Research On Broadband High Efficiency Power Amplifier And GaN HEMT Device Modeling In Wireless Communication

In response to the growing demand for high-speed broadband data in 4G and 5G communication systems,the 4G evolved air interface design and the 5G high-frequency new air interface design put forward the demand of amplifying high peak to average power ratio?PAPR?modulated signal with high efficiency and no distortion over a wide operating band on the power amplifier?PA?module in the wireless transmitter.Therefore,it is of great significance to study the operation bandwidth,efficiency and linearity of the power amplifiers?PAs?.Accurate GaN HEMT device modeling is one of the critical steps to design PAs successfully.Therefore,research on GaN HEMT device modeling method is very important for designing broadband high efficiency PAs with new semiconductor materials.In view of the challenges raised by 4G and 5G communication technologies for broadband high efficiency PA,this paper has conducted in-depth research on broadband high efficiency linearized PA design technology,dynamic load modulation?DLM?technology and GaN HEMT device modeling technology.The main research contents include:1.Research on the wideband high efficiency linearized PAs.An analytical method is proposed to reduce the memory effects and third-order intermodulation distortions?IMD3?for improving the linearity of wideband PAs.Excellent linearity is achieved by reducing the second-harmonic output power levels and the envelope voltage components in the megahertz range.An improved wideband Chebyshev low-pass matching network is proposed to validate the proposed method.The measured results indicate that a wideband high efficiency linearized PA is realized from 1.35 GHz to 2.45GHz with power added efficiency?PAE?of 60⁷8%,power gain of 10.8¹2.3 dB and output power of 40.0⁴1.2 dBm.For a 20 MHz LTE modulated signal,the adjacent channel leakage ratio?ACLR?of the proposed PA with digital pre-distortion?DPD?linearization are-55.7^-53.9 dBc across 1.5².4 GHz at an average output power of32.4³3.6 dBm.For a 40 MHz two-carrier LTE modulated signal,the ACLR of the proposed PA with DPD linearization are-51.1^-48.2 dBc at an average output power of approximately 30.5 dBm in the frequency range from 1.5 GHz to 2.4 GHz.2.Research on the load modulated?LM?continuous Class-B/J PAs.Mathematical design space of LM continuous Class-B/J PAs is proposed.The combination of LM technique and continuous mode is introduced to enhance the wideband performance of LM PAs.An inversely proportional relationship between Z_L and C_out is derived,which indicates that the nonlinear C_out can affect the optimal load impedances at output power back-off?OPBO?and the design parameter?should be appropriately adjusted.The measured results of a PA prototype show that the PAE is 39⁴5%under load modulation when OPBO=5 dB across 1.6².4 GHz.Compared with the same PA with fixed V_var,the proposed PA with optimum V_var at 2 GHz achieves a PAE improvement with 11%when OPBO=5 dB.V_var is the varactor control voltage.Based on the Pedro load-line theory,the impact of knee voltage effect and soft turn-on characteristic of practical transistor on the design space of LM continuous Class-B/J PAs is analyzed.A generalized design space of LM PAs at the current generator plane?CGP?is proposed based on the theory of LM continuous Class-B/J PAs.By using a biasing operation factor?,the theory of LM PAs provides the analytical solutions for all the operation modes from Class-B/J mode to Class-A mode.3.Research on the load modulated inverse Class-F PAs.After introducing the“continuous concept”and second harmonic manipulation method,the mathematical design space of inverse Class-F PAs with extended conduction angle is proposed.The effects of the input driven level factor?and the biasing operation factor?on the third-harmonic generation are discussed.The definition of the inverse Class-F mode is consistently valid under the circumstance of load modulation in a limited OPBO range.Meanwhile,the conduction angle?₀ can be extended from?/2 to a limited value?<110°?to keep the standard waveforms of inverse Class-F mode.Calculation shows that the purely conductive load modulation can enable high back-off efficiency operation for LM inverse Class-F PAs.As proof of concept,a demonstrator amplifier is fabricated and measured.The experimental results show that the PAE with optimum V_ctrl is improved by 5%over an OPBO range of 6 dB compared with the same PA with fixed V_ctrl.On account of the introduced“continuous concept,”the proposed design space also has good application prospects for wideband LM harmonic-tuned?HT?switch-mode PAs.4.Research on the GaN HEMT device modeling.A parameter extraction technique and small signal modeling method for asymmetric GaN HEMT devices are proposed.An efficient systematic searching procedure based on pinch-off and cold weak-forward S parameters has been developed to consider the asymmetric structure of GaN HEMT devices,thereby obtaining the optimum values of the parasitic capacitances C_pg and C_pd.Considering that the depletion region extension is varied with the gate bias voltage V_gss slightly even below pinch-off voltage,the obtained initial values of the extracted parameters are optimized by artificial bee colony?ABC?algorithm to improve the reliability of parameter extraction.The developed approach is validated by using 150nm process 2×100?m GaN HEMT device.To ensure the nonlinear drain-source current model in the high voltage breakdown region has good predictive properties,a nonlinear drain-source current model combining artificial neural network model with mathematical analytical formula is proposed,and an ANN based large-signal modeling method for GaN HEMT devices is presented.