Power consumption and battery life are of critical importance for medical implant devices. For this reason, devices for Wireless Body Area Network (WBAN) applications must consume very little power. To save power, it is desirable to turn off or put to sleep a device when not in use. However, a transceiver, which is the most power hungry block of a wireless sensor node, needs to listen for the incoming signal continuously. An alternative scheme, is to listen for the incoming signal at a predetermined internal, which saves power at the cost of increased latency. Another and more sophisticated scheme is to provide a wake-up receiver, which listens for the incoming signal continuously, and upon detection of an incoming signal, it wakes the primary transceiver up. A wake-up receiver is typically simple and dissipates little power to make the scheme useful. This thesis proposes a low-power wake-up receiver, which listens for a wake-up signal, identifies the target node, and wakes up the primary receiver only when that specific node is called upon. When a wake up signal is transmitted to all of the nodes on a network, our wake-up receiver allows all the nodes on a network except the targeted node to remain asleep to save power. Several wake-up receiver topologies have been proposed. This work uses a passive Cockcroft-Walton multiplier circuit as an RF envelope detector followed by a simple detector circuit. A novel serial code detector is then used to decode the pulse width modulated input signal to wake-up the designated node. A passive RF front end and simple decoding circuit reduce power consumption substantially at the cost of low sensitivity. The sensitivity of the wake-up receiver can be improved though the addition of an RF amplifier, but at the cost of increased power consumption. / Master of Science

This work presents design and full implementation of a fast switchable and band-tunable 5 - 7.5 GHz low noise amplifier (LNA) in a 45nm CMOS SOI technology. The target application are wake-up receivers that employ aggressive duty cycling. Based on a cascode topology, the LNA utilizes a transformer for its 50 input matching as well as a balun with a capacitor bank to realize 8 digitally selectable bands. According to measurement results, the fabricated LNA exhibits a voltage gain of 18 - 21 dB while drawing a current of merely 2.2mA from a 1V supply. At all the 8 bands from 5 to 7.5 GHz, the input reflection coefficient lies below -8 dB, and the noise figure ranges from 7.8 to 6.2 dB. The LNA is able to settle in less than 9.5 ns

Grâce au confort d’utilisation qu’elles procurent, les technologies sans fil se retrouvent aujourd’hui dans un vaste panel d’applications. Ainsi le nombre d’éléments de transmission/réception radio se multiplie. Aujourd’hui pour réduire les consommations des éléments radio, il faut les rendre davantage efficaces notamment pour la partie réception. En effet, pour les communications asynchrones, les récepteurs consomment inutilement de l’énergie à attendre qu’une transmission soit faite. Dans l’objectif de réduire ce gaspillage d’énergie, des nouveaux standards ont vu le jour tel que le Zigbee et le Bluetooth Low Energy. Les performances en consommation procurées par ces deux standards résident sur leur fonction périodique à très faible rapport cyclique. Une nouvelle solution émergente pour réduire drastiquement la consommation des récepteurs en les rendant plus efficaces est l’utilisation de récepteur d’activation. Les récepteurs d’activation ou récepteur de réveil sont des récepteurs simples ce qui leur permet d’atteindre une ultra basse consommation uniquement en charge de guetter l’arrivée d’une trame et de réveiller le récepteur principal, placé en veille au préalable, pour traitement de cette dernière. Le récepteur d’activation proposé ici a été réalisé dans la technologie CMOS 160 nm de NXP. Il offre une sensibilité de -54 dBm, pour une consommation moyenne de 35 μA, prodiguant une portée de 70m à 433,92 MHz pour une puissance de 10 dBm émis. Ce récepteur ASK se distingue des autres récepteurs d’activation par le système de calibration breveté avec ajustement automatique la tension de référence requise pour la démodulation. Ce système rend le circuit robuste au problème d’offset DC et ne consomme aucun courant lorsque le circuit est en écoute. Le récepteur d’activation reconnaît un code de Manchester de 24 bits à 25 kbps, programmable grâce à une interface SPI. / Wireless technologies are now widespread due to the easiness of use they provide. Consequently, the number of radio devices increases. Despite of the efforts to reduce radio circuits power consumption as they are more and more numerous, now they must achieve ultra-low power consumption. Today, radio devices are made more efficient to reduce their power consumption especially for the receiving part. Indeed, for asynchronous communication, a lot of energy is wasted by the receiver waiting for a transmission. In order to avoid this waste, new standards have been created such as Zigbee and Bluetooth Low Energy. Due to periodic operation with ultra-low duty cycle, they provide ultra-low power consumption. Another solution to drastically