Stimulation and Artifact-Suppression Techniques for In Vitro High-Density Microelectrode Array Systems

Abstract

We present novel voltage stimulation buffers with controlled output current, along with recording circuits featuring adjustable high-pass cut-off filtering to perform efficient stimulation while actively suppressing stimulation artifacts in high-density microelectrode arrays. Owing to the dense packing and close proximity of the electrodes in such systems, a stimulation through one electrode can cause large electrical artifacts on neighboring electrodes that easily saturate the corresponding recording amplifiers. To suppress such artifacts, the high-pass corner frequencies of all available 2048 recording channels can be raised from several Hz to several kHz by applying a “soft-reset” or pole-shifting technique. With the implemented artifact suppression technique, the saturation time of the recording circuits, connected to electrodes in immediate vicinity to the stimulation site, could be reduced to less than 150 μs. For the stimulation buffer, we developed a circuit, which can operate in two modes: either control of only the stimulation voltage, or control of current and voltage during stimulation. The voltage-only controlled mode employs a local common-mode feedback operational transconductance amplifier with a near rail-to-rail input/output range, suitable for driving high capacitive loads. The current/voltage controlled mode is based on a positive current conveyor generating adjustable output currents, while its upper and lower output voltages are limited by two feedback loops. The current/voltage controlled circuit can generate stimulation pulses up to 30 μA with less than ±0.1% linearity error in the low-current mode, and up to 300 μA with less than ±0.2% linearity error in the high-current mode.

Real-Time Artifact Removal System for Surface EMG Processing During Ten-Fold Frequency Electrical Stimulation

“…As a result, the direct artifact may be many orders of magnitude larger than the underlying EMG. Therefore, the main challenge in vEMG recording during FES is that high voltage stimulation pulses generate immense amplitude interference accompanied with broadband spectrum distribution mixing with EMG [11][12][13]. In addition, the large amplitude stimulation pulses cause the recording amplifier to saturate rapidly and cannot be fully recovered during the interval [14].…”

Anti-artifacts techniques for neural recording front-ends in closed-loop brain-machine interface ICs

“…Similar to Blanking technology, soft-reset technology also uses the periodicity of artifacts to shield them ( Liu et al, 2016 ; Viswam et al, 2016 ; Shadmani et al, 2019 ; Erbsloh et al, 2021 ). The difference is that blanking technology performs shielding in the time domain, while soft-reset technology performs shielding in the frequency domain.…”

Overcoming temporal dispersion for measurement of activity-related impedance changes in unmyelinated nerves

“…Since the membrane of nerve fibres is more resistive than the surrounding connective tissue and physiological solution interface, part of the current applied during stimulation will flow through the conductive pathways along the nerve and an increase in the potential will be therefore measured by the recording electrodes (figure 5). In addition, the voltage generated by the stimulation current is usually orders of magnitude higher than the recorded physiological voltages, so, the insufficient input range of the amplifier or small charge imbalance between stimulation electrodes may lead to saturation of the recording circuits which can last significantly longer than stimulation pulse itself [46,47]. To avoid saturation in the current study, charge-balanced biphasic stimulation was used together with an actiCHamp amplifier (Brainproducts GmbH, Gilching, Germany) having a wide input range of ±400 mV [16].…”