The ATLAS level-1 central trigger system
The central part of the ATLAS Level-1 trigger system consists of the central trigger processor (CTP), the local trigger processors (LTPs), the timing, trigger, and control (TTC) system, and the read-out driver busy (ROD/spl I.bar/BUSY) modules. The CTP combines information from calorimeter and muon trigger processors, as well as from other sources, and makes the final Level-1 accept decision (L1A) on the basis of lists of selection criteria, implemented as trigger menus. Timing and trigger signals are fanned out to about 40 LTPs, which inject them into the subdetector TTC partitions. The LTPs also support stand-alone running and can generate all necessary signals from memory. The TTC partitions fan out the timing and trigger signals to the subdetector front-end electronics. The ROD/spl I.bar/BUSY modules receive busy signals from the front-end electronics, and send them to the CTP (via an LTP) to throttle the generation of L1As. An overview of the ATLAS Level-1 central trigger system will be presented, with emphasis on the design and tests of the CTP modules.
Optical timing, trigger and control distribution for LHC detectors
At CERN's future Large Hadron Collider, timing, trigger-accept and control signals must be distributed from a small number of sources to many thousands of front-end electronics destinations located on the ATLAS and CMS detectors. The LHC timing reference must be delivered with sub-nanosecond jitter and programmable phase. First-level trigger decisions must be broadcast from the central trigger processor to all the front-end pipeline controllers and delivered synchronously with the appropriate bunch identification, compensated for particle flight times and detector, electronics and propagation delays. In addition, broadcast control signals and individually-addressed controls and parameters such as calibration data have to be distributed. This paper describes how it is planned to broadcast all the signals over entirely passive multichannel optical fiber networks with uncontrolled path lengths. It reviews some of the technology options which are currently available and those which are likely to mature within the time frame of LHC preparation. It discusses how synchronization can be established over the system and describes how different distribution network configurations, laser transmitters and encoding methods can be used to deliver the signals using optoelectronic receivers which are becoming affordable for extensive deployment. >
TTC distribution for LHC detectors
At each of the CERN LHC experiments, timing, trigger and control (TTC) signals must be distributed to numerous electronic systems from a single location in the vicinity of the central trigger processor. A multichannel optical distribution system has been developed which can broadcast the signals to several thousand destinations from a few relatively high power laser sources over a passive optical fiber network with uncontrolled path lengths. The system delivers the LHC timing reference and first-level trigger decisions with the corresponding bunch and event numbers. It incorporates facilities to compensate for particle flight times and detector, electronics and propagation delays. In addition it provides for the simultaneous transmission of synchronized broadcast commands and individually-addressed controls and parameters, such as channel masks and calibration data.