Timing model for two stage buffer and its application in ECSM characterization

At nanometer technology nodes, variability is a major roadblock for circuit performance. This has made timing estimation of circuits a tedious task. Effective Current Source Model (ECSM) characterization of standard cells has been evolved to solve this issue. In this paper, an analytical Threshold Crossing Point (TCP) model for a two stage buffer is derived. Proposed model relates TCPs with the input transition time (T_R) and load capacitance (C_l). Region of validity of the model is also derived in (C_l, T_R) space. Relationship of model coefficients and region of validity with cell size is also derived. Furthermore, the proposed model is implemented in ECSM characterization of the buffer cell. It has been shown that ECSM characterization using proposed model results in 50% reduction of HSPICE simulations. Thus proposed model can be used to simplify the standard cell characterization methodology as it requires lesser number of simulations and gives values differing by a maximum of 2% from the actual values obtained using HSPICE simulations.