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This paper presents a wide-dynamic-range, DC-coupled, time-based neural-recording integrated circuit (IC), which is resilient against stimulation artifacts, for bidirectional neural interfaces. The proposed neural-recording IC based on delta-sigma modulation consists of an input Gm cell, current-controlled oscillator (CCO)-based integrator, phase quantizer, and tri-level current-steering DACs. The feedback current-steering DACs embedded in the current sources of the input Gm cell enable the recording IC to achieve a wide enough dynamic range to directly digitize the neural signals on top of stimulation artifacts while maintaining a moderately high input impedance. Moreover, the free-running frequency of the CCO-based integrator is set to be the optimum frequency of 0.49 times the sampling rate, thereby achieving high loop gain while utilizing inherent clocked averaging (CLA). Designed and post-layout simulated in a 65-nm process, the neural-recording IC achieves an SNDR of 76.3 dB over a signal bandwidth of 10 kHz while consuming low power of $5.04~\mu $ W with a sufficiently wide linear input range of 200 mVPP.

Abstract Individuals who are unable to walk independently spend most of the day in a wheelchair. This population is at high risk for developing pressure injuries caused by sitting. However, early diagnosis and prevention of these injuries still remain challenging. Herein, we introduce battery-free, wireless, multimodal sensors and a movable system for continuous measurement of pressure, temperature, and hydration at skin interfaces. The device design includes a crack-activated pressure sensor with nanoscale encapsulations for enhanced sensitivity, a temperature sensor for measuring skin temperature, and a galvanic skin response sensor for measuring skin hydration levels. The movable system enables power harvesting, and data communication to multiple wireless devices mounted at skin-cushion interfaces of wheelchair users over full body coverage. Experimental evaluations and numerical simulations of the devices, together with clinical trials for wheelchair patients, demonstrate the feasibility and stability of the sensor system for preventing pressure injuries caused by sitting.

An automatically reconfigurable switched-capacitor DC-DC converter with multiple regulated outputs is presented for wireless-powered multi-unit implantable medical devices (IMDs). In such devices, the main controller unit is powered wirelessly and provides supply voltages to the circuits of the main unit as well as multiple connected sub-units. The proposed DC-DC converter simultaneously generates two regulated voltages for the main unit and two unregulated voltages for the sub-units, which have on-site low-dropout regulators. The converter consists of i) an input-adaptive DC-DC conversion stage with two switched-capacitor (SC) DC-DC converters in series and ii) a regulating stage. In the DC-DC conversion stage, the proposed converter automatically reconfigures the conversion ratio and connection order of the two SC DC-DC converters and selects the output nodes by load selection switches depending on the input level. Thanks to these adaptive configurations, the proposed converter offers high conversion efficiencies over a wide input voltage range even with fewer flying capacitors required for the reconfigurable conversion ratios. Moreover, the selection switches are reused to regulate the output voltages to desired levels, minimizing the overhead for subsequent regulation. The IC fabricated in a 180-nm standard CMOS process achieves a conversion efficiency of 95.5% for the unregulated voltages and up to 77.4% for the regulated voltages over a wide input range of 1 V to 4 V with 0.74-mV output ripple for a load current of 20 mA, while providing four outputs (2 regulated, 2 unregulated).

Abstract As a promising future treatment for stroke rehabilitation, researchers have developed direct brain stimulation to manipulate the neural excitability. However, there has been less interest in energy consumption and unexpected side effect caused by electrical stimulation to bring functional recovery for stroke rehabilitation. In this study, we propose an engineering approach with subthreshold electrical stimulation (STES) to bring functional recovery. Here, we show a low level of electrical stimulation boosted causal excitation in connected neurons and strengthened the synaptic weight in a simulation study. We found that STES with motor training enhanced functional recovery after stroke in vivo. STES was shown to induce neural reconstruction, indicated by higher neurite expression in the stimulated regions and correlated changes in behavioral performance and neural spike firing pattern during the rehabilitation process. This will reduce the energy consumption of implantable devices and the side effects caused by stimulating unwanted brain regions.

