[SI-LIST] Self Inductance and TDR measurements

Hello All
        I just signed on to the SI list and the discussions have been very
useful. 
 I have been puzzling over the Maxwellian Capacitance and Inductance
matrices produced by ANSOFT TPA and I have some questions based on this

a) Pat has confirmed the method I was using to calculate the self
capacitance. However for inductance I have just been using L11 as the self
inductance. Is this correct?

b) However I am still puzzled over which # to use to compare with TDR
measurements. 
The TDR measurements we do use a fixture from ALTAIR microwave which has a
Cu sheet on which the package balls sit and grounds all other pins in the
package except for the pin of interest.

 I have not got a good answer yet as to which number in the simulation
matrix I should compare the TDR meas. to. 

Appreciate it if anybody has a suggestion.
Thanks

       Anil Pannikkat
        MTS Package Development         Ph : 408-544-7542
        Altera Corporation              Fax: 408-544-6419
        101, Innovation Drive, M/S 4101 Email: apannikk@xxxxxxxxxx
        San Jose, CA 95134              WWW: http://www.altera.com


-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@xxxxxxxx]
Sent: Friday, August 31, 2001 10:40 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: non-negative off diagonal capacitive matrix
elements ??



Ray,

The electrostatic induction matrix (note: this is NOT
the capacitance matrix) represents mutual capacitance
as negative numbers in the off-diagonal elements.
Accordingly, as Mick pointed out, the off-diagonal 
elements must be non-negative.

For the one positive off-diagonal you do have, it is
five orders of magnitude lower than the self
capacitance, so I would tend to believe the error
was due to numerical round off.  You can try increasing
the accuracy of the tool, but the value is so low,
I recommond manually setting the value to zero.

Simply FYI: the on-diagonal elements of the electrostatic
induction matrix are not self-capacitance as some folks
tend to believe.  The on-diagonal values represent 
the capacitance of that element assuming all 
other elements were at ground
potential.  To obtain self capacitance, simply add all
the values in the matrix row (i.e., C11 = B11 + B21 + B31 + ..).

Pat

 
> 
> I've just extracted the RLGC matrices for 5 coupled
> striplines using Apsimtech RLGC.
> 
> As expected, the diagonal elements of the capacitive matrix are
> positive capacitance values. All the off-diagonal elements are
> negative EXCEPT one. Is this correct. It has been a while since I've 
> thought about this, but I was under the impression the capacitive
> off diag element were all negative. Anyone know for sure ??
> 
> The element in column 1 row 5 is the one I question:
> 
> 
>    3.1600e-15                        
>   -4.9360e-16   3.2540e-15            
>   -2.0080e-17  -4.8990e-16   3.2540e-15                        
>   -1.3380e-18  -1.9820e-17  -4.8990e-16   3.2540e-15            
>    3.1280e-20  -1.3380e-18  -2.0080e-17  -4.9360e-16   3.1600e-15
> 
> 
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