Design of a low-power, implantable electromyogram amplifier

This paper describes the design of a low-power BiCMOS preamplifier for electromyogram signal detection in an implantable neural prosthetic device. The device is inductively powered and has to detect bioelectric signals in the range of 10 Hz to 10 kHz in the presence of large dc voltages at the detection electrodes. This was achieved by using a feedback loop to set the input common-mode voltage and obtain a high impedance input and biasing structure, then allowing the use of low-valued dc blocking capacitors. The proposed amplifier was designed and fabricated to provide a nominal differential voltage gain of 100, an ac input impedance of over 80 MΩ and an input referred noise voltage of 9.7 μVrms in the 10 Hz to 10 kHz bandwidth. The amplifier consumes 122 μW (37 μA) when operating off a 3.3 V supply and occupies an area of 0.125 mm² using a double-metal 0.8 μm BiCMOS process.