This thesis presents time difference (TD) circuits that are important for measuring fluorescence lifetime, building LIDAR systems, and optimizing digital systems. The contribution of this thesis is to present a systematic organization of TD circuits and to present novel designs for digital-to-time conversion (DTC) and time-to-digital conversion (TDC). Four basic time difference circuits are presented: TD adder, arbiter, time-difference MUX, and time-difference memory. Specifications, symbols, and multiple circuit implementations are presented for each block. Then the basic blocks are combined to form two compound blocks: DTC and TDC. Novel designs are presented for both blocks along with detailed simulation results. The DTC was fabricated in TSMC’s 0.35um high-voltage process. A printed circuit board was designed to interface the DTC chip to a computer and test instruments. The DTC demonstrated 80ps resolution.