THE COMPASS RICH-1 READ-OUT SYSTEM
INFN, Sezione di Trieste and ICTP, Trieste, Italy
on behalf of the COMPASS RICH group
COMPASS RICH-1 is a gas radiator RICH employing MWPCs with
CsI photo cathodes as photon detectors; the total active area is about 5.5
m2. The electronics takes the analog signals coming from the
~83 thousand channels.
The read-out system is mainly performed by 192 BORA boards.
The BORA is a large front-end board (432 channels) with local intelligence
based on a tightly interacting DSP-FPGA couple. The 192 front-end boards
are controlled via a dedicated PC resident board: DOLINA, equipped with 8
DSPs. Eight parallel DSP nets consisting of 25 DSPs each (one in DOLINA
and the others in 24 BORA boards) allow data transfer from / to the PC.
All BORAs are optoisolated from the DOLINA board, and each
BORA has two optical fibres to communicate with the DAQ electronics,
avoiding this way grounding interference. One optical fibre is used to
receive the trigger and the other is used to send data.
The BORA front-end electronics starts with 27 16-channel
COMPASS-Gassiplex chips which take the 432 signals coming from the photon
detectors. The analog output of these chips are digitised in 10bits at 40
MSamples/sec and these digital values are written into FIFO memories which
can store up to 100 events. The content of these FIFOs is read and
processed by the FPGA. The FPGA stores absolute thresholds of all channels
and subtract them from the digitised signals. Only values above thresholds
are framed and sent through the optical fibre to the global DAQ. The FPGA
works in different modes (calibration, acquisition, etc.) according to
what is requested by the DSP. The DSP calculates pedestal and noise of all
channels if it is required.
The board has built in self-test facilities, and provides
engineering frames containing hoard temperatures and voltages for
monitoring purposes. The read-out system can steadily work up to an event
rate of 75 kHz with occupancies up to 20%, reaching an effective
transmission data rate of 8.64 Gbytes/sec.
The system is described in details and its performances during the first
year of COMPASS experiment operation are given.