Sudarshan, One thing that I haven't seen in any of the responses yet is the definition of Vmeas. From the IBIS specification: | The Vmeas subparameter is the timing reference voltage level | that the semiconductor vendor uses for the model. Include | Cref, Rref, Vref, and Vmeas information to facilitate | board-level timing simulation. In other words, this is the voltage at which Tco is measured with the load circuit which is described by Rref, Cref, Vref. This information is usually available in the data sheet of a chip. You need to have an understanding of what Tco means, how it is measured for the data sheet, and what it is used for in the timing spreadsheet together with the flight time and setup and hold time parameters. Welcome to signal integrity! If you have a buffer that cannot drive through this value using the give Vref, Rref and Cref load, Vmeas becomes useless. Arpad =============================================================== ________________________________ From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Sudarshan Honnudike Sent: Wednesday, November 08, 2006 12:22 AM To: Lynne D. Green; Bob Ross Cc: ibis-info@server.eda.org; ibis-users@server.eda.org Subject: RE: [IBIS-Users] Warnings in V-t curves Hi Bob & Lynne, I want to get some more clarifications on your answers. Lynne told that , Vmeas should be between Vinl and Vinh. As Vin = 1.2 V , Vinl and Vinh would be 0.36 and 0.84 V respectively . In that case Vmeas should be between 0.36 and 0.84. But if we connect R_fix to VDDE(2.5 V) then in falling waveform, it will fall to 1.25V. So in that case it will not cross Vmeas. So according to what Bob suggested, Vmeas should be between 1.25 and 2.5 V. Please correct me if i am wrong in explanation. And as Bob said, it is an open drain cell. I have taken R_fix as 44 ohm. I have changed R_ref to 50 ohm , Vmeas to 1.25 V and V_ref to 1.3V. Now I am able to get rid of those warnings. From the cookbook I understood that Vref, Cref, Rref and Vmeas are AC test load conditions. i.e, under this setup, buffer's delay information is measured. Can we use the same value of R_fix, C_fix and V_fix to Rref , Cref and Vref parameters, as under these parameters we measure the V-t waveforms. ? Please let me know your answers. Best Regards, Sudarshan HN NXP Semiconductors/CTO /PLT # 1 Murphy Road, Ulsoor, Bangalore - 560 008 , India. Ph:+91-80-40247073 Fax: +91-80-4024 7855 seri:sudarsha@inpsblr E-mail: sudarshan.honnudike@nxp.com "Lynne D. Green" <lgreen22@mindspring.com> 2006-11-08 12:22 PM To "'Sudarshan Honnudike'" <sudarshan.honnudike@nxp.com> <ibis-users@eda.org> <ibis-info@eda.org> cc Subject RE: [IBIS-Users] Warnings in V-t curves Classification Hello, Sudarshan, 1) Please use ibischk4. This is capable of checking [IBIS ver] 3.2 models. Bug fixes and enhancements are not patched back into older versions of ibischk. 2) Rref, Cref, Vref and Vmeas are used for hardware testing, and should be on the I/O data sheet or on the I/O interface specification. Vmeas is normally between Vinl and Vinh. 3) Rref default value is 50 ohms. 1E+9 is not a reasonable value. 4) Vcc_core is not used in the IBIS model. It is used only in simulation to drive the "core" pins (Enable, Data) on the I/O buffer. 5) There are two good sources of modeling help. These are the IBIS Cookbook http://www.eigroup.org/ibis/tools.htm and the IBIS Quality Checklist http://www.vhdl.org/pub/ibis/quality_wip/ Best regards, Lynne "IBIS training when you need it, where you need it." Dr. Lynne Green Green Streak Programs http://www.greenstreakprograms.com 425-788-0412 lgreen22@mindspring.com- Lynne ________________________________ From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of Sudarshan Honnudike Sent: Tuesday, November 07, 2006 9:25 PM To: ibis-users@eda.org; ibis-info@eda.org Subject: [IBIS-Users] Warnings in V-t curves Hi Experts, I am getting the following warnings while running ibischk3 on the buffer models. WARNING - Model 'bsppon3mchpt3v3_p': TYP VI curves cannot drive through Vmeas=0.6V given load Rref=1e+09 Ohms to Vref=0V WARNING - Model 'bsppon3mchpt3v3_p': MIN VI curves cannot drive through Vmeas=0.6V given load Rref=1e+09 Ohms to Vref=0V WARNING - Model 'bsppon3mchpt3v3_p': MAX VI curves cannot drive through Vmeas=0.6V given load Rref=1e+09 Ohms to Vref=0V Our buffer models will be operating at 2 voltages coreside voltage and pad side voltage. In this case, coreside voltage(VDD) is 1.2 v and pad side voltage(VDDE) is 2.5v. So in V-t waveforms 1. Rising waveform with R_fix connected to VDDE(2.5v): waveforms are varying from 1.249v to 2.5v 2. Falling waveform with R_fix connected to VDDE(2.5v):waveforms are varying from 2.5v to 1.254v I have a confusion regarding the selection of Vmeas. Should it be half of corevoltage(1.2/2) or half of pad voltage (2.5/2)? Please let me know how this parameter is used in the application (may be in SI or somewhere else). I even changed Vmeas to 1.25 V. Still I am getting warnings like WARNING - Model 'bsppon3mchpt3v3_p': TYP VI curves cannot drive through Vmeas=1.25V given load Rref=1e+009 Ohms to Vref=0V WARNING - Model 'bsppon3mchpt3v3_p': MIN VI curves cannot drive through Vmeas=1.25V given load Rref=1e+009 Ohms to Vref=0V WARNING - Model 'bsppon3mchpt3v3_p': MAX VI curves cannot drive through Vmeas=1.25V given load Rref=1e+009 Ohms to Vref=0V Please let me know your answers. Best Regards, Sudarshan HN NXP Semiconductors/CTO /PLT # 1 Murphy Road, Ulsoor, Bangalore - 560 008 , India. Ph:+91-80-40247073 Fax: +91-80-4024 7855 seri:sudarsha@inpsblr E-mail: sudarshan.honnudike@nxp.com -------------------------------------------------------------------- |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 Wed, 8 Nov 2006 08:43:45 -0800
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