Wireless in vivo EMG sensor for intelligent prosthetic control

High-quality real-time muscle activity signals are important for advanced natural control of intelligent powered prosthetic limbs. This paper presents a wireless implantable electromyogram (EMG) sensing microsystem design for intelligent myoelectric control of powered prostheses. The implantable system, consisting of two Pt-Ir epimysial EMG electrodes, a custom-designed ASIC and an RF coil, is capable of wirelessly transmitting digitized EMG data to an external receiver. 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 2V and 2.7V supplies with a DC current driving capability up to 100 µA. The EMG electrodes are interfaced with a differential capacitively-coupled amplifier exhibiting a 38 dB closedloop gain, 1 kHz bandwidth, and 78 nV/√Hz input-referred noise floor. The amplified EMG signal is then digitized by an 11-bit algorithmic ADC, followed by Manchester encoding and wireless data transmission to an external receiver by using passive phase shift keying (PSK) modulation scheme over the same wireless link as the inductive powering system. Animal testing demonstrates that the prototype system can wirelessly detect real-time EMG activity signals from a laboratory rat hind limb with a minimum detectable signal of 20 μVRMS, limited by the EMG background noise.