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 $695~\mu \text{W}$ power from a single 1.8 V supply. The implemented FICI system can safely stimulate neurons for more than 18 days (with 16-hour 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.
Highlights
Half a billion people around the world, which is more than 5% of the world population, suffer from disabling hearing loss
The current amplitude is set to 500 μA by 6-bit patient fitting digital to analog converter (DAC) and the stimulator voltage is controlled with DC-DC converter
The implemented fully implantable cochlear implants (FICIs) interface circuit is tested with single channel animal cochlear platinum electrode and piezoelectric transducer
Summary
Half a billion people around the world, which is more than 5% of the world population, suffer from disabling hearing loss. Digital control blocks generate the stimulator circuit inputs from ADC output and synchronize the whole system with enable and clock signals. D. STIMULATOR CIRCUIT AND PATIENT FITTING DAC Single supply H-bridge stimulator is used for the biphasic current output generation.
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