Increase in delay uncertainty by performance optimization

Abstract
SUMMARY This paper discusses a statistical effect of per- formance optimization to uncertainty in circuit delay. Perfor- mance optimization has an effect of balancing the delay of each path in a circuit, i.e. the delay times of long paths are shortened and the delay times of short paths are lengthened. In these path- balanced circuits, the uncertainty in circuit delay, which is caused by delay calculation error, manufacturing variability, fluctuation of operating condition, etc., becomes worse by a statistical char- acteristic of circuit delay. Thus, a highly-optimized circuit may not satisfy delay constraints. In this paper, we demonstrate some examples that uncertainty in circuit delay is increased by path- balancing, and we then raise a problem that performance opti- mization increases statistically-distributed circuit delay.

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