RE: [IBIS] More Details about Vinh+, Vinh-, Vinl+, Vinl-

Sudarshan,
 
Thanks for your interest in IBIS.  The hysteresis thresholds here are
not directly related to PVT variations any more than normal Vinh and
Vinl thresholds are.  The difference for these thresholds is that they
are used for receiver designs which support hysteresis or bistable
latching of logic levels based on input signals.
 
For example, LVTTL recognizes 0.8 V as Vinl and 2.0 V as Vinh. Signals
below Vinl are definitively "low" while those above Vinh are
definitively "high," as these represent the guaranteed outer limits of
logic switching by the buffer design.  An individual buffer may have its
actual switching threshold in-between these levels, so a signal that is
seen as "low" for a voltage between these levels for one buffer may not
be seen as "low" for another buffer of the same design, due to
variations.  The outer limits set the guaranteed levels, and so are used
for worst-case timing and SI evaluation.
 
A receiver that exhibits hysteresis, on the other hand, might not switch
using the same threshold voltage for input signals going low-to-high
versus those going high-to-low.  An incoming signal which is rising may
therefore cause the hysteresis buffer to switch its output at a voltage
higher than that used for an incoming signal which is falling. 
 
In the case of the IBIS usage rules, the specification clearly states
that Vinh+ and Vinh- are to be used for low-to-high transitions, while
Vinl+ and Vinl- are to be used for high-to-low transitions.  A drawing
is included for reference.
 
I hope this helps...
 
- Michael Mirmak
  Intel Corp.
  Chair, EIA IBIS Open Forum
 
________________________________

From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] On
Behalf Of Sudarshan Honnudike
Sent: Monday, September 11, 2006 04:43
To: ibis@server.eda-stds.org
Subject: [IBIS] More Details about Vinh+, Vinh-, Vinl+, Vinl-



Hello Experts, 

I referred some of the IBIS documents regarding the explanation for
Vinh+, Vinh-, Vinl+, Vinl-. 
But what I got was, 

| Vinh+                         Hysteresis threshold high max Vt+ 
| Vinh-                         Hysteresis threshold high min Vt+ 
| Vinl+                         Hysteresis threshold low max Vt- 
| Vinl-                         Hysteresis threshold low min Vt- 

From the cookbook I came to know that "these parameters are used for
defining two thresholds for the rising edges and 
two thresholds for falling edges ". 

        But I didn't understand what "2 thresholds " mean. Is it
something related to PVT variations (Vinh at fast corner and Vinh at
slow corner )? 

Please let  me know the exact meaning of these parameters as soon as
possible. 

Thanks ! 

Best Regards,

Sudarshan HN
CTO /Process & Library Technology
NXP Semiconductors
Banglore-08
Ph:080-25579000  Extn:1586
seri:sudarsha@inpsblr
E-mail: sudarshan.honnudike@philips.com 

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