Search

In multi-electrode arrays (MEAs), for electrical recording and electrical stimulation, high voltage (HV) switches are employed to build an analog multiplexer to conduct either a HV stimulation signal from the pulse generator circuit to an electrode or a low-voltage noise-sensitive signal from the electrode to a recording stage. In this brief, a new circuit structure is proposed for HV switches that significantly improves their switching speed, reduces their power dissipation, and also employs a minimum number of bulky HV devices. In order to reduce the transition time of the proposed switch without consuming a large amount of power, during the transition time that the switch is turning on/off, a large current flows through the driver circuit of the switch to turn the switch on/off rapidly; however, after the transition times, this current is significantly reduced to save power. Based on the proposed HV switch, a multiplexer structure has been implemented in 25-V, 0.18- $\mu \text{m}$ CMOS IC technology and the measurement results prove its efficacy. Supplied with 25 V and operating with 300 nA current consumption, this switch swings over 20 V with a relatively constant on-resistance of $100 \Omega $ and features a 80 ns transition time. [ABSTRACT FROM AUTHOR]

Closed-loop vagus nerve stimulators (VNSs) are used to treat refractory epilepsy (RE) and provide an alternative treatment modality with fewer side effects for RE. This work proposes a closed-loop VNS that senses the scalp EEG via a wearable EEG recorder (WER) and stimulates the vagus nerve via an implantable VNS (IVNS), the combination of which is referred to as a “HybridVNS”. First, the architecture and system control (by an App) of the HybridVNS are presented. Next, discrete component implementations of its key building blocks including the multichannel preamplifier, pulse generator and wireless power link are provided. Further, a 4-channel preamplifier magnifies the recorded EEG signals, and each channel consists of a capacitively coupled instrumentation amplifier (CCIA) cascaded by a 2nd-order low pass filter. The measured gain and the input-referred noise (IRN) of the preamplifier are 45.8 dB and 4.9 ${\mu}$ Vrms (1 Hz–200 Hz), respectively. We propose a switched-resistor array pulse generator for constant-current stimulation, and a novel distance-frequency adaptive inductive coupling link (DFAICL) to automatically tune the resonance frequency. A maximum wireless power transmission efficiency of 17% is achieved in the DFAICL when the supply power is 30dBm and the distance is 20 mm at 2 MHz. Finally, we demonstrate that in the WER, the onset of an epileptic seizure can be detected by a threshold of coastline length (294 ${\mu}$ V) combined with a threshold of slope (7.3 ${\mu}$ V/ms) within a unit time segment (780 ms), which provides an average accuracy of 88.2%. The feasibility of the IVNS was tested in an acute rodent epilepsy experiment. However, the closed-loop experiment was not conducted. [ABSTRACT FROM AUTHOR]

For impulse radio ultrawideband communications an 'antenna plus generator' system is co-designed and an on chip generator is integrated into the antenna. This approach does away with the need for intermediate transmission lines conventionally placed between an RF device/generator and an antenna and therefore eliminates the need for a balun, prevents excitation of the common-mode currents and allows the device to be mounted directly on the antenna. The antenna and generator are designed taking into account both impedance matching and the generator's influence on the antenna's radiation properties. The suggested approach is verified experimentally at a scaled up version of the antenna. Index Terms--Antenna feed, antenna matching, balun, impulse radio (IR), integrated circuits, ultrawideband (UWB) antenna.

A novel procedure to approximate wavelet bases using analog circuitry is presented. First, an approximation is used to calculate the transfer function of the filter, whose impulse response is the required wavelet. Next, for low-power low-voltage applications, we optimize the state-space description of the filter for dynamic range, sensitivity and sparsity requirements. The filter design that follows is based on an orthonormal ladder structure with log-domain integrators as the main building blocks. Simulations demonstrate that it approximates the required wavelet base (i.e., Morlet) in an excellent way. The circuit operates from a 1.2-V supply voltage and a bias current of 1.2 [micro]A. Index Terms--Analog electronics, log-domain filters, orthonormal ladder filter, wavelet transform (WT).

Analog RF front-end circuits are typically designed to perform one specific task, while key parameters such as dynamic range, bandwidth and selectivity are fixed by the hardware design and not by the communication system in an adaptive way. As a result, today's receiver topologies are designed to function under the most stringent conditions, which increases circuit complexity and power consumption. However, the conditions under which the RF circuits operate are not fixed but vary widely and depend upon a multitude of factors. Therefore, a concept of design for adaptivity is introduced in this paper. It establishes a trajectory for an all-round performance characterization of adaptive oscillators with an explicit qualitative and quantitative description of all the existing relations and tradeoffs among the oscillator performance parameters. As a proof of concept, an 800-MHz adaptive voltage-controlled oscillator is designed with phase-noise tuning range of 7 dB and more than a factor 3 saving in power consumption, suitable for unobtrusive mobile equipment, foreseen to operate in this band. Index Terms--Adaptive circuits, analog circuits, loop gain, low-power integrated circuit (IC) design, phase-noise tuning, RF circuits, voltage-controlled oscillators (VCOs).

