16-Channel biphasic current-mode programmable charge balanced neural stimulation

Abstract

BackgroundNeural stimulation is an important method used to activate or inhibit action potentials of the neuronal anatomical targets found in the brain, central nerve and peripheral nerve. The neural stimulator system produces biphasic pulses that deliver balanced charge into tissue from single or multichannel electrodes. The timing and amplitude of these biphasic pulses are precisely controlled by the neural stimulator software or imbedded algorithms. Amplitude mismatch between the anodic current and cathodic current of the biphasic pulse will cause permanently damage for the neural tissues. The main goal of our circuit and layout design is to implement a 16-channel biphasic current mode programmable neural stimulator with calibration to minimize the current mismatch caused by inherent complementary metal oxide semiconductor (CMOS) manufacturing processes.MethodsThis paper presents a 16-channel constant current mode neural stimulator chip. Each channel consists of a 7-bit controllable current DAC used as sink and source current driver. To reduce the LSB quantization error and the current mismatch, an automatic calibration circuit and flow diagram is presented in this paper. There are two modes of operation of the stimulator chip—namely, stimulation mode and calibration mode. The chip also includes a digital interface used to control the stimulator parameters and calibration levels specific for each individual channel.ResultsThis stimulator Application Specific Integrated Circuit (ASIC) is designed and fabricated in a 0.18 μm High-Voltage CMOS technology that allows for ±20 V power supply. The full-scale stimulation current was designed to be at 1 mA per channel. The output current was shown to be constant throughout the timing cycles over a wide range of electrode load impedances. The calibration circuit was also designed to reduce the effect of CMOS process variation of the P-channel metal oxide semiconductor (PMOS) and N-channel metal oxide semiconductor (NMOS) devices that will result in charge delivery to have less than 0.13% error.ConclusionsA 16-channel integrated biphasic neural stimulator chip with calibration is presented in this paper. The stimulator circuit design was simulated and the chip layout was completed. The chip layout was verified using design rules check (DRC) and layout versus schematic (LVS) design check using computer aided design (CAD) software. The test results we presented show constant current stimulation with charge balance error within 0.13% least-significant-bit (LSB). This LSB error was consistent throughout a variety stimulation patterns and electrode load impedances.

Wired for Success: Probing the Effect of Tissue-Engineered Neural Interface Substrates on Cell Viability

“…This stimulation mimics standard square wave charge balance current stimulation used in many devices such as cochlear implant 36,37 and deep brain stimulators. 38 Here, voltage transient measurements (VTM) were employed to analyze the capacitance density of electrodes, essential for understanding their efficiency and stability. Therefore, VTM was collected daily before each stimulation cycle or after the three cycles of electrical stimulation.…”

“…Square wave stimulation, a standard in bioelectronic applications, plays a crucial role in assessing the electrode performance. This stimulation mimics standard square wave charge balance current stimulation used in many devices such as cochlear implant , and deep brain stimulators . Here, voltage transient measurements (VTM) were employed to analyze the capacitance density of electrodes, essential for understanding their efficiency and stability.…”

First Steps Towards Designing Electrotactons: Investigating Intensity and Pulse Frequency as Parameters for Electrotactile Cues

“…This has been done by manipulating pulse frequency, pulse width amplitude, and type of electrical current. The electrical current can be biphasic which is a positive current (anodic) followed by an equal negative current (cathodic) to maintain the current balance, or monophasic which is either positive or negative current [26]. When a higher current intensity is used, it becomes electrical muscle stimulation (EMS) which has also been used for interaction [27].…”

Neurostimulators for high-resolution artificial retina: ASIC design challenges and solutions

“…On the contrary, the current size mismatch is unavoidable because of the process variation during fabrication. Fortunately, adopting proper analog layout techniques, the current size mismatch of the current mirror between cathodic pulse and anodic pulse can be repressed under 2% [66,67]. Nonetheless, a careful calculation is needed to verify if this mismatch level is compatible with passive discharging.…”