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ITERATIVE CMOS MAGNITUDE COMPARATOR CELL

IP.com Disclosure Number: IPCOM000005561D
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2001-Oct-16
Document File: 2 page(s) / 81K

Publishing Venue

Motorola

Related People

Ken Au: AUTHOR

Abstract

An iterative cell for digital magnitude comparision is described. This cell uses the fast-carry propagation chain principle. The generation, propagation, and inhibition of generation of the cell logic signals are described. Finally, a CMOS realization is illustrated as one possible implementation of this cell.

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MO7WROLA Technical Developments Volume 5 October 1985

ITERATIVE CMOS MAGNITUDE COMPARATOR CELL

by Ken Au

ABSTRACT

   An iterative cell for digital magnitude comparision is described. This cell uses the fast-carry propagation chain principle. The generation, propagation, and inhibition of generation of the cell logic signals are described. Finally, a CMOS realization is illustrated as one possible implementation of this cell.

INTRODUCTION

   The motivation to use fast-carry iterative arrays in a VLSI design are expandability, area savings, and design throughput. Fast-carry iterative networks have been used extensively in the past in the carry chain of ALU struc- tures. This paper illustrates a non-ALU application of the basic fast-ripple chain. Although the example cites a CMOS implementation, it is possible to realize this architecture in other technologies.

DESCRIPTION

We wish to digitally compare two numbers A and B. The functions Greater Than and Less Than, G and L, respectively are defined as follows:

A = {aO"al%2%3.....},
B = {bO"bl"b2"b3 .}, G = {gO'gl=g2"93 . ...}.
L = (10"11"12"13 .}, where G =A>B,
and L =A<B.

The algorithm we want to use is a bit-by-bit comparison and ripple the result from the most significant bit (MSB) to the least significant bit (LSB). The function Greater Than is defined as follows:

Generate a "1" if ai > bi and ai+l < bi+l. Propagate the next higher order gi if ai 5 bi

Similarly, we can define the Less Than function as:

Generate a "1" if ai < bi and ai+l > bi+l. Propagate the next higher order Ii if ai 2 bi.

   Note that the second...