RE: [IBIS-Users] RE: [IBIS] C_comp value

Mey-Yee,
 
True, the waveforms in the waveform tables of an IBIS
model do include the buffer's internal capacitance
effects, and if we just added a C_comp capacitor to
the buffer model's output we would double count for
those effects.  However, most simulators I know have a
special compensation algorithm to prevent this from
happening because the capacitor has to be there,
because the model's current source doesn't behave
as a capacitor and when reflected waves arrive at
the buffer, it will not look capacitive and the
reflection coefficients from the buffer will be
incorrect.  I like to summarize this the following
way:
 
The C_comp capacitor has to be made visible when you
look into the buffer from the outside, but invisible
to the internals of the buffer model.
 
Arpad
=======================================================

________________________________

From: NG,MEI-YEE [mailto:mei-yee.ng@avagotech.com] 
Sent: Sunday, September 28, 2008 7:05 PM
To: Muranyi, Arpad; ibis@server.eda.org
Cc: ibis-users@server.eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] C_comp value



Hi Arpad,

 

Just one quick question, if the netlist I used for the pad is an
extracted netlist, does that mean the C_comp value is already
incorporated inside (parasitics and all)? In that case, if I still put
in an additional C_comp value, it would mean that I'm double-counting
the C_comp?

 

Thank you.

 

Best regards,

Mei Yee

MCPD, Avago Technologies (Malaysia)

Tel no.: +604-6108515

________________________________

From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Muranyi, Arpad
Sent: Friday, September 26, 2008 9:03 PM
To: ibis@server.eda.org
Cc: ibis-users@server.eda.org
Subject: [IBIS-Users] RE: [IBIS] C_comp value

 

Timmy,

 

You can do it either way, it depends on your needs.

If you want to correlate to your SPICE model, match

it to that, if you want to correlate to real life,

match it to your measurements.

 

Arpad

====================================================

 

________________________________

From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] On
Behalf Of Timmy Leon
Sent: Thursday, September 25, 2008 8:46 PM
To: ibis@server.eda.org
Cc: ibis-users@server.eda.org
Subject: [IBIS] C_comp value

Dear Sir/Madam,

 

I have a question regarding the c_comp value that we should put in IBIS
model. Should the c_comp value be based on measurement, or can we tune
value so that IBIS model correlate with its spice model or measurements?
Thank you.

 

Best regards,

Timmy Leon



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