天文接收機之低雜訊放大器與毫米波功率放大器之研製

Abstract

在射頻天文應用中，需要對來自宇宙中的微弱信號進行高靈敏度的探測。因此，這些射頻望遠鏡的操作頻率通常是非常寬的。另外，天文應用對訊雜比的要求非常嚴格。作為接收器中的第一個主動電路，低雜訊放大器在接收機系統中扮演非常重要的角色。阿塔卡瑪大型毫米及次毫米波陣列(ALMA)計畫主要有十個子頻帶，其頻率範圍從35 GHz到950 GHz，其中一個子頻帶涵蓋35 GHz到50 GHz。此外，隨著射頻應用的工作頻率增加，毫米波的研究已經引起越來越多的關注。然而，毫米波具有較高的自由空間損耗和較高的大氣衰減，這使得有用的傳播比低頻的傳播短得多。為了滿足5G基站和衛星通信的要求，具有高功率密度和高效率功率放大器的重要性正在增加。 本論文包含兩個部分。第一部分是應用於天文接收機的Q頻段低雜訊放大器，使用0.15微米砷化鎵假型高速電子遷移率電晶體(pHEMT)製程設計。第二部分是應用於5G基地台或衛星通訊的Ka頻段功率放大器，使用0.15微米氮化鎵高速電子遷移率電晶體(HEMT)製程設計。 論文中首先提出了一個應用於射頻天文接收器系統的Q頻段低雜訊放大器之研究。此低雜訊放大器採用了四級共源極的架構。首先，第一級中使用源極退化技術用於實現雜訊和增益性能之間的平衡。其次，在後面三級設計了R-C回授技術以實現寬帶性能。為了提高最大增益、穩定因子和匹配阻抗點，將討論反饋電容和電阻的組合。然後，通過採用π型匹配網絡完成寬頻的阻抗匹配。最後，討論了由代工廠提供CPW配置的電晶體模型所引起的測量結果和模擬結果之間的誤差。該低雜訊放大器在21.5 GHz至50 GHz範圍內展示了 22.5 dB 峰值小信號增益，在所需頻寬內，功率消耗為 36 mW。從 21.5 GHz到50 GHz的雜訊指數為3 dB到4.6 dB。量測的輸入1-dB功率壓縮點(IP1dB)範圍為從-23.8 dBm到-17.3 dBm，而輸出1-dB功率壓縮點(OP1dB)範圍從-6.5 dBm到1.4 dBm。 另外介紹一個高輸出功率的Ka頻段功率放大器，其架構為由兩路三級的共源放大器組成。考慮到散熱對最大輸出功率和耐用性的影響，對電路佈局做了一些改進。測量結果顯示了5.5 GHz的3-dB頻寬，即從26.5 GHz到32 GHz。峰值增益出現在30.3 GHz，而增益為20.3 dB。此電路在28 GHz 時實現了32.3 dBm的輸出飽和功率(Psat)及27.7%的峰值功率附加效率(PAEpeak)，還得到31.4 dBm的輸出1-dB功率壓縮點，其輸出功率下的功率附加效率(PAE1dB)也達到23.3%。

RF astronomy applications require highly sensitive detection of weak signals from the universe. Therefore, the operating frequency of these RF telescopes is usually very wide. In addition, the signal-to-noise ratio requirements for astronomy applications are very strict. As the first active circuit in the receiver, the low noise amplifier plays a very important role in the receiver system. The Atacama Large Millimeter/submillimeter Array (ALMA) project has ten main sub-bands with frequency ranges from 35 GHz to 950 GHz, with one of the sub-bands covering 35 GHz to 50 GHz. However, millimeter wave has higher free space loss and higher atmospheric attenuation, which makes the useful propagation much shorter than that of lower frequencies. To meet the requirements of 5G base stations and satellite communications, the importance of PAs with high power density and high efficiency is increasing. This thesis consists of two parts. The first part is a Q-band low noise amplifier (LNA) fabricated in 0.15-?m GaAs pHEMT process for astronomical receivers. The other describes a Ka-band power amplifier (PA) fabricated in 0.15-?m GaN HEMT process for 5G base stations or satellite communications. The first part presents the research of Q-band LNA for RF astronomical receiver systems. This LNA adopts four common-source stages. First, source degeneration technique is used in the first stage to achieve a balance between noise and gain performance. Secondly, the R-C feedback technique is designed at the latter three stages to achieve wideband performance. In order to improve maximum gain, stability factor, and the matched impedance points, the combination of feedback capacitance and resistance is discussed. Then, broadband impedance matching is accomplished by using a π-type matching network. Finally, the errors between the measured and simulated results caused by the transistor model of the CPW configuration provided by the foundry is discussed. This LNA demonstrates a 22.5-dB peak small-signal gain from 21.5 to 50 GHz within the desired bandwidth with 36 mW power consumption. The noise figure is 3 to 4.6 dB from 21.5 to 50 GHz. The measured IP1dB ranges from -23.8 to -17.3 dBm while the OP1dB ranges from -6.5 to 1.4 dBm. The other part illustrates a high output power Ka-band PA, which is composed of two-way three-stage common source amplifiers. The layout of the circuit has been modified to consider the effect of heat dissipation on maximum output power and durability. The measured results of the proposed PA show a 3-dB bandwidth of 5.5 GHz, i.e., from 26.5 GHz to 32 GHz. The peak gain occurs at 30.3 GHz with 20.3 dB of gain. This PA achieves a saturated output power (Psat) of 32.3 dBm with 27.7% peak PAE, and 31.4-dBm OP1dB with 23.3% PAE1dB at 28 GHz.