-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Somebody in the thread at some point said:
| Only answer I'm interested in is: why don't we already have those | beads/EMI-filters in GTA02A7, though it's been validated to fix buzz since What was actually done on A7 revision? For example, what about the increased caps for Vref Vmid, are they present on A7 (or A6 for that matter)? The BOM teenie put on internal Wiki seems to be gone. I heard that there was some reduction in audio noise on A7, but what was that exactly? Why don't we do more of the communications taking place about these things in public. That way there can be better understanding not only internally (since private mails on this do not reach me either) but evidently we have people with real RF expertise on this list and there is every reason to let them know the details we find. | more than a month now, and we seemingly all accepted it's a viable fix for | GSM-buzz (or at least we agree it's safe to have those beads even for GTA03: | U4906, U4907!)? When are we going to give them a try on GTA02? Is anybody | assuming we could spoil GTA02 design to a point where even replacing those | EMI-filters by 0R would break the device? Adding the bead is one of only two things that seemed to impact the symptom, the other being removal of headset jack. Has the same bead been tried on the headset mic net and did it help there? | I urgently recommend to start to do a PCB with pads for EMI-filters *now*. | I absolutely veto on producing GTA02 with a 100uF on C4306. For those reading along at home, C4306 is new on GTA02 A7 and is between MIC1 net and 0V. I agree it's not clear 100uF there is going to do anything good about the problem, unless the dips are introduced directly on MICBIAS then trying to smooth them there is the wrong place since they have already been amplified on to there and we fight the blameless amplifier. But actually, I didn't see we proved quite where the buzz starts from as LF so we are not in a position to write this off as insane. I found I can reliably make buzz by scope probe on Vref, which is the source for input of MICBIAS amp, that's a bit of a clue I think. | @Sean: you asked me to solve this issue. That's my result for now. For going forward, we did reportedly find the bead helped for internal mic. So Joerg's point is right if we are looking at A8 then you would make a place for a bead on the PCB same as done for GTA03. It's the only doable thing that actually impacted anything we saw so far. I don't know it helps for external mic net, or if it is really a "fix", but it should do something for half the symptoms anyway. For both going forward and to solve issue for phones in the field, I get the feeling we can't do justice to understanding this problem internally and need to go talk to people experienced in this kind of RF issue. Uwe and his folks sound like a first port of call. I know a commercial outfit in UK I worked with before we can approach as well if needed. - -Andy -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iEYEARECAAYFAkjXZskACgkQOjLpvpq7dMrQ5gCfVa+d1UiN4u4/LI7jfGTwPvpL KEQAn3mJuI1NREzlQam7YpneURq7fUk7 =I5QX -----END PGP SIGNATURE----- _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
