A Low-Voltage Mobility-Based Frequency Reference for Crystal-Less ULP Radios

The design of a 100 kHz frequency reference based on the electron mobility in a MOS transistor is presented. The proposed low-voltage low-power circuit requires no off-chip components, making it suitable for application in wireless sensor networks (WSN). After a single-point calibration, the spread of its output frequency is less than 1.1% (3 ) over the temperature range from -22 C to 85 C. Fabricated in a baseline 65 nm CMOS technology, the frequency reference circuit occupies 0.11 mm

A 65-nm CMOS Temperature-Compensated Mobility-Based Frequency reference for wireless sensor networks

For the first time, a temperature-compensated CMOS frequency reference based on the electron mobility in a MOS transistor is presented. Over the temperature range from -55°C to 125 °C, its frequency spread is less than ±0.5% after a two-point trim and less than ±2.7% after a one-point trim. These results make it suitable for use in Wireless Sensor Network nodes. Fabricated in a baseline 65-nm CMOS process, the 150 kHz frequency reference occupies 0.2 mm2 and draws 42.6 μA from a 1.2-V supply at room temperature.\ud \u

A 2.4GHz 830pJ/bit duty-cycled wake-up receiver with −82dBm sensitivity for crystal-less wireless sensor nodes

A 65 nm CMOS 2.4 GHz wake-up receiver operating with low-accuracy frequency references has been realized. Robustness to frequency inaccuracy is achieved by employing non-coherent energy detection, broadband-IF heterodyne architecture and impulse-radio modulation. The radio dissipates 415 ¿W at 500 kb/s and achieves a sensitivity of -82 dBm with an energy efficiency of 830 pJ/bit.\u

A 120nW 18.5kHz RC oscillator with comparator offset cancellation for ±0.25% temperature stability

Integrated low-frequency oscillators can replace crystal oscillators as sleep-mode timers to reduce the size and cost of wireless sensors [1]. Since the timer is one of the few continuously functioning circuits, minimizing its power consumption can greatly reduce sleep-mode power of highly duty-cycled systems. Temperature stability of the oscillator is important in order to minimize timing uncertainly and guard time for the radios, and thus maximizing sleep time. The voltage-averaging feedback method described in [2] achieves high stability in the MHz frequencies, but when scaled to the kHz range, requires very large filters. On the other extreme, gate leakage-based timers have been designed for sub-nW power consumption, but operate in the sub-Hz frequencies [3]. In the past, high accuracy RC oscillators in the kHz range have been designed with feed-forward correction [1] and self-chopped operation [4]. In this work, an offset cancellation architecture achieves long-term frequency stability and temperature stability while operating at lower power

Energy-Efficient Wireless Connectivity and Wireless Charging For Internet-of-Things (IoT) Applications

During the recent years, the Internet-of-Things (IoT) has been rapidly evolving. It is indeed the future of communication that has transformed Things of the real world into smarter devices. To date, the world has deployed billions of “smart” connected things. Predictions say there will be 10’s of billions of connected devices by 2025 and in our lifetime we will experience life with a trillion-node network. However, battery lifespan exhibits a critical barrier to scaling IoT devices. Replacing batteries on a trillion-sensor scale is a logistically prohibitive feat. Self-powered IoT devices seems to be the right direction to stand up to that challenge. The main objective of this thesis is to develop solutions to achieve energy-efficient wireless-connectivity and wireless-charging for IoT applications. In the first part of the thesis, I introduce ultra-low power radios that are compatible with the Bluetooth Low-Energy (BLE) standard. BLE is considered as the preeminent protocol for short-range communications that support transmission ranges up to 10’s of meters. Number of low power BLE transmitter (TX) and receiver (RX) architectures have been designed, fabricated and tested in different planar CMOS and FinFET technologies. The low power operation is achieved by combining low power techniques in both the network and physical layers, namely: backchannel communication, duty-cycling, open-loop transmission/reception, PLL-less architectures, and mixer-first architectures. Further novel techniques have been proposed to further reduce the power the consumption of the radio design, including: a fast startup time and low startup energy crystal oscillators, an antenna-chip co-design approach for quadrature generation in the RF path, an ultra-low power discrete-time differentiator-based Gaussian Frequency Shift Keying (GFSK) demodulation scheme, an oversampling GFSK modulation/demodulation scheme for open loop transmission/reception and packet synchronization, and a cell-based design approach that allows automation in the design of BLE digital architectures. The implemented BLE TXs transmit fully-compliant BLE advertising packet that can be received by commercial smartphone. In the second part of the thesis, I introduce passive nonlinear resonant circuits to achieve wide-band RF energy harvesting and robust wireless power transfer circuits. Nonlinear resonant circuits modeled by the Duffing nonlinear differential equation exhibit interesting hysteresis characteristics in their frequency and amplitude responses that are exploited in designing self-adaptive wireless charging systems. In the magnetic-resonance wireless power transfer scenario, coupled nonlinear resonators are proposed to maintain the power transfer level and efficiency over a range of coupling factors without active feedback control circuitry. Coupling factor depends on the transmission distance, lateral, and angular misalignments between the charging pad and the device. Therefore, nonlinear resonance extends the efficient charging zones of a wireless charger without the requirement for a precise alignment.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169842/1/omaratty_1.pd

