CAREER: High Frequency Integrated Voltage Regulator to Support Dynamic Voltage and Frequency Scaling for Mobile Devices

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Voltage regulators have been used widely in computing systems to deliver power from energy sources such as batteries to microprocessors. Today's voltage regulator is usually constructed using discrete components and assembled on the motherboard. The discrete passive components such as inductors and capacitors are bulky and occupy a considerable footprint on the motherboard. Furthermore, the power delivery path from the voltage regulators to the microprocessors is relatively long. Recently there has been great demand for a very high-frequency integrated voltage regulator that can be placed very close to the microprocessor to support dynamic voltage and frequency scaling, which is a very effective power consumption reduction technique for microprocessors. This would entail the supply voltage changing dynamically according to the microprocessor workload (a lower workload leads to a lower supply voltage; a lower supply voltage also leads to a lower clock frequency). As a result, both the dynamic and static power consumption of the microprocessor can be greatly reduced. However, traditional discrete voltage regulators are not able to realize the full potential of dynamic voltage and frequency scaling since they are not able to modulate the supply voltage fast enough due to the high parasitic interconnect impedance between the voltage regulators and the microprocessors. This project focuses on developing a 20-50MHz three-dimensional integrated voltage regulator for mobile devices such as smartphones. The research is expected to have a significant impact on power management solutions for smartphones as well as other mobile applications. The work will help to make the integrated voltage regulator a feasible approach to significantly reduce power consumption in mobile devices, which will greatly extend battery life and reduce electricity consumption. The integrated education plan will help to maintain the competitive vitality of the United States power electronics workforce by quickly incorporating high-frequency power converter design into the curriculum, and by retraining industry power electronics workers through short courses. The planned education activities also include outreach to students in grades K-12 and underrepresented groups to increase familiarity and attractiveness of the area of power electronics. The research goal of this project is developing a 20-50MHz three-dimensional integrated multi-phase voltage regulator that can support dynamic voltage and frequency scaling for mobile devices such as smartphones. A unique lateral flux inductor structure will be used to integrate multiple inductors into a single-piece magnetic core. The proposed single-core multi-phase lateral flux inductor structure can simultaneously achieve low-profile, high-density, low winding resistance and confined-flux. It can also have controllable nonlinear inductance (the smaller the inductor current, the larger the inductance) to increase voltage regulator light-load efficiency, which is very important for the smartphone application. This unique magnetic component will serve as a substrate stacked with semiconductor devices to realize three-dimensional integration. Two different technologies will be used to realize integration. One is printed circuit board embedding. This technique is compatible with today's printed circuit board fabrication process, which will help to speed industry's adoption of integrated voltage regulators. The second technology is three-dimensional printing. A three-dimensional printer capable of co-dispensing different pastes will be used to construct the inductor substrate which includes both a magnetic layer and a non-magnetic layer. The magnetic layer is used to build a multi-phase lateral flux inductor; the non-magnetic layer is used to build metal traces to realize a necessary electrical connection for the integrated voltage regulator. This technique will enable the integration of a very complicated inductor structure, which will bring a paradigm shift in power converter packaging and integration. Furthermore, a high bandwidth non-ripple-based constant on-time control will be developed for the proposed integrated multi-phase voltage regulators. This new control will have phase overlapping and turn-on-time extension capability for fast transient speed.