The Level-1 Trigger Pre-Processor
The KIP group carries responsibility for the concept, the construction and the operation of the
preprocessor system (PPr) of the ATLAS level-1 calorimeter trigger. The calorimeter trigger receives
analogue inputs from approximately 8000 calorimetric channels with a rate of 40 MHz. The rate is given by
the collision frequency of the LHC. At the highest LHC luminosities of 10
34 cm
-2s
-1 this will correspond
to more than 20 inelastic collisions every 25 ns. The accept rate of the level-1 trigger is expected
to be around 100 kHz. The large data reduction has to work reliably and without creating any
deadtime for data acquisition.
The level-1 trigger and the PPr are key components for the ATLAS experiments and are expected to
reach a 100% duty cycle of reliable operation.
The challenges described above have been solved by a group of 7 institutes. The complete system consists
of the following 4 components :
The PPr has been built by the Heidelberg group. The system has been validated by the construction and
operation of several prototypes. The PPr performs 10 processing steps on the calorimeter data :
- Conversion of an analogue differential into an analogue unipolar signal
- Coarse analogue calibration in units of transverse energy
- Extraction of a timing signal from the unipolar analogue pulse
- 10-bit digitalisation ranging to transverse energies of 250 GeV
- Digital Noise-Filtering
- Extraction of 2 timing signals from the digitised pulse
- Calibration of the digitised signal in energy and time
- Generation of 2 output paths for readout and realtime triggering
- Serialisation of the real-time path with 400 Mbit/s
- Readout of trigger data with a fast GLINK serial bus
The 10 steps have been mapped to the following hardware configuration :
