Modular time interval counter

This paper presents the design, operation and test results of a modular multichannel time interval counter built with the use of programmable devices. Its resolution is below 45 ps and the measurement range reaches 1 s. The counter contains 6 independent measurement modules, each built with the use of precise time counter implemented in a single FPGA (Field Programmable Gate Array) device Spartan-3 (Xilinx). To obtain both high precision and wide measurement range the counting of periods of a reference clock is combined with the two-stage interpolation within a single period of clock signal [1]. The interpolation involves a four-phase clock in the first interpolation stage and a time coding line in the second interpolation stage [2]. Modular architecture of the time counter increases its versatility and reliability. The measurement precision of device model is better than 150 ps in a full measurement range. As the acid test the time differences between signals of 1 PPS (Pulse Per Second) from tested clock sources and the reference 1PPS signal was also performed.