Modeling the dynamic behavior of series-connected MOSFETs for delay analysis of multiple-input CMOS gates

In this paper the dynamic behavior of series-connected MOSFETs is studied, in order to compute the propagation delay of multiple-input static CMOS gates. A method for the reduction of series-connected MOSFETs to a simple MOSFET with the same behavior is proposed. The effective width of the equivalent transistor is not constant as in some previous works. So all cases of input slopes, the load capacitance, the number and the position of the switching inputs, and the body effect, are considered in order to determine the equivalent transistor's width. Along with the reduction process, an accurate analytical inverter timing model is used to compute the propagation delay of multiple-input static gates. The produced results are in very good agreement with SPICE simulations.