Monday, August 5th, 2024

# Planar spiral coil inductor design

Push image to enlarge 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 first four 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) Fill factor Square (nH) Hexagonal (nH) Octagonal (nH) Circular (nH) Modified Wheeler Current Sheet Monomial Fit

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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