Multi-Band Outphasing Power Amplifier Design for Mobile and Base Stations

New generations of wireless communication systems require linear efficient RF power amplifiers (PAs) for higher transmission data rates and longer battery life. On the contrary, conventional PAs are normally designed for peak efficiency under maximum output power (Pout). Thus, in power back-off, the overall efficiency degrades significantly and the average efficiency is much lower than the efficiency at maximum Pout. Chireix outphasing PA, also called LINC (Linear amplification using Non-linear Components), is one of the most promising techniques to improve the efficiency at power back-off. In this method, a variable envelope input signal is first decomposed into two constant-envelope phase-modulated signals and then amplified using two highly efficient non-linear PAs. The output signals are combined preferably in a loss-less power combiner to build the desired output signal. In this way, the PA exhibits high efficiency with good linearity. In this thesis, first we analyze a complex model of outphasing combiner considering its nonidealities such as reflection and loss in transmission lines (TL). Then we propose a compact model with analytical formula that is validated through several comparative tests using ADS and Spectre RF. Furthermore, we analyze the effect of reactive load in Chireix combiner with stubs (a parallel inductor and capacitor), while distinguishing between its capacitive and inductive parts. It is demonstrated that only the capacitive part of the reactive load degrades the performances. Based on this, a new architecture (Z LINC) is proposed where the power combiner is designed to provide a zero capacitive load to the PAs whatever the outphasing angle. The theory describing the operations of the system is developed and a 900 MHz classical LINC and Z-LINC PAs are designed and measured. In addition, a miniaturization technique is proposed which employs λ/8 or smaller TLs instead of conventional λ/4 TLs in outphasing power combiner. This technique is applied to implement a 900 MHz PA using LDMOS power transistors. Besides single-band PAs, dual-band PAs are more and more needed because of an increasing demand for wireless communication terminals to handle multi-band operation. In chapter 5, a new compact design approach for dual-band transmitters based on a reconfigurable outphasing combiner is proposed. The objective is to avoid the cumbersome implementations where several PAs and matching network are used in parallel. The technique is applied to design a dual band PA with a fully integrated power combiner in 90 nm CMOS technology. An inverter-based class D PA topology, particularly suitable for outphasing and multimode operations is presented. The TLs in the combiner, realized using a network of on-chip series inductors and parallel capacitors, are reconfigurable from λ/4 in 1800 MHz to λ/8 in 900 MHz. In order to maximize the efficiency, the on-chip inductors are implemented using high quality factor on chip slab inductors. The measured maximum Pout at 900/1800 MHz are 24.3 and 22.7 dBm with maximum efficiencies of 51% and 34% respectively

Vidutinių dažnių 5G belaidžių tinklų galios stiprintuvų tyrimas

This dissertation addresses the problems of ensuring efficient radio fre-quency transmission for 5G wireless networks. Taking into account, that the next generation 5G wireless network structure will be heterogeneous, the device density and their mobility will increase and massive MIMO connectivity capability will be widespread, the main investigated problem is formulated – increasing the efficiency of portable mid-band 5G wireless network CMOS power amplifier with impedance matching networks. The dissertation consists of four parts including the introduction, 3 chapters, conclusions, references and 3 annexes. The investigated problem, importance and purpose of the thesis, the ob-ject of the research methodology, as well as the scientific novelty are de-fined in the introduction. Practical significance of the obtained results, defended state-ments and the structure of the dissertation are also included. The first chapter presents an extensive literature analysis. Latest ad-vances in the structure of the modern wireless network and the importance of the power amplifier in the radio frequency transmission chain are de-scribed in detail. The latter is followed by different power amplifier archi-tectures, parameters and their improvement techniques. Reported imped-ance matching network design methods are also discussed. Chapter 1 is concluded distinguishing the possible research vectors and defining the problems raised in this dissertation. The second chapter is focused around improving the accuracy of de-signing lumped impedance matching network. The proposed methodology of estimating lumped inductor and capacitor parasitic parameters is dis-cussed in detail provi-ding complete mathematical expressions, including a summary and conclusions. The third chapter presents simulation results for the designed radio fre-quency power amplifiers. Two variations of Doherty power amplifier archi-tectures are presented in the second part, covering the full step-by-step de-sign and simulation process. The latter chapter is concluded by comparing simulation and measurement results for all designed radio frequency power amplifiers. General conclusions are followed by an extensive list of references and a list of 5 publications by the author on the topic of the dissertation. 5 papers, focusing on the subject of the discussed dissertation, have been published: three papers are included in the Clarivate Analytics Web of Sci-ence database with a citation index, one paper is included in Clarivate Ana-lytics Web of Science database Conference Proceedings, and one paper has been published in unreferred international conference preceedings. The au-thor has also made 9 presentations at 9 scientific conferences at a national and international level.Dissertatio

