Newbie PCB

[linobi]

Hi there!

I need some advice. I want to make a circuit to drive a VGA monitor. I'v
done it with the FPGA trainer boards with Xilinx chips, but now I want t
design a custom board that host only the necessary circuitry to do so an
not depend on eval boards with lot of stuff I don't need.

I've got already a bit experience on designing PCBs, I get pretty muc
along with the EagleCad, I've build mostly boards with microcontrollers an
simply stuff. But now for what I see, handling FPGA is a completel
different thing.

For what I've been reading, FPGA need a lot of requirements, 50-ohm
impedance for some clock traces, copper layer thickness, lots of differen
power planes,... heck, there is even some excel spreasheet from altera t
calculate power supply stage decoupling caps =S

Now I realize this might be a project beyond my current training, however
I want to give it a shot. I just need the basics: voltage regulators
configuration ROM, 50MHz clock, downloading cable interface; and of course
the VGA dac and some extra broke out pins to interface a microcontroller.

Now, my question is... from the two FPGA biggest names, Altera and Xilinx
which one do you think would be easier to implement? Like in th
programming interface, in meeting the power requirements, clock sources
etc...
I mean, it's not that I want to start a flame war, I suppose there must b
one superior in this particular aspect, or maybe not, and both are equall
easy/difficult to use.

And of course, as a last thought, if you thing I better should stick with
demo board and leave this for the future when I get to study more abou
transmision lines, advanced CAD tools, etc...

Regards



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[Tim Wescott]

On Mon, 08 Aug 2011 06:52:10 -0500, linobi wrote:

Hi there!

I need some advice. I want to make a circuit to drive a VGA monitor.
I've done it with the FPGA trainer boards with Xilinx chips, but now I
want to design a custom board that host only the necessary circuitry to
do so and not depend on eval boards with lot of stuff I don't need.

I've got already a bit experience on designing PCBs, I get pretty much
along with the EagleCad, I've build mostly boards with microcontrollers
and simply stuff. But now for what I see, handling FPGA is a completely
different thing.

For what I've been reading, FPGA need a lot of requirements, 50-ohms
impedance for some clock traces, copper layer thickness, lots of
different power planes,... heck, there is even some excel spreasheet
from altera to calculate power supply stage decoupling caps =S

The copper layer thickness requirement comes from current supply
requirements. 50 ohms impedance on clock traces _hopefully_ only applies
if you're going fast.

Now I realize this might be a project beyond my current training,
however, I want to give it a shot. I just need the basics: voltage
regulators, configuration ROM, 50MHz clock, downloading cable interface;
and of course, the VGA dac and some extra broke out pins to interface a
microcontroller.

Now, my question is... from the two FPGA biggest names, Altera and
Xilinx, which one do you think would be easier to implement? Like in the
programming interface, in meeting the power requirements, clock sources,
etc...
I mean, it's not that I want to start a flame war, I suppose there must
be one superior in this particular aspect, or maybe not, and both are
equally easy/difficult to use.

And of course, as a last thought, if you thing I better should stick
with a demo board and leave this for the future when I get to study more
about transmision lines, advanced CAD tools, etc...

I don't know about which is better, but I would hazard a guess that if
you're just running a 50MHz clock then you can get by with a lot less
precision in the board than if you're trying to run right at the limit of
the part. The biggest clock issue I'd be concerned with would be
reflections causing false clocks, and that can be cured by putting your
oscillator as close to the FPGA as you can get it, and/or terminating the
clock line.

I would recommend using a leaded package, as those can, with only
moderate difficulty, be soldered by hand. If you're willing to forgo
being able to use all the pins, you may even be able to use a two-layer
board, although it's probably smarter to go with at least a four-layer
board with ground and power planes.

I think you could do this with EagleCad, if you're careful and know what
you're doing.

--
www.wescottdesign.com

 

[maxascent]

The best thing you could do is to have a look at some of the schematics an
gerber files from the Xilinx boards. Getting a schematic that i
functionally correct shouldnt be too much of a problem but you need to be
bit more carefull with the pcb. The lower the frequency you use the easie
things will be, so you may be better off sticking to around 50MHz for you
first board. BGAs are not hard to work with, however you can forget abou
soldering them yourself. So if you plan to do the soldering yourself the
use a non BGA package. I mainly use Xilinx devices but I doubt there is to
much difference between them and Altera.

Jon


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[glen herrmannsfeldt]

linobi <linobi@n_o_s_p_a_m.msn.com> wrote:

I need some advice. I want to make a circuit to drive a VGA monitor. I've
done it with the FPGA trainer boards with Xilinx chips, but now I want to
design a custom board that host only the necessary circuitry to do so and
not depend on eval boards with lot of stuff I don't need.

So one of the smaller FPGAs in the series...

I've got already a bit experience on designing PCBs, I get pretty much
along with the EagleCad, I've build mostly boards with microcontrollers and
simply stuff. But now for what I see, handling FPGA is a completely
different thing.

I believe that some of the smaller ones have simpler to work
with packages. BGA is likely not easy for a first try.
(I haven't tried, so I can't really say.)

