應用於WCDMA頻段之適應性前饋式補償功率放大器設計

Abstract

本論文研製一應用於WCDMA系統之高線性功率放大器，此功率放大器利用前饋式(Feed forward)線性化技術來改善其線性度，並利用適應性補償控制電路降低溫度的影響。 前饋式線性度補償電路包含兩個迴路：載波消除迴路與交調信號消除迴路。前者是消除載波信號並擷取交調信號，後者是將交調信號來消除主功率放大器之交調信號。適應性補償控制電路則是利用運算放大器實現。 原功率放大器在WCDMA波段運作時經前饋式線性度補償電路，其三次交調信號對載波比達-60dbc以上，輸出功率達到32dbm以上並符合WCDMA ACPR規格，較未經補償功率放大器的28.8dbm，增加3.2db，達到預期效果。另外，交調信號相消的原理亦被運用於另一種預失真補償電路，在870-880MHz輸出功率40dbm時，IMD3 改善超過12db，符合經濟效益。

A highly linear power amplifier for WCDMA applications is developed . The power amplifier utilizes the feedforward linearized technique to improve linearity. The temperature variation is stabilized by an adaptive circuit with OP amplifiers. Feedforward linearized technique is consisted of two loops: the carrier cancellation loop and the IMD cancellation loop. The former cancels the carrier signal and provide a sample of IMD and the latter uses the previous IMD signal to substrate the IMD of the main power amplifier. The IMD3 at the output achieves -60dbc at the 2.15GHz(more than 20db improved) and satisfies 3GPP WCDMA ACPR Specification with output power 32dbm.The output power is raised more than 3.2db. The principle of IMD cancellation is also applied to another power amplifier with predistortion compensation. It can achieve 12 db improved of IMD3 during the 870-880MHz band as output power is 40dbm.