Energy-Efficient Wireless Circuits and Systems for Internet of Things

As the demand of ultra-low power (ULP) systems for internet of thing (IoT) applications has been increasing, large efforts on evolving a new computing class is actively ongoing. The evolution of the new computing class, however, faced challenges due to hard constraints on the RF systems. Significant efforts on reducing power of power-hungry wireless radios have been done. The ULP radios, however, are mostly not standard compliant which poses a challenge to wide spread adoption. Being compliant with the WiFi network protocol can maximize an ULP radio’s potential of utilization, however, this standard demands excessive power consumption of over 10mW, that is hardly compatible with in ULP systems even with heavy duty-cycling. Also, lots of efforts to minimize off-chip components in ULP IoT device have been done, however, still not enough for practical usage without a clean external reference, therefore, this limits scaling on cost and form-factor of the new computer class of IoT applications. This research is motivated by those challenges on the RF systems, and each work focuses on radio designs for IoT applications in various aspects. First, the research covers several endeavors for relieving energy constraints on RF systems by utilizing existing network protocols that eventually meets both low-active power, and widespread adoption. This includes novel approaches on 802.11 communication with articulate iterations on low-power RF systems. The research presents three prototypes as power-efficient WiFi wake-up receivers, which bridges the gap between industry standard radios and ULP IoT radios. The proposed WiFi wake-up receivers operate with low power consumption and remain compatible with the WiFi protocol by using back-channel communication. Back-channel communication embeds a signal into a WiFi compliant transmission changing the firmware in the access point, or more specifically just the data in the payload of the WiFi packet. With a specific sequence of data in the packet, the transmitter can output a signal that mimics a modulation that is more conducive for ULP receivers, such as OOK and FSK. In this work, low power mixer-first receivers, and the first fully integrated ultra-low voltage receiver are presented, that are compatible with WiFi through back-channel communication. Another main contribution of this work is in relieving the integration challenge of IoT devices by removing the need for external, or off-chip crystals and antennas. This enables a small form-factor on the order of mm3-scale, useful for medical research and ubiquitous sensing applications. A crystal-less small form factor fully integrated 60GHz transceiver with on-chip 12-channel frequency reference, and good peak gain dual-mode on-chip antenna is presented.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162975/1/jaeim_1.pd

Integrated Circuit and System Design for Cognitive Radio and Ultra-Low Power Applications

The ubiquitous presence of wireless and battery-powered devices is an inseparable and invincible feature of our modern life. Meanwhile, the spectrum aggregation, and limited battery capacity of handheld devices challenge the exploding demand and growth of such radio systems. In this work, we try to present two separate solutions for each case; an ultra-wideband (UWB) receiver for Cognitive Radio (CR) applications to deal with spectrum aggregation, and an ultra-low power (ULP) receiver to enhance battery life of handheld wireless devices. Limited linearity and LO harmonics mixing are two major issues that ultra-wideband receivers, and CR in particular, are dealing with. Direct conversion schemes, based on current-driven passive mixers, have shown to improve the linearity, but unable to resolve LO harmonic mixing problem. They are usually limited to 3rd, and 5th harmonics rejection or require very complex and power hungry circuitry for higher number of harmonics. This work presents a heterodyne up-down conversion scheme in 180 nm CMOS technology for CR applications (54-862 MHz band) that mitigates the harmonic mixing issue for all the harmonics, while by employing an active feedback loop, a comparable to the state-of-the art IIP3 of better than +10 dBm is achieved. Measurements show an average NF of 7.5 dB when the active feedback loop is off (i.e. in the absence of destructive interference), and 15.5 dB when the feedback loop is active and a 0 dBm interferer is applied, respectively. Also, the second part of this work presents an ultra-low power super-regenerative receiver (SRR) suitable for OOK modulation and provides analytical insight into its design procedure. The receiver is fabricated in 40 nm CMOS technology and operates in the ISM band of 902-928 MHz. Binary search algorithm through Successive Approximation Register (SAR) architecture is being exploited to calibrate the internally generated quench signal and the working frequency of the receiver. Employing an on-chip inductor and a single-ended to differential architecture for the input amplifier has made the receiver fully integrable, eliminating the need for external components. A power consumption of 320 µW from a 0.65 V supply results in an excellent energy efficiency of 80 pJ/b at 4 Mb/s data rate. The receiver also employs an ADC that enables soft-decisioning and a convenient sensitivity-data rate trade-off, achieving sensitivity of -86.5, and -101.5 dBm at 1000 and 31.25 kbps data rate, respectivel

Integrated Circuit and System Design for Cognitive Radio and Ultra-Low Power Applications

