A Sub-500 $\mu$ W Interface Electronics for Bionic Ears

• Published in: IEEE access 2019, Vol.7, p.132140-132152
• Main Authors: Ulusan, Hasan, Muhtaroglu, Ali, Kulah, Haluk
• Format: Article
• Language: English
• Subjects: bionic ear; current-mode; Fully implantable cochlear implant; neural stimulation; ultra-low power
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2019.2940744

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.