Minkyu Je

High-Efficiency Wireless Power Transfer for Biomedical Implants by Optimal Resonant Load Transformation

Wireless power transfer provides a safe and robust way for powering biomedical implants, where high efficiency is of great importance. A new wireless power transfer technique using optimal resonant load transformation is presented with significantly improved efficiency at the cost of only one additional chip inductor component. The optimal resonant load condition for the maximized power transfer efficiency is explained. The proposed technique is implemented using printed spiral coils with discrete surface mount components at 13.56 MHz power carrier frequency. With an implantable coil having an area of 25 mm × 10 mm and a thickness of 0.5 mm, the power transfer efficiency of 58% is achieved in the tissue environment at 10-mm distance from the external coil. Compared to previous works, the power efficiency is much higher and the structure is compact with planar integration, easy to tune, and suitable for batch production, as well as biocompatible owing to no incorporation of ferromagnetic core.

A simple and analytical parameter-extraction method of a microwave MOSFET

A simple and accurate parameter-extraction method of a high-frequency small-signal MOSFET model including the substrate-related parameters and nonreciprocal capacitors is proposed. Direct extraction of each parameter using a linear regression approach is performed by Y-parameter analysis on the proposed equivalent circuit of the MOSFET for high-frequency operation. The extracted results are physically meaningful and good agreement has been obtained between the simulation results of the equivalent circuit and measured data without any optimization. Also, the extracted parameters, such as g/sub m/ and g/sub ds/, match very well with those obtained by DC measurement.

Low-Power Ultrawideband Wireless Telemetry Transceiver for Medical Sensor Applications

An integrated CMOS ultrawideband wireless telemetry transceiver for wearable and implantable medical sensor applications is reported in this letter. This high duty cycled, noncoherent transceiver supports scalable data rate up to 10 Mb/s with energy efficiency of 0.35 nJ/bit and 6.2 nJ/bit for transmitter and receiver, respectively. A prototype wireless capsule endoscopy using the proposed transceiver demonstrated in vivo image transmission of 640 × 480 resolution at a frame rate of 2.5 frames/s with 10 Mb/s data rate.

A precision relaxation oscillator with a self-clocked offset-cancellation scheme for implantable biomedical SoCs

Recently, there has been an increasing demand for SoCs in the biomedical field [1]. In implantable applications, SoCs are designed under very stringent power and area constraints. The analog and mixed-signal circuits as well as digital circuits in those SoCs require a clock source, because clock-based signal-processing techniques, such as sampling and chopper stabilization, are often used. The primary clock source for such SoCs needs to provide good accuracy and long-term stability of the oscillation frequency ƒOSC to minimize variations and drifts of the system characteristics. A fairly pure clock signal is required to avoid signal distortion when sampling or chopping techniques are applied. Considering such a source is typically a free-running oscillator, and biomedical signals of typical interest reside at low frequencies, the close-in phase noise is important.

A 100-Channel 1-mW Implantable Neural Recording IC

This paper presents a fully implantable 100-channel neural interface IC for neural activity monitoring. It contains 100-channel analog recording front-ends, 10 multiplexing successive approximation register ADCs, digital control modules and power management circuits. A dual sample-and-hold architecture is proposed, which extends the sampling time of the ADC and reduces the average power per channel by more than 50% compared to the conventional multiplexing neural recording system. A neural amplifier (NA) with current-reuse technique and weak inversion operation is demonstrated, consuming 800 nA under 1-V supply while achieving an input-referred noise of 4.0 μVrms in a 8-kHz bandwidth and a NEF of 1.9 for the whole analog recording chain. The measured frequency response of the analog front-end has a high-pass cutoff frequency from sub-1 Hz to 248 Hz and a low-pass cutoff frequency from 432 Hz to 5.1 kHz, which can be configured to record neural spikes and local field potentials simultaneously or separately. The whole system was fabricated in a 0.18-μm standard CMOS process and operates under 1 V for analog blocks and ADC, and 1.8 V for digital modules. The number of active recording channels is programmable and the digital output data rate changes accordingly, leading to high system power efficiency. The overall 100-channel interface IC consumes 1.16-mW total power, making it the optimum solution for multi-channel neural recording systems.

