In this paper, a design method for the co-design and integration of a CMOS rectifier and small loop antenna is described. In order to improve the sensitivity, the antenna-rectifier interface is analyzed as it plays a crucial role in the co-design optimization. Subsequently, a 5-stage cross-connected differential rectifier with a 7-bit binary-weighted capacitor bank is designed and fabricated in standard 90 nm CMOS technology. The rectifier is brought at resonance with a high-Q loop antenna by means of a control loop that compensates for any variation at the antenna-rectifier interface and passively boosts the antenna voltage to enhance the sensitivity. A complementary MOS diode is proposed to improve the harvester's ability to store and hold energy over a long period of time during which there is insufficient power for rectification. The chip is ESD protected and integrated on a compact loop antenna. Measurements in an anechoic chamber at 868 MHz demonstrate a -27 dBm sensitivity for 1 V output across a capacitive load and 27 meter range for a 1.78 W RF source in an office corridor. The end-to-end power conversion efficiency equals 40% at -17 dBm.

Co-Design of a CMOS Rectifier and Small Loop Antenna for Highly Sensitive RF Energy Harvesters

Materials, device designs and manufacturing approaches are presented for classes of RF electronic components that are capable of complete dissolution in water or biofluids. All individual passive/active components as well as system-level examples such as wireless RF energy harvesting circuits exploit active materials that are biocompatible. The results provide diverse building blocks for physically transient forms of electronics, of particular potential value in bioresorbable medical implants with wireless power transmission and communication capabilities.

Materials for bioresorbable radio frequency electronics.

A battery-less, multi-node wireless body area network (WBAN) system-on-a-chip (SoC) is demonstrated. An efficiency tracking loop is proposed that adjusts the rectifier's threshold voltage to maximize the wireless harvesting operation, resulting in a minimum RF sensitivity better than –20 dBm at 904.5 MHz. Each SoC node is injection-locked and time-synchronized with the broadcasted RF basestation power (up to a sensitivity of –33 dBm) using an injection-locked frequency divider (ILFD). Hence, every sensor node is phase-locked with the basestation and all nodes can wirelessly transmit TDMA sensor data concurrently. Designed in a 65 nm-CMOS process, the fabricated sensor SoC contains the energy harvesting rectifier and bandgap, duty-cycled ADC, digital logic, as well as the multi-node wireless clock synchronization and MICS-band transmitter. For a broadcasted basestation power of 20 dBm (30 dBm), experimental measurements verify correct powering, sensor reading, and wireless data transfer for a distance of 3 m (9 m). The entire biomedical system application is verified by reception of room and abdominal temperature monitoring.

0.56 V, –20 dBm RF-Powered, Multi-Node Wireless Body Area Network System-on-a-Chip With Harvesting-Efficiency Tracking Loop

Radio Frequency Identification (RFID) sensors, integrating the features of Wireless Information and Power Transfer (WIPT), object identification and energy efficient sensing capabilities, have been considered a new paradigm of sensing and communication for the futuristic information systems. RFID sensor tags featuring contactless sensing, wireless information transfer, wireless powered, light weight, non-line-of-sight transmission, flexible and pasteable are a critical enabling technology for future Internet-of-Things (IoT) applications, such as manufacturing, logistics, healthcare, agriculture and food. They have attracted numerous research efforts due to their innovative potential in the various application fields. However, there has been a gap between the in-lab investigations and the practical IoT application scenarios, which has motivated this survey of this research to identify the promising enabling techniques and the underlying challenges. This study aims to provide an exhaustive review on the state-of-art RFID sensor technologies from the system implementation perspective by focusing on the fundamental RF energy harvesting theories, the recent technical progresses and commercial solutions, innovative applications and some RFID sensor based IoT solutions, identify the underlying technological challenges at the time being, and give the future research trends and promising application fields in the rich sensing applications of the forthcoming IoT era.

https://www.mdpi.com/1424-8220/19/18/4012/pdf

Radio Frequency Identification and Sensing Techniques and Their Applications-A Review of the State-of-the-Art.

This letter presents a novel adaptive rectifier for wireless power transmission (WPT) applications. By utilizing a depletion-mode field-effect transistor (FET) switch, the configuration of the rectifier can automatically adapt to the input power level. Compared with traditional rectifiers, it can provide a consistent high RF-to-dc power conversion efficiency (PCE) over a significantly extended operating input power range. Measured results show that the PCE of this proposed adaptive rectifier keeps above 50% in the input power range spanning from -14 up to 21 dBm. Additionally, maximum PCE of more than 75% is achieved in the input power range from 5 to 15 dBm.

An Adaptive Reconfigurable Rectifier for Wireless Power Transmission

An inherent shortcoming of rectifiers designed using standard CMOS devices is poor low input power performance. It is shown that this can be overcome through the use of intrinsic devices with close to zero-threshold voltage available in a 0.25 μm silicon-on-sapphire (SOS) CMOS process. A novel complementary bridge rectifier structure based on a combination of cross-connected and diode bridge rectifier topologies is introduced to avoid the excessive leakage current incurred through the use of intrinsic devices. A design strategy which maximizes efficiency and produces an input impedance which will interface well with the inductive coil type antennas used in biomedical implants is presented for this new rectifier type. The fabricated rectifier achieves a 1 μW DC output power for an input power of -26.5 dBm at 100 MHz. A peak measured power conversion efficiency of 67% is achieved at 100 MHz, but more importantly >;30% PCE is attained for a wide output power range which reaches as low as -40 dBm. At the target 1 μW output power a PCE of 44% was achieved.

C. D. Presti

Papers

A $\mu$ W Complementary Bridge Rectifier With Near Zero Turn-on Voltage in SOS CMOS for Wireless Power Supplies