Ka頻段寬頻功率放大器之研究

Abstract

大部分已發表的Ka頻段寬頻功率放大器功率頻寬都是窄頻的，但寬頻功率放大器在大訊號操作下應該也要是寬頻的，而不是僅由增益與返回損耗認定。這篇論文提出了在Ka頻段的射頻功率放大器以及緩衝放大器之研究。為了驗證電路設計的方法，我們設計並實作了兩個Ka頻段放大器。 我們介紹了一個20 dBm單晶微波積體電路功率放大器，它的操作頻率涵蓋了整個Ka頻段，製程使用砷化鎵假型高速電子移動電晶體，並採用了疊接組態以提供高增益。量測中出現了振盪，可使用晶片外旁路電容以及調高共閘極電晶體的閘極端偏壓消去振盪。量測結果顯示輸出功率1 dB功率壓縮點為19.3 dBm，功率附加效益15.5%以上；在整個Ka頻段中量測的峰值功率附加效益達到22.5%，並有22.7 dBm的飽和輸出功率。因為量測結果和模擬相去甚遠，我們發現是電晶體模型在操作的偏壓不精確，因而提出了修正過的模型。因為電路有振盪的問題，所以我們提出了Q值的分析以穩定電路，並重新設計了放大器。 我們使用65奈米CMOS製程設計並製造了一個頻寬27-34 GHz的緩衝放大器，量測結果顯示輸出功率1 dB功率壓縮點為7.7 dBm，此時能維持21.8 dB的小訊號功率增益，以及13%以上的功率附加效益，峰值功率附加效益達到23.3%並有10.6 dBm的飽和輸出功率。這在所知已發表的Ka頻段緩衝放大器中有最寬的功率頻寬。

Most reported broadband power amplifiers in Ka band have narrowband power characteristics. A broadband power amplifier should have wideband characteristics which include not only gain and return losses but also power performance. In this dissertation, the design and analysis of broadband amplifiers is demonstrated. To verify the proposed method, two Ka-band amplifiers are designed and implemented. A full Ka-band 20-dBm power amplifier is implemented in 0.15-um GaAs pHEMT technology. The cascode configuration is adopted to provide higher gain. Spurious oscillations are observed in measurement and can be suppressed by off-chip bypass and raising the gate bias of CG transistor. The measurement result shows a power added efficiency (PAE) at 1-dB compression point (P1dB) up to 15.5% and 19.3-dBm OP1dB. Peak PAE higher than 22.5% and saturation output power (Psat) higher than 22.7 dBm are obtained at 27 GHz. Since the measurement results differ from simulation, we find that the transistor model is not precise at the desired bias, thus a modified model is introduced. Because the amplifier suffers from oscillations, the Q factor of bypass network is analyzed to stabilize the amplifier, and the proposed amplifier is redesigned. A 27-34 GHz buffer amplifier (BA) is fabricated in 65-nm CMOS process. The measurement results show a PAE at P1dB up to 13% while maintaining 21.8-dB gain and 7.7-dBm OP1dB at 30 GHz. The peak PAE and Psat are higher than 23.3% and 10.6 dBm, respectively. To the best of our knowledge, the 27-34 GHz BA has the highest PAE among reported Ka-band CMOS BAs.