Tuesday 20 October 2015

How To Fix Hold Time Violations

What is Hold time?

The hold time is the interval after the clock where the data must be held stable. Hold time can be negative, which means the data can change slightly before the clock edge and still be properly captured. Most of the current day flip-flops has zero or negative hold time. 

Way of fixing the hold time violation is just opposite of setup time violation.Below are few methods to fix hold time violation.

1. introducing the delay in data path, you can do this by adding the buffers in data path
2. Downsizing the cells
3. VT swapping, you can swap the the LVT buffers to SVT or HVT buffers


  1. Can't we swap HVT to LVT for fixing hold violation? if no, why?

    1. for correcting hold violation u need to add delay. LVT i.e Lower VT will take less time to get activated whereas HVT i.e Higher VT will take more time. This additional time taken by HVT will compensate for the required delay.

  2. Chance of hold violation increases if we swap HVT to LVT , the delay will decrease , so the arrival time will reduce. Hold is Arrival minus Required time , hence lesser arrival time leads to hold violation.