Dynamic voltage scaling is widely used to reduce the power consumption,but it need to guarentee that all critical paths can run correctly.This may seem tooconservative becasue too long path only account for a very small percent of all paths.

So this paper propose to use a shadow register to sample the critical path a little bit later than the real register,and then compare them. If the result is not the same,then a circuit is used to roll back the correct state.

One major overhead of "Timing Speculation" is the need to pad the short paths,to prevent them from making the comparator to think that a too long path has cause a timing error.