1Ultra-Low Voltage Power Management Circuit and Computation Methodology forEnergy Harvesting ApplicationsChi-Ying Tsui, Hui Shao, Wing-Hung Ki and Feng SuDepartment of Electrical and Electronic Engineeringthe Hong Kong University of Science and TechnologyClear Water Bay, Hong Kong SAR, Chinathe 11thAsia and South Pacific Design Automation Conference, University Design ContestJanuary 25, 2006, Japan2Proposed Energy Harvesting System Applications which utilize the energy harvested from the environment are emerging.solarvibration heat Small harvested voltage challenges the design ofthese applications. Voltage regulator is avoided to reduce the cost of application and unstablevoltage power source poses robust operation problems. Ultra-low voltage power management circuit should be proposed. New computation strategy to control the correct operation is required. Micro-sensor Networks Biomedical Applications Environmental Management Energy Harvesting MechanismnXCharge PumpClock GeneratorComputation ModuleCharge-based Control UnitPower Management System1V+ for jump startInput voltage around 150mVVsVout Proposed System: Energy Harvesting Mechanism Power Management System Computation Module Charge-based Control Unit3Ultra-Low Voltage Power Management16X Exponential Charge Pump with Start-Up Circuit1a211122S t a g e 11 2 bM1 3 bM1 1 bM1 2 aM1 3 aM1 1 aM1 bC1 aC2a2b1b3a211122S t a g e 22 2 bM2 3 bM2 1 bM2 2 aM2 3 aM2 1 aM2 bC2 aC4a4b3b5a2 h1 h11 h22 hS t a g e 33 2 bM3 3 bM3 1 bM3 2 aM3 3 aM3 1 aM3 bC3 aC6a6b5b7a2 h1 h11 h22 hS t a g e 44 2 bM4 3 bM4 1 bM4 2 aM4 3 aM4 1 aM4 bC4 aC8a8b7b12LCLRoVStage Output aoMboMi nV_ s t a r t u pVS t a r t U p C i r c u i t This charge pump has a cross-coupled structure which has 2 symmetrical branches. The cap voltages on one branch are pushed by caps on the other and exponential voltage gain is achieved. Pump the voltage from around 150mv to more than 1V. A start-up circuit is needed which only functions at the beginning of the circuit running.4Charge Based Computation Methodology Without the regulator, the power supply becomes unsteady and timing problems may encountered. Self-timed asynchronous pipeline design is proposed to implement the computation module to track the supply fluctuations and adjust the circuit performance.reg regBundle DelayComputational Logic A 4-Tap FIR filter is implement for the computation module Energy source may not be sufficient for the computation during some time interval and robustness problem emerges when carry the computation out. Charge Based Computation methodology is presented where the atomic computation is only carried out when theres enough charge on the capacitor at the supply side for the operation. Simple start-stop control: a hysteretic comparator is used to monitor the capacitor charge status at the supply side and generate the control signal for correct operation.5Experimental Results Harvested energy source fluctuation between 169mV and 190mV Solar cell as the energy source In order to measure the robustness of the proposed system, 1012output samples were collected and no error was found when comparing with the correct samplesDie Photo of the Tested Chip