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.

Charge balancing is a major concern in functional electrical stimulation. Any excess charge accumulation over time leads to electrolysis with the electrode dissolution and tissue destruction. Therefore, charge balance circuits are used for mitigating the effects of charge accumulation in tissues. This work introduces an active synchronous charge balance circuit for constant current neural stimulators that operates without requiring negative supply for remaining charge detection. The charge balance circuit detects the residual charge by monitoring the electrode voltages just before the stimulation. If the voltage difference between the electrodes is above a certain threshold, a balance current is generated to achieve net zero charge at the electrode. Balancing current and the main stimulation current are injected simultaneously, preventing any interference in other electrodes. The charge balance circuit is dynamically disabled to reduce the system power when the charge detection is not active. The circuit can operate for the stimulation currents up to 1.4 mA and hold the electrode charge under 8 nC/phase while consuming only 6.36 µW power.

No abstract

No abstract