Transcript Document 7601470

http://www.phys-astro.sonoma.edu/people/students/baker/SouthPoleFoucault.html
Clock
Distribution
for IceCube
Gerald. Przybylski
Lawrence Berkeley National Laboratory,
Design Review, September 16, 2005
History
• string 18 implementation:
o Rubidium module slaved to GPS Clock
o fan-out port for each domcom card.
• string 21 implementation:
+ OCXO GPS clock, Symmetricom ET-6000
+ Passive fan-out to each DOM Hub (DSB Card)
+ Sub-nanosecond skew and jitter demonstrated
+ Simple and Reliable, but not scalable
MCU Requirements
• Straightforward; conceptually very simple
• 5ns absolute accuracy (skew and jitter), within the IceCube counting house
> Across all DOM Hubs (at DOR cards)
> Fixed and stable offset from Universal Time, Coordinated (UTC)
> Based on Scattering Length in the ice
• Distribute 10 MHz, 1Hz and Time Value String
• Free from Metastable states/events; no glitches
• Measurable and Verifiable
• Single driver per output-port; no shared drivers
• Robustness requirements in ERD
x Mainly dealing with satellite drop-out and loss of availability
x Also dealing with tracking multiple GPS clocks
• Phase accuracy: 0.4ns at fan-out, 0.7ns at DSB, and 1.0 ns at DOR
IceCube + IceTop + AMANDA
• IceTop same as IceCube
• IceCube to AMANDA
*** Zeuthen/Wuppertal; Install 05/06; Holger et. al. ***
Fiberoptic transmitter driven by GPS clock
Fiberoptic receiver drives TWR (GPS4TWR)
Autonomous from the MCU Clock Fan-Out subsystem
10 MHz BNC, 1Hz BNC, IRIG-B BNC
10 ns precision with respect to IceCube time
•Justification:
AMANDA to IceCube
***realized
Same players
“We
for Amanda that any artifial jitter below 15 ns in the MC has no
Triggeronsystem
signalsorover
Fiberoptic
link to IceCube counting house
influence
reco accuracy
background
rejection.
DOM
Main
Board(s)
on a “String
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then said on
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Then others
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NOT COVERED
IN DETAIL
IN THIS TALK
vertical tracks close to a string scattering may be negligible and a 5 nsec request
makes sense.”
-- Christian
Our GPS clock
ET-6000:
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Time to first fix: < two minutes
Outputs operational: < five minutes
Timing accuracy better than 2 µS & frequency accuracy better than 1E-8
Full system accuracy (100nS) within one hour.
10 MHz output, 1Hz output, Time burst output
GPS from US Naval Observatory
clock ~2x10-15 Accuracy
MCU Brick-Walls
ET-6000 Specifications:
• 1Hz output is:
positive (rising) edge on time,
within ±100 nanoseconds relative to either UTC or GPS
with six or more satellite averaging with 95% confidence. (± 150ns peak)
• 40ns RMS accuracy (jitter not specified)
• Cannot “Vote” multiple clocks; Neighboring clocks don’t track!
x Tracking Algorithms in GPS clock “PLLs”
x Variations in path, and multipath
x Constellations and satellite switch-over
Unlock Behavior
• Power Up:
+ Sync to Satellites within an hour
> Elapsed Time Format until “Tracking”
- Hic-ups while searching; every 2 hours…
• Potential Loss of lock:
x Clock Firmware (a-la TrueTime 2000 problem)
x Power Outage
x Misadventure (Murphy…)
x Wind/Weather damage to Antenna (speculative)
x National Security outage (speculative)
Flywheeling/Freewheeling
• TCXO Clock “continues” for hours
• Optional OCXO “continues” > 1 week
Aging
±5 x 10-10 per day, ±5 x 10-8 per year
Phase Noise
-115 dbc/Hz @ 10Hz
-94 dBc/Hz @1Hz
• Optional Rubidium Oscillator clock ~100ns per day slew WRT
Aging
< ± 5 x 10-8 over 20 years,
Phase Noise
-90 dBc/Hz @10Hz
~ -80 dBc/Hz @ 1 Hz
Ru: Good short term stability, best hang time
OCXO: best short term stability, good hang time
Based on Symmetricom ET6000 series product specifications/experiences11
2004-2005 Implementation
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One GPS clock, an ET6000-OCXO
Simple Passive fan-out (resistive splitters)
All 9 DOM Hubs driven; All clock BNCs used!
0.35ns Jitter and Skew measured in situ at NPX
DOR Firmware Improvements fixed NPX GPS “glitches”
Not scalable to 90 Hubs
2005-2006 Implementation
• 2U chassis with 24 port fan-out (2 cards)
o Modulates 1Hz signal
o RJ-45 distribution cables carry 10 MHz , modulated 1Hz, & TVS
o All balanced signaling
• < 0.6ns skew and jitter measured on the bench
• Passed MOAT: sps-ichub04, sps-ichub05, domhubjr, domhub51
• Good Noise Immunity
• Stepping stone; scalable to needs of IceCube
Design Goals/Drivers
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> 90 ports plus Spares
Meet accuracy, jitter and skew requirements
Convenience: Single distribution cable per DOM Hub
Measurability/Verifiability: Easy to confirm phase across all ports
Reliability/Robustness: Quality components. No electrolytics.
