A single-channel implantable microstimulator for functional neuromuscular stimulation

The single-channel implantable microstimulator device measures 2×2×10 mm ³ and can be inserted into paralyzed muscle groups by expulsion from a hypodermic needle. Power and data to the device are supplied from outside by RF telemetry using an amplitude-modulated 2-MHz RF carrier generated using a high-efficiency class-E transmitter. The transmitted signal carries a 5-b address which selects one of the 32 possible microstimulators. The selected device then delivers up to 2 μC of charge stored in a tantalum chip capacitor for up to 200 μs (10 mA) into loads of <800 Ω through a high-current thin-film iridium-oxide (IrO _x) electrode (∼0.3 mm ² in area). A bi-CMOS receiver circuitry is used to: generate two regulated voltage supplies (4.5 and 9 V), recover a 2-MHz clock from the carrier, demodulate the address code, and activate the output current delivery circuitry upon the reception of an external command. The overall power dissipation of the receiver circuitry is 45-55 mW. The implant is hermetically packaged using a custom-made glass capsule.