RE: another C_comp confusion question

Hi All,

I have also had a problem with Ccomp, but the other extreme. I have seen
Ccomp values of 5pF. Recall according to the IBIS spec, "Ccomp defines the
silicon die capacitance". I find it difficult to beleive that the
capacitance of a die (we deal with memory here) is 5pF. Has anyone had
similar concerns? Has anyone addressed this with any of the silicon
vendors?

Bob.

-----Original Message-----
From: Wilco Hamhuis [mailto:w.hamhuis@transfer.nl]
Sent: Wednesday, May 16, 2001 9:40 AM
To: Ibis
Subject: another C_comp confusion question

Hi all,

Betty Luk initiated this topic a few months ago. Recently I received a
differential IBIS model from a vendor. I noticed that the C_comp value was
very small, 162fF. Apparently the C_comp value is also included in the VT
tables. In my case I don't have the VT tables. The driver model only
consists out of the pullup and down curves. Gnd, power, rise and fall aren't
present (ramp data is present). When I use this model in a XTK simulation I
see very large oscillation, straight through the logic threshold levels.
Increasing the C_comp value a bit and the results become significant better.
I find it VERY disturbing that C_comp has such a large impact on the
simulation results. My questions:

 - is 162fF a realistic C_comp value according to your experience?
 - does anyone have any experience with questionable simulation results due
to C_comp value?
 - what is the relationship between the VT tables and C_comp?

Tanks in advance,

Wilco
Signal Integrity Expert
 
Received on Wed May 16 07:50:25 2001