GATE ECE
Digital Circuits
Logic Gates
Previous Years Questions

## Marks 1

Consider a Boolean gate (D) where the output Y is related to the inputs A and b as, Y = A + $$\overline B$$, where + denotes logical OR operation. Th...
The minimum number of 2-input NAND gates required to implement a 2-input XOR gate is
The output of the combinational circuit given below is ...
In the figure shown, the output ܻ is required to be ܻ Y=AB+ $$\overline C$$$$\overline D$$. The gates G1 and G2 must be, respectively, ...
In the circuit shown, diodes $${D_1}$$ ,$${D_2}$$ and $${D_3}$$ are ideal, and the inputs $${E_1}$$ , $${E_2}$$ and $${E_3}$$ are “0 V” for logic ‘...
In the circuit shown in the figure, if C = 0, the expression for Y is ...
A bulb in a staircase has two switches, one switch being at the ground floor and the other one at the first floor. The bulb can be turned ON and also ...
The output Y in the circuit below is always ‘1’ when ...
For the output F to be 1 in the logic circuit shown, the input combination should be ...
Match the logic gates in column A with their equivalents in column B. ...
If the input to the digital circuit (in the figure) consisting of a cascade of 20 XOR-gates is X then the output Y is equal to ...
For the ring oscillator shown in the figure, the propagation delay of each inverter is 100 pico sec. What is the fundamental frequency of the oscillat...
For the logic circuit shown in Figure, the required input condition (A, B, C) to make the output (X)=1. ...
The output of the logic gate in figure is ...
The minimum number of NAND gates required to implement the Boolean function $$A + A\overline B$$ $$+ A\overline B C$$ is equal to
A ring oscillator consisting of 5 inverters is running at a frequency of 1.0 MH$$_z$$. The progagation delay per gate is ______
For the logic circuit shown in Figure, the output is equal to ...
Boolean expression for the output of XNOR (equivalence) logic gate with inputs A and B is
Indicate which of the following logic gates can be used to realize all possible combinational Logic functions:
Minimum number of 2-input NAND gates required to implement the function, f=($$\overline X$$+$$\overline Y$$)(Z+W) is
For the circuit shown below the output Fis given by ...
The minimum number of 2-input NAND gates required to implement the Boolean function Z=A$$\overline {B\,}$$C, assuming that A, B and C are available, ...
The Boolean function A+BC is a reduced form of
For the identity AB+$$\overline A$$ C + BC= AB + $$\overline A$$ C, The dual form is

## Marks 2

The logic gates shown in the digital circuit below use strong pull-down nMOS transistors for LOW logic level at the outputs. When the pull-downs are o...
A universal logic gate can implement any Boolean function by connecting sufficient number of them appropriately. Three gates are shown. Which on...
All the logic gates shown in the figure have a propagation delay of 20 ns. Let A = C = 0 and B = 1 until time t = 0. At t = 0, all the inputs flip (i....
A 3-input majority gate is defined by the logic function M (a,b,c) = ab+bc+ca. Which one of the following gates is represented by the function M$$\le... The output F in the digital logic circuit shown in the figure is ... Which of the follwing Boolean expression correctly represents the relation between P, Q, R and M1? ... The gates G1 and G2 in figure have propagation delays of 10nsec and 20nsec respectively. If the input Vi makes an abrupt change from logic 0 to 1 at t... In the figure the LED ... For the logic circuit shown in the figure, the simplified Boolean expression for the output Y is ... ## Marks 5 For the digital block shown in Figure. 2(a), the output Y=f(S3,S2,S1,S0) where S3 is MSB and S0 is LSB. Y is given in terms of minterms as$$Y\, = \,\...
The operating conditions (ON = 1, OFF = 0) of three pumps (x,y,z) are to be monitored. x = 1 implies that pump X is on. It is required that the indica...
The truth table for the output Y in terms of three inputs A, B and C are given in table. Draw a logic circuit realization using only NOR gates. ...

## Marks 8

A combinational circuit has three inputs A, B and C and an output F. F is true only for the following input combinations? A is false and B is true A ...
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