About a week ago I placed a query asking for information on planer inductor
calculations with this form, I also sent the quire to Rick Hartley. Rick
responded with 30 plus pages of calculus from "Transmission Line Design
Handbook" by Brian C. Wadell (sorry no isdn number as yet). I have reviewed
the formulas and assumption used and think that the system can be reduced to
2 or 3 fairly useful equations.  They are:

Archimedes Spiral Inductors

L= n^2*a^2/8.0a+11.0c (Burkett, assumes ground plane)

or

L= 0.8*n^2*a^2/6.0*a+10.0*c (Wheeler, assumes no trace interaction)

where:

L is inductance in nHy
n is number of turns
a is (outer radius + inner radius)/2.0
c is outer radius - inner radius

radii to be measured in mils

Rectangular Spiral Inductors

L=8.5(A*n^5/3)^1/2

where:

L is inductance in nHy
n is number of turns
A is the area occupied by the inductor in cm^2

I hope someone else finds these as useful as I did.

Jeffrey A. McGlaughlin, C.I.D.
Sr. PCB Designer
Battelle Memorial Institute
Columbus Ohio
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-----Original Message-----
From: Matthew Lamkin
[mailto:[log in to unmask]]
Sent: Monday, June 05, 2000 10:08 AM
To: [log in to unmask]
Subject: Re: [DC] Planer Inductors


Hi there, methinks me & others have been asking the same thing.
Could not find any web addresses, but here the text of the only reply
follows.
Please keep us informed if you manage to find anything on the subject.
Many thanks - Matt
<SNIP>
1) a circular inductor with an outer diameter of D and an inner diameter
of d will have an inductance of approximately :
0.492 L [nH] = ----------------- (D[mm]+d[mm])^2 n^2 2.25D[mm]-0.25d[mm]
if you use a central via then d becomes 0.
Elektronische Bauelemente, Michael Reisch, Springer-Verlag Berlin
Heidelberg 1998, p. 135
2.) a circular inductor with an outer diameter of E[cm] and a radius of
r[cm] will have an inductance of approximately;
21.5 n^2 (E-r) L[nH] = ----------- r 1+2.72 ----- (E-r)
Das grosse Werkbuch Elektronik Bd2, Dieter Nuehrmann, Franzis' Verlag
1998, p.1153
<SNIP>

>-----Original Message-----
>From:  McGlaughlin, Jeffrey A [SMTP:[log in to unmask]]
>Sent:  Monday, June 05, 2000 2:09 PM
>To:    [log in to unmask]
>Subject:       [DC] Planer Inductors
>
>Does anyone know of a good set of design guides and equations for designing
>a planer inductor?
>The specifications I have are 22 uH (microHenry) with  4 ohm resistance
>maximum O.D. of 2mm on FR-4.
>I don't think this is possible but would like the math to prove it.
>
>TIA,
>Jeffrey A. McGlaughlin, C.I.D.
>Sr. PCB Designer
>Battelle Memorial Institute
>Columbus Ohio
>[log in to unmask]