The idea of wireless power transfer (WPT) has been around since the inception of electricity. In the late 19th century, Nikola Tesla described the freedom to transfer energy between two points without the need for a physical connection to a power source as an ?all-surpassing importance to man? [1]. A truly wireless device, capable of being remotely powered, not only allows the obvious freedom of movement but also enables devices to be more compact by removing the necessity of a large battery. Applications could leverage this reduction in size and weight to increase the feasibility of concepts such as paper-thin, flexible displays [2], contact-lens-based augmented reality [3], and smart dust [4], among traditional point-to-point power transfer applications. While several methods of wireless power have been introduced since Tesla?s work, including near-field magnetic resonance and inductive coupling, laser-based optical power transmission, and far-field RF/microwave energy transmission, only RF/microwave and laser-based systems are truly long-range methods. While optical power transmission certainly has merit, its mechanisms are outside of the scope of this article and will not be discussed.

Harvesting Wireless Power: Survey of Energy-Harvester Conversion Efficiency in Far-Field, Wireless Power Transfer Systems

This paper presents an efficient energy harvester for RF-powered sensor networks. The circuit is based on an improved multi-stage rectifier, which exploits a fully passive threshold self-compensation scheme to overcome the limitation due to the input dead zone. A CAD-oriented design methodology is also proposed, which is aimed at maximizing the overall power conversion efficiency of the harvester through an optimum trade-off among matching losses, power reflection and rectifier efficiency. According to the proposed methodology, a 915-MHz harvester comprising an integrated input matching network and a 17-stage self-compensated rectifier has been designed and fabricated in a 90-nm CMOS technology. The rectifier exhibits a remarkably low input power threshold, as it is able to deliver a 1-V dc output voltage to a capacitive load with a very small input power of -24 dBm (4 μW). When driving a 1-MΩ load, the device can supply a 1.2-V output with an input power of -18.8 dBm (13.1 μW). The achieved results exceed the performance of previously reported RF multi-stage rectifiers in standard analog CMOS technology.

A 90-nm CMOS Threshold-Compensated RF Energy Harvester

A new charge pump circuit with consideration of gate-oxide reliability is designed with two pumping branches in this paper. The charge transfer switches in the new proposed circuit can be completely turned on and turned off, so its pumping efficiency is higher than that of the traditional designs. Moreover, the maximum gate-source and gate-drain voltages of all devices in the proposed charge pump circuit do not exceed the normal operating power supply voltage (VDD). Two test chips have been implemented in a 0.35-/spl mu/m 3.3-V CMOS process to verify the new proposed charge pump circuit. The measured output voltage of the new proposed four-stage charge pump circuit with each pumping capacitor of 2 pF to drive the capacitive output load is around 8.8 V under 3.3-V power supply (VDD = 3.3 V), which is limited by the junction breakdown voltage of the parasitic pn-junction in the given process. The new proposed circuit is suitable for applications in low-voltage CMOS processes because of its high pumping efficiency and no overstress across the gate oxide of devices.

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Design of charge pump circuit with consideration of gate-oxide reliability in low-voltage CMOS processes

This paper presents an adaptive RF-DC power converter designed to efficiently convert RF signals to DC voltages utilizing auxiliary transistors to control the threshold voltage of the transistors in the main rectifier chain dynamically. The proposed circuit passively reduces the threshold voltage of the forward-biased transistors to increase the harvested power and the output voltage and increases the threshold voltage of the reverse-biased transistors to reduce the leakage current to prevent the loss of previously stored energy. A 12-stage adaptive threshold-compensated rectifier is designed and implemented in IBM's 0.13 $\mu{\rm m}$ CMOS technology. The proposed rectifier exhibits measured maximum power conversion efficiency (PCE) of 32% at $-$ 15 dBm (32 $\mu{\rm W}$ ) of input power while delivering 3.2 V to a 1 M $\Omega$ load. At a remarkably low input power of $-$ 20.5 dBm (8.9 $\mu{\rm W}$ ) for a 1 M $\Omega$ load, the rectifier produces an output voltage of 1 V.

A 3.2 V –15 dBm Adaptive Threshold-Voltage Compensated RF Energy Harvester in 130 nm CMOS

An improved charge pump circuit efficiently utilizes multiple charge pump stages to produce output voltages much larger than the power supply voltage by incorporating, in some embodiments, two parallel strings of series-coupled charge pump stages. Each corresponding charge pump stage in one string is controlled at least by a node in the corresponding charge pump stage of the other string.

Charge pump circuit incorporating corresponding parallel charge pump stages and method therefor

The present invention relates to a charge-pumping circuit for low-supply voltage. A small charge-pumping circuit was added at the gates of the original Dickson charge-pumping circuit's each stage for bias voltage and the first transistor group was added between well and gate. The second transistor group was added between the gate and drain of original transistor. Thus, the charge-pumping circuit for low-supply voltage can supply a higher positive or negative voltage.

Charge-pumping circuits for a low-supply voltage

Novel charge pumping circuits for low supply voltages utilizing N-MOSFET's or P-MOSFET's with capacitors to generate positive and negative boosted voltages are presented. The two major factors limiting the pumping gain and efficiency are the body effect and the threshold voltage. Two techniques are proposed to minimize the influence of them. One is the new substrate connected technique to eliminate the body effect. The other one is the small pumping circuit providing higher gate voltages for the major pumping circuit to enhance pumping gain. With these two new techniques, the new pumping circuits have high positive and negative boosted voltages at low supply voltages.

Novel high positive and negative pumping circuits for low supply voltage

A semiconductor integrated circuit includes a first charge pumping circuit connected to an input node. The first charge pump circuit includes a plurality of first driving transistors and charges an input voltage at the input node to a control voltage. A second charge pumping circuit includes a plurality of second driving transistors that each receive the control voltage from the first charge pump. The received control voltage controls the driving of the second transistors when charging an output node to an output voltage. To eliminate body effects, the semiconductor integrated circuit further includes a plurality of body transistors that connect the source and body terminals of the driving transistors.

Kai-Hsun Chang

Papers

Charge-pumping circuits for a low-supply voltage

Novel high positive and negative pumping circuits for low supply voltage

Charge pump circuits for low supply voltages