26.6 A 6.5µW 10kHz-BW 80.4dB-SNDR Continuous-Time ΔΣ Modulator with G<sub>m</sub>-Input and 300mV<sub>pp</sub> Linear Input Range for Closed-Loop Neural Recording
Changuk Lee, Taejune Jeon, MoonHyung Jang, Sanggeon Park, Yeowool Huh, Youngcheol Chae
Abstract
Closed-loop neural recording requires a front-end with a wide DR to record small neural signals without distortion in the presence of a DC electrode offset (~50mV) and a large stimulation artifact (~ 200mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> ). To remove DC offset, a conventional architecture uses an AC-coupled LNA and a subsequent ADC [1]. However, to realize a small HPF cut-off frequency (<; 1Hz), the LNA requires a large input capacitor, resulting in a reduced input impedance and an increased area. Additionally, the LNA is prone to be saturated by large stimulation transients. To address these issues, direct digitization for neural recording is increasingly popular [2], [5] and offers great potential for reducing area and power consumption [5]. However, to digitize small neural signals without amplification, such ADCs require a high DR (>80dB), a large linear operating range (>250mV), a high DC input impedance (>1GΩ), and a large common-mode rejection (>70dB). Fulfilling all these requirements often leads to ADCs with poor energy-efficiency [2], [3]. This paper presents a continuous-time delta-sigma modulator (CT-ALM) with G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> -input for closed-loop neural recording. It achieves a high input impedance, 300mV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> linear input range, 80.4dB SNDR, and 76dB CMRR, and consumes only 6.5μW with a signal bandwidth of 10kHz. This corresponds to a 172.3dB FOM.