The stimulator under development will take advantage of the selectivity inherent in the USEA or UEA, and could, for example, be used in next-generation prosthetic devices to provide tactile and proprioceptive sensation to people with amputations. Injecting and retracting charge from sensory nerves in the residual limb could create the internal feedback. The stimulator could also activate motor fibers in nerves to reanimate paralyzed muscles, or activate cortical neural tissue to restore lost sensory function. This integrated neural interface (INI) stimulator project is an extension of and a complementary design to an INI neural recording system also developed by our group [27].

Voltage-controlled stimulation (VCS) is a highly efficient way to stimulate using a power-supply voltage, but it is difficult to control the amount of charge being injected and is highly dependent on the electrode tissue impedance.

Constant-charge or switched-capacitor stimulation (SCS) is able to control the amount of charge injected in to the tissue by discharging a series of capacitors. However, capacitors are either very costly in terms of chip area or must be implemented off-chip.

Constant-current stimulation (CCS) is achieved by providing a constant current into an electrode. Allows for a high controllability of charge injection independent of electrode impedance.

Stimulation occurs when there is charge exchange over an electrode, creating an oxidation-reduction reaction at the electrode-tissue interface. In order to reduce electrode corrosion or cell death, no net charge should be transferred from the electrode into tissue.

Using a biphasic pulse, rather than a monophasic pulse, maintains charge balance. The charge delivered during the cathodic pulse is neutralized with the anodic pulse [16]. However, due mainly to second-order effects, a net charge can remain in the tissue. An important technique that has been implemented on many stimulators is a charge-balancing circuit to recover the charge.