A Research For CMOS Envelope Tracking RF Power Amplifier In Portable Applications

So far,most of the Front-End-Module(FEM)in radio frequency(RF)portable applications includes several power amplifiers(PA)in different bands which are fabricated in GaAs process and standard CMOS digital control component and radio frequency switch which is fabricated in GaAs process or SOI CMOS process.Those parts are combined in a multi-chips package(MCP).This kind of FEM satisfies the applications in 3G and 4G such as WCDMA and LTE.The MCP and high performance GaAs PAs which are expensive make the FEM complex and expensive.Therefore,it is a hot point for researching that to fabricate all FEM components especially PA in a single CMOS process.However,it is difficult to design CMOS PA in FEM because of the low allowable drain voltage swing and poor linearity.The high peak-to-average ratio(PAPR)non-constant envelopemodulation signal has been used in modern communication system to makethe data transfer ratehigher in the limited bandwidth.The communication system using high PAPR signal demands that the PA have high linearity.To satisfy the high linearity,PA has to work in a back-off region.It makes that the efficiency of the PA is low.Among many kinds of techniques,envelope tacking(ET)are paid attention by researchers because that there are less bottlenecks than other kinds of technologies.ET-PA is feedforward.The key of ET-PA is to makes the drain voltage go with the different output power.The supply voltage is high when the PA outputs high power and low when the PA outputs low power.In this way,the unnessecery power comsuption is avoided.In this paper,we research CMOS PA and ET technique based on SOI CMOS process.We research the possibility of the CMOS FEM in a single chip with ET technique.We have designd a CMOS PA and an ET supply modulator which are the key components in the CMOS FEM.In this paper,we present a 2-stages single-end SOI CMOS PA working in 2.3GHz LTE band and 2.4GHGz WIFI band employs stacked-FET along with optimal bias and cancelling capacitance variation linearization method which are used to overcome the low breakdown voltage and AM-AM/AM-PM distortion.The supply modulator employs hybrid topology for linearity and efficiency trade-off.We also set up the whole ET-PA system using the designed PA chip,supply modulator chip,some equipment and software.In measurement,the CMOS ET-PA met LTE signal mask without using a digital pre-distortion technique.