High Voltage Compliance Research Articles

A Fully Integrated Stimulator With High Stimulation Voltage Compliance Using Dynamic Bulk Biasing Technique in a Bulk CMOS Technology

A Fully Integrated Stimulator With High Stimulation Voltage Compliance Using Dynamic Bulk Biasing Technique in a Bulk CMOS Technology

Design, Implementation, and Characterization of a Compact Lock-in Add-on for Low-Frequency Impedance Measurements

Impedance measurements are crucial in a variety of applications, from the characterization of lithium batteries, microbial fuel cells, and biosensors to the study of polymers and material degradation, where strict requirements have to be met in terms of frequency bandwidth and current level. Here, we present a cost-effective compact solution for ultra-low-frequency impedance measurements, operating in a wide range, from 1 mHz to 250 kHz. Coupled to a lock-in amplifier, the designed circuit is based on a Howland current pump cascaded by a precision current divider in order to set the conversion factor at 100 nA/V, 1 μA/V, or 100 μA/V. Therefore, it is possible to generate very low-current signals to measure resistive impedances up to 100 MΩ. In addition, a feedback network is inserted to null the voltage drift induced by leakage currents and offset voltages, thus allowing the measurement of low-capacitance loads, experimentally tested down to 10 nF. Remarkably, the feedback network allows to perform measurements also in the presence of high voltage bias of the load and experimental results performed up to 60 V demonstrate the excellent stability of the designed system, thus a high voltage compliance. The proposed circuit is particularly interesting for the conditioning of both resistive and capacitive sensors and it is likely to be an effective solution for the implementation of a portable instrument for measuring signals from biosensors.

Wearable High Voltage Compliant Current Stimulator for Restoring Sensory Feedback

Transcutaneous Electrical Nerve Stimulation (TENS) is a promising technique for eliciting referred tactile sensations in patients with limb amputation. Although several studies show the validity of this technique, its application in daily life and away from laboratories is limited by the need for more portable instrumentation that guarantees the necessary voltage and current requirements for proper sensory stimulation. This study proposes a low-cost, wearable high-voltage compliant current stimulator with four independent channels based on Components-Off-The-Shelf (COTS). This microcontroller-based system implements a voltage-current converter controllable through a digital-to-analog converter that delivers up to 25 mA to load up to 3.6 kΩ. The high-voltage compliance enables the system to adapt to variations in electrode-skin impedance, allowing it to stimulate loads over 10 kΩ with currents of 5 mA. The system was realized on a four-layer PCB (115.9 mm × 61 mm, 52 g). The functionality of the device was tested on resistive loads and on an equivalent skin-like RC circuit. Moreover, the possibility of implementing an amplitude modulation was demonstrated.

Erratum to “A High-Voltage Compliance, 32-Channel Digitally Interfaced Neuromodulation System-on-Chip”

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A High-Voltage Compliance, 32-Channel Digitally Interfaced Neuromodulation System on Chip

This article presents the integration of a 32-channel neuromodulation system on chip (SoC) that is developed for chronic implantation in humans. The application-specific integrated circuit (ASIC) offers low-noise recording, a state-of-the-art (SotA) neurostimulator capable of both current- and voltage-controlled stimulation with high-voltage compliance, on-chip 16-bit data digitization as well as safety features such as electrode impedance estimation and charge balancing. The chip communicates through two distinct SPI interfaces for independent command and data transfer. Thus, the developed system constitutes a fully digital, bidirectional 32-channel interface to the brain.

An Extremely Low-Voltage and High-Compliance Current Mirror

In this paper, a novel ultrahigh-compliance, low-voltage and low-power current mirror is proposed. The proposed structure utilizes the cooperative positive–negative local feedback to achieve ever-interesting high output voltage compliance. The structure takes the advantage of the current compensation scheme to boost the positive feedback at high current values, in which, otherwise the positive feedback and consequently the output voltage compliance tend to be degraded. The performance of the proposed architecture is validated by HSPICE simulation in TSMC 180 nm CMOS, BSIM 3 and Level 49 technology. The simulation results of the proposed structure show input/output minimum voltages of 0.059 V/0.038 V, output resistance of 121.36 GΩ and bandwidth of 211 MHz, while it consumes only 42.5 µW considering 1 V supply voltage. The current transfer error is interestingly less than 0.4% throughout its current dynamic range.

