A GaAs HBT Power Amplifier For IEEE 802.11ax Applications

As a wireless short-range data transmission method of high rate,WLAN has developed rapidly and grown quickly in popularity in recent years.In the mean time,new WLAN standard protocols have been developed to meet the needs of users.In order to enhance the spectrum efficiency and data throughput in ultra-dense scenarios,IEEE launched a WLAN standard protocol of the next generation recently,which was named IEEE802.11ax.Hence,wireless communication systems for this new standard became a new research hotspot.Radio Frequency Integrated Circuit is the cornerstone of a Wireless Communication System,and MMIC Power Amplifier(PA)is one of the key components which determines the performance of the whole system,which makes PA a research priority of many manufacturers and institutes.In this thesis,a GaAs HBT MMIC PA for IEEE 802.11ax FEM is designed.This PA is designed for 5 GHz mode of IEEE 802.11ax standard and operates in the frequency range of 5.15?5.85 GHz.The research purposes of 802.11ax are summarized,the design specifications of the PA are established basing on the parameters of existing WLAN FEM products.MMIC products in use are looked into and the characteristics of different materials and devices are contrastively analyzed.Therefore,this MMIC PA is chosen to be InGaP/GaAs HBT-based.In order to realize high power gain and high output power,the proposed PA is realized with a three-stage cascaded amplifying circuit structure,of which the first two stages operate in Class A mode and the last stage operates in Class AB mode,ensuing the linearity of the PA and achieving relatively high efficiency simultaneously.A series RLC negative feedback network is added between the base and the collector of each power transistor of the first two stages to compensate the gain difference between the lower end and the higher end of the working band,improving the gain flatness of the PA in the working band.Adaptive bias networks are used for the base biasing of the power transistors,stabilizing the bias points of the power transistors under high power and high temperature condition.Base stability resistor is used to make the HBTs biased stably of HBTs and prevent the current gain collapse from occurring in the HBTs,whose structure is that each HBT is in series with a base stability resistor.The method adopted in the design of the proposed MMIC PA is CAD.Each stage of the three-stage cascaded PA is designed separately using Advanced Design System(ADS2015)and then chained together,forming the completed PA circuit.The schematic of the PA is drew and then optimized based on the simulation results.After the completion of the schematic,the initial layout of the PA is drew according to the schematic,and then the initial layout is adjusted and optimized according to the results of EM simulation in which the parasitic effects in MMIC are taken fully account of.Thereafter,DRC is used to ensue that there is no violation of layout design rules of the HBT process line,and then the layout which satisfies the design specifications is completed.The post-layout simulation results show that with a supply voltage of 5.0 V,the power gain is about 36.5 d B and the output P_{-1d B}is about 30.6 d Bm.At 1d B compression,the PA shows a PAE of about 37%,an second order harmonics and a third order harmonics of-50?-40 d Bc and-80?-40 d Bc respectively.Besides,in the two-tone test the PA exhibits an IMD3 of about-24?-22 d Bc and an OIP3 of about 41 d Bm at 1 d B compression.