Implantable System for Long- and Short-Term Active Charge Balancing in Neural Electrical Stimulation
Final Report Abstract
The electrostimulation (FES and FNS) is already successfully used in many applications. In this context, the issue of charge balancing for safe stimulation is very important and essential especially in chronic stimulation experiments. In this project, charge balancing circuits have been developed which can be combined with a wide range of CMOS integrated neural stimulators. This requires a high degree of adaptability and flexibility. For this reason, the charge balancing circuits offer adjustable safety limit ranges and output current limits as well as adaptive high voltage compatibility up to 38 V. General requirements for implantable systems, such as low power consumption and small chip area, were also given high priority. The main design and implementation challenge was to minimize the power consumption and overcome the high voltage limitations of the available CMOS process. All circuits were designed in a 0.35 μm High-Voltage CMOS process and characterized using transistor-level simulations. They were also verified after fabrication by measurements in the lab using an electrical model of the electrode as well as in vitro measurements. In detail, two complementary (cause-based and consequence-based) charge balancing methods were developed for different stimulation goals, i.e., for long- and short-term experiments. Each method represents a self-contained control loop that has been investigated for stability. Both control loops can be operated independently, but improve their effectiveness when used in combination. Here, the main challenge was to combine the two control loops, resulting in a MIMO system. The behavior of the latter was analyzed through simulation and measurements. Proof of concept and further validation tests were performed under laboratory conditions. The combination of the charge balancing ASIC with a CMOS integrated nerve stimulator developed at the Fritz Hüttinger Chair of Microelectronics to a small device, gave us the opportunity to perform in-vitro validations and demonstrations as well. Support for the in-vitro setup was provided by the cooperation with the Laboratory for Biomedical Microtechnology - IMTEK and the Neuroloop GmbH.
Publications
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22.6 A 22V compliant 56µW active charge balancer enabling 100% charge compensation even in monophasic and 36% amplitude correction in biphasic neural stimulators. 2016 IEEE International Solid-State Circuits Conference (ISSCC), 390-391. IEEE.
Butz, Natalie; Taschwer, Armin; Manoli, Yiannos & Kuhl, Matthias
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Intra-Pulse Charge Control, EP 3 100 766 B1, 27.12.2017 US 10,166,399 B2
N. Butz, M. Kuhl & Y. Manoli
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A 22 V Compliant 56 μ W Twin-Track Active Charge Balancing Enabling 100% Charge Compensation Even in Monophasic and 36% Amplitude Correction in Biphasic Neural Stimulators. IEEE Journal of Solid-State Circuits, 53(8), 2298-2310.
Butz, Natalie; Taschwer, Armin; Nessler, Sebastian; Manoli, Yiannos & Kuhl, Matthias
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A Charge Balanced Neural Stimulator with 3.3 V to 49 V Supply Compliance and Arbitrary Programmable Current Pulse Shapes. 2018 IEEE Biomedical Circuits and Systems Conference (BioCAS), 1-4. IEEE.
Taschwer, Armin; Butz, Natalie; Kohler, Manuel; Rossbach, Daniel & Manoli, Yiannos
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Active Charge Balancer with 6.6 to 40 V Quad-Rail Power Supply Compliance for Neural Stimulators. 2018 IEEE International Symposium on Circuits and Systems (ISCAS), 1-4. IEEE.
Butz, Natalie; Kalita, Utpal; Kuhl, Matthias & Manoli, Yiannos
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Active Charge Balancer With Adaptive 3.3 V to 38 V Supply Compliance for Neural Stimulators. IEEE Transactions on Circuits and Systems I: Regular Papers, 68(10), 4013-4024.
Butz, Natalie; Kalita, Utpal & Manoli, Yiannos
