IMEC Reports 3 Major Breakthroughs for Wireless Autonomous Sensor Nodes

2/6/2006 - Today at the International Solid-State Circuits Conference (ISSCC) IMEC, Europe's largest independent nanoelectronics and nanotechnology R&D center, announced three major advances in technologies that will be used in wireless autonomous sensor nodes: (1) a read-out front-end for portable biopotential acquisition systems; (2) a fully integrated low-power UWB receiver for low-data-rate applications; and, (3) a high-speed analog-to-digital converter (ADC) with a record low-power consumption of 0.16pJ/conversion step. The ADC architecture has been implemented within the UWB receiver.

The three technology advances will benefit IMEC's Human++ program, which addresses medical, lifestyle and entertainment applications.

The read-out front-end allows the extraction of bio-potential signals produced by portable electroencephalography (EEG), electrocardiography (ECG) and electromyography (EMG) systems. It is also suitable for autonomous applications. The front-end has an equivalent input referred noise of 60nV/Hz and a total power dissipation of 60W.

EEG, ECG and EMG waves are V-range signals that suffer from a large amount of common-mode (CM) interference. Furthermore, the bio-potential electrodes that are needed to view the signals generate a non-negligible offset. To achieve signal extraction, a front-end is needed with high CM rejection ratio (CMRR); low-noise, high-pass filter (HPF) characteristics; and configurability for bio-potentials originating from the heart, muscles or the brain. Very low power consumption is necessary to enable long-term power autonomy. The aim is to increase the patient's autonomy and quality of life, as well as extending the devices to sports, entertainment, comfort monitoring, and other health and lifestyle products and services.

The bio-potential front-end, which was fabricated in a 0.5m CMOS process through AMI Semiconductor, has a core area measuring less than 2mm2. It is capable of operating more than three years from two conventional AA batteries, making it ideal for autonomous applications.

Integrated low-power UWB receiver for low-data-rate sensor networks IMEC has also developed a fully integrated UWB impulse radio (IR) receiver in UMC's 0.18m CMOS technology. The UWB receiver operates between 3GHz and 5GHz and can process pulses with 500MHz up to 2GHz bandwidth thanks to a variable channel select filter.

IMEC's receiver front-end is suitable for most IR approaches and very convenient for carrier-based IR (CB-IR) which enables sufficient flexibility in spectrum definition while keeping the system complexity as low as possible. It comprises an LNA and a quadrature down-conversion mixer. The chip's total current consumption is 16mA, measured on a 1.8V supply at 20MHz clock rate. It demonstrates the potential of IR-UWB for low-data-rate sensor-network applications.

Innovative ADC breaks through power barriers in low-power wireless applications
IMEC's 90nm RF CMOS program has designed a 4-bit, 1.25Gsamples/s, 2.5mW high-bandwidth ADC prototype, which has achieved a world-record figure of merit of 0.16pJ/conversion step. The circuit has been processed in IMEC's 90nm RF CMOS prototype manufacturing technology which features an effective oxide thickness of 1.5nm and physical gate length of 70nm. The NMOS cutoff frequency is 170GHz. The maximum oscillation frequency is 240GHz. The NMOS and PMOS threshold voltage matching coefficients are respectively 4.0 and 3.0 mV m.

To reduce the power consumption, all the non-essential blocks (track-and-hold, preamplifiers, reference ladder and bubble error correction) of the flash architecture have been removed. First, 15 comparators sample the data and amplify it. The output comparator outputs are stored in 15 set-reset latches. The stored thermometer code is then converted into a 4-bit gray code by the ROM-based encoder which has intrinsic error correction properties.

The implemented comparator circuit combines the sampling, amplifying and reference levels functions with high accuracy and high sampling speed at low power. The reference levels are generated by an intentional imbalance that is introduced in the input differential pair. The threshold voltages are then calibrated with DC input signals and are sufficiently accurate to reduce the integral non-linearity to less than 0.15 LSB (last significant bit).

About IMEC's Human++ Program
IMEC's Human++ research develops generic technologies that can be used in the fabrication of devices that improve the quality of life. Hence, Human++ complements the needs of a changing society that will utilize medicine, sports and entertainment in new ways. Ultimately, the technology will lead to the development of a personal body-area network (BAN) that delivers services to the wearer. These services include the management of chronic disease, medical diagnostic, home-monitoring, biometrics, and sports and fitness tracking.

The technologies being developed within the Human++ program are generic and can be tuned to other wireless autonomous system applications.

Human++ is structured around 5 main technology programs: ultra-low-power signal processing, ultra-low-power radio, micropower systems, sensors and actuators and integration and implementation.

A number of research areas within these programs (i.e., ultra-wide-band technology, low-power digital signal processing, micropower scavenging, power management, sensors and actuators) will be transferred to the Holst Centre. The Holst research center was initiated by IMEC and TNO in September 2005 to develop generic technologies for future generations of wireless autonomous transducer solutions and systems-in-foil.

About IMEC
IMEC is heading the consortium that runs the Europractice IC Service. IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. Its research focuses on the next generations of chips and systems, and on the enabling technologies for ambient intelligence. IMEC's research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network of companies, universities and research institutes worldwide position IMEC as a key partner for shaping technologies for future systems.

As an expansion of its wireless autonomous microsystems research, IMEC has created a legal entity in the Netherlands. Stichting IMEC Nederland runs activities at the Holst Centre, an independent R&D institute that develops generic technologies and technology platforms for autonomous wireless transducer solutions and systems-in-foil.

IMEC is headquartered in Leuven, Belgium, and has representatives in the US, China and Japan. Its staff of about 1400 people includes close to 500 industrial residents and guest researchers. In 2005, its revenues are estimated to be close to EUR 200 million.

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