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# fringe capacitance calculation

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#### vbhupendra

##### Full Member level 4
fringe capacitance

How can we minimize the fringe capacitance ?

#### qtarch

##### Newbie level 3
fringing capacitance

Do not use adjacent metal layers and keep distance between wires especially differential ones.

raj1987

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raj1987

### raj1987

Points: 2

#### YESH_23

##### Member level 4
fringe capacitance formula

can u plz tell me what is Fringe Capacitance

#### tuza2000

##### Full Member level 2
fringing capacitance calculation

Is there any material about fringe capacitance?
thanks!

#### milkdragon

##### Member level 3
fringing capacitance formula

Fringe capacitance means the capacitance from the side wall of a material to any other object around it

To minimize it, only way is to put object far apart from each other

##### Full Member level 4
fringe capacitance

Also make your caps have a high ratio of area to perimeter.

#### protonixs

##### Full Member level 3
what is fringe capacitance

Also make your caps have a high ratio of area to perimeter.

yes, larger unit area minimizes fringe capacitance.

#### fly6987

##### Newbie level 6
fringing cap

but larger unit area increases also unit perimeter!!!
moreover, larger unit area increases the total area of your circiut!!!

for me, the better solution is to use metal of different layer to route the circuit.

#### protonixs

##### Full Member level 3
fringe cap

fly6987 said:
but larger unit area increases also unit perimeter!!!
moreover, larger unit area increases the total area of your circiut!!!

for me, the better solution is to use metal of different layer to route the circuit.

consider having a square with an area of 4square unit.
i think the perimeter of it is lesser than the total perimeter of 4 squares having 1 square unit each. that is what i mean.

#### quaternion

##### Full Member level 4
capacitance fringe

Also make your caps have a high ratio of area to perimeter.

I think this is to minimize the uncertainty of the cap absolute value !

#### protonixs

##### Full Member level 3
calulating capacitor fringing

quaternion said:
Also make your caps have a high ratio of area to perimeter.

I think this is to minimize the uncertainty of the cap absolute value !

yes you are right. and that uncertainty is due to the effect of the fringe capacitance.
nowadays, there is formula for getting the actual value of the capacitor and fringe capacitance is already included in the calculation.

##### Full Member level 4
fringe capacitance model

No - the reason to maximize the perimeter has to do with the fact that fringing capacitance is proportional to perimeter of the cap. When we model a parallel plate cap, we disregard the fringing capacitance and say that all of the capacitance is due to the area. We can't make this assumption when there is a large perimeter.
Look up Hajimiri & Lee's paper of lateral flux capacitors (fractal capacitors) for more information.
As far as mismatch / uncertainty goes, Pelgram shows that the variance of capacitance is inversely proportional to cap area.

#### banihashemi

##### Newbie level 5
capacitance calculation fringe

Fringe capacitance depends on the layer. For metals, upper layers are thiker and so there is more fringe capacitance between two upper metal layers with the same kind.

#### rexcheung727

##### Newbie level 4
calcuration fringe capacitance

#### DSC

##### Newbie level 1
I found this which might be useful

Section 3.3 talks about Fringe Caps.

Dave C

#### Attachments

• Capacitance_Calcs.pdf
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jjr and mvj

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