[gta02-core] Audio ECN update
rehar at saweb.de
Tue Sep 1 18:36:09 CEST 2009
Werner Almesberger wrote:
> Rene Harder wrote:
> ECN0038: 39pF+18pF ~= 56 pF ?
You found it! ;-)
I picked 47pF because we already have this value in our BOM, and for
this purpose i think a 47pF cap is sufficient.
> Speaking of filters, building LC with
> discrete components adds a lot of stuff. I did't realize you were
> planning to use discrete bits, sorry. How about just using an
> integrated filter ? We may need filters for SIM as well, and also
> the UART to GPS looks like a filtering candidate to me. Not sure what
> C4128 does.
Do you mean the EMI protection of the headset jack! Sure using an
integrated filter works with me, I just thought we do not want too many
And actually, I'm not very happy with the current bead choice (DC
resistance is quite high) so we probably would have needed a new
The only problem I see is finding the right one, wolfson recommends
filter with a gentle impedance profile otherwise they could introduce
ringing and those are usually unsuitable for clock or digital signal
lines (SIM/UART). So we would probably need different filters for audio
However, I think discrete filter are more flexible regarding vendor or
parameter changes. For example, if attenuation is to low, just replace
the caps or the bead with a different one, with an integrated filter
tough you have to replace the whole filter in hope that you find one
which fits your demand and footprint.
>> Another ECN where we haven't decided yet what we are going to do is
>> ecn0019 "Consider applying buzz fix", so comments are welcome.
> I asked Joerg and he thinks it would be safer this way. He also
> suggested to protect the headset mic as well. Not sure if we have
> the space, though. This is already a very busy area.
Hmm, indeed that's a crowded area and I'm not complete sure if that
would be necessary.
I'll move this one to done.
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