Monitoring the electrical neural signals is an important method for understanding the neuronal mechanism. In particular, in order to perform a cell-type-specific study, it is necessary to observe the concentration of calcium ions using fluorescent indicators in addition to measuring the electrical neural signal. This paper presents a multimodal multichannel neural activity readout integrated circuit that can perform not only electrical neural recording but also fluorescence recording of neural activity for the cell-type-specific study of heterogeneous neuronal cell populations. For monitoring the calcium ions, the photodiode generates the current according to the fluorescence expressed by the reaction between the genetically encoded calcium indicators and calcium ions. The time-based fluorescence recording circuit then records the photodiode current. The electrical neural signal captured by the microelectrode is recorded through the low-noise amplifier, variable gain amplifier, and analog-to-digital converter. The proposed integrated circuit is fabricated in a 1-poly 6-metal (1P6M) 0.18- $\mu \text{m}$ CMOS process. The fluorescence recording circuit achieves a recording range of 81 dB (75 pA to 860 nA) and consumes a power of 724 nW/channel. The electrical recording circuit achieves an input-referred noise of $2.7~\mu \text{V}_{\mathrm {rms}}$ over the bandwidth of 10 kHz, while consuming the power of $4.9~\mu \text{W}$ /channel. The functionality of the proposed circuits is verified through the in vivo and in vitro experiments. Compared to the conventional neuroscience tools, which consist of bulky off-chip components, this neural interface is implemented in a compact size to perform multimodal neural recording while consuming low power.

Laparoscopic surgery is a technique in which surgeons insert laparoscopic instruments into the body through a small incision and conduct surgical operations. It offers a shorter recovery period, less blood loss, and less postoperative pain than open surgeries. In order to maximize these benefits of this surgery technique, it is important to localize the lesion accurately without palpation, minimizing the surgical area. It is because surgeons cannot palpate the organ during laparoscopic surgeries. For accurate localization, we propose a lesion localization system (LLS). This adopts an endoscopic clip with a small-size magnet as a marker and an improved magnetometer as a probe for measuring the magnetic field from the magnet. The magnetometer, which consists of two Hall sensors, can cancel out the fluctuating magnetic baseline mainly caused by external environments so that it can detect a smaller change in the target magnetic field. As a result, the LLS improves the detection range up to 40 mm while using a weak magnet with a small volume of 17.1 mm3, which is compatible with the use of commercial clip appliers. An error of less than 0.1% is achieved at a distance of 40 mm, and the maximum error is kept below 6% even when the rotation angle is varied to ±90°. This LLS does not cause discomfort to the surgery operation because it uses a marker small enough and does not require external coils.

This paper presents an ultra-low-power receiver based on the injection-locked oscillator (ILO), which is compatible with multiple modulation schemes such as on-off keying (OOK), binary frequency-shift keying (BFSK), and differential binary phase-shift keying (DBPSK). The receiver has been fabricated in 0.18-μm CMOS technology and operates in the ISM band of 2.4 GHz. A simple envelope detection can be used even for the demodulation of BFSK and DBPSK signals due to the conversion capability of the ILO from the frequency and phase to the amplitude. In the proposed receiver, a Q-enhanced single-ended-to-differential amplifier is employed to provide high-gain amplification as well as narrow band-pass filtering, which improves the sensitivity and selectivity of the receiver. In addition, a gain-control loop is formed in the receiver to maintain constant lock range and hence frequency-to-amplitude conversion ratio for the varying power of the BFSK-modulated receiver input signal. The receiver achieves the sensitivity of -87, -85, and -82 dBm for the OOK, BFSK, and DBPSK signals respectively at the data rate of 50 kb/s and the BER lower than 0.1% while consuming the power of 324 μW in total.

This paper presents an ultra-low power, low cost demodulator for gaussian frequency shift keying (GFSK) receivers that use low intermediate frequencies (IF). The demodulator employs a direct IF to digital data conversion scheme by using an injection-locked ring oscillator (ILRO) with a 1-bit flip-flop. It consumes 2.7 μW from a 1.0 V supply at a data rate of 500 kbps achieving an energy efficiency of 5.4 pJ/bit which is 30 times better than that of the recently presented works. The demodulator also achieves 17.5 dB SNR at 0.1 % BER while operating at the same date rate. The demodulator is implemented in a 0.18 μm standard CMOS process and occupies an active area of 0.012 mm2.

