An improved small signal model of a mos transistor in millimeter wave band considering longitudinal distributed effects

Two kinds of distributed effects may appear in a MOS transistor in high frequencies: the non-quasi-static (NQS) effect along the channel and the longitudinal distributed effect (LDE) along the gate finger, especially with long finger length. The former can be modeled by NQS resistance and has been widely adopted, while the latter has not been accurately accounted for. Therefore, in this paper, we first calculate the two-port Y-parameters of a long gate finger MOS transistor considering LDE, using transmission line equations. Then, based on the distributed Y-parameters, a modified small-signal model is proposed. Finally, the modified model is verified by ADS and TCAD simulations. It is demonstrated that within the range of 0.1 GHz to 10 GHz, the maximum error is less than 1%, and even up to 100 GHz, the error does not exceed 5%. The results manifest that the modified model proposed in this paper is adequate for modeling LDE in high frequencies.