A. Dollberg, H.G. Graf, B. Höfflinger, W. Nisch,
J.D. Schulze Spuentrup, K. Schumacher, an
Retinal Implant, Visual Prosthesis , Testability,
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