Re: performance problem
When temperature increases, performance degrades.. because the carrier mobility degradation leads to slower slew rates... and hence the slower the speed.
So when temperature increases, to keep circuit working(i.e. avoiding timing violations) you can slow down the frequency to avaiod the timing violations.... or you can increase the voltage(if permited and should be within tolerance) so that delays will be less and it will compensate the delay increase by tempaerature and hence it will work at freq. you targated for.
BTW, while doing timing clouser, once must make sure that circuit works and meets timing for all the corners(i.e. best corner and worst corner).
Best corenter : High Vdd, Lowest temperature,Best process
Worst Cornter : Low Vdd, highest temperature, Worst process.
Hope this will help you....