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A Fully Integrated Frequency-Domain Diffuse Optical Imaging System in 180 nm Standard CMOS


Frequency-domain diffuse optical imaging (fd-DOI) systems require accurate phase and amplitude measurement of the modulating signal for precise calculation of optical properties of a medium. To reach this accuracy, the current time-resolved DOI methods are prohibitively complex, bulky, and expensive, and generally not compatible with the vision of compact wearable devices. In this dissertation, for the first time, a complete fd-DOI transceiver unit is implemented on a chip. Using only standard CMOS technology to reduce the cost, this transceiver paves the way for complete integration of a time-resolved DOI SoC. Novel methods for measuring phase and amplitude are introduced to enable accurate measurement over more than a decade of frequencies and 60 dB input dynamic range. The systems reaches an optical sensitivity of -57 dBm at 400 MHz modulation frequency with phase and amplitude measurement accuracy of 2 degree and 1dB, respectively. Works like this along with the advances in the vertical cavity surface emitting lasers (VCSELs) and CMOS-integrated photodiodes will enable the development of new methods and devices with the accuracy, precision, and power of time-resolved techniques, but the simplicity, low cost, and wearability of CW devices.

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