A digital system of acquisition and coincidence for SANS

We have developed multi-channel signal acquisition with a coincidence digital circuit for a two-dimensional detector array of the small-angle neutron scattering spectrometer (SANS) of the Institute of Nuclear Physical Chemistry at the Chinese Academy of Engineering Physics. This paper discusses how to determine such factors as the coincidence time window and program dead time according to the characteristics of the detector signal and how to correct the timer to realize the data coincidence. The whole system can support up to 192 analog channels connected to a fast analog-to-digital converter, supporting speeds of 50 MSPS for each channel managed by a field-programmable gate array (FPGA). The internal clock of the FPGA is 50 MHz and the time accuracy is 20 ns. Preliminary experiments are carried out and the results are presented and discussed. The whole design can fully meet the needs of the spectrometer.