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Digital Logic

In RTL Design Interviews, you will often be asked to explain basic digital design concepts. Before diving into advanced sections, make sure that your foundation is strong.

Basic Questions

  1. What are some of the most commonly used types of Flip-Flops in Digital Design? Can you elaborate about their Truth Tables and Excitation Tables?
  2. Design a 4:1 Multiplexer using logic gates.
  3. Design a 16:1 Multiplexer using 4:1 Multiplexers.
    Can you come up with multiple topologies and explain the pros and cons of each approach?
  4. Design a T-FF (Toggle Flip-Flop) using a D Flip-Flop.
  5. What are the various types of State Machines typically used in Digital Design? What are the pros and cons of each type?
  6. What are the different types of State Machine Encodings typically used in Digital Design? What conditions dictate the preferred encoding style?
  7. What is the difference between a Flip-Flop and a Latch?
  8. Design the following gates using only NAND Gates - Inverter, OR Gate, AND Gate, XOR Gate.
  9. What is the difference between a JK Flip-Flop and an RS Flip-Flop?
  10. What are Static Hazards in Digital Design? How can you avoid the occurrence of these hazards?
  11. What are Mealy and Moore Machines? What is the advantage of one over the other? (Link to Answer)
  12. What are Tri-State Buffers? Can you talk through a real-world application of a Tri-State Buffer?

Advanced Questions

  1. What are the advantages of using a JK Flip-Flop over the more commonly used D Flip-Flop?
  2. What do the parameters - setup and hold time specify in relation to a Flip-Flop?
  3. What is meant by critical path in a digital design?
    Can you explain the timing equation for a critical path?
  4. Some datasheets specify sequential logic components with a negative value for Hold Time. What is the physical implication of the negative value?
  5. What is clock skew in digital circuits? Does a large clock skew affect the design adversely?
  6. What is Metastability? How does it affect the behavior of digital circuits?
  7. What is a Ring Counter and a Johnson Counter? What are the practical applications of these circuits?
  8. Design a Universal Shift Register capable of both Serial and Parallel loading and unloading.
  9. What are some basic Error Detection techniques in digital data transmission? (Link to Answer)