RE: [IBIS-Users] Logic Threshold for min/max cases

Hi Fabio,

There are two methods that already exist in the IBIS specification for tracking changes in Vinl and Vinh relative to VCC changes. Both [Model Spec] and [Receiver Thresholds] provide mechanisms for this. Check out these keywords taken from a DDR3 model:

[Model Spec]
| Input threshold voltage corners
Vinl 0.5750V 0.5375V 0.6125V
Vinh 0.9250V 0.8875V 0.9625V

[Receiver Thresholds]
Vth = 0.750V
Vth_min = 0.735V
Vth_max = 0.765V
Vinh_ac = 0.175V
Vinh_dc = 0.100V
Vinl_ac = -0.175V
Vinl_dc = -0.100V
Tslew_ac = 5.000ns |Not specified, so set to high value
Threshold_sensitivity = 0.50
Reference_supply Pullup_ref
|
[Voltage Range] 1.5000V 1.4250V 1.5750V
[Pullup Reference] 1.5000V 1.4250V 1.5750V

[Model Spec] doesn't indicate whether the Vinh and Vinl levels are AC or DC thresholds. [Receiver Thresholds] allows for a more complex breakdown of threshold levels that track a Vref level along with AC and DC levels. This keyword works quite well with DDR2 and DDR3 switching thresholds. The mechanism for tracking corner case variation relative to power supply changes with [Receiver Thresholds] is with the Reference_supply and Threshold_sensitivity subparameters.

Check out the IBIS 4.2 or 5.0 specification for more details on these keywords.

Regards,
Randy

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of Fabio BRINA
Sent: Friday, March 02, 2012 4:24 AM
To: 'ibis-users'
Subject: [IBIS-Users] Logic Threshold for min/max cases

Hello experts,

I was reading about Threshold sub-parameters Vinh , Vinl:

Sometimes the Voltage supply extremes are quite different
from the typical value ( in the ibis generation).
Could be useful (?) , especially for these cases, to define three
 different Threshold values:

Vinl , Vinl_min , Vinl_max
 Vinh , Vinh_min , Vinh_max

(often datasheet have already these different values
  associated to the VCC typ, min, max cases)

What your opinion about this?
Could these info improve synchronism?

Best Regards,
Fabio

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