Title: A Digital Camera Trigger for the Cherenkov Telescope Array

Authors: K.-H. Sulanke, Y. Awane, R. Paoletti, A. Kretzschmann, H. Kubo,
T. Nakamori, U. Schwanke, M. Shayduk,  S. Vorobiov, R. Wischnewski
for the CTA Consortium

Type of presentation: Poster

The cameras of the Cherenkov Telescope Array (CTA) will be equipped 
with a local trigger logic that uses the pixel amplitudes to enrich
possible shower images and to suppress background signatures. We 
describe a possible camera trigger, based on the processing of overlapping pixel 
regions in a camera. The trigger consists of three stages. The first stage (L0) is
an accurate high speed PMT pulse discriminator. The second stage (L1) is a
single, low cost FPGA, processing overlapping 49- or 37-pixel regions. Different
trigger algorithms (such as three-next-neighbor trigger or more sophisticated schemes) can be
implemented and can even run in parallel. Besides its flexibility, the possibility to 
adjust the individual L0-delay in the sub nanosecond range is another
major advantage of the FPGA-based trigger. Overall, a 1 ns trigger window can be achieved this way. 
The third stage (L2) is either implemented in a central clusters FPGA or as a separate 
hardware unit. First successful tests of the digital trigger schema will be presented.