### Author Topic: Wider trace is a lower induction trace?  (Read 2451 times)

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#### king.oslo

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##### Wider trace is a lower induction trace?
« on: June 17, 2013, 01:59:16 pm »
Hello there,

Longer traces increase inductance, as become evident from the series inductance formula.

And, by the parallel equation, it looks like wider traces would decrease inductance.

Can you confirm this?

Thanks

#### jpb

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##### Re: Wider trace is a lower induction trace?
« Reply #1 on: June 17, 2013, 02:30:20 pm »
Yes, as a general principle.
Though remember that wider traces will also increase capacitance to the ground plane.

I used to work with microwave devices and it was very important to minimise source inductance (in FETs) so generally tape rather than wire was used
or else several wires in parallel to connect the source pad to the microstrip.

#### king.oslo

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##### Re: Wider trace is a lower induction trace?
« Reply #2 on: June 17, 2013, 04:35:49 pm »
Thank you M

#### onlooker

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##### Re: Wider trace is a lower induction trace?
« Reply #3 on: June 18, 2013, 12:40:37 pm »
The parallel formula is not valid here. It applies only to Ls away from each other. When you consider wider trace as a parallel of several narrow traces, mutual inductance comes into play. To a good approximation, the inductance can be considered as independent of width as far as I remember ( or google it)

#### jpb

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##### Re: Wider trace is a lower induction trace?
« Reply #4 on: June 18, 2013, 12:49:07 pm »
The parallel formula is not valid here. It applies only to Ls away from each other. When you consider wider trace as a parallel of several narrow traces, mutual inductance comes into play. To a good approximation, the inductance can be considered as independent of width as far as I remember ( or google it)

You are right that the parallel formula doesn't hold - I didn't want to complicate matters by raising that - but inductance does decrease with width.

A better model is microstrip line, assuming that the traces are above a ground plane.

The following web-site gives a formula and calculator (though, as with all these equations, assumptions are made in deriving them such as there is no other metal around other than the ground plane and the strip line itself).

http://www.daycounter.com/Calculators/Microstrip-Inductor-Calculator.phtml

The formula is derived by taking the ground plane to act as a mirror essentially so there is another stripline an equal distance below it. You then need to do a contour integral with the assumption that the microstrip has no thickness and uniform current flow. (Using the integral form of Maxwell's equations.) It's a long time since I was into this sort of thing but I seem to remember it is quite fun.
« Last Edit: June 18, 2013, 12:59:01 pm by jpb »

Smf