Research On Large Signal Model For Millimeter Wave/Terahertz MOSFET

Si MOSFET is widely used in power amplifier,oscillator,low noise amplifier and other large signal circuits because of its mature process,low cost,low power consumption and high integration.In the circuit design process,transistor is the most basic component in RF circuits,and the accuracy of the transistor model is the key to shorten the circuit design cycle and reduce the design cost.With the development of CMOS technology,transistors exhibits complex physical effects and parasitic effects at high frequencies.How to establish accurate MOSFET high-frequency large signal model has been the focus of researchers.The millimeter wave/terahertz MOSFET large signal model are studied in this thesis.Firstly,the intrinsic capacitance model of long channel MOSFET satisfying the charge conservation law is derived from the surface potential equation.On this basis,the frequency characteristics of the intrinsic capacitance of MOSFET are studied,and the nonlinear intrinsic capacitance frequency model is obtained by solving the continuity equation using Bessel function.The model has good accuracy up to 10f _T.The effects of short channel effect and channel length modulation effect on nonlinear intrinsic capacitance of MOSFET are also analyzed.In addition,a new method to extract the source/drain parasitic series resistance has been proposed,which requires only simple dc measurements.Compared with traditional dc extraction method,the proposed method reduces erros associated with the previous parameters extraction,such as the threshold voltage(V_T),the effective channel length(L_eff)and so on.This method also considers the influence of mobility degradation factors on source drain parasitic series resistance.The results show that the error was lower than 10%.Based on the MESFET empirical dc models,an improved DC model is proposed considering the effects of source/drain parasitic series resistance and the influence of gate voltage on the channel length modulation factor.The accuracy of the model is verified by experiment.The results show that this DC model can accurately reflect the DC characteristics of transistors,and then an expandable nonlinear DC model is proposed by using simple scaling rules.Furthermore,the RF nonlinear drain current model is studied.Finally,considering the high frequency parasitic effect of transistors,an millimeter wave/terahertz large signal equivalent circuit model is established.To verify the large-signal model,the equivalent circuit model was incorporated in ADS through SDD components.Simulations show that the model has high precision in terms of small signal S parameter,output power,gain and power added gain.