Speaker
Description
Summary
The CMS silicon Preshower is a fine grain detector placed in front of the endcap
Electromagnetic calorimeter. Its primary function is to detect photons with good
spatial resolution in order to perform pi0 rejection. The detector comprises around
4300 silicon sensors, each measuring 6.3cm x 6.3cm divided into 32 strips, with
strip
capacitance in the region of 50 pF. Each sensor is attached to a single PACE3
frontend ASIC, which performs amplification and shaping of the signals from the
silicon, followed by voltage sampling into an onchip analogue pipeline memory 192
cells deep. Upon reception of a first level trigger the analogue signals are
multiplexed out of the PACE3 to a 12bit 40MHz ADC (AD41240). The Kchip ASIC then
takes the digitized data from up to 4 PACE3, reformats the data and transmits them
to
the offdetector readout boards (ESDCC) via Gigabit Optical Hybrids (GOH). The PACE3
is situated on a PCB bonded to a silicon sensor mounted on a ceramic support and an
aluminium tile (to allow overlapping in one direction of adjacent sensors) to form a
micromodule . This PCB also contains a DCU chip for calibration of the PACE3, and
connects to the System MotherBoard (SMB) via an embedded polyimide cable. Four types
of SMB are used, connecting to 7, 8 or 10 PACE3. The SMBs contain the ADCs, Kchips
and GOH boards, as well as a set of control chips the CCU, LVDSmux4P, PLL, QPLL,
DCU, LVDSbuf used for setup of the ASICs and distribution of the fast timing signals
(clock, trigger). Up to 12 SMBs are connected together via polyimide cables to form
control rings . Each ring communicates with the offdetector VME modules (Clock and
Control System CCS) via Digital Optical Hybrids (DOH) placed on two adjacent SMBs
(for redundancy purposes). The low voltage is supplied to the system by CAEN
Easy3000
series modules through voltage regulators situated on the SMBs. Each SMB contains a
control regulator (CR) for supplying the control chips, and a group of readout
regulators (RR) for the PACE3, ADCs, DCUs, Kchips and GOHs. The CAEN system can
control the CRs and groups of RRs to allow the switching on/off of relatively small
units within the ES whilst still maintaining the integrity of the control rings
whenever possible. The micromodules are connected to the large ES lead absorber
plates. The possibilities of commonmode pickup by these plates, as well as the
possibilities of return current flow through them, have necessitated a precise
grounding and shielding scheme. With exception of the ESDCC, which is still in the
development phase, all components of the ES electronics system have been prototyped
and most are in full production. System tests have been performed with excellent
results in terms of functionality and performance.
