title: Redundant safety features in a high-channel-count retinal neurostimulator.
abstract: Safety features embedded in a 256-channel retinal prosthesis integrated circuit are presented. The biology of the retina and the electrochemistry of the electrode-tissue interface demand careful planning and design of the safety features of an implantable retinal stimulation device. We describe the internal limits and communication safety features of our ASIC, but we focus on monitoring and protection circuits for the electrode-tissue interface. Two independent voltage monitoring circuits for each channel measure the electrode polarization voltage at two different times in the biphasic stimulation cycle. The monitors ensure that the charged electrode stays within the electrochemical water window potentials, and that the discharged electrode is within a small window near the counter electrode potential. A switch to connect each electrode to the counter electrode between pulses protects against a wide range of device failures. Additionally, we describe work on an active feedback system to ensure that the electrode voltage is at zero.
authors.affiliation: Department of Veterans Affairs and Carnegie Mellon University, Pittsburgh, PA, USA, skkelly@cmu.edu.
authors.forename: Shawn K
authors.initials: SK
authors.lastname: Kelly
authors.affiliation: Analog Circuit Works, Sudbury, MA, USA.
authors.forename: William F
authors.initials: WF
authors.lastname: Ellersick
authors.affiliation: Carnegie Mellon University, Pittsburgh, PA, USA.
authors.forename: Ashwati
authors.initials: A
authors.lastname: Krishnan
authors.affiliation: Harvest Automation, Billerica, MA, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Doyle
authors.affiliation: Cornell University, Ithaca, NY, USA.
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Shire
authors.affiliation: Massachusetts Institute of Technology, Cambridge, MA, USA.
authors.forename: John L
authors.initials: JL
authors.lastname: Wyatt
authors.affiliation: Massachusetts Eye and Ear Infirmary, Boston, MA, USA.
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Rizzo
keywords: Biomedical engineering; biomedical electrodes; integrated circuit design; retinal implant; retinal prosthesis