**From:** Larry Smith (*ldsmith@lisboa.eng.sun.com*)

**Date:** Fri Mar 17 2000 - 09:42:02 PST

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Out of the four parameters below, only two are independent. Given

any two of the four parameters, the others are calculated.

Inductance = L, inductance/length

Capacitance = C, capacitance/length

velocity = 1/sqrt(LC)

Impedance = sqrt(L/C)

The best place to start is with the universal constant: the speed of

light. Einstein said that time and distance are not constants (nor

are inductance and capacitance) but the speed of light (3x10**8 M/Sec,

12 inches/nSec) is. Assuming that we have no ferrous (magnetic)

materials in our environment, the velocity of electromagnetics in all

of our structures is:

light_speed/sqrt(eR), eR = relative permeability

As mentioned in a previous note on this thread, it is generally

easier to calculate capacitance than inductance. This is done

for transmission lines and power plane structures. Given the

fundamental velocity above and the capacitance, both inductance

and impedance are calculated. Usually we assume that all the

charge is on the surface of conductors (skin effect, high

frequency approximation) when making capacitance calculations.

Given constant materials (ie FR4 or Ceramic with eR properties),

the velocity is known. Geometry's can be changed that will affect

the capacitance, inductance and impedance. But the 4 parameters

are fundamentally related by the above equations.

regards,

Larry Smith

Sun Microsystems

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**Next message:**Muranyi, Arpad: "RE: [SI-LIST] : Bad IBIS models!"**Previous message:**Peterson, James F (FL51): "FW: [SI-LIST] : A basic question"**Maybe in reply to:**Peterson, James F (FL51): "[SI-LIST] : A basic question"**Next in thread:**amit agrawal: "Re: [SI-LIST] : A basic question"

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