An Integrated Amplifier With Passive Neutralization of Myoelectric Interference From Neural Recording Tripoles

This paper describes an integrated amplifier for neural recording from tripolar electrode books connected in the quasi-tripole arrangement. The same tripole is used in the implant for neural stimulation. To remove myoelectric interference from neural recordings, a resistor-capacitor network is used to balance the electrode impedances in the tripole. The amplifier is programmable (recording mode, passband, gain, and trimming impedance) via a serial peripheral interface. Its front-end instrumentation amplifier employs current feedback to achieve high common-mode rejection ratio. The circuit was implemented in 0.35- μm CMOS technology and occupies an area of ~1.2 mm². In the very-low noise mode, the analog front-end features a maximum of 0.68 μVrms input-referred noise in the passband and consumes ~310 μA from a 3 V supply. The measured common-mode rejection ratio of the instrumentation amplifier (CMRRIA) approaches 100 dB. The effect of component mismatch on the CMRRIA and the noise performance of the instrumentation amplifier are examined. In addition, the recording tripole is analyzed to derive the overall common-mode rejection ratio that is shown to exceed 80 dB. The ability of the neural amplifier to reduce myoelectric interference is demonstrated. The amplifier is also tested with a tripole immersed in saline in the stimulate-record mode.