[gta02-core] ECN0010: LDO2/LDO4 swap implemented

[Werner Almesberger]

Joerg Reisenweber wrote:
> * C4119..22, +..28 move to other side of choke

This change is in ECN0038, which has been in "execute" for a while.
Rene, do you want to implement it ?

> *rename C3016 -> c4496 (complementary to C4406), to make mic path
> pseudo-sym. GND of C4496 next to gnd of jk4401 

Hmm, I'm not so sure about this one. The idea is to keep the
schematics similar to the ones of Openmoko GTA02, so that we can
find differences more easily. Particularly the audio subsystem
has evolved quite a bit by now, but I'd still be reluctant to
give up on this policy.

Of course, for anything done with the gta02-core material after
gta02-core, such historical ballast should be dropped.

> *suggestion: 1nF jk4401:6 to GND, to RF short HS MIC path when
> nothing plugged in

Wouldn't MICBIAS already be sufficient to keep this path calm ?

> *r4303, c4306 buzzfix not implemented ... ?

Why fit your hens with full-body armor if you can prevent the fox from
getting into the henhouse in the first place ? ;-) The design is still
buzzfix-ready (see ECN0019), so if the EMI filters go the way of other
plans of men and mice, we can implement the fix easily.

>   thought we go make that path symmetric like formerly done
>   anyway, so r4303 mustn't 0R

Indeed. What happened with that ?

>   c4307 is a nonsense, even to have pads for it. Remove C4307 footprints

So you're saying RF noise on MICx per se is okay, as long as it doesn't
creep into MICBIAS ?

>   we should replace (A)-R4305-(B) by (A)-R4305-(X), (X)-C4306_NC-(GND),
> (X)-R4399_0R-(B)
>   move C4303, C4304, R4305 next to wm8753, behind B3005

Ah, push the choke towards the mic and reverse the RC filter for the
buzz fix, with the option of reversing it again. Well, let's think
about this after considering the fate of C4307, above.

> *make B3005 (and B4105, B3004) look like decent C-L-C filters, like e.g B4419

Not sure what you mean. Are you saying the symbol, the visual
arrangement, or the circuit is flawed ?

> *kill R3004, R3005 finally!

Okay, that will be ECN0042, "Assorted AUDIO cleanup".

> *c3017 -> 1uF ?

I have to admit that the ACOP-ACIN path is a bit of a mystery to me.
Is there any description of what it actually does ? A search in the
data sheet didn't help :-(

> *c3003 AND c3008??? Seems we don't need both
>  c3002 same

Looks like the usual HF/LF pair, with the 100 nF cap right next to
the chip and the much larger 10 uF cap at some distance.

>  do we need B3001??

I'm not sure. Neither side of the bead should be infested with RF noise.
If in doubt, I'd keep it.

>  esp if we kill B3001, then c3001 AND c3005 also one of both is senseless

Agreed.

> *suggestion: place 100pF RF suppressor C parallel to C3014, C3012 and C3013
> -  we 
>   learned RF creeps in here and causes buzz. the uF-Cs are not sufficient
> for RF

This sounds like a good idea. Perhaps ECN0019 is a good place for
this, even if it isn't part of the GTA02 buzz fix.

Thanks a lot !

- Werner