Global clock and trigger signals are needed in virtually all electronic circuits in the LHC accelerator and experiments. Therefore, a common distribution system based on optical fibers has been developed by RD12 [58] at CERN.
The Timing, Trigger and Control (TTC) system consists of various transmitter, fanout and receiver modules. Miniaturized receiver ASICs (TTCrx) will be integrated in FEC and FED.
The TTC transmits two time-multiplexed channels (A and B) at 
. Channel A is
reserved for the first level trigger signal, while channel B can be used for
custom purposes. The clock is recovered from signal transitions.