Digital Electronics : 100 Most Important Questions with Solutions

1. The duty cycle of the most significant bit (MSB) from a 4-bit BCD counter is ____________

A. 20%
B. 50%
C. 10%
D. 80%

Answer ||| A

Solution:

There are 10 states, out of which MSB is high only for (1000, 1001) 2 times. Hence duty cycle is 2/10*100 = 20%. Since the duty cycle is the ratio of on-time to the total time.

2. Identify the combinational logic circuit(s) from the following list:

1. Full adder
2. J-K flip-flop
3. Counter

A. 2 only
B. 3 only
C. 2 and 3
D. 1 only

Answer ||| D

Solution:

The combinational circuits are:

1. Full adder
2. Full subtractor
3. Multiplexers
4. De-multiplexers
5. Encoders
6. Decoders

3. UP-DOWN counter is also known as ___________.

A. Dual counter
B. Multi counter
C. Multimode counter
D. Two Counter

Answer ||| C

Solution:

UP-DOWN counter is also known as multimode counter because it has capability of counting upward as well as downwards.

4. A JK flip-flop can be made to function like a T flip-flop by simply,

A. connecting the J and K inputs together as one-input
B. connecting J = 0 and K = 0
C. resetting all inputs of the JK
D. connecting earth ground the JK inputs

Answer ||| A

Solution:

If you short the J and K terminals of JK flip-flop it becomes T flip-flop.
Because if you give J = 0 and K= 0 present state remains as it is and if you give J = 1 and K= 1 present state gets toggled.

5. The smallest resistor in an 8 bit weighted resistor DAC is 5kΩ, what will be the largest resistor value?

A. 2.56MΩ
B. 1.28MΩ
C. 1.28KΩ
D. 2.56KΩ

Answer ||| B

Solution:

The largest resistor value for 8-bit DAC= 2ⁿ×R = 2⁸×5kΩ = 256×5kΩ =1.28MΩ

6. 

The state of the flip-flop after the occurrence of a clock pulse is called as its
A. current state
B. present state
C. next state
D. current input

Answer ||| C

Solution:

The state of the flip-flop before the occurrence of clock pulse is called as its next state.

7. For a serial in serial out register of 4 bits time taken for output of 4 bits is

A. 4
B. 5
C. 3
D. 1

Answer ||| C

Solution:

For serial In serial Out the date to be seen at output (n-1) clock pulse will be needed where n is number of bits. 4 bits are there so (4-1)=3 clock pulse will be needed to obtain In at Out. 
At 3^rd clock pulse data at In will be shown at Out.

8. If F = AB + A'B' Boolean expression is to be implemented using decoders and OR gates, the connection involves

A. 2 to 4 line decoder with 3 OR gates
B. 3 to 8 line decoder with 2 OR gates
C. 2 to 4 line decoder with 1 OR gates
D. 3 to 8 line decoder with 4 OR gates

Answer ||| C

Solution |||

F = AB + A'B' Boolean expression is to be implemented using decoders and OR gates, the connection involves 2 to 4 line decoder with 1 OR gates.

If you add D1 and D2 with OR gate you will get F = AB + A'B'.

 You can avail of Online Classroom Program for all AE & JE Exams:

Online Classroom Program for AE & JE Exams (12+ Structured LIVE Courses and 160+ Mock Tests)

You can avail of BYJU'S Exam Prep Test Series specially designed for all AE & JE Exams:

BYJU'S Exam Prep Test Series AE & JE (160+ Mock Tests) 

thanks, 

Team BYJU'S Exam Prep

Sahi Prep Hai to Life Set HAI