Harmke de Groot

A 2.4GHz/915MHz 51µW wake-up receiver with offset and noise suppression

In order to simultaneously optimize network lifetime and latency in wireless sensor networks (WSN), an always-on wake-up receiver (WuRx) can be used to monitor the radio link continuously. For truly autonomous sensor nodes employing energy scavenging, only 50µW power is available for the WuRx [1]. An envelope detector is a popular choice in WuRx because of its low power consumption. However, the detector is always the bottleneck of the receiver sensitivity since it attenuates low level input signal and adds excessive noise. One way of improving sensitivity is to amplify the signal before the detector, for example at RF [2, 3] or IF [4] stages, to enhance the SNR at the output.

Low-power wireless sensor nodes for ubiquitous long-term biomedical signal monitoring

In the past few years, the use of wireless sensor nodes for remote health care monitoring has been advocated as an attractive alternative to the traditional hospital-centric health care system from both the economic perspective and the patient comfort viewpoint. The semiconductor industry plays a crucial role in making the changes in the health care system a reality. User acceptance of remote health monitoring systems depends on their comfort level, among other factors. The comfort level directly translates to the form factor, which is ultimately defined by the battery size and system power consumption. This article introduces low-power wireless sensor nodes for biomedical applications that are capable of operating autonomously or on very small batteries. In particular, we take a closer look at component-level power optimizations for the radio and the digital signal processing core as well as the trade-off between radio power consumption and on-node processing. We also provide a system-level model for WSNs that helps in guiding the power optimization process with respect to various trade-offs.

A voltage-scalable biomedical signal processor running ECG using 13pJ/cycle at 1MHz and 0.4V

Recent work on designing ultra-low-power systems has focused on the sub-threshold regime [1–3] and an energy efficiency of a few pJ/cycle was reported. While operating at the minimum energy point is attractive for energy-frugal devices like those used for wireless biomedical signal monitoring, the achieved clock frequency is usually in the kHz range. The low frequency combined with limited processing capacity, small on-chip memory, and low computation precision prevents the use of these systems for complex ambulatory monitoring beyond a simple ECG algorithm. Low-voltage systems with more computational power are demonstrated in [4] and [5].

A 345 µW Multi-Sensor Biomedical SoC With Bio-Impedance, 3-Channel ECG, Motion Artifact Reduction, and Integrated DSP

This paper presents a MUlti-SEnsor biomedical IC (MUSEIC). It features a high-performance, low-power analog front-end (AFE) and fully integrated DSP. The AFE has three biopotential readouts, one bio-impedance readout, and support for general-purpose analog sensors The biopotential readout channels can handle large differential electrode offsets ( ±400 mV), achieve high input impedance ( >500 M Ω), low noise ( 620 nVrms in 150 Hz), and large CMRR ( >110 dB) without relying on trimming while consuming only 31 μW/channel. In addition, fully integrated real-time motion artifact reduction, based on simultaneous electrode-tissue impedance measurement, with feedback to the analog domain is supported. The bio-impedance readout with pseudo-sine current generator achieves a resolution of 9.8 m Ω/ √Hz while consuming just 58 μW/channel. The DSP has a general purpose ARM Cortex M0 processor and an HW accelerator optimized for energy-efficient execution of various biomedical signal processing algorithms achieving 10 × or more energy savings in vector multiply-accumulate executions.

A 2.4GHz ULP OOK single-chip transceiver for healthcare applications

Wireless body-area networks (WBAN) are used for communication among sensor nodes operating on, in or around the human body, e.g. for healthcare purposes. In view of energy autonomy, the total energy consumption of the sensor nodes should be minimized. Because of their low complexity, a combination of the super-regenerative (SR) principle [1–3] and OOK modulation enables ultra-low power (ULP) consumption. This work presents a 2.4GHz ULP OOK singlechip transceiver for WBAN applications. A block diagram of the implemented transceiver is shown in Fig. 26.3.1. Next to the direct modulation TX [4] and SR RF [5] front-ends, this work integrates analog and digital baseband, PLL functionality and additional programmability for flexible data rates, and achieves ultra-low power consumption for the overall system.

9.8 An 860μW 2.1-to-2.7GHz all-digital PLL-based frequency modulator with a DTC-assisted snapshot TDC for WPAN (Bluetooth Smart and ZigBee) applications

Ultra-low-power (ULP) transceivers enable short-range networks of autonomous sensor nodes for wireless personal-area-network (WPAN) applications. RF PLLs for frequency synthesis and modulation consume a significant share of the total transceiver power, making sub-mW PLLs key to realize ULP WPAN radios. Compared to analog PLLs [1], all-digital PLLs (ADPLLs) are preferred in nanoscale CMOS as they offer benefits of smaller area, programmability, capability of extensive self-calibrations, and easy portability [2]. However, analog PLLs dominate the field of ULP WPAN radios [1], since the time-to-digital-converter (TDC) of an ADPLL has traditionally been power hungry. We present a 2.1-to-2.7GHz 860μW fractional-N ADPLL in 40nm CMOS for WPAN applications, which breaks the 1mW barrier and consumes at least 5× lower power compared to state-of-the-art ADPLLs.

