Millimeter-Wave Wireless Power Transfer Systems for the Internet of Things (2016)

The Internet of Things (IoT) would add computational power to a plethora of ordinary objects. Potential applications are vast and vary in terms of maturity from sensors tracking energy usage to smart wearables and many more futuristic applications. A challenge shared by many of such small devices, in the order of a few centimeters in length and width, is battery and power. Cost, size, weight, and lifetime of the battery motivate alternative methods for providing energy to such devices. A practical Wireless Power Transfer (WPT) system which can power battery-less and charge coil-free smart everyday-objects has a tremendous potential to address this demand. In this work we offer a reliable solution. The 60-GHz WPT system that is built in this project can be employed by any smart device which can be placed at a reasonably close distance to its power transmitter, without the alignment and proximity challenges which are associated with the magnetic charging solutions. The leading applications to benefit enormously from this new 60-GHz WPT technology are miniature IoT devices, smart charge cards, business cards and IDs, smart posters, sensor fusion, and wireless flash memories.In this work, the first reported full-system 60-GHz WPT solution which can power battery-less and charge coil-free compact smart devices is presented. The system is fabricated in a 40-nm digital CMOS process and an inexpensive 500-µm CCL-HL832MG antenna packaging material. The rectenna (RX) of this 60-GHz WPT system consists of a grid antenna with a measured gain of 10.7 dBi, integrated with a tuned complementary cross-coupled oscillator-like rectifier. It harvests DC power at a rate of 1 mW with a 28.2% RF-to-DC Power Conversion Efficiency (PCE). This PCE rate is significantly higher than the prior art and reaches 32.8% for 1.4 mA output current. A novel theoretical analysis of the unique rectifier circuitry is presented which helps formulating all key specifications and identifying the design trade-offs. We present a cascode version of the energy harvester that produces higher DC output voltage and higher PCE in low current regime. The theoretical analysis and the results of the measurement for that harvester is also presented. The transmitter (TX) is equipped with a quad-core power amplifier which produces a total saturated output power (Psat) of 24.6 dBm, which is the highest reported power delivery in digital CMOS technology at mm-wave bands. The TX peak PAE is 9.4%. The quad-core PA performs a 4 × 8-way differential power combining and implements a binary-tree architecture by using power-splitting transformers which perform intra-stage matching too. The designed 2 × 2 grid array antenna helps the TX produce a peak EIRP level of 35.3 dBm. The coupling between the TX and RX antennas within 4 cm spacing is between -18.9 and -17.4dB. The results of full-system characterizations of the WPT solution and the measurements data of the individually-fabricated grid antennas, harvester, transmitter, and all building blocks are reported. Programmability in the input polarities of the quad-core PA offers output power control and beam-steering capabilities to this 60-GHz WPT system. A four-input grid antenna is designed for the TX which in simulation shows an effective 70° beam-steering range in the broadside direction.In order to demonstrate how the design and implementation of all the 60-GHz circuitry has been as successful as they are, the design of the VCOs, quadrature VCOs, PAs, unit-cell devices, pads and calibration circuitry, passive components like inductors, transformers, capacitors, the patch antennas, and the grid array antennas that have been done before the final implementation of the full wireless power transfer system are presented as well and the key design points are specified and explained. The architecture study for the transmitter and the energy harvester are also included in this dissertation since they have been most vital parts of accomplishing the design of the highest transmit power delivery and highest rectenna power conversion efficiency in digital CMOS technology. The 60-GHz WPT system designed for this work can serve miniature sized smart everyday-objects which require milliwatt-level power delivery and work in contact-less and close-proximity distances. The full-system measurement results of the proposed 60-GHz wireless power transfer solution demonstrate the suitability of this mm-wave WPT system for addressing the demand for wireless power of batteryless and coil-free devices with stringent size constraints of new applications, like the IoT.