Subject: RE: [IBIS-Users] C_comp issue?
From: Angulo, John (john_angulo@mentorg.com)
Date: Mon Nov 11 2002 - 15:07:17 PST
This is a subtle issue, and you're right Todd. In an actual device, driver behavior obviously depends on capacitance characteristics. If you raise the overall capacitance, you might decrease the slew rate, and the IBIS model would record both a higher C_comp and slower waveforms in its V-T tables. But the simulation tool must always obey the slew rate information in the [Rising Waveform]/[Falling Waveform] or the [Ramp] keywords, whatever the value of C_comp. A good simulator will always produce waveforms that match the V-T tables when you attach the resistive loads documented in those tables, and must assume that whatever C_comp value the model provides is consistent with those V-T data. When you change the C_comp value in the IBIS model, the reflection behavior will certainly change, but you must also provide updated V-T information to give the model a new slew rate.
John Angulo
Hyperlynx Products
Mentor Graphics Corp.
john_angulo@mentor.com
425-869-2320
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