4G communications technologies such as WiMAX and LTE have been developed to satisfy the demand for higher and higher wireless data rates. These use spectral\y efficient modulation schemes which have large channel bandwidths and high peak to average power ratios, challenging the communications engineer to design highly linear power amplifiers. At the same time, reducing power consumption is essential as part of mobile operator's commitments to "Green Radio", This comes with a commercial incentive too, with operators needing to cut costs in developed countries in order to remain competitive and to reduce the cost of power generation equipment in rapidly growing emerging markets where access to a reliable power source is not guaranteed. The radio frequency power amplifier (RFPA) is the single greatest consumer of power in a base station and is typically one of the least efficient components. Switching-mode power amplifiers offer one possible solution. They have a much higher potential efficiency than traditional classes of operation yielding a maximum theoretical efficiency of 100%. They are, however, complex to design, requiring accurate fundamental and harmonic impedance termination. This thesis presents a simple design process for GaN devices operated as high -efficiency, green RFPAs. A switch-based equivalent circuit element model for GaN devices is proposed and a sensitivity analysis shows that the device's parasitic capacitances have the greatest effect on the efficiency and output power of a switching-mode power amplifier. Furthermore, manufacturing variations in device parasitic can lead to significant performance penalties if left unmitigated. A simple extraction method using S-parameter measurements of the "cold" device with no drain bias provides an initial characterisation of the device from which more accurate models can be derived. Waveform measurements of a "hot" device under typical operating conditions are used to characterise the non-linear "intrinsic" device as an alternative to using more specialised load-pulling equipment and to verify the mode of operation using de-embedded waveforms. Finally, this model is used as part of a design process for creating switching-mode power amplifiers and verified using continuous c1ass-F, c1ass-J and Doherty designs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:601209 |
| Date | January 2013 |
| Creators | Paynter, Michael |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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