reduce the power consumption has emerged, wake-up receiver. Wake-up receivers are based in simple architecture to provide ultra-low power consumption, they are only in charge to wait for a frame and when it occurs, wake-up the main receiver put in standby mode before that. The proposed wake-up receiver has been designed in NXP CMOS technology 160 μm. It provides a-54 dBm sensitivity, consuming 35 μA which allows a 70m range considering a 10 dBm emitter at 433,92 MHz. This wake-up receiver operates with ASK modulation, compared to others it provides a smart patented calibration system to get the necessary reference voltage for demodulation. This mechanism provide DC offset robustness and does not drain any current while the wake-up receiver is operating. To wake up the main receiver a 24 bits programmable Manchester code is required. This code at 25 kbps is programmable by the use of an SPI interface.

With the introduction of Internet of Things (IoT) technology in several sectors, wireless, reliable, and energy-saving communication in distributed sensor networks are more important than ever. Thereby, wake-up technologies are becoming increasingly important as they significantly contribute to reducing the energy consumption of wireless sensor nodes. In an indoor environment, the use of wireless sensors, in general, is more challenging due to signal fading and reflections and needs, therefore, to be critically investigated. This paper discusses the performance analysis of wakeup receiver (WuRx) architectures based on two low frequency (LF) amplifier approaches with regard to sensitivity, power consumption, and package error rate (PER). Factors that affect systems were compared and analyzed by analytical modeling, simulation results, and experimental studies with both architectures. The developedWuRx operates in the 868MHz band using on-off-keying (OOK) signals while supporting address detection to wake up only the targeted network node. By using an indoor setup, the signal strength and PER of received signal strength indicator (RSSI) in different rooms and distances were determined to build a wireless sensor network. The results show a wake-up packets (WuPts) detection probability of about 90% for an interior distance of up to 34 m.

The Internet of Things (IoT) is leading the world to the Internet of Everything (IoE), where things, people, intelligent machines, data and processes will be connected together. The key to enter the era of the IoE lies in enormous sensor nodes being deployed in the massively expanding wireless sensor networks (WSNs). By the year of 2025, more than 42 billion IoT devices will be connected to the Internet. While the future IoE will bring priceless advantages for the life of mankind, one challenge limiting the nowadays IoT from further development is the ongoing power demand with the dramatically growing number of the wireless sensor nodes. To address the power consumption issue, this dissertation is motivated to investigate low-power wake-up receivers (WuRXs) which will significantly enhance the sustainability of the WSNs and the environmental awareness of the IoT. Two proof-of-concept low-power WuRXs with focuses on two different application scenarios have been proposed. The first WuRX, implemented in a cost-effective 180-nm CMOS semiconductor technology, operates at 401−406-MHz band. It is a good candidate for application scenarios, where both a high sensitivity and an ultra-low power consumption are in demand. Concrete use cases are, for instance, medical implantable applications or long-range communications in rural areas. This WuRX does not rely on a further assisting semiconductor technology, such as MEMS which is widely used in state-of-the-art WuRXs operating at similar frequencies. Thus, this WuRX is a promising solution to low-power low-cost IoT. The second WuRX, implemented in a 45-nm RFSOI CMOS technology, was researched for short-range communication applications, where high-density conventional IoT devices should be installed. By investigation of the WuRX for operation at higher frequency band from 5.5 GHz to 7.5 GHz, the nowadays ever more over-traffic issues that arise at low frequency bands such as 2.4 GHz can be substantially addressed. A systematic, analytical research route has been carried out in realization of the proposed WuRXs. The thesis begins with a thorough study of state-of-the-art WuRX architectures. By examining pros and cons of these architectures, two novel architectures are proposed for the WuRXs in accordance with their specific use cases. Thereon, key WuRX parameters are systematically analyzed and optimized; the performance of relevant circuits is modeled and simulated extensively. The knowledge gained through these investigations builds up a solid theoretical basis for the ongoing WuRX designs. Thereafter, the two WuRXs have been analytically researched, developed and optimized to achieve their highest performance. Proof-of-concept circuits for both the WuRXs have been fabricated and comprehensively characterized under laboratory conditions. Finally, measurement results have verified the feasibility of the design concept and the feasibility of both the WuRXs.