Evaluation of 90nm 6T-SRAM as Physical Unclonable Function for secure key generation in wireless sensor nodes

Due to the unattended nature of WSN (Wireless Sensor Network) deployment, each sensor can be subject to physical capture, cloning and unauthorized device alteration. In this paper, we use the embedded SRAM, often available on a wireless sensor node, for secure data (cryptographic keys, IDs) generation which is more resistant to physical attacks. We evaluate the physical phenomenon that the initial state of a 6T-SRAM cell is highly dependent on the process variations, which enables us to use the standard SRAM circuit, as a Physical Unclonable Function (PUF). Important requirements to serve as a PUF are that the start-up values of an SRAM circuit are uniquely determined, unpredictable and similar each time the circuit is turned on. We present the evaluation results of the internal SRAM memories of low power ICs as PUFs and the statistical analysis of the results. The experimental results prove that the low power 90nm commercial 6T-SRAMs are very useful as a PUF. As far as we know, this is the first work that provides an extensive evaluation of 6T-SRAM-based PUF, at different environmental, electrical, and ageing conditions to representing the typical operating conditions of a WSN.

A meter-range UWB transceiver chipset for around-the-head audio streaming

Any around-the-body wireless system faces challenging requirements. This is especially true in the case of audio streaming around the head e.g. for wireless audio headsets or hearing-aid devices. The behind-the-ear device typically serves multiple radio links e.g. ear-to-ear, ear-to-pocket (a phone or MP3 player) or even a link between the ear and a remote base station such as a TV. Good audio quality is a prerequisite and mW-range power consumption is compulsory in view of battery size. However, the GHz communication channel typically shows a significant attenuation; for an ear-to-ear link, the attenuation due to the narrowband fade dominates and is in the order of 55 to 65dB [1]. The typically small antennas, close to the human body, add another 10 to 15dB of losses. For the ear-to-pocket and the ear-to-remote link, the losses due to body proximity and antenna size reduce, however the distance increases resulting in a similar link budget requirement of 80dB.

A Lightweight Security Scheme for Wireless Body Area Networks: Design, Energy Evaluation and Proposed Microprocessor Design

In order for wireless body area networks to meet widespread adoption, a number of security implications must be explored to promote and maintain fundamental medical ethical principles and social expectations. As a result, integration of security functionality to sensor nodes is required. Integrating security functionality to a wireless sensor node increases the size of the stored software program in program memory, the required time that the sensor’s microprocessor needs to process the data and the wireless network traffic which is exchanged among sensors. This security overhead has dominant impact on the energy dissipation which is strongly related to the lifetime of the sensor, a critical aspect in wireless sensor network (WSN) technology. Strict definition of the security functionality, complete hardware model (microprocessor and radio), WBAN topology and the structure of the medium access control (MAC) frame are required for an accurate estimation of the energy that security introduces into the WBAN. In this work, we define a lightweight security scheme for WBAN, we estimate the additional energy consumption that the security scheme introduces to WBAN based on commercial available off-the-shelf hardware components (microprocessor and radio), the network topology and the MAC frame. Furthermore, we propose a new microcontroller design in order to reduce the energy consumption of the system. Experimental results and comparisons with other works are given.

A 2.7nJ/b multi-standard 2.3/2.4GHz polar transmitter for wireless sensor networks

This paper presents an ultra-low-power (ULP) 2.3/2.4GHz multi-standard transmitter (TX) for wireless sensor networks and wireless body area networks. Several 2.3/2.4GHz wireless standards have been proposed for such applications, including IEEE802.15.6 (BAN) for body area networks, IEEE802.15.4 (Zigbee) and Bluetooth Low Energy (BLE) for sensor networks and IEEE802.15.4g (SUN) for smart buildings. Recent standard compliant short-range TXs [1-6] typically consume DC power in the range of 20 to 50mW. This is rather high for autonomous systems with limited battery energy. Implemented in a 90nm CMOS technology, the presented TX saves at least 75% of power consumption by replacing several power-hungry analog blocks with the digitally-assisted circuits. This TX is compliant with all 4 of these standards, while dissipating only 4.5mA from a 1.2V supply.