具線性度補償之互補金氧半層疊E類功率放大器設計

Abstract

本論文針對可應用於極座標調變傳送機之互補式金氧半層疊E類功率放大器提出AM-AM和AM-PM失真補償之設計。本文探討之E類功率放大器為使用小電感值dc-feed之層疊式架構，主要考量為互補式金氧半製程中，大電感值電感不易取得以及主動元件的低崩潰電壓特性。而當層疊E類功率放大器應用於極座標調變（亦即調變放大器之供給電壓）時，在放大器的輸出訊號上會產生AM-AM和AM-PM失真特性。 本文除探討AM-AM和AM-PM失真產生之原因，並且提出一失真補償技術 ― 藉由改變層疊電晶體之閘極偏壓，使電晶體操作如一電阻性元件，進而改進放大器之非線性效應。由設計的2.6 GHz 層疊E類功率放大器實驗結果顯示，經由外部改變偏壓的方式，在供給電壓大於0.6伏特時，補償後之輸出訊號相位偏移可從30度降低到6度，輸出訊號振幅相對供給電壓可成線性變化。而另一2.6 GHz 層疊E類功率放大器整合自我偏壓控制電路設計之實驗結果顯示，輸出訊號振幅與供給電壓成1V/V之線性關係外，並有5度輸出訊號相位的偏移；在1.8伏特供給電壓和輸入功率為6 dBm下，輸出功率為12 dBm，汲極效率為17.8％，PAE為16.6％。實驗結果顯示，所提出的補償技術可有效的改進功率放大器之AM-AM和AM-PM失真。 並且利用射頻/基頻共同驗證方法，輸入為一OFDM訊號時，放大器經過補償後，模擬結果顯示，在16QAM的調變下，EVM可從-17dB到-19.2dB；在64QAM的調變下，EVM可從-21dB到-25.1dB。最後針對矽基底電感的低品質因素造成放大器效率的降低，因此整合多層金屬層之懸空式電感於放大器匹配電路中，模擬結果顯示可使放大器有最大17%的效率提昇。

The dissertation presents the design of the cascode Class E power amplifier with AM-AM and AM-PM compensation for polar applications. For integration and reliability analysis in CMOS process, the Class E designed with small dc-feed and using cascode topology has been presented. When the Class E is in supply modulation, the AM-AM and AM-PM distortion is introduced at the RF output signal. This work not only analyzes the cause of the distortion but also presents a compensation technique. When modulating the gate bias voltage of the cascode transistor, the transistor operates as a resistance alike to improve the distortion of the amplifier. The experimental result of proposed 2.6 GHz cascode Class E power amplifier shows that when the PA is compensated the AM-PM is reduced from 30° to 6° and the output envelope voltage is linearly to supply voltage in VDD > 0.6 V. The experimental result of the 2.6 GHz cascode Class E power amplifier with self-biased control circuit shows that the voltage slope of AM-AM is 1 V/V and the phase error of AM-PM is 5°. The PA has a output power of 12 dBm, drain efficiency of 17.8% and PAE of 16.6% from a 1.8 V supply and an input driving of 6 dBm. Therefore, the experimental results demonstrate the proposed compensation technique can effectively improve the AM-AM and AM-PM distortion of the cascode Class E amplifiers. In addition, the simulation results of the RF/baseband co-verification platform with OFDM-based signal source show that the EVM is improved from -17 dB to -19.2 dB at 16QAM modulation and from -21 dB to -25.1 dB at 64QAM modulation. Finally, due to the low quality factor of silicon-based inductor causing the degradation on PA efficiency, the PA with multi-metal layer suspended inductors has been presented. The simulation result shows that the PA can have a maximum efficiency improvement of 17%.