Neural stimulation interface with ultra-low power signal conditioning circuit for fully-implantable cochlear implants

This paper presents an ultra-low power interface circuit to stimulate auditory nerves through fully-implantable cochlear implants (FICIs). The interface circuit senses signals generated from a multi-frequency piezoelectric sensor array, and generates neural stimulation current according to input sound level. Firstly, piezoelectric sensor output is amplified, and compressed with an ultra-low power logarithmic amplifier (LA). This significantly reduces power by eliminating the compression in the next stages. Then, amplified signal is envelope-detected, and utilized as a reference for stimulation current generation using a voltage controlled current source. Finally, biphasic stimulation current is delivered to the nerves through a switch matrix. The circuit has been designed and fabricated in 180nm high-voltage CMOS technology. 8-channel stimulator dissipates about 667 μW as it generates 110 μA biphasic stimulation current, while the front-end signal conditioning unit dissipates only 51.2 μW.