On 9/22/08, Andy Green <[EMAIL PROTECTED]> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Somebody in the thread at some point said: > | On 9/22/08, Andy Green <[EMAIL PROTECTED]> wrote: > | > |> 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. > | > | If you have problems with HF "infestation" a big cap will usually not > help. > > Completely agree, but MICBIAS gets something different from HF during > the buzz behaviour, it gets small depressions (like 100mV IIRC) in it at > ~200Hz period. Basically it is exactly like the PSRR was very low and PSRR? > the impact of GSM TX action on the battery rail (also 200Hz "dents" from > high current draw at TX time) was showing up on MICBIAS. > > MICBIAS as it sounds provides DC to power the microphone, now it has > 200Hz noise in audio range we assume this forms the basis of the "buzz". > > Someone has seen that with a 'scope and had the idea to put a big cap on > it to iron out the 200Hz dents. > > What I don't understand is how we get from 1.7GHz "infestation", which > is clearly an issue since a bead on p4 of the headset jack does > something, to these LF "dents" on MICBIAS.
Do we have a sound recording of this buzz? uwe _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
