Field Programmable Gate Array based Front-End Data Acquisition Module   for the COSMICi Astroparticle Telescope System
  We describe an FPGA based Front-End Data Acquisition Module (FEDAM) for implementing Time-over-Threshold (ToT) Time-to-Digital conversion (TDC) of pulses obtained from the COSMICi astroparticle telescope detector system photomultiplier tubes. The telescope system consists of a minimum of three scintillation detectors configured to detect particle airshowers likely initiated by Ultra High Energy Cosmic Rays (UHECR). The relative time delay of detection events between the detectors is used to estimate the angle of incidence of the shower. The FEDAM provides time-over-threshold measurements with a resolution of 2 ns. This allows determination of shower direction to an error of 0.035 (cos {\theta})-1 radians where {\theta} is the angle between the baseline axis through a pair of detectors and the plane representing the shower front. 
Darryl W. McGowan Jr, David R. Grosby, Michael P. Frank, Sachin   Junnarkar, Ray H. O'Neal Jr
astro-ph.IM