A near-infrared non-invasive imager using correlated double sampling

In this paper, a NIR non-invasive imager prototype using discrete components (all CMOS integrated circuits) was built which incorporates correlated double sampling (CDS) technique. Low frequency noise and offsets of amplifiers are removed by subtracting it from signal through CDS. The imager is comprised of a current-to-voltage preamp (I-V), post-gain amplifier and the CDS system, which consists of several sample & hold and subtracter circuits. The system is being used to quantify the change of oxy- and deoxy-hemoglobin. The circuit operates at 3 V. The I-V has achieved an output dynamic range of 58 dB. Later on, a transmitter will be included and the entire system will be integrated into an IC.