Challenges in Realizing a Chronic High-Resolution Retinal Prosthesis - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 147

Conclusions
We have examined several challenges in the electronics design toward the imple-
mentation of chronic high-resolution retinal prosthesis. The key challenges are
to reduce power consumption, provide more flexibility, and reduce the size.
As seen through the examples in the above sections, solving these challenges
often involve direct tradeoffs among themselves. The stimulator circuit faces
the challenge of providing maximum flexibility, which increases the power
and area. The power telemetry faces the challenge of increase in area in the
form of off-chip components like coil, diode and capacitor, while maintaining a
high efficiency and long battery life. The data telemetry faces the challenge of
supporting high data rate for maximum flexibility hence requiring an additional
coil pair. A system design is highly critical in realizing a chronic high-resolution
retinal prosthesis, during which the above tradeoffs should be considered to
make the suitable choices. In addition to the design of the electronics, the choice
of technology for implementing the circuits deserves careful attention. A small
feature size technology with more metal layers is preferred to reduce the size
of the IC. This in turn requires the stimulation voltages to be small enough to
allow the use of such a process technology. This also poses challenge for circuit
design to accommodate high voltages. Passive components such as the storage
capacitor, coils, and active components such as the back telemetry switch are
difficult to implement in an IC. Off-chip versions of these components, which
can lend themselves to be integrated with the ICs through post-processing on
the surface of the IC, are highly preferred over components that require to be
connected using wires.
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