A 15.2-ENOB 5-kHz BW 4.5-μW Chopped CT ΔΣ-ADC for Artifact-Tolerant Neural Recording Front Ends

Implantable closed-loop neural stimulation is desirable for clinical translation and basic neuroscience research. Neural stimulation generates large artifacts at the recording sites, which saturate existing recording front ends. This paper presents a low-power continuous-time delta-sigma analog to digital converter (ADC), which along with an 8x gain capacitively-coupled chopper instrumentation amplifier (CCIA), realizes a front end that can digitize neural signals from 1 Hz to 5 kHz in the presence of 200-m V-pp differential artifacts and 700-mV(pp) common-mode (CM) artifacts. A modified loop-filter is used in the ADC along with new linearization techniques to significantly reduce power consumption. Fabricated in 40-nm CMOS, the ADC occupies an area of 0.053 mm(2), consumes 4.5 mu W from a 1.2-V supply, has an input impedance of 20 M Omega and bandwidth (BW) of 5 kHz, and achieves a peak signal to noise and distortion ratio (SNDR) of 93.5 dB for a 1.77-V-pp differential input at 1 kHz. The ADC's figure of merit (FOM) (using SNDR) is 184 dB, which is 6 dB higher than the state of the art in high-resolution ADCs. The complete front end occupies an area of 0.113 mm(2), consumes 7.3 mu W from a 1.2-V supply, has a dc input impedance of 1.5 G Omega, input-referred noise of 6.35 mu V-rms in 1 Hz-5 kHz, and total harmonic distortion of -81 dB for a 200-mV(pp) input at 1 kHz, and is immune to 700-mV(pp) CM interference. Compared to front ends intended for closed-loop neural recording, this paper improves the linear input range by 2x, the signal BW by 10x, the dynamic range by 12.6 dB, the FOM by 12.4 dB and remains immune to large CM interference while maintaining comparable power, area, and noise performance.