A charge balancing technique for neurostimulators
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A charge balancing technique for neurostimulators Zhuangguang Chen1 • Xu Liu1 • Zheng Wang1 Received: 22 May 2020 / Revised: 23 August 2020 / Accepted: 26 September 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract A charge balancing technique that is applicable to dual-edge current nerve stimulators is proposed herein, which is primarily directed to achieving charge balance by controlling discharge times. Compared to the charge balancing technique proposed in other papers, the number of single-cycle imbalanced charges is less than 15 pC. In order to reduce the amount of imbalanced charge, indirect shunt technology, leakage current compensation technology and offset voltage compensation technology was proposed in this paper to build up a synchronization system. To ensure that the neural stimulator can still be in charge balance after performing multiple stimulation cycles, a short pulse insertion technique is applied to the circuit. The circuit was designed based on the TSMC 180 nm process and verified its functionality under the Cadence platform. Keywords Charge balancing technique Leakage current compensation Stimulators IC design
1 Introduction For some neurological diseases, the use of functional electrical stimulation (FES) is extremely effective [1]. As an example, for some patients with brain injury, blindness, or spinal damage, FES therapy with a neurostimulator can restore brain function [2], vision [3], and even spine function [4, 5] to such patients. There are three types of functional electrical stimulation treatments: switched capacitor stimulation [6, 7], voltage controlled stimulation [8, 9], and constant current stimulation [10, 11]. The voltage-controlled stimulation can make the electrode reaching the target potential, thereby achieving the purpose of stimulation. However, due to the resistance between the electrode and the nerve cell tissue is different in different stages, the amount of charges which are inject into the electrode cannot be determined. Therefore, using voltage-controlled stimulation is not safe. The switched capacitor stimulation method can accurately control the amount of charges which are inject into the electrode, therefore it is a safer stimulation method.
& Xu Liu [email protected] 1
College of Microelectronics, Beijing University of Technology, Beijing, China
However, for the reason that the capacitance’s area is large and cannot be integrated on a small chip, this method is not used in the design of neural stimulators with multiple stimulation channels. The constant current stimulation method uses the DC current source to charge and discharge the electrode. After the current amplitude and duration were determined, the amount of charge on the electrode can be controlled more accurately. In addition, large-scale integration can be easily performed by using the current source. Therefore, there are a lot of current neurostimulator designs use constant current stimulation. Due to the process errors and the other
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