[gta02-core] ECN0032 (EMI and ESD protection for headset jack)

[Rene Harder]

Werner Almesberger wrote:
> 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.
>   

C4405 is already gone! I'll add the removal of R4404 to ECN0010.

> - he suggests to switch to a symmetrical configuration for the
>   microphone, like in earlier GTA02 variants or in GTA01.
>   

Okay, as discussed on IRC we'll change R4305 and R4303 to 1 kOhm. (ECN0022?)

>   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.
>
>