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Old 23rd August 2011, 10:40 AM   #11
infinia is offline infinia  United States
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hi new
Look up the part number for the clock recovery device. In the data sheet or other app notes, you will see typical methods on input data circuits, choose what is close to your PCB or mod it to adapt to better schemes like pulse transformers and such. use approved parts from their source list.
PS Is there a schematic for the PCB or what>you want help but you not have given any information on the kit you have. If it's not a turnkey kit and there is no instruction provided then what did you expect to happen.
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Last edited by infinia; 23rd August 2011 at 10:53 AM.
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Old 24th August 2011, 05:53 PM   #12
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Thanks marce!

infinia, the receiver is CS8414. Ya! It was turnkey type kit, my first one. However, I'll be starting one from scratch once I finalize which one to use.

The purpose of the post was to establish practical methodology for S/PDIF termination independent of what the underlying kits are.
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Old 24th August 2011, 06:13 PM   #13
qusp is offline qusp  Australia
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marce thanks for the informative posts, while i have you here and i believe its within topic, i have read many times that a longer length (like 6-7') of properly terminated coax for spdif is better than a really short cable wrt reflections, is there any truth to this, simply a bandaid solution for improperly terminated lines, or just mumbo jumbo?

I have taken to using w.fl cables and smd bnc wherever possible and use usb->i2s in preference to spdif these days, but i still have an AES on lemo, 75r bnc with belden coax and a glass optical to round out the inputs on my dac, so i'm interested in your comment all the same, as i like your thorough but no nonsense approach backed with deep understanding.

I had to laugh at your external clock 'upgrade' post hehe, i find this a little humorous also

Last edited by qusp; 24th August 2011 at 06:15 PM.
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Old 25th August 2011, 12:32 PM   #14
marce is offline marce  United Kingdom
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Qusp
Before I answer I am going to prepare some simulations to illustrate my answer, as I also saw this thread. I believe there are some interesting Audiophile beliefs building up regarding digital signal transmission, that I have found rather interesting.
Again I am collating some links and references as well to go with my answer, as I want it to be as compherehensive as possible, as I quite often get shot down in flames for some of my views, also the simulations will show the effects of cable length and terminations.
I believe this may be from the thread regarding SPDIF attenuators (!).
What I will say initialy is that we strive to minimise the length of any digital interconnect and select termination schemes by using our simulation software,
empiral data and engineering practices, and measurement
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Old 25th August 2011, 02:32 PM   #15
qusp is offline qusp  Australia
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hehe, no problem marce, yeah it was mentioned there in that thread, but i have seen it elsewhere here and on other sites too. it never made a lot of sense to me, but like all good audiophile myths there is usually just enough truth in there to make it interesting and gain momentum (though the context maybe often incorrect)

i look forward to your post.
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Old 25th August 2011, 04:03 PM   #16
marce is offline marce  United Kingdom
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I had a look round and found some basic simulations I had set up around the time of some interesting (read humorous) threads regarding USB to SPDIF etc. I set up two basic co-ax lines with a driver and receiver, both 75r, one 50mm long another 200mm long, both un-terminated and terminated with a simple far end termination of 75r parallel down to 0V reference (shows how effective this simple termination is). The topography for the simulations are shown in co-ax#1.pdf and co-ax#2-terminated.pdf respectively. The stimulus was a 12MHz 50% duty cycle square wave, the line drivers have a 20-80% rise time of approx 3ns, should be about average for an SPDIF interface. I didn't model the connectors but can do with more time.
The simulation results are shown in the following PDF files:
IC1-IC3 is the 200mm co-ax cable
IC2-IC4 is the 50mm co-ax cable
I think the results speak for themselves, shorter is always better, and choosing the correct method of termination is critical and becomes more so as clock frequency and signal rise times increase. As to the accuracy of the simulation software, I use it for all clocks and high speed interfaces such as DDR/Gigabit interfaces and in conjunction with the electrical engineers have checked the results and waveforms using a 13GHz scope. I use the software to both check out my layouts and where we have a problem to simulate different termination options to find the best option.
I do believe that the cable length thread was getting into myth territory.
The best source of information for termination is Howard Johnson, High speed digital design, chapter 6.
When I do get more time, and training I want to do more audio based work with the software as I can also do analogue (similar to pspice, but it will take into account both the physical PCB layout and cables) and look closer at some of the digital ideas floating about. Hopefully we will be able to have some fun with the software in future. I also did simulations of the Hi-face vs cheap Chinese adaptor, that was around at the same time, and found that the very fast rise time of the hi-face (1ns) was causing the reflection problems, whereas the more benign rise time of the cheaper module (30ns) made it more tolerant of badly terminated interfaces.
Attached Files
File Type: pdf co-ax#1.pdf (14.3 KB, 58 views)
File Type: pdf IC1-IC3-200mm-no-termination.pdf (9.6 KB, 72 views)
File Type: pdf IC2-IC4-50mm-no-termination.pdf (7.4 KB, 52 views)
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Old 25th August 2011, 04:04 PM   #17
marce is offline marce  United Kingdom
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Terminated
Attached Files
File Type: pdf co-ax#2-terminated.pdf (17.0 KB, 42 views)
File Type: pdf IC1-IC3-200mm-75R-terminated.pdf (8.8 KB, 46 views)
File Type: pdf IC2-IC4-50mm-75R-terminated.pdf (7.8 KB, 39 views)
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Old 25th August 2011, 04:15 PM   #18
marce is offline marce  United Kingdom
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Cable length increased to 1500mm one has simple termiantion 75r to 0V, and one has no termination.
The termination can be further tweaked by adding a capictor to ac terminate the line, this would reduce the attenuation of the signal level. that does happen with dc terminated parralel end termination.
Forgot to add, the signal and reflections will cover a 1m cable in approx 5ns, so in 10ns your first reflection is back at the transmitter, but will already cause peaks and dips after 5ns. The 50mm cable the signal will do in approx 0.25ns, the 200m in 1ns, based on the rough velocity factor of co-ax cable being around 0.66C.
Attached Files
File Type: pdf 1500mm-both.pdf (9.3 KB, 49 views)

Last edited by marce; 25th August 2011 at 04:21 PM.
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Old 25th August 2011, 04:28 PM   #19
marce is offline marce  United Kingdom
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some good signal integrity sites:
beTheSignal.com
Welcome
Publication Index by Title - Dr. Howard Johnson
Speeding Edge consultants specialize in high-speed PCB and system design disciplines

"Right The First Time" Lee W Ritchey a free download, worth the effort.
Right the First Time

And the SI Bible:
"high Speed Digital Design" Howard Johnson

and a couple more links.
http://www.sabritec.com/technotes/PD...l_Tutorial.pdf

Design for Signal Integrity: Unit 02 Integrity of Digital Signals

Data Communications Basics
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Old 25th August 2011, 08:47 PM   #20
qusp is offline qusp  Australia
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wow, thanks mate, thats a great resource that i'm going to have to pick over thoroughly when i have a more functional brain, its 5.45am here after a long day. yeah the hiface spdif version had a fair few issues, the oem usb-i2s module isnt quite as bad, but i'm not using either anymore. thanks a bunch! in my own experiments proper line termination (and yes a basic filter too) and the w.fl, or u.fl interconnects has given best results, so yours dont surprise me. perhaps this could even be made a sticky with a few more contributions
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