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Scholar
Scholar
1,085 Views
Registered: ‎12-07-2018

Sending 10Mhz clock over Fiber

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Hello,  I would like to sample a 10Mhz GPS clock and then transmit the clock over fiber. What transceiver could I use to do this?

 

Thank you,

Joe

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Explorer
Explorer
833 Views
Registered: ‎03-16-2019

You should consider that with no-encoding data transmition, your CDR clock of reciever will be loss.

See some applications in this range frequency to get a hint.

For instancee, 100 Mb/s ethernet use 4b/5b

1G ethernet use 8b/10b and 10G use 64b/66b with scrambler.

Check your reciever module to find out your prefer encoding.

It may be easy based on your experience, but for me is as like as walk a tightrope.

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Xilinx Employee
Xilinx Employee
1,050 Views
Registered: ‎03-30-2016

Hello @joe306 

I believe you can use any GTH/GTY, but I am not sure if I can understand your usecase correctly.

 

Please let me clarify:
(a) Do you want to transmit 10MHz sampled clock with GTH/GTY transmitter ?
(b) or Do you want to sampling 10MHz GPS clock input with GTH/GTY receiver ?


for (a),
Since GTH/GTY has a minimum line-rate=500 Mbps. You will need to send repetitive "0" or "1" to mimic 10MHz clock behavior.
unfortunately, You will need to consider clock duty and clock jitter performance yourself.

for (b)
Same limitation. GTH/GTY has a minimum line-rate=500 Mbps. So, you will need to set GTH/GTY in oversampling mode.
(It means recovered-clock mode is unusable, you need to set GTH/GTY to work with local clock )


Thanks & regards
Leo

Explorer
Explorer
1,031 Views
Registered: ‎03-16-2019

xapp1240 and it's reference design is so helpful for oversampling and sending and receiving data.

https://www.xilinx.com/support/documentation/application_notes/xapp1240-k7-us-clk-data-recovery.pdf

 

 

Teacher
Teacher
1,017 Views
Registered: ‎07-09-2009
its only 10 MHz,
you can use any IO pins on the FPGA

just use a pair in differential mode

the real question is what optical driver chip do you have.?

If its single mode fibre then you have a very different requirement to multi mode plastic over a much shorter distance,

a simple fibre led in one, would work great, but if you have a laser, then your in a different world,

Once you have defined what your driving, then we can help you decide what encoding you might need.
<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
Scholar
Scholar
976 Views
Registered: ‎12-07-2018

Leo,

 

Hi, thank you very much for responding to my message. Yes I want to do what is described in a). What IP should I look into from the IP Catalog?

 

Thank you very much,

Joe

Scholar
Scholar
962 Views
Registered: ‎12-07-2018

Hello, I'm looking at using a 10G CWDM SFP+ 1470nm~1610nm 80km Transceiver for SMF part# CWDM-SFP10G-80L.

 

https://img-en.fs.com/file/datasheet/cwdm-sfp-plus-1470nm-1610nm-80km-transceiver-datasheet.pdf

 

Let me know what you think of this transceiver.

 

Thank you,

Joe

 

 

Teacher
Teacher
945 Views
Registered: ‎07-09-2009
Your using a 10 Gb/s SFP to send a 10 MHz signal !

what length do you need to send over ?

this sort of stuff is a LOT cheaper and more rugged, and more than capable of sending 10 MHz clock

https://uk.farnell.com/broadcom-limited/hfbr-rus100z/cable-fibre-optic-1-fibre/dp/1247714

https://uk.farnell.com/broadcom-limited/hfbr-1531etz/transmitter-fibre-optic-5mbd-20m/dp/2393434?st=Vlink

http://www.farnell.com/datasheets/1812660.pdf?_ga=2.29282815.2110613125.1570030173-2072545025.1569659196

and you just drive it with TTL.
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Scholar
Scholar
934 Views
Registered: ‎12-07-2018

Hello, thank you very much for taking the time to give those suggestions. My requirments is that wavelength needs to be 1470,1510,1550,1590,1490, 1530,1570,1610 because we are interfacing to a 8 Channels 1470-1610nm, with Monitor, Expansion and 1310nm Port, LC/UPC, Dual Fiber CWDM Mux Demux, FMU Plug-in Module (https://www.fs.com/products/72428.html)

If you have any other ideas please share them with me please.

 

Joe

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Explorer
Explorer
929 Views
Registered: ‎03-16-2019

Wavelength is deteemine by yiur SFP. The most suitable is using Gth transievers. Read Xapp1240 completely. How the oversampling in transmitter works and how the receiver module woeks.

By the way l, if you want to send a clock signal be careful about your phase noise.

In an electrical domain we obly generate signal SFP is resoonsible for changing electrical signal to optical signal. If you have changable wavelength SFP, it may have imterface to control its wavelength.

https://www.xilinx.com/support/documentation/application_notes/xapp1240-k7-us-clk-data-recovery.pdf

Give kudos or accept as a solution 

If this reply doesnt helpful for you, dont hesitate to ask 

Thanks

Teacher
Teacher
921 Views
Registered: ‎07-09-2009
OK,
in that case you need the correct SFP with the correct frequency / power, and these connect to the GTx ports of the FPGA,,

So question now is , how are you going to encode the 10 MHz,
does you system need any specific encoding to get it to work.

A 10 MHz could just be an on / off ,
but network products need an encoding scheeme to work,

Are you looking at TCP/IP , UDP, NTP ?

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
Scholar
Scholar
887 Views
Registered: ‎12-07-2018

Hello, thank you for responding to my message. I really appreciate your time in helping me. So I have a GPS receiver on my board that has a 1PPS output and a 10Mhz output. I want to bring that signal in the FPGA and send it out on Fiber. If encoding is required then that is what I must do but I don't know which IP transceiver to us. There must be a simple way of doing this because I see some commerical products that appear to do what I am trying:

https://www.foxcom.com/satcom-solutions/platinum-series-rf-fiber-links/10mhz-ref
https://www.hubersuhner.com/en/products/radio-frequency/rf-over-fiber-series/gps-over-fiber/gps-over-fiber

I'm using a Zinq Ultrascale+ FPGA that has six ARM cores so I have that as a resource that could be used. 

If you have any ideas, I very much appreciate them.

 

Respectfully,

Joe

 

 

Teacher
Teacher
846 Views
Registered: ‎07-09-2009
Easy ?
look at the cost of those beasts !

sort out what encoding you need to do ,
and that will dictate what procseeing power you need ,

for instance, if your trying to emulate the units you reference, it looks like they do no processing, they say they transmit a sine wave , just an amplitude modulated diode would do that.

But , all the SFP modules I know of are digital,

work out what encoding on the fibre you need ,
then get back in a new question,
<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
Explorer
Explorer
834 Views
Registered: ‎03-16-2019

You should consider that with no-encoding data transmition, your CDR clock of reciever will be loss.

See some applications in this range frequency to get a hint.

For instancee, 100 Mb/s ethernet use 4b/5b

1G ethernet use 8b/10b and 10G use 64b/66b with scrambler.

Check your reciever module to find out your prefer encoding.

It may be easy based on your experience, but for me is as like as walk a tightrope.

View solution in original post