Failure analysis and performance improvement of fNIRS IC

Abstract

A Receiver(Rx) of functional near-infrared spectroscopy(fNIRS) IC designed to obtain hemodynamics of the human brain, which requires high SNR measurement, is largely composed of TIA, PGA, and OTA-C-based matched filters and a single-slope ADC. However, there is a 'Dead-Zone' problem in which an unstable voltage level appears in a specific section near 0V among signals measured using an IC. This is not completely eliminated even if the offset is calibrated with its own current DAC since each IC has a inconsistent input offset value of the comparator. In this paper, in order to minimize the instability of the measured values by the 'MSB detector' and the comparator of the ADC, we remove the 'MSB detector' and assign a period in which the comparator of the ADC first checks the sign information of the PGA output, and apply the charge extractor to the charge extractor. The effect of the 'Dead-Zone' was minimized by improving the system to deliver discharge direction information and quantize it.