[gta02-core] Modem schematic / RF help needed
rehar at saweb.de
Mon Sep 7 21:31:54 CEST 2009
Dave Ball wrote:
> I've had a first stab at schematics for the Telit modem. Comments,
> feedback, abuse all welcome :-)
Do we need the transistors Q8101/Q8102?
Telit mentioned that an open collector output is required but I'm not
sure if the GPIOs of the CPU are Hi-Z outputs or can be switched into
this state. However the PMU's GPIO lines are all open drain outputs so
there we wouldn't need them.
I think the current should not be a big problem for the GPIOs because
Telit specifies the max current on MODEM_ON is limited to 100uA.
> Noted missing is the antenna circuit. Is the external antenna
> connection something we want for gta02-core? I know I'll not use it,
> but I guess others might? Also, I was hoping someone else might want to
> have a look at the RF bits - I've no idea what's appropriate here, and
> me guessing probably isn't the best approach! Any takers?
If we only use one internal antenna, the antenna circuit doesn't require
any additional components (assumed antenna Zin=50Ohm). The only
requirement is that the antenna is connected through a plain 50 Ohm
transmission line with less than 0.3dB loss.
What type of antenna are we going to use, is it a commercially available
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