UC Irvine

In this dissertation design of a fully integrated frequency-domain Near Infrared Spectroscopy (fd-NIRS) system is discussed. The fd-NIRS system measures optical properties of the tissue under test to detect if there is any anomaly. Two chips are introduced for fd-NIRS application. The proposed systems measure phase and amplitude of the modulated optical signal with high precision and compare with the detected light to accurately calculate the optical properties of the tissue under test. The first chip, implemented in a 180nm CMOS process, is measured to characterize the phase and amplitude detection accuracy. The second chip is designed and implemented using a 65nm CMOS process. The proposed heterodyned fd-NIRS system includes a high-resolution wide-band phase-locked loop that provides modulating frequenciesfrom 50 MHz to 1GHz. A logarithmic analog amplitude detector provides accurate measurements of the modulated signal attenuation. The heterodyne receiver architecture includes a novel phase detector designed based on a three-stage limiting sense amplifier that allows for precise measurement of the phase with 1◦ phase resolution. The integrated circuit is designed to work with an external laser diode and avalanche photodiode (APD) to implement the complete fd-NIRS sensing system. The digital phase detector interface is designed to facilitate the optical measurements. The overall measurement result shows a promising path toward scalable and wearable optical sensing systems based on frequency-domain near-infrared spectroscopy.