# Sample Paper for Digital Electronics

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Digital Electronics

Sample Paper

Note: Attempt any five questions.

1. What are Registers?Why are they used in digital electronics?

Ans: Registers are data storage devices that can store a group of bits.They are the cascaded group of flip flops.

2. Derive the boolean expression for the following logic circuit: Figure:1

Ans: C(A+B)DE

3. From the truth table below,determine the standard SOP boolean expression: Figure:2

Ans: Abar Bbar C + Abar BC + ABCbar

4. Define the various logic gates used in digital electronics.

Ans:  The various logic gates are:

i) AND GATE= a.b

ii) NOT GATE = a bar

iii) OR GATE = a+b

iv) EXOR GATE = a bar b + b bar a

v) NOR GATE = (a+b) bar

5. What is S-R flip flop.Define its implementation.

Ans: S-R flip flop is a circuit that has two stable states and can be used to store state information. Figure:3

6. Determine the output frequency for a frequency division circuit that contains 12 flip flops with an input clock frequency of 20.48MHz.

Ans: 5 KHz

7. What is race around condition?

Ans: In J-K flip flop, when the value of J and K =1 and at the same time value of clock is 1,so according to the truth table of J=K=1, the output should be toggled so the value keeps on changing till the change in clock pulse,which is not acceptable.

8. What is an ADC?Explain with an example.

Ans: An analog to digital converter is a device that converts a continuous physical quantity to a digital number that represents the quantity’s amplitude. 