利用功率回收技術提升效率之平衡式功率放大器

Abstract

一般來說，無線收發機中最耗電的元件即為功率放大器 ( PA ) 。因此，功率放大器效率越高，行動裝置便可以使用越久。線性度與效率為決定無線發射機的兩個關鍵參數，功率放大器的線性率與效率必須有所取捨，換言之，當我們得到較高的效率，線性度便會降低。本論文提出一利用功率回收技術提升效率之平衡式功率放大器，而反射功率將被 90°分合波器之隔離埠吸收，使用射頻-直流轉換器將反射功率轉換為直流功率回收至供應電源。整體電路架構將被實現並驗證此想法，輸入訊號採用 836.5 MHz 之 W-CDMA 訊號在電壓駐波比為 2:1 與 4:1 時的負載相位角作測試。 量測功率回收技術提升整體效率，當輸出功率為 25 dBm ，而電壓駐波比為 2:1 時，最高提升效率量為 14.7 % ，當輸出功率為 25 dBm ，而電壓駐波比為 4:1 時，最高提升效率量為 22.1 %。提出之利用功率回收技術提升效率之平衡式功率放大器，相信此電路是個有效提升效率的設計方向。

In general, the power amplifier ( PA ) is one of the most power-hungry devices in a wireless transceiver. Therefore, the longer the mobile devices can operate when the higher the PA efficiency. Linearity and efficiency are two key parameters to determine the performance of wireless transmitters, so linearity and efficiency must be traded-off in the PA. That is, we got more efficiency while the linearity is decreased. This thesis is a method for improving the efficiency of a balanced PA under load mismatch by recycling the reflected power. The reflected power will be directed to the isolated port of a 90° hybrid coupler. The reflected power can then by rectified and converted back to dc power to assist in supplying the PA. A prototype system was built to validate the concept and tested under various phase angles with 2:1 and 4:1 VSWR using a W-CDMA voice signal at 836.5 MHz. Measurement results show that the power recycling technique improves the overall efficiency by as much as 14.7% and 22.1 % when 2:1 and 4:1 VSWR of the output power level is 25 dBm. The proposed an efficiency improved balanced PA using power recycling technique, we believe our designs are valid and effective directions to achieve improving the efficiency of PAs.