Abstract
This paper presents an ultra-low power current-mode circuit for a bionic ear interface. Piezoelectric (PZT) sensors at the system input transduce sound vibrations into multi-channel electrical signals, which are then processed by the proposed circuit to stimulate the auditory nerves consistently with the input amplitude level. The sensor outputs are first amplified and range-compressed through ultra-low power logarithmic amplifiers (LAs) into AC current waveforms, which are then rectified through custom current-mode circuits. The envelopes of the rectified signals are extracted, and are selectively sampled as reference for the stimulation current generator, armed with a 7-bit user-programmed DAC to enable patient fitting (calibration). Adjusted biphasic stimulation current is delivered to the nerves according to continuous inter-leaved sampling (CIS) stimulation strategy through a switch matrix. Each current pulse is optimized to have an exponentially decaying shape, which leads to reduced supply voltage, and hence ~20% lower stimulator power dissipation. The circuit has been designed and fabricated in 180nm high-voltage CMOS technology with up to 60 dB measured input dynamic range, and up to 1 mA average stimulation current. The 8-channel interface has been validated to be fully functional with 472μW power dissipation, which is the lowest value in the literature to date, when stimulated by a mimicked speech signal.
Highlights
Hearing in mammals is induced by mechanical vibration at the ear drum, which is transferred to the inner ear via ossicles
DESIGN SPECIFICATIONS Fig. 1 shows the fully-implantable cochlear implants (FICIs) system proposed at FLAMENCO Project1 as a bionic ear with five distinct units: PZT transducers for multi-frequency sound detection, signal conditioning electronics to stimulate the auditory neurons according to transducer outputs, a cochlear electrode for neural stimulation, a rechargeable battery to supply the system, and an RF coil for patient fitting and battery charging
The interface circuit can be attached to the flexible interconnects through wire bonds or a small package such as QFN32, which has an area of 5x5 mm2 and can be fit into the middle ear
Summary
Hearing in mammals is induced by mechanical vibration at the ear drum, which is transferred to the inner ear via ossicles. Travelling waves in the cochlea of the inner ear bend different hair cells on the basilar membrane, depending on the frequency. The hair cells release electrochemical substances that stimulate the auditory neurons [1]–[3]. Traditional hearing aids treat moderate hearing disorders by amplifying the sound [4], [5]. Middle ear transducer implants convert incoming sound to micro-vibrations through a microphone in order to address disorders related to eardrum and ossicles [6], [7]. Damage of the hair cells on the other hand causes loss of fine tuning of the incoming sound, resulting in hearing loss from severe-to-profound level
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