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.
The ATLAS local trigger processor (LTP)
The local trigger processor (LTP) receives timing and trigger signals from the central trigger processor (CTP), and injects them into the timing, trigger, and control (TTC) system of a subdetector front-end TTC partition. The LTP allows stand-alone running by using local timing and trigger signals or by generating them from memory. In addition, several LTPs of the same subdetector can be daisy- chained. The LTP can thus be regarded as a switching element for timing and trigger signals with input from the CTP or the daisy chain, from local input, or from the internal data generator, and with output to the daisy chain, to the TTC partition, or to local output. Finally, in combined mode, several LTPs can be connected together using their local outputs and local inputs to allow stand-alone running of combinations of different subdetectors.
Cycle Slips in Phase-Locked Loops: A Tutorial Survey
Cycle slips in phase-locked loops are statistical, nonlinear phenomena. This makes a mathematical analysis extremely difficult. As a consequence, the results of such an analysis are not easily accessible to the practicing engineer. It is the purpose of this survey paper to present a self-contained discussion of cycle slips in phase-locked loop avoiding advanced mathematical tools. Based on the results of an extensive experimental study we explain the underlying principle of the complex interaction between nonlinearity and noise. The results are complemented by simple, approximate analysis which agrees well with the experimental findings. In addition, we present a new and complete set of diagrams on cycle slip statistics not presently available in the literature.