hi Tom In the s2i file we have following switches: [Vinl], [Vinh], [Vmeas], [Vref], [Rref] and [Cref] . Are these values really used while generating ibis model or these are just the information in ibis file for board level simulations. thanks sujit Tom Dagostino wrote: > Yes, you still need to have C_comp in the model. Most simulators, > from what I have heard, don't use C_comp when they are using the > buffer as a driver. But when the buffer is receiving a signal, such > as a reflection, the simulator puts C_comp into the simulation.. Ask > your specific simulator company for details on how they handle this > situation. > > > > Tom Dagostino > Teraspeed(R) Labs > 13610 SW Harness Lane > Beaverton, OR 97008 > 503-430-1065 > tom@teraspeed.com > www.teraspeed.com > > Teraspeed Consulting Group LLC > 121 North River Drive > Narragansett, RI 02882 > 401-284-1827 > > -----Original Message----- > From: NG,MEI-YEE [mailto:mei-yee.ng@avagotech.com] > Sent: Wednesday, December 20, 2006 3:26 PM > To: tom@teraspeed.com; April.Hachenburg@smsc.com; > ibis-users@server.eda.org > Cc: akvarma@ncsu.edu > Subject: RE: [IBIS-Users] Ramp vs. Rising/Falling waveforms, Cref > missing ... > > Hi Tom, > > > > I find your reply very useful. Thank you for the information. > There is one question regarding C_comp that I would like to ask. > When I run simulation to extract V-T curves, I used an extracted > RC netlist, which means it has taken into account parasitic R and > C of the buffer. In that case, do I still need to specify another > C_comp value? Would that mean double-calculating this C_comp? > > > > Kindly advice. > > > Thank you. > > > > Best regards, > > Mei Yee > > IC Design Engineer > > Avago Technologies > > > > ------------------------------------------------------------------------ > > From: owner-ibis-users@server.eda.org > [mailto:owner-ibis-users@server.eda.org] On Behalf Of Tom Dagostino > Sent: Thursday, December 21, 2006 4:14 AM > To: April.Hachenburg@smsc.com; ibis-users@server.eda.org > Cc: akvarma@ncsu.edu > Subject: RE: [IBIS-Users] Ramp vs. Rising/Falling waveforms, Cref > missing ... > > > > April > > > > R_load is the load the buffer is placed under when the ramp data > is acquired. 50 Ohms is the typical value and it is usually > terminated to ground for the dV/dT rise and to power for the dV/dT > fall. > > > > R_fixture is the load the buffer is placed under when the VT > waveforms as acquired. This value is typically 50 Ohms and is > terminated to ground for both a rising and falling waveform and > then terminated to power for the other set of rising and falling > waveforms. C_fixture would be any capacitance associated with the > R_fixture. But its not a good idea to have any C_fixture when > extracting VT waveforms. I've seen simulator give very wrong > answers when C_fixture is present. > > > > Rref is the manufacturer's timing test load's resistive > component. This can be any value (within reason) and can be > terminated to any reasonable voltage Vref the manufacturer deems > appropriate for the buffer technology. It is usually terminated > to the typical value the buffer would see in an actual > application. If the buffer was an ECL output then 50 Ohms to > Vcc-2Volts would be the load. Most CMOS devices have just a Cref, > a capacitor terminated to ground. > > > > C_comp is the capacitance associated with the I/O buffer. It > includes all the capacitance from metal, active or passive devices > on the silicon. It forms the majority of the buffer's impedance > reactive component. > > > > R_fixture should match the load the buffer is seeing in an actual > application. Most circuit boards trace impedance runs between 40 > and 70 Ohms or there about. Most buffers are characterized into a > 50 Ohm load which is close to the board impedance. Since the > model developer cannot predict every application 50 Ohms is a good > compromise for most models. There are some technologies that are > better served with a non 50 Ohm load such as RAMBUS, which is > specified into 27 Ohms or very weak CMOS drivers that cannot drive > a 50 Ohm load to Vinl or Vinh. I'd caution against using a 500 > Ohm load in your model making unless there is a very good reason > to do so. > > > > The Ramp key word is a legacy key word that was used before the VT > waveforms were added to IBIS. It is still required to be present > in the model. If R_fixture is not specified it defaults to 50 Ohm > in the model. > > > > > > Tom Dagostino > Teraspeed(R) Labs > 13610 SW Harness Lane > Beaverton, OR 97008 > 503-430-1065 > tom@teraspeed.com > www.teraspeed.com > > Teraspeed Consulting Group LLC > 121 North River Drive > Narragansett, RI 02882 > 401-284-1827 > > -----Original Message----- > From: owner-ibis-users@server.eda.org > [mailto:owner-ibis-users@server.eda.org] On Behalf Of > April.Hachenburg@smsc.com > Sent: Wednesday, December 20, 2006 9:39 AM > To: ibis-users@server.eda.org > Cc: akvarma@ncsu.edu > Subject: [IBIS-Users] Ramp vs. Rising/Falling waveforms, Cref > missing ... > > > IBIS Users, > I wondered if anyone could clarify for me the usage of Rload > vs. Rref vs. Rfixture and similarly Cref vs. Cfixture. > > I am using s2ibis3 and discovered that the Cref parameter > specified in my .s2i file does not appear in my .ibs model > file. After looking at the netlists and reading the IBIS > documentation, it appears Cref is not used for any > simulations. What is the purpose of Cref? And why isn't it > showing up in the .ibs file? > > Also, I read that C_comp is taken into account for the > rising/falling V-T waveforms though I cannot find that > paramater in any of the corresponding netlists. How is C_comp > used? > > As for Rref vs. Rfixture, I thought I read somewhere that for > best results Rref should match Rfixture. Is that true? In > my model, I am using the keywords Rising/Falling Waveform. I > found that if I do not specify Rload even though I am not > specifying the [Ramp] keyword, then 50ohms is used in one of > the transient simulations despite Rref and Rfixture being set > to 500 ohms. Should I be specifying the [Ramp] keyword along > with the [Rising/Falling Waveform] keywords? If so, how do > they work together? > > - April > > --------------------------------------------------- > April Hachenburg > Core Technology Design Engineer > SMSC > -- thanks sujit kumar +91-120-4396069 +91-09910168788 -------------------------------------------------------------------- |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 1993Received on Tue Dec 26 20:37:33 2006
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