New-Tech Europe | July 2018

Figure 7: Modelled vs measured large signal CW results.

Figure 6: Comparison of modelled vs measured small signal gain and input return loss.

in the band 1.805 – 1.88 GHz using a wideband code division multiple access (WCDMA) test signal with PAPR = 7.8 dB. A balanced version of this amplifier is under construction. Including imperfect hybrids, it was predicted to have performance that achieves +37 dBm with an average efficiency of ~34 percent and a linearity of 30 dBc at fcenter +/- 1.25 MHz. The linearity performance could be improved through linearization techniques such as digital pre- distortion or envelop tracking. It is interesting to note that achieving a high-efficiency class of operation at signal peaks enables operation at greater peak compression, so the amplifier is operated at higher relative power over the whole signal dynamic range. Hence the efficiency and/or linearity is improved even on high PAPR signals. Conclusion This paper has presented a design for a broadband, linear, and efficient output back-off mode RFPA, emphasizing the importance of minimizing design uncertainties wherever possible. Using this approach, excellent agreement between the modelled and measured datasets has been proven and a first- pass design achieved. The design methodology used four stages: device selection using

qualitative and quantitative analysis, optimization in Microwave Office of load and source impedance matching networks using load/source pull, passive network synthesis (including EM verification), and waveform engineering using intrinsic voltage and current nodes. Together these techniques have proved to provide a systematic approach to designing the entire RFPA. In addition, a measurement technique for fabricated source and load networks, enabling comparison of modelled and measured impedances at the transistor tabs, has been demonstrated using a three-piece jig. Passive network synthesis using an SRFT technique combined with analysis using mismatch loss and transducer power gain has produced a broadband match using relatively simple source and load impedance matching networks. The results indicate that this particular RFPA could be well suited to operate as a multipurpose driver or output stage. Acknowledgements The author would like to thank Andy Wallace of AWR Group, NI and Qorvo / Modelithics for the device model. References [1] D. T. Wu, F. Mkadem and S. Boumaiza. “Design of a broadband

and Highly Efficient 45W GaN Power Amplifer via Simplified Real Frequency Technique”, IEEE MTT-S Int. Microwave Symposium, pp 1091- 1092, May 2010.
 [2] R. A. Beltran. “Class-F and Inverse Class-F Power Amplifier Loading Networks Design Based upon Transmission Zeros”, IEEE MTT-S Int. Microwave Symposium, June 1-6 2014.
 [3] P. L. D. Abrie. Design of RF and Microwave Amplifiers and Oscillators, 1st edition, Artech House, 1999.
 [4] D. M. Pozar. Microwave Engineering, 2nd ed, Wiley, 1998.
 [5] S. C. Cripps. RF Power Amplifiers for Wireless Communications, 2nd edition, Artech House, 2006. Figure 8: Intermodulation sideband performance measured using modulated test signal.

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