A Receiver (RX) for functional near-infrared spectroscopy (fNIRS) IC was previously 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 in the conventional design, 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. Revised IC is proposed to solve this problem.

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. Revised IC had a 0.48-bit ENOB enhancement in simulation domain, but failed to measure full scheme due to design-time issues.