氮化鋁鎵/氮化鎵高電子遷移率電晶體之小訊號及大訊號模型

Abstract

基於現今移動通信的發展趨勢，其系統中所使用的功率放大器須具備更好的線性度和效率，而氮化鎵高電子遷移率電晶體因為能在高功率操作下保有這些良好特性，成為了最具希望用於功率放大器中的主動元件。我們通常會利用電腦輔助軟體來設計並優化放大器電路，所以一個能準確預測元件特性的非線性模型就至關重要。因此，本篇研究將針對 100ｕｍ 氮化鋁鎵/氮化鎵高電子遷移率電晶體，說明其小訊號及大訊號模型的建立過程及驗證結果。 我們採用由 16 個集總元件所組成的等效電路結構作為小訊號模型，在所有元件參數值從三組特定偏壓下的 S 參數量測而萃取得到後，成功驗證此模型可準確模擬元件的小訊號特性。而大訊號模型則使用安捷倫所發展的 EEHEMT 模型，並且透過 IC-CAP 進行一系列量測及模型參數的萃取。此模型在 DC 電流跟 S 參數的驗證中得到很好的結果，而在功率特性模擬上也與量測值有好的一致性，但交互調變失真的驗證則呈現較大的誤差，說明了 EEHEMT 在電荷及電流方程式無高次連續微分的特性，所以不能準確描述元件線性度。

Nowadays, the power amplifiers (PAs) are required to have high linearity and high efficiency for the applications of mobile communication. To meet the requirements, GaN HEMTs become the most promising candidate as active devices in the systems, because it can operate at high power level with good efficiency and linearity. The design of PAs needs an accurate nonlinear device model which can be implemented in the computer-aided design(CAD) environment. Therefore, in this thesis, the modeling procedures and verifications of small-signal and large-signal models for 100 um AlGaN/GaN HEMT are described. A small-signal equivalent circuit with sixteen elements is adopted, and the values of these elements are extracted by using three sets of S-parameter measurements at particular bias conditions. The simulations of S parameter under different bias conditions exhibit good agreement with measurements. The EEHEMT model is used for large-signal model, and the model parameters are extracted from DC and AC measurements by the help of IC-CAP. Both of DC-IV and S-parameter simulations show good consistency with measurements, and the simulations of single-tone power test at 2 GHz also show good agreement with measured data. However, the result of IM3 verification demonstrates a larger difference between measured and simulated data, indicating EEHEMT can't accurately predict the linearity of device.