[SI-LIST] Re: Transmission Line calculator Problem!

There isn't any such thing as a default dielectric constant for FR4.  You
must specify the glass to resin ratio and the frequency of interest and
then look in the data tables from the laminate supplier for the correct
dielectric constant.  ONce you do this, all of the tools based on Maxwell's
Equations yield very good results.

All of the equations used to calculate impedance a sweet spot within which
the deliver reasonable results.  Outside the sweet spots the results can be
very far off.
Best to use a tool such as Polar SI9000, Hyperlynx or Cadence Sigexplorer.

Lee Ritchey


> [Original Message]
> From: Mikhail Matusov <matusov@xxxxxxxxxxxx>
> To: Mohamad Haghtalab <mohaghtalab@xxxxxxxxx>; <SI-LIST@xxxxxxxxxxxxx>
> Date: 3/15/2009 9:58:26 AM
> Subject: [SI-LIST] Re: Transmission Line calculator Problem!
>
> 1.Transmission line calculators use empiric formulae, so they are just 
> estimates.
> 2. Check if the default dielectric constant for FR4 is slightly different
in 
> these tools.
>
> /Mikhail
>
>
> ----- Original Message ----- 
> From: "Mohamad Haghtalab" <mohaghtalab@xxxxxxxxx>
> To: <SI-LIST@xxxxxxxxxxxxx>
> Sent: Sunday, March 15, 2009 10:35 AM
> Subject: [SI-LIST] Transmission Line calculator Problem!
>
>
> > Hi all
> >  
> > I want to design diff Lines for carrying LVDS Signals(pulses with
100MHz 
> > and rise time of <1 ns) in form of Stripline and MicroStrip,but I have 
> > problem with calculating exactly their characteristic Impedance.
> > In both HyperLynx(from mentor) and Cadence Allegro(V16.2) (Transmission 
> > Line Calculator) I tryed to calculate this,but what I obtained in both
is 
> > different with each other
> >  
> > I want to achieve 100 ohm for Zdiff, I derived (from formula and 
> > constraints)  :
> >                                                                
Stripline 
> > :  W=5 mil   S=5 mil    h$mil
> >
                                                                microstrip: 

> > W mil  S=5 mil   h mil
> >
                                                                           
> > dielectric : FR4
> >                                                                      
> > copper thickness : 1.4 mil
> >  
> > for Stripline
> >  
> > HyperLynx : 85.5 ohm
> > Allegro      : 74.34 ohm
> >  
> > for  microstrip
> >  
> > HyperLynx  :97 ohm
> > Allegro       : 92.37 ohm
> >  
> > so What Should I do ? (for exactly calculating Z0) 
> >  
> > Thanks for Help
> >  
> > Best Regards
> >  
>
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