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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 [1]. This paper presents the design, integrated circuit (IC) implementation and measurement results of a power...
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... value of current is used, then the value of the resistance needs to increase proportionally. Hence, the time constant associated with the charging and discharging of the parasitic gate-to-source capacitance of Transistor M P also increases proportionally. This makes Switch M P slower to be turned on and off, which directly impacts the efficiency. Fig. 5 shows the cross section view of the PMOS thickdrain transistor used in this design. Its rating voltages are V SGM AX = 2 V, V SDM AX = 20 V. The parasitic diode highlighted in green is of relevant interest for the designer. The diode always needs to be reversed biased. Since the source terminal is usually connected to the bulk ...
Context 2
... Its rating voltages are V SGM AX = 2 V, V SDM AX = 20 V. The parasitic diode highlighted in green is of relevant interest for the designer. The diode always needs to be reversed biased. Since the source terminal is usually connected to the bulk terminal, the sourceto-drain voltage always needs to be positive. This makes the device shown in Fig. 5 non symmetrical with respect to its source and drain terminals. In literature such device is often called Lateral Double-Diffused MOSFET ...
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Resonant and quasi-resonant dc-dc converters have been introduced to increase the operating frequency of switching power converters, with advantages in terms of performance, cost and/or size. In this paper, we focus on class-E resonant topologies and we show that about twenty different architectures proposed in the last three decades can be reduced...
Citations
... Most approaches focus on stimulation patterns used to excite neural activity and, therefore, on frequencies below 500 Hz. These can be divided into CB methods that modify the stimulation pattern in timing [4] or amplitude [10,11], when there is access to its programmability, and CB methods that inject charge in addition to the stimulation pulse [12]. A popular method of charge injection is pulse insertion, as described in [5]. ...
Safety is a critical consideration when designing an electrical neural stimulator, given the direct contact with neural tissue. This paper presents the design of a charge balancing system suitable for frequencies up to the kilohertz domain, to be used as an add-on system for stimulators over a wide range of frequencies, also covering nerve conduction blocking. It operates independently of the stimulator timing by continuously sensing the offset voltage, and applying a corrective current to the electrode, using the offset compensation technique. To ensure its stand-alone capability, the system is battery-powered, and includes a safety and start-up circuit. Electrical measurements verified the functionality of the circuit, demonstrating a residual offset of only 0.7 mV for 1 V biphasic pulses at 50 kHz. When tested for 20 kHz biphasic pulse at a 5 V amplitude, the offset was measured at-11.6 mV, which is still within the (commonly used) ±50 mV safety window.
... To address this concern, several supply voltage scaling methods have been proposed in the literature [7]- [15]. Notably, in [8] and [7], the supply voltage level is modulated to achieve a controlled current and eliminate the need for current drivers. However, both of these works are based on inductive converters and thus require external components, and have no/limited support for multi-channel scenarios and arbitrary stimulation waveforms. ...
This paper presents a novel multi-channel stimulation backend with a multi-bit delta-sigma control loop, which enables precise adjustment of the stimulation current through modulation of the supply voltage. This minimizes the overhead voltage of series circuitry to the stimulation load and avoids the associated energy loss. Additionally, to address the bandwidth limitations commonly encountered in battery-less implants, we propose incorporating amplitude and duration scaling of the arbitrary stimulation waveform. The waveform is programmable with 64 7-bit samples and 4 scaling factors per channel, resulting in a minimum of 68% data reduction per channel compared to using the waveform without scaling. The proposed circuits are designed and simulated in 180nm BCD technology occupying a total silicon area of 9mm 2. The fully integrated backend has a minimum compliance voltage of 8.5V and features a switched-capacitor multi-output DC-DC converter (MODDC) with pulse-skipping capability, a CMOS-only high-voltage (HV) multiplexer, and a unique HV H-bridge. Programming a sine-wave stimulus with a 4mA amplitude and a duration of 256µs achieved a signal-to-noise ratio of 40dB within a 10kHz bandwidth. For the same waveform, power efficiencies of 94% and 68% were observed without and with MODDC, respectively. Additionally, when programming constant-current stimuli ranging from 0.26mA to 4mA, high efficiencies of 78-97% and 23-79.4% were achieved without and with MODDC, respectively.
