A flexible power management system for interfacing with energy harvesting transducers

Highly efficient energy harvesting, energy storage and voltage regulation are critically important to implement autonomous wireless sensor systems with long lifetimes. A power supply for mixed-signal systems with energy harvesting capabilities is described. This power supply includes novel transducers for solar and vibrational energy harvesting, a low-power mixed-signal controller, a flexible DC/DC converter and an efficient AC/DC converter.;To investigate integrated solar energy harvesting as a power source for low power systems, an array of integrated energy scavenging photodiodes based on a passive-pixel architecture for imagers has been fabricated together with storage capacitors implemented using on-chip interconnect in a 0.35 mum CMOS logic process.;Multiple-electrode piezoelectric-disk-shaped transducers are proposed for converting mechanical vibrations into electrical energy. By exciting a traveling wave in a multiple electrode piezoelectric disk, output voltages with approximately 90° relative phase shifts may be obtained. An equivalent circuit model of the multimode piezoelectric generator is derived. To rectify the vibrational energy from the piezoelectric generator a switched-capacitor AC/DC boost converter is presented.;Alternatively, a CMOS controlled rectifier with integrated peak detection is also proposed for interfacing with the piezoelectric generator. The full-wave rectifier was fabricated in 0.35mum CMOS. Peak detection circuitry allows quadrature input phases from a multiple-electrode piezoelectric transducer to be rectified with reduced output ripple. The rectifier has a measured power efficiency of 98.3% while delivering 90muW and occupying 0.007mm 2.;In addition, this work analyzes the power supply needs for an energy harvesting wireless sensor node, and explores the tradeoffs between various power regulators for this application. A regulator that satisfies the flexibility, efficiency and performance requirements for energy harvesting is analyzed. A mixed-signal sliding-mode controller is proposed to regulate the harvested energy. To further understand the steady state operation of the sliding-mode controller, a theoretical analysis of the mixed-signal regulator based on the two-sinusoidal-input describing function is presented. This theoretical model can then be used to program an adaptive compensation method for reducing the limit-cycle's dependence on the duty cycle for the SM controller.;An interpretation and estimation of the future trends in energy harvesting design is provided. Continued integration and scaling will further reduce power consumption in electrical circuits, allowing energy harvesters to power more complex systems. The integration of energy harvesters on the same die as silicon circuitry may eventually limit performance for both the system and the harvester. For instance, using a photodiode next to a sensitive SRAM may cause bit errors due to lateral photocurrent or direct optical generation. Miniaturization, which has continued to improve the performance of integrated circuits, will increase the resonant frequency of vibrational energy harvesters. This increase in frequency will result in less electrical energy generation for most environments. Emerging energy harvesting systems must be highly flexible in order to meet the system demands of analog, digital, and wireless circuit blocks over a wide range of sensing and environmental conditions.