Date: Mon Aug 18 2008 - 09:38:25 PDT
No, no and no. The load resistor used for extracting the VT waveforms should represent the load seen by the driver on the circuit board. Most reasonable circuit boards will have trace impedances between 40 and 75 Ohms and usually the design targets 50 Ohms. So the IBIS model should characterize the buffer into an impedance close to that. The generally accepted value is 50 Ohms. It has nothing at all to do with the output impedance of the driver. You are not trying to match load/output impedance or maximize power transfer, you are trying to get a macro model to be characterized near its operating conditions. There are no such things as IV VT curves. There are no loads associated with extracting IV curves. Extending the simulation time may or may not "fix" IV/VT curve mismatches. Extending simulations times will only fix mismatches if the original simulations did not allow the VT waveforms to reach their final value. If you have a problem understand the cause before jumping to a solution. Just jumping to a solution in most cases will not work. Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 503-430-1285 FAX tom@teraspeed.com www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Chetana Raghuwanshi Sent: Monday, August 18, 2008 6:51 AM To: Sudarshan H N Cc: ibis@server.eda.org; ibis-users@server.eda.org; owner-ibis-users@server.eda.org Subject: Re: [IBIS-Users] Re: [IBIS] Different PMOS and NMOS driver impedence Hi Sudarshan, You are right. My concern is IV VT mismatch error. How would it disappear by increasing the simulation time ? Best Regards Chetana -------------------------------------------------------- Chetana Raghuwanshi CTO / Process & Library Technology NXP Semiconductors India NXP Block C, 4th Floor MFAR Manyata Tech Park Nagavara, Bangalore-560045 Tel : +91 80 4024 7072 -------------------------------------------------------- Inactive hide details for "Sudarshan H N" <hn.sudarshan@gmail.com>"Sudarshan H N" <hn.sudarshan@gmail.com> "Sudarshan H N" <hn.sudarshan@gmail.com> Sent by: owner-ibis-users@server.eda.org 2008-08-18 06:43 PM To "Chetana Raghuwanshi" <chetana.raghuwanshi@nxp.com> cc ibis-users@server.eda.org, ibis@server.eda.org Subject [IBIS-Users] Re: [IBIS] Different PMOS and NMOS driver impedence Hello Chetana, You can use any of the 2 values for Rfixture to generate Vt curves. There is no rule that , your Rfixture should match to the PMOS or NMOS driver resistance. But you should always use one value to generate the one set of rising and falling waveforms(experts, correct me if i am wrong). If you are seeing any errors with respect to IV and Vt curve mismatch , just simulate for more time so that it will reach the saturation. Regards Sudarshan On Mon, Aug 18, 2008 at 6:37 PM, Chetana Raghuwanshi < <mailto:chetana.raghuwanshi@nxp.com> chetana.raghuwanshi@nxp.com> wrote: Hello Experts, One of my IO cell has a buffer with different PMOS and NMOS impedences. PMOS impedence is approx 200 Ohms and that for NMOS is 96 Ohms. In this case what should be the value of Rfixture for calculating IV VT curves ? Would it be Rfixture1 for calculating pull down and falling waveforms and Rfixture2 for calculating pull up and rising waveforms ? If I do rise/pullup and fall/pulldown simulations with different Rfixture values, is it acceptable ? Best Regards Chetana -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. -------------------------------------------------------------------- |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
