A CMOS Sensor for Measurement of Cerebral Optical Coefficients Using Non-Invasive Frequency Domain Near Infrared Spectroscopy

A heterodyned architecture is integrated with a 180 nm CMOS chip for use in portable frequency domain near infrared spectroscopy (fdNIRS) tools for real time monitoring of tissue oxygenation in the brain. The design and performance measurement results of this chip are summarized in this paper to demonstrate its applicability in multi-distance fdNIRS to measure the absorption and scattering coefficients of tissue. The 2.25 mm(2) chip is integrated with four sensor channels, which have a high frequency low noise front end and information processing circuitry to interface with an avalanche photodiode to detect the high speed weak light signal. The four-channel sensor draws 40 mA of current from a 1.8 V power supply and uses an off-chip counter implemented on an FPGA to quantify the amplitude and phase information required for tissue characterization with < 6.5% and < 2.5% linearity error, respectively. An experiment using the multi-distance measurement is used to measure the optical properties of a homogeneous tissue phantom using the CMOS integrated instrument.