A Chopper-Stabilized Switched-Capacitor Front-End for Peripheral Nervous System Recording.

Peripheral nervous system (PNS) recording plays an essential role in the development of neural-controlled prosthetics. Compared to cortical recording, PNS requires front-end circuitry with lower input-referred noise and higher accuracy. A chopper-stabilized front-end with its transfer function set by precision capacitor ratios that meets these goals is introduced. Using a windowed integration sampling technique, the continuous-time anti-aliasing filter that usually precedes the lowpass switched-capacitor (SC) filter can be eliminated. High gain accuracy is achieved using a closed-loop switched-capacitor topology wherein a chopper-modulated sinc function is realized. The corner frequencies of the front-end are determined by a downstream switched-capacitor filter and a DC servo-loop-based SC integrator. The overall energy efficiency is further improved using correlated level shifting in the SC filter and integrator stages to simplify the operational amplifier topology. A positive feedback loop is also incorporated to increase the input impedance. The PNS front-end implemented in 180 nm CMOS has a gain of 58.1 dB and an integrated input-referred noise of 2.2 mu V-rms over the -3 dB bandwidth from 170 Hz - 9.68 kHz; the input impedance is > 61M Omega @ 1 kHz. The total harmonic distortion is -66.6 dB with a 1.8V(pp) output swing. The complete front-end including clock generation circuitry occupies 0.136 mm(2), draws 16.1 mu A from a 1.8 V supply, and achieves a noise efficiency factor of 3.5.