... Most of the devices operate at low voltages (i.e., lower than 1 V) with power supply of diverse batteries [5]. The effective input voltage converted by battery is regulated by power management units to support reliable system operations with less power consumption [6], [7]. Therefore, power management unit (PMU) should be well designed to provide better regulating performances and lower quiescent currents [8], [9], especially the demand for sustainable and stable power supply with low area on the flexible printed circuit board (FPCB) has been ever-increasing on the wearable electronic system-on-chip [10], [11]. 1 shows the universal block diagram of (a) a respiration sensing system and (b) its interface circuit with low-dropout voltage regulators (LDOs). ...
In this study, a 0.8-V-
$V_{in}$
200-mA-
$I_{o}$
capless low-dropout voltage regulator (LDO) is developed for a wireless respiration monitoring system. The biaxially driven power transistor (BDP) technique is proposed in the LDO, with a current driven stimulation on the bulk and a voltage on the gate terminal. With the BDP technique, an adaptively biased current-driven loop (ABCL) is designed which can reduce the high threshold voltage of power transistor, thus presenting lower input voltage and reduced power consumption. Moreover, this loop can provide an improved dynamic response due to its increased discharging current. Based on an error amplifier with enhanced DC gain and gain bandwidth, the capless LDO achieves superior power supply rejection (PSR) and stability without a complex frequency compensation mechanism. The proposed LDO is fabricated in the SMIC 180 nm process with a chip area of 0.046 mm
$^{2}$
. Measurement results indicate that this LDO can obtain a 200-mA load current range and greater than -66 dB PSR up to 1 kHz at a supply voltage as low as 0.8 V.
... A possible solution to reduce the overhead losses in CMS is dynamic voltage scaling (DVS) [8][9][10][11][12][13][14][15]. In DVS, the supply voltage is dynamically scaled to minimize the voltage drop across the current driver. ...
... The first method scales the supply voltage by modulating the incoming AC power signal [8,9]. The second method uses (on-chip) adaptive DC/DC converters, for example, inductive buck/ boost converters [10,11] or switched-capacitor charge pumps [12][13][14][15]. The signal modulation and inductive DC/DC converter approaches benefit from a continuous output voltage range but suffer from limited scalability. ...
Power efficiency in electrical stimulator circuits is crucial for developing large-scale multichannel applications like bidirectional brain-computer interfaces and neuroprosthetic devices. Many state-of-the-art papers have suggested that some non-rectangular pulse shapes are more energy-efficient for exciting neural excitation than the conventional rectangular shape. However, additional losses in the stimulator circuit, which arise from employing such pulses, were not considered. In this work, we analyze the total energy efficiency of a stimulation system featuring non-rectangular stimuli, taking into account the losses in the stimulator circuit. To this end, activation current thresholds for different pulse shapes and durations in cortical neurons are modeled, and the energy required to generate the pulses from a constant voltage supply is calculated. The proposed calculation reveals an energy increase of 14-51% for non-rectangular pulses compared to the conventional rectangular stimuli, instead of the decrease claimed in previous literature. This result indicates that a rectangular stimulation pulse is more power-efficient than the tested alternative shapes in large-scale multichannel electrical stimulation systems.
... Furthermore, even within a single channel, in the course of a conventional rectangular stimulus, the required compliance will vary over time due to the capacitive-resistive nature of the ETI. These issues have been addressed in the literature by adjusting the supply voltage to the required voltage compliance at the output stage [3]- [7], [9], or by generating the output current from defluxing an inductor without an intermediate voltage [8]. ...
