Speaker
Description
Summary
The Inner Tracking System (ITS) of the ALICE experiment contains six coaxial
cylindrical layers. Layers 3 contains 14 ladders each one hosting 6 SDDs (Silicon
Drift Detectors), while layer 4 contains 22 ladders each one hosting 8 SDDs. The
CARLOS end ladder board is placed on both sides of each ladder with the purpose of
acquiring and compressing data coming from each SDD before sending them towards the
data concentrator card CARLOSrx in counting room through optical fibers. The board
contains the compression chip CARLOS that performs a bi-dimensional compression of
the data coming from the SDD front-end electronics (called SDD module). CARLOS 16-bit
output bus is encoded with 8B/10B Ethernet protocol and sent to a 800 MBit/s single
mode optical fiber using a 1310 nm optical laser.
The CARLOS end ladder board receives the trigger signals and the configuration
parameters through a 40 MBit/s serial signal coming from CARLOSrx through an optical
fiber and converted using a photodiode.
An other photodiode is used for receiving the 40.08 MHz clock coming from the TTC
system. The QPLL ASIC on the end ladder board allows to obtain a clock with a
peak-to-peak jitter lower than 50 ps that is used both for the serializer (ASIC GOL)
of the board and for the front-end electronics.
A special control unit has been developed with the purpose of monitoring parameters
such as voltage, current and temperature related to the whole readout chain. The
control unit is remotely controlled from the DCS (Detector Control System) board
through the I2C bus. The CARLOS end ladder board also provides power for the analog
and digital voltages of the front-end boards under the control of the DCS system.
Each ladder has been tested with the use of the complete readout electronics system,
developed for ALICE SDD experiment, including its cooling system. The same test was
repeated when the ladder was assembled in cylindrical layers (layer 3 and 4) and, in
particular, the noise level due to different ladders working at the same time was
observed. The system was successfully tested, especially for what concerns data
transmission and reception of information via optical links (780 Optical Links are
used to process signals from the SDD-detectors and to send the results to the
off-detector electronics). Moreover the low voltage distribution and the DCS feature
were fully tested and the results confirm the efficiency of the readout electronics,
chosen for ALICE SDD experiments, which is integrated in the CARLOS end ladder board.
