[SI-LIST] Re: PCB Trace impedance algorithms

Sam,
  A good place to start would be  'Transmission Line Design Handbook' by =

Brian C Wadell published by Artech House ISBN 0-89006-436-9 which has=20
various formulae for just about any type of transmission line you'll=20
ever come across.

Dave Instone
Oxford Semiconductor Ltd
25 Milton Park
Abingdon
Oxon ox14 4sh
UK
www.oxsemi.com
+44 (0)1235 824963



Sam Sam wrote:
> Dear si-list members,
>   =20
>   I am learning tool support for pcb designs. I have some questions reg=
arding calculating impedance of a traces in PCB. I use allegro's built im=
pedance calculator. I am also aware that there are various other calculat=
or tools from UltraCAD, Polar Instruments etc. I am wondering how efficie=
nt and accurate these calculations are. I guess most of them use some kin=
d of assumptions and have simplified closed form formulas to qucikly exti=
mate the impedance. But can you people guide me as what is the exact tech=
nique or algorithm to calculate the impedance of a pcb trace say for a mi=
crostrip structure. Any papers or links to this study would be appreciate=
d. In specific, since i am using allegro 's calculator i would like to kn=
ow how they calculate the impedance and what are the assumptions they tak=
e. I have seen most calculator allow single ended and differential trace =
calculations. Is it possible to extend these techniques to multiple trace=
s. More importantly the accuracy of the
>  formulas is of concern to me. When compared to full wave results these=
 formulas from different tools give different result. So i am looking to =
learn what is the background behind these? Please advise me on this. Than=
ks in advance. Looking forward for your answers....
>   =20
>   =20
>   Sam
>       =09
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