This work investigates a 5.5–7.5-GHz band-configurable duty-cycled wake-up receiver (WuRX) fully implemented in a 45-nm radio-frequency (RF) silicon-on-insulator (SOI) complementary-metal-oxide-semiconductor (CMOS) technology. Based on an uncertain intermediate frequency (IF) super-heterodyne receiver (RX) topology, the WuRX analogue front-end (AFE) incorporates a 5.5–7.5-GHz band-tunable low-power low-noise amplifier, a low-power Gilbert mixer, a digitally controlled oscillator (DCO), a 100-MHz IF band-pass filter (BPF), an envelope detector, a comparator, a pulse generator and a current reference. By application of duty cycling with a low duty cycle below 1%, the power consumption of the AFE was significantly reduced. In addition, the on-chip digital bank-end consists of a frequency divider, a phase corrector, a 31-bit correlator and a serial peripheral interface. A proof-of-concept WuRX circuit occupying an area of 1200 μm by 900 μm has been fabricated in a GlobalFoundries 45-nm RF-SOI CMOS technology. Measurement results show that at a data rate of 64 bps, the entire WuRX consumes only 2.3 μW. Tested at 8 operation bands covering 5.5–7.7 GHz, the WuRX has a measured sensitivity between −67.5 dBm and −72.4 dBm at a wake-up error rate of 10−3. With the sensitivity unchanged, the data rate of the WuRX can be scaled up to 8.2 kbps. To the authors' best knowledge, this work offers the largest RF bandwidth from 5.5 to 7.5 GHz, the most operation channels (≥8) and the fastest settling time (<115 ns) among the WuRXs reported to date.

The integration of wireless communication, e.g., in real- or quasi-real-time applications, is related to many challenges such as energy consumption, communication range, quality of service, and reliability. The improvement of wireless sensor networks (WSN) performance starts by enhancing the capabilities of each sensor node. To minimize latencies without increasing energy consumption, wake-up receiver (WuRx) nodes have been introduced in recent works since they can be always-on or power-gated with short latencies by a power consumption in the range of some microwatts. Compared to standard receiver technologies, they are usually characterized by drawbacks in terms of sensitivity. To overcome the limitation of the sensitivity ofWuRxs, a design of a low noise amplifier (LNA) with several design specifications is required. The challenging task of the LNA design is to provide equitable trade-off performances such as gain, power consumption, the noise figure, stability, linearity, and impedance matching. The design of fast settling LNA for a duty-cycled WuRx front-end operating at a 868 MHz frequency band is investigated in this work. The paper details the trade-offs between design challenges and illustrates practical considerations for the simulation and implementation of a radio frequency (RF) circuit. The implemented LNA competes with many commercialized designs where it reaches single-stage 12 dB gain at a 1.8 V voltage supply and consumes only a 1.6 mA current. The obtained results could be made tunable by working with off-the-shelf components for different wake-up based application exigencies.

