A Trigger Interface Board for the Large and Medium Sized telescopes of the Cherenkov Telescope Array

Abstract

This paper presents the Trigger Interface Board (TIB), a system in charge of managing the trigger and clock signals in the cameras for the Large- and Medium-Sized telescopes in the Cherenkov Telescope Array (CTA). The TIB includes interfaces with the neighboring telescopes and with other subsystems in the camera. It receives trigger pulses from different origins and decides when those trigger signals should cause the camera readout. The decision is based on slow control parameters, the TIB internal state, the busy state of the camera, and the coincidence in time with other telescopes in a hardware stereo trigger scheme. Depending on the trigger origin, the TIB also generates an event data fragment, that is delivered to the camera Event Builder as part of the full raw event data. Additionally, it provides camera data-taking information to CTA central instances for monitoring purposes. The design of the TIB is based on two main components, namely an FPGA and a microcomputer. This structure provides fast digital processing capabilities, high-level software features for slow control and TCP/IP communication, and, especially, great flexibility to develop functionalities by working on the firmware and software levels separately.