Modeling of Distributed Effects in Modern MOS Transistors for Millimeter Wave Applications

Distributed effects in a MOS transistor are modeled in available small signal models, e.g., BSIM4.7 and BSIM6 models, using approximated methods. These approximations cause to inaccurate results in millimeter wave band, when the gate finger length is long. We have developed a simple approach to accurately incorporate the distributed effects in the available small signal models. In our approach, the circuit elements of a BSIM small signal model are modified using some new correction coefficients. To clarify the distributed effects, in the first step, we have simulated a single-finger nMOS transistor with W = 10 μm using the foundry design kit for Taiwan Semiconductor Manufacturing Company 90-nm RF-CMOS technology, one time as a single transistor and the other time as a cascade of 20 small transistors. The later captures the longitudinal distributed effect accurately, and hence, it is a reference to validate the proposed modifications. Y-parameters obtained from this step clearly show the difference of single transistor with the distributed one. In the second step, we have calculated the Y-parameters in MATLAB using the BSIM4 model parameters of the transistor, after applying the correction coefficients. The results show that the modified model is in very good agreement with the distributed transistor model.