Abstract
This paper describes a clocked AC-DC charge pump to enable full integration of power converters into a sensor or radio frequency (RF) chip even with low open circuit voltage magnetostrictive vibration energy transducer operating at a low resonant frequency of 10 Hz to 1 kHz. The frequency of the clock to drive an AC-DC charge pump was up-converted with an on-chip oscillator to increase output power of the charge pump without significantly increasing the circuit area. A model of the system including the charge pump and vibration energy transducer is shown. It was validated by HSPICE simulation and measured, resulting in a prototype chip with an area of 0.11 mm2 fabricated in a 65 nm 1 V CMOS process. The fabricated charge pump was also measured together with a magnetostrictive transducer. The charge pump converted the power from the transducer to an output power of 4.2 μW at an output voltage of 2.0 V. The output power varied below 3% over a wide input frequency of 10 Hz to 100 kHz, which suggests that universal design of the clocked AC-DC charge pump can be used for transducers with different resonant frequencies. In a low-input voltage region below 0.8 V, the proposed circuit has higher output power compared with the conventional circuits.
Highlights
In recent years, the Internet of things (IoT), in which information possessed by various machines and humans is collected by sensors and shared among objects via the Internet, has attracted attention
Charge pump (CP), which has been used for energy harvesting and radio In Reference [8], an AC-DC charge pump (CP), which has been used for radio frequency (RF) energy harvesting and frequency identification (RFID), is used for vEH
Even though POUT increases with the proposed clocked AC-DC CP, there should be room to because the impedance at the interface between EH and CP is significantly mismatched
Summary
The Internet of things (IoT), in which information possessed by various machines and humans is collected by sensors and shared among objects via the Internet, has attracted attention. Energy harvesting (EH) obtaining power from surrounding environmental energy is expected to become a power source for IoT sensor devices [1,2]. The AC power is extracted by applying vibration to the piezoelectric element. Since a voltage amplitude of 1 V or greater can be obtained, an AC-DC voltage down converter provides DC power to the sensor integrated circuit (IC). The output impedance of the generating element is very high, and the output voltage amplitude can be higher than 10 V. It requires high voltage rectifiers followed by a buck converter with many external components [6].
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