All cell phone users know that you sometimes get a better connection by turning in another direction or by keeping the phone a bit from the body. This “shadowing” is one of the challenges that Jonas Lindstrand addressed in his PhD thesis. Another challenge has been to reduce the energy consumption of the power amplifier in the cell phone transmitters. On 8 November he defends his PhD thesis in E:B at LTH in Lund.
The title of Jonas Lindstrand’s thesis is “Integrated Transmitters for Cellular User Equipment–Wideband CMOS Power Amplifiers and Antenna Impedance Tuners”. The main scope of the thesis project has been to reduce the power consumption of the radio electronics in cell phones in two different areas.
“The primary target has been the energy consumption of the power amplifier in the transmitter, but we have also investigated why and how the performance of the transmission degrades due to how the user handles their cell phone”, Jonas Lindstrand says.
To reduce the performance degrading effects caused by the cell phone user, a component called an impedance tuner can be used. The impedance tuner reduces the impedance mismatch caused by the physical presence of the user.
“This helps the electronics inside the cell phone to work as intended – and this without any costly re-design of all the electronics, Jonas Lindstrand says.
Regarding the other objective Jonas explains that in the transmitter the power amplifier is the main power consumer and one of the hardest circuits to design, and also the most expensive component in cell phone radio. During his thesis project Jonas has designed, implemented, and verified low cost power amplifier solutions in CMOS*, with reduced cost as result.
The need for low cost, and for wideband circuits, has increased in the last few years, mainly due to new frequency bands in what is called the Sub-6 GHz frequencies. This means that more components with higher performance is required. Consequently, the cost of the cell phone has increased and will continue to increase with the upcoming releases of the full 5G solution.
“So by reducing the number of components in the cell phone, especially the expensive ones, this yields lower overall cost and less fabricated components, which also effects environmental impact in a positive manner”, Jonas continues.
What made you want to pursue a PhD?
“I have always loved science and these days it has mainly been the science of electronics. What really made me make this choice, a PhD in engineering is a way to maximize your chance, to live anywhere you desire and you also have a great potential to keep working with something you really love. As a PhD-student, I could do research that is very rare in the industry and it also helped me in my development as a person, which I think is the most important”, Jonas Lindstrand says.
What have you found most interesting with your subject?
“The challenge, how hard it actually was to get some of the circuits to work as intended, and also the complexity of the circuits and their theory. The most interesting to me is the future. We are more or less in one of the forks in the road for wireless communication so far, and it is mainly the release of 5G and together with new higher frequency bands in the mm-wave spectrum. In academia, mm-wave circuits for consumer products have been researched for the last 15-20 years. Now finally a commercialization has started to happen.
What results from your research do you believe will be applied in practice?
“I think that some of the measurement practices I used for impedance tuner is used today, I must add that they might have been used long before I used them, but to my knowledge, I had not seen them before we published them”, Jonas Lindstrand says.
“I also believe mostly bits and pieces will be used at first, the best chance is for the wideband matching network and only because it is relatively simple with low degradation of circuit performance and it also has low cost in terms of added components. The main power amplifier circuit might be useful in the next 5-10 years, but requires more research and more theoretical understanding. I think this circuit can be improved to further increase efficiency and also take fully integrated power amplifiers in CMOS to the next level, regarding efficiency and power consumption”, Jonas Lindstrand continues.
What are your plans?
“I will continue to work for a Lund start-up called BeammWave AB, the company mainly works with integrated mm-wave circuits for 5G consumer products, and as a matter of fact, I will dedicate all my office hours with them after the defence of this thesis”, Jonas Lindstrand says.