Ziyue Xu’s PhD Proposal Review

“High Efficiency RF Energy Harvesting and Power Management Circuits Techniques for IoT Application”

Abstract:

As the number of Internet of Things (IoT) devices is continuing to grow, there is a need that a significant percentage these devices operate at ultra-low power (ULP) levels, either using harvested energy or using a small battery with a long lifetime. Energy harvesting techniques can help to achieve long lifetimes, but the system should be able to operate efficiently with a small amount of harvested energy and often from low voltages. Energy harvesting from solar, thermal, vibration, and radio-frequency (RF) are increasingly being used to realize batteryless operation for IoT and biomedical applications. A typical multi-input energy harvesting system including multiple energy transducers, maximum power point tracking (MPPT), matching network (MN), and DC-DC converter. Solar cells and thermoelectric generators have a few mV to hundreds of mV open-circuit voltage that require maximum power tracking to make sure the optimal power extraction is achieved. The piezoelectric transducer is modeled as AC source with internal resistance from 10s Ω to kΩ that requires AC-DC conversion, known as rectification to better use the energy. And the following DC-DC regulation stage is to regulate the output voltage to deal with the sudden change of the load or the input voltage drop.
Among these techniques, RF energy harvesting system is particularly promising for biomedical and IoT devices where other sources are not readily available. Several of these applications are utilizing widely used WiFi and Bluetooth low-energy (BLE) communication standards. These applications along with the wirelessly-powered neural implantable medical devices (n-IMD) for neural stimulation and recording are also benefiting from ultra-low power (ULP) circuits and systems design advancements. Since the available RF power decreases rapidly with distance, it is desirable to design rectifiers that are able to operate with low incident power. This Ph.D. proposal presents a simplified design approach and analysis of RF energy harvesting rectifiers for different design objectives. The proposal also includes the design of a new self-biased gate (SBG) rectifier with a non-linear gate biasing technique. At lower power levels, the SBG rectifier drops the entirety of output voltage to create a higher gate bias. However, to address the issue of leakage at higher input power levels, the gate-biasing technique drops only a fraction of the output voltage. This approach helps to realize high efficiency across input power range. The fully integrated, high-efficiency SBG-based RF energy harvesting circuit can also provide a high output voltage of 9.3 V with a 30% end-to-end efficiency (PHE). Further, to enhance the available RF energy to a remotely located RF energy receiver, the proposal presents a highly efficient distributed RF beamforming technique. To improve the power delivery in the downstream power management circuits, a boost converter architecture that can reduce switching noise injection by changing its switching frequency is also presented. The associated power management system includes a boost converter operating in DCM, FVC and a digital control loop. The system is capable of providing a stable 1V supply for RF receiver front-ends with very low performance impact.

Committee Members:

Prof. Aatmesh Shrivastava (Advisor)

Prof. Marvin Onabajo

Prof. Nian X. Sun