應用於數位無線通信高功率線性放大器之研製

Abstract

本論文介紹一應用於數位通訊系統之高線性寬頻功率放大器。此功率放大器運用Feedforward技巧來改善其線性度。Feedforward電路包含兩個迴路：主信號消除迴路，和諧波消除迴路。主信號消除迴路是消除載波信號並擷取無載波之諧波信號，而諧波消除迴路則是利用主信號消除迴路產生無載波之諧波信號來消除功率放大器放大造成之諧波信號，兩迴路利用可調衰減器電路和可調相角位移電路來調整Feedforward電路之最佳狀態。原本功率放大器(P1dB=34dBm)經過Feedforward電路改善之後，在900MHz頻段，三次諧波被消除達30dB，三次諧波對載波差達到-64dBc，對Narrow-Band CDMA ACPR ( IS-95標準)規格，輸出功率達到27dBm較原放大器輸出功率24dBm 增加3dB，操作頻寬達到25MHz (869~894MHz)，達到其寬頻高線性之要求

This thesis describes a high-linear wide-band power amplifier for modern digital communication .The power amplifier use the feedforward technique to improve linearity. Feedforward contains two loops : the signal cancellation loop, and the third–order intermodulation products (IMD3) cancellation loop. The signal cancellation loop cancels the carrier signal and provides a sample of IMD3. The IMD3 cancellation loop uses the sample to substract the distortion in the main power amplifier. Each loop uses variable attenuator and variable phase shifter to adjust the best performance. The IMD3 cancellation reaches about 30dB and IMD3 to carrier are less than –64dBc for two-tone test in the 900MHz region after feedforward linearization. Then feedforward power amplifier can pass N-band CDMA ACPR ( IS-95 standard) to provide output power 27dBm .The output power of feedforward power amplifier improves 3dB than the origin power amplifier.The operation bandwidth is more than 25Mhz(869~894Mhz).