Asynchronous I2S FIFO project, an ultimate weapon to fight the jitter - Page 87 - diyAudio
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Old 18th August 2012, 03:49 PM   #861
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Quote:
Originally Posted by rdowdall View Post
Hello Ian - Do you have documentation I2S FIFO project that I could look at?. I am currently building a BIII

Thanks,

Rick
Please go to the link below my name. All the docs are at the bottom of the post. You can download them.

Ian
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Old 19th August 2012, 07:38 AM   #862
marce is offline marce  United Kingdom
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One caveat of using scope probes is they load the line being measured and so will alter the result. From the photo I couldn't see the probe return (GND) connection, it is also critical to keep this as short as possible and connect it as near to the probed signal as possible.
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Old 20th August 2012, 02:09 AM   #863
nattawa is offline nattawa  Canada
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I do see a return ground clip by the probe tip maybe your display monitor doesn't do as good job as mine does....

Low capacitance probes in high speed digital design era nowadays can reduce the line loading to a negligible degree. They usually load the line with only 1 - 1.5pf //1k-ohm and form a 20:1 wide band attenuator with the 50-ohm coaxial able and the 50-ohm far end terminating resistance inside the scope with excellent signal integrity.
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Old 20th August 2012, 08:25 AM   #864
marce is offline marce  United Kingdom
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Seen the return now zoomed in more, still a long return lead.
have a look at the info on the scope manufacturers sites on robe loading because from experience I disagree, the loading of probes is significant, when doing high speed digital simulation (even when doing a 12Mhz I2C clock) we have to moddel the probes, so we can see the before and after waveforms and what the wave form will look like when you probe it. That is using the best probes possible on a 13GHz scope used toinvestigate he signalintegrity of some designs including he DDR2 interface.
Notes on this from Howard Johnson:
http://www.signalintegrity.com/Pubs/straight/probes.htm

Last edited by marce; 20th August 2012 at 08:36 AM.
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Old 20th August 2012, 01:28 PM   #865
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Quote:
Originally Posted by marce View Post
Seen the return now zoomed in more, still a long return lead.
.....
.....
That is using the best probes possible on a 13GHz scope
Hi marce

Can't see but " still a long return lead" ... have to be bad day, ugh ...

Well....
Dying to see Your "real pro" measurements ...
Maybe You will "switch on" that 13GHz scope, You have on Your bench..
Hope return leads are short enough ..

Rosendorfer
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Old 20th August 2012, 01:56 PM   #866
marce is offline marce  United Kingdom
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It isn't on my bench, as I dont do that sort of thing, thats what the EE's are for, I do the simulations and the PCB's. And I wont be publishing any screen shots, not allowed its very high reliability stuff and covered by NDA's amongst other stuff.
Obviosly there is nothing an audiophile can learn from the wider world of electronics, in the real world probes affecting results is a real problem, and having long return current leads for digital is like a slot in the ground plane it creates an impedance miss match so will alter the signal. Hell here is even some real data from a chap called Howard Johnson regarding the problem, but as always audiophiles no best. As said in the real world it is a problemand has to be fatored in to what results you see, as a lot of this site is for achieving the ultimate sound reproduction then every detial of the reproduction chain should be examined.

Last edited by marce; 20th August 2012 at 02:14 PM.
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Old 20th August 2012, 02:06 PM   #867
nattawa is offline nattawa  Canada
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Quote:
Originally Posted by marce View Post
Notes on this from Howard Johnson:
Probing High-Speed Digital Designs
The low cap probe I was describing in my last post is the one shown in figure 3 of the page your link pulls. We use that probe daily at work, and we sometimes even put a 1-kohm 0402 resister leading to a 50-ohm SMA connector into the PCB design as a test point in our products. I personally don't see a more suitable and cost-effective probe than that for the application in question of this thread.
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Old 20th August 2012, 02:16 PM   #868
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Quote:
Originally Posted by nattawa View Post
The low cap probe I was describing in my last post is the one shown in figure 3 of the page your link pulls. We use that probe daily at work, and we sometimes even put a 1-kohm 0402 resister leading to a 50-ohm SMA connector into the PCB design as a test point in our products. I personally don't see a more suitable and cost-effective probe than that for the application in question of this thread.
That's a really good idea.

Ian
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Old 20th August 2012, 03:08 PM   #869
marce is offline marce  United Kingdom
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sorry having a very bad day, I do agree it is a good probe, still has an effect on the high rise time signals.
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Old 21st August 2012, 12:02 AM   #870
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Originally Posted by marce View Post
sorry having a very bad day, I do agree it is a good probe, still has an effect on the high rise time signals.
Yes, with a really nice oscilloscope, you can see more details of the real world. But you have to figure out what the 'real world' is from the screen of a low level one.

Do you have any idea about how to make it seeing more 'real world' from a normal oscilloscope?

Regards,

Ian
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