research of long distance clock distribution system université libre de bruxelles (iihe) yifan...

Research of long distance clock distribution system

Université Libre de Bruxelles (IIHE)Yifan Yang, Kael Hanson, Aongus Ó Murchadha, Thomas Meures, Michael Korntheuer

SEP 2012 TWEPP 2

OVERVIEW

• Askaryan Radio Array background

• Clock distribution over optical fiber based on low cost FPGA and jitter cleaner.

• Fixed latency link implementation.

• Conclusion and future plan.

SEP 2012 TWEPP 3

• Askaryan Radio Array background

• Clock distribution over optical fiber based on low cost FPGA and jitter cleaner.

• Fixed latency link implementation.

• Conclusion and future plan.

SEP 2012 TWEPP 4

37 stationsSpacing: 2 kmDepth under ice surface: 200 mSurface coverage: ~160 km2

Ice thickness below: ~3000 m

Each station:16 + 4 sub-firn antennas (sensitive between 250 and 800 MHz):8 vertically polarized8 horizontally polarized4 calibration pulsers (v-pol + h-pol)X surface antennas

Askaryan Radio Array

SEP 2012 TWEPP 5

Askaryan Radio Array

• Current ARA uses analog optical fiber • Easy, COTS (commercial off-the-shelf) item  • 1 antenna = 1 fiber => 4 fibers per hole • slightly high power draw• price > 10 kEUR per station  • 4 ADC board on surface controlled by single processor board

• Digital system• Custom designed• 4 antenna =1 fiber => 1 fiber per hole• Half the price• Extended communication system • 1 ADC board downhole controlled by one FPGA board • 50 ps skew stability is required in one station• 800Mbps data rate

SEP 2012 TWEPP 6

• Askaryan Radio Array background

• Clock distribution over optical fiber based on low cost FPGA and jitter cleaner.

• Fixed latency link implementation.

• Conclusion and future plan.

SEP 2012 TWEPP 7

Clock embedded in data

• self-clocking signal

SEP 2012 TWEPP 8

GTP

To SFP

From SFP

Recovered clock is synchronized with transfer clock but with larger jitter

SEP 2012 TWEPP 9

SI5368

Generates any frequency from 2 kHz to 945 MHzUltra-low jitter clock outputs with jitter generation aslow as 300 fs rms (50 kHz–80 MHz)Integrated loop filter with selectable loop bandwidth

Footprint compatible Interface compatiblewith on-surface processor board

SEP 2012 TWEPP 10

Evaluation board and measurement setting

IRS2 Control module

System clock

After switching to recovered clock, a synchronized link is established

Spartan 6 lx45t with 4 GTPs

SI5368

SEP 2012 TWEPP 11

Clock and data measurements

SEP 2012 TWEPP 12

Latency measurements

Before clock switching After clock switching

SEP 2012 TWEPP 13

Clock skew measurement

SEP 2012 TWEPP 14

• Askaryan Radio Array background

• Clock distribution over optical fiber based on low cost FPGA and jitter cleaner.

• Fixed latency link implementation.

• Conclusion and future plan.

SEP 2012 TWEPP 15

Latency uncertain from GTP

SEP 2012 TWEPP 16

Latency uncertain from GTP

SEP 2012 TWEPP 17

Latency uncertain from jitter cleaner

Fixed phase difference between input and output of the jitter cleaner is also needed to establish a fixed latency link.Cdce62005 and LMK03200 both are used in new evaluation board.

IRS2 Control module

System clock

SEP 2012 TWEPP 18

New evaluation board and measurement setting

Spartan 6 lx45t with 4 GTPs

Cdce62005(fixed delay)

Lmk03200(0 delay)

SEP 2012 TWEPP 19

Mean

(ps)

Std dev(ps)

P-p

(ps)

Popul-ation

1 934.46 9.7717 105.37 1.375M

2 925.43 10.100 99.239 1.25M

3 908.4 10.001 105.68 1.25M

4 934.98 10.047 103.64 1.25M

Clock skew measurement

SEP 2012 TWEPP 20

• Askaryan Radio Array background

• Clock distribution over optical fiber based on low cost FPGA and jitter cleaner.

• Fixed latency link implementation.

• Conclusion and future plan.

SEP 2012 TWEPP 21

Conclusion and future plan

• Achieved:• Clock distribution over optical fiber

• 50ps skew stability achieved

• Latency of the link is kept in a certain range after power cycle on both direction

• Things to do:• Long term, long distance, low temperature experiments

• Automatic calibration

• Remotely firmware upgrade

• System optimum

SEP 2012 TWEPP 22

Thank you!

SEP 2012 TWEPP 23

backup

SEP 2012 TWEPP 24

Clock separate with data transfer

250 meters standard cat5 cable