Date: Wed Sep 18 2013 - 08:31:04 PDT
Andrey, I am not sure that your PD I-V curve is correct. First of all, it should have a positive sign, but its shape doesn't look right either. Can you describe how you generated these I-V curves? Thanks, Arpad ======================================================== From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of Andrey Babintsev Sent: Wednesday, September 18, 2013 9:38 AM To: ibis-users@eda.org Subject: Re: [IBIS-Users] {Spam?} {Filename?} LVDS IBIS model - simulation issue Re-sending with updated attachment Hi, I am making IBIS models for LVDS (low voltage differential signal) IO buffer. To model an LVDS buffer I created the following test circuit, assigned the generated IBIS model to both buffers, set one buffer as inverted output. [cid:image001.png@01CEB45A.2C60C9C0] Problem: In the image below the YELLOW waveform is what I saw and the PURPLE waveform is what I expected to see. [cid:image002.png@01CEB45A.2C60C9C0] YELLOW = IBIS model PURPLE = Spice ( reference ) model Here is combined pullUp (yellow) and pullDown (green) IV curves (actually it is spice curves from which IV tables were derived): [cid:image003.png@01CEB45A.2C60C9C0] Lets assume that simulator tries to find operational point for LVDS buffer driving high. Then for the non-inverted buffer a point (Vp, Ip) will be taken from pullUp table, for the inverted buffer a point (Vn, In) from pullDown table, the following conditions should be satisfied: Ip = In, Vp - Vn = Ip*50. On the image above it is seen that there are 2 points satisfying the condition: Vp =~ 1.45V and Vp =~ 2.2V. Seems that something like that happened during simulation and simulator got to the second point. (BTW, there are 60 points for the region 0.9 - 1.6V and 10 points for the region 1.6-2.5V in the IBIS model IV tables). Question: What can be done to resolve this situation? Should IV tables or another IBIS structures be modified and how? I am making ibis ver. 4.2 models. Thanks, Andrey On 09/18/2013 06:33 PM, Andrey Babintsev wrote: Warning: This message has had one or more attachments removed (fail.min.png). Please read the "EDA-Attachment-Warning.txt" attachment(s) for more information. Hi, I am making IBIS models for LVDS (low voltage differential signal) IO buffer. To model an LVDS buffer I created the following test circuit, assigned the generated IBIS model to both buffers, set one buffer as inverted output. [cid:part1.07090501.06090707@freescale.com] Problem: In the image below the YELLOW waveform is what I saw and the PURPLE waveform is what I expected to see. [cid:part2.00080404.04020708@freescale.com] YELLOW = IBIS model PURPLE = Spice ( reference ) model Here is combined pullUp (yellow) and pullDown (green) IV curves (actually it is spice curves from which IV tables were derived): [cid:part3.05090108.02030307@freescale.com] Lets assume that simulator tries to find operational point for LVDS buffer driving high. Then for the non-inverted buffer a point (Vp, Ip) will be taken from pullUp table, for the inverted buffer a point (Vn, In) from pullDown table, the following conditions should be satisfied: Ip = In, Vp - Vn = Ip*50. On the image above it is seen that there are 2 points satisfying the condition: Vp =~ 1.45V and Vp =~ 2.2V. Seems that something like that happened during simulation and simulator got to the second point. (BTW, there are 60 points for the region 0.9 - 1.6V and 10 points for the region 1.6-2.5V in the IBIS model IV tables). Question: What can be done to resolve this situation? Should IV tables or another IBIS structures be modified and how? I am making ibis ver. 4.2 models. Thanks, Andrey -- This message has been scanned for viruses and dangerous content by MailScanner<http://www.mailscanner.info/>, 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 mikelabonte@eda-stds.org |or ibis-request@eda-stds.org | |IBIS reflector archives exist under: | | http://www.eda-stds.org/ibis/email_archive/ Recent | http://www.eda-stds.org/ibis/users_archive/ Recent | http://www.eda-stds.org/ibis/email/ E-mail since 1993
