Radio and Sensor Interfaces for Energy-autonomous Wireless Sensing

Along with rapid development of sensing and communication technology, Internet of Things (IoTs) has enabled a tremendous number of applications in health care, agriculture, and industry. As the fundamental element, the wireless sensing node, such as radio tags need to be operating under micro power level (e.g, 100 μW, Pico radio) for energy autonomy. The evolution of electronics towards highly energy-efficient systems requires joint efforts in developing innovative architectures and circuit techniques. In this dissertation, we explore ultra-low power circuits and systems for micropower wireless sensing in the context of IoTs, with a special focus on radio interfaces and sensor interfaces. The system architecture of ultra-high frequency/ultra-wideband (UHF/UWB) asymmetric radio is introduced. Taking full benefits of the UWB, the active UWB radio is employed for the tag-to-reader communication while the conventional UHF radio is used to power up and inventory the tag. On the tag side, an ultra-low power, high pulse swing, and power scalable UWB transmitter is studied in 180 nm complementary metal-oxide-silicon (CMOS). The baseband-like architecture promises a mostly digital architecture and an inherent filter, enabling package co-design. The measured pulse swing is 1.27 V and the radiated energy is 1.47 pJ, corresponding to 8.2% energy efficiency. In order to pair the tags for demonstrating of the system concept, an asymmetric UHF/UWB reader is designed in 90 nm CMOS. The UHF transmitter delivers 160 kb/s amplitude shift keying (ASK) modulated data by an integrated modulator and a digital controlled oscillator (DCO). The UWB receiver supports on off key (OOK) and pulse-position modulation (PPM) with data rate up to 33 Mb/s. The front-end of UWB receiver exhibits a noise figure of 8.5 dB with 0.5 nJ/bits energy consumption. Measurement results show that the receiver achieves an input sensitivity of -79 dBm with 10 BER at 10 Mb/s data rate. In order to eliminate power-hungry frequency synthesis circuitry and facilitate the synchronization, an energy-efficient UWB transmitter with wireless clock harvesting in 180 nm CMOS is presented. The transmitter is powered by 900 MHz UHF signals radiated by a reader wirelessly and responds UWB pulses by locking-gating-amplifying the sub-harmonic of the UHF signal. Thanks to the fast setup time (< 50 ns at -15 dBm input power), the proposed transmitter is fully power scalable with 35 pJ/pulse energy consumption. When -15 dBm UHF carrier signal power is injected, 21% locking range can be achieved to prevent PVT variations. To comply with the federal communications commission (FCC) regulation, the maximum pulse rate is up to 5 MHz with 0.75 V peak to peak pulse amplitude. Finally, radio-sensing interface co-design is explored. Taking the advantage of RC time-constant-based readout circuit and ultra-low power UWB pulse generator, the sensing information is directly extracted and transmitted in the time domain, exploiting high time-domain resolution UWB pulses. This approach eliminates the need of analog-to-digital converters (ADC) and baseband blocks of the sensor interface, meanwhile, it reduces the number of bits to be transmitted for energy saving. The interface measures the discharging time of the RC time constant proportional to the sensor variation. The UWB pulses are triggered with intervals of RC discharging time, without any digitizing or modulations. A resistance measurement results show that the proposed system exhibits 7.7 bits effective number of resolution bits (ENOB) with an average relative error of 0.42% in the range of