300+ [UPDATED] Static Timing Analysis Interview Questions

1. What Is Positive Slack?

The difference between required arrival time and actual arrival time is positive, then is called as positive slack. If there is positive slack, The design is meeting the timing requirements and still it can be improved.

2. In Back-end Design Which Violation Has More Priority? Why?

In back-end design, Hold violation has more priority than Setup Violation. Because hold violation is related to data path and not depends on clock. Setup violation can be eliminated by slowing down the clock (Increasing time period of the clock).

3. What Is Negative Slack?

The difference between required arrival time and actual arrival time is Negative, then it is called as Negative slack. If there is negative slack, the design is not meeting the timing requirements and the paths. which have negative slack called as violating paths. We have to fix these violations to make the design meeting timing.

4. What Is Slack?

The difference between Required Arrival Time and Actual Arrival Time is called as Slack. The amount of time by which a violation (Either setup or Hold) is avoided is called the slack.

5. How Can You Avoid Hold Time Violations?

1. By adding delays using buffers
2. By adding lockup-latches

6. What Is Static Timing Analysis(sta)?

Static timing analysis is a method for determining if a circuit meets timing constraints without having to simulate. So, it validates the design for desired frequency of operation, without checking the functionality of the design.

7. What Is Setup Time?

Setup time is the amount of time before the clock edge that the input signal needs to stable to guarantee it is properly accepted on the clock edge.

8. What Is Hold Time?

Hold time is the amount of time after the clock edge that the input  should be stable to guarantee it is properly accepted on the clock edge.

9. What Is Setup And Hold Time Violations?

Violating above setup and hold time requirements is called setup and hold time violations. If there is setup and hold time violations in the design does not meet the timing requirements and the  functionality of the design is not reliable. STA checks this setup and hold violations.

10. How Can You Avoid Setup Time Violations?

1. Play with clock (Useful) skew.
2. Redesign the flip flops to get lesser setup time
3. The combo logic between flip flops should be optimized to get minimum delay
4. Tweak launch flip-flop to have better slew at the clock pin, this will make launch flip-flop to be fast there by helping fixing setup violations.