Silicon Integrated Circuits and Systems for Frequency Domain Near Infrared Spectroscopy

The design and measurement details of a silicon integrated frequency domain near infrared spectroscopy (fdNIRS) sensor system are presented in this work. fdNIRS is used to non-invasively measure absolute tissue hemodynamics. This can be used to indicate the presence of tumors, measure brain function, in- dicate stress levels and tissue health by non-invasively detecting physiological parameters. Portable instruments such as these, have the potential to be es- sential diagnostic and health monitoring tools.;The challenges in designing a miniaturized fdNIRS instrument using silicon integration technology are discussed. An optimal circuit architecture for amplication, amplitude and phase detection is proposed. Methods to reduce hardware and power consumption for a scalable fdNIRS system are discussed. Digitization of the amplitude and phase in low voltage CMOS processes by using peak detectors and time-to-digital converters is implemented, which reduces complexity while maintaining accuracy.;A prototype chip that has multiple fdNIRS sensors interfaced with external photodiodes on a 180nm CMOS IC is implemented. The prototype chip has time coded output signals that represent the information that needs to be measured. The optical performance as well as the amplitude and phase digitizer response is measured.;A second chip implemented in a 130nm Silicon-Germanium BiCMOS process utilizes SiGe Bipolar transistors at the front-end with higher gain to improve the sensitivity and dynamic range of the sensor. The complete phase digitization and amplitude detection circuitry are implemented on chip using Silicon CMOS transistors. The sensor is characterized to show sub-nW optical sensitivity, 60dB linear dynamic range and 0-360° phase measurement on chip. These measurements show the promise of a miniaturized solution for in-vivo non-invasive detection of absolute concentrations of Oxy and de-Oxy-Hemoglobin in highly scattering media.