Top 100 Digital Electronics Interview Questions And Answers

In this article, we are going to learn about the Digital Electronics Interview Questions And Answers in a very detailed manner. This question we have covered is most important for interviews.

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Digital Electronics Interview Questions

Que.1: Given two X-OR gates, make one as a buffer and one as an inverter.

Answer: If we tie one input of X-OR as 1 then it will act as an Inverter. If we tie one input of X-OR as 0 then it will act as a Buffer.

Que.2: Tell some applications of Buffer.

Answer: They are used to introduce delays in digital circuits. They are used to eliminate cross-talk due to inter-electrode capacitance due to close routing. They are used to support high fan-out.

Que.3: Give two methods of converting a two-input NAND gate to an inverter.

Answer: Method 1: Short both the inputs of the NAND gate and apply the signal then it will act as an Inverter. Method 2: Connect the output to one of the inputs and the other to the input signal.

Que.4: Why are most interrupts active low?

Answer: If you consider the transistor level of a module, active low means the capacitor in the output terminal gets charged or discharged based on low-to-high and high-to-low transition respectively. When it goes from high to low it depends on the pull-down resistor that pulls it down and it is relatively easy for the output capacitance to discharge rather than charge. hence people prefer using active low signals.

Que.5: Difference between Latch and Flip-flop.

Answer: The latch is a level-sensitive device whereas the flip-flop is an edge-sensitive device. flip-flops are made up of latches only.

Que.6: What is a multiplexer?

Answer: It is a combinational circuit that selects binary information from one of many input lines and directs it to a single output line.

Que.7: What is a major advantage of R-2R ladder DAC as compared to binary-weighted DAC?

Answer: The R-2R ladder uses only two values of resistors in the circuits while n binary-weighted DAC various values of resistors are required which depends on the number of binary bits.

Que.8: What is the accuracy of a Digital to Analog Converter?

Answer: It is the comparison between the actual output of the converter and its expected output.

Que.9: No. of unused states in the 3-bit Jhonson’s counter is?

Answer: To find out the unused states in Jhonson’s Counter we can use the formula: 2n-2n. So unused states in the 3-bit Jhonson’s counter = 23-6 =2

Que.10: What is Digital Gate?

Answer: Digital gates are basically electronic components that are used for switching and manipulating binary data

Que.11: What do you mean by the universal gate?

Answer: The universal gates are those from which we can make any gate by using them. The universal gates are: NAND and NOR

Que.12: What is a magnitude comparator?

Answer: A digital comparator or magnitude comparator is a hardware electronic device that takes two numbers as input in binary form and determines whether one number s greater than, less than, or equal to the other number.
Comparators are used in the central processing units (CPU) and microcontrollers.

Que.13: What is Flip-flop?

Answer: Flip-flop is a sequential device that is used to store 1 bit.

Que.14: How many types of flip-flops are used in digital circuits?

Answer: J-K flip-flop, S-R flip-flop, D flip-flop, T flip-flop.

Que.15: What is the disadvantage of SR flip-flop?

Answer: In SR flip-flop, if both the inputs are at logic 1 then it gives invalid output.

Que.16: What is the disadvantage of the JK flip-flop?

Answer: In JK flip-flop there will be a race around the condition that occurs when both the inputs are at logic 1. To remove race-around conditions, we have to use a master-slave flip-flop or we have to use an edge-sensitive flip-flop.

Que.17: What is the race-around condition of the JK flip-flop?

Answer: For the JK flip-flop, if J=K=1, and if clk=1 for a long period of time, then output Q will toggle as long as CLK remains high which makes the output unstable or uncertain. This is called a race-around condition in the JK flip-flop.

Que.18: What is the Shift register?

Answer: The shift register is a device that is used for storing and processing the bit in serial or parallel.

Que.19: What are the types of Shift registers?

Answer: Serial In Serial Out (SISO), Serial In Parallel Out (SIPO), parallel In Serial Out (PISO), Parallel In Parallel Out (PIPO)

Que.20: What is Setup Time?

Answer: A minimum time period during which data must be stable before the clock makes a valid transition. For example: For a positive edge-triggered flip-flop having a setup time of 2 ns then input data should be stable for 2 ns before the clock make a valid transition from zero to one.

Que.21: What is Hold Time?

Answer: A minimum time period during which data must be stable after the clock has made a valid transition. For example: For an edge-triggered flip-flop, with a hold time of 1 ns, then input data should be stable for at least 1 ns after the clock has made the transition.

Que.22 What does Boolean algebra deal with?

Answer: Boolean algebra is the category of algebra in which the variable’s values are the truth values, true and false, ordinarily denoted 1 and 0 respectively. It is used to analyze and simplify digital circuits or digital gates. It is also called Binary Algebra or logical algebra.

Boolean Algebra Operations:

  • The basic operations of Boolean algebra are as follows:
  1. Conjunction or AND operation
  2. Disjunction or OR operation
  3. Negation or Not operation

Que.23 What are the different ways of minimizing logical expressions in a digital system?

Answer: To minimize a logical expression 3 different methods are used:

  • Boolean algebra: when a number of variables are less and the output is 0 or 1.
  • The k-map technique: can be used for up to 5 variables.
  • Tabulation method: this method can be used for any number of variables.

Que.24 What are the different Boolean theorems? What is the advantage of using Boolean theorems?


  • Different Boolean theorems used to minimize the logic expressions are:
  1. Distribution theorem
  2. Consensus theorem
  3. De Morgan’s theorem
  4. Transposition theorem
  • Advantages of using Boolean theorems:
  1. The number of logic gates was reduced.
  2. Speed of operation improves.
  3. Power dissipation decreases.
  4. Complexity reduces. 

Que.25 What is Dual Expression in a digital system? What is a self-dual expression?


  • Dual expression is used to convert positive logic into negative logic or vice-versa.
  • Self-dual expression: when a variable dual is equal to the variable itself, it is called self-dual.
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Hello friends, my name is Trupal Bhavsar, I am the Writer and Founder of this blog. I am Electronics Engineer(2014 pass out), Currently working as Junior Telecom Officer(B.S.N.L.) also I do Project Development, PCB designing and Teaching of Electronics Subjects.

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