20.8 A 500nW batteryless integrated electrostatic energy harvester interface based on a DC-DC converter with 60V maximum input voltage and operating from 1μW available power, including MPPT and cold start

Abstract

Battery life is a major concern in wireless sensing applications, as it causes a trade-off between system size and power consumption of the electronic circuits connected to it. Even if electronic circuit power consumption is steadily decreasing, the energy density of common energy storage systems is still extremely low in space-constrained applications. In this scenario, energy harvesting is a valuable solution to extend, in theory indefinitely, the autonomy of ubiquitous sensing systems. In particular, vibrational energy harvesters are an excellent solution to power sensors in industrial and automotive applications. This paper presents an electrostatic energy harvester (EEH) interface. Recently, electret-based EEHs have attracted considerable attention because of their capability to generate large powers, even at low accelerations [1]. Unfortunately, these devices are characterized by extremely high internal impedances and their interfacing circuits need to be simultaneously ultra-low-power and capable of working reliably with several tens of Volts applied to the input. To the best of our knowledge, only one solution has been proposed to efficiently interface high-voltage energy harvesters [2]. However, that circuit did not allow fully autonomous battery-less operation and did not work under 25μW available power.The proposed system has been designed in TSMC 0.25 BCD (option 60V) and its block diagram is depicted in Fig. 20.8.1. The system requires 5 discrete components to operate: 1 inductor (L=10mH), 2 capacitors (C IN =100nF and C OUT =2μF-10mF) and 2 resistors (R BIAS =100MΩ and R DC of several GΩ). The system bias current of 10nA is generated by forcing the 1V reference voltage across the resistance R BIAS . Since the input voltage can be as large as 60V and is dependent on the harvested power, the system is powered by its output voltage. For that reason, input and output are shorted in start-up conditions; the Direct-charge circuit has to charge the load capacitance between 0V and a certain programmable threshold before the rest of the system gets activated. When this happens, the main 10nA bias current and the DC-DC buck converter are enabled. In order to maximize the efficiency at low power levels, the inductive converter operates in deep discontinuous conduction mode (DCM) with a new ultra-low-power modulating scheme based on inductor current sensing. The proposed control method optimally controls both on-time, T ON , and off-time of the p-switch, M P , at each cycle, in order to keep peak current and converter equivalent input resistance constant. It can be demonstrated that, in opposition to what happens in conventional PFM and PWM schemes, the proposed simultaneous optimization of T ON and T avoids the increased power consumption (due to the increase of the p-switch duty-cycle T ON /T) when the input voltage gets close to the output voltage.As shown in Fig. 20.8.1, a current sensor is used to generate the copies I LC1 and I LC2 of the inductor current I L, with an attenuation factor of 1000. The first...

A Fully Integrated AC-DC Converter in 1 V CMOS for Electrostatic Vibration Energy Transducer with an Open Circuit Voltage of 10 V

“…Bandgap reference (BGR) operates with VDD, which is controlled by the output voltage VREF. IoT edge device with an ES-ET and (a) a buck converter with FBR and PMC in a BCD process [6] or (b) a proposed shunt regulator integrated into an IoT chip.…”

“…Circuit features are compared in Table 3. In [6], the AC-DC converter was composed of FBR and a buck DC-DC converter. To allow for a high voltage input of 60 V at the peak, a BCD process was used, which provided 60 V transistors.…”

“…As a result, with sufficient amplitude in the voltage at the capacitor node, the battery can be charged with vibration energy. Another power converter is proposed in [5,6] based on a full bridge rectifier (FBR) followed by a DC-DC buck converter, as shown in Figure 1a. An HV rectifier is composed of four diodes for converting the AC power of ES-ETs into DC power to the converter.…”

“…Figure 1. IoT edge device with an ES-ET and (a) a buck converter with FBR and PMC in a BCD process[6] or (b) a proposed shunt regulator integrated into an IoT chip.…”

A CMOS MPPT power conditioning circuit for energy harvesters

“…Only a few circuits offer a wide input voltage range and power range and they make use of either passive or active rectification leading to a reduction in efficiency. Some MPPT circuits were specifically designed to work for a particular harvester [1][2][3].…”