Method of early clock implementation for efficient time borrowing
Publication Date: 2012-Nov-19
The IP.com Prior Art Database
• Useful clock skew is very powerful technique for setup timing critical paths closure. It’s done by both delaying specific clock branch or reducing its delay to increase cycle duration between specific FF’s
· Useful clock skew is very powerful technique for setup timing critical paths closure. It’s done by both delaying specific clock branch or reducing its delay to increase cycle duration between specific FF’s
Ø In many cases there is not optimal logic/interconnect timing critical paths distribution between following paths. Usual solution is time borrowing, when clock of the intermediate FF is shifted back (if the first path much shorter, than second one) and thus time for the second path is longer, than for the first one. But ability to shift clock back is limited by clock tree structure and shifting forward other clocks impacts clock tree quality.
Fig. 1 demonstrates the typical scheme of the problematic situation
Ø The proposal solution is to generate early clock, as delayed clock with delay slightly higher, than short path and use it for intermediate FF. Obviously such solution can cause race on the end FF at low frequency. For that reason at low frequency normal clock will be used at intermediate FF to avoid race – setup condition will be ok for the long path due to the same reason of low frequency.
Fig. 2 shows the sheme of proposed implementation.