Wirelessly Powered Sensor Design with On-Chip Antenna in CMOS Technology
Babakhani, Aydin; Knightly, Edward
Doctor of Philosophy
In recent years, we have experienced a significant growth of the Internet of Things (IoT), wireless sensor network (WSN) and bio-implantable devices. There are 7 billion of IoT devices in use in 2018, which starts to surpass the number of the mobile devices. To extend the next level of connectivity from smart phone or tablet to each of the everyday objects, a battery-less small-footprint low-cost IoT circuit with sensing, computation and communication capability is critical for the advancement of the applications. In this thesis, to eliminate the need of battery and miniaturize the system size to millimeter scale, wireless power harvesting front-end with on-chip antenna is utilized to extend the operating distance. The operating frequency of the wireless power link is optimized for mm-sized on-chip antenna to minimize the device size and to achieve a higher received rectified power. Moreover, for wirelessly-powered transmitter design, a frequency-division scheme is adopted to solve the self-interference issue in conventional Radio-Frequency Identification (RFID) system. A duty cycle operation of the circuit is also proposed by utilizing power management unit, which reduces the minimum required harvested power for more power-hungry applications. Based on these methodologies, several wireless-powered CMOS circuits are implemented and tested for different applications. The first chip is a wirelessly-powered dielectric sensor with the size of 3.9 by 0.7mm2. It can detect the dielectric constant of different materials such as oil and epoxy shown on top of the chip. The second chip is targeted for absorption spectroscopy application by using a wirelessly-powered injection-locked oscillator to achieve wide tuning range from 4 to 5 GHz. The third chip is a millimeter sized wirelessly-powered pH sensor together with customized IrOx sensing electrode. The pH sensor transmits a pH-sensitive frequency signal that is converted from the sensed electrode reduction potential. In addition to sensor applications, a wirelessly-powered transmitter with on-chip antenna in 180 nm CMOS is designed, which achieves a data-rate up to 50 Mbps with on-off key modulation scheme. Moreover, a wirelessly-powered miniaturized pacemaker chip in 180 nm CMOS process is also implemented. The total size of the pacemaker chip with PCB package is 16 by 3.8mm2. The in-vivo experiment is demonstrated successfully on a live pig heart, that the heart rate can be tuned from 100 bpm to 172 bpm by the changing the stimulation from the chip.