AC characteristics of the MOSFET parasitic channel series resistances when absorbed into the current description

The AC behavior of absorbed parasitic series resistances of MOSFET models were compared to the conventional lumped resistance approach both theoretically and with real device values. The result suggested that absorbing the parasitic channel series resistances into the current description decreases the AC accuracy of the MOS model compared to conventional model with lumped resistances. Comparison were made with the input, output and gain and backward gain characteristics and it seems that the largest differences can be seen in the input and output behavior. The simple theoretical study of the two modeling approaches is confirmed by empirical comparisons of an 80 x 1.0 mum x 90 nm NMOS device characteristics up to 110 GHz.