Timing analysis in presence of power supply and ground voltage variations

Given the sensitivity of circuit delay to supply and ground voltage values, static timing analysis (STA) must take into account supply voltage variations. Existing STA techniques allow one to verify the timing at different process corners which effectively only considers cases where all the supplies are low or all are high. Cases of mismatch between the supplies of driver and load are not considered. In practice, supply voltages are neither totally independent nor totally dependent. In this work, we consider the supply and ground nodes of a logic gate to be either totally independent variables, or to be directly tied or connected to those of some other gate(s) in the circuit. We also assume that the exact supply voltage values are not known exactly, but that only upper/lower bounds on them are known. In this framework, we propose new timing models for logic gates and identify the worst-case voltage configurations for individual gates and for simple paths. We then give an STA technique that provides the worst-case circuit delay taking supply variations into account.