... As illustrated in Fig. 1.c, [7] proposes directly driving the electrodes with an inductive buck-boost converter and controlling it through closed-loop sensing of the ETI's instant voltage and current. Alternatively, in [8] (Fig. 1.d), an open-loop approach is chosen to charge an inductor with the target current and periodically discharge it to the tissue. While an inductive approach benefits from continuous resolution for generating the voltage and current required at the output stage, it comes at the expense of off-chip inductor(s) and more limited MRI compatibility. ...
... Thus, in the case of multiple channels demanding different supply levels simultaneously, either the adaptive circuit needs to be duplicated per channel (Fig. 1.c), or the supply rail has to adapt to the highest required level, which would not be optimized for other channels ( Fig. 1.a&e). To avoid this, [8] has proposed high-frequency interleaving of ultra-high frequency pulsed stimuli (UHFPS) between multiple channels ( Fig. 1.d) at the cost of longer stimulation duration or higher amplitude for the highfrequency pulsed stimuli. Alternatively, a multi-output charge pump has been proposed in [4] (Fig. 1.f), where each channel connects to one of the charge pump outputs based on its instant voltage/current requirement, independent of other channels. ...
In neuromodulation applications, conventional current mode stimulation is often preferred over its voltage mode equivalent due to its good control of the injected charge. However, it comes at the cost of less energy-efficient output stages. To increase energy efficiency, recent studies have explored non-rectangular stimuli. The current work highlights the importance of an adaptive supply for an output stage with programmable non-rectangular stimuli and accordingly proposes a system-level architecture for multi-channel stimulators. In the proposed architecture, a multi-output DC/DC Converter (DDC) allows each channel to choose among the available supply levels (i.e., DDC outputs) independently and based on its instant voltage/current requirement. A system-level analysis is carried out in Matlab to calculate the possible energy savings of this solution, compared to the conventional approach with a fixed supply. The energy savings have been simulated for a variety of supply levels and waveform amplitudes, suggesting energy savings of up to 83% when employing 6 DDC outputs and the lowest current amplitude explored (250 µA), and as high as 26% for a full-scale amplitude (4 mA).
... FOM evaluation versus tissue safety criterion [32] of current trends in stimulation.(♯1: [33], ♯2: [34], ♯3: [35], ♯4: [36], ♯5: [37], ♯6: [38]). ...
... A large majority aim to improve energy efficiency, by replacing standard topology with switched mode DC-DC converter architecture. In [38], the authors propose an inductor-based buck-boost DC-DC converter which does not require an external output capacitor. This is made possible by replacing the biphasic waveform with high-frequency pulses. ...
... A large majority aim to improve energy efficiency, by replacing standard topology with switched mode DC-DC converter architecture. In [38], the authors propose an inductorbased buck-boost DC-DC converter which does not require an external output capacitor. This is made possible by replacing the biphasic waveform with high-frequency pulses. ...
Electrical stimulation of the nervous system is commonly based on biphasic stimulation waveforms, which limits its relevance for some applications, such as selective stimulation. We propose in this paper a stimulator capable of delivering arbitrary waveforms to electrodes, and suitable for non-conventional stimulation strategies. Such a system enables in vivo stimulation protocols with optimized efficacy or energy efficiency. The designed system comprises a High Voltage CMOS ASIC generating a configurable stimulating current, driven by a digital circuitry implemented on a FPGA. After fabrication, the ASIC and system were characterized and tested; they successfully generated programmable waveforms with a frequential content up to 1.2 MHz and a voltage compliance between [−17.9; +18.3] V. The system is not optimum when compared to single application stimulators, but no embedded stimulator in the literature offers an equivalent bandwidth which allows the wide range of stimulation paradigms, including high-frequency blocking stimulation. We consider that this stimulator will help test unconventional stimulation waveforms and can be used to generate proof-of-concept data before designing implantable and application-dedicated implantable stimulators.
