A Direct Digitizing Chopped Neural Recorder Using a Body-Induced Offset Based DC Servo Loop

• Published in: IEEE transactions on biomedical circuits and systems Vol. 16; no. 3; pp. 409 - 418
• Main Authors: Sporer, Markus, Reich, Stefan, Kauffman, John G., Ortmanns, Maurits
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.06.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Area-efficient; Bandwidth; biomedical; Capacitors; chopping; continuous-time delta–sigma modulator (CTDSM); Couplings; Cutting; DC servo loop; Digitization; Digitizing; direct digitizing neural recorder; Electrophysiological recording; Impedance; Input impedance; low noise; neural recorder; neurorecording; offset cancellation; Recording; Servomotors; Signal to noise ratio
• ISSN: 1932-4545; 1940-9990
• DOI: 10.1109/TBCAS.2022.3177241

This article presents a direct digitizing neural recorder that uses a body-induced offset based DC servo loop to cancel electrode offset (EDO) on-chip. The bulk of the input pair is used to create an offset, counteracting the EDO. The architecture does not require AC coupling capacitors which enables the use of chopping without impedance boosting while maintaining a large input impedance of 238 M<inline-formula><tex-math notation="LaTeX">\Omega</tex-math></inline-formula> over the whole 10 kHz bandwidth. Implemented in a 180 nm HV-CMOS process, the prototype occupies a silicon area of only 0.02 mm 2 while consuming 12.8 μW and achieving 1.82 μV<inline-formula><tex-math notation="LaTeX">_{\text{rms}}</tex-math></inline-formula> of input-referred noise in the local field potential (LFP) band and a NEF of 5.75.