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





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