Low-power transcutaneous current stimulator for wearable applications

BackgroundPeripheral neuropathic desensitization associated with aging, diabetes, alcoholism and HIV/AIDS, affects tens of millions of people worldwide, and there is little or no treatment available to improve sensory function. Recent studies that apply imperceptible continuous vibration or electrical stimulation have shown promise in improving sensitivity in both diseased and healthy participants. This class of interventions only has an effect during application, necessitating the design of a wearable device for everyday use. We present a circuit that allows for a low-power, low-cost and small form factor implementation of a current stimulator for the continuous application of subthreshold currents.ResultsThis circuit acts as a voltage-to-current converter and has been tested to drive + 1 to − 1 mA into a 60 kOmega load from DC to 1 kHz. Driving a 60 kOmega load with a 2 mA peak-to-peak 1 kHz sinusoid, the circuit draws less than 21 mA from a 9 V source. The minimum operating current of the circuit is less than 12 mA. Voltage compliance is ± 60 V with just 1.02 mA drawn by the high voltage current drive circuitry. The circuit was implemented as a compact 46 mm × 21 mm two-layer PCB highlighting its potential for use in a body-worn device.ConclusionsNo design to the best of our knowledge presents comparably low quiescent power with such high voltage compliance. This makes the design uniquely appropriate for low-power transcutaneous current stimulation in wearable applications. Further development of driving and instrumentation circuitry is recommended.

An IC-based controllable stimulator for respiratory muscle stimulation investigations.

Functional Electrical Stimulation can be used to restore motor functions loss consecutive to spinal cord injury, such as respiratory deficiency due to paralysis of ventilatory muscles. This paper presents a fully configurable IC-centered stimulator designed to investigate muscle stimulation paradigms. It provides 8 current stimulation channels with high-voltage compliance and real-time operation capabilities, to enable a wide range of FES applications. The stimulator can be used in a standalone mode, or within a closed-loop setup. Primary in vivo results show successful drive of respiratory muscles stimulation using a computer-based dedicated controller.

A wireless wearable surface functional electrical stimulator

ABSTRACTIn this paper, a wireless wearable functional electrical stimulator controlled by Android phone with real-time-varying stimulation parameters for multichannel surface functional electrical stimulation application has been developed. It can help post-stroke patients using more conveniently. This study focuses on the prototype design, including the specific wristband concept, circuits and stimulation pulse-generation algorithm. A novel stimulator circuit with a driving stage using a complementary current source technique is proposed to achieve a high-voltage compliance, a large output impedance and an accurate linear voltage-to-current conversion. The size of the prototype has been significantly decreased to 17 × 7.5 × 1 cm3. The performance of the prototype has been tested with a loaded resistor and wrist extension/flexion movement of three hemiplegic patients. According to the experiments, the stimulator can generate four-channel charge-balanced biphasic stimulation with a voltage amplitude up to 60 V, and the pulse frequency and width can be adjusted in real time with a range of 100–600 μs and 20–80 Hz, respectively.

