RE: output impedance of a driver

If you do both you will find there is usually a difference in pullup and
pulldown impedance. Makes the design job more interesting. What trade-off
are you going to make?

Tom Dagostino
IBIS and Tau Modeling Manager
SDD
Mentor Graphics Corp.
503-685-1613
tom_dagostino@mentor.com

-----Original Message-----
From: Jason Leung [mailto:jleung@cid.alcatel.com]
Sent: Monday, April 09, 2001 9:41 AM
To: Scott McMorrow
Cc: ibis-users@eda.org
Subject: Re: output impedance of a driver

Hi Scott McMorrow :
Thanks very much for your advice!
So if we wanted to find the output impedance for the driver ,we just have to

go to 1V row and then read off the corresponding current value eh?
Should I do that on the Pull up curve or the pull down curve?

thanks
Regards
Jason Leung

> Jason,
>
> If the ibis model has been extracted correctly, then the Ramp data
> will tell you what the saturated output impedance is.
>
> The IBIS V/I curves give you the impedance of an output buffer
> at any voltage. I usually use 1 volts as a good place to measure
> impedance, since it is in the linear portion of the buffer curve.
> For the pullup and pulldown curve, go to the 1V row and read
> off the current. Since R=V/I, the output channel resistance can
> be calculated.
>
> For example, if at 1 Volt the current is 35mA, then the
> output impedance is 28.57 ohms.
>
> regards,
>
> scott
>
> --
> Scott McMorrow
> Principal Engineer
> SiQual, Signal Quality Engineering
> 18735 SW Boones Ferry Road
> Tualatin, OR 97062-3090
> (503) 885-1231
> http://www.siqual.com
>
> Jason Leung wrote:
>
> > 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 09:48:46 2001