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# Variable Function Logic Block

IP.com Disclosure Number: IPCOM000092017D
Original Publication Date: 1968-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 38K

IBM

## Related People

Greeson, JC: AUTHOR

## Abstract

This logic block is used in high-density integrated circuit applications and provides considerable flexibility by incorporating both Boolean and Majority logic functions in a single unit. Using a differential amplifier, the output from the block can be made to appear as an And, an Or, a majority logic block or a latch. The function performed by the circuit in response to the normal logical inputs is determined by an additional pair of inputs.

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Variable Function Logic Block

This logic block is used in high-density integrated circuit applications and provides considerable flexibility by incorporating both Boolean and Majority logic functions in a single unit. Using a differential amplifier, the output from the block can be made to appear as an And, an Or, a majority logic block or a latch. The function performed by the circuit in response to the normal logical inputs is determined by an additional pair of inputs.

The variable function logic block at A consists of differential amplifier 1 provided with inputs a, b, c, y, and z and a single output d. The tolerance of the circuit components is accurately controlled since the switching of all logic is between 0 and 1 volt. The logical identity of this logic block is controlled by the inputs y and z applied to one input node 3 of amplifier 1. The normal logical inputs a, b, and c are applied to the other input node 2. When input node 3 is more negative than input node 2, the output at d is positive.

In truth table B, if a logical 1, i.e., +1 volt, signal is applied to y but not z, or vice versa, the output function at d appears as majority logic. A logical 1 signal, applied simultaneously to y and z, causes the block to produce an output at d when only a logical 1 signal is also applied to each input a, b and c simultaneously, e.g., an And function. If, however, logical 0, 0 volts, inputs are applied to inputs y and z, the block provides an Or function and pr...