Radio Frequency Power Amplifier for Green Communications

Abstract

After finishing the literature survey of this work, it is concluded that GaN material is a promising semiconductor material for future efficient high-power, high-frequency applications. Therefore, this thesis has focused on some of the problems related to characterization of high power density devices like GaN based HEMTs, as well as the possibilities given by the new nonlinear simulation and characterization systems. This thesis presents a comprehensive comparison of two heterojunction bipolar transistors (HBTs); the AlGaAs/GaAsHBT and the AlGaN/GaN HBT. This comparative study is based on common Figure of Merit (FOM) definitions.The simulation results showed that AlGaN HBT can operate at higher power levels and withstand a higher dissipated power. In case of S-parameter simulations, the cut-off frequency and output gain of AlGaN HBT are very limited as compared with AlGaAs HBT transistors. Inaddition, the minimum noise figure of AlGaN is noticeably greater than the AlGaAs. Furthermore, the μu stability measure of AlGaN is more stable than the AlGaAs. It can be concluded thatup till now no real solutions were found to solve the fabrication problems ofAlGaN/GaN HBT. In addition, it does not have a general simulation model to be used in wireless applications. It was found that the main problem is in the limitations of the base resistance and the low gain of AlGaN/GaN.Those limitations occur mainly because ofthemismatch of nitride atom lattice and aluminum lattice. Therefore, it is understood that why researchers are taking the direction ofGaN HEMT instead of GaN HBT .

This thesis proposean optimized nonlinear model of GaN HEMT transistor that shows enhancement in efficiency, linearity, output power, and spectrum transmission mask in the adjacent channels. It has also shown enhancement of the 1dB compression point. This has led to reduced radiation and has proved its suitability in green communications systems. This means that the new model of GaN HEMT can be used instead of a conventional GaAs Transistor. The efficiency is actually doubled while the maximum output power is enhanced by 7dB. In addition, the adjacent channel power ratio is increased by (15-20) dB which makes the transmission mask deeply complies with the WiMax standard. In addition, this thesis presents a study of simulation nonlinear model using ADS design tool.to apply an improvement on traditional Angelov model to optimize the best parameters that can represent the device more effectively. The large signal modeling of GaN HEMT is studied and a novel nonlinear model of GaN HEMT transistors is introduced. It is compared to nonlinear modeling based on conventional Angelov model. The modified model is applied on the AlGaN/GaN HEMT TriQuent TGF2023-01 to be compared to datasheet and verified. I-V characterization and S-parameter simulations agree well with the original datasheet results which verifies the proposed nonlinear model. In addition, AlGaAs/GaAs HEMT NEC900175 transistor is modeled and simulated to give an overview comparisons between GaN and GaAs HEMT versus GaN HBT, although the latest is not available due to the previously discussed fabrication problems. The proposed model of GaN HEMT transistor has shown enhancement in efficiency, linearity, output power, and spectrum transmission mask in the adjacent channels. It has also shown enhancement of the 1dB compression point. This has led to reduced radiation and has proved its suitability in green communications systems. This means that the new model of GaN HEMT can be used for PA design instead of a conventional GaAs HEMT. The efficiency is actually doubled while the maximum output power is enhanced by 7dB. In addition, the adjacent channel power ratio is increased by (15-20) dB which makes the transmission mask deeply complies with the Wi-MAX standard. There is a problem which exists through implementation stage because the TGF 2023-01 is a die transistor. It needs special bonding, this technique is not available. Therefore, another transistor is chosen to complete the fabrication and measurement cycle of our proposal. A GaN HEMT transistor produced from Cree Inc. gives us the same requirements and a suitable output power for this design.