Noise Immunity: Balanced signals to DSB cards
Minimize hard connections between racks: Magnetic coupling
Modularity/Extensibility/Maintainability
Hot-Swappable Port Cards
Independent Port Drivers for each signal
Low power
Off the Shelf Components
No heroic solutions
Simplicity! (no programmable logic in clock distribution)
Signaling Details
• Balanced 10 MHz 500mV P-P through ‘ethernet magnetics’
- High common-mode immunity
- Suppress EMI emission & RFI pick-up
- Avoid ‘Ground Bounce’ pick-up in the counting house
- Commodity components: compact, inexpensive…
• Modulate* the 1Hz signal (180deg Phase Modulation)
* required to pass through ethernet magnetics…
• RS-422/RS-485 differential serial
+12/-7V CM range
2
5
U44
S N7 4LV C1 G1 4DB V
U45
S N7 4LV C1 G1 4DB V
C131 DO NOT LOAD
2
4
C131
10 pF
Registered 1Hz
U47-4
3
3
2
R56
10 0
1Hz/1PPS
4
1
10 MHz
10 MHz
3.3V
5
3.3V
Modulated
1Hz
3.3V
2
D
CLK
U47
S N7 4LV C1 G7 9DB V
4
Q
U46
S N7 4LV C1 G8 6DB V
1
4
2
3
1
3
1Hz
GND V dd
5
5
3.3V
MOD_1Hz
Rev 0 Fan-Out Card
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12 Port
0.6ns port to port skew, worst pair
<200 ps jitter
Symmetry matters!
Passes MOAT
Revised DOR Firmware now supports Modulated 1Hz
Inputs directly from GPS clock in Stand-Alone configuration
Passes Fluorescent Lamp noise immunity test
Status LEDs & Test Header
2006 Implementation and Beyond
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VME form factor conditioner card (1)
in 2006
VME backplane fanout mezzanine card (1)
in 2006
VME form factor 12 channel fan-out cards (9)
proto now
VME form factor Monitor card (1)
2006 goal
(Least well defined)
DOM
Hub
Coax Cable (2)
GPS Clock
…
Serial Cable
RJ-45 Cable (90+)
DSB
Port Card Features, Rev 1
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2-wideVME form factor; 12 RJ-45 port
Common 10 MHz from Backplane
Common modulated 1Hz from Backplane
Common Serial from Backplane
LVDS inputs, instead of direct GPS clock signals
One Point Signal conditioning
2 minor schematic corrections
Skew tweaks
Additional Monitoring points: P2 and Header
(e.g. demodulated 1Hz)
Backplane Fan-Out
• Active Piggy-back card mated to “Back-of-Crate”
style VME backplane over Socket “2”
• Independently drive each EVEN socket
• Match phase at each driven socket
• 1-to-10 LVDS-to-LVDS fan-out chips
• Match skew to each driven socket
Piggy-back
Card
Industry Standard “Back of Crate”
style Backplane
Conditioner card
• Driven by GPS clock 10 MHz, 1Hz, and Serial
• Modulate 1Hz signal
• Control skew by design
• Ensure symmetry of port signals
• Drive LVDS backplane fan-out
• Status indicators/LEDs
Prototyped on the Fan-Out card
Monitor Card
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Occupies an Odd Slot in VME card cage (e.g. #1)
Implement GPS clock Monitoring specified by PDR Document
Could contain FPGA, & SOPC, or SBC in a DIMM form factor
Could report via ethernet
Scope TBD
Watch List/Wish list
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“Lock” status from GPS clocks
“Tracking” status from GPS clock
“Power” status from GPS clock
Parse time strings for error conditions
Parse GPS Clock console port output
Rich set of Status bits/words
Satellite constellation
• Monitor phase offset between multiple GPS clocks
Verification
• Reference signals on header
10 pin header on DSB
10 pin header on Fan-Out card
4 pin header on DOR card (inside DOM Hub)
The Bottom Line
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Fan-Out card comfortably meets the 5ns Requirement
Our GPS clock is a good choice, for the money
No speed bumps this year
On track for the final assault
Single unit, flexible, modular design
Builds on previous successes
Avoids heroics and death marches.
Fin
Verifications in situ
IceCube
AMANDA
Opt 1: Measure Fiber Round-Trip time (2 fibers)
4”
Opt 2: Use Portable Atomic Clock
- packaged PRS-10
- battery power
Steps:
1. Measure/calibrate WRT IceCube clock
2. Transport clock to MAPO
3. Measure fiber distribution signals in MAPO against Atomic Clock
4. Transport clock back to IceCube Clock
5. Check Calibration
Repeat 1 – to – 5 until satisfied
• Measure/Verify within 1ns should be achievable.