An implantable microvolt-level signal amplifying circuit may be used for resolving electrical signals generated by nerves in the presence of larger amplitude signals generated by muscles, the heart, or external noise sources. The circuit has a low-noise, high Common Mode Rejection Ratio (CMRR) preamplifier, followed by a cascade of stages, which provide filtering and further amplification of the neural signal. The band-pass amplifying circuit can also present high Power Supply Rejection Ratio (PSRR). The output is offset-compensated by a DC restoration stage. Nerve protection circuitry minimizes or blocks DC current flow through the input terminals in the event of semiconduc- tor failure in the preamplifier. The circuit may be incorporated onto a common monolithic circuit with follow-up circuitry for controlling Functional Electrical Stimulation (FES) devices.
IMPLANTABLE SIGNAL AMPLIFYING CIRCUIT FOR ELECTRONEUROGRAPHIC RECORDING