In ultra-low power Wireless Sensor Networks (WSNs) sensor nodes need to interact, depending on the application, even at a rapid pace while preserving battery life. Wireless communication brings thereby quite the burden as the radio transceiver requires a relative huge amount of power during both transmission or reception phases. In WSNs with on demand communication, the sensor nodes are required to maintain responsiveness and to act the sooner they receive a request, reducing the overall latency of the network. The aspect is more challenging in asynchronous WSN as the receiver possesses no information about the packet arrival time. In a purely on-demand communication, duty-cycling shows little to almost no improvement. The receiving node, in such scheme, is expected to last for years while also being accessible to other peers. Here arises the utility of an external ultra-low power radio receiver known as Wake-up Receiver (WuRx). Its essential task is to remain as the only part of the system running while the rest of the systems enters the lowest power mode (i.e., sleep state). Once a request signal is received, it notifies the host processor and other peripherals for an incoming communication. With the sensor node being in sleep state (WuRx active only), substantial power levels can be achieved. If the WuRx is able to interact rapidly, the added latency remains negligible. As crucial performance figures, the sensitivity and bit rate are immediately affected by the extreme low-power budget at diifferent magnitudes, depending mainly on the incorporated architecture. This thesis focuses on the design of a feature-balanced WuRx. The passive radio frequency architecture (PRF) relies on passive detection while consuming zero power to extract On-Off-Keying (OOK) modulated envelopes. The featured sensitivity, however, is reduced compared to more complex architectures. A WuRx based on PRF architecture can effectively enable short-range applications. The sensitivity can vary with respect to several parameters including the total generated noise, circuit technology and topology. Two variants of the PRF WuRxs are introduced with the baseband amplifier being the main change. The first revision employs a high performance amplifier with reduced average energy consumption, thanks to a novel power gating control. The second variant focuses on employing an ultra-low power baseband amplifier as it is expected to be in a continuous active state. This thesis also brings the necessary analysis on the passive front-end with the intention to enhance the overall WuRx sensitivity. Proof of concepts are embedded in sensor node boards and feature -61 dBm and -64 dBm of sensitivity for the first and the second variant, respectively, at a packet-error-rate (PER) of 1% whilst demanding a similar power of 7.2 µW during packet listening. During packet decoding, the first variant demands a 150 µW of power, caused greatly by the baseband amplifier. The achieved latency is less than 30 ms and the bit rate is 4 kbit/s, Manchester encoding. For long-range applications, a higher sensitivityWuRx is proposed based on Tuned-RF (TRF) architecture. By embedding a low-noise amplifier (LNA) in the receiver chain, very weak radio signal can be detected. TheWuRx emphasizes higher sensitivity of -90 dBm. The design of the LNA prioritized the highest gain and lowest bias current by sacrifcing the linearity that poses little impact on signal integrity for the OOK modulated signals. The total active power consumption of the TRF WuRx is 1.38 mW. In this work, a fast sampling approach based on power gating protocol allows a drastic reduction in energy consumption on average. By