Generalized Frequency Dependent Small Signal Model for High Frequency Analysis of AlGaN/GaN MOS-HEMTs

Abstract

Traditional lumped small signal equivalent circuit models of AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOS-HEMTs) are made up of constant valued circuit elements. Such models are unable to capture the high frequency behavior (above 20 GHz) of the device. In this work, a modified small signal equivalent circuit model of AlGaN/GaN MOS-HEMTs is presented. The key feature of the proposed model is that the values of the different circuit elements in the model are considered to be frequency dependent in nature and not constants. The frequency dependent value of each circuit element is mathematically represented using polynomial functions where the coefficients of the functions are determined via a least-square curve fitting approach. This frequency dependent attribute of the circuit element values ensures that the proposed model is very accurate at high frequencies without sacrificing the compactness of the model topology. The accuracy of the proposed model has been verified up to 50 GHz using experimentally measured Y-parameters of AlGaN/GaN MOS-HEMTs having a different gate dielectric and gate length.

An Accurate Approach to Develop Small Signal Circuit Models for AlGaN/GaN HEMTs Using Rational Functions and Dependent Current Sources

“…In our previous study, we have shown that the conventional SSC model of Fig. 1 (b) can match the experimentally measured S-or Y-parameters of an AlGaN/GaN (MOS)-HEMT only if the corresponding circuit element values are considered to be a function of frequency [10]; also evident in Fig. 2 of this paper.…”

“…However, as observed in Fig. 2, the values of gm and τ derived from the experimentally measured Y-parameters of AlGaN/GaN HEMTs also show a significant deviation across a broadband frequency range [10]. Both these features end up reducing the accuracy of the modified SSC model of [13].…”

“…Traditionally, the circuit element values making up the SSC model are derived by fitting the model parameters to experimentally measured Y-parameters only at low frequencies [9]. Consequently, the conventional SSC models of AlGaN/GaN HEMTs fail to capture the high frequency behavior of the device [10]- [12]. To overcome the limitations of the conventional SSC model of AlGaN/GaN HEMT at broadband frequency range, several empirical models has been reported in the literature.…”

“…To overcome the limitations of the conventional SSC model of AlGaN/GaN HEMT at broadband frequency range, several empirical models has been reported in the literature. An overview of some of these empirically derived SSC models can be found in [10]. In a recent study, we have demonstrated a novel approach to develop modified SSC models that can better capture the experimentally measured Y-parameters of AlGaN/GaN metal oxide semiconductor HEMTs (MOS-HEMTs) over a broadband frequency range [13].…”

Equivalent‐circuit extraction for gallium nitride electron devices: Direct versus optimization‐empowered approaches

“…Over the last half century or so, many efforts have been devoted to the equivalent‐circuit extraction for modeling the scattering S‐parameter measurements of active electron devices 1–21 . Although the frequency‐dependent behavior of the scattering parameters can be easily and quickly reproduced by using alternative representations (e.g., artificial neural networks 22–26 ), the calculation of a small‐signal equivalent‐circuit model is essential as this circuit can be utilized as a foundation for developing large‐signal 27–32 and noise 33–38 models.…”