Test: Comparators - 2 - Electrical Engineering (EE) MCQ

Comparator


A magnitude digital Comparator is a combinational circuit that compares two digital or binary numbers in order to find out whether one binary number is equal, less than, or greater than the other binary number.
For N ≤ 2^k bit comparator circuit, k output lines are required.

Calculation
Given, N = 5
5 ≤ 2^k
k = 3

2-bit comparator
A comparator used to compare two binary numbers each of two bits is called a 2-bit magnitude comparator.
It consists of four inputs and three outputs to generate less than, equal to, and greater than between two binary numbers.

The truth table for the 2-bit comparator is given below:

The output of the A=B is:

Given that output is 1.

To get the output y = 1, all the inputs of OR gate should not be zero.

From the options, A₃ A₂ A₁ A₀ = 0010, B₃ B₂ B₁ B₀ = 1011 satisfies this condition.

Concept:

The conversion time of different types of n-bit ADC is shown:

• From the above table, it is clear that the dual-slope is the slowest ADC and Flash Type is the fastest ADC.
• The conversion type of Flash type is independent of the number of bits 

Application:

n = 8

• Maximum conversion time in clock cycles of 8-bit Successive approximation type ADC  = n=  8
• Maximum conversion time in clock cycles of 8 bit Dual slope type ADC = 2ⁿ⁺¹ = 2⁹ = 512
• Maximum conversion time in clock cycles of 8 bit Successive approximation type ADC = 1

x = x₁ x₀ y = y₁ y₀
The Boolean function S that satisfies condition,
If x > y, then s = 1.
We can represent the above condition through a truth table.

By using k-maps

Minimized form:

From the given circuit we can find the outputs expression as follows:

So, the given circuit in question behaves like a comparator circuit. 

• 74LS85 is a 4-bit magnitude comparator of two binary format inputs.
• 74LS85 can compare two 4-bit binary data and output can be given in a 3-bit parallel form.
• The IC has low power consumption and gives output in the TTL form which makes it compatible with other TTL devices and microcontrollers.

The block diagram is as shown:

The only possible combinations are
A = 01 and B = 0 0
A = 10 and B = 00, 01
A = 11 and B = 00, 01, 10
So there are only 6 combinations
Tips and Tricks:

where n = 2 bit

 High voltage gain causes comparator output voltage to switch between saturation levels. High CMRR rejects noise at input terminal and input offset (voltage & current) help to keep changes in temperature variation very slight.

Comparators are used in mass production where components are checked at a fast rate. These can be used as inspection purposes, laboratory standards and working standards or gauges.