This paper presents an error-tolerant and power-efficient impedance measurement scheme for bioimpedance acquisition. The proposed architecture measures the magnitude and the real part of the target complex impedance, unlike other impedance measurement architectures measuring either the real/imaginary components or the magnitude and phase. The phase information of the target impedance is obtained by using the ratio between the magnitude and the real components. This can allow for avoiding direct phase measurements, which require fast, power-hungry circuit blocks. A reference resistor is connected in series with the target impedance to compensate for the errors caused by the delay in the sinusoidal signal generator and the amplifier at the front. Moreover, an additional magnitude measurement path is connected to the reference resistor to cancel out the nonlinearity of the proposed system and enhance the settling speed of the low-pass filter by a ratio-based detection. Thanks to this ratio-based detection, the accuracy is enhanced by 30%, and the settling time is improved by 87.7% compared to the conventional single-path detection. The proposed integrated circuit consumes only 513 μW for a wide frequency range of 10 Hz to 1 MHz, with the maximum magnitude and phase errors of 0.3% and 2.1°, respectively.

Radiation sensor interfaces for battery-powered mobile dosimeters must consume low power to monitor the amount of radiation exposure over a long period. This paper proposes a power-efficient radiation sensor interface using a peak-triggered sampling scheme. Since the peak of the analog-to-digital converter’s (ADC’s) input represents radiation energy, our ADC only operates around the peak value thanks to the proposed sampling scheme. Although our ADC operates with a high sampling frequency, this proposed sampling scheme reduces the power consumption of the sensor interface because of the reduced operation time of the ADC. Our sensor interface does not have signal distortion caused by a conventional shaper because the interface quantizes the peak value using the high sampling frequency instead of the shaper. When the radiation input occurs once every 10 μs, the power consumption of the ADC with the proposed sampling scheme is only about 21.5% of the ADC’s power consumption when the ADC continuously operates. In this worst case, the fabricated radiation sensor interface in a 0.18-μm complementary metal-oxide-semiconductor (CMOS) process consumes only 1.11 mW.

This paper presents a reconfigurable time-to-digital converter (TDC) used to quantize the phase of the impedance in electrical impedance spectroscopy (EIS). The TDC in the EIS system must handle a wide input-time range for analysis in the low-frequency range and have a high resolution for analysis in the high-frequency range. The proposed TDC adopts a coarse counter to support a wide input-time range and cascaded time interpolators to improve the time resolution in the high-frequency analysis without increasing the counting clock speed. When the same large interpolation factor is adopted, the cascaded time interpolators have shorter measurement time and smaller chip area than a single-stage time interpolator. A reconfigurable time interpolation factor is adopted to maintain the phase resolution with reasonable measurement time. The fabricated TDC has a peak-to-peak phase error of less than 0.72° over the input frequency range from 1 kHz to 512 kHz and the phase error of less than 2.70° when the range is extended to 2.048 MHz, which demonstrates a competitive performance when compared with previously reported designs.

This paper proposes a novel smart surgical navigation system for intramedullary nailing in orthopedic surgery. Using a handle-integrated laser guidance module, the system can target a drill insertion point onto skin, indicating an accurate target position to perpendicularly access an invisible distal hole. The proposed handle-integration-based fixation of the laser guidance module precisely defines the relative position of the module with respect to the distal hole. Consequently, unlike conventional systems, the proposed system can indicate the target insertion point without any help from bulky and costly external position-tracking equipment that is usually required for compensating disturbances generated by external impacts. After insertion, a correct drilling direction toward the distal hole is guided by real-time drilling angle measurement modules-one integrated with the nail handle and the other with the drill body. Each module contains a 9-axis inertial sensor and a Bluetooth communication device. These two modules work together to provide real-time drilling angle data, allowing calculation of the directional error toward the center of the distal hole in real time. The proposed system removes the need for fluoroscopy and provides a compact and cost-effective solution compared with conventional systems.

Individuals with tetraplegia lack independent mobility, making them highly dependent on others to move from one place to another. Here, we describe how two macaques were able to use a wireless integrated system to control a robotic platform, over which they were sitting, to achieve independent mobility using the neuronal activity in their motor cortices. The activity of populations of single neurons was recorded using multiple electrode arrays implanted in the arm region of primary motor cortex, and decoded to achieve brain control of the platform. We found that free-running brain control of the platform (which was not equipped with any machine intelligence) was fast and accurate, resembling the performance achieved using joystick control. The decoding algorithms can be trained in the absence of joystick movements, as would be required for use by tetraplegic individuals, demonstrating that the non-human primate model is a good pre-clinical model for developing such a cortically-controlled movement prosthetic. Interestingly, we found that the response properties of some neurons differed greatly depending on the mode of control (joystick or brain control), suggesting different roles for these neurons in encoding movement intention and movement execution. These results demonstrate that independent mobility can be achieved without first training on prescribed motor movements, opening the door for the implementation of this technology in persons with tetraplegia.