DESIGN OF A TIME-AMPLIFIED, STOCHASTIC PHASE INTERPOLATION TIME-TO-DIGITAL-CONVERTER FOR BIOMEDICAL IMAGING APPLICATIONS

Abstract

Time-to-digital converters (TDC) and single-photon avalanche diodes (SPAD) can be integrated together into SPAD-imagers. TDC is a mixed-signal circuit that can convert the time differences between the two input signals. In SPAD-imagers, the electrical pulses triggered by incident photons are measured against the reference clock to extract time-of flight (ToF) data. The performance of TDC is directly related to the temporal performance of the SPAD-imagers in biomedical imaging systems, such as positron emission tomography (PET) and diffuse optical tomography (DOT). In recent years, the evolution of modern complementary metal-oxide-semiconductor (CMOS) technology made it possible to implant SPAD-imagers for imaging neural activities in moving subjects. This work proposes a new TDC design to further improve future SPAD-imager based time-domain imaging systems. Firstly, this thesis provides a detailed review of the current research on brain imaging and neural activity recording methods. Next, the operating principles of different TDC architectures are presented. In the following chapter, the proposed time amplified, stochastic phase interpolation (TASPI) TDC architecture was designed and tested in TSMC 65 nm standard CMOS technology nodes that can achieve a ~16 ps resolution with 6 effective number of bits in a 0.06 mm2 silicon area is presented. Based on the results, areas for future improvements are identified and discussed in detail.