The Design Of High Efficiency Envelope Tracking Power Amplifier

Modern wireless communication systems employ complex modulation schemes forhigher data rate and spectral efficiency, which lead to non-constant envelope and theresulting high peak-to-average power ratio (PAPR). Traditionally, the linear poweramplifiers (PA) are utilized and operate at a large back-off for high linearity, whichresult in low efficiency. With the advantage of high efficiency and wide bandwidth,envelope tracking (ET), one of supply-modulation technique, is one of the mostpromising technique for the average efficiency enhancement. This thesis focuses on thedesign of highly efficient ET amplifier. Firstly, we briefly introduce the principle ofoperation and construction of ET, and then the design and analysis of both envelopeamplifier and the corresponding PA are presented.The design of highly efficient and wide bandwidth envelope amplifier is achallenge for ET. This thesis analyzes the operation and design of the hybrid envelopeamplifier which is parallel combination of linear stage and Buck switching stage. Thevoltage ripple and switching frequency are deduced. Based on the theory, a low power(<500mW) and low output voltage (<5V) Envelope Amplifier is designed. Themeasured efficiency is about51%~75%for single-tone envelope signal below5MHz. Inaddition, the design of both linear and switch stage is improved for high output voltage(15V) and power (10W). Experimental results show that the efficiency is about61%~80%for several single-tone envelope signals below5MHz. Also a new EnvelopeAmplifier based on class E DC-DC converter is introduced and the simulation of class EDC-DC converter is presented.The highest efficiency of RF power amplifier (PA) limits the efficiency of ETtechnique. The impact of the transistor parasitic parameters on the design of realisticClass F PA is analyzed; especially the nonlinear output capacitor which induces thechanges of load impedance due to its variation with supply voltage in ET. For the bestaverage efficiency, the load impedance is optimized according to the probability densityfunction of the signal (WCDMA). And a Class F PA for ET based on the GaAs pHEMTMRFG35010from Freescale is implemented. The measured drain efficiency reached 70.5%, corresponding output power of39.1dBm, at an input power of28.9dBm andsupply voltage of12V for a single tone.Finally, the PA characterization and envelope shaping in ET design are discussedand the ET based on ideal envelope amplifier is simulated. The improvement onefficiency by ET and the improvement on linearity by “isogain” envelope shaping arevalidated by simulation. In the end, the simplified ET system experiment based onEnvelope Amplifier, RF PA and signal generators is implemented.