Precyzyjny przetwornik czas-liczba z powielaniem i uśrednianiem czasu trwania impulsu

This paper describes the design and test results of a time-to-digital converter with 1.9 ps resolution and measurement uncertainty below 12.2 ps (Fig. 4). The time-to-digital conversion is based on time width averaging. Information about the measured time interval is contained in the width of a pulse that circulates in a closed delay loop and its width is measured by the counting method with use of a high frequency multiphase clock (Fig. 1). The converter resolution is directly proportional to the number of cycles of the measured pulse in the delay loop, the number of phases and frequency of a clock used (2). However, increase in the number of loop cycles causes growth in the jitter of circulating pulse edges that finally leads to deterioration in the measurement precision. Therefore, in order to obtain the highest precision of conversion, the number of cycles for which the converter provides the smallest measurement uncertainty was experimentally determined. In addition, to minimize a disadvantageous impact of unequal propagation times of the loop elements for the rising and falling pulse edges on the value of the measured time interval, the information about the measured time interval is contained between the rising edges of the pulse-pair instead of the opposite (rising and falling) edges of a single pulse (Fig. 2). The converter was implemented in a programmable device Spartan-6 manufactured by Xilinx. (Xilinx).