Re: [Discuss-gnuradio] USRP RF Daughterboards

[Matt Ettus]

David Bengtson wrote:
> Hi Matt:
> 
> Quick question on powering rf daughter boards. Looking at the schematic
> for the USRP, it looks like the external power connector goes to U502,
> which is a 3.3 V Regulator. DVDD comes right off the output of U502, and
> then AVDD is derived from DVDD by the filter's around L511, L510, L600,
> L601. It seems that there are two separate analog rails, AVDD1 and
> AVDD2, which power different thing's  on the USRP. How quiet are these
> lines?
> I'm right now leaning towards hanging a 3.3V regulator off the +5Vdc
> supply to power the GPS daughter board I'm working on.
> Also, where does the reference voltage for the ADC's come from?


The supply going to the dboards called 5V is actually the unregulated 6V
from the main supply.  That way you can use an LDO to regulate it down
to a clean 5V.  This is done on the TVRX board, and all the other boards
which are coming soon.

The AVDD going onto the dboards is the same one powering the
corresponding AD9862 codec chip.  It should be pretty clean, but you'll
end up with an even cleaner supply if you use your own regulator.

AVDD1 and AVDD2 each power one half of the analog stuff.  One is for the
"A" side, one for the "B" side.  This is the supply which becomes AVDD
on the dboards.

Matt