Research On Novel Broadband And High Efficiency Class-J Power Amplifiers

Power amplifier (PA) is one of the key components in the RF front end. With the rapid development of wireless communication technology, broadband power amplifiers with high efficiency and high output power are needed for new standards and new systems of wireless communication. And the enhancement of efficiency and extending the operating bandwidth of power amplifiers have always been two important directions of PA research. Nowadays, the concept of energy saving and environment protecting has deeply rooted in our consensus. So the enhancement of efficiency of power amplifiers, which consume the most power in the whole system, has a significant impact on reducing operating costs, energy consumption, extending battery life and so on. Extending the operating bandwidth of power amplifiers becomes more and more important in the communication systems of multi-standards and multi-bandwidths.Classic methodology of power amplifiers is difficult to meet the requirements of broad bandwidth, high efficiency and high power at the same time. The recently proposed Class-J power amplifiers make a satisfactory compromise among output power, efficiency, linearity and bandwidth and thus can operate over a broad bandwidth with high efficiency. The broadband, high efficiency Class-J power amplifier is the leading subject of the paper with detailed presentations of the classic design methods of power amplifiers, theories and practical implementation methodologies of Class-J power amplifiers.At first, general principles and common methods in the design of power amplifiers are summarized. Among them, the load-pull technique and the mechanism of harmonic tuned power amplifiers are high-lighted, which is necessary for the research of Class-J power amplifiers.In Chapter3, theories of Class-J power amplifiers are summarized and discussed. Firstly, the process of derivation of Class-J power amplifiers is presented. The specific fundamental and second harmonic impedances of Class-J PA are derived in closed forms. Then the concepts of continuous mode PA and design space, which are the most important and most valuable parts of the theories of Class-J PA are introduced. The idea of design space and continuous mode offers a new way of thinking about designing broadband high efficiency PA. Right following the theories in Chapter3, Chapter4focuses on the practical implementation of Class-J PA. The impact of parasitic elements of the transistor is evaluated at the beginning. Then, several design methods and implementation structures are proposed, based on the overall analysis of some common implementation structures. The main studies are as follows:1. A methodology is proposed that can integrate the fundamental impedance matching, harmonic controlling and DC supply circuit into a simple and compact structure. The trajectory of impedances of the output matching network just changes in accordance with the change of the optimum impedances in design space of Class-J PAs. And the designed PA can operate with high efficiency over a broad bandwidth.2. A new method for designing broadband high efficiency power amplifier with harmonic suppression is presented, based on the combination of the design principles of traditional broadband PAs and Class-J PAs. In the method, the equivalent mode of the parasitic elements of the transistor need not to be known beforehand. Just conduct the load-pull to find the optimum fundamental and second harmonic impedances that meet the required properties and then analyze the distribution of these impedances to design matching network to correspond to the optimum design space. A new structure is proposed to demonstrate the method. And the structure is simple and effective in fundamental matching and harmonic suppression.3. A dual-frequency transformer with two sections of serial microstrips is adopted to extend the operating frequency of Class-J PAs to dual bands to take full advantages of Class-J PAs’ broadband capabilities. A brief discussion is also made to analyze the conflicts of fundamental impedance matching and harmonic control at the inevitably overlapped frequencies within the broadband.All the three kinds of PAs entioned above have been realized and experimentally verified.