# Digital Electronics Interview Questions

## Digital Design or Digital Electronics Interview Questions If anyone is preparing for VLSI interviews, then you are in the right place. Here we will share some most frequently asked digital electronics questions in written tests and interviews.

I am sharing some of the most frequently asked digital design questions in interviews & written tests.

## QUESTIONS:

### Basic Questions to Prepare in Combinational Circuits:

1. What is a combinational circuit?
2. Difference between combinational & sequential circuits
3. What are universal gates?
4. Which logic gate is used more in real-life applications?
5. Applications of Buffer
6. Realize the equation Y=AB+C using only 2 input NAND gates
7. Realize XOR gate using only 2 input NOR gates
8. Implement a NOT gate using the XOR gate
9. Explain the difference between NAND and negative input AND gate
10. Explain the differences between MOSFETs and BJTs, and why we use MOSFET in digital design.
11. Draw 2 input NAND & NOR gates using CMOS logic
12. What are pull-up & pull-down networks?
13. Explain the operation of the CMOS Inverter
14. Draw the VTC curve of the CMOS Inverter
16. Design an OR gate using half adders
17. Design a Full adder using only NAND gates
18. In how many ways, a full adder can be implemented using logic gates?
19. Draw the Full subtractor truth table & circuit
21. Design a logical circuit that performs both addition and subtraction
22. What is a comparator?
23. Differences between Encoder and Decoder
24. Applications of Encoder & Decoder
25. Design 4 to 16 decoder using 2 to 4 decoders
26. What is a priority encoder?
27. What is a Multiplexer? Applications of MUX
28. Why MUX is called a universal circuit?
29. Design 4:1 MUX using 2:1 MUX
30. Design logic gates (AND, OR, NOT, NAND, NOR, XOR) using 2:1 MUX
31. How many 2:1 MUX are required to design 64:1 MUX?
32. Realize 2 input AND gate using 4:1 MUX
33. Implement 2 input NOR gate using 1:2 DEMUX
34. Implement a full adder using 4:1 Muxes
35. Explain tri-state buffers (notif1, notif0, bufif1, bufif0)
36. Implement basic gates (AND, OR, NOT) using tri-state buffers
37. Design a 4:1 MUX using tri-state buffers
38. Design a 2:1 MUX using decoder & tri-state buffers
39. Design a combinational circuit that converts a 4-bit gray code number to a 4-bit binary number using only XOR gates
40. Design a combinational circuit, which doubles the input frequency. (frequency multiplier by 2)

### Basic Questions to Prepare in Sequential Circuits:

1. What is a latch? Explain using NOT, NAND, and NOR gates.
2. Why do we use NAND gates more when compared with NOR gates?
3. Difference between Latch and Flip-flop?
4. Why flip-flops are preferred when compared with latches?
5. What is a transparent latch?
6. What is race condition?
7. What is master-slave configuration?
8. What is a glitch?
9. Which is more sensitive to glitches (latch or flip flop)?
10. Draw & explain D-flip flop vs D-latch timing diagrams.
11. Draw a D-latch using 2:1 MUX.
12. Draw a D-flip flop using 2:1 MUX.
13. Which flip flop is most widely used?
14. Application of flip flops?
15. Explain Clock to Q (C2Q) delay.
16. What is the setup time & hold time?
17. What is metastability?
18. How to avoid setup time & hold time violations?
19. What is clock skew?
20. Draw the excitation table for the SR flip-flop.
21. Design a JK flip flop using a D flip flop?
22. Design a T flip flop using a D flip flop?
23. Design a 4-bit up-down counter?
24. Design a frequency divider by 3 circuit.
25. Design & explain the MOD-5 counter.
26. How many flip-flops are required to design a MOD-535 counter?
27. Draw a 4-bit counter using one D flip-flop and one adder.
28. Difference between synchronous and asynchronous counters?
29. What is asynchronous reset & how is it different from synchronous reset?
30. How many bits a flip-flop can store?
31. What is a register & how many bits it can store?
32. What is a shift register & the types of shift registers?
33. Draw a 4-bit Johnson counter?
34. Design a PISO Shift register?
35. Draw & Explain the 4-bit Linear Feedback Shift Register.
36. Draw & Explain a 4-bit Barrel Shifter using MUX.
37. What is a Finite State Machine?
38. Explain Mealy Vs Moore FSM.
39. Which is more preferred (Mealy or Moore)?
40. Draw a state diagram for the 101 sequence. (both Mealy & Moore non-overlap)
41. Draw a state diagram for the JK flip-flop.
42. Design a sequence detector that detects both 1010 & 0101(both mealy & moore overlap)
43. Design a sequence detector that detects 1X1X (Moore overlap)
44. What is a Clock Domain Crossing (CDC)?
45. How to overcome CDC?
46. What is a 2-stage synchronizer?
47. What is MTBF?
48. What is FIFO? Explain Synchronous vs Asynchronous FIFO
49. Explain Dual port RAM
50. What are full and empty conditions in FIFO?
51. Difference between RAM & ROM?
52. Difference between Static and Dynamic RAM?
53. Buffer vs D flip-flop