Biomedical Engineering Reference
In-Depth Information
FIgURE 7.15:
Component diagram and assembly of the Florida wireless implantable recording elec-
trode system.
around the battery for a very compact package assembly and enables wireless battery recharging.
The CMOS ICs are flipchip-bonded onto the flexible substrate, which is encased in medical grade
silicone for isolation from fluids. Mechanical stability of the patterned flexible substrate is provided
by the underlying battery/coil, supporting substrate, and screws, which attaches the platform to the
skull of the behaving animal and provides the required ground reference for the on-chip electron-
ics. Multiple electrode attachment sites onto the flexible substrate using micromachined flexible
polyimide ribbon cable provide additional flexibility for experimentation. The metal traces and cor-
responding bond sites can be made to any size specification and spacing distance via photolithog-
raphy. The initial prototypes of the electrode array shown in Section
7.1
consists of a row of eight
(30 µm diameter with 50 µm pitch) gold-plated nickel electrodes with parylene-C insulated shanks
that extend 4 mm from the edge of the flexible polyimide cable [
58
]. In vivo studies produced a
high neuronal yield with SNR ranging from 10 to 27 dB. The resulting FWIRE platform is a highly
modular architecture that takes into consideration the mechanical and physical constraints of the
implant site, and facilitates independent development and testing of its individual components.
7.5.1 Neural Signal Processing and Representation
To achieve these objectives, very fundamental aspects of both the electronics and signal processing
must be modified. We believe that a hybrid analog-digital signal processing approach is necessary,
and started some preliminary steps in that direction. The first is to rethink Nyquist sampling, which
