A Fully Testable Retinal Implant

A. Dollberg, H.G. Graf, B. Höfflinger, W. Nisch, J.D. Schulze Spuentrup, K. Schumacher, an

Keywords

Retinal Implant, Visual Prosthesis , Testability, Environmental Qualification

Abstract

A new retinal implant circuit is presented. It consists of 1500 analog amplifier cells. The local illumination and the medium illumination across the whole implant are compa red and output impulses are generated by means of 1500 analog amplifiers. It is necessary to consider many electri cal requirements to avoid any harm to the retinal tissue. The amplifiers must work according to the biological con ditions to achieve a successful stimulation of the retina. To supply the right amount of charge and voltage for stimula tion they must be designed carefully. Thus the characteri zation and the testability of the amplifiers after production plays a major role in development of the retinal implant. Usually there is a need of additional test circuitry which allows the selection of each amplifier cell separately and connects the test signals to the amplifiers. Only in this way it is possible to qualify each amplifier of the circuit. Unfor tunately the test circuitry uses much additional chip area and reduces the active area of the retinal implant. In the in troduced implant a test circuitry for selection and charac terization of each amplifier cell is implemented at the edge of the implant. This circuitry can be used for tests on wafer level and it is cut off after characterization of the implant. In this way the area is minimized. The circuit was implemented in a 0.8m p-well CMOS pro cess. Chip-photos and an exemplary measurement are pre sented.

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