Design of a Bone-Guided Cochlear Implant Microsystem With Monopolar Biphasic Multiple Stimulations and Evoked Compound Action Potential Acquisition and Its In Vivo Verification

A CMOS bone-guided cochlear implant (BGCI) microsystem is proposed and verified. In the implanted System on Chip (SoC) of the proposed BGCI, the evoked compound action potential (ECAP) acquisition and electrode–tissue impedance measurement (EAEIM) circuit is integrated to measure both ECAP and electrode–tissue impedance for clinical diagnoses. Both positive-/negative-voltage charge pumps and monopolar biphasic constant-current stimulation (CCS) stimulator are designed on-chip to realize monopolar biphasic CCS or double-electrode multiple stimulations with a maximum stimulation current of 1.2 mA and a step of 10 $\mu \text{A}$ . With the double-electrode multiple stimulations, the electric field can be shifted and localized under the stimulating electrode to stimulate the auditory nerves. The wireless bilateral data telemetry circuits with a full-wave active rectifier and the pulsed load-shift keying (PLSK) modulators/demodulators are designed for power and data transmission. In vivo animal tests on guinea pigs have shown that the Wave III of electrically evoked auditory brainstem responses (EABRs) can be evoked successfully by electrical stimulation. Moreover, the decreasing latency gradient of evoked Wave III has been measured under the double-electrode multiple stimulations where the location of peak electric field can be shifted to the stimulating electrode in the apical site to stimulate the auditory nerves. Thus, the desired frequency resolution and spatial specificity of stimulation can be achieved. Both electrical measurement and in vivo animal tests have verified that the proposed BGCI microsystem is a feasible solution to eliminate the symptoms for patients with high-frequency hearing loss.