[SI-LIST] Re: need help on RLGC
- From: "Steve Rogers" <SRogers@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 11 Aug 2003 11:01:05 +0100
Lets keep this simple,
Basic TX Line theory shows us that we can represent any tx line with a =
combination of lumped elements R, L, C and G.
So you can get a feeling for this just think about R and the resistance =
of the copper of the line, L as its inductance, C as the capacitance =
between the conductors and G and the conductance between the conductors. =
You can estimate these quantities in a number of ways such as:-
1. Look them up in a book for the particular structure (normally given =
per unit length)
2. Calculate them using a handbook method such as those given in the =
classic book by grover or others
3. Use an E-M simulator to determine them for you.
The E-M simulator works out the values of R L C and G from the field =
distributions it found on its simulation runs. However, the way it =
arrives at the values depends on what quantity the simulator found to =
start with and how it found it. Most simulators will give you pretty =
good values for C and L but you need to take care with the R and G. The =
values of R and G are the losses in the system. Some simulators use =
formulae to account for skin effect etc so don't be surprised to find =
that high frequency losses are not that accurate! If the simulator is a =
true 3D beast and you have a good fine mesh into the metal/Substrate you =
should get a good idea of R and G.
Heres the basics of how you get at R L C and G
For Capacitance
C =3D Q/V (By definition)
then we use Maxwell's First Equation [Guass's Law for Electric =
Fields]which is the surface integral of the electric flux density to get =
Q. We get V from Maxwell's Third Equation [Faraday's Law] which is =
simply the integral of the electric field over the distance of interest. =
The solver can do all this sad maths for you.
For Inductance
L =3D Flux linkages/Current The linkages or flux you get from the flux =
density multipled by area. Flux densisty comes from Amperes law.=20
For resistance
At DC and low frequencies the resistance of any conducting structure is =
easily ascertained from the conductor cross sectional area 'A', length ' =
l' and material conductivity 'r':-
Rdc =3D r.l /A
However, at higher frequencies the resistance of a conducting structure =
becomes a function of frequency, conductor geometry and the material =
properties of its local environment. Not surprisingly, it is very =
difficult to determine precise values of resistance at high frequencies. =
=20
Your probably asleep now so that will be enough
steve
=20
Steve Rogers B.Eng (Hons) C.Eng IEE
RF Design Engineer
Micromill Electronics Limited
Leydene House
Waterberry Drive=20
Waterlooville Hampshire
PO7 7XX
Tel: +44 (0) 23 9236 6600
Fax: +44 (0) 23 9236 6673
Registered No. 1456922 (England). =20
Registered Office Brook Road
Wimborne, Dorset BH21 2BJ
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-----Original Message-----
From: karan bagga [mailto:kbagga31@xxxxxxxxx]
Sent: Monday, August 11, 2003 9:11 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] need help on RLGC
Hi=20
I am new to this and need to know the basics on how to represent a PCB =
Track using RLGC matrix ?
How does 3d extractor works and extracts the RLGC matrix for a given PCB =
track or a via.
Any pointers or links will be of great help
Thanks in Advance,
Best Regards
Karan
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