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Post subject: Analytical parasitic estimation Posted: Thu
May 10, 2007 9:26 am
Joined: Fri Jan 19, 2007
I hope it is not a too much weird
We all know that if you have two metal layer with a distant
d and thickness th1, th2, we could calculate the capacitance for area
unit with C = (Er*Eo)/d. My question is, in order to get merely an estimation,
does someone know if exists such as similar formula for calculating
the capacitance for perimeter unit between the edge th1 of the first
layer with the surface (with infinite extension) of the second?
Thank you very much!
Post subject: Posted: Fri May 11, 2007 10:33 am
Joined: Fri Feb 17, 2006 12:07 pm
I suspect that the structure you are enquiring
about is the structure that actually makes the formula value of C =
the measured value of C.
The classic formula assumes the electric
field is perpendicular to the plane of the plates. Without the device
you seem to be mentioning, the field at the edge of both plates actually
curves outwards before returning to the plates. In consequence the formula
in that case does not predict an accurate answer corresponding to what
you will measure with a bridge.
The extra plate is called a fringing
plate (I think) and is always used for constructing a standard reference
capacitor. It has the effect of restoring parallelism to the E field
between the plates, a situation for which the formula is valid.