RE: [IBIS-Users] Non-existence of C_load in [Ramp] keyword

Tom's comments are also valid for L_fixture.
If you ever wonder how you can design a test
load that looks like a pure resistor, just
make a nice long T-line so that the reflection
doesn't come back to the driver before it is
done with the transition...
 
To understand why Tom's suggestions are correct,
look at my presentation:
 
http://www.eda.org/ibis/summits/mar06/muranyi1.pdf
 
Arpad
===============================================

________________________________

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Tom Dagostino
Sent: Thursday, September 16, 2010 11:07 AM
To: surendra.deshmukh@wipro.com; ibis-users@eda.org
Subject: RE: [IBIS-Users] Non-existence of C_load in [Ramp] keyword

The RAMP key word only allows a purely resistive load which is the load
that should be used for extraction of VT curves and thus ramps. My
experience with models that have had non zero C_fixture is not good.
The simulators that I used with these models did not produce acceptable
results showing incredible amounts of waveform distortion. It is my
recommendation (and from members of the IBIS committee that I have
discussed this with) not to use C_fixture when extracting the VT curves.
If you are making a model from SPICE there is no need to have any
capacitance in the load when doing the simulations. If you are making
the model from measurements you should be able to design the test
fixture to minimize any stray parasitic. BUT IN ANY CASE DO NOT INCLUDE
CREF IN THE MODEL UNDER C_FIXTURE!!!

Regards,

Tom Dagostino

Teraspeed Labs

13610 SW Harness Lane

Beaverton, OR 97008

503-430-1065

tom@teraspeed.com

www.teraspeed.com

Teraspeed Consulting Group LLC

121 North River Drive
Narragansett, RI 02882

401-284-1827

www.teraspeed.com

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of surendra.deshmukh@wipro.com
Sent: Thursday, September 16, 2010 4:56 AM
To: ibis-users@eda.org
Subject: [IBIS-Users] Non-existence of C_load in [Ramp] keyword

Hi,

    The [Ramp] keyword used in IBIS initial version is still there in
new versions along with VT tables. This Ramp keyword also gives Rload
value.

 My question is as far as these VT tables are calculated only for
Rixture (or Rload), simulator has a choice to take value from [Ramp]
keyword without any problem but if these tables are generated for
Rfixture and C_fixture values (non-zero C_fixture value) then there is
no any keyword C_load inside the [Ramp] section.

        How the simulator handles this case where [Ramp] is calculated
for Rfixture and C_fixture but there is no any C_load keyword in ramp
section? Does [Ramp] require any C_load keyword?

Regards

Surendra

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