Modeling Of AlGaN/GaN HEMT And Amplifier Design

GaN is the representative of the third generation of semiconductor materials owing to its high electron drift mobility and thermal conductivity. With the progress of epitaxial material growth technology and the development of technique, gallium nitride material has been paid more and more attention by all sectors, including its application in the power amplifier field. Simulating the circuit with CAD is the first step to complete a circuit design, so premise and focus on circuit design is the accurate models and the precise parameter extraction in order to increase the reliability of the circuit design and reduce research time, thus simplifying and accurate models is the focus of current research.The first part of this thesis is the introduction of the applications of GaN HEMT amplifier applications. Firstly, the fundamental of GaN HEMT is introduced briefly, Secondly, several differences and their advantages and disadvantages of several kinds of power amplifier are analyzed detailedly. Lastly, some basic knowledge about power amplifier are presented including output power, efficiency, stability, bias circuit, several kinds of matching mode and microstrip line theory.The second part is the introduction of GaN HEMT modeling. Firstly, Accurate mearsured S-parameter is of great importance to extract small signal model parameters, so Y-parameter matrix,Z-parameter matrix and S-parameter matrix are introduced. Secondly, One 19 elements equivalent circuit which is more suitable for GaN is considered based on the classic Ga As smallsignal model, and its equivalent circuit and the way parameter extracted is also researched. To extract extrinsic parameter, S-parameter was converted to Y-parameter based on the measured cold- fet S-parameter(Vgs<Vth;Vds=0V) and open structure S-parameter, then the initial capacitance parameters at low frequenc y are extracted, followed by converting Y-parameter to Z-parameter. And then the initial inductance parameters and resistance parameters at high frequency are extracted. To extract intrinsic parameter, S-parameter are measured at Vds=30V, Vgs=-1.75 V.and the intrinsic parameter can be extracted after de-embedding the extrinsic part. Lastly, one method which can optimize the initial parameters is proposed and the small signal model is achieved according to the fitting curve.The third part is the introduction of the circuit design. One two-stage small-signal circuit using the prior small signal equivalent circuit model is designed based on maximum gain characteristic, whose gain can reach 20 d B and reflecting is less than-25 d B. One two-stage class AB amplifier is designed using Cree's CGHV1J006 D transistors. When Vds is biased at 40 V and Vgs is biased at-2.2V the gain can reach 25 d B, saturated output power can reach 26 W and efficiency can reach 60% at the operating frequency of 8GHz. The gain is more than 20 d B, the output power is more than 20 W and the PAE is more than 50% from 6.5GHz to 9.5GHz.The fourth part is a summary of the full text and future work worth to research.