A wireless integrated circuit for 100-channel constant current charge-balanced neural stimulation

There has recently been research activity into applications for electrical neural stimulation including deep brain stimulators, visual and auditory neural stimulators, and neuromuscular stimulators for the purpose of contracting paralyzed or otherwise disabled muscles. This dissertation presents the results of research into the design of integrated circuits for wireless neural stimulation, along with bench-top and in-vivo experimental results. The design and implementation of a low-power, implantable, 100-channel wireless neural stimulator using biphasic constant current stimulation, a novel active charge-recovery circuit, and local digital control for timing of individual electrodes are presented. The chip has the ability to drive 100 individual stimulation electrodes with constant-current pulses of varying amplitude, duration, interphasic delay, and repetition rate. The stimulation uses a biphasic (cathodic and anodic) current source, injecting and retracting charge from the nervous system. An active charge-recovery circuit bleeds off or supplies excess charge after stimulation to maintain charge balance. The recovery circuit acts as a small secondary sink or source dependent on the residual charge remaining in the tissue. Wireless communication and power are delivered over a 2.765-MHz inductive link. Only three off-chip components are needed to operate the stimulator: a 10 nF capacitor to aid in power supply regulation, a small capacitor (< 100 pF) for tuning the coil to resonance, and a coil for power and command reception. The chips were fabricated in a commercially available 0 6 pm 2P3M BiCMOS process. The first integrated circuit design was able to activate motor fibers to produce muscle twitches via a Utah Slanted Electrode Array implanted in a cat sciatic nerve, and to activate sensory fibers to recruit evoked potentials in somatosensory cortex.