Time-to-digital converters (TDC) are widely used in light-detection-and-ranging (LIDAR) systems to measure the time-of-flight. Conventional TDCs are sensitivity to process, voltage, and temperature (PVT) variations. Recent work utilizing the stochastic delay-line TDC architecture has demonstrated excellent robustness against PVT variations. But important issues affecting the linearity of a stochastic delay-line TDC has yet to be recognized and addressed.This thesis rigorously analyzes the problem of linearity of a stochastic delay-line TDC and formulates an intuitive theory to predict the linearity performance. Apolarvisualization of the phase distribution of a delay line is proposed to aid the analysis. Based on the results of this study, this thesis proposes a stochastic delay-line TDC employing a delay-locked loop (DLL) to guarantee linearity over PVT variations and to reduce the number of redundant bits. The proposed TDC is implemented in a 0.18 µm CMOS process to validate the linearity theory and the proposed solution. The 8-bit TDC samples at 60 MHz and demonstrates a linear-number-of-bit of 6.36 with only 2-bit redundancy. Consuming 25 mW from a 1.8 V supply, the TDC yields a figure-of-merit of 5.04 pJ/conversion-step. With the DLL turned off, the integral nonlinearity (INL) degrades by about a factor of two, verifying the effectiveness of the proposed solution. The TDC is measured at different temperatures and supply voltages to demonstrate robustness against PVT variations. The measurement results show excellent agreement with the behavioral simulations.



College and Department

Ira A. Fulton College of Engineering and Technology; Electrical and Computer Engineering



Date Submitted


Document Type



Time-to-digital converter, TDC, stochastic, PVT tolerance, delay-locked loop, DLL, LIDAR



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Engineering Commons