[gta02-core] ECN0032 (EMI and ESD protection for headset jack)
werner at openmoko.org
Thu Oct 8 16:09:32 CEST 2009
Rene Harder wrote:
> Yes [ R4401 ] looks pretty much like a current limiter.
Joerg and I had a quick discussion on IRC:
- he agrees that R4401 is probably a current limiter to protect the
codec's MIC1 input. Can't hurt to have it.
- he also agrees that C4405 should go. Also, R4404 can safely meet
the same fate.
- he suggests to switch to a symmetrical configuration for the
microphone, like in earlier GTA02 variants or in GTA01.
The change to single-ended in GTA02v6 was an unsuccessful attempt
to solve the buzz problem. A symmetrical design would have the
advantage of better common-mode rejection.
In the symmetrical design, R4301 and R4302 would be useless, so
it's not any more complicated than the asymmetrical design. Plus,
it would actually be a bit clearer what things do.
Regarding component choices, I looked for filter arrays which would
save even more space, e.g., Murata's NFA series. Alas, they all
seem to be difficult to source.
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