[IBIS-Users] Re: [IBIS] Re: hspice vs IBIS model correlation at different capacitive loads

All,

Thanks for the information and replies.
The buffer is using a feedback which changes the drivestrengths.

Currently we are going to chop the ringing portion
of the IBIS V-T data which looks the safer option
and go ahead.

Thanks again
vinayak

Muranyi, Arpad wrote:

>Andy,
>
>You are absolutely correct, there are different
>types of feedbacks, and I should have defined
>which one I was referring to in my posting...
>
>I was thinking of one that adjusts the drive
>strength real time as the buffer is switching.
>Legacy IBIS can't do that.  (Although one could
>model these too using the *-AMS extensions of
>IBIS).
>
>On the other hand, buffers which adjust their
>own drive strength only once and a while to
>compensate for temperature variations, for
>example, can be modeled in IBIS as if they were
>normal buffers, because they don't change skins
>while driving signals onto the bus.  You may
>need the [Model Selector] keyword to make a
>few different driver models available for the
>various strengths, but that's all.
>
>Arpad
>------------------------------------------------
>
>-----Original Message-----
>From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Andrew Ingraham
>Sent: Wednesday, January 04, 2006 9:31 AM
>To: ibis-users@eda.org; ibis@eda.org
>Subject: [IBIS] Re: hspice vs IBIS model correlation at different capacitive loads
>
>  
>
>>I think he is saying that the oscillations happen
>>because of the feedback in the buffer is trying to
>>settle to a steady state condition.
>>
>>If so, legacy IBIS can not model your buffer, since
>>there are no provisions for describing feedback.
>>    
>>
>
>Yes.
>
>Although it depends on the feedback.
>
>Linear negative feedback, such as used on op-amps to reduce output
>impedance, should work OK, I think.  It's probably also possible that some
>forms of feedback to reduce variations in drive strength (for example),
>ought to be somewhat compatible with conventional IBIS.  But things like
>positive feedback to give hysteresis, don't play well in IBIS.
>
>Regards,
>Andy
>
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