線性調變系統之線性放大器研製

Abstract

本論文設計一應用於線性調變系統之高效率線性放大器,並發展出一 套簡易的設計 及調整步驟,在不劣化調變頻寬之下能儘量提昇操作效 率,按此設計程序,可縮短研發 時間,並得到一高效率同時高線性度之 放大器。 文中採用串接式 放大器,並個別分析共源極和共閘極放大器等效電路,針對主要元 件的 變化對於相位偏移的影響,找出導致相位偏移的機制,最後提出補償方式, 改善 AM/PM之非線性效應。由負載拖曳置具上得到在P3dB時輸出功 率19.4dBm,相位偏移維持 在2 deg.以內,此時效率可高達42.3%,輸出信 號頻譜符合NADC系統移動台之調變頻寬規格 。 A high efficiency and linear power amplifier with applications to linear modulation system has been developed in this study. It consists of two MESFET in cascode configuration. With the complementary property of phase in cascode structure, the amplifier can be driven into more nonlinear region without spectrum degradation. Therefore, the efficiency can be improved. In the mean time,a simple tuning procedure for linearization is proposed. The cascode amplifier, Unbalance BIas Cascode Amplifier, is used to compensate the phase deviation in weak saturation region. With appropriate load pull tuning, the amplifier reaches its highest efficiency 49% and has output power 20.4dBm at P3dB. By the simple tuning for phase deviation under 2 degree, the output power becomes 19.4dBm at 3dB compression point. The efficiency is 42.3%. With NADC input, the output signal modulation bandwidth appears 26dBc at offset 30kHz and 50dBc at offset 60kHz signal, which satisfy the standard of NADC.