Precise three-channel integrated time counter

We present a design, FPGA-based implementation and test results of a new three-channel time interval counter developed for a project called Legal Time Distribution System (LTDS). The main aim of the counter is to gather information about time drift of clocks involved into the LTDS, then to evaluate their stability, and finally to select the most stable one as a local clock. The counter provides a high measurement precision (<; 15 ps) and wide range (> 1s) that are obtained by combining period counting with two-stage time interpolation. The time counter is implemented in a universally available and relatively cheap programmable device from family Spartan-6 (Xilinx).