From Murmann Mixed-Signal Group
BSEE, Sharif University of Technology, 2007
MSEE, Stanford University, 2009
Admitted to Ph.D. Candidacy: 2011-2012
Research Project: An Energy-Harvesting, Power-Aware Sensor Platform for Wireless Data Acquisition Applications
Email: mahmoud [at] stanford [dot] edu
Conventional wireless sensor devices utilize batteries as the main power source for the sensing circuits and wireless transceiver. However, it is often desired to eliminate the battery from a system due to its size, cost (mainly maintenance cost), environmental impact, operating limits, and limited capacity and lifetime. Ambient energy harvesting has found to be the most viable alternative source for low power, low data-rate wireless sensing applications, where the sensor monitors a physical quantity that changes slowly and needs to be transmitted infrequently. Depending on the application, a sensor node can harvest solar, thermal, vibrational, RF, or other forms of ambient energy.
This project involves design and implementation of high performance Power Management Integrated Circuits (PMIC) for ambient energy harvesting. The core of the PMIC is a high-efficiency, ultra-low voltage, low-quiescent current, DC-DC converter which can harvest energy from one or more energy transducers and provide multiple supply rails to power the subsequent blocks and charge a temporary storage component.
The available power from energy harvesting sources can range from few micro-watts to hundreds of milli-watts and the design of a power converter to cover such a wide operating power range limits the performance. Therefore, the PMIC is split into two sub-converters: (1) a mW-converter aimed at harvesting energy from devices that generate milli-watts of power. Switching-inductor DC-DC converter is chosen here because of its high power conversion efficiency. (2) A uW-converter aimed at harvesting energy from chip-scale devices that typically generate micro-watts of power. Reconfigurable charge-pump architecture is chosen for the design of the uW-converter because it can be fully integrated (does not require any off-chip component) and have good efficiency at low power levels. The following block diagram of the PMIC illustrates both sub-converters in more details.
The current phase of this project focuses on the design of a closed-loop switched-capacitor DC-DC converter for the uW-converter section of the PMIC. The design of the uW-converter involves architecture selection for switched-capacitor power conversion stage, open-loop analysis and modeling, control design, and on-chip implementation. The following figure shows the block diagram of the uW-converter based on series-parallel charge-pump core architecture.