Fully Implantable Cochlear Implant Interface Electronics With 51.2- $\\mu$ W Front-End Circuit

Abstract

This paper presents an ultralow power interface circuit for a fully implantable cochlear implant (FICI) system that stimulates the auditory nerves inside cochlea. The input sound is detected with a multifrequency piezoelectric (PZT) sensor array, is signal-processed through a front-end circuit module, and is delivered to the nerves through current stimulation in proportion to the sound level. The front-end unit reduces the power dissipation by combining amplification and compression of the sensor output through an ultralow power logarithmic amplifier. The amplified signal is envelope detected, and fed to a voltage-controlled current source as a reference for stimulation current generation. The single channel performance has been tested with a thin film pulsed-laser deposition (PLD) PZT sensor for sound levels between 60- and 100-dB sound pressure level (SPL). The proposed front-end signal conditioning unit, which can support different back-end stimulators, dissipates only 25.4 and 51.2 <inline-formula> <tex-math notation= LaTeX >$\\mu \\text{W}$ </tex-math></inline-formula> based on measurement, for 1- and 8-channel operation, respectively. This represents the lowest in the literature. The interface generates linear stimulation current of 110–<inline-formula> <tex-math notation= LaTeX >$430~\\mu \\text{A}$ </tex-math></inline-formula> for the given sound range. The single-channel and eight-channel stimulator consume 105 and <inline-formula> <tex-math notation= LaTeX >$691~\\mu \\text{W}$ </tex-math></inline-formula>, respectively, for 110-<inline-formula> <tex-math notation= LaTeX >$\\mu \\text{A}$ </tex-math></inline-formula> biphasic stimulation current.