A 2-µW 45-nV/√Hz Readout Front End With Multiple-Chopping Active-High-Pass Ripple Reduction Loop and Pseudofeedback DC Servo Loop

This brief presents an ultra-low-power low-noise chopped capacitively coupled instrumentation amplifier (CCIA) that is suitable for neural recording applications. An active highpass filter is embedded in the ripple reduction loop (RRL) to suppress the residual noise and relax the capacitor size. Multiple chopping is employed to further reduce the residual output ripple due to the RRL offsets. A dc servo loop (DSL) using a 14-nA pseudofeedback amplifier is proposed to achieve a subhertz high-pass corner while using only a 15-pF on-chip capacitor. The complete CCIA is implemented in a standard 0.18-μm CMOS process. It occupies an area of 0.23 mm2 (including the DSL) and consumes 1.7 μA from a 1.25-V supply, achieving a noise efficiency factor of 2.9 that compares favorably with the state of the art.