It is interesting to note that the output pulsewidth of the SPICE netlist, is much wider than the "D" input pulsewidth. Therefore, your SPICE model appears to have a sizeable delay asymmetry in it, which may be missing from your IBIS model. By very quick inspection, your V-T tables don't seem to have the same asymmetry. Were the rising and falling tables time-coordinated with one another? Two other things you might try doing: (1) What happens if you use wider pulses on the "D" stimulus input? There could be some interaction going on, due to the fact that the stimulus pulsewidth is less than the length of the V-T tables; i.e., the buffers are being told to switch before they have completed "playing back" the previous transition. Many simulators have problems doing that. Alternatively, just invert the "D" input, and see if it is the second transition or just the falling "D" edge that always has the trouble. (2) Presumably this "D" input, or something like it, is being applied to both the SPICE model and the IBIS model in your simulator. Try using much faster edges on the "D" input waveform. IBIS models have no knowledge of input edge rates, their inputs are binary (either Low or High). Having slow edges increases ambiguity because "slicing" happens at some point on the waveform, which almost definitely differs between the SPICE and IBIS models. IBIS itself has no concept of threshold (or switching reference) voltage, but your simulator is probably using something when it slices the "D" signal, and it's probably not the same threshold as your SPICE model. Regards, Andy |------------------------------------------------------------------ |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 Sat Jun 4 08:20:22 2005
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