Smart Internet Lab: Tommaso Cappello

13 October 2021, 11.00 AM - 13 October 2021, 12.00 PM

Speaker: Dr Tommaso Cappello

Talk Title: Design and Characterization of Power Converters and Amplifiers for Supply-Modulated Transmitters



Abstract: The rapid evolution of telecommunication systems has strongly influenced our lives, and the way we communicate and exchange information. Nevertheless, much progress is expected to happen in the next years with the introduction of new generations of wireless communications standards, which require signals with large bandwidth and very high Peak-to-Average Power Ratio (PAPR) in order to enhance the spectral efficiency and maximize the data rate. However, such developments can only take place through the evolution of Radio-Frequency (RF) and microwave technology which should be capable of working at higher frequencies, higher bandwidth and with higher efficiencies than before. In order to meet these demanding specifications, transmitter architectures have to evolve from a single linear RF Power-Amplifier (PA) into more complex architectures. Envelope Tracking (ET) is one of the most promising solutions for the efficiency-enhancement of next generation transmitters. In ET, the performance and the efficiency of the supply modulator affects directly the overall performance of the transmitter. The research described in this thesis aims to provide solutions to enhance the efficiency of the RF PA by means of an ET architecture. To this purpose, a novel discrete level supply modulator is investigated, which is based on a direct digital-to-analog power conversion. This supply modulator is capable of synthesizing eight voltage steps by means of three isolated voltage sources, thus behaving like a Power Digital-to-Analog Converter (Power-DAC). This fine voltage resolution allows for almost continuous tracking, with very small steps, of the ideal supply voltage that maximizes the efficiency of the PA, while maintaining the high efficiency typical of a switching converter. A hybrid version of the Power-DAC exploiting very fast GaN devices is developed and tested with an L-band PA achieving efficiency improvement up to $13\%$ with 10\,MHz of bandwidth. Furthermore, a monolithic GaN version of the Power-DAC is prototyped and tested with an X-band PA both with radar and telecommunication signals achieving efficiency improvement up to $20\%$ and bandwidth of 20\,MHz. This supply modulator is tested with even more non-linear PAs such as the ones used in the outphasing architecture showing promising results with modulated signals and efficiency improvement up to $9\%$. Finally, dispersive phenomena, which affect PAs and switches in supply modulators, are investigated, characterized and modeled.


Tommaso Cappello received his Laurea degree (cum laude) in electrical engineering and his Ph.D. degree from the University of Bologna, Italy, in 2013 and 2017, respectively. Since 2020, he is a Lecturer in Electrical and Communication engineering at the University of Bristol, UK. Between 2017 and 2019, he was a Post-doctoral Research Associate with the Microwave and RF Research Group at the University of Colorado Boulder, CO, USA. His current research interests include design and characterisation of RF and power electronic circuits.

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