Design of integrated neural stimulating and recording frontend for bladder control prosthesis

Functional electrical stimulation has been widely used for the restoration of bladder functions after spinal cord injury or other neurological disorders. However, most of the neuroprostheses for bladder control are still imperfect due to lack of the feedback information about the state of the controlled bladder. The purpose of this study is to develop an implantable system which allows us to stimulate the nerves and record the nerve signals related to the condition of the bladder. The proposed stimulator consists of three parts: a digital-to-analog converter (DAC), a current driver, and a switch network. Using the same current source with a switch network eliminates the need for separate current sources for anodic and cathodic sections and reduce the need for interconnect lines of control signals which is an area-saved and power-efficient configuration. A symmetrical regulated cascode current driver is used to implement a high voltage compliance and a high output impedance which improves its ability with load. The amplitude, frequency and the pulse width of the stimulating current are adjusted by encoding the DAC and switch sequences, respectively. In addition, we also present two-stage fully differential capacitively-coupled amplifiers for neural recording. The neural amplifier's parameters are carefully chosen according to the characteristics of neural signal; meanwhile, we analyzed theoretically the main noise sources, especially the pseudo-resistor in the feedback path which gives little attention by previous studies. The integrated neural stimulating and recording frontend for bladder control prosthesis has been designed and simulated, using a TSMC's 0.18-μm CMOS process. The proposed stimulator can provide a symmetrical cathodic-first biphasic current pulse with interphasic gap, a low headroom voltage of 0.168 V corresponding to 2.48 mA full-scale current, an adjustable pulse width of 100---500 μs and frequency of 1---40 Hz. The recording amplifier with a low input-referred noise of 3.62 μV, an NEF of 3.88 and a low power dissipation of 7.2 μW has a gain of 61.6 dB and a frequency bandwidth from 300 Hz to 5.3 kHz. Both circuit analysis and simulations are presented to examine the performance of the proposed designs.

Design of a pulse-triggered four-channel functional electrical stimulator using complementary current source and time division multiplexing output method.

In this paper, a four-channel pulse-triggered functional electrical stimulator using complementary current source and time division output method is proposed for the research and application of functional electrical stimulation (FES). The high-voltage compliance and output impedance is increased by adopting the complementary current source, which can also realize the linear voltage-to-current conversion and high channel isolation. A high-voltage analog switch chip MAX14803, combined with a FIFO queue algorithm in the microprocessor, is used to setup the H-bridge and multiplexers for the four-channel time division multiplexing output. With this method, the size and cost of the key components are reduced greatly. The stimulating core circuit area is 30 × 50 mm(2). According to the experiments, the stimulator can achieve the four-channel charge-balanced biphasic stimulation with a current range between 0 and 60 mA and a single-phase pulse amplitude up to 60 V.

A programmable high-voltage compliance neural stimulator for deep brain stimulation in vivo.

Deep brain stimulation (DBS) is one of the most effective therapies for movement and other disorders. The DBS neurosurgical procedure involves the implantation of a DBS device and a battery-operated neurotransmitter, which delivers electrical impulses to treatment targets through implanted electrodes. The DBS modulates the neuronal activities in the brain nucleus for improving physiological responses as long as an electric discharge above the stimulation threshold can be achieved. In an effort to improve the performance of an implanted DBS device, the device size, implementation cost, and power efficiency are among the most important DBS device design aspects. This study aims to present preliminary research results of an efficient stimulator, with emphasis on conversion efficiency. The prototype stimulator features high-voltage compliance, implemented with only a standard semiconductor process, without the use of extra masks in the foundry through our proposed circuit structure. The results of animal experiments, including evaluation of evoked responses induced by thalamic electrical stimuli with our fabricated chip, were shown to demonstrate the proof of concept of our design.

A programmable low power current source for bioimpedance measurement: Towards a wearable personalized health assistant.

Bioimpedance is a noninvasive measurement method that facilitates body composition analysis, besides being indicative of many other health parameters. In this work a novel programmable, low complexity, high output impedance, high voltage compliance and wideband current source for bioimpedance applications is presented. Previously, we designed, fabricated and tested in vivo a bio-patch for acquisition of multiple bio-signals. Upon integration with our previous work, this circuit is envisioned to constitute part of a personalized health assistant. Simulation at worst case corners and real operation conditions was carried out using UMC-180 nm 1 poly 6 metal CMOS process. Full duty cycle, shortened or stepped square waves can be generated. Amplitude control of 8 different current levels is supported. Frequency can be tuned up to 1 MHz and an output impedance of 2.8 MO @ 250 KHz is achieved at full current capacity. Total current consumption is comparable to the injected current, making the circuit highly efficient.