For what I've been reading, FPGA need a lot of requirements, 50-ohms
impedance for some clock traces, copper layer thickness, lots of different
power planes,... heck, there is even some excel spreasheet from altera to
calculate power supply stage decoupling caps =S

VGA doesn't need the top speed, but you still need to do some for
both decoupling and impedance. Series termination is not so hard,
and should work for VGA speeds. What else will your FPGA do besides
drive a VGA? I can imagine a while graphical terminal, which should
fit in a fairly small one.

Now I realize this might be a project beyond my current training, however,
I want to give it a shot. I just need the basics: voltage regulators,
configuration ROM, 50MHz clock, downloading cable interface; and of course,
the VGA dac and some extra broke out pins to interface a microcontroller.

Also some data input source?

(snip)

And of course, as a last thought, if you thing I better should stick with a
demo board and leave this for the future when I get to study more about
transmision lines, advanced CAD tools, etc...

You should know a little about impedance matching before you do
much electronics at all these days.

-- glen

 

[glen herrmannsfeldt]

maxascent <maxascent@n_o_s_p_a_m.n_o_s_p_a_m.yahoo.co.uk> wrote:

BGAs are not hard to work with, however you can forget about
soldering them yourself.

I believe I have heard stories about people doing BGA in a
toaster oven. No idea about the success rate, though.

-- glen

 

[linobi]

Yes, I think I've seen some videos in Youtube where people does BGA rewor
even with hot air. But no, definitely no; I'll stick with some QFP packag
I can do by hand, so preferably one without pad.

The thing is I noticed the 50-ohms impedance for the JTAG clock in th
Spartan-6 Configuration guide, and then I found the excel spreadsheet fo
decoupling caps for the Cyclone IV power requirements. That's when
started wondering which one would give me somewhat of a bigger erro
margin. I'll go either with a Spartan 6 or 3A, or a cyclone IV, tqfp 100 o
144 max

Yes, I'll try to follow from some schematics I found, but on the othe
hand, I don't think is very easy to mimic PCB routing, maybe just fo
isolated parts like the VGA dac.

Thanks everyone, this is a really nice place to ask for help.

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[sbattazzo]

Hello all,

HumanData in Osaka, Japan offer some Spartan3-AN and Spartan6 FPGAs, in BG
package, but on a nifty little breakout board that fits into a PLCC6
socket.
It's a tad expensive at 12,000 yen per unit (the FPGA itself is only mayb
about 20 dollars in single unit prices on Digi-key) but then you don't hav
to worry about your carrier board being only two layers (or probably eve
hand wired on proto-board!), and for a hobbyist or otherwise one-off kin
of thing, it would save you the cost of doing a four-layer board.
Plus, you can simply pop it out of the socket and reuse it as you please!

Here's a link:
http://www.hdl.co.jp/en/index.php/plcc68-series-menu/xp68-02.html

Maybe not super economical, but it's an idea.

Cheers,

Steve



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[Steve]

On 08/08/2011 09:52 PM, linobi wrote:

Hi there!

I need some advice. I want to make a circuit to drive a VGA monitor. I've
done it with the FPGA trainer boards with Xilinx chips, but now I want to
design a custom board that host only the necessary circuitry to do so and
not depend on eval boards with lot of stuff I don't need.

I've got already a bit experience on designing PCBs, I get pretty much
along with the EagleCad, I've build mostly boards with microcontrollers and
simply stuff. But now for what I see, handling FPGA is a completely
different thing.

For what I've been reading, FPGA need a lot of requirements, 50-ohms
impedance for some clock traces, copper layer thickness, lots of different
power planes,... heck, there is even some excel spreasheet from altera to
calculate power supply stage decoupling caps =S

Now I realize this might be a project beyond my current training, however,
I want to give it a shot. I just need the basics: voltage regulators,
configuration ROM, 50MHz clock, downloading cable interface; and of course,
the VGA dac and some extra broke out pins to interface a microcontroller.

I've just released a product that's very close to what you're looking for:

http://www.sioi.com.au/shop/product_info.php/products_id/48

Price is $79 for one, cheaper for 3+ boards.

I has an FPGA big enough to hold a VGA controller plus a MicroBlaze
microcontroller, 256Mb DRAM for your frame buffer, 62.5MHz clock,
voltage regs, JTAG port for programming, configuration ROM, 38 break out
pins.

You'd need to add the VGA DAC yourself, that would involve making a
simple PCB with the VGA DAC and VGA connector to plug into the expansion
connector (64 way edge connector with 38 available FPGA connections).

Stephen Ecob

Silicon on Inspiration
www.sioi.com.au

 

[maxascent]

maxascent <maxascent@n_o_s_p_a_m.n_o_s_p_a_m.yahoo.co.uk> wrote:

BGAs are not hard to work with, however you can forget about
soldering them yourself.

I believe I have heard stories about people doing BGA in a
toaster oven. No idea about the success rate, though.

-- glen

To be honest its not that expensive to get a BGA device soldered (I got on
done for about $15). I would rather pay that then blow around $300 dollar
on a pcb and device.

Jon

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