Xuan-Dien Do

A Long Reset-Time Power-On Reset Circuit With Brown-Out Detection Capability

A compact low-power on-chip power-on reset circuit with a brown-out detection capability is presented. With a pico-farad-order on-chip MOS capacitor, a long reset time is achieved. A prototype design implemented in a 0.18-μm CMOS process provides a reset signal with duration of hundreds of milliseconds. The embedded brown-out detection circuit can detect the event, as long as the brown-out duration is longer than the millisecond range. The chip consumes only 1 μA under a 1.8-V supply and occupies a 120 μm × 100 μm active area.

A Self-Powered High-Efficiency Rectifier With Automatic Resetting of Transducer Capacitance in Piezoelectric Energy Harvesting Systems

This paper presents a self-powered rectifier for piezoelectric energy harvesting applications, and the key idea of the proposed system is to reset the transducer capacitor at optimal instants to maximize the extracted power. The proposed rectifier consists of two switches and two active diodes. The switches discharge the transducer capacitor at optimal instants two times for every cycle. The active diodes are based on op-amps with a preset dc offset, which reduces the voltage drop and the leakage current and avoids instability. In addition, the controller for the proposed rectifier is simple to reduce the circuit complexity and the power dissipation. The proposed rectifier was designed and fabricated in 0.18-μm CMOS technology. Measured results indicate that it achieves power efficiency of 91.2%, and the amount of power extracted by the proposed rectifier is 3.5 times larger when compared with the conventional rectifiers. The proposed rectifier does not require any off chip components to enable a full chip integration, and the die area of the proposed circuit is 0.08 × 0.20 mm2.

A high efficiency piezoelectric energy harvesting system

Nowadays, harvested energy from surrounding environment plays an important role in the human life. This green energy gradually replaced for traditional energy such as fossil energy. Several methods have been used to capture green energy from environmental source. One of the most popular method is using piezoelectric material to harvest energy from vibration source. A piezoelectric energy harvesting system include two sections: a transducer to convert potential energy to the electrical energy and an electrical interface to manage this energy. Normally, a rectifier and voltage regulator are two main components in the electrical interface. In this paper, a new high efficiency piezoelectric energy harvesting system is proposed to increase extracted power from piezoelectric. By using two synchronized switches, the extracted efficiency of the rectifier is double. Furthermore, the passive diode of the conventional rectifier is replaced by active diode to increase the conversion efficiency of rectifier. The simulation result show that the power extraction efficiency of the rectifier is 3.5 times that of the conventional full bride rectifier, and more than 93% of power conversion efficiency can be achieved. To completely piezoelectric energy harvesting system a Low-drop regulator (LDO) is used to regulate voltage at the output of rectifier. The LDO gets maximum 90% efficiency with 3mV voltage ripple. The overall efficiency of proposed system gets 83.3%.

A rectifier for piezoelectric energy harvesting system with series Synchronized Switch Harvesting Inductor

In this paper, a rectifier with series Synchronized Switch Harvesting Inductor (Series SSHI) is proposed for piezoelectric (PE) energy harvesting system. The serial inductor helps to flip the voltage across the internal capacitor of the PE transducer instead of wasting the capacitor voltage by discharge. Active diodes are used for the switches to further improve the extraction efficiency. From measurements, the proposed rectifier shows a power extraction efficiency of 3.3 times that of the active full bridge (FB) rectifier, and more than 90% of the power conversion efficiency.

Optimization of piezoelectric energy harvesting systems by using a MPPT method

This paper proposes an optimization of a piezoelectric energy harvesting system by using a maximum power point tracking (MPPT) method. A full-bridge rectifier is implemented with a MPPT unit to obtain maximum extracted power by controlling a DC-DC converter following the rectifier. By using the MPPT unit, the extracted power efficiency of the rectifier is always larger than 80% regardless of the load condition. Furthermore, another DC-DC converter is applied to regulate the output voltage to the desired level. The simulation results show that the system can extract a maximum of 51 uW power with 64% total efficiency.

An active rectifier with optimal flip timing for the internal capacitor for piezoelectric vibration energy harvesting

This paper presents an active rectifier, which aims to extract maximum power from piezoelectric generators for vibration energy harvesting. A nonlinear impedance matching scheme called Synchronized Switch Harvesting on Inductor (SSHI) is highly effective [1]. However, control of the internal capacitor flip timing is complicated to result in a complex controller or suboptimal flip timing. We proposed an active rectifier based on the series SSHI configuration [2]. It ensures an optimal capacitor flip timing, yet the controller is simple to dissipate low power and hence achieve high efficiency. One potential problem of the series SSHI scheme is a non-robust operation due to parasitics and a variety of characteristics of the piezoelectric generators. We present an improved rectifier, which address the problem. The improved rectifier is designed in 0.25 μm BiCMOS process. Post-layout simulation results indicate robust operation and high efficiency of 93%, which is comparable to the original design in [2] and far higher than other existing SSHI rectifiers reported.

A Piezoelectric Energy Harvester with High Efficiency and Low Circuit Complexity

This paper presents an efficient vibration energy harvester with a piezoelectric (PE) cantilever. The proposed PE energy harvester increases the efficiency through minimization of hardware complexity and hence reduction of power dissipation of the circuit. Two key features of the proposed energy harvester are (i) incorporation synchronized switches with a simple control circuit, and (ii) a feed-forward buck converter with a simple control circuit. The chip was fabricated in 0.18 μm CMOS processing technology, and the measured results indicate that the proposed rectifier achieves the efficiency of 77%. The core area of the chip is 0.2 mm2.

An area saving inductor current sensor with load transient enhancement in DC-DC converter

Among the on-chip current sensing techniques, inductor current sensing method is the most feasible one for high switching frequency converter, which aids reduction of the filter inductor size. This paper presents a reduction of area design for the combined AC and DC inductor current sensor with load transient enhancement for the systems-on-chip applications. The proposed current sensor is simulated under several switching frequencies. Finally, the transient enhancement function of the proposed circuit is simulated in a buck converter at 4.5MHz switching frequency. When the load current changes by 500mA, by increasing time-constant delay for the sensed DC current ten times, the output voltage overshoot/undershoot reduces from 126mV/229mV to 76mV/74mV.

Low power consumption for detecting current zero of synchronous DC-DC buck converter

A low power consumption for detecting current zero of synchronous DC-DC buck converter is proposed. By using the synchronous regulator, the efficiency of the DC-DC buck converter increase several percents, however the problem of the synchronous regulator is the power loss when the converter operates at the discontinuous conduction mode. A current zero detector is needed to detect when the step down regulator operates in the discontinuous conduction mode avoiding waste power flowing in to ground. By using CLK signal to control the operation of the block, the power consumption of block is reduce 50%. The block is only active when the power transfer from inductor to load an capacitors.