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%0 Thesis
%A Chalermwisutkul, Suramate
%T Large signal modeling of GaN HEMTs for UMTS base station power amplifier design taking into account memory effects
%C Aachen
%I Publikationsserver der RWTH Aachen University
%M RWTH-CONV-123322
%P VIII, 139 S. : Ill., graph. Darst.
%D 2007
%Z Aachen, Techn. Hochsch., Diss., 2006
%X Compared to GSM, the data-rate of UMTS is considerably increased so that mobile broadband applications are possible. However, the specifications of UMTS mobile phones and base stations are more stringent. Due to the high crest factor of UMTS-signals, RF-frontends of UMTS base stations are required to provide high linearity while high efficiency and high output power are also typically desirable. The most critical element consuming the largest fraction of power in a mobile base station is the power amplifier (PA) which must be carefully designed for high efficiency and high linearity. State-of-the-art power devices for base station PAs are Si-LDMOSFETs. However, since requirements of communication standards are consistently increased, it is expected that LDMOSFETs will reach their limitations regarding power level, linearity and efficiency in the near future. Considering the global market of mobile communication, several standards and frequency bands of operation exist. Commonality of base stations for different communication standards leads to reduced product spectrum and thus to lower production and maintenance costs. For frequency agile base stations, specific device properties e.g. a high output impedance and a marginal memory effect, which are not provided by LDMOSFETs, are necessary.Compared to Si-LDMOSFETs, recently emerging GaN HEMTs offer higher power density, higher frequency of operation, higher operating voltage and higher operating temperature which lead to less cooling requirement and smaller component size. Due to the high output impedance of GaN HEMTs (10 times as high as LDMOSFET with the same power level), the structure of the output matching network can be simplified. Moreover, regarding the bandwidth and the memory effects, GaN HEMTs have been shown in the literature to be potential power devices for reconfigurable base station PAs (Eckl et al.: “Suitability of different device technologies for reconfigurable, multiband, multicarrier amplifiers”, WSC Symposium Workshop, IMS 2004, Ft. Worth, TX, USA, June 2004). Therefore, GaN HEMTs are expected to establish themselves as standard power devices for communication and power applications. Investigations in this work are parts of the ERGAN-project supported in part by the German Federal Ministry of Education and Research (BMBF). The main objective of the project is to investigate the suitability of GaN HEMTs as RF power transistors for frequency agile mobile base station systems. GaN HEMTs investigated here have been processed by the Ferdinand-Braun-Institut für Höchstfrequenztechnik, Berlin. The dissertation focuses on the characterization and the modeling of devicelevel memory effects due to charge carrier trapping. Different measurement methods of charge carrier trapping proposed in the literature were compared to define appropriate measurement setups for the devices investigated in this work. The measurements were performed at different temperatures as well as under different bias- and lighting-conditions, respectively, to investigate their effects on the time constants of trap-charging and discharging processes. From the measurement results, parameters characterizing the charge carrier trapping can be extracted and integrated into the device model. Moreover, scaling rules of these parameters regarding the device size and the temperature were determined. Then, the large signal models taking into account charge carrier trapping were used for simulations with UMTS signals to examine the influences of the device-level memory effects on the system performance. As a verification, comparisons between measurements and simulations in time- and frequency domains are shown. Envelope simulations were performed to investigate the influence of trap-related memory effects on the output spectral shape. Considering the simulation results, the suitability for the reconfigurable multiband amplifier of the GaN HEMTs investigated in this work can be evaluated. The information gained from such simulation results contributes to further device and circuit optimization and the understanding of memory effects in power amplifiers for wireless communications.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%U https://publications.rwth-aachen.de/record/61686