A DC-Coupled Neural Recording Analog Front-End with Bi-Level Bulk Modulation-Based EDO Compensation in 40nm Bulk CMOS

This paper presents a compact, low-power analog front-end (AFE) for high-density micro-electrocorticography (μECoG) recordings. The AFE integrates a DC-coupled, chopper-stabilized low-noise boxcar sampler, a passive switched-capacitor low-pass filter, and a 10-bit single-slope analog-to-digital converter (ADC). The boxcar sampler minimizes noise folding, enhances anti-aliasing and reduces chopping ripple. To prevent AFE saturation, a novel electrode DC offset (EDO) compensation loop is introduced. It features an embedded digital-to-analog converter (DAC) by modulating the bulk terminals of the input transistors, and a bi-level compensation scheme, thereby eliminating the requirements for high-resolution digital low-pass filters and explicit DACs typically used in traditional DC servo loops. Simulation results in 40nm bulk CMOS show an input-referred noise of 1.69 μV<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</inf> over a 1-500 Hz bandwidth, an EDO compensation range of 110 mV<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</inf>, with a power consumption of 2.28 μW and an estimated area of 0.0028 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> per channel.