Content originally posted in LPCWare by Pacman on Wed Nov 20 08:56:01 MST 2013
Strange that people can't send me email anymore. This used to work. Perhaps I'm marked as a spammer, as I wrote a long reply to a blog-post, which was rejected; and I didn't even try to sell anything. ;)
Anyway... It's strange that there are still errors; and you aren't even switching channels.
Unfortunately I can't do much testing in that area here.
Quote:
I have tried different chokes on the Vdda/Vssa/Vrefp/Vrefn pins without any effect
Uhm.. You say "Chokes" - are they 'coils' or are they ferrite beads ?
-If they're coils, try ferrite beads instead; for instance 330R/200mA (BLM18BD331SN1D) or 470R/1A (BLM18PG471SN1D).
Between the ferrite-bead and the pin, connect a 100nF capacitor to GND.
If you have access to a data-logger/-analyzer, you could perhaps check if the input signal changes drastically.
Just in case; I think you've already checked this, as you've isolated the power supply too: Make sure there's enough power available to your microcontroller.
But you mention that noise is coming down the data-lines. Is this noise on the ADC pins, or on other GPIO pins ?
Since it's a prototype PCB... If the noise is coming in on other (GPIO) pins, it might help to run a GND trace on both sides of those data lines as far as you can, and VIAs to a GND plane on the back-side.
Running a GND trace on both sides of your ADC traces plus a GND plane below them might also be a good idea.
I don't know if there is any help in any of those things I mentioned; you probably tried them all, but if there's a chance that I hit anything, it's been worth it. :)
I think I've run completely out of ideas.
[color=#00f]Are there any ADC experts in here, who can assist ?[/color] :)