| With the rapid development and upgrading of mobile communication system, the transmitter system, as the key module of mobile communication system, is faced with more stringent requirement: higher efficiency and better linearity. LINC(Linear Amplification with Nonlinear Components) technique, as one of the mainstream linearization techniques nowadays, usually separates a modified signal into two out-phase and constant-envelope signals with equal amplitude, then the two signals are amplified by two same highly efficient power amplifier, and finally get combined through a power combiner. The output signal of LINC transmitter is non-distortedly amplified in theory, and thus theoretically solves the contradictions between efficiency and linearity.The efficiency of LINC system is mainly decided by its power amplifier and power combiner. Due to the development and improvement of switch-mode(C lass-D, E, F and so on) power amplifier technique, it is easy for us to design a highly efficient power amplifier(theoretically 100%), so it is of great significance and importance to study the efficiency of power combiner. In this paper, we are highly focused on the study of highly efficient combining technique that suits to the LINC system, and the research content is presented as follows:1. In this part, we mainly analyze the several mostly used power combiners, and choose Chireix combiner as the high efficient combiner studied in this paper by utilizing circuit analysis and simulation.2. Analyzing the relationships among the combining efficiency, linearity and the Chireix combiner’s circuit parameter in detail by utilizing circuit design principles. Finding out the maximum combining efficiency and its determined condition through simplified calculations, during the calculations, we find the combining efficiency is not only related with the circuit parameters but also the phase angle of input signal, then verify the accuracy of the conclusions showed above using simulation. At last, according to the obtained simplified relationships, we are focused on designing two Chireix combiners aimed at the modified input signal of 16-QAM, which are designed to work at 2.14 GHz frequency, one is designed to acquire the highest average combining efficiency(simulation efficiency 94.7%) and poor linearity(EVM 22.4%), the other with relatively high efficiency(simulation efficiency 54%) and good linearity(EVM 7.9%).3. Choosing saturated C lass-B power amplifier which can be seen as an ideal voltage source as the suitable type of high efficiency power amplifier applied to C hireix combiner. Designing a saturated C lass-B power amplifier centering at 2.14 GHz using simulation software ADS, the simulation results showed the drain-efficiency achieved around 70%. Testing the real object and results showed a drain-efficiency of 67% and output power of 42.5d Bm with the input power of 27 d Bm and working center frequency of 2.14 GHz. In addition, the drain-efficiency and output power within the bandwidth of 100 MHz kept above 60% and 42 d Bm.4. Establishing a simple LINC system to make measurements using the designed Chireix combiners and saturated Class-B power amplifier. Tests demonstrated that the combining efficiency achieved 80.2% and 35%, while the ACPR compressed to-24 d Bc and-37 d Bc, which validate the accuracy of the design method showed previously. |
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