Kiseok Song

The Signal Transmission Mechanism on the Surface of Human Body for Body Channel Communication

The signal transmission mechanism on the surface of the human body is studied for the application to body channel communication (BCC). From Maxwells equations, the complete equation of electrical field on the human body is developed to obtain a general BCC model. The mechanism of BCC consists of three parts according to the operating frequencies and channel distances: the quasi-static near-field coupling part, the reactive induction-field radiation part, and the surface wave far-field propagation part. The general BCC model by means of the near-field and far-field approximation is developed to be valid in the frequency range from 100 kHz to 100 MHz and distance up to 1.3 m based on the measurements of the body channel characteristics. Finally, path loss characteristics of BCC are formulated for the design of BCC systems and many potential applications.

A 0.24-nJ/b Wireless Body-Area-Network Transceiver With Scalable Double-FSK Modulation

An energy-efficient wireless body-area-network (WBAN) transceiver is implemented in 0.18-μm CMOS technology with 1-V supply voltage. For the low energy consumption, the body channel communication (BCC) PHY is utilized with the theoretical results of Maxwells equation analysis behind the BCC. Based on the channel analysis, the resonance matching (RM) and contact impedance sensing (CIS) techniques are proposed to enhance the quality of the body channel. A double-FSK modulation scheme is adopted with high scalability to fulfill the IEEE 802.15.6 Task Group specifications. In addition, a low-power double-FSK transceiver is implemented by five circuit techniques: 1) a reconfigurable LNA with CIS; 2) a current-reuse wideband demodulator; 3) a divider-based local oscillator (LO) generation with duty-cycle correction in the receiver; 4) a reconfigurable driver with RM; and 5) a divider-based digital double-FSK modulator in the transmitter. As a result, fully WBAN compatible receiver and transmitter consume 2.4 and 2 mW, respectively, at a data rate of 10 Mb/s, corresponding to energy consumption of 0.24 nJ per received bit and 0.2 nJ per transmitted bit.

A 3.9 mW 25-Electrode Reconfigured Sensor for Wearable Cardiac Monitoring System

A low power highly sensitive Thoracic Impedance Variance (TIV) and Electrocardiogram (ECG) monitoring SoC is designed and implemented into a poultice-like plaster sensor for wearable cardiac monitoring. 0.1 Ω TIV detection is possible with a sensitivity of 3.17 V/Ω and SNR > 40 dB. This is achieved with the help of a high quality (Q-factor > 30) balanced sinusoidal current source and low noise reconfigurable readout electronics. A cm-range 13.56 MHz fabric inductor coupling is adopted to start/stop the SoC remotely. Moreover, a 5% duty-cycled Body Channel Communication (BCC) is exploited for 0.2 nJ/b 1 Mbps energy efficient external data communication. The proposed SoC occupies 5 mm × 5 mm including pads in a standard 0.18 μm 1P6M CMOS technology. It dissipates a peak power of 3.9 mW when operating in body channel receiver mode, and consumes 2.4 mW when operating in TIV and ECG detection mode. The SoC is integrated on a 15 cm × 15 cm fabric circuit board together with a flexible battery to form a compact wearable sensor. With 25 adhesive screen-printed fabric electrodes, detection of TIV and ECG at 16 different sites of the heart is possible, allowing optimal detection sites to be configured to accommodate different user dependencies.

A Low-Energy Crystal-Less Double-FSK Sensor Node Transceiver for Wireless Body-Area Network

An energy-efficient crystal-less double-FSK transceiver for wireless body-area-network (WBAN) sensor nodes is implemented in 0.18-μm CMOS technology with a 1-V supply. The injection-locking digitally controlled oscillator (IL-DCO) replaces the crystal oscillator (XO), which leads to significantly reduce the energy consumption and system cost. With the proposed calibration method using an injection-locking detector (IL-detector), the frequency drift of DCO can be calibrated within 100-kHz accuracy over 100° temperature variation. For the full satisfaction to the WBAN requirements, such as wide range of quality of service in terms of data rate, bit error rate, and network coexistence, we adopt a scalable double-FSK modulation scheme with divider-based transmitter by a power-efficient switching modulator. As a result, the fabricated crystal-less double-FSK WBAN compatible sensor node transceiver consumes 1 and 2 mW in calibrating and transmitting modes, respectively, at a data rate of up to 10 Mb/s, providing an 80 MHz reference source with 100-kHz accuracy by auto-calibrated DCO.

