Ultra-low power circuits for power management

Abstract: Recent developments in energy harvesting techniques allowed implementation of completely autonomous biosensor nodes. However, an energy harvesting device generally demands a customized power management unit (PMU) in order to provide the adequate voltage supply for the biosensor. One of the key blocks within this PMU is a regulation DC-DC converter. In this Master Thesis, the most relevant switched-capacitor DC-DC converter topologies that are suitable for biosensors are compared. The topology that can achieve the best efficiency and has the minimum area is chosen and designed. In order to maintain the supply voltage of the biosensor constant when the input voltage and the output current vary, a traditional Pulse-Frequency-Modulation (PFM) control is employed. An ultra-low-power PFM control circuit is designed to operate in weak inversion region. The post-layout simulations show that the designed DC-DC converter can provide an output voltage of 900mV when the output current varies between 5μA and 40μA. Additionally, the post layout simulations of the entire system, which includes the DC-DC converter and PFM control, show that the selected topology can achieve 87% peak efficiency, when the control losses are included. The main advantages of the proposed topology are its smaller chip area and its high efficiency during processing ultra-low power levels.