A 2.2-ps Time-of-Flight Resolution Frequency-Domain fNIRS Readout IC With a Dynamic Architecture and Cross-Coupling-Free Intensity and Phase-to-Digital Converter

This article presents a fully integrated frequency-domain (FD) functional near-infrared spectroscopy (fNIRS) detection integrated circuit (IC) designed for non-invasive measurement of tissue metabolite optical properties. Departing from traditional static architectures, a dynamic light sensing architecture is proposed, which allows for the decoupling of time-of-flight (ToF) resolution from the system power consumption through duty-cycle modulation, thereby enhancing energy efficiency. In addition, to improve the measurement precision of both ToF and intensity loss, an inter-stabilized intensity and phase-to-digital converter (IS-IPDC) is proposed to resolve coupling issues between intensity and phase quantification. The chip is implemented in a standard 180-nm CMOS process. Test results indicate that the light ToF resolution is 2.2 ps within a 10-Hz bandwidth, while consuming only 12.5 mW. Thanks to its high resolution and crosstalk-free characteristics, compared with the high-precision instrument-based reference system, the maximum measurement errors for the absorption coefficient ( $\boldsymbol {\mu _{a}}$ ) and reduced scattering coefficient ( $\boldsymbol {\mu '_{s}}$ ) are 4.2% and 4%, respectively. Finally, comprehensive in vitro and in vivo demonstrations demonstrate the IC’s capabilities for metabolic imaging and long-term monitoring.