RE: [IBIS-Users] {Spam?} {Filename?} LVDS IBIS model - simulation issue

From: Muranyi, Arpad <Arpad_Muranyi@mentor.com>
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

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Received on Wed Sep 18 08:31:20 2013

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