Performance Improvement Analysis of fNIRS IC

Bumjun Koh; Kyeongha Kwon; Hyeon-Min Bae

doi:10.23075/jicas.2024.10.3.003

Bumjun Koh Korea Advanced Institute of Science and Technology
Kyeongha Kwon Korea Advanced Institute of Science and Technology
Hyeon-Min Bae Korea Advanced Institute of Science and Technology

DOI: https://doi.org/10.23075/jicas.2024.10.3.003

Keywords: Near-infrared spectroscopy, dead-zone, offset, comparator, charge extractor

Abstract

A Receiver (RX) for functional near-infrared spectroscopy (fNIRS) IC is designed to obtain hemodynamics of the human brain, requiring high SNR measurements. It is largely composed of TIA, PGA, and OTA-C-based matched filters, along with a single-slope ADC. However, a dead-zone problem arises, wherein an unstable voltage level appears in a specific section near 0V among signals measured using the IC system. This phenomenon persists despite offset calibration with its own current DAC, as each IC exhibits an inconsistent input offset value in the comparator. In this work, we address the issue by removing the current MSB detector and allocating a period for the ADC's comparator to verify the sign information of the PGA output. The dead-zone effect is mitigated by enhancing the system to provide discharge direction information and quantize it.

Author Biographies

Bumjun Koh, Korea Advanced Institute of Science and Technology

Bumjun Koh received the B.S. and M.S. degrees in electrical engineering from the Korea Advanced Institute of Science and Technology (KAIST), Dae-jeon, Korea, in 2019 and 2021, respectively. He is currently working toward a Ph.D. degree at KAIST.

His research interests include near-infrared spectroscopy, analog front-end design for biomedical sensor applications, and mixed-signal design for biomedical circuit systems.

Kyeongha Kwon, Korea Advanced Institute of Science and Technology

Kyeongha Kwon received the B.S. and Ph.D. degrees in electrical engineering from the Korea Advanced Institute of Science and Technology (KAIST), Dae-jeon, Korea, in 2011 and 2018, respectively.

She is currently working at KAIST as an assistant professor. Her research interests are in high-speed wireline communications and wearable medical devices and technologies.

Hyeon-Min Bae, Korea Advanced Institute of Science and Technology

Hyeon-Min Bae received the B.S. degree in electrical engineering from Seoul National University, Seoul, Korea, in 1998 and the M.S. and Ph.D. degrees in electrical and computer engineering from the University of Illinois at Urbana-Champaign, Champaign, IL, USA, in 2001 and 2004, respectively.

From 1995 to 1996, he served his military duty in Dokdo in the East sea. From 2001 to 2007, he led the analog and mixed-signal design aspects of OC-192 MLSE based EDC ICs at Intersymbol Communications, Inc, Champaign, IL, USA. From 2007 to 2009, he was with Finisar Corporation (NASDAQ: FNSR), Sunnyvale, CA, USA, after its acquisition of Intersymbol Communications Inc.. Since 2009, he has been on the faculty of the electrical engineering at Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea, where he is currently an associate professor. In 2010, he founded Terasquare, Inc., Seoul, South Korea, a venture-funded fabless semiconductor start-up which provided low power all digital 100 Gb/s IC solutions. Teresquare, Inc. was acquired by Gigpeak (NYSE:GIG) in 2015. In 2013, He also founded OBElab, Inc., Seoul, Korea, a bio startup that manufactures portable functional brain imaging systems. His research interests span a wide range of topics in wireline communication and medical imaging systems.

Prof. Bae received the Excellence Award from the National Academy of Engineering of Korea in 2013 and the 2006 IEEE Journal of Solid-State Circuits Best Paper Award.

Homepage : https://nais.kaist.ac.kr/