The ubiquitous presence of wireless and battery-powered devices is an inseparable and invincible feature of our modern life. Meanwhile, the spectrum aggregation, and limited battery capacity of handheld devices challenge the exploding demand and growth of such radio systems. In this work, we try to present two separate solutions for each case; an ultra-wideband (UWB) receiver for Cognitive Radio (CR) applications to deal with spectrum aggregation, and an ultra-low power (ULP) receiver to enhance battery life of handheld wireless devices. Limited linearity and LO harmonics mixing are two major issues that ultra-wideband receivers, and CR in particular, are dealing with. Direct conversion schemes, based on current-driven passive mixers, have shown to improve the linearity, but unable to resolve LO harmonic mixing problem. They are usually limited to 3rd, and 5th harmonics rejection or require very complex and power hungry circuitry for higher number of harmonics. This work presents a heterodyne up-down conversion scheme in 180 nm CMOS technology for CR applications (54-862 MHz band) that mitigates the harmonic mixing issue for all the harmonics, while by employing an active feedback loop, a comparable to the state-of-the art IIP3 of better than +10 dBm is achieved. Measurements show an average NF of 7.5 dB when the active feedback loop is off (i.e. in the absence of destructive interference), and 15.5 dB when the feedback loop is active and a 0 dBm interferer is applied, respectively. Also, the second part of this work presents an ultra-low power super-regenerative receiver (SRR) suitable for OOK modulation and provides analytical insight into its design procedure. The receiver is fabricated in 40 nm CMOS technology and operates in the ISM band of 902-928 MHz. Binary search algorithm through Successive Approximation Register (SAR) architecture is being exploited to calibrate the internally generated quench signal and the working frequency of the receiver. Employing an on-chip inductor and a single-ended to differential architecture for the input amplifier has made the receiver fully integrable, eliminating the need for external components. A power consumption of 320 µW from a 0.65 V supply results in an excellent energy efficiency of 80 pJ/b at 4 Mb/s data rate. The receiver also employs an ADC that enables soft-decisioning and a convenient sensitivity-data rate trade-off, achieving sensitivity of -86.5, and -101.5 dBm at 1000 and 31.25 kbps data rate, respectivel

Design Considerations of a Sub-50 {\mu}W Receiver Front-end for Implantable Devices in MedRadio Band

Emerging health-monitor applications, such as information transmission through multi-channel neural implants, image and video communication from inside the body etc., calls for ultra-low active power (<50${\mu}$W) high data-rate, energy-scalable, highly energy-efficient (pJ/bit) radios. Previous literature has strongly focused on low average power duty-cycled radios or low power but low-date radios. In this paper, we investigate power performance trade-off of each front-end component in a conventional radio including active matching, down-conversion and RF/IF amplification and prioritize them based on highest performance/energy metric. The analysis reveals 50${\Omega}$ active matching and RF gain is prohibitive for 50${\mu}$W power-budget. A mixer-first architecture with an N-path mixer and a self-biased inverter based baseband LNA, designed in TSMC 65nm technology show that sub 50${\mu}$W performance can be achieved up to 10Mbps (< 5pJ/b) with OOK modulation.Comment: Accepted to appear on International Conference on VLSI Design 2018 (VLSID

Efficient and Interference-Resilient Wireless Connectivity for IoT Applications

With the coming of age of the Internet of Things (IoT), demand on ultra-low power (ULP) and low-cost radios will continue to boost tremendously. The Bluetooth-Low-energy (BLE) standard provides a low power solution to connect IoT nodes with mobile devices, however, the power of maintaining a connection with a reasonable latency remains the limiting factor in defining the lifetime of event-driven BLE devices. BLE radio power consumption is in the milliwatt range and can be duty cycled for average powers around 30μW, but at the expense of long latency. Furthermore, wireless transceivers traditionally perform local oscillator (LO) calibration using an external crystal oscillator (XTAL) that adds significant size and cost to a system. Removing the XTAL enables a true single-chip radio, but an alternate means for calibrating the LO is required. Innovations in both the system architecture and circuits implementation are essential for the design of truly ubiquitous receivers for IoT applications. This research presents two porotypes as back-channel BLE receivers, which have lower power consumption while still being robust in the presents of interference and able to receive back-channel message from BLE compliant transmitters. In addition, the first crystal-less transmitter with symmetric over-the-air clock recovery compliant with the BLE standard using a GFSK-Modulated BLE Packet is presented.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162942/1/abdulalg_1.pd