Device level characterization of outphasing amplifiers

The outphasing technique proposed by Chireix in 1935 is one of the classical methods of addressing power amplifier (PA) efficiency degradation caused by operating in output back-off (OBO) conditions, where PA efficiency is typically low. Essentially, the envelope from the input signal is eliminated, and two CW signals are constructed; these have constant amplitude, while their relative phase offset holds the original information contained by amplitude modulation. Consequently, efficiency improvements are achieved by amplifying signals with constant amplitude using PAs operating in saturation, where efficiency typically peaks. The envelope is restored at the output by means of a vector summation of both signals, using a non-isolating combiner at the output stage The main focus of the work described in this thesis was placed on extending bandwidth of the inherently narrowband technique of outphasing and then adopting this method to modern telecommunication standards. Two prototype PAs were designed to investigate whether bandwidth improvements can be achieved by adopting a broadband balun as a combining structure in the outphasing PA. Two baluns were designed and fabricated to be used in the demonstrator circuits; one using a section of semirigid coaxial cable and the other, a planar balun realized on 10 mil thick Alumina substrate. A novel method of fabrication was proposed for the former structure, which achieved more than double octave bandwidth, from 1.25 GHz to 4.7 GHz with losses lower than 1dB, an amplitude imbalance (trace separation) below 0.75 dB and phase imbalance within ±5 degrees. The measured CW performance of the prototype circuits produced results comparable with the state-of-the-art solutions available in literature. Moreover, this work demonstrated that a balun with sufficient bandwidth allows load modulation to be prescribed at fundamental and second harmonic frequencies, opening the possibility of waveform engineering to implement continuous PA modes such as class J in outphasing PAs. The desired harmonic load termination was achieved without any specialized matching networks, and solely by means of load modulation provided through active device interaction. The thesis concludes with the formulation, analysis and description of the novel concept derived from Chireix outphasing. Several outdated assumptions still prevalent in outphasing analysis included in literature today are challenged and reformulated for modern semiconductor devices such as GaN HEMTs. Through this process, a new concept of Current Mode Outphasing (CMOP), is proposed and described in detail. One of the significant advantages of the proposed approach is it allows the elimination of the combiner structure, which typically dominates the size of the final outphasing circuit, due to the presence of λ/4 transmission lines. Consequently, the demonstrator MMIC circuit, containing DC bias, stability elements and pre-matched to 50 Ω on input and output, has been deployed on an area of 2.3 mm x 2.8 mm. The CMOP circuit was fabricated using 0.25 µm GaN technology and achieved a bandwidth of 1.6 GHz centered at 3.35 GHz, whereas the maximum CW output power remains within 43 dBm ± 0.5 dB. A total gain of more than 12 dB is reported from 2.95 to 3.95 GHz, while a maximum Power Added Efficiency was measured as 68.5% at 3.25 GHz and remains greater than 60% from 2.85 to 3.8 GHz, and above 50% for almost the entire frequency range. The output back-off (OBO) efficiency peaks at 3.25 GHz with 53.5% and 45.6% for 6 dB and 8 dB back-off, respectively, and remains above 30% and 23.7% for the entire frequency range. To the best of the authors’ knowledge, this is the largest fractional bandwidth achieved in an outphasing PA, that has been reported in literature