being able to sample in matter of few microseconds, the WuRx is able to detect the presence of a packet and return to sleep state right after packet decoding. Being power-gated dropped the average power consumption to 2.8 µW at a packet detection latency of 32 ms for less than 2 s of interval time between communication requests. The proposed solutions are able to decode a minimum length of 16-bit pattern and operate in the license-free ISM band 868 MHz. This thesis also includes the analysis and implementation of low-power front-end building blocks that are employed by the proposed WuRx.:1 Introduction 1.1 Motivation 1.2 Wake-up Receiver Design Requirements 1.2.1 Energy Consumption 1.2.2 Network Coverage and Robustness 1.2.3 Wake-up Packet Addressing 1.2.4 WuPt Detection Latency 1.2.5 Hosting System, Form-factor and Fabrication Technology 1.3 Thesis Organisation 2 Wireless Sensor Networks 2.1 Radio Communication 2.1.1 Electromagnetic Spectrum 2.1.2 Link Budget Analysis 2.2 Asynchronous Radio Receiver Duty-cycle Control 2.2.1 B-MAC and X-MAC Protocols 2.2.2 Energy and Latency Analysis 2.3 Power Supply Requirements 2.3.1 Low Self-discharge Battery 2.3.2 Energy Harvester 2.4 Summary 3 State-of-the-Art of Wake-up Receivers 3.1 Wake-up Receiver Architectural Analysis 3.1.1 Passive RF Detector 3.1.2 Classical Radio Architectures 3.2 Wake-up Receiver Back-end Stages 3.2.1 Baseband Amplifiers 3.2.2 Analog to Digital Conversion 3.2.3 Wake-up Packet Decoder 3.3 Power Consumption Reduction at Circuit Level 3.3.1 Power Gating 3.3.2 Interference Rejection and Filtering 3.4 Summary 4 Proposal of Novel Wake-up Receivers 4.1 Ultra-low Power On-demand Communication in Wireless Sensor Networks: Challenges and Requirements 4.2 Passive RF Wake-up Receiver 4.3 Power-gated Tuned-RF Wake-up Receiver 5 Low-power RF Front-end 5.1 Narrow-band Low-noise Amplifier (LNA) 5.1.1 Topology 5.1.2 Voltage Gain 5.1.3 Stability 5.1.4 Noise Figure 5.1.5 Linearity 5.2 Envelope Detector 5.2.1 Theory of Square-law Detection and Sensitivity Analysis 5.2.2 Single-Diode Envelope Detector 5.2.3 Voltage Multiplier Envelope Detector 5.3 Hardware Assessment 5.3.1 LNA 5.3.2 Envelope Detector 5.4 Summary 6 Passive RF Wake-up Receiver 6.1 Circuit Implementation 6.1.1 Address Decoder 6.1.2 Envelope Detector 6.1.3 Power-gated Baseband Amplifier 6.1.4 Ultra Low-power Baseband Amplifier 6.2 Experimental Results 6.2.1 Wireless Sensor Node 6.2.2 Measurements 6.3 Summary 7 Power-gated Tuned-RF Wake-up Receiver 7.1 Power-gating Protocol 7.2 Circuit Design 7.2.1 Radio Front-end 7.2.2 Data Slicer 7.2.3 Digital Baseband 7.3 Performance Evaluation 7.4 Summary 8 Conclusion 8.1 Performance Summary 8.2 Future Perspective 8.3 Applications A Two-tone Simulation Setup B Diode Models and Simulation Setup C Preamble Detection C Code Implementation Bibliography Publications / In drahtlosen Sensornetzwerken (WSNs) mit extrem geringem Stromverbrauch müssen Sensorknoten je nach Anwendung kurze Latenzzeiten erreichen ohne die Batterielebensdauer zu beeinträchtigen. Die drahtlose Kommunikation bringt dabei eine ziemliche Belastung mit sich, da der Funktransceiver sowohl während der Sende- als auch der Empfangsphase relativ viel Strom benötigt. Einige marktfähige Funktransceiver benötigen durchschnittlich ca. 10 mA im Empfangsmodus sowie 30 mA im Sendemodus. Deshalb wird heutzutage das sogenannte Duty-Cycling mit bestimmten Sende-, Empfangs- und langen Schlafzeitintervallen eingeführt. Während der Schlafphase ist der Empfänger nicht ansprechbar. Was wiederum zu einer massiven Erhöhung der Latenzzeit führen kann. In vielen Anwendungen und insbesondere im Rahmen der Digitalisierung von Prozessen wird