Variation Alphabet Soup


On-chip variation (OCV) is a major issue in timing signoff, especially at low voltages or in 20/16/14nm processes. For example, the graph below shows a 20nm inverter. At 0.6V the inverter has a delay of 2 (nominalized) units. But due to on-chip variation this might be as low as 1.5 units or as high as 3 units, which is a difference from slow to fast of 100%. Variation is not so bad at 1V but, for power reasons, everyone wants to get the voltage as low as possible since it is squared in the power equation also reduces leakage. Voltage is like sailing, if you want to win races, you have to sail close to the wind even though it is more difficult...