Binhee Kim

A 5.2mW self-configured wearable body sensor network controller and a 12µW 54.9% efficiency wirelessly powered sensor for continuous health monitoring system

Recently, several attempts have been made to continuously monitor chronic diseases in everyday life, but their large form factors or battery power limitations still remain to be solved. Security and/or requirements of interference resilience are stringent for health monitoring, and therefore, using an open-air wireless ISM band [1] is not suitable for a health monitoring body sensor network (BSN). This paper presents a self-configured wearable BSN system with high efficiency wirelessly powered sensors that continuously monitor ECG and other vital signals at the selected locations on the body with low power consumption.

A 0.5-

A wirelessly powered patch-type healthcare sensor IC is presented for a wearable body sensor network (W-BSN) to continuously monitor personal vital signals. Thick-film electrodes are screen printed on a fabric by planar-fashionable circuit board (P-FCB) technology on which stainless steel powder with a grain size of 100 μ m is added to reduce both contact impedance as well as motion artifacts. A nested chopped amplifier (NCA) is designed and optimized for the proposed patch-type healthcare sensor with a reduced electrode referred noise of 0.5 μVrms. A programmable gain and bandwidth amplifier (PGA) stage is also implemented to accommodate various dynamic ranges of vital signals. A 10-b folded successive approximation register (SAR) analog-to-digital converter (ADC) reduces capacitive digital-to-analog conversion size by 94% and relaxes the power budget of the ADC driver by 36%. Measured sensor resolution is 9.2 b and rejects common-mode interference larger than 100 dB while consuming only 12 μ W of power supplied wirelessly. A 2.0 mm × 1.3 mm sensor IC is fabricated in 0.18-μm 1P6M CMOS technology. The chip is directly integrated between two screen printed electrodes and stacked by a screen printed fabric inductor. With the proposed patch-type sensor, personal healthcare without expensive batteries is possible in W-BSN and greatly improves wearability and convenience in use.

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A new flexible electronics technology, named P-FCB (Planar Fashionable Circuit Board), is introduced. P-FCB is a circuit board technology implemented on the plain fabric patch for wearable electronics applications. In this paper, the manufacturing of PFCB, and its electrical characteristics such as sheet resistance, maximum current density, and frequency characteristics are reported. The fabrication methods and their electrical characteristics of passive devices such as resistor, capacitor, and inductor in P-FCB are discussed. In addition, how to integrate silicon chip directly to the fabric for the flexible electronics system are described. Finally, examples of P-FCB applications will be presented.

V

A method to fabricate circuits on the cloth, planar fashionable circuit board (P-FCB), is proposed. And its applications such as fabric passive elements, user I/O interface, and the fabric package are introduced. The electrical and the mechanical characteristic analysis of P-FCB and the system integration methodology establishment improve the system performance and productivity. A complete wearable system is implemented by P-FCB technology for the continuous sweat monitoring and the RFID tag antenna applications.

_{\rm rms}

An attachable ECG sensor adhesive bandage is implemented for continuous ECG monitoring system by using Planar-Fashionable Circuit Board (P-FCB) technology. The sensor patch improves convenience at low cost: it is composed of dry electrodes and an inductor directly screen printed on fabric, and the sensor chip is also directly wire bonded on fabric. The sensor patch is wirelessly powered to remove battery for safety. Dry electrodes minimize skin irritation to enable long term monitoring. The implemented sensor patch successfully demonstrates capturing of ECG signal while dissipating only 12uW power.

