This is a VME card that may be used to receive and recover the RF
signal, bunch and revolution clocks over a White Rabbit network.
Whilst this board is targeting a specific application at CERN, this
design could be used for the general recovery of RF signals, related
event clocks and triggers transmitted via a White Rabbit network.
The project is specifically targeted as a replacement for the existing
BOBR (Beam Synchronous Timing Receiver Interface for the Beam
Observation System) and will therefore use the same VME format factor.
We require a BOBR replacement card because the RF will no longer be
distributed via the TTC network. The RF will be directly sourced from
the Low Level RF system. The LLRF is responsible for driving the
cavities with the appropriate RF. The LLRF utilises a DDS to generate
the required RF, enabling the Frequency Tuning Words (FTWs) to be
extracted and directly encoded into packets and then broadcast on a
White Rabbit network.
This VME card receives packets containing FTW and IQ setpoints from the
LLRF system. Then, using a FPGA with an assortment of analog components,
this design is able to recover the original RF signal.
This VME card can recover two RF channels, each comprising:
RF signal (up to ~500 MHz tbc).
Bunch or event Clock.
Turn or orbit Clock.
Contains monitoring options for the White Rabbit clocks:
10 MHz in/out SMA/SMC.
White Rabbit clock.
General purpose LEMO connections:
4x GPIO LEMO.
External clock input.
External stop/sync input.
Dual SFP connectors with White Rabbit compliant interfaces.
Beam Synchronous Timing Message
In addition to recovering the RF signal, bunch and turn clocks the BOBR
card needs to receive the Beam Synchronous Timing
This BST message should also be transmitted over the White Rabbit
network. Therefore, it would be beneficial if this design could also
behave as a CTG-BST
and inject the BST Message into a WR network.
The BST Message currently contains three types of information:
UTC timing - now provided directly via White Rabbit
BI specific triggers - we need a new way to implement these
Beam properties - for example; momentum, turn number, etc.
Time of Flight Corrections
BE-BI have a requirement that:
Bunch clocks are compensated for time of flight.
Turn clocks are compensated for time of flight.
For the SPS accelerator the time of flight for the particles changes as
they are accelerated.
Distributing the timing and triggers via a White Rabbit network will
incur a latency cost. Each switch may contribute up to 10 microseconds
of delay (equivalent to 2 km of fibre cable) in worst case conditions.
Therefore, it is likely that the implementation will have to work with a
latency measured in multiples of the turn or orbit period (23.1
microseconds for SPS).
Functional block diagram
Connectivity and IO
A 6U VME format factor that supports BI's VME crates and connections
to the PO connector.
Dual SFP connectors that are White Rabbit compliant.
External high performance 10 MHz oscillator/PLL, for White Rabbit 10
MHz clock clean-up.