Gain Compression Mechanisms、Power Saturation Mechanisms and Linearity in Power MESFETs

由於無線通訊的快速發展，展開了對具有高功率以及良好線性度的功率放大器的需求。然而，輸出功率以及線性度會受限於某些機制，例如:崩潰電壓、膝部電壓、最大汲極電流以及載止電壓。這些機制會隨著輸入信號的功率而增加壓縮增益接而飽合輸出的功率。 在本論文中，我們藉著觀察閘極電流與汲極電流以分析這些機制的發生。不同摻雜濃度及不同凹形(recess)結構的場效電晶體在各個偏壓條件的操作都已作分析。當遭受增益壓縮機制所限制時，線性度減低得很嚴重。任何輸出波形的變形都會劇烈地降低線性度。在我們的分析中：A級操作可以避免增益壓縮機制並有良好的線性度。摻雜濃度低的元件，可以有良好的大信號效能及線性度。狹窄凹形的場效電晶體因為有較高的最大汲極電流將會有較高的輸出功率及較好的線性度。The rapid growth of wireless communication has opened up the request for high power and good linearity power amplifier. However, the output power and linearity is limited by some mechanisms, such as breakdown voltage, knee voltage, the maximum drain current and pinch-off voltage. These mechanisms compress constant gain and then saturate output power as input power increases. In this thesis, we analyze and identify gain compression mechanisms by observing the gate current and drain current. The gain compression mechanisms for FETs with different doping and recess structures at various bias points are analyzed. Linearity is seriously degraded when devices suffer gain compression mechanisms. Any distortion in output waveform decreases linearity drastically. In our analysis: Class A operation avoids the gain compression mechanisms and has good linearity. FET devices with low doping density can have good linearity. Narrow recess FETs have high Imax which results in high output power and good linearity.Abstract(in Chinese)………………………………………… i Abstract(in English)………………………………………… ii ACKNOWLEDGMENTS…………………………………………………iii Content……………………………………………………………v Figure captions…………………………………………………vii Chapter 1 Introduction………………………………………1 Chapter 2 Basic Theory of Load Pull Measurement………5 2.1 Introduction to load pull measurement…………5 2.2 Intermodulation distortion………………………10 2.3Two tone measurement…………………………………19 2.4 General bias condition analysis of power FETs21 2.4.1 Class A amplifier……………………………23 2.4.2 Class B amplifier……………………………27 Chapter 3 Gain Compression Mechanism and Bias Condition for MESFET with Different Doping Density………………………44 3.1 Device structure and d. c. characteristics.…45 3.2 Gain compression mechanisms for various bias conditions………………………………………………52 3.3 Intermodulation distortion…………………………71 Chapter 4 MESFET with Wide Recess and Narrow Recess Structure………………………………………………78 4.1 Device structure and d. c. characteristics……78 4.2 Gain compression mechanism and power saturation mechanism in wide recess and narrow recess FETs………82 4.3 Intermodulation distortion…………………………98 Chapter 5 Conclusions……………………………………106 References…………………………………………………… 10