System Definition
The SCT links have to perform the following functions:
-
transfer binary data from each of the 4088 SCT modules to the RODs. There
are two streams of 40 Mbits/s data from each SCT module. Each link reads
out the data from one side of an SCT module. In the event of a link failure,
the data can be rerouted through the other link.
-
transfer the 40 MHz bunch crossing (BC) clock and the L1 trigger and all
fast and slow commands (TTC data) from the RODs to the SCT modules. BiPhase
mark encoding is used to send a 40 Mbits/s data stream down the same fibre
as the 40 MHz BC clock..One fibre provides all the TTC data for one
SCT module. In the event of a failure, then the TTC data can be taken
from a redundancy link from a neighbouring module.
The system is based on optical links and is described in the Inner
Detector TDR except that LEDs have been replaced by VCSELs. The components
are:
On-Detector
-
Custom low mass, non-magnetic package of 2 VCSELs and 1 PIN diode
-
DORIC4 chip to decode the biphase mark encoded TTC data.
-
VDC driver chip for driving the VCSELs
-
Rad hard fibre. Fujikura 50/60/125/250, pure silica core SIMM fibre
-
Opto-flex. A flex-rigid cable to mount the opto-package and the DORIC4
and VDC chips, that connects to the low mass Al power tape.
-
patch panels at PPB1,PPB2,PPF1(?),PPF2.
Off-Detector
-
PIN diode array to recieve the data stream
-
Amplifier/dicsriminator chip (DRX) to detect the PIN signal
-
VCSEL arrays to send the TTC data from the RODs to the Modules
-
BPM chip to encode the TTC data and drive the VCSELs
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Weidberg