Many vendors will use the same I/O cell for an Input buffer as an I/O
buffer. The parasitics will be about the same for both. Sometimes the
designer will select different cells for input and outputs and you should
see differences in C_comp. Many vendors will just specify the maximum
capacitance at the pin, which will include the package C, so you have to be
careful. Also, many vendors will just publish a max number and then they
will not have to reject anything that comes out of the oven.
We are seeing C_comp values as low as 400fF. Most values on modern
processes run 2 to 3 pF. Older processes could be as high at 8 or 10 pF.
Tom Dagostino
Teraspeed Consulting Group LLC
503-430-1065
tom@teraspeed.com
www.teraspeed.com
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of RODRIGUEZ_LECONA_RAMIRO
Sent: Thursday, August 05, 2004 4:35 PM
To: ibis-users@eda.org
Cc: ibis-info@eda.org
Subject: [IBIS-Users] C_comp values
Hi, I am using some buffers models and I have a question:
Is C_comp value for input structure greater than for I/O or Output
structure? This question is because some vendors specify the same values for
both structures.
Are there limits for C_comp values? Does IBIS standard specify
limits?
What are typical values for C_comp (input structure and I/O
structure)?
Thanks for your answer
Regards,
Ramiro Lecona
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Received on Thu Aug 5 18:04:10 2004
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