The Research And Implementation Of Feed-forward Power Amplifier

Multi-carrier transmitting system can effectively reduce the cost of the radio and TV system and enhance their competitiveness, so the system has broad pros-pects for development and practical value. Power amplifier is the key circuit of broadcast transmitter, which indicator will determine the performance of the transmitter. Therefore, highly linear broadband power amplifiers have become a bottleneck of development of multi-carrier transmission system. Through the re-search found that feed-forward technology for wideband and multi-carrier trans-mitting systems. This paper is based on the technology to develop a multi-carrier power amplifier. The testing results show that the output power is greater than 53dBm and third-order ratio less than -65dBc, meeting the system indicant.Main works that this paper completed include the theoretical analysis of feed-forward system , the principles of efficiency enhancement techniques, design of highly efficient feed-forward system, the implementation of the main power amplifier and the deduction of the transfer model of S parameters and so on. The main innovation includes the following four aspects:1. The implementation of feed-forward system utilizing negative group delay circuitry is developed. The negative group delay circuits reduce the length of the delay lines to significantly improve system efficiency. Negative group delay cir-cuitry, small size, easy integration into other modules, can effectively reduce costs.2. The general model of coaxial impedance transformer is proposed. The model is equivalent to a piece of coaxial line, reduces the analysis difficulty and simpli-fies the analysis process.3. The transfer matrix method of branch coupler is developed. The method is based on the definition of S parameters, the transfer parameter matrix and symme-try, and achieved a more precise analysis of the branch coupler parameters.4. A conversion model of S-parameter is proposed for plural characteristic im-pedances in common mode and differential mode. The model is based on Helmholtz Equation and Thevenin's theorem. S-parameters among arbitrary characteristic im-pedances and different operating modes could be transformed using analysis me-thod of signal flow graph. This model has made up for inadequacy of S-parameter measurement using the Vector Network Analyzer (VNA)。...