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

Abstract

Low powered fully implantable cochlear implants (FICIs) untangle the aesthetic concerns and battery replacement problems of conventional cochlear implants. However, the reported FICIs lack proper charge balancing and require multiple external supplies to operate. In this work, a complete low power FICI interface circuit is designed that operates with a single supply and uses short-pulse-injection method for charge balancing. The system takes input from multi-channel piezoelectric transducers and stimulates the auditory neurons with pulse width modulated (PWM) output currents. By utilizing pulse width modulation technique with continuous interleaved sampling (CIS) sound processing strategy, a time gap is formed between two consecutive channels. Then, this gap is used for charge balancing operation. Overall power consumption of the low power FICI interface is decreased by clocked gated subthreshold amplifier and rectifier design. Furthermore, power efficient design of analog to digital converter (ADC) enhances the power reduction. The system is tested with an in-vitro test setup and it stimulates a single channel cochlear electrode with 50 dB input dynamic range while consuming 695 µW power from a single 1.8 V supply. The implemented FICI system can safely stimulate neurons for more than 18 days (with 16hour daily operation) with an implantable 200 mWh battery without recharging. Furthermore, the short charge balance current pulses keep the electrode voltage difference after the stimulation within ±100 mV range, which ensures the residual charge is not hazardous for the auditory neurons.INDEX TERMS Charge balanced neural stimulation, fully implantable cochlear implant, low power electronics.

The hidden cochlear implant

“…It is known that energy consumption could be decreased up to one-thousandth of the current level with an integrated chip design. 29,30 Tissue heating could be discussed as a potential risk of an infrared emitter. But the power efficient LED technology and the deep penetration of infrared reduces the risk of a harmful local heating.…”

“…It is known that energy consumption could be decreased up to one-thousandth of the current level with an integrated chip design. 29,30…”

A Fully-Implantable Mems-Based Autonomous Cochlear Implant

“…Furthermore, the power reduction is enhanced by power efficient design of analog to digital converter. The overall stimulation system is tested with an in-vitro test setup and 50 dB input dynamic range is achieved while consuming 695 μW power from a single 1.8 V supply [13].…”