Collapsing the transistor chain to an effective single equivalent transistor

The most common practice to model the transistor chain, as it appears in CMOS gates, is to collapse it to a single equivalent transistor. This method is analyzed and improvements are presented in this paper. Inherent shortcomings are removed and an effective transistor width is calculated taking into account the operating conditions of the structure, resulting in very good agreement with SPICE simulations. The actual time point when the chain starts conducting which influences significantly the accuracy of the model is also extracted. Finally, an algorithm to collapse every possible input pattern to a single input is presented.