Re: [Discuss-gnuradio] 4702 board

[cfk]

    All right. Let me flesh out the idea a little bit more and ask a few
questions for you and Matt. First a procedural thing. Although I am most
partial to Linux (capitalization intentional), my schematic capture skills
are best with Orcad and Orcad Layout. I hope that you have no problem with
me doing the schematic in capture. I believe that I have Acrobat Distiller
on my windows (non-capitalization intentional) machine and can transfer both
capture design files and pdf files for the schematic and both layout
database and gerber (and perhaps pdf) files for the layout. This only has to
do with the fact that I can think & draw faster in capture/layout then
xcircuit/pcb.

    I was originally thinking of a companion board about the same size as
the usrp, but the notion of a daughter board implies a slightly smaller
board then the one to which it is attached. I think we need to ensure that
the size, mounting configuration and connector placement of all the parts on
this board are consistent with your and Matt's vision of how it should look.
If we are clever, then we can have a form factor which makes a 1.2Ghz,
2.4Ghz, VLF or other form factor all the same.

    In thinking of the output circuit from the 4702, would you or Matt have
an idea of the quadrature demodulator you might like to use. I did a search
on Maxim and found a MAX2451 about an hour or so ago, but I have not used
this particular chip before so I am a little unfamiliar with its care and
feeding. Perhaps you might have a better one in mind. Additionally, I
suspect we may want to buffer with a dual or quad opamp the output of the
quadrature demodulator chip as it leaves this board on the way to the
AD9862.

    I am thinking of a four layer board with power/ground in the middle and
signals on top and bottom. Not because it will be tight (it wont), but I
believe we get a better noise floor with a power/ground sandwhich. Its a
little better if the ground/power are on the outside by a dB or so, but then
you cant change things on the circuit board hardly at all.

    On the 24LC0224/025, which do you want? The 024 or the 025? Do you care
if its a DIP or do you wish the TSSOP package. I see this is also an IIC
device, so I presume tying their SCL/SDA to the other chips in one bus with
the WP* brought to a pin of yours or Matts choice on the interface connector
is the appropriate circuit for this one. I have used IIC eeproms before,
although I have been partial to Philips, the Microchip ones look very
similar. VCC=5V for the 024, I presume.

    You'll have to help me out on the IEC connector a bit. From the data
sheet it appears it is an "IEC 169-2", which looks like a european version
of a cable TV inlet connector. I'll have to get my $6 to Matt and get two of
these down here so I can scope that one out and make sure we are not trying
to put square pegs into round holes for our US engineers.

    My original thought on the LNA was that it would be in one of those
seperate little boxes with a male connector to mate with the tuner on one
side and a female BNC on the other. Those little guys are about 1 inch X 1
inch X 0.5 inch thick with ground a terminal on the case and power as a
feedthru. I think mini-circuits, Triquint and others have that sort of
thing. Perhaps you might have a part/model number in mind. I'll also look
over our LNA's on Monday and see what we are using in the lab. The thought
went that we provide a 2 pin MTA-100 header with power/ground for the LNA
box on the 4702 input since the 4702 is a big item sitting off the board a
couple of inches with its input snout off the edge of the board.

    I think I can get a fur piece along the path if I can get an assembly or
top layer gerber of the usrp, along with a sketch of how you and Matt would
like the form factor to look. In the meantime, I'll gather my thoughts
together and start the schematic capture. I will plan on iterating the
schematic and layout a couple of times. It is a lot easier to move the
little pixels around on the screen before the board is fabbed. A design
review via e-mail would also let me have confidence that this is what we
want. I shant draw that out, I'll put it together, publish it, iterate it
once, accept comments a second time and them we cast the result in
fiberglas.

    Maybe Brian can jump in here with his Maxim knowledge and help us out
with the schematic a bit as it fleshes out over the next week or so.

Charles, WA6LWB

----- Original Message -----

> Definitely.  It would make a great daughterboard for the new USRP
> revision that right now is in layout.  Matt can provide you the
> mechanical and electrical specs.  In the meanwhile, here are some of
> the relevant signals on the daughterboard bus: differential analog
> input to main board, I2C bus, SPI bus, about 8 digital i/o pins that
> can be controlled from the host software, 3.3V power and an
> unregulated +5V supply.  The analog signal will connect directly to
> the VIN+ and VIN- inputs of an AD9862.  You've also got access to the
> AUX DAC {A,B,C} and AUX ADC {A,B} of the AD9862 if you need them.
> Sure.  Each Rx daughterboard provides both I & Q.
> FYI, the 4702 has an IEC connector, not an F connector.  Perhaps you
> build your LNA (switchable in and out) on the daughterboard, cable it
> up to the IEC connector and provide either a BNC or F-connector as you
> see fit.
> We should have enough power through the daughterboard bus to power the
> module.  There won't be enough juice for high power xmitters, but that
> won't be a problem with this Rx module.
> We're all on the same page.  When Matt gets some breathing room he'll
> be publishing the mechanical and electrical specs for the whole system,
> but particularly the specs for the Tx and Rx daughterboards.
> Great idea.  We definitely want lots of "plug and play" daughterboards
> for the new USRP.  Each daughterboard will also have a bit of EEPROM
> (24LC024 or 24LC025) on it that identifies the board.  The host
> software will be able to query the motherboard and determine what
> daughterboards are loaded.

> Eric