TDC module for time-of-flight

Time-to-digital (TDC) technique was proposed to measure time-of-flight (TOF) that can determine the distance which is produced by the associated particle imaging (API) techniques including neutron methods with neutron generator and secondary radiation detection. The purpose of API method is for the elemental analysis and TDC shows the location of target object. In order to manage high resolution TDC timing, we used the propagation delay on the internal wires of field programmable gate array (FPGA) chips, utilized the place and route (P&R) delay difference. By setting P&R area constraints, we generated two precise ring oscillators with slightly different frequencies. The time difference between two ring oscillators is the time bin resolution of TDC. The multi-channel number of alpha-gamma event depends on the size of FPGA gates and configurable. Experimental results showed that the time interval of two ring oscillators of FPGA is about 100 ps, and varied by the lock detection between the operating frequencies of two ring oscillators that differ within 100 ps. After implementation of TDC counter TOF tagging schemes such as time stamp and control logic were generated and the event rate at each channel was more than 1 MHz. Finally, we investigated that TOF FPGA was useful in the multi-channel analyzer to measure the time interval between alpha-gamma of API system.