Biomedical Engineering Reference
In-Depth Information
be.shared.globally,.such.as.packet.header.detector,.packet.parser,.error.detector,.and.clock.
divider,.are.implemented.in.a.global.digital.controller.(GDC)..An.on-chip.network.gener-
ates.pixel.addresses.and.distributes.the.data.from.the.GDC.to.individual.pixels..Each.pixel.
has.a.copy.of.the.local.digital.controller.(LDC),.which.generates.stimulation.waveform.pat-
terns.according.to.the.data.input..To.reduce.the.power.consumption.of.LDCs,.a.program-
mable.low-frequency.clock.is.utilized.to.reduce.unnecessary.transitions.
A.large.number.of.bonding.pads.bridging.circuitry.and.electrodes.is.required.for.a.high-
density. stimulator. array.. This. imposes. additional. dificulties. in. system. integration. and.
realization..A.circuit.under.pad.(CUP).structure,.which.is.compatible.with.lip-chip.bond-
ing.technology,.is.used.to.facilitate.system.integration..In.the.CUP.structure,.an.area.pad.
is.made.of.the.top.three.metal.layers,.under.which.an.ESD.protection.circuit,.a.charge.can-
celation.switch,.and.part.of.a.current.driver.are.inserted..As.a.result,.the.size.of.a.pixel.with.
the.CUP.structure.is.reduced.by.13.5%,.compared.with.one.without.the.CUP.structure.
16.8 BenchtopTesting
The. 256-pixel. epiretinal. chip. is. fabricated. in. a. 0.18. µm,. 32. V. complementary. metal-oxide-.
semiconductor. (CMOS). process. and. tested. on. the. benchtop.. Figure 16.9a. shows. the. die.
photograph..The.chip.includes.power.regulators,.data.receiver,.digital.controllers,.and.256-
channel.stimulation.pixels.occupying.an.area.of.5.1.×.5.3.mm
2
..For.a.full-path.demonstra-
tion,.as.shown.in.Figure 16.9b,.a.commercial.camera.captures.images.and.encodes.them.to.
a.2.Mbps.DPSK.data.packet.passing.through.a.data.acquisition.board.made.by.National.
Instrument.(NI)..A.ield-programable.gate.array.followed.by.an.NI.card.generates.a.2.MHz.
clock.and.inputs.2.Mbps.data.to.the.data.transmitter..The.2.MHz.clock.is.also.used.to.drive.
the.class.E.power. ampliier. to.generate. a.2.MHz.sinusoidal. RF.power. signal. coupled. to.
the.implant.side.through.coils..In.Figure 16.9c,.the.measured.data.stream.recovered.from.
the.data.demodulator/global.digital.controller.(cyan.trace).and.output.voltage.patterns.of.
two.randomly.picked.stimulation.channels.(magenta.and.green.traces).are.displayed..This.
demonstrates.the.functionality.and.lexibility.of.the.system.
16.9 Conclusion
Research.in.neural.prosthesis.has.progressed.rapidly.in.recent.years,.fueled.by.the.unique.
interdisciplinary. efforts. fusing. engineering,. medicine,. and. biology.. This. chapter. pre-
sented.an.extensive.outline.in.developing.a.retinal.prosthesis.implant.system.through.its.
design,.analysis,.and.realization..The.major.design.challenges,.such.as.implant.heat.dissi-
pation,.high-compliance.stimulation.voltage,.and.system.integration.and.miniaturization,.
are.analyzed.and.addressed.using.the.different.techniques.presented.in.this.chapter..The.
corresponding. realization. of. the. epiretinal. implant. includes. a. power. telemetry. system.
that.delivers.100.mW.to.the.implant,.a.data.telemetry.system.that.provides.2.Mbps.data.
for. controlling. the. implant,. and. 256-channel. stimulators. enabled. by. digital. modules. to.
perform.parallel.stimulation.matching.arbitrary.patterns.at.a.rate.of.50.Hz.or.more.
