Logic Circuit

The logic block disclosed acts as an AND gate or as an OR gate instantly. The principle adopted is shown in Figure A in terms of single pole switches. If Q1 and Q2 are open, the output is an AND function A, B AND C. If Q1 and Q2 are closed, A, B, OR C will give an output = 1. Thus Q1 and Q2 together comprise a gate which converts the AND function to an OR function. This mode of operation can be extended to any number (n) of switches of types A, B and C, the only requirement being that (n - 1) gates of the type Q1 and Q2 are needed to put the functional change into effect.

A mode of implementing this principle with bipolar saturating switches is shown in Figure B, in which inverted transistor action is used. When Q is DOWN the output is a normal NAND function of A, B AND C. However, if Q raises to the UP level, A B OR C will be enough independently to bring the output to the DOWN level, realizing the NOR function. It is seen that while T1 and T2 always act in the forward mode, T2 has to conduct in the inverse mode, i.e. the current through R flows via T4 --> T2 reverse --> T5 to ground, in the NOR operation. As before, the principle can be extended to more than three inputs. It can be used with FETs as well.

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