A 0.0046-mm² Two-Step Incremental Delta–Sigma Analog-to-Digital Converter Neuronal Recording Front End With 120-mVpp Offset Compensation

This article presents a recording front end for high-density CMOS neuronal probes with in situ digitization and electrode offset voltage compensation. The analog front end (AFE) is based on a continuous-time (CT) two-step (TS) incremental delta–sigma ( $\text{I}\Delta \Sigma $ ) analog-to-digital converter (ADC) with an extended counting technique and features an input offset voltage compensation of 120 mVpp. Hardware sharing in the TS quantization process allows the integration of the front end in an area of only 0.0046 mm 2 and, thus, directly under the recording electrodes on the shank of a probe in 180-nm CMOS. The average integrated noise is as low as 4.88 $\mu \text{V}_{\text {rms}}$ , 4.46 $\mu \text{V}_{\text {rms}}$ , and 2.51 $\mu \text{V}_{\text {rms}}$ in the full bandwidth of 0 Hz–10 kHz, in the frequency band of action potentials (AP, 0.3–10 kHz) and local field potentials (LFP, 0.5 Hz–1 kHz), respectively. Each recording front end consumes 8.57 $\mu \text{W}$ , and transmitting the digitized data to an external host needs additionally 6.05 $\mu \text{W}$ per channel.