mittlerweile die Fähigkeit On-Demand mit sehr kurzen Latenzzeiten zu kommunizieren verlangt. Diese Anforderung steht in einem Wiederspruch zum genannten Duty-cycle Betrieb. Um dieses Dilemma zu lösen wird im Rahmen dieser Doktorarbeit ein Funkempfänger mit extrem geringen Stromverbrauch untersucht und entwickelt. Mit Hilfe des extrem niedrigen Stromverbrauches kann der Funkempfänger ständig empfangsbereit sein. Er wird zum Hauptempfänger mit dem hohen Stromverbrauch zugeschaltet, so dass nur nach Aufforderung der Hauptempfänger aktiv sein wird. Dieser Empfänger wird Wake-up Empfänger (WuRx) genannt. Seine wesentliche Aufgabe besteht darin, als einziger Teil des Gesamtknotens aktiv zu sein, während der Rest in den Modus mit dem niedrigsten Stromverbrauch versetzt wird. Sobald ein Anforderungssignal empfangen wird, weckt er den Haupt-Prozessor und andere Peripheriegeräte über eine eingehende Kommunikation. Somit ist der Aufweckempfänger essenziell für die Zuverlässigkeit der drahtlosen Kommunikation. Sein Stromverbrauch sollte im µA Bereich sein. Seine Empfangsbereitschaft hängt entscheidend von seiner Empfindlichkeit sowie Bitrate ab. Eine Verbesserung der Empfindlichkeit und Erhöhung der Bitrate würden zwangsläufig zu einer Erhöhung des Stromverbrauches führen. Im Rahmen dieser Doktorarbeit werden unterschiedliche Architekturen von Aufweckempfängern untersucht und umgesetzt. Zusammenhänge zwischen Empfindlichkeit, Bitrate und Stromverbrauch wurden analysiert und mögliche Grenzen gezeigt. Ein wesentliches Augenmerk war dabei, Off-the-Shelf Komponenten zu verwenden. Im Rahmen dieser Doktorabeit wurden in Abhängigkeit von der zu erreichenden Reichweite und Häufigkeit der Kommunikation zwei wesentliche Architekturen mit geeigneten Empfindlichkeiten und extrem geringem Stromverbrauch entwickelt. Für kurze Reichweiten wurde eine passive Hochfrequenzarchitektur (PRF Architektur) basierend auf einer passiven Erkennung von OOK-modulierten (On-Off-Keying) Signalen mittels Hüllkurvenbildung entwickelt. Die erreichte Empfindlichkeit von ca. -64 dBm stellt eine wesentliche Verbesserung gegenüber dem Stand der Technik und Forschung mit einer Empfindlichkeit von ca. -52 dBm dar. Die Empfindlichkeit kann in Bezug auf verschiedene Parameter variieren, einschließlich des insgesamt erzeugten Rauschens, der Schaltungstechnologie und der Topologie. Zwei Varianten der PRF WuRxs wurden realisiert, wobei der Basisbandverstärker die Hauptänderung darstellt. Die erste Version verwendet einen Hochleistungsverstärker mit reduziertem durchschnittlichen Energieverbrauch dank einer neuartigen Leistungssteuerung. Die zweite Variante konzentriert sich auf die Verwendung eines Basisbandverstärkers mit extrem geringer Leistung, da erwartet wird, dass er sich in einem kontinuierlichen aktiven Zustand befindet. Diese Arbeit bringt auch die notwendige Analyse des passiven Front-Ends mit der Absicht, die allgemeine WuRx-Empfindlichkeit zu verbessern. Nachweise der Wirksamkeit sind in Sensorknotenmodulen eingebettet und verfügen über -61 dBm und -64 dBm Empfindlichkeit für die erste bzw. die zweite Variante bei einer Paketfehlerrate (PER) von 1 %, während beim Abhören von Paketen eine ähnliche Leistung von 7.2 µW gefordert wird. Während der Paketdecodierung erfordert die erste Variante eine Leistung von 150 µW, die stark durch den Basisbandverstärker verursacht wird. Die erreichte Latenz beträgt weniger als 30 ms und die Bitrate beträgt 4 kbit/s mit einer Manchester-Codierung. Für Anwendungen mit großer Reichweite wird ein WuRx mit höherer Empfindlichkeit vorgeschlagen. Dieser basiert auf einer TunedRF (TRF) -Architektur. Dabei werden sehr schwache Funksignale