Mumbai University > Information Technology > sem 3> Analog and Digital Circuits

Marks: 8M

Year: Dec15

comparator

• A comparator used to compare two bits, i.e., two numbers each of single bit is called a single bit comparator. It consists of two inputs for allowing two single bit numbers and three outputs to generate less than, equal and greater than comparison outputs.

• The figure below shows the block diagram of a single bit magnitude comparator. This comparator compares the two bits and produces one of the 3 outputs as L (A<b), e="" (a="B)" and="" g="" (a="">B).

• The truth table for the single bit comparator is given below. When A0 B0 = 00 & 11, both inputs are equal, therefore A=B output will be high. When A0 B0 = 01, B is more than A and hence AB is active.

From the truth table logical expressions for each output can be expressed as

• In the figure, one AND gate has inputs of A0 (B0) ̅ and another has inputs (A0) ̅ B0. Therefore, one AND gate output is 1 if A0 > B0 (i.e., A0 =1 and B0 =0) and is zero if A0 < B0 (i.e., A0 =0 and B0 =1). Similarly, other AND gate output is one if A0 < B0 (i.e., A0 =0 and B0 =1) and is zero if A0 > B0 (i.e., A0 =1and B0 =0).

• The Ex-NOR gate has inputs A0 B0, hence the output of the Ex-NOR gate will be 1 if A0 = B0 and the output will be 0 if A0 is not equal to B0.