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High Speed Digital Comparators

IP.com Disclosure Number: IPCOM000088495D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Weinberger, AW: AUTHOR

Abstract

The structure of comparisons may be simplified, by its use of equal to or greater or equal to or less instead of equal, to aid in generating greater than or less than functions, respectively, and by the use of (EGR*)ij or (EL*)ij, instead of Eij to generate GRij or Lij, respectively, where (EGR*)ij is Eij with GRij included as don't care conditions, while (EL*)ij is Eij with Lij included as don't care conditions. Furthermore, a variety of carry-look-ahead methods can be used to speed up and/or reduce hardware of the comparator.

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High Speed Digital Comparators

The structure of comparisons may be simplified, by its use of equal to or greater or equal to or less instead of equal, to aid in generating greater than or less than functions, respectively, and by the use of (EGR*)ij or (EL*)ij, instead of Eij to generate GRij or Lij, respectively, where (EGR*)ij is Eij with GRij included as don't care conditions, while (EL*)ij is Eij with Lij included as don't care conditions. Furthermore, a variety of carry-look-ahead methods can be used to speed up and/or reduce hardware of the comparator.

     Let Ai, Bi be the two n-bit numbers to be compared, where i = 0, ..., n1, high-to-low order

E = the function A equal to B

L = the function A less than B

GR = the function A greater than B

U = the function A unequal to B

EGR = the function A equal to ir greater than B

EL = the function A equal to or less that B

     The functions L (A less than B) can be expressed as a function of single- bit functions, as show in Equations (1).

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     Similarly, the function GR (A greater than B) can be expressed as a function of single-bit functions, as shown in Eqs. (2).

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The complement functions are shown in Eqs (3) and (4).

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Eqs. (5) and (6) illustrate one level of intermediate functions.

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     Efficient implementations of (EL*)ij and (EGR*)ij generally take form of Eqs. (7) and (8).

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The complement functions of Eqs. (5) and (6) are shown in eqs. (9) and
(10).

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