A High-Voltage Compliant Microelectrode Array Driver for Neuro Prosthesis: Effects of Process Variation

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1. INTRODUCTION
The loss of physiological functions can be restored partially or completely using functional electrical stimulation and this mechanism has been used in a number of biomedical devices such as the mo- tor nerves stimulator [1], pacemaker, urinary implant [2], and cochlear implant [3]. The advance in microelectronic technologies is allowing the researchers to engineer highly miniaturized implantable integrated microsystems [4]. Some of these implantable advanced prosthetic devices use intracorti- cal functional electrical microstimulation for recovering diseases such as Parkinson and epilepsy [5].
Another serious dysfunction, called blindness, may be caused by some diseases that affect the ocu- lar structures, such as
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Among these locations, retina and primary visual cortex are the most used ones. Retinal implants
[7] are used to treat only those diseases where the optic nerve and the central visual pathways remain undamaged. The second approach, intracortical implants, encompasses a large number of diseases to treat and this advantage has made this approach very attractive in visual prostheses. A large number of electrodes can be implanted in the primary visual cortex due to its large physical extent, which is expected to allow the restoration of a very high resolution visual function. Researchers have paid atten- tion to this area since the work of Brindley [8]. They have studied the visiotopic mapping between the stimulation sites and the phosphene positions in the visual field [9], the stimulation parameters [10] and chronic implantation of microelectrode arrays in the V1 area [11].
The general architecture for a visual prosthetic device involves processing the real world images by an image sensor and transmitting the data using radio frequency (RF) inductive link to the implantable device. Power is usually supplied by RF inductive link. The stimulation module, next, provides stimu- lation current based on the stimulation parameters to high-impedance microelectrode arrays using either monopolar or bipolar stimulation strategy to generate a specific phosphene pattern in the visual field.
Some common basic parameters, such as, complex electrode-tissue interface impedance

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