[SI-LIST] Re: SSO of a Spartan3 in a PQ208 package
- From: Heyfitch <heyfitch@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 20 Mar 2006 14:07:16 -0800 (PST)
Hello Henrik,
your idea of temporally separating the outputs by several hundred picoseconds
is unlikely to work. The resonant frequency for the power rail are low enough
that the rail will ring with a period of several nanoseconds. By delaying the
switching time of the other group, you may incidentally align it with the dip
of the power rail voltage making things worse. Generally, your vendor may be
able to provide you with some guidance on what to expect from the proposed
design.
Regards,
-Vadim
Altera
Disclaimer: the opinion expressed here is strictly mine and not of my
employer.
henrik@xxxxxxxxxxxxxxxxxxx wrote:
Hi!=0D
=0D
As a hobby I'm designing a graphics card for the atari computers containing=
a=0D
Spartan3 (XC3S400) that will implement a 16-bit DDR1 interface at 166MHz=0D
(DDR333). I know I've asked you about this board before (but not this parti=
cular=0D
question), but new questions keep coming up. I hope you have patience with =
me. :-)=0D
=0D
I've chosen the PQ208 package for my prototype because I want to be able to=
=0D
solder this board myself without paying for mounting a BGA package (like th=
e=0D
FT256). Now I'm concerned about the SSO limitations of the PQ208 package. T=
he=0D
datasheet says that only 4 outputs of type SSTL2 class 1 or 2 outputs of ty=
pe=0D
SSTL2 class 2 would be able to switch in the same direction at the same tim=
e=0D
without problems, but I wonder if I can avoid this limitation by splitting =
up the=0D
outputs into groups of four pins where each group would switch a few hundre=
d=0D
picoseconds from the other group. This would result in two groups per bank =
(8=0D
data pins for each bank). When switching 4 SSTL2 class 1 outputs in a bank =
would=0D
the power rail in the package be so heavily loaded that even waiting 500ps =
until=0D
switching the next 4 outputs wouldn=E2=80=99t be possible without the signa=
ls being=0D
severly affected? I=E2=80=99m asking for your general feeling about this, s=
hould I give=0D
it a try or just forget it?=0D
=0D
=0D
=0D
Thanks=0D
=0D
/Henrik Gild=C3=A5=0D
=0D
=0D
=0D
=0D
=0D
=0D
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