Protecting Chips Against Hold Time Violations Due to Variability

The logical consequence of this parameter variation is that circuit characteristics, as delay and power, also become random variables. Because of the delay variability, not all circuits will now have the same performance, but some will be faster and some slower. However, the slowest circuits may be so slow that they will not be appropriate for sale. On the other hand, the fastest circuits that could be sold for a higher price can be very leaky, and also not very appropriate for sale. A main consequence of power variability is that the power consumption of some circuits will be different than expected, reducing reliability, average life expectancy and warranty of products. Sometimes the circuits will not work at all, due to reasons associated with process variations. At the end, these effects result in lower yield and lower profitability.

To understand these effects, it is necessary to study the consequences of variability in several aspects of circuit design, like logic gates, storage elements, clock distribution, and any other that can be affected by process variations. The main focus of this book will be storage elements.