Wifi / let's have RF stuff powered with high current source all the time because...

Andy Green andy at openmoko.com
Mon Aug 25 21:53:16 CEST 2008

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Somebody in the thread at some point said:
| Am Mo  25. August 2008 schrieb Werner Almesberger:
|> Andy Green wrote:
|>> It can be prototyped and the final PA spectral performance compared to
|>> "piece of wire", so this is something we can know rather than scare
|>> ourselves about.
|> You mean in GTA02 or in GTA03 ? For GTA03, that's definitely something
|> we should look into, also given that this subsystem is completely
|> different from GTA01 or GTA02. At last now we know what sort of problem
|> to look for, instead of just some "generalized badness".

I was thinking about current GTA02 situation which was discussed here,
with separate PA power arrangements. --->

| For GTA03 we have a datasheet that's very specific about ripple and
| resistance on VDD. Doesn't look good for a FET - IIRC.
| Also consider this module has battery support, so there is a decent
| supposed to be inside already.

Some of the modern high current MOSFET have Rdson that looks like a
short length of PCB track when the gate is driven hard.  Peak current
was ~2A, having a hard time getting my head around anything being able
to tell let alone care.  We already know from looking at buzz that VB
gets pushed down during TX somewhat in the characteristic gsm slot
pattern, it does not seem to kill spectral purity.

Point taken about the GTA03+ module though -- it should take care of
power switching inside the module boundary in a reliable way or the
module is broken, so we presumably should be able to just use the module
boundary power arrangements.  But still I guess we learn about it during
GTA03 EVB.  There was that guy who saw his GTA02 battery consumption was
stuck at 500mA on VB when he made no call, I really did not like to hear
about it since only the GSM side TX stuff gets that hungry and it seemed
there to be doing its own thing.

- -Andy
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