Wire inductance on PCB,is this right ?

Thread Starter

majd-ghadab

Joined Dec 25, 2012
23
Hello everyone
i want to made impedance on specific frequency between tow pads on the PCB
i am using altuim designer (length tuning) to have a specific wire length , so if i used this site :
http://chemandy.com/calculators/flat-wire-inductor-calculator.htm
to calculate 55 nH with 6 cm wire length, 0.2 cm width , and as in picture i have put this length between the pads do i get the inductance required inductance between them ??
 

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kubeek

Joined Sep 20, 2005
5,776
A snake like that will be mostly non-inductive, that´s why these shapes are used to match the length of traces like for example differential pairs to DRAM.
You need a spiral shape or simply just a piece of arc to get inductance.
 

Thread Starter

majd-ghadab

Joined Dec 25, 2012
23
A snake like that will be mostly non-inductive, that´s why these shapes are used to match the length of traces like for example differential pairs to DRAM.
You need a spiral shape or simply just a piece of arc to get inductance.
so you mean if i used this shape it will kill the inductance ?
and why do they use tow equal wires lengths positive and negative >> to remove the inductive affect between each other ?
 

kubeek

Joined Sep 20, 2005
5,776
so you mean if i used this shape it will kill the inductance ?
You see that the current goes in such way that the magnetic field of each wire going left is cancelled by the wire going right, so the whole pattern should have almost no inductance. Noninductive resistors are done in a similar way.

Designers use this to match the length of the data lines, so that the delay in them is the same on all the data pins. At high data rates this really starts to matter.
 
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