Apr 172012
 


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Square planar spiral coil Hexagon spiral coil inductor Octagon spiral coil inductor Sircular spiral coil inductor
InfoThe first approximation is based on a modification of an expression developed by Wheeler; the second is derived from electromagnetic principles by approximating the sides of the spirals as current-sheets; and the third is a monomial expression derived from fitting to a large database of inductors (and the exact inductance values).
All three expressions are accurate, with typical errors of 2 – 3%, and very simple, and are therefore excellent candidates for use in design and synthesis. The thickness of the inductor has only a very small effect on inductance and will therefore be ignored.
Notes:
Fill in appropriate values in the white fields.Then push “calculate”.
1μm =0.001mm
1μm =0.00003937007874015748 inch
Number of turns (n): turns
Spacing between turns (s): μm
Turn width (w): μm
Outer Diameter (dout): μm
Calculated Inner diameter (Din) μm
Fill factor p=(Dout-Din)/(Dout+Din)
  Square Hexagonal Octagonal Circular
Modified Wheeler nH nH nH nH
Current Sheet nH nH nH nH
Monomial Fit nH nH nH nH

 

Reference:
S.S. Mohan, M. Hershenson, S.P. Boyd and T.H. Lee
Simple Accurate Expressions for Planar Spiral Inductances
IEEE Journal of Solid-State Circuits, Oct. 1999, pp. 1419-24.
For multilayer spiral pcb coils see here:
A new calculation for designing multilayer planar spiral inductors

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