Research On The Efficiency Enhancement Technology Of Transmitters For Wireless Communication Systems

The wireless communication networks are being enhanced to better serve the diverse multitude in modern and the next generation commercial communication system.As one of the key components in the wireless communication systems,the RF transmitter should also evolve to improve both its performance and flexibility for these multiple application scenarios.Therefore this dissertation focuses on the study of various high performance transmitters for different application scenarios.The research involves both the transmitters for base stations and those of mobile devices,which serve as two ends of a wireless communication systems.This dissertation can be divided into three major parts: analysis and design of high linearity power amplifier(PA)for base stations,study on the match techniques of wideband and multi-band PAs for base stations,and the research on all-digital high efficient Outphasing transmitter for mobile devices.The main contents and innovations are listed as follows:1,Using the equivalent non-linear model of the transistor,an analysis is conducted on the effects of harmonic impedances and of various bias conditions on PA linearity.Besides,the continuous Class-F mode is studied and extended to get wider design space of fundamental and harmonic load impedance.Then,a design method,which embraces harmonic tuning,is proposed to get a PA with high efficiency and high linearity.This method is used to design,fabricate and characterize a PA prototype which allowed verification.2,The optimum load impedances of several transistors,which are identified through load pull,are scattered across a wide frequency range.An overview of broadband matching methods is presented in order to design a wideband matching network to fit the device.Then,a general Class-J mode,which is extended from Class-J,is introduced.It can offer a bigger design space for fundamental and harmonic impedances,while keeping high efficiency.According to the greater freedom on load impedances,a low complexity matching network could be employed to implement the wideband PA.3,The demands on the performance of PA for multi-band application are discussed together with the needs for sufficient inter-band suppression.The performance on interband suppression is analyzed and evaluated with the conventional wideband matching network.Then,a tri-band matching structure is proposed.Design equations for this tri-band structure are presented based on ABCD-parameters and used to design an impedance transformer that imitates a quarter-wavelength line at the desired frequency.Using the frequency selectivity of this single transmission line structure,good in-band matching and effective inter-band suppression are achieved.4,A silicon-based digital Outphasing transmitter is proposed.It employs Chireix compensation and branch PAs that can be segmented using a digital amplitude control word.In this way,the well-known highly reactive and extreme loading modulation conditions of the standard Outphasing operation can be avoided,thus minimizing the power losses and improving the efficiency at power back-off,simultaneously the system efficiency is also enhanced due to less working logic at power back-off.Meanwhile,with the digital approached amplitude segmentation,this structure has lower bandwidth expansion of input signal,and higher tolerance to amplitude/phase unbalance.5,The demands on PA for Outphasing transmitter are discussed.Based on these demands,the design coefficients of the Class-E PA with an additional nominal condition at power back-off,are calculated using numerical tools.And the Class-E PA is employed to implement the digital Outphasing transmitter in a differential fashion.Other contents are as follows:1,The coupling between the signal branches through the primary windings in silicon-based Outphasing transmitter are analyzed and are found to be detrimental to PA efficiency because the real-to-imaginary ratio of loading impedance reduced.This is done by using an equivalent model for analysis and simulation which showed reduced efficiency.2,A test bench for the characterization of digital Outphasing transmitter is built.In this setup input signal is pre-processed and optimized so that the digital Outphasing transmitter achieves its highest performance.The measurement results obtained while using continuous wave and wideband modulated signals verified an efficiency enhancement at power back-off and its capability to support a high speed up-link.