Wireless implantable EMG sensor for powered prosthesis control

This paper presents a wireless, subfascially implantable electromyogram (EMG) sensing microsystem for intelligent myoelectric control of powered prostheses. The implantable system consists of a custom-designed ASIC, an RF telemetry coil, and two Pt-Ir epimysial EMG electrodes, and is capable of wirelessly transmitting digitized EMG data to an external telemeter mounted in a prosthetic socket. The prototype microsystem is powered by a near-field inductive link operating at 8 MHz with 10% DC power transfer efficiency. On-chip rectification and regulation produce stable 2 V and 2.7 V supplies with a DC current driving capability up to 100 ¿A. The EMG electrodes are interfaced with a differential capacitively-coupled amplifier with 38 dB closed-loop gain, 1 kHz bandwidth, and 78 nV/¿(Hz) input-referred noise floor. The amplified EMG signal is then digitized on chip by using an 11-bit algorithmic ADC. The digital EMG data can be Manchester-coded and transmitted to the external telemeter using passive phase shift keying (PSK) modulation scheme over the same wireless link as the inductive powering system. The implantable microsystem consumes 83 ¿A and achieves 8.7-bit resolution when wirelessly powered by an external RF energy source. Animal implant experiments have been successfully conducted to demonstrate EMG signals from a laboratory rat hind limb can be detected and wirelessly transmitted to an external telemeter with high signal fidelity.