Energy-Detecting Receivers for Wake-Up Radio Applications

In the energy-limited wireless sensor node applications, wake-up radios are required to reduce the average power consumption of the node. Energy-detecting receivers are the best fit for such low power operations. This thesis presents the energy-detecting receiver design; challenges; techniques to enhance sensitivity, selectivity; and multi-access operation. Self-mixers instead of the conventional envelope detectors are proposed and proved to be optimal for signal detection. A fully integrated wake-up receiver uses the self-mixer and time-encoded baseband signal processing to provide a sensitivity of -79.1dBm at 434MHz with 420pW of power, providing an 8dB better sensitivity at 10dB lower power consumption compared to the SoA. A novel approach using narrowband interferers as local oscillators will be presented to further enhance sensitivity and selectivity, effectively operating the energy-detector receiver as a direct down-conversion receiver. Additionally, a clockless continuous-time analog correlator will be introduced to enhance the selectivity to wide-band AM interferers. The architecture uses pulse-position-encoded analog signal processing with VCOs as integrators and pulse-controlled relaxation delays; it operates as a code-domain matched filter to de-spread asynchronous wake-up codes. This code-domain matched filtering also provides code-division multiple access (CDMA) for simultaneous wakeups. Additional enhancement in the link can be achieved using directional antennas, providing spatial gain and selectivity. Certain applications can leverage a nearby reflector similar to a Yagi antenna to enhance the directivity. A low power directional backscatter tag is proposed, it uses multiple antennas acting as a reflectarray by configuring constant phase gradients depending on the direction of arrival (DoA) of the signal. Thus, instead of harvesting energy, the same energy and the surrounding environment can be leveraged to enhance functionality (e.g. interferer as LO, using a backscatter tag on a wall) for low power operation. Innovations spanning both system and circuit architectures that leverage the ambient energy and environment to enable power-efficient solutions for next-generation wake-up radios are presented in this work

Ultra-Low-Power Sensors and Receivers for IoT Applications

The combination of ultra-low power analog front-ends and CMOS-compatible transducers enable new applications, such as environmental monitors, household appliances, health trackers, etc. that are seamlessly integrated into our daily lives. Furthermore, wireless connectivity allows many of these sensors to operate both independently and collectively. These techniques collectively fulfil the recent surge of internet-of-things (IoT) applications that have the potential to fundamentally change daily life for millions of people.In this dissertation, the circuit and system design of wireless receivers and sensors is presented that explores the challenges of implementing long lifespan, high accuracy, and large coverage range IoT sensor networks. The first is a wake-up receiver (WuRX), which continuously monitors the RF environment to wake up a higher-power radio upon detection of a predetermined RF signature. This work both improves sensitivity and reduces power over prior art through a multi-faceted design featuring an impedance transformation network with large passive voltage gain, an active envelope detector with high input impedance to facilitate large passive voltage gain, a low-power precision comparator, and a low-leakage digital baseband correlator.Although pushing the prior WuRX performance boundary by orders of magnitude, the first work shows moderate sensitivity, inferior temperature robustness, and large area with external lumped components. Thus, the second work shows a miniaturized WuRX that is temperature-compensated, yet still consumes only nano-watt power and millimeter area while operating at 9 GHz. To further reduce the area, a global common-mode feedback is utilized across the envelope detector and baseband amplifier that eliminates the need for off-chip ac-coupling components. Multiple temperature-compensation techniques are proposed to maintain constant bandwidth of the signal path and constant clock frequency. Both WuRXs operate at 0.4 V supply, consume near-zero power and achieve ~-70 dBm sensitivity.Lastly, the first reported CMOS 2-in-1 relative humidity and temperature sensor is presented. A unified analog front-end interfaces on-chip transducers and converts the inputs into a frequency vis a high-linearity frequency-locked loop. An incomplete-settling switched-capacitor-based Wheatstone bridge is proposed to sense the inputs in a power-efficient fashion

