Date: Thu Aug 03 2006 - 08:37:35 PDT
Hi experts, sorry that I trigger the same topic once again, but now it keeps me busy already more than one week and I am pretty sure that the problem is not a way how I extract IBIS model, but somewhere else! Before I elaborate the problem let me notice that I get the same result if I use 2ibis2 or s2ibis3 or if I use HSpice or some company internal analog simulator for extraction of IBIS model. Let me elaborate the problem: 1. IBIS model is generated (say with s2ibis2, but irrelevant, since there is a same result with s2ibis3) 2. I take one of spice decks for extracting rising waveform generated by extraction tool (say a00DQ40.spi) - this should be spice deck for generating 1st rising waveform in typical case. This spice deck of course contains the netlist of my circuit. 3. I modify this spice deck only that I instantiate in it just generated IBIS buffer model (in step 1.) as a B-element - in other words, I just put there IBIS model - B-element and do nothing else 4. stimuli and load for netlist remains the same and I use exactly the same stimuli and load for IBIS model as well (of course, netlist, IBIS model and their stimulus and loads are separated) 5. simulate such modified spice deck with HSpice and compare the outputs: netlist vs. IBIS model Problem: What I expect to get on output is very good overlap between Hspice simulation of netlist and IBIS model, BUT what I get on output is a fact that falling or rising edges don't overlap i.e. there is some 30ps delay (Please take a look on attached snapshots "zoom1.gif" and "zoom2.gif"). Signal "dq_40_ohm" is output of netlist, signal "io_ron_040_hspice_typ". You can see a real delay and not some different slopes due to different loads. Transient analysis is done with (.TRAN 1.36e-11 1.36e-09) - i.e. simulation step (for IBIS extraction) is 13.6ps. What worries me even more is a fact that in some cases (for different stimuli frequencies) I see that rising edges are overlapping and falling are delayed and in some cases (some other frequency of stimuli) I see that falling edges are overlapping and rising are delayed, so I don't know even where should I cut ("taylor") my V-t curves when behavior seems to be so arbitrary and frequency dependant. I know, some of you would say that 20-30ps are no problem, but exactly this 20-30ps are shifting (upwards or downwards) crossing point of rising and falling edges and destroy duty cycle and data eye diagram (target is 800MHz). Problem is independent on slope of stimuli (so with 1ps slope or 100ps of slope of stimuli I see the same result) I know that we should not speak on this forum about tools and vendors and I terribly apologize that I will still mention some of them - but on the end all our models are used with some these tools and I think that it is necessary that we exchange information about our experiences with this tools as well. So the problem is analysed with different tools: - I see above mentioned problem when simulating with HSpice (versions 2004.09, 2005.03 and 2006.03) netlist vs. IBIS model - I see effect of above mentioned problem when simulating with ADS - using only IBIS model - rising and falling edge crossing points are shifted same as in HSpice - with SpecctraQuest (also simulating only with IBIS model) I see the right results! So I am pretty confused, what is correct? A few different simulators, but only one is showing a right result (or at least result that I consider as a proper). What is your experience? Have you noticed something similar? Can somebody from you do the same procedure on one of your designs (compare IBIS vs. HSpice on the same way as I done)? Has somebody an idea, proposal? Best regards / Mit freundlichen Grüßen / S po¹tovanjem Radovan Vuletiæ Qimonda AG QAG PD PDE MUC/10.2.236 AP 3 Am Campeon 1-12 D-85579 Neuebiberg Phone: +49 (0)89 234 20108 Fax (PC): +49 (0)89 234 955 5305 E-mail: radovan.vuletic@qimonda.com <<zoom2.gif>> <<zoom1.gif>> -------------------------------------------------------------------- |For help or to subscribe/unsubscribe, e-mail majordomo@eda-stds.org |with 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 e-mail a request to ibis-request@eda-stds.org. | |IBIS reflector archives exist under: | | http://www.eda-stds.org/pub/ibis/email_archive/ Recent | http://www.eda-stds.org/pub/ibis/users_archive/ Recent | http://www.eda-stds.org/pub/ibis/email/ E-mail since 1993
