gms | German Medical Science

Artificial Vision 2013

The International Symposium on Visual Prosthetics

08.11. - 09.11.2013, Aachen

High Frequency Pulse-Density Modulated Switched-Capacitor Based Functional Electrical Stimulation of Retinal Bipolar Cells

Meeting Abstract

  • Abdel Moneim Marzouk - Universität Duisburg-Essen, Fachgebiet Elektronische Bauelemente und Schaltungen, Duisburg, Germany
  • A. Stanitzki - Fraunhofer IMS Duisburg, Germany
  • R. Kokozinski - Universität Duisburg-Essen, Fachgebiet Elektronische Bauelemente und Schaltungen, Duisburg, Germany

Artificial Vision 2013. Aachen, 08.-09.11.2013. Düsseldorf: German Medical Science GMS Publishing House; 2014. Doc13artvis09

doi: 10.3205/13artvis09, urn:nbn:de:0183-13artvis095

Published: February 13, 2014

© 2014 Marzouk et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.



Objective: To introduce a high frequency electrical stimulation mechanism tailored to stimulate retinal bipolar cells.

Materials and Methods: The decreasing size of stimulation electrodes results in a higher impedance of the electrode due to the reduced surface area. This makes current-controlled stimulation unsafe as the stimulus current pulse could easily force the electrode potential to exceed the water window. Voltage-controlled stimulation has no control over the amount of charge injected into the tissue because the stimulus current is not controlled. For such a situation, the pulse-density modulated switched-capacitor based stimulation (PDM-SCS) has been engineered. The technique cyclically charges a capacitor to a predetermined voltage that is then discharged into the tissue every cycle. By pre-charging a capacitor to a predefined voltage it can be guaranteed that the electrode potential is maintained within the water window. The amount of charge injected is controlled by the size of the capacitor. The slow wave response of bipolar retinal cells to an electrical stimulus mimics the electrical behavior of a low-pass filter. The proposed PDM-SCS approach utilizes such low-pass behavior by injecting the required stimulus charge in the form of high frequency pulses in relation to the membrane properties. The injected charge and the resolution of the stimulus amplitude are controlled through the capacitor charge voltage and modulator sampling frequency.

Discussion: The PDM-SCS stimulation chip is designed, and is currently being fabricated and prepared for evaluation in clinical investigations.

Acknowledgement: This work was supported by the Deutsche Forschungsgemeinschaft (DFG) funding the project (PAK 468).