RE: output impedance of a driver

You have to add up all of the curves which are ON and then
calculate the impedance. This may consist of a pulldown
plus GND_clamp, plus Vcc_clamp if it is driving low, or
pullup, and the same two clamps when it is driving high.

I hope this helps,

Arpad
========================================================

-----Original Message-----
From: Jason Leung [mailto:jleung@cid.alcatel.com]
Sent: Monday, April 09, 2001 11:17 AM
To: Muranyi, Arpad
Cc: ibis-users@eda.org
Subject: Re: output impedance of a driver

Hi Muranyi, Arpad:
Thanks for your advice!
one more question I would like to ask you: because I have been asked from
my colleague to use
XTK/XNS to find the output impedance of the driver, I know that in the
spawn -> VI viewer ,
we can import the corresponding .wvi curve to observe the waveform.
Among all those waveform, you can just pick on one waveform, and then do a

delta x and delta y function, then you will be able to find the impedance.

However, there are so many curves I have to choose(shunt and high, shunt
and low and many
many more) , do u know which one I have to choose for an accurate
approximation of the
output impedance of the driver .
The whole point here is , since I know I can find the output impedance of
the driver in the IBIS model
I also wanted to try and find the output impedance of the driver in the
XNS (QUAD) model ,so that
I am able to compare what we have before the simulation and after the
simulation( i.e. how the XTK/XNS
interpret the output impedance of that driver ).

thanks alot
Jason Leung

> Jason,
>
> The DC impedance can be found by dividing V/I on the IV curve of
> the buffer. You will find that you get a different value at
> practically any of the voltages due to the non linear shape of
> the IV curve. Plus, the process variation of a chip can give
> you a variation on the order of 2-3x. So finding the impedance
> and matching the T-line to it is like shooting at a moving target.
>
> The reason I said DC impedance above is because the capacitive
> components of the buffer will also alter the impedance of the
> buffer a higher frequencies.
>
> Arpad Muranyi
> Intel Corporation
> ================================================================
>
> -----Original Message-----
> From: Jason Leung [mailto:jleung@cid.alcatel.com]
> Sent: Monday, April 09, 2001 6:14 AM
> To: ibis-users@eda.org
> Subject: Re: output impedance of a driver
>
> Hi all:
> Morning!
> I am trying to obtain the output impedance of a driver, so that I can
> match the driver with a transmission line and proper termination.
> The way that I have tried is I used the IBIS model and then translate
> the model into QUAD model, so that I can used the XNS to observe their
> rising and falling waveform. Moreover I am trying to find its output
> impedance in XNS.
> My question is : Does anyone ever try finding the output impedance of a
> driver? AND how did you achieve that?
>
> Thanks very much for your comment!
> Jason leung

 
Received on Mon Apr 9 12:51:10 2001