GSM-noise "buzz" issue / ways forward

Joerg Reisenweber joerg at
Mon Sep 22 18:15:10 CEST 2008

Am Mo  22. September 2008 schrieb Andy Green:
> Somebody in the thread at some point said:
> |> What I don't understand is how we get from 1.7GHz "infestation", which
> |> is clearly an issue since a bead on p4 of the headset jack does
> |> something, to these LF "dents" on MICBIAS.
> | My theory is RF is spoiling VREF, by entering the Wolfson chip via
> arbitrary
> | path (actual path doesn't matter, as RF can "jump" inside chip) and being
> | rectified on some nonlinear component of the circuitry inside chip
> You might remember I repeatedly proposed this ever since I found the
> errors around Vmid and Vref caps, and keep noting I can make the buzz
> come by scope probe on Vref.  Most recently, earlier today on this thread...
> Still, it sounds encouraging we found something to agree about.
> | Well maybe luckily we *might* eventually find a magic place for a
> (33pF) C
> | somewhere near Wolfson chip, to rework GTA02 out in the field this way.
> | Anyway I'd rather expect this magic fix to be found by try and error,
> rather
> | than probing on a setup that's completely changed by mere applying a
> probe to
> | it.
> We even agree about the possibility to find a better rework too now,
> excellent.
> -Andy

I agreed with you on nearly everything with regard to this buzz issue. I only 
am somewhat upset in the meantime we don't see any action on implementing 
bead fix to actual MP ASAP. Instead every time I suggest to fix new devices, 
and *then* continue to look for good fixes for already existing ones, this 
request gets torn down by an immediate vivid discussion about contamination 
pathes etc., leaving impression to TPE EE we are not on same page about doing 
new PCB to include EMI-filters on 3 contacts of JK4401.

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