FPGA Board design basics

Hi,

I have been developing applications in Xilinx FPGAs using VHDL for the
past 3 years for a small company in Virginia. As our designs are
getting larger and more complex, the off-the-shelf boards we have been
using are proving to be insufficient. I am interested in learning
about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
board design and am wondering where to start. Any suggestions would be
greatly appreciated.

Thanks,
Poonam

On Dec 12, 7:13 am, Poonam <poonam.mur...@gmail.com> wrote:
> Hi,
>
> I have been developing applications in Xilinx FPGAs using VHDL for the
> past 3 years for a small company in Virginia. As our designs are
> getting larger and more complex, the off-the-shelf boards we have been
> using are proving to be insufficient. I am interested in learning
> about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
> board design and am wondering where to start. Any suggestions would be
> greatly appreciated.
>
> Thanks,
> Poonam

Without communicating the level of engineer you are, it's hard to
communicate what it takes to succeed in board design.  Are you even a
hardware engineer?  Do you prototype hardware with flying wires, a
soldering iron, and cheap plastic cases?  Do you know anything about
power regulators, amplifiers, transmission line theory, or PCB
manufacturing issues?

Please tell us a little more about what you bring to the table.

On Dec 12, 1:26 pm, John_H <newsgr...@johnhandwork.com> wrote:
> On Dec 12, 7:13 am, Poonam <poonam.mur...@gmail.com> wrote:
>
> > Hi,
>
> > I have been developing applications in Xilinx FPGAs using VHDL for the
> > past 3 years for a small company in Virginia. As our designs are
> > getting larger and more complex, the off-the-shelf boards we have been
> > using are proving to be insufficient. I am interested in learning
> > about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
> > board design and am wondering where to start. Any suggestions would be
> > greatly appreciated.
>
> > Thanks,
> > Poonam
>
> Without communicating the level of engineer you are, it's hard to
> communicate what it takes to succeed in board design.  Are you even a
> hardware engineer?  Do you prototype hardware with flying wires, a
> soldering iron, and cheap plastic cases?  Do you know anything about
> power regulators, amplifiers, transmission line theory, or PCB
> manufacturing issues?
>
> Please tell us a little more about what you bring to the table.

You are right.. I should've mentioned before that I don't have any
hardware experience, but do have some theoretical knowledge about
amplifiers, transmission line theory etc. I am a complete newbie in
PCB design..

Poonam

On Dec 12, 1:45 pm, Poonam <poonam.mur...@gmail.com> wrote:
> On Dec 12, 1:26 pm, John_H <newsgr...@johnhandwork.com> wrote:
>
>
>
> > On Dec 12, 7:13 am, Poonam <poonam.mur...@gmail.com> wrote:
>
> > > Hi,
>
> > > I have been developing applications in Xilinx FPGAs using VHDL for the
> > > past 3 years for a small company in Virginia. As our designs are
> > > getting larger and more complex, the off-the-shelf boards we have been
> > > using are proving to be insufficient. I am interested in learning
> > > about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
> > > board design and am wondering where to start. Any suggestions would be
> > > greatly appreciated.
>
> > > Thanks,
> > > Poonam
>
> > Without communicating the level of engineer you are, it's hard to
> > communicate what it takes to succeed in board design.  Are you even a
> > hardware engineer?  Do you prototype hardware with flying wires, a
> > soldering iron, and cheap plastic cases?  Do you know anything about
> > power regulators, amplifiers, transmission line theory, or PCB
> > manufacturing issues?
>
> > Please tell us a little more about what you bring to the table.
>
> You are right.. I should've mentioned before that I don't have any
> hardware experience, but do have some theoretical knowledge about
> amplifiers, transmission line theory etc. I am a complete newbie in
> PCB design..
>
> Poonam

Here's some basics on board design for the relatively uninitiated.

1)  Get the eval board schematics for each major part in your design.

2)  Assume all eval boards are overdesigned and try to get a grasp of
the subset of the eval design required for your system.

3)  Don't assume anyone smarter than you has done the mundane parts
of the eval design such as power supplies and bypass caps.  Look at
the recommended bypassing from manufacturer appnotes.  Use the data
sheet values for power consumption where available, or use the power
estimator when using a programmable part.  Some power estimators also
provide estimated bypass cap requirements.

4)  If possible get another engineer to review your schematics.  For
programmable parts like FPGA's make sure you can fit a design with
the pinout assignments in the schematic.  If you don't have the design
already finished, at least set up a project with the appropriate
inputs,
outputs, and IO standards to check for issues like banking or clock
routing.