durch einen rauscharmen Verstärker (LNA) erkannt und verstärkt. Der WuRx erreicht eine bessere Empfindlichkeit von ca. –90 dBm. Dabei wurde das Augenmerk auf die höchste Verstärkung verbunden mit dem niedrigsten Vorspannungsstrom gelegt. Der LNA wird dann im nicht-linearen Bereich betrieben. Dieser Betriebsmodus beeinflusst nur im geringeren Maße die Signalintegrität der OOK-modulierten Signale. Der gesamte Leistungsverbrauch des TRF WuRx beträgt 1.38 mW. Um den Gesamtleistungsverbrauch im µW Bereich zu reduzieren, wird im Rahmen dieser Arbeit das sogenannte Power-Gating-Protokoll eingeführt. Dabei wird das Funkkanal zyklisch abgetastet. Der WuRx kann innerhalb von wenigen Mikrosekunden das Vorhandensein eines Pakets erkennen und direkt nach der Paketdecodierung in den Ruhezustand zurückkehren. Durch diesen Ansatz konnte der durchschnittliche Stromverbrauch bei einer Paketerkennungslatenz von ca. 32 ms innerhalb einer Abtastrate von 2 s auf 2.8 µW reduziert werden. Die vorgeschlagenen Lösungen können eine Mindestlänge von 16-Bit-Mustern decodieren und im lizenzfreien ISM-Band 868 MHz arbeiten.:1 Introduction 1.1 Motivation 1.2 Wake-up Receiver Design Requirements 1.2.1 Energy Consumption 1.2.2 Network Coverage and Robustness 1.2.3 Wake-up Packet Addressing 1.2.4 WuPt Detection Latency 1.2.5 Hosting System, Form-factor and Fabrication Technology 1.3 Thesis Organisation 2 Wireless Sensor Networks 2.1 Radio Communication 2.1.1 Electromagnetic Spectrum 2.1.2 Link Budget Analysis 2.2 Asynchronous Radio Receiver Duty-cycle Control 2.2.1 B-MAC and X-MAC Protocols 2.2.2 Energy and Latency Analysis 2.3 Power Supply Requirements 2.3.1 Low Self-discharge Battery 2.3.2 Energy Harvester 2.4 Summary 3 State-of-the-Art of Wake-up Receivers 3.1 Wake-up Receiver Architectural Analysis 3.1.1 Passive RF Detector 3.1.2 Classical Radio Architectures 3.2 Wake-up Receiver Back-end Stages 3.2.1 Baseband Amplifiers 3.2.2 Analog to Digital Conversion 3.2.3 Wake-up Packet Decoder 3.3 Power Consumption Reduction at Circuit Level 3.3.1 Power Gating 3.3.2 Interference Rejection and Filtering 3.4 Summary 4 Proposal of Novel Wake-up Receivers 4.1 Ultra-low Power On-demand Communication in Wireless Sensor Networks: Challenges and Requirements 4.2 Passive RF Wake-up Receiver 4.3 Power-gated Tuned-RF Wake-up Receiver 5 Low-power RF Front-end 5.1 Narrow-band Low-noise Amplifier (LNA) 5.1.1 Topology 5.1.2 Voltage Gain 5.1.3 Stability 5.1.4 Noise Figure 5.1.5 Linearity 5.2 Envelope Detector 5.2.1 Theory of Square-law Detection and Sensitivity Analysis 5.2.2 Single-Diode Envelope Detector 5.2.3 Voltage Multiplier Envelope Detector 5.3 Hardware Assessment 5.3.1 LNA 5.3.2 Envelope Detector 5.4 Summary 6 Passive RF Wake-up Receiver 6.1 Circuit Implementation 6.1.1 Address Decoder 6.1.2 Envelope Detector 6.1.3 Power-gated Baseband Amplifier 6.1.4 Ultra Low-power Baseband Amplifier 6.2 Experimental Results 6.2.1 Wireless Sensor Node 6.2.2 Measurements 6.3 Summary 7 Power-gated Tuned-RF Wake-up Receiver 7.1 Power-gating Protocol 7.2 Circuit Design 7.2.1 Radio Front-end 7.2.2 Data Slicer 7.2.3 Digital Baseband 7.3 Performance Evaluation 7.4 Summary 8 Conclusion 8.1 Performance Summary 8.2 Future Perspective 8.3 Applications A Two-tone Simulation Setup B Diode Models and Simulation Setup C Preamble Detection C Code Implementation Bibliography Publications

