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

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 472 µW power dissipation, which is the lowest value in the literature to date, when stimulated by a mimicked speech signal. INDEX TERMS Fully implantable cochlear implant, bionic ear, neural stimulation, ultra-low power, current-mode.

Single Supply PWM Fully Implantable Cochlear Implant Interface Circuit With Active Charge Balancing

“…The DNL and INL errors of the DAC are smaller than 1 LSB and calibration of the minimum and the maximum comfort levels of each channel can be done according to the patient. The DAC inputs are digital bits and do not require extra cascode stage unlike [18] and using single stage DAC extends the voltage headroom of the stimulator. The combined stimulator and DAC block decrease the power consumption of the system compared with the previous stimulators [17], [27] due to less current steering operation.…”

“…After filtration and compression of the digitalized signal, the electrodes are stimulated with arbitrary waveform. In [18], the sound input is taken from 8 channel input transducers [14] and clock gated logarithmic amplifiers amplify and compress it. The logarithmically compressed sound envelope is taken with a peak detector and its level determines the amplitude of the biphasic current.…”

“…Although it is a reliable method; it suffers from area limitations because of the large capacitors. The system in [18] use electrode shorting method, where a switch is presented between the electrodes and enabled after the stimulation to dissipate the accumulated charge. This technique generates an uncontrollable current at the electrode and may harm the tissue and the charge balancing currents may interfere with other channels in multichannel applications.…”

An Adaptive Converter for Current Neural Stimulators Achieving up to 79% Power Dissipation Reduction

“…To create the biphasic pulse from a single supply, the H-bridge shown in Fig. 3 (a), which is similar to the one in [3], is controlled with the PA and PC control signals. It is supplied by VHIGH created by the charge pump.…”

A Low-Profile Autonomous Interface Circuit for Piezoelectric Micro-Power Generators

“…Although energy consumption of such systems has drastically shrunk in the last decade, they still rely on bulky batteries for reliable operation. Considering their limited capacity and lifespan, batteries need to be charged or replaced for the sake of operation continuity; however, this may not be achievable in some applications due to location of the device [1] or extensive maintenance cost [2]. Energy scavenging provides an opportunity to power wireless sensor networks (WSNs) while eliminating usage of ponderous batteries.…”