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Title: Investigation on a new type of power amplifier linearization technique : dynamic IMD sweetspot
Other Titles: Yi zhong xin xing gong lü fang da qi xian xing hua ji shu yan jiu : dong tai shi zhen jiao tiao tian dian
一種新型功率放大器線性化技術研究 : 動態失真交調甜點
Authors: Wu, King Cheung (胡景翔)
Department: Department of Electronic Engineering
Degree: Master of Philosophy
Issue Date: 2010
Publisher: City University of Hong Kong
Subjects: Power amplifiers -- Design and construction.
Amplifiers, Radio frequency -- Design and construction.
Modulation (Electronics)
Electric distortion.
Notes: CityU Call Number: TK7871.58.P6 W8 2010
xiv, 140 leaves : ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2010.
Includes bibliographical references (leaves [135]-140)
Type: thesis
Abstract: Wireless communication engineering has been a very hot research topic in the past few decades. The development of wireless communication technique is driven by the enhanced mobility that carried to people by the mobile phone. Furthermore, due to the increasing need for more information exchange, the resulting demand in enhancing data rate for modern communication technologies has been the biggest momentum in driving the technologies forward. Hence, to better utilize the available channel bandwidth such that higher data rate can be obtained, more complex modulation techniques with carriers modulated linearly in both multi-level amplitude and phase have been adopted. As a result, the signal linearity requirement is very high for modern communication system. In a wireless communication system, the radio frequency (RF) frontend play an important role. The amplifying linearity of power amplifier (PA) is notoriously known as very poor especially in the power saturated regime. In highly carrier modulated communication system, the linearity requirement is very critical such that the modulated signal can be correctly recovered at the receiver. In order to improve the linearity of a PA, numerous techniques have already been proposed, such as feedforward, feedback, pre-distortion, etc. In this research, the characteristics of the intermodulation distortion sweetspot (IMD Sweetspot) for suppressing the third-order in-band IMD (IMD3) have been investigated. IMD Sweetspot is a special phenomenon for PA where a sudden drop in the corresponding output IMD level is found. In addition, this phenomenon is found to be dependent on the PA biasing as well as the input/output loading network. To evaluate the impact of those mentioned parameters on the IMD Sweetspot characteristics, experiments have been conducted on PAs based on current and voltage controlled transistor respectively. In the first experiment for a bipolar junction transistor (BJT) amplifier, it has been shown that the IMD Sweetspot is observable up to the saturated power region. By varying the bias condition and the input capacitive loading, the location of the IMD Sweetspot can be controlled. The IMD3 reduction achieved by utilizing the IMD Sweetspot is among 20-30 dB which keeps the third-order intermodulation ratio (IMR) above 40dBc within all the output power range of the PA. Size consideration is another vital factor for the modern mobile system. To develop cost effective handheld system featuring compact size, integrated circuits (ICs) implementation is always preferred over the discrete circuit one. Hence, a 0.5μm InGaAs pseudomorphi high electron mobility transistor (pHEMT) technology for radio frequency integrated circuit (RFIC) has been employed for further IMD Sweetspot study. From the fabricated PA IC, similar controlling capability on the IMD Sweetspot was observed as compared to the previous BJT PA experiment. The IMR level can be kept above 30dBc for a wide range of output level, while the saturated power and maximum power added efficiency (PAE) achieved are 26dBm and more than 45% respectively.
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