A two step process has dominated the digital design flow a long time. That means, a design was fixed and afterwards it was checked whether it is signoff clean regarding the manufacturing issues and operating conditions. The nominal values of the design parameters are chosen in a way such that the design goals are achieved with these values. Extreme deviations between actual and nominal design parameters and limits of operating conditions are described by corners. These corners characterize Process, Voltage and Temperature (PVT) limits. The signoff step of the design flow checks whether or not the design goals are violated by applying extreme values.