A multistandard/multiband adaptive voltage-controlled oscillator (VCO) satisfying the phase-noise requirements of both second- and third-generation wireless standards is described in this paper (1.8-GHz DCS1800, 2.1-GHz wide-band code division multiple access, and 2.4-GHz wireless local area network, Bluetooth, and digital enhanced cordless telecommunications standards). The design procedure for the VCO is based on an adaptive phase-noise model. A factor of 12 reduction in power consumption with a phase-noise tuning range of 20 dB is demonstrated by adapting the VCO bias to the desired application. The VCO achieves -123-, -110-, and -103-dBc/Hz phase noise at 1-MHz offset in a 2.1-GHz band at supply currents of 6, 1.2, and 0.5 mA, respectively. Index Terms--Adaptive circuits, loop gain, multistandard (MS)/multiband (MB) circuits, phase noise, phase-noise tuning, voltage-controlled oscillators (VCOs).

The first two objectives were to establish which stimulation parameters of kilohertz frequency alternating current (KHFAC) neuromodulation influence the effectiveness of pudendal nerve block and its safety. The third aim was to determine whether KHFAC neuromodulation of the pudendal nerve can relax the pelvic musculature, including the anal sphincter. Simulation experiments were conducted to establish which parameters can be adjusted to improve the effectiveness and safety of the nerve block. The outcome measures were block threshold (measure of effectiveness) and block threshold charge per phase (measure of safety). In vivo, the pudendal nerves in 11 male and 2 female anesthetized Sprague Dawley rats were stimulated in the range of 10 Hz to 40 kHz, and the effect on anal pressure was measured. The simulations showed that block threshold and block threshold charge per phase depend on waveform, interphase delay, electrode-to-axon distance, interpolar distance, and electrode array orientation. In vivo, the average anal pressure during unilateral KHFAC stimulation was significantly lower than the average peak anal pressure during low-frequency stimulation (p < 0.001). Stimulation with 20 kHz and 40 kHz (square wave, 10 V amplitude, 50% duty cycle, no interphase delay) induced the largest anal pressure decrease during both unilateral and bilateral stimulation. However, no statistically significant differences were detected between the different frequencies. This study showed that waveform, interphase delay and the alignment of the electrode along the nerve affect the effectiveness and safety of KHFAC stimulation. Additionally, we showed that KHFAC neuromodulation of the pudendal nerves with an electrode array effectively reduces anal pressure in rats. [ABSTRACT FROM AUTHOR]

For mm-sized implants incorporating silicon integrated circuits, ensuring lifetime operation of the chip within the corrosive environment of the body still remains a critical challenge. For the chip's packaging, various polymeric and thin ceramic coatings have been reported, demonstrating high biocompatibility and barrier properties. Yet, for the evaluation of the packaging and lifetime prediction, the conventional helium leak test method can no longer be applied due to the mm-size of such implants. Alternatively, accelerated soak studies are typically used instead. For such studies, early detection of moisture/ion ingress using an in-situ platform may result in a better prediction of lifetime functionality. In this work, we have developed such a platform on a CMOS chip. Ingress of moisture/ions would result in changes in the resistance of the interlayer dielectrics (ILD) used within the chip and can be tracked using the proposed system, which consists of a sensing array and an on-chip measurement engine. The measurement system uses a novel charge/discharge based time-mode resistance sensor that can be implemented using simple yet highly robust circuitry. The sensor array is implemented together with the measurement engine in a standard 0.18  $\mu$ m 6-metal CMOS process. The platform was validated through a series of dry and wet measurements. The system can measure the ILD resistance with values of up to 0.504 peta-ohms, with controllable measurement steps that can be as low as 0.8 M $\Omega$. The system works with a supply voltage of 1.8 V, and consumes 4.78 mA. Wet measurements in saline demonstrated the sensitivity of the platform in detecting moisture/ion ingress. Such a platform could be used both in accelerated soak studies and during the implant's life–time for monitoring the integrity of the chip's packaging. [ABSTRACT FROM AUTHOR]

