Title: Fully-integrated CMOS DC-AC Converters
Other Titles: Volledig geïntegreerde CMOS DC-AC convertoren
Authors: Callemeyn, Piet
Issue Date: 1-Jul-2015
Abstract: Monolithic integration of electronic systems is one of the major techniques to reduce cost, size and power consumption in consumer applications. The integration paradigm states that the trend is to look for opportunities to integrate more functionality on a single siliconnbsp;or in the same integrated circuit. The paradigm has been true in RF circuits where an immense step towards integration has been done in the last two decades. Mobile communication was the major driver in this evolution. This trend has been made possible thanks to the invention of the integrated circuit, and the ever continuing scaling of CMOS technology. This scaling has been closely following Moore’s law. However, the increasing power density starts to pose challenging limitations to this continuing scaling.
The trend that has been present in RF CMOS is now also continuing in the field of Power CMOS. One can determine a trend towards the integration of power supply blocks thanks to the advances in CMOS technology. A major driver here is cost reduction by reducing the bill of materials. The use of on-chip converters provides an elegant and compact solution with a minimum of external components. Moreover, the efficiency is boosted compared to linear regulators.
In this research, the author wants to take the next step in this Power CMOS evolution. After the integrated DC-DC conversion and attempts for integrated AC-DC conversion, the next leap has to be taken. This work will set out to explore the different possibilities to realize fully-integrated DC-AC conversion. Three major challenges will be encountered in this thesis.
A first challenge is to keep the control logic as simple and straightforward as possible. Therefore, it is paramount to have a linear relationship between the control signals and the modulated output waveform. The buck-buck topology will be the most designated topology as it has a strictly linear voltage characteristic. This will simplify the control system and straightforward modulation will be possible. Next to this topology, resonant converter topologies will be discussed and investigated as well. A first on-chip implementation will be presented to demonstrate these concepts.
A second important challenge in the integration is the limit imposed by the low supply voltages in standard CMOS technologies. These constrain the on-chip voltages to be within the defined supply voltage. At higher voltages outside of the nominal range, breakdown mechanisms and hot carrier degradation effects will be present. In this work, one presented approach to tackle this problem will be the series-stacking of several dies as to achieve higher output voltage while still respecting the on-chip voltage limits. Another approach will be the use of full-bridge topologies to achieve bipolar output voltages. A combination of the series-stacking approach in a full-bridge topology will be demonstrated in a second on-chip implementation.
A third design challenge is thenbsp;for integration of filtering inductors and capacitors. These will demand a certain chip area. Since they are used for filtering, they tend to be relatively large compared to the circuitry. Therefore there is an associated big area-cost. In this work, the author will present an approach to alleviate the integration of these blocks. By combining two half-bridges, therenbsp;be no DC-offset present in the output voltage. This enables the elimination of the output LC low-pass filter that is needed otherwise. Removing these external components for the LC filter decreases the cost and the volume so that the complete DC-AC converter can be made smaller and cheaper.
To conclude, a self-contained fully-integrated photovoltaic DC-AC converter design will be presented. This design will be demonstrated with an on-chip implementation. It serves as a proof of concept to take the next leap in the Power CMOS evolution. A photodiode will be integrated on-chip to power the complete DC-AC converter design.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:ESAT - MICAS, Microelectronics and Sensors

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