... It should be noted that high-frequency (> 1 kHz) stimulation can also block the action potential propagation. Although electrical stimulation can be accomplished by means of voltage, current, and charge [17], [19], [20], most stimulators use current sources to build up and remove the charge from the tissue. A generic biphasic, constant current stimulation setup is shown in Figure 6. ...
... Traditionally, the driver circuits of these electrodes are operated from a single high-voltage supply [17], [18], degrading the overall power efficiency as not all electrodes develop the same voltage; as a consequence, a lot of voltage headroom is being wasted. Therefore, the best power efficiency of multichannel stimulator circuits cannot be achieved by driving every electrode from its own (current or voltage) driver circuit but rather by using an ultrahigh-frequency (UHF) pulse-based technique that builds up the right amount of charge at every electrode via rapid (e.g., 1-ns duration) current pulses [19]. In such a UHF pulse-based current-stimulator circuit, each stimulation phase is produced from a sequence of current pulses injected into the tissue at a high rate. ...
The total economic cost of neurological disorders exceeds £100 billion per annum in the United Kingdom alone, yet pharmaceutical companies continue to cut investments due to failed clinical studies and risk [1]. These challenges motivate an alternative to solely pharmacological treatments. The emerging field of bioelectronics suggests a novel alternative to pharmaceutical intervention that uses electronic hardware to directly stimulate the nervous system with physiologically inspired electrical signals [2]. Given the processing capability of electronics and precise targeting of electrodes, the potential advantages of bioelectronics include specificity in the time, method, and location of treatment, with the ability to iteratively refine and update therapy algorithms in software [3]. A primary disadvantage of the current systems is invasiveness due to surgical implantation of the device.
This article proposes an inductor-charging switched-capacitor stimulation (iSCS) system capable of high-efficiency capacitor charging and high-efficacy decaying exponential stimulation. The iSCS system adopts a fast inductor-based charger with level-adaptive duty modulation and charging range detection that can efficiently charge capacitors from any residual voltage levels to the target voltages up to 3 V. The offset-control charge balancing (OC-CB) adaptively reduces the mismatch between cathodic and anodic charges. The iSCS prototype can charge 1-
$\mu$
F capacitor from 0 V (1.5 V) to 3 V within 50
$\mu$
s (28
$\mu$
s), achieving 90% (92.7%) capacitor charging efficiency. The iSCS system efficiency was measured up to 92%, which is
$>$
10% higher than state-of-the-art works. The iSCS also achieved higher stimulus efficacy thanks to its decaying exponential waveform. In vivo experiments for ocular muscle stimulation using the iSCS system resulted in a 20% increase in eye movement distance while consuming 13% less energy compared to the current-controlled stimulation system. This ensures higher system efficiency and enhanced stimulus efficacy.
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
${\mu}$
V
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(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.
This article proposes a neural stimulation integrated circuit design with multiple current output modes. In the cathodic stimulation phase and anodic stimulation phase, each output current waveform can be independently selected to either exponential waveform or square wave, so the stimulator holds four stimulation modes. To minimize the headroom voltage of the output stage and enhance the power efficiency of the proposed stimulator, we introduce the exponentially decaying current which is realized by the exponential current generation circuit in this work. It can enhance the longer duration of the stimulation pulse as well. In case the residual charge may cause harm to patients, a charge balancing technique is implemented in this work for all operation modes. The four-channel stimulator IC is implemented in a 180-nm CMOS process, occupying a core area of 1.93 mm
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. The measurement results show that the proposed stimulator realized a maximum power efficiency of 91.3% and the maximum stimulation duration is 3 times larger than previous works. Moreover, even in exponential output waveform mode, the maximum residual charge in a single cycle is only 255 pC due to the proposed charge balancing technique. The experiment results based on the PBS solution also show that the stimulator IC can remove residual charges within 60 μs, and the electrode voltage remains stable within a safe range under multicycle stimulation.
