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optical SFP multichannel transport
optical SFP multichannel transport
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Old 31st August 2019, 12:37 PM   #1
Asasl is offline Asasl
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Join Date: Apr 2013
Default optical SFP multichannel transport

Hi hobby colleagues!
I have long planned to develop and assemble a multi-channel audio system based on fiber optic connections.
Now optical SFP modules are inexpensive.

I know electronics well, PCB in Eagle,
writing in C and Python language, including for microcontrollers. I know the DSP, but only in theory. Never wrote for FPGA.

Join the open-project, especially FPGA specialists are needed.

Click the image to open in full size.

Mono module 60 W

Click the image to open in full size.

Last edited by Asasl; 31st August 2019 at 02:49 PM.
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Old 31st August 2019, 07:36 PM   #2
phofman is offline phofman  Czech Republic
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I see master clock at the XMOS. Would the remote units use PLL for clock recovery from the incoming stream? In that case why not use regular TOSLINK for the transfer?
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Old 31st August 2019, 08:23 PM   #3
Asasl is offline Asasl
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No PLL on remote devices will be used. The master clock is transmitted in the common TDM stream, the jitter of the SFP modules is very very small...
TOSLINK cannot transmit 8 channels 24 x 192 kbis/s x 8 ch = 36,864 Mbit/s
via SFP 1Gb, 200 such channels can be transmitted or over 60 channels 32x384 kbit/s
TOSLINK it's already yesterday.
SFP optics are much faster and cheaper, I wrote the prices in the figures

TDM frame for example

tdm_frame.PNG

Last edited by Asasl; 31st August 2019 at 08:37 PM.
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Old 31st August 2019, 10:36 PM   #4
phofman is offline phofman  Czech Republic
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Interesting. I know almost nothing about the SFP technology. How does it technically route audio clock through a switch without introducing any jitter/phase delays?
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Old 1st September 2019, 08:57 AM   #5
Asasl is offline Asasl
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Output / Input jitter SFP

jitter.png

For 1Gb interface jitter less than 200 ps
for perfectionists, you can take 10 Gb modules - 20 ps


Here's an example of what you can do for music and film

mch.png

Last edited by Asasl; 1st September 2019 at 09:17 AM.
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Old 1st September 2019, 09:46 AM   #6
phofman is offline phofman  Czech Republic
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OK, no switch, but splitter. Still I do not understand - can you run the SPF line at any frequency you want, or does it support just a set of fixed frequencies you can switch between?
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Old 1st September 2019, 10:11 AM   #7
Asasl is offline Asasl
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it is possible at any frequency in a certain band, for example 100 MHz - 1 GHz
The module does not know anything about this.
What came from the differential input LVPECL went to the laser and vice versa...
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Old 1st September 2019, 11:43 AM   #8
phofman is offline phofman  Czech Republic
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Thanks. IIUC the rate-select pin should switch the module to lower freq support, depending on params of the given module converter - SFP pin requirement - Electrical Engineering Stack Exchange

That jitter is comparable to decent SPDIF receiver https://statics.cirrus.com/pubs/whit...ansceivers.pdf
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Old 1st September 2019, 12:08 PM   #9
Asasl is offline Asasl
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I indicated the above values jitter tolerance. For SFP is equal 0.2 UI
For TOSLINK 0.2 UI
real jitter SFP will be much smaller - about 10 ps
Jitter is inversely proportional to the maximum channel transfer rate !!!

SFP module can be set/read parameters via bus I2C...

Last edited by Asasl; 1st September 2019 at 12:33 PM.
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Old 3rd September 2019, 05:29 PM   #10
CharlieLaub is offline CharlieLaub  United States
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I see you using this image to represent jitter in your system:
Click the image to open in full size.

I assume this is supposed to be a digital signal, alternating between high and low? Only at the very bleeding edge of what sample rates can be supported would such "rounding" occur...

I really do not think that picture of jitter in a digital audio signal area really all that applicable to the "real" world, and if so they would only be a of concern where the digital audio is rendered via a DAC. This is under the assumption that the bandwidth of the signal transmission system is more than capable of carrying such a signal, and that the digital signal is not being bandlimited elsewhere. At what frequency do you expect to see such a pattern?

Would not a simple buffer and re-clocker at the DAC end of the chain make all of this a moot point ?
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