FreeLists / si-list / [SI-LIST] Re: Inductance of Via

["Yibing Tang" <ytang@xxxxxxxxxxxxxxxxx>]

Let me say it simple.
For some reason, I needs to use a surface mount edge SMA connector to work
with my transmission line. So I need to connect the ground plane to the
toplayer by vias. What I want to know is how to make this vias?

Yibing

-----Original Message-----
From: Tsuk, Michael [mailto:Michael.Tsuk@xxxxxxxxxx]
Sent: Monday, June 11, 2001 7:38 AM
To: si-list@xxxxxxxxxxxxx
Cc: ytang@xxxxxxxxxxxxxxxxx
Subject: RE: [SI-LIST] Inductance of Via


Yibing Tang wrote:

> I use a formula to calculate the inductance of through hole via,
> L=5.08h[ln(4h/d)+1]
> However, I find that it is not suitable for small ratio of h to d.
>From this
> formula,if decrease the ratio, I could get very lower inductance, even
> negative.

It makes no sense to talk about the inductance of a via in isolation.
None at all.  Inductance is a quality of a loop of current; without
knowing where your return path is, you can't get a meaningful value for
the total inductance.

In any case, it seems that your formula isn't applicable to vias; this
was discussed back in March.  See:

http://www.qsl.net/wb6tpu/si-list/0117.html

> My question is how far I can go to low the inductance.

You have two main choices:

1.  Bring the return path vias closer to the signal via
2.  Shorten the length of the via

The effect of the diameter is relatively weak.

--
Michael Tsuk
Compaq AlphaServer Product Development
(508) 467-4621

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