利用低頻二階項前饋方法之24 GHz互補式金氧半導體線性化功率放大器之研製

Abstract

這篇論文題出一個可以使用在24 GHz的低頻二階項前饋技術，它可以改善互補式金氧半導體功率放大器的線性度。電路的主路徑由疊接組態組成，用來放大功率與提供足夠的增益，而電路的附屬路徑產生與主路徑相同的三階項電流，並利用兩路徑的反相特性消除三階項電流，另外，藉疊接組態電流鏡和直流位準移位器設計二階項電流以產生足夠的三階項電流。文中分析了此電路的操作原理及細節，並與已發表的其他線性化技術做比較。 此電路使用180奈米互補式金氧半導體製作一個操作在24 GHz頻段且具有線性化技術的單級放大器。量測的結果，此電路具有8.5 dB的小訊號增益， 17 dBm的飽和輸出功率以及在1-dB 壓縮點有14.4 dBm的輸出功率和12.3%的功率附加效率。為了驗證此電路的線性功能，量測的三階項訊號在甜蜜點(sweet-spot)改善了超過20 dBc，而在64 QAM數位調變訊號的注入下，此電路的頻譜成長可以改善 8 dB，顯示此功率放大器的線性化效果。

In this thesis, a new low-frequency IM2 feed-forward method is proposed to enhance the linearity of the 24 GHz CMOS power amplifier. The power amplifier consists of main and auxiliary paths. The main path consists of cascode topology to provide enough gain and amplify the output power. The auxiliary path consists of two transistors to provide the same IM3 current compared to the main path. The cascode current mirror and DC-level shifter are designed to feed the IM2 current in the auxiliary path. The operation detail of the linearized circuit is investigated, and the comparison of this new method versus other previous reported linearization methods is provided. A 24 GHz power amplifier with the proposed linearization method is fabricated in 0.18-um CMOS technology. According to the measurement, the proposed PA provides 8.5-dB small signal gain, 14.4-dBm OP1dB and 17-dBm Psat. The peak power-added-efficiency (PAE) and PAE at OP1dB is 15% and 12.3%, respectively. To verify the linearization effect, the measured IM3 signal is reduced more than 20 dBc at sweet-spot. Under the 64-QAM modulation, the ACPR and EVM are improved by 8 dB and 2%, respectively. It can be verified that the linearization effect of this power amplifier.