GPS External antenna detect issue
werner at openmoko.org
Mon Apr 28 23:49:34 CEST 2008
Andy Green wrote:
> But at our normal situation with internal antenna and no load on
> external antenna, we drive VCONT to 810mV (26% Vdd).
Wow. Nice catch ! That seems to explain a lot of weirdness.
> the output is not so low impedence itself yet drives PNP base Q7602 by
> 10K, affecting the source.
Hmm, with LNA_AVDD = VCCRF = RF_3V, we get for R7617 and R7616 alone
VCONT = 3/(10+5.6)*5.6 = 1.08V
Perhaps increasing R7617 to 100k could help ? Not sure if it would
still let enough current through, though.
Well, if all else fails, we could just change R7616 to 0R, and
forget about external antennas and the problems they bring ;-)
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