Static Timing Analysis (STA) Interview Questions

Static Timing Analysis Interview Questions - Blog Post

Static Timing Analysis (STA) Interview Questions

Static Timing Analysis is called timing sign-off methodology in the ASIC cycle because it ensures the chip is running accurately at all corners. As the sign-off cycle is complex the ST interview questions asked are also complex. I am sharing some of the commonly asked STA questions which will help fresher as well as experienced candidates.

  • What is Setup and Hold time?
  • Where is the setup and hold values are defined and how and where we encounter these values?
  • What is slack and how it is calculated to analyze the timing violations.
    • Expectation: Again, the interviewer wants to know your hands-on experience, you should explain here how you calculate the slack value for both setup and hold.
  • How can we remove setup violations give methods?
  • How can we remove hold violations give methods?
    • Expectation: Same as the setup you should tell how can it improved.
  • What all things you will consider if asked to write SDC file?
    • Expectation: The interviewer wants to know your understanding of the constraints and the SDC file.
  • If you are given a large number of clocks in the design, How would you define the relationship between the clocks?
    • Expectation: Here, the expectation is how you handle the clock-related constraints and clock groups.
  • How we define input and output delays?
  • What are timing exceptions and why we consider them while doing timing analysis?
  • What are virtual clocks and how we use them?
    • Expectation: You should know how we declare a virtual clock and what its use.
  • How we handle and declare high fanout nets in the SDC file.
    • Expectation: How we take care of the high fanout nets like clock, resets, and enable signals.
  • What are OCV and AOCV what is the difference between them?
  • What is CRPR and how we handle it in STA? Where you see its report and tool behaves on it.
  • How many corners did you use to close the design to analyze timing?
    • Expectation: Here, you should know how many corners you used, who gave you the corner list and how many iterations was used to fix the timing.
  • What was the skew value of the design?
  • What is the difference b/w SPEF and DEF and where they used?
    • Expectation: Theoretical knowledge on this is sufficient but you must know what it all contains and where they are used.
  • How you handle asynchronous clocks in a design.
    • Expectation: Again this question is timing-related you must have knowledge of the clock groups and the relationship between clocks.
  • Can we ignore any setup or hold violation before tap-out? If yes which and why?
    • Go ahead it’s to your knowledge.
  • Which violation you fix first and why (DRC/Setup/Hold)
  • How you fix max trans, max cap, and max fanout violations.
    • Give them an example of how you fix these violations.
  • If you have a max trans violation but not any setup or hold violation then can you send the design to tap-out? If no then why?
    • Expectation: Here you are expected to have conceptual knowledge of this violation.

Leave your thought here