5) Use a reputable design house to lay out your circuitry.  Don't
assume you can pick up a copy of PADS layout and push the autoroute
button to design a board.

I'm sure there are a lot more items that could be added to this list,
but its a starting point.  You may also find that hiring an outside
design firm to do at least your first design will be worth it in the
long run.  Later designs that are variations on the original will then
have a solid starting point.

Regards,
Gabor

Your are entering a very big subject area that most people make the
classic mistake that "it's just drawing lines on the screen". We
entered the manufacturing market 4 years ago with some substantial
practical experience being involved in customer designs but it was
still a very big jump to doing it all yourself. I know, from many
years helping customers out of problems, that our own hit rate in
delivering perfect boards is exceptional. Some our boards are still
effectively in their first revision. Even now after our having design
something like 100 major designs in the last 4 years we still are
learning things about the process and even new tricks. Some companies
that we see actually think they are doing well if they get it right in
3 revisions of a particular board. I have seen some customer designed
projects go to 7+ revisions before they called us in.

That all said it can be a very pleasant task to layout boards somthing
like tacking a jigsaw pauzzle. Whether you find doing boards yourself
good fun, or frustrating and expensive when you make mistakes, you
might want to start doing a simple design on a cheap package like
Eagle and then going through the manufacturing process. Having learned
some of the ropes you can then make better judgements on what tools to
buy and even if the own layout process works for you.

John Adair
Enterpoint Ltd. - Home of CR1 the J1962 solution.



On 12 Dec, 18:45, Poonam <poonam.mur...@gmail.com> wrote:
> On Dec 12, 1:26 pm, John_H <newsgr...@johnhandwork.com> wrote:
>
>
>
>
>
> > On Dec 12, 7:13 am, Poonam <poonam.mur...@gmail.com> wrote:
>
> > > Hi,
>
> > > I have been developing applications in Xilinx FPGAs using VHDL for the
> > > past 3 years for a small company in Virginia. As our designs are
> > > getting larger and more complex, the off-the-shelf boards we have been
> > > using are proving to be insufficient. I am interested in learning
> > > about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
> > > board design and am wondering where to start. Any suggestions would be
> > > greatly appreciated.
>
> > > Thanks,
> > > Poonam
>
> > Without communicating the level of engineer you are, it's hard to
> > communicate what it takes to succeed in board design.  Are you even a
> > hardware engineer?  Do you prototype hardware with flying wires, a
> > soldering iron, and cheap plastic cases?  Do you know anything about
> > power regulators, amplifiers, transmission line theory, or PCB
> > manufacturing issues?
>
> > Please tell us a little more about what you bring to the table.
>
> You are right.. I should've mentioned before that I don't have any
> hardware experience, but do have some theoretical knowledge about
> amplifiers, transmission line theory etc. I am a complete newbie in
> PCB design..
>
> Poonam- Hide quoted text -
>
> - Show quoted text -

On Dec 12, 2:42 pm, John Adair <g...@enterpoint.co.uk> wrote:
> Your are entering a very big subject area that most people make the
> classic mistake that "it's just drawing lines on the screen". We
> entered the manufacturing market 4 years ago with some substantial
> practical experience being involved in customer designs but it was
> still a very big jump to doing it all yourself. I know, from many
> years helping customers out of problems, that our own hit rate in
> delivering perfect boards is exceptional. Some our boards are still
> effectively in their first revision. Even now after our having design
> something like 100 major designs in the last 4 years we still are
> learning things about the process and even new tricks. Some companies
> that we see actually think they are doing well if they get it right in
> 3 revisions of a particular board. I have seen some customer designed
> projects go to 7+ revisions before they called us in.
>
> That all said it can be a very pleasant task to layout boards somthing
> like tacking a jigsaw pauzzle. Whether you find doing boards yourself
> good fun, or frustrating and expensive when you make mistakes, you
> might want to start doing a simple design on a cheap package like
> Eagle and then going through the manufacturing process. Having learned
> some of the ropes you can then make better judgements on what tools to
> buy and even if the own layout process works for you.
>
> John Adair
> Enterpoint Ltd. - Home of CR1 the J1962 solution.
>
> On 12 Dec, 18:45, Poonam <poonam.mur...@gmail.com> wrote:
>
>
>
> > On Dec 12, 1:26 pm, John_H <newsgr...@johnhandwork.com> wrote:
>
> > > On Dec 12, 7:13 am, Poonam <poonam.mur...@gmail.com> wrote:
>
> > > > Hi,
>
> > > > I have been developing applications in Xilinx FPGAs using VHDL for the
> > > > past 3 years for a small company in Virginia. As our designs are
> > > > getting larger and more complex, the off-the-shelf boards we have been
> > > > using are proving to be insufficient. I am interested in learning
> > > > about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
> > > > board design and am wondering where to start. Any suggestions would be
> > > > greatly appreciated.
>
> > > > Thanks,
> > > > Poonam
>
> > > Without communicating the level of engineer you are, it's hard to
> > > communicate what it takes to succeed in board design.  Are you even a
> > > hardware engineer?  Do you prototype hardware with flying wires, a
> > > soldering iron, and cheap plastic cases?  Do you know anything about
> > > power regulators, amplifiers, transmission line theory, or PCB
> > > manufacturing issues?
>
> > > Please tell us a little more about what you bring to the table.
>
> > You are right.. I should've mentioned before that I don't have any
> > hardware experience, but do have some theoretical knowledge about
> > amplifiers, transmission line theory etc. I am a complete newbie in
> > PCB design..
>
> > Poonam- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