A Neural Stimulator Frontend With High-Voltage Compliance and Programmable Pulse Shape for Epiretinal Implants

This paper presents an integrated neural stimulator with highly efficient and flexible frontend which is intended for an epiretinal implant with 1024 electrodes. It features programmable stimulation pulse shapes, a high-voltage (HV) output driver with compliance monitor for supply voltage adaptation, active and passive charge balancers, and electrode impedance measurement. Area and power efficiency is achieved by global timing assignment and local amplitude control over a bus at the local stimulation units. Major power savings in the distributed digital control units are realized by implementing global and local clock gating. Two stimulator frontends have been fabricated in a 0.35 μm HVCMOS process. Each frontend features four demultiplexed outputs and consumes 0.2 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> core area. A maximum voltage compliance of 20 V is achieved and up to 1 mA of output current can be adjusted with up to 50 dB dynamic range. In vitro experimental results performed on a platinum black electrode in 0.9% saline solution are given.

Low noise constant current source for bias dependent noise measurements

A low noise constant current source used for measuring the 1∕f noise in disordered systems in ohmic as well as nonohmic regime is described. The source can supply low noise constant current starting from as low as 1 μA to a few tens of milliampere with a high voltage compliance limit of around 20 V. The constant current source has several stages, which can work in a standalone manner or together to supply the desired value of load current. The noise contributed by the current source is very low in the entire current range. The fabrication of a low noise voltage preamplifier modified for bias dependent noise measurements and based on the existing design available in the MAT04 data sheet is also described.

A versatile multichannel direct-synthesized electrical stimulator for FES applications

Functional electrical stimulation (FES) has been applied to restore or maintain the muscle activity of paralyzed patients who suffer from spinal cord injuries and related neural impairments for several decades. In this paper, a direct-synthesized arbitrary waveform stimulator for multichannel FES applications is described. A novel element-envelope method is proposed for flexible waveform generation and implemented by a digital signal processor based system. We also designed an output circuit that can provide bi-phasic, voltage-controlled, constant-current outputs while keeping high-voltage compliance and wide signal bandwidth. High time-resolution and arbitrary stimulating waveforms can thus be synthesized, and more flexible closed-loop feedback controllers can be achieved. The proposed stimulator can be considered as a full-featured electrical stimulator for various FES applications with its flexibility in pattern generation and feedback processing capabilities.

A high performance CMOS compatible 8-bit current scaling D/A convertor

An 8-bit current scaling D/A convertor has been implemented in a standard 3 mu m p-well CMOS process. This convertor requires an active area of 1 mm/sup 2/ and is capable of operating at full scale currents ranging from 50 nA to 1 mA. High linearity at low full-scale (FS) currents is achieved by using CMOS compatible lateral bipolar transistors rather than MOS transistors or precision resistors to create the weighted currents. High switching speed is obtained at low current levels through improved current switch design. Test results show that differential nonlinearity is typically +or-0.1% FS, integral nonlinearity is +or-0.07% FS and the settling time is 35 ns. Two complementary output currents with high output impedance and high voltage compliance are provided.

A gated, high voltage iontophoresis system with accurate current monitoring

A circuit description for a multichannel constant current source for microiontophoresis is presented. The circuitry allows a high voltage compliance, accurate monitoring of ionotophoretic current without use of batteries, and automatic current neutralization. Drugs may be applied either manually or with an external digital gate signal. A monitor to detect current unbalance greater than a preselected level is also included.

High Voltage Compliance Constant Current Ballast

A ballast circuit employing a constant current diode and a vacuum tube that can provide a constant current over a voltage range of 1000 volts. The simple circuit can prove useful in studying voltage breakdown characteristics.