gms | German Medical Science

We have developed monolithic package of the artificial retina with liquid crystal polymer (LCP) and successfully showed its feasibility in the animal study. However, due to the availability of the medical-quality LCP, we investigated other material for the hermetic package. Cyclic olefin copolymer (COC) is a relatively new material with excellent properties for implantable devices. We were able to successfully fabricate planar neural electrode and confirmed its biocompatibility and performance by cytotoxicity test and elution test, and impedance analysis, respectively. With our findings, we are currently integrating wireless data/power transfer module and stimulation chip to our new COC packaging for artificial retina. For the wireless data/power transfer, near field wireless transmission scheme was selected due to its distinct advantages over biological tissues. With series tuned primary coil and parallel tuned secondary coil, reasonable coil parameters values were achieved even with low coupling factor between the two inductors. Class-D power amplifier and butterworth 2nd low pass filter were followed after non-overlapping clock generator to attain enough power for current stimulation. Rectifier and Dickson charge pump were also designed to provide driving voltage to the stimulator. For data transmission, pulse delay modulation scheme was chosen to detect time delay between each data beat for high data rate and efficiency. Finally, we are designing an optimal circuit suitable for retinal stimulation parameters that has been accumulated by many studies. Multi-channel sharing and demultiplexer were used to optimize the performance of a single stimulator to drive multi-channel electrode, and the layout was design to minimize crosstalk. In addition, finite state machine was used in place of the conventional SIC protocol for providing received data to the digital controller of the stimulator to reduce power consumption.