Abstract The Internet of Things (IoT) is already providing solutions to various tasks related to monitoring the environment and controlling devices over wired and wireless networks. It is estimated by several well-known research facilities that the number of IoT devices will be in the order of tens of billions by 2020. This inevitably brings challenges and costs in deployment, management, and maintenance of networks. The focus of this thesis is to provide solutions that mainly help in the deployment and maintenance of various wireless IoT networks. Different applications have different requirements for a wireless link coverage. It is important to utilize suitable radio technology for a particular application in order, e.g., to maximize the lifetime of a device. A wireless body area network (WBAN) typically consists of devices that are within couple of meters from each other. The WBAN is suitable for, e.g., measuring muscle activity and transferring data to a storage for processing. The wireless link can use air as a medium, or alternatively, an induced electric field to a body can be used. In this thesis, it is shown that a location of the electrodes in the body have impact to the attenuation. Home automation IoT applications are typically implemented with mid-range wireless technologies, known as wireless personal area networks (WPAN). In order to minimize and get rid of battery change operations, a wake-up receiver could be utilized in order to improve the device’s energy efficiency. The concept is introduced and performance of the current state-of-the-art works are presented. In addition, a control loop enabling a passive device to have control over an energy source is proposed. Applications that have low bandwidth requirements can be implemented with low-power wide area networks (LPWAN). One technology – LoRaWAN – is evaluated, and it is recommended as based on the results to use it in non-critical applications. / Tiivistelmä Esineiden internet (Internet of Things, IoT) mahdollistaa jo laajan kirjon erilaisia ratkaisuja ympäristön monitorointiin ja laitteiden hallintaan hyödyntäen sekä langattomia että langallisia verkkoja. Usea hyvin tunnettu tutkimusorganisaatio on arvioinut, että vuonna 2020 IoT laitteiden määrä tulee olemaan kymmenissä miljardeissa. Se luo väistämättä haasteita laitteiden sijoittamisessa, hallinnassa ja kunnossapidossa. Tämä väitöskirja keskittyy tarjoamaan ratkaisuja, jotka voivat helpottaa langattomien IoT laitteiden sijoittamisessa ja kunnossapidossa. IoT sovellusten laaja kirjo vaatii erilaisia langattomia radioteknologioita, jotta sovellukset voitaisiin toteuttaa, muun muassa, mahdollisimman energiatehokkaasti. Langattomassa kehoverkossa (wireless body area network, WBAN) käytetään usein hyvin lyhyitä langattomia linkkejä. WBAN on soveltuva esimerkiksi lihasten aktiivisuus mittauksessa ja mittaustiedon siirtämisessä talteen varastointia ja prosessointia varten. Linkki voidaan toteuttaa käyttäen ilmaa rajapintana, tai vaihtoehtoisesti, kehoa. Tässä työssä on näytetty, että käytettäessä kehoa siirtotienä, elektrodien sijainnilla on merkitystä signaalin vaimennuksen kannalta. Kotiautomaatio IoT sovellukset ovat tyypillisesti toteutettu käyttäen langatonta likiverkkoa, jossa linkin pituus sisätiloissa on alle 30 metriä. Jotta päästäisiin eroon pariston vaihto-operaatiosta tai ainakin vähennettyä niiden määrää, herätevastaanotinta käyttämällä olisi mahdollista parantaa laitteiden energiatehokkuutta. Herätevastaanotin konsepti ja tämänhetkistä huipputasoa edustavien vastaanottimien suorituskyky ovat esitetty. Lisäksi, on ehdotettu menetelmä joka takaa energian saannin passiiviselle IoT laitteelle. IoT sovellukset jotka tyytyvät vähäiseen kaistanleveyteen voidaan toteuttaa matalatehoisella laajan alueen verkolla (low-power wide area network, LPWAN). Yhden LPWAN teknologian, nimeltään LoRaWAN, suorituskykyä on evaluoitu. Tulosten perusteella suositus on hyödyntää kyseistä teknologiaa ei-kriittisissä sovelluksissa.