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Old 05-24-2006, 01:11 PM
John Adair
Posts: n/a
Default Re: FPGA delay generator

I don't understand where the there are issues of jitter unless you use a DCM
in which case you will have issues with all Xilinx FPGAs and to varying
extent other vendors too. The point of our board is that you can have a high
speed clock with low jitter and not necessarily using the DCM which does
have jitter of some 10s of picoseconds. If you have a look at a ICS8442 and
it's spec that is the chip we use for our LVDS clock module. Utimately your
clock source is highly important if jitter is the issue. Other factors like
power supply and decoupling will be possibly an issue.

What you may thinking about is either bond out flight time which does vary
from pin to pin and more so on the Spartan-3 FG packages than the Flip-Chip
packaged Virtex-4, Otherewise there may be an internal routing delay
variation. The latter varies by usually small amounts but can be checked in
tools. I believe flight time figures are available for the Spartan-3 but I
don't have them with me at present.

On trace lengths we do have I/O pairs of signals on Hollybush1 generally
tracked to have match lengths to about 0.1mm variation. this is principally
for LVDS operation but also useful for applications like yours.

John Adair
Enterpoint Ltd. - Home of Broaddown2. Spartan-3 board now with added V4.

"amko" <[email protected]> wrote in message
news:[email protected]
> We will also have a V4 FX12 module for this board in design shortly
> that
> will be capable of higher clock rates and hence resolution. Hollybush1
> can
> take an add on module with up to something like 110 I/O connecting to
> the
> Spartan-3 available
> I see this board with Spartan 3 and I think that with this board are
> possiable problems with jitter.
> Do you have any jitter measurment on Spartan 3 I/O pins, that you
> arrived on connectors.

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