A 5.5mW IEEE-802.15.6 wireless body-area-network standard transceiver for multichannel electro-acupuncture application

In this paper, we present a state-of-the-art WBAN transceiver satisfying all of the specifications for the IEEE 802.15.6 standard. Especially, the driver active-digital-bandpass filter (ADF) is proposed to fulfill the tight spectral mask requirement without using external components. Moreover, the WBAN transceiver SoC is applied to multichannel electro-acupuncture, which is one of the most prominent emerging medical applications and is useful to verify the successful operation of the transceiver [6].

A Low-Energy Inductive Coupling Transceiver With Cm-Range 50-Mbps Data Communication in Mobile Device Applications

A low-energy inductive coupling transceiver is proposed for Cm-range multimedia data transmission in mobile device applications. The Transmission Time Control (TTC) scheme is proposed to reduce the transmitter energy consumption to 0.475 pJ/b, and the Adaptive Gain Control (AGC) scheme is adopted to make the receiver energy consumption be 0.825 pJ/b. The planar-type inductor with self-resonance frequency of about 200 MHz fabricated on the flexible substrate achieves a data rate over 50 Mbps. To compensate for the weakly coupled channel, the receiver sensitivity is enhanced by the differential detection method (DDM) of the nodal voltages across the receiver inductor. With this method, the communication distance is increased up to 7 cm, and channel misalignment tolerance is enhanced up to 2 cm. The proposed transceiver is implemented within 1.5 × 2.37 mm2 in 0.18-μ m CMOS process and operates with 1-V supply.

The compact electro-acupuncture system for multi-modal feedback electro-acupuncture treatment

The compact electro-acupuncture (EA) system is proposed for the multi-modal feedback EA treatment. It is composed of a needle, a smart patch, and an interconnecting conductive thread. The 3cm diameter compact EA patch is implemented with the EA controller integrated circuit (IC) and the small coin battery on the planar-fashionable circuit board (P-FCB) technology. It can achieve the user convenience and the low manufacturing cost at once by removing the wire connections. The EA controller IC programs the stimulation current and also monitors the electromyography (EMG) and the skin temperature during the EA stimulation. The measured data can be wirelessly transmitted to the external EA analyzer through the body channel communication with low power consumption. The external EA analyzer can check the patients status, such as the muscle fatigue and the change of the skin temperature, and the practitioner can change the stimulation parameters for the optimal curative value. The proposed compact EA system is fully implemented and tested on the human body.

A 3.9mW 25-electrode reconfigured thoracic impedance/ECG SoC with body-channel transponder

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.

An Impedance and Multi-Wavelength Near-Infrared Spectroscopy IC for Non-Invasive Blood Glucose Estimation

A multi-modal spectroscopy IC combining impedance spectroscopy (IMPS) and multi-wavelength near-infrared spectroscopy (mNIRS) is proposed for high precision non-invasive glucose level estimation. A combination of IMPS and mNIRS can compensate for the glucose estimation error to improve its accuracy. The IMPS circuit measures dielectric characteristics of the tissue using the RLC resonant frequency and the resonant impedance to estimate the glucose level. To accurately find resonant frequency, a 2-step frequency sweep sinusoidal oscillator (FSSO) is proposed: 1) 8-level coarse frequency switching (fSTEP = 9.4 kHz) in 10-76 kHz, and 2) fine analog frequency sweep in the range of 18.9 kHz. During the frequency sweep, the adaptive gain control loop stabilizes the output voltage swing (400 mVp-p). To improve accuracy of mNIRS, three wavelengths, 850 nm, 950 nm, and 1,300 nm, are used. For highly accurate glucose estimation, the measurement data of the IMPS and mNIRS are combined by an artificial neural network (ANN) in external DSP. The proposed ANN method reduces the mean absolute relative difference to 8.3% from 15% of IMPS, and 15-20% of mNIRS in 80-180 mg/dL blood glucose level. The proposed multi-modal spectroscopy IC occupies 12.5 mm 2 in a 0.18 μm 1P6M CMOS technology and dissipates a peak power of 38 mW with the maximum radiant emitting power of 12.1 mW.

A Wearable Neuro-Feedback System With EEG-Based Mental Status Monitoring and Transcranial Electrical Stimulation

A wearable neuro-feedback system is proposed with a low-power neuro-feedback SoC (NFS), which supports mental status monitoring with electroencephalography (EEG) and transcranial electrical stimulation (tES) for neuro-modulation. Self-configured independent component analysis (ICA) is implemented to accelerate source separation at low power. Moreover, an embedded support vector machine (SVM) enables online source classification, configuring the ICA accelerator adaptively depending on the types of the decomposed components. Owing to the hardwired accelerating functions, the NFS dissipates only 4.45 mW to yield 16 independent components. For non-invasive neuro-modulation, tES stimulation up to 2 mA is implemented on the SoC. The NFS is fabricated in 130-nm CMOS technology.