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Wireless sensor networks (WSNs) are autonomous networks of spatially distributed sensor nodes that are capable of wirelessly communicating with each other in a multihop fashion. Among different metrics, network lifetime and utility, and energy consumption in terms of carbon footprint are key parameters that determine the performance of such a network and entail a sophisticated design at different...
An efficient magnetically coupled wireless power transfer system using a conical coil structure is presented. The use of conical inductors instead of traditional planar coils increases the self-resonance frequency of the transmitter resonator while maintaining the flux linkage to the receiver side. Electromagnetic (EM) and circuit simulation results predict an increase in the efficiency achieved by...
This paper presents a efficiency enhanced rectifier for wireless energy harvesting (WEH) systems. A prototype of the proposed technique is implemented with discrete components and a microcontroller. Measurement results verify the performance of the approach for small input levels which corresponds to a WEH system operating over a long range.
We propose an e-health sensor security scheme using a physically unclonable function (PUF) of the sensor. As a proof-of-concept, we present the approach in the context of silicon photodiodes and use their dark current variations as the desired PUF. The challenge to authenticate the system is generated by quadratic residues. We show that using such a design provides a two-fold security measure in both...
An adaptive control mechanism to improve the efficiency of magnetically coupled resonators (MCRs) used in wireless power transmission is presented. To minimize the degradation in power transfer efficiency, the proposed system dynamically adjusts the capacitance of MCRs as the distance between the transmitter (TX) and receiver (RX) coils changes. The control unit operates in a self-sufficient manner...
The Internet of Things (IoT) is an emerging computing concept that describes a structure in which everyday physical objects, each provided with unique identifiers, are connected to the Internet without requiring human interaction. Long-term and self-sustainable operation are key components for realization of such a complex network, and entail energy-aware devices that are potentially capable of harvesting...
This paper presents a digitally assisted low-dropout voltage regulator. In lieu of the analog error amplifier, the proposed structure uses an analog-to-digital converter, a digital-to-analog converter, and a digital processor. It offers flexibility in terms of stability and regulation accuracy. The measurement results verify the performance of the proposed structure.
This paper presents a fully integrated monitoring system for diagnosing restenosis in coronary-artery stents. Power is transferred wirelessly to the 0.13-µm CMOS monitoring circuit that is embedded on the stent and reads and transmits the sensory data from the pressure sensors which are also embedded on the stent. An auxiliary circuit is introduced to facilitate the alignment of the external reader...
An ultra-low-power CMOS voltage-controlled ring oscillator (VCRO) for passive ultra-high-frequency (UHF) radio-frequency identification (RFID) tags is presented. The gates of the complementary CMOS transistors in pseudo-differential (PD) delay cells are biased through quasi-floating gate (QFG) technique. The boosted gate-drive voltage enables operation of the differential delay cells with supply voltages...
Efficiency enhancement techniques for CMOS rectifiers used in wireless power harvesting applications such as radio-frequency identification (RFID) or biomedical implants are overviewed. More specifically, three recently proposed efficiency enhancement techniques, namely, switched-capacitor gate-boosting scheme, auxiliary cell scheme and quasi-floating-gate biased scheme are presented in which based...
A high-sensitivity fully passive 868-MHz wake-up radio (WUR) front-end for wireless sensor network nodes is presented. The front-end does not have an external power source and extracts the entire energy from the radio-frequency (RF) signal received at the antenna. A high-efficiency differential RF-to-DC converter rectifies the incident RF signal and drives the circuit blocks including a low-power...
In this paper, an ultra wideband analog voltage-mode buffer is presented which can drive a load impedance of 50 Ω. The presented feedback-based buffer uses a compound amplifier which is a parallel combination of a high-DC gain operational amplifier and a operation transconductance amplifier to achieve a high unity gain bandwidth. A proof-of-concept prototype is designed and fabricated in a 0.13 μm...
A CMOS rectifier with a wide input signal range for radio-frequency identification (RFID) applications is presented. Using quasi-floating gate technique, a gate-biasing scheme is proposed to provide a relatively flat power conversion efficiency (PCE) curve for a wide input voltage (power) range. The proposed technique also enables an efficient operation for input voltage levels well below the standard...
A high-efficiency CMOS rectifier with low start-up voltage for ultra-high-frequency (UHF) radio-frequency identification (RFID) applications is presented. To enhance the power conversion efficiency (PCE) of the conventional rectifier when the input voltage (power) is low, appropriate gate-drive voltages for each stage of the rectifier are generated using a chain of auxiliary floating rectifier cells...
In this paper, an ultra-low-power system for wireless monitoring of inductively coupled biomedical implants is presented. The system is fully integrated and composed of custom rectifier, alignment and monitoring circuits with enhanced performance. The proposed system is described in the context of a smart-stent system that monitors the re-narrowing of blood vessels at the smart-stent site. The building...
A high-efficiency CMOS rectifier for radio-frequency identification (RFID) applications is presented. Using an on-chip generated clock signal, a new switching scheme is proposed to enhance the power efficiency of the conventional 4 transistor (4T)-cell rectifier. By switching the gate of charge-transfer transistors to the intermediate nodes of preceding and succeeding stages, low on-resistance and...
An ultra-low-power area-efficient 8-bit successive approximation register (SAR) analog-to-digital converter (ADC) is presented. To achieve ultra-low-power performance a DAC architecture is proposed that employs two rail-to-rail low-power unity-gain buffers and only 4 minimum-size capacitors instead of the conventional binary-weighted capacitor array. Thereby, power consumption and area are drastically...
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