In order to recruit neurons in excitable tissue, constant current neural stimulators are commonly used. Recently, ultra high-frequency (UHF) stimulation has been proposed and proven to have the same efficacy as constant-current stimulation. UHF stimulation uses a fundamentally different way of activating the tissue: each stimulation phase is made of a burst of current pulses with adjustable amplitude injected into the tissue at a high (e.g., $\text{1 MHz}$) frequency. This paper presents the design, integrated circuit (IC) implementation, and measurement results of a power efficient multichannel UHF neural stimulator. The core of the neurostimulator is based on our previously proposed architecture of an inductor-based buck–boost dc–dc converter without the external output capacitor. The ultimate goal of this work is to increase the power efficiency of the UHF stimulator for multiple-channel operation, while keeping the number of external components minimal. To this end, a number of novel approaches were employed in the integrated circuit design domain. More specifically, a novel zero-current detection scheme is proposed. It allows to remove the freewheel diode typically used in dc–dc converters to prevent current to flow back from the load to the inductor. Furthermore, a gate-driver circuit is implemented which allows the use of thin gate-oxide transistors as high-voltage switches. By doing so, and exploiting the fundamental working principle of the proposed current-controlled UHF stimulator, the need for a high-voltage supply is eliminated and the stimulator is powered up from a $\text{3.5 V}$ input voltage. Both the current detection technique and the gate driving circuit of the current implementation allow to boost the power efficiency up to $\text{300}\%$ when compared to previous UHF stimulator works. A peak power efficiency of $\text{68}\%$ is achieved, while 8 independent channels with 16 fully configurable electrodes are used. The circuit is implemented in a $\text{0.18}\,\mu\text{m}$ HV process, and the total chip area is $\text{3.65 mm}^2$. [ABSTRACT FROM AUTHOR]

Due to their DC-blocking characteristic, coupling capacitors are widely used to prevent potentially harmful charge buildup at the electrode-tissue interface. Although the capacitors can be an effective safety measure, it often seems overlooked that coupling capacitors actually introduce an offset voltage over the electrode-tissue interface as well. This work investigates this offset voltage both analytically and experimentally. The calculations as well as the experiments using bipolar-driven platinum electrodes in a saline solution confirm that coupling capacitors introduce an offset, while they barely contribute to the passive charge balancing. In particular cases, this offset is shown to reach potentially dangerous voltage levels that could induce irreversible electrochemical reactions. This work therefore suggests that when the use of coupling capacitors is required, the offset voltage should be analyzed for all operating conditions to ensure it remains within safe boundaries. [ABSTRACT FROM AUTHOR]

A low-power mixed-signal IC for implantable pacemakers is presented. The proposed system features three independent intracardiac signal readout channels with pulse-width-modulated outputs. Also, the proposed system is capable of measuring the amplitude and phase of the bioimpedance with pulse-width-modulated outputs for use in rate adaptive pacemakers. Moreover, a stimulation system is embedded, offering 16 different amplitudes from 1 to 7.8 V. A backscattering transmitter transfers the output signals outside the body with very little power consumption. The proposed low-power mixed-signal IC is fabricated in a 0.18-μm HV CMOS process and occupies 2.38 mm2. The biopotential channels extract the heart signals with 9.2 effective number of bits and the bioimpedance channels measure the amplitude and phase of the heart impedance with 1.35 Ωrms accuracy. The complete IC consumes only 4.2 μA from a 1-V power supply. [ABSTRACT FROM AUTHOR]

Cardiac signal acquisition with high linearity and accuracy of the high-pass cut-off frequency imposes a challenge on the implementation of the analog preprocessing and the analog-to-digital converter. This paper describes a state-space-based methodology for designing high-pass sigma-delta (HP $\Sigma \Delta$ ) topologies with high linearity, targeting high accuracy of the high-pass cut-off frequency. Intermediate functions are evaluated mathematically to compare the proposed HP $\Sigma \Delta$ topologies with respect to dynamic range. A sensitivity performance analysis of the noise transfer function with respect to integrator nonidealities and coefficient variations is also described. Finally, to illustrate the design approach, an orthonormal HP $\Sigma \Delta$ modulator is designed to be implemented in 0.18  $\mu$ m CMOS technology, is tested with real prerecorded ECG signals. [ABSTRACT FROM AUTHOR]

This paper presents an implantable bio-impedance measurement system for cardiac pacemakers. The fully integrated system features a low power analog front-end and pulse width modulated output. The bio-impedance readout benefits from voltage to time conversion to achieve a very low power consumption for wirelessly transmitting the data outside the body. The proposed IC is fabricated in a 0.18 μm CMOS process and is capable of measuring the bio-impedance at 2 kHz over a wide dynamic range from \text100\,\Omega to \text3.3\;\textk\Omega with \text1.35\;\Omega {\rm{rms}} accuracy and \text1\; \mu\textA maximum current injection while consuming just \text1.55\;\mu\textA from a 1 V supply. [ABSTRACT FROM PUBLISHER]