Date: Wed Sep 04 2013 - 22:14:03 PDT
The differences you see are due to improper time step selection. Please try your experiment again but set the simulation controls so that you force HSPICE to use much smaller time steps. Try something like .OPTIONS RMAX=0.5 or similar. I expect that your waveforms will be identical if you did that... Thanks, Arpad ==================================================================== From: Ling Li Ong [mailto:llong@altera.com] Sent: Thursday, September 05, 2013 12:09 AM To: Muranyi, Arpad; ibis-users@eda.org Cc: Siong Hee Lim Subject: RE: Role of C_comp Hi Muranyi, Do you mean for an output buffer, if purely changing the c_comp value between 0.1pF and 50pF and maintain other parameters as identical, it should not generate any different waveforms? I tried out the a simple output buffer simulation ran on HSPICE 2011.09-SP1. No transmission line or termination impedance but mainly the ibis model. C_comp swept at 3.5pF (purple) and 5pf (green). I observed the waveforms are not overlapped. Is this the correct result from HSPICE? If it is not, what will be the expected result? [cid:image001.jpg@01CEA9CC.D2F97770] Regards, Ling Li From: Muranyi, Arpad [mailto:Arpad_Muranyi@mentor.com] Sent: Thursday, September 05, 2013 11:48 AM To: Ling Li Ong; ibis-users@eda.org<mailto:ibis-users@eda.org> Cc: Siong Hee Lim Subject: RE: Role of C_comp Ling Li, Regarding: "it has no difference between the simulation on C_comp 0.1pF and 50pF". That's correct (for the case when the buffer model is driving), and that's the way HyperLynx 9.0 should also behave. Thanks, Arpad ====================================================================== From: Ling Li Ong [mailto:llong@altera.com] Sent: Wednesday, September 04, 2013 2:19 AM To: Muranyi, Arpad; ibis-users@eda.org<mailto:ibis-users@eda.org> Cc: Siong Hee Lim Subject: RE: Role of C_comp Hi Arpad, Thanks for your fast response. I was referring to the mentor's website which commented with using the version 8.2.1, it has no difference between the simulation on C_comp 0.1pF and 50pF. This version may be outdated compare to latest as I noticed the posting date was on last year. However, I assume it should perform the same simulation result after this version. http://communities.mentor.com/mgcx/thread/6935 May I know is this comment align to your understanding? Thanks. Regards, Ling Li From: Muranyi, Arpad [mailto:Arpad_Muranyi@mentor.com] Sent: Wednesday, September 04, 2013 2:46 PM To: Ling Li Ong; ibis-users@eda.org<mailto:ibis-users@eda.org> Cc: Siong Hee Lim Subject: RE: Role of C_comp Ling Li, It seems that your conclusion from reading Todd Westerhoff's email in the link you provided is not quite correct. Todd seems to say (correctly) that the output waveform of a driver will not change when C_comp is changed in the IBIS [Model]. You should only see differences in the waveforms when a reflection hits the driver and that reflection bounces back off of the driver. This secondary reflection from the driver should depend on the C_comp value. Similarly, if an I/O buffer model is in the receive mode (i.e. input state), you should see different waveforms when you change the C_comp value. As far as I can tell from my days when I worked at Intel and used HSPICE in my work, HSPICE does what I described above correctly. Now that I work for Mentor, I can also tell you that the results of HyperLynx are correct the same way. I am actually surprised to hear that you see different results. Are you sure your test case is designed well to show and observe these effects correctly? By the way, the latest HyperLynx version is now 9.0 (not 8.2.1). I hope this helps answering your question. Thanks, Arpad ======================================================================= From: owner-ibis-users@eda.org<mailto:owner-ibis-users@eda.org> [mailto:owner-ibis-users@eda.org] On Behalf Of Ling Li Ong Sent: Wednesday, September 04, 2013 12:47 AM To: ibis-users@eda.org<mailto:ibis-users@eda.org> Cc: Siong Hee Lim Subject: [IBIS-Users] Role of C_comp Hi, I saw some discussions on c_comp issue at user archive at link: http://www.eda.org/ibis/users_archive/0487.html I am confused by the c_comp whether it is double-counted and the different result obtained when using different tools. According to the comment in the link above, varying the c_comp may see the changes in rise/fall curve. This is definitely true when using the HSPICE simulator. But, if you using the latest Hyperlynx version 8.2.1, changing the c_comp will not reflect the changes in rise/fall curve. Can you please advise which tools are showing the correct response on c_comp when sweeping at different value? Thanks. 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