Abstract ▼ AI-Helper

Emerging small-scale electronic devices should be highly-efficient to prolong the battery life-time. The conventional batteries require additional battery management circuit and cause the maintenance problem. The energy harvesting utilizing the environmental energy can be a powerful alternative. The...

Emerging small-scale electronic devices should be highly-efficient to prolong the battery life-time. The conventional batteries require additional battery management circuit and cause the maintenance problem. The energy harvesting utilizing the environmental energy can be a powerful alternative. The ambient energy sources are limited and sporadic. Therefore, the conversion process of the energy has to be very efficient so researches on the low-power circuit design for the energy harvesting are urgent. This research analyzes the recent energy harvesting techniques, especially, for the small-scale devices such as wireless sensor network and wearable devices. First, the general architecture of the energy harvesting is analyzed. Basic units of the architecture are suggested and their recent trends and considerations for building the system are also explored. Then, four results of this research are explained: solar energy harvesting, thermoelectric energy harvesting, vibration energy harvesting, and general low-voltage energy harvesting charge pump. Four voltage converters are fabricated in different technologies. The proposed circuits are successfully verified with simulation and experimental results. Four researches are as follows. The first research proposes a regulated charge pump with an integrated optimum power point tracking (OPPT) algorithm designed for indoor solar energy harvesting. The proposed OPPT circuit does not require a current sensor that consumes a power proportionally to the load. The solar cell voltage is regulated at the optimum power point; the charge pump output is regulated according to the target voltage. The controller of the OPPT circuit and charge pump dissipates only 450nW, so the proposed technique is appropriate for indoor solar energy harvesting applications under dim lighting conditions. The second research presents a DC-DC boost converter with the maximum power point tracking (MPPT) technique for thermoelectric energy harvesting applications. The technique realizes variation tolerance by adjusting the switching frequency of the converter. A finely controlled zero-current switching (ZCS) scheme together with the accurate MPPT technique enhances the overall efficiency of the converter because of an optimal turn-on time generated by a proposed one-shot pulse generator. Moreover, the ZCS technique can deal with low and high temperature differences applied to the thermoelectric generator. This allows a wider range of conversion ratios compared to those of conventional converters used for thermal energy harvesting. Experimentally, the converter implemented in a 0.35-μm BCDMOS process had a peak efficiency of 72% at the input voltage of 500mV while supplying a 5.62V output. In the third research, an AC-DC rectifying system for vibration energy harvesting is proposed to generate outputs of four different voltage levels with a single power source. The proposed dual-output rectifier uses only four diodes, similar to a conventional single-output full-bridge rectifier. A switched-capacitor down-converter provides two output voltages from a single input of the voltage doubler by using the proposed load balancer with a low design complexity. The proposed system is implemented in a 0.35-μm CMOS process, and it occupies an area of 0.143 mm2. In the last research, a charge pump using 0.13-μm CMOS process for low-voltage energy harvesting is proposed. The switching body bias (SBB) and switch-conductance enhancement techniques are applied to a unit stage of the three-stage charge pump. A low-power adaptive dead-time (AD) circuit automatically optimizes the dead-time according to the input voltage. A negative charge pump is also utilized for high efficiency at low input voltages. The AD circuit improves the efficiency by 17% at the input voltages of 0.2V as well as enables the charge pump to work at the input voltages down to 0.15V. The reverse current flowing through the cross-coupled NMOS switches is prevented and the current transfer is also maximized by the conventional switching body bias. The design methodology for the low-voltage charge pump in the energy harvesting application is presented. Together with the SBB technique, the maximum output current was improved by 240% compared to the conventional charge pump design using only the forward body bias.

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