> Capacitance of a parallel plate capacitor (or parallel copper planes)
> is given as:
>
>       C = Eo x Er x A
>           -----------
>                D
>
> Where:
>        C  = capacitance in Farads      (F)
>        Eo = permittivity of free space (8.854 x 10exp-12) (F/m)
>        Er = relative permittivity  (typically FR-4 is 4.6 at 1 MHz)
(no units)
>        A  = area of the plates (or planes) (m x m)
>        D  = distance between plates (or planes) (m)
>
> This equation neglects fringing effects.
------------------------------------------------------------------------------------------------------------

Also assume that:

D << length (for "A" dimension)

D << width (for "A" dimension)

Er >> Eo


From "Transmission Line Design Handbook"
by Brian C. Wadell
A book all designers of RF and high speed circuits should invest in.
It includes formulas for all types of printed devices.
spiral inductors, capacitors, resistors, T junction, Y junction,
microwave bends etc.

Raymond Smith
Sr. PCB Designer
Tellium
Oceanport, N.J. 07757
[log in to unmask]

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