At today's IBIS teleconference, I raised the issue of whether a bug report should be logged against ibischk for its treatment of I-V tables inappropriate to the model type. Specifically, there should be no [Pullup] table, or at least no non-zero currents for the [Pullup] table in a model using open drain/sink topology, and there should be no non-zero [Pulldown] table in a model using open source topology. If an inappropriate I-V table is present (with non-zero currents), ibischk issues a warning message. However, it goes on to check I-V/V-t endpoint agreement using all the model's I-V tables. Should ibischk instead ignore the I-V table incompatible with the model_type? A motivation for doing this is that sometimes model makers mistakenly put internal bias characteristics for open_* parts into the [Pullup] and [Pulldown] tables. Ignoring inappropriate I-V tables during I-V/V-t checking would expose this by causing I-V/V-t mismatches. However, if using the inappropriate I-V table causes an I-V/V-t mismatch, the current parser behavior exposes the problem. So it may be valuable to report both when ignoring the table causes a problem and when using the table causes a problem. I can report that at least one popular SI tool does not ignore the inappropriate table. The existing parser behavior has in fact encouraged this policy. It is not safe for the SI tool to ignore one of the I-V tables the parser depended on to "bless" the model, unless it does the alternative endpoint checking itself. Would it be worth adding a separate I-V/V-t endpoint check under the assumption of open_* topology to highlight models that depend on significant currents in the inappropriate table? Would it equivalently be worth elevating the inappropriate-table warning to an error? It seems unsafe to drop the existing I-V/V-t test policy for open_* models. John Angulo Software Development Engineer Hyperlynx Products Mentor Graphics Corp. |------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993Received on Fri Oct 28 14:07:29 2005
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