A CMOS Rectifier With a Cross-Coupled Latched Comparator for Wireless Power Transfer in Biomedical Applications

A highly efficient rectifier for wireless power transfer in biomedical implant applications is implemented using 0.18-m CMOS technology. The proposed rectifier with active nMOS and pMOS diodes employs a four-input common-gate-type capacitively cross-coupled latched comparator to control the reverse leakage current in order to maximize the power conversion efficiency (PCE) of the rectifier. The designed rectifier achieves a maximum measured PCE of 81.9% at 13.56 MHz under conditions of a low 1.5-Vpp RF input signal with a 1- k output load resistance and occupies 0.009 mm2 of core die area.

Multiple Functional ECG Signal is Processing for Wearable Applications of Long-Term Cardiac Monitoring

In this paper, an integrated electrocardiogram (ECG) signal-processing scheme is proposed. Using a systematic wavelet transform algorithm, this signal-processing scheme can realize multiple functions in real time, including baseline-drift removal, noise suppression, QRS detection, heart beat rate prediction and classification, and clean ECG reconstruction. Utilizing the novel low-cost hardware architecture, the proposed ECG signal-processing scheme is implemented in application-specific integrated circuits with 0.18 μm CMOS technology. This ECG signal-processor chip achieves low area and power consumptions, and is highly suitable for wearable applications of long-term cardiac monitoring.

A simple and accurate method for extracting substrate resistance of RF MOSFETs

In this paper, a simple and accurate method was proposed for extracting substrate resistance of an RF MOSFET, the substrate of which is represented by a single resistor. The extraction results from the measured network parameters are presented for various bias conditions. Excellent agreement between the results of measurements and the model for the extracted substrate resistance was obtained up to 18 GHz. Also, the resistance extracted using the proposed method was shown to give scalable results.

Design and in Vitro Test of a Differentially Fed Dual-Band Implantable Antenna Operating at MICS and ISM Bands

The design of a novel differentially fed dual-band implantable antenna operating at 402-405 MHz Medical Implant Communication Services (MICS) band and 2.4-2.5 GHz Industrial, Scientific, and Medical (ISM) band is introduced. The proposed implanted antennas are for both planar and flexible implantation scenarios. Biocompatible material parylene-C is adopted to cover the implanted antenna. The size of the proposed antennas including the encapsulation for planar and flexible case is 179.0 mm3 and 186.3 mm3 respectively. The Specific Absorption Rate (SAR) distribution and the radiation pattern at both frequencies induced by the implanted antenna are evaluated. The performance of the communication link between the implanted antenna and an external half-wavelength dipole at two resonant frequencies is also presented. In vitro test in minced pork is performed to test the reliability of the antenna in the real implantation cases.

Differentially Fed Dual-Band Implantable Antenna for Biomedical Applications

A novel differentially fed dual-band implantable antenna is proposed for the first time for a fully implantable neuro-microsystem. The antenna operates at two center frequencies of 433.9 MHz and 542.4 MHz, which are close to the 402-405 MHz medical implant communication services (MICS) band, to support sub-GHz wideband communication for high-data rate implantable neural recording application. The size of the antenna is 480.06 mm3 (27 mm × 14 mm × 1.27 mm). The simulated and measured bandwidths are 7.3% and 7.9% at the first resonant frequency, 5.4% and 6.4% at the second resonant frequency. The specific absorption rate (SAR) distribution induced by the implantable antenna inside a tissue-mimicking solution is evaluated. The performance of the communication link between the implanted antenna and external half-wavelength dual-band dipole is also examined.