Re: output impedance of a driver

Hi Michael:
Thanks for showing me the way to find the output impedance!! It really helps me.

Now, I would like to show you some interesting results:
Right now I am working on LVT162244 from TI and I am trying to measure the
output impedance of the driver .I have used the method you show me to do (i.e.
-motive and I am able to get the output impedance for the high state which is
36.5 ohms and output impedance for the low
state which is 29.81 ohms) .
The schematic that I have used for testing is :

[Image]

where I have got a driver ->tline of 0.01 inch 60 ohms , series resistance
->tline of 10 inch 60 ohms-> and receiver.

Since I wanted to compare the real value for the output impedance of the driver
, I have tried different values for the series termination.
The calculations are like these: I assumed the output impedance of the driver
is in high state , so RH=36.5 , in order to match that with the tline,
I have to use 23.5 ohms for the series termination, and I do the same thing by
assuming the output impedance of the driver is in low state, then
the series termination is 30.19 ohms . The third case is (RH+RL)/2 =33.2 so the
series termination 60-33.2 =26.8 ohms.the last case is when the series
termination is 60 ohms

and you can see from the output waveform :

[Image]

here we see that the red curve is with series termination of 23.5 ohms , and the
one below the red curve is when series termination of 26.8 ohms
and the third one is when series termination of 30.15 ohms and finally series
termination of 60 ohms.
This is interesting to us because at the red curve where series termination is
23.5 ohms the rising edge is ok , but the falling edge is not ok .
When the series termination is 26.845 ohms , the rising edge is not ok , but
the falling edge is ok. Also when the series termination is 30.19 ohms , the
rising edge is not ok , but the falling edge is ok.Finally for the series
termination is 60 ohms , the rising edge is not ok , but the falling edge is
not ok.
My question is how do we determine the output impedance for the driver in this
case, whether we should use RH , RL or (RH+RL)/2 . ???
Please feel free to comment.
Thanks
Jason Leung

Michael Mayer wrote:

> You can use ibis2xtk. One of the options generates a BLAST (formerly MOTIVE)
> model. This is a simple linear model that includes the high and low
> impedance. Try ibis2xtk -motive
>
> It will generate a .src file. At the bottom of the file will be a DEFDRIVER
> statement for each buffer. RL and RH are the low and high impedances.
>
> =======================================================================
> Mike Mayer mmayer@innoveda.com
> Applications Engineer Office: (608)523-1960
> Innoveda, Inc Mobile: (608)575-2732
>
> -----Original Message-----
> From: Jason Leung [mailto:jleung@cid.alcatel.com]
> Sent: Monday, April 09, 2001 8:14 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 Tue Apr 10 11:14:56 2001