Planar Spiral Inductor Calculator

Inductance Formula:

\[ L = \frac{\mu_0 \times N^2 \times d_{avg}}{2} \times \left(\ln\left(\frac{2.46}{\phi}\right) + 0.2 \phi^2\right) \]

Inductance (L):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is a Planar Spiral Inductor Calculator?

Definition: This calculator estimates the inductance of a planar spiral inductor based on the number of turns, average diameter, and fill factor.

Purpose: It helps electrical engineers and circuit designers determine the inductance of spiral coils used in integrated circuits and RF applications.

2. How Does the Calculator Work?

The calculator uses the modified Wheeler formula:

\[ L = \frac{\mu_0 \times N^2 \times d_{avg}}{2} \times \left(\ln\left(\frac{2.46}{\phi}\right) + 0.2 \phi^2\right) \]

Where:

\( L \) — Inductance (henrys)
\( \mu_0 \) — Permeability of free space (4π×10⁻⁷ H/m)
\( N \) — Number of turns
\( d_{avg} \) — Average diameter of the coil (meters)
\( \phi \) — Fill factor (ratio of inner to outer diameter)

Explanation: The formula accounts for the geometry of the spiral coil and provides a good approximation for square planar spirals.

3. Importance of Spiral Inductor Calculation

Details: Accurate inductance calculation is crucial for designing RF circuits, filters, and impedance matching networks in integrated circuits.

4. Using the Calculator

Tips: Enter the number of turns, average diameter in meters, and fill factor (default 0.5). Fill factor must be between 0 and 1.

5. Frequently Asked Questions (FAQ)

Q1: What is the fill factor (φ)?
A: The fill factor is the ratio of inner diameter to outer diameter (d_inner/d_outer) of the spiral coil.

Q2: What's a typical fill factor value?
A: Most designs use fill factors between 0.3 and 0.7, with 0.5 being a common default value.

Q3: How accurate is this formula?
A: The modified Wheeler formula provides about 5-10% accuracy for typical spiral inductors.

Q