Thesis or Dissertation Power gain mechanism and methods for power gain improvement of quantum and conventional transistors


pp.1 - 139 , 2016-03-25 , The University of Electro-Communications
This thesis aims to study power gain, methods for its improvement and various power gain related microwave performances including stability, isolation, efficiency and linearity for various devices and independently biased circuit configurations. For the purpose of studying power gain, one of the most important characteristics of active devices, a quantum device named the single-electron transistor (SET), and an independently biased heterojunction bipolar transistor (HBT) cascode configuration were chosen to investigate using the methods of current transfer control and resistance transfer control, respectively. By using the current transfer control method for power gain improvement, power gain and output power of the SET were found to be significantly improved by 39.45 dB and 39.45 dBm, respectively if its source resistance was reduced by 99.3 MΩ which is equivalent to the reduction by 1.25 nm of the source junction thickness. In addition to the power gain, frequency characteristic which relates to the operation speed of the SET was also investigated. The frequency characteristic of the proposed SET model reveals the fact that it can operate well at THz regime, thus it can be regarded as an ultra-high speed device for possible high data rate wireless communication application in the future. Besides SET, power gain enhancement for a novel circuit construction which is so-called the independently biased cascode InGaP/GaAs HBT was also studied by taking the advantage of resistance transfer control method of the cascode configuration. Its power gain can be enhanced thanks to the use of the independently biased feature to control its output resistance through adjusting the second stage collector bias current. Its power gain was experimentally confirmed to be higher than that of a conventional configuration by more than 5dB at an operation frequency of 1.9 GHz. For the purpose of studying power gain related microwave performances, two independently biased configurations, namely 3-stack InGaP/GaAs heterojunction bipolar transistor (HBT) and 3-stack AlGaN/GaN high mobility electron transistor (HEMT) were chosen to investigate. In this research topic, not only power gain but various important microwave performances of the two configurations were studied under the investigation of various bias conditions by taking the advantage of the two added bias terminals. It was concluded that the fabricated amplifier which was based on the independently biased InGaP/GaAs HBT 3-stack monolithic microwave integrated circuit (MMIC) chip can deliver an optimum performance at an operation frequency of 1.6 GHz for superior power gain and low distortion as: PAE = 23.5 %, Pout = 12 dBm; Gain = 32.6 dB at IMD3 = -35 dBc. In addition, the small-signal and large-signal performances of the proposed configuration also exhibited better than that of a conventional configuration if its bias condition is controlled appropriately. For the independently biased Al-GaN/GaN HEMT 3-stack configuration, by setting appropriate bias condition for each transistor using independently biased feature, the simulated results at an operation frequency of 2.1 GHz demonstrated a high output power, high efficiency and high gain performance as: PAE = 46.45 %, Pout = 28.82 dBm; Gain = 23.96 dB at IMD3 = -32.34 dBc. These results has confirmed the superior advantages of the proposed configurations.

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