Tuesday, September 16, 2008

Inductor High-Frequency Performance

High frequency performance of inductors is approximated by the schematic shown below

Therefore, a 10-mH inductor has a reactance of 628 Ω at 10 kHz, which increases to
6.28 MΩ at 100 MHz. Right?

In reality, one will never see the 6.28 MΩ with this inductor. Parasitic resistances are easy
to understand — the inductor is constructed of wire, which has a given resistance per unit
length. Parasitic capacitance is harder to visualize, unless one considers the fact that
each turn of wire in the inductor is located next to adjacent turns, forming a capacitor. This
parasitic capacitance limits the upper frequency of this inductor to under 1 MHz. Even
small wire-wound inductors start to become ineffective in the 10 MHz to 100 MHz range.

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