Large-signal Modeling Of Ka-band GaN HEMTs

Due to its excellent characteristics such as high power density,high temperature and high voltage resistance,in recent years,GaN HEMTs have been receiving special attention from various countries,and have been developed and made significant progress,and are widely applied in next-generation mobile communications as well as in aerospace applications.In order to characterize the output characteristics of GaN HEMT devices and as guidance for circuits design,it is essential to establish accurate device models.At the meanwhile,with the continuous evolution of the device process,the requirements for the model are always increasing,so there is a need to continuously study and update the GaN HEMTs model.As the core of the device model,the drain current equation is the focus of the present research in the modeling field.For the establishment of the largesignal model of GaN HEMT devices in Ka-band,the research in this thesis is as follows:1.Studying on GaN HEMTs small-signal modeling.For subsequent large-signal modeling,the parasitic and intrinsic parameters are extracted for GaN HEMT devices based on the 19-element small-signal model topology network in this thesis,and afterwards the small-signal model is established in the simulation software,which achieves 95% accuracy in characterizing the small-signal S-parameters of devices with frequencies up to 40 GHz,thus verifying the correctness of the small-signal model.2.Studying on GaN HEMTs empirical large-signal modeling.To address the problem that traditional models seldom pay attention to the nonlinear characteristics of GaN HEMT devices and therefore cannot be adapted to the demand of high linearity device models,firstly,an empirical current model considering dispersion effects is proposed in this thesis.Then,the verification of the higher order transconductance of the device is introduced into the modeling process,and the new approach is used to optimize the model parameters,which improves the simulation accuracy of the device linearity effectively.The nonlinear capacitance model is established immediately afterwards.Finally,the comparison of the measured values with the simulated values of the largesignal model shows that its prediction error of the third-order intermodulation distortion characteristics of a GaN HEMT device is within 2 d Bc.In moreover,the accuracy of the model for predicting S-parameters and large-signal output characteristics is above 90%,with a relatively good simulation of load pull.3.Studying on GaN HEMTs quasi-physical large-signal modeling.To address the problem that the empirical current model is lack of clearly physical meaning,a quasiphysical current model based on the harmonic mean is proposed in this thesis.The current in the saturation region uses the Chih-Tang Sah equation with clear physical meanings,while the empirical equation is used in the linear region,and the current equations in both regions are combined into a unified expression by introducing the harmonic mean.Then,the current model is verified by using the test data of pulsed current and DC current respectively,and the current output characteristics of a GaN HEMT device can be well characterized by the model.Finally,a large-signal model is established and accurately simulate the large-signal output characteristics of a GaN HEMT device,and the correctness of this current model is further demonstrated.