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Timing analysis and CDC

In clock uncertainty settings, period jitter is often included for setup but not for hold. Why?

  1. ABecause the hold check is performed only at falling clock edges
  2. BBecause jitter occurs only at high frequencies, and hold analysis is done at a lowered frequency
  3. CBecause hold compares against the same clock edge, so variation in the edge timing affects the launching and capturing sides equally and cancels out
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Answer: C. Because hold compares against the same clock edge, so variation in the edge timing affects the launching and capturing sides equally and cancels out

Period jitter is variation in the interval between one edge and the next. Setup is judged on the interval between the launching edge and the next edge, so with ±30 ps of jitter on a 1.0 ns period, the available time shrinks to 0.97 ns in the worst case. Hold compares launch and capture at the same edge, so whether that edge is early or late, both sides move together and the effect of jitter almost cancels out. However, the estimate of skew before the clock tree is built is included in the hold uncertainty as well.

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More Timing analysis and CDC questions

  1. In STA, which combination correctly gives the corner conditions mainly used to check setup and hold?
  2. For OCV derating in setup analysis, the launch clock path and data path delays are multiplied by 1.1 and the capture clock path delay by 0.9. With a launch clock path of 1.0 ns, a data path (including clock-to-output) of 1.5 ns, a capture clock path of 1.0 ns (no common portion), a period of 3.0 ns and a setup time of 0.1 ns, what is the setup slack?
  3. In STA with OCV derating, when the launch and capture clock paths share a common portion, which correctly describes CRPR (common path pessimism removal)?
  4. In a circuit running on a 2.0 ns clock, a path has a data arrival time (clock-to-output plus combinational logic delay) of 3.3 ns and a setup time of 0.1 ns. Since this path only needs to capture once every two cycles, a setup multicycle path of 2 is set. What is the setup slack?
  5. When a setup multicycle path of N (N ≥ 2) is set, a hold multicycle path of N − 1 is normally set as well. Why?