12-

Recently, wearable heart monitoring systems have been developed for cardiovascular-related disease [1] with wearable body sensor network (WBSN) [2–3]. The WBSN introduced in [3] monitored ECG at maximum 48 points, and transferred data using arrayed inductive link for cm-range wireless inter-connectivity. However, most of the previous attempts were limited to sense only ECG signals at limited points [2] on the body with limited network coverage [3]. Thoracic impedance variance (TIV) from the change of aortic blood volume and velocity at each cardiac cycle provides important hemodynamic information (stroke volume, cardiac output). Combined with ECG signals from more than 6 points, it enables the early detection of abnormal symptoms of pandemic diseases like hypertension and heart failure so that the patients can take prophylactic measures [6]. In spite of its importance, the TIV detection was not realized in WBSN due to its requirement of high impedance (≪0.2Ω) detection sensitivity which needs to detect AM signal with modulation depth as low as less than 3%. A pure single tone sinusoidal current signal at 1kHz–100kHz [6] is required to realize such a high sensitivity, and only a bulky implementation was reported so far [7]. In this paper, we report a 3.9mW low power SoC with body-channel-transceiver (BCT), which can detect TIV (0.1Ω) and ECG (up to 8 points) concurrently. The chip is integrated on a 4-layer fabric circuit board with thin flexible battery as a poultice-like plaster. In addition, it can reconfigure the 25-electrode array and optimize them in-situ to automatically consider the user dependency of the TIV/ECG signals. The recorded data is transmitted at 1Mbps through body-channel-communication (BCC) [8] with duty cycle modification to extend battery life time and enlarge the network coverage.

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This paper presents an energy-efficient SAR ADC which adopts reduced MSB cycling step with dual sampling of the analog signal. By sampling and holding the analog signal asymmetrically at both input sides of comparator, the MSB cycling step can be hidden by hold mode. Benefits from this technique, not only the total capacitance of DAC is reduced by half, but also the average switching energy is reduced by 68% compared with conventional SAR ADC. Moreover, switching energy distribution is more uniform over entire output code compared with previous works.

W Wirelessly Powered Patch-Type Healthcare Sensor for Wearable Body Sensor Network

A 2.88 nJ/Conversion low energy biopotential acquisition system is designed for portable healthcare device. Two dry copper contact electrodes with 1.2-cm diameter are used to easily interface between skin and healthcare device. Chopping technique is adopted at readout front end to obtain thermal noise floor of 1.3 uVrms over 0.5~200 Hz and CMRR over 100 dB to mitigate common-mode body potential induced from AC power line. A 4-stage gain control and band selection blocks are integrated to digitally calibrate for different types of biomedical signal and an 8-bit synchronous successive approximation register (SAR) A/D is used to digitize sensed biopotentials. A test chip is implemented in 0.18 um, 1.8 V supply CMOS technology and successively verified by readout ECG signal with two electrodes contact at chest of body with separating 6 cm.

Planar Fashionable Circuit Board Technology and Its Applications

Arm-band type textile-MP3 player using direct chip integration technique into textile named Planar Fashionable Circuit Board (P-FCB) is designed. The multi-layered board manufacturing technique improves the integration level so that more complex system can be implemented using P-FCB. Also, wearable user input-output (I/O) interface makes people control the system freely without any disturbance. Finally, Arm-band type textile-MP3 player system is developed and demonstrated to show the possibility of using P-FCB in wearable entertainment system.

A Wearable Fabric Computer by Planar-Fashionable Circuit Board Technique

A 0.5μVrms, 12μW wirelessly powered patch type fabric sensor is presented for wearable body sensor network to continuously monitor personal bioelectric signals. Thick film electrodes are screen printed on the fabric with various metal components and their impedances of ≈100kΩ are characterized. A 2-stage nested chopped analog readout front end (AFE) is optimized for the fabric sensor with reduced electrode referred noise performance of 0.5μVrms. A 10b folded SAR ADC reduces capacitive DAC (CDAC) size and relaxes the power budget of ADC driver by 94%. The proposed fabric sensor operates with system resolution of 9b and CMRR>106dB. The chip fabricated with 0.18μm CMOS technology, the fabric sensor stacked by screen printed inductor (diameter=3cm and # turns=4) can measure the ECG and EMG signals with wirelessly transmitted power through inductive coupling.