Clock distribution and absolute time calibration in NEMO phase 1

1
Clock distribution and absolute time calibration
in NEMO phase 1

• Martino Ruppi
• INFN di Bari

2
Outlook

• NEMO phase 1 mini-tower
• Clock Requirements
• Clock Shore Station implementation
• Time data flow
• The console

3
NEMO phase 1 mini-tower
Floor Control Module (FCM)

• FCM
• Symmetric systems offshore and onshore
• Dense Wavelength Division Multiplexing (DWDM)
  based on passive AddDrop
• Synchronous Protocol FCM onshore ? offshore
• Recovery clock offshore from data flow
• OM
• Front End (FE) and time-stamping in OM
• Analog signal sampled at fixed rate (200 MHz)
• Data recording triggered when signal exceeds a
  remotely-set threshold
• The clock recovered by FCM is sent to OM
• Synchronous Protocol FCM ? OM

Optical Module (OM FE)
Synchronous protocol
220 m
40 m
DWDM AddDrop
800 Mbps Synchronous protocol
100 m
Junction Box
4
Clock Requirements

• Time counting in OMs is based on clock recovered
  in FCM
• ?
• Each onshore FCM has to be synchronized by a
  low-jitter common clock
• We need to compare the OM time flow with UTC
• ?
• Onshore clock has to be extracted from GPS clock
  and time information has to be sent to the
  apparatus
• System scaling to KM3 size
• ?
• The clock produced has to guarantee a very high
  fan-out

5
Clock Shore Station

• Recovery clock from GPS receiver
• Clock Fan-out toward FCMs onshore
• Data and time recovery by IRIG B format
• UTC data flow sent to FCMs onshore in synchronous
  protocol
• Go-and-Back time measurements with each pair of
  onshore/offshore FCM by TDC
• Network Time Protocol (NTP) server
  synchronization of PCs by ethernet

NTP
RS232
GPS Antenna
GPS Receiver
PC
Ck 10MHz
IRIG B
Startx
SCSI
TDC
Connecting Board
FPGA
Stopx
4 X LVDS Ck 4MHz
4 X LVDS Time Data 4Mbit/s

• TDC 25ps sensitive
• GPS receiver (/-30 ns RMS)
• GPS Antenna (now on the roof ot the onshore
  station)
• PC control
• Modular PXI Crate FPGA board National Instr.

6
Data flow protocol to FCM
Data absolute time
Acoustic absolute time
UTC
sec.
min
hous
days
frames since 01/01/2006
start
Idle

stop
sec since 01/01/2006
Idle
Idle
Idle
Idle
500 bit 1/8000 seconds

• 8b/10b code (reveling error, scrambling 0/1, byte
  function embedded)
• Time upgraded each 125 ?s
• Data (and Slow-Control) absolute time
• Acoustic data absolute time
• Room to accomodate more information or commands

7
The Console (1)

• LabView enviroment

• FPGA Xilinx programming
• PC interface
• Instrument remote control
• Information storage in DB
• Logging
• Check alarms
• Accessible for control through ethernet

8
The Console (2)

Off shore time calibration


On shore Time calibration
Satellite signal GPS locking
FPGA monitoring and management
Go and Back time measurements TDC Management
9
Conclusions

• The system is currently working in the NEMO Phase
  1 control station
• Extension for a full-size 16-floor tower is
  undergoing (NEMO Phase 2)
• The setup can be easily adapted to serve even a
  KM3-size apparatus (it only needs more modules
  for the PXI crate)