Thank you Gabor and John. I know I am entering a whole new area and
that it will take a lot of time (years...) and effort to get good at
it. But I will try out the suggestions you guys have posted. I will
start out with some cheap CAD package and see how it goes. Thanks
again for the replies.

Poonam wrote:
> 
> Thank you Gabor and John. I know I am entering a whole new area and
> that it will take a lot of time (years...) and effort to get good at
> it. But I will try out the suggestions you guys have posted. I will
> start out with some cheap CAD package and see how it goes. Thanks
> again for the replies.

After designing a simple board, a very handy thing to do is to submit 
the design files to
http://www.freedfm.com/
It will tell you quickly about a number of ordinary board design 
problems you might have. There is no obligation to purchase boards, 
though for simple boards the price is decent.

On Dec 12, 6:22 pm, Duane Clark <junkm...@junkmail.com> wrote:
> Poonam wrote:
>
> > Thank you Gabor and John. I know I am entering a whole new area and
> > that it will take a lot of time (years...) and effort to get good at
> > it. But I will try out the suggestions you guys have posted. I will
> > start out with some cheap CAD package and see how it goes. Thanks
> > again for the replies.
>
> After designing a simple board, a very handy thing to do is to submit
> the design files tohttp://www.freedfm.com/
> It will tell you quickly about a number of ordinary board design
> problems you might have. There is no obligation to purchase boards,
> though for simple boards the price is decent.

Can anybody suggest some books I could start with?

Thanks,
Poonam

> Can anybody suggest some books I could start with?

It's probably a bit dated, but when I was working on PCB design, I
found the following book to be quite useful ...

http://www.amazon.com/High-Speed-Digital-Design-Semiconductor/dp/0133957241

(I worked for a company that brought the author in for an afternoon to
give a talk & answer questions.  It was pretty interesting.)


K.

On Dec 12, 3:13 pm, Poonam <poonam.mur...@gmail.com> wrote:
> Hi,
>
> I have been developing applications in Xilinx FPGAs using VHDL for the
> past 3 years for a small company in Virginia. As our designs are
> getting larger and more complex, the off-the-shelf boards we have been
> using are proving to be insufficient. I am interested in learning
> about designing boards myself with FPGAs, ADCs, DACs etc. I am new to
> board design and am wondering where to start. Any suggestions would be
> greatly appreciated.
>
> Thanks,
> Poonam

Hi Poonam,

In my experience it is good design practise to design contigency plans
into the board so that mistakes can be rectified easily without having
to hack the board around with a scapel. For example, bring some unused
IO out to test pads, tie pins high or low via a zero ohm resistor,
track the JTAG port to a header. I would never expect a design to be
correct on the first spin and if the only changes for the respin are
to remove redundant test points etc, you're doing well.

Also, I'd avoid BGA packages if at all possible as it is significantly
more difficult to design the board, fabricate it, rework faults and
rectify design mistakes.

I'd also check the website of your FPGA vendor as they usually have
lots of information on PCB design.

Finally, the PCB design difficulty goes up as the clock frequencies go
up. If you are designing something slow with small FPGAs then I'd say
have a crack at it and learn as you go. If it's something with lots of
high speed logic signals you may be better off going to the experts
and paying a third party design house to do the work for you.

Rob