FreeLists / si-list / [SI-LIST] Re: pci driver strength

["Peterson, James F (FL51)" <james.f.peterson@xxxxxxxxxxxxx>]

Ivor,

This is kind of related to the another question I raised about buffer driver
strengths in general.

How does one describe a buffer's drive strength? I believe the only answer
is with it's source impedance. This can be derived from a transmission line
by measuring the porch voltage of the signal as it is launched onto the
t-line (since you know the porch voltage level, Vdd, and the impedance of
the t-line, you can solve for the source impedance).

So to answer your question : you're right, there is no reflection level
requirement. But there is a VI curve requirement that source impedance can
be derived from (Zs should be the slope of the curve). If you look at the VI
curves in the spec it shows a shaded area where the drive strength (or
source Z) can be in. 

You can then compare it to your measurements from your spice sim's. (Spice
sim should include a long t-line of a known value. Measure the initial
voltage launched onto the t-line (sometimes referred to as the porch
voltage)and solve for Zsource.

regards,
Jim

-----Original Message-----
From: IVOR TING [mailto:ivor.ting@xxxxxxxxxxx]
Sent: Wednesday, August 01, 2001 7:42 PM
To: SI
Subject: [SI-LIST] pci driver strength



Hi,

I am working on an ASIC that has a 3.3V PCI 2.1 complianace interface
and  I am doing hspice simulation on the output buffer.  I understand
PCI uses reflected wave switching, so a buffer must not be too strong.
My question is, is there a requirement saying that if the output before
reflection is higher than a certain voltage, the driver is too strong?
I couldn't find it in the specification itself.

Thanks.

Ivor.
--
**************************************************************
Ivor Ting                         Email: ivor.ting@xxxxxxxxxxx
ASIC Development, Alcatel CID     Phone: (604)-453-3208
Suite 400-4190 Still Creek Drive  Fax  : (604)-421-2644
Burnaby, B.C., Canada, V5C 6C6    Web  : www.cid.alcatel.com
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