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Magnitude Comparator

Date: 29 Apr 2015

Magnitude Comparator is a combinational circuit capable of comparing the relative magnitude of two binary numbers. It is one of the two types of digital comparator.

Block diagram of n-bit comparator

Figure(a): Block diagram of n-bit comparator

Figure(a) shows the block diagram of n-bit magnitude comparator. It accepts two n-bit binary numbers, say A and B as inputs and produces one of the outputs: A>B, A=B and A<B.

One of the outputs will be high depending upon the relative magnitude. That is, output A>B will be high if A is greater than B, output A=B will be high if A and B are equal, and output A<B will be high if A is less than B.

Its logic behaviour is same as adder. It does not return sum or carry.

Magnitude comparators are used in central processing units and microcontrollers.

This basic circuit for a magnitude comparator can be extended for any number of bits.

Four bit magnitude comparators are very popular circuits and are commercially available.

Examples: 74HC85 and CMOS 4063. These are four bit magnitude comparators.

Logic Diagram

Four bit magnitude comparator

Figure(b): Four bit magnitude comparator