A 1.2-V 10- µW NPN-Based Temperature Sensor in 65-nm CMOS With an Inaccuracy of 0.2 °C (3σ) From 70 °C to 125 °C

An NPN-based temperature sensor with digital output transistors has been realized in a 65-nm CMOS process. It achieves a batch-calibrated inaccuracy of ±0.5 ◦C (3¾) and a trimmed inaccuracy of ±0.2 ◦C (3¾) over the temperature range from −70 ◦C to 125 ◦C. This performance is obtained by the use of NPN transistors as sensing elements, the use of dynamic techniques, i.e. correlated double sampling and dynamic element matching, and a single room-temperature trim. The sensor draws 8.3 μA from a 1.2-V supply and occupies an area of 0.1 mm2

Ultra Low Power Communication Protocols for UWB Impulse Radio Wireless Sensor Networks

This thesis evaluates the potential of Ultra Wideband Impulse Radio for wireless sensor network applications. Wireless sensor networks are collections of small electronic devices composed of one or more sensors to acquire information on their environment, an energy source (typically a battery), a microcontroller to control the measurements, process the information and communicate with its peers, and a radio transceiver to enable these communications. They are used to regularly collect information within their deployment area, often for very long periods of time (up to several years). The large number of devices often considered, as well as the long deployment durations, makes any manual intervention complex and costly. Therefore, these networks must self-configure, and automatically adapt to changes in their electromagnetic environment (channel variations, interferers) and network topology modifications: some nodes may run out of energy, or suffer from a hardware failure. Ultra Wideband Impulse Radio is a novel wireless technology that, thanks to its extremely large bandwidth, is more robust to frequency dependent propagation effects. Its impulsional nature makes it robust to multipath fading, as the short duration of the pulses leads most multipath components to arrive isolated. This technology should also enable high precision ranging through time of flight measurements, and operate at ultra low power levels. The main challenge is to design a system that reaches the same or higher degree of energy savings as existing narrowband systems considering all the protocol layers. As these radios are not yet widely available, the first part of this thesis presents Maximum Pulse Amplitude Estimation, a novel approach to symbol-level modeling of UWB-IR systems that enabled us to implement the first network simulator of devices compatible with the UWB physical layer of the IEEE 802.15.4A standard for wireless sensor networks. In the second part of this thesis, WideMac, a novel ultra low power MAC protocol specifically designed for UWB-IR devices is presented. It uses asynchronous duty cycling of the radio transceiver to minimize the power consumption, combined with periodic beacon emissions so that devices can learn each other's wake-up patterns and exchange packets. After an analytical study of the protocol, the network simulation tool presented in the first part of the thesis is used to evaluate the performance of WideMac in a medical body area network application. It is compared to two narrowband and an FM-UWB solutions. The protocol stack parameters are optimized for each solution, and it is observed that WideMac combined to UWB-IR is a credible technology for such applications. Similar simulations, considering this time a static multi-hop network are performed. It is found that WideMac and UWB-IR perform as well as a mature and highly optimized narrowband solution (based on the WiseMAC ULP MAC protocol), despite the lack of clear channel assessment functionality on the UWB radio. The last part of this thesis studies analytically a dual mode MAC protocol named WideMac-High Availability. It combines the Ultra Low PowerWideMac with the higher performance Aloha protocol, so that ultra low power consumption and hence long deployment times can be combined with high performance low latency communications when required by the application. The potential of this scheme is quantified, and it is proposed to adapt it to narrowband radio transceivers by combining WiseMAC and CSMA under the name WiseMAC-HA