In this paper, a summary of published techniques for power conditioning within energy harvesting systems is presented. The focus is on low-power systems, e.g, <;10 mW, for kinetic energy harvesting. Published concepts are grouped according to functionality and results contrasted. The various techniques described are considered in terms of complexity, efficiency, quiescent power consumption, startup behavior, and utilization of the harvester compared to an optimum load. This paper concludes with an overview of power management techniques that aim to maximize the extracted power and the utilization of the energy harvester.

Review of Power Conditioning for Kinetic Energy Harvesting Systems

We present, in this paper, a new full-wave CMOS rectifier dedicated for wirelessly-powered low-voltage biomedical implants. It uses bootstrapped capacitors to reduce the effective threshold voltage of selected MOS switches. It achieves a significant increase in its overall power efficiency and low voltage-drop. Therefore, the rectifier is good for applications with low-voltage power supplies and large load current. The rectifier topology does not require complex circuit design. The highest voltages available in the circuit are used to drive the gates of selected transistors in order to reduce leakage current and to lower their channel on-resistance, while having high transconductance. The proposed rectifier was fabricated using the standard TSMC 0.18 μm CMOS process. When connected to a sinusoidal source of 3.3 V peak amplitude, it allows improving the overall power efficiency by 11% compared to the best recently published results given by a gate cross-coupled-based structure.

A High-Efficiency Low-Voltage CMOS Rectifier for Harvesting Energy in Implantable Devices

This paper presents a highly efficient, ultra-low-voltage active full wave rectifier. A two-stage concept is used including a first passive stage and only one active diode as second stage. A bulk-input comparator working in the subthreshold region is used to drive the switch of the active diode. The voltage drop over the rectifier is some tens of millivolt, which results in voltage and power efficiencies of over 90%. The design was successfully implemented in an 0.35 μm CMOS technology. The measured power consumption of the comparator is 266 nW@500 mV and the minimum operating voltage is 380 mV. Input voltages with frequencies up to 10 kHz can be rectified.

A Sub-500 mV Highly Efficient Active Rectifier for Energy Harvesting Applications

This paper presents a fully autonomous power converter IC for energy harvesting from multiple and multitype sources, such as piezoelectric, photovoltaic, thermoelectric, and RF transducers. The converter performs an independent self-adapting input power tracking process for each source. The peak power conversion efficiency measured during single-source operation is 89.6%. With all sources enabled, the intrinsic current consumption is as low as 47.9 nA/source. A self-starting battery-less architecture has been implemented in a 0.32-μm STMicroelectronics BCD technology with a 2142 μm × 2142 μm die area. The IC only requires a single-shared inductor and an external storage capacitor for the basic working configuration. With respect to other multisource energy harvesters, this design specifically introduces a series of nanopower design techniques for extreme minimization of the intrinsic consumption during operation. The small chip size combined with the limited number of required external component, the high conversion efficiency, and the state-of-the-art intrinsic nanocurrent consumption make the IC suitable for many critical applications with very limited available power, such as wearable devices or unobtrusive wireless sensor networks.

A Nanocurrent Power Management IC for Multiple Heterogeneous Energy Harvesting Sources

In this paper, we present an active rectifier with high power conversion efficiency (PCE) implemented in a 0.5- mum 5 V standard CMOS technology with two modes of built-in back telemetry; short- and open-circuit. As a rectifier, it ensures a PCE > 80%, taking advantage of active synchronous rectification technique in the frequency range of 0.125-1 MHz. The built-in complementary back telemetry feature can be utilized in implantable microelectronic devices (IMD), wireless sensors, and radio frequency identification (RFID) applications to reduce the silicon area, increase the data rate, and improve the reading range and robustness in load shift keying (LSK).

Active High Power Conversion Efficiency Rectifier With Built-In Dual-Mode Back Telemetry in Standard CMOS Technology

This paper presents a novel architecture for a highly efficient rectifier circuit. The rectifier can be fully integrated using a standard CMOS process without special process options. The needed dynamic bulk regulation transistors are inherent in the first stage. A full wave rectifier with only one threshold voltage drop and an efficiency of approximately 50% is realized. In combination with a low-power active diode the proposed rectifier shows nearly no voltage drop and the efficiency rises up to 90%.

O. Kessling

Papers

CMOS Integrated Highly Efficient Full Wave Rectifier