Ultra Low Power FM-UWB Transceiver for High-Density Wireless Sensor Networks

The WiseSkin project aims to provide a non-invasive solution for restoration of a natural sense of touch to persons using prosthetic limbs. By embedding sensor nodes into the silicone coating of the prosthesis, which acts as a sensory skin, WiseSkin targets to provide improved gripping, manipulation and mobility for amputees. Flexibility, freedom of movement and comfort demand unobtrusive, highly miniaturized, low-power sensing capabilities built into the artificial skin, which is then integrated with a sensory feedback system. Wireless communication between the sensor nodes provides more flexibility, better scalability and robustness compared to wired solution, and is therefore a preferred approach for WiseSkin. Design of an RF transceiver tailored for the specific needs of WiseSkin is the topic of this work. The properties of FM ultra-wide band (FM-UWB) modulation make it a good candidate for High-Density Wireless Sensor Networks (HD-WSN). The proposed FM-UWB receivers take advantage of short range to reduce power consumption, and exploit robustness of this wideband modulation scheme. The LNA, identified as the biggest consumer, is removed and signal is directly converted to dc, where amplification and demodulation are performed. Owing to 500 MHz bandwidth, frequency offset and phase noise can be tolerated, and a low-power, free-running ring oscillator can be used to generate the LO signal. The receiver is referred to as an approximate zero-IF receiver. Two receiver architectures are studied. The first one performs quadrature downconversion, and owing to the demodulator linearity, provides the multi-user capability. In the second receiver, quadrature demodulation is replaced by the single-ended one. Due to the nature of the demodulator, sensitivity degrades, and multiple FM-UWB signals cannot be resolved, but the consumption is almost halved compared to the first receiver. The proposed approach is verified through two integrations, both in a standard 65 nm bulk CMOS process. In the first run, a standalone quadrature receiver was integrated. Power consumption of 423 uW was measured, while achieving -70 dBm sensitivity. Good narrow-band interference rejection and multiuser capability with up to 4 FM-UWB channels could be achieved. In the second run, a full transceiver is integrated, with both quadrature and single-ended receivers and a transmitter, all sharing a single IO pad, without the need for any external passive components or switches. The quadrature receiver, with on-chip baseband processing and multi-user support, in this case consumes 550 uW, with a sesensitivity of -68 dBm. The low power receiver consumes 267 uW, and provides -57 dBm sensitivity, at a single FM-UWB channel. The implemented trantransmitter transmits a 100 kb/s FM-UWB signal at -11.4 dBm, while drawing 583 uW from the 1 V supply. The on-chip clock recovery allows reference frequency offset up to 8000 ppm. Since state of the art on-chip RC oscillators can provide below 2100 ppm across the temperature range of interest, the implemented transceiver demonstrates the feasibility of a fully integrated FM-UWB radio with no need for a quartz reference or any external components. In addition, the transceiver can tolerate up to 3 dBm narrow-band interferer at 2.4 GHz. Such a strong signal can be used to remotely power the sensor nodes inside the artificial skin and enable a truly wirelessWiseSkin solution

Improving practical sensitivity of energy optimized wake-up receivers: proof of concept in 65nm CMOS

We present a high performance low-power digital base-band architecture, specially designed for an energy optimized duty-cycled wake-up receiver scheme. Based on a careful wake-up beacon design, a structured wake-up beacon detection technique leads to an architecture that compensates for the implementation loss of a low-power wake-up receiver front-end at low energy and area costs. Design parameters are selected by energy optimization and the architecture is easily scalable to support various network sizes. Fabricated in 65nm CMOS, the digital base-band consumes 0.9uW (V_DD=0.37V) in sub-threshold operation at 250kbps, with appropriate 97% wake-up beacon detection and 0.04% false alarm probabilities. The circuit is fully functional at a minimum V_DD of 0.23V at f_max=5kHz and 0.018uW power consumption. Based on these results we show that our digital base-band can be used as a companion to compensate for front-end implementation losses resulting from the limited wake-up receiver power budget at a negligible cost. This implies an improvement of the practical sensitivity of the wake-up receiver, compared to what is traditionally reported.Comment: Submitted to IEEE Sensors Journa

Interference-robust CMOS receivers for IoT:Highly linear RF front-ends at low power

Wireless technologies have brought Internet access to more than half of the world’s population in the last decade. Nowadays, Internet-of-Things (IoT) technology extends the internet connectivity to sensor nodes embedded in machines, animals, and plants. It will soon put us in a realm of billions of interconnected sensor nodes networking and communicating with each other. Such unprecedented growth of wireless devices puts a big challenge of sustainable and robust connectivity in front of us. Concretely, this challenge demands a wireless sensor node with low power and robust connectivity. Radios are the physical interface for sensor nodes with the external world and are one of the power-hungry components in sensor nodes. Hence it is imperative to make them energy-efficient and interference-robust. This thesis explores CMOS passive mixer-first receiver topology to enhance the interference tolerance of receivers in IoT radios. The dissertation proposes a novel N-path filter/mixer topology at the circuit level and a multipath cross-correlation technique at the system level. Two test-chips of mixer-first receiver front ends, using these techniques, are implemented in CMOS FDSOI 22nm technology as a proof-of-concept. The experimental prototypes demonstrate voltage gain in passive mixers and exhibit high-Q widely-tunable RF filtering, large out-of-band and harmonic interferer tolerance, and moderate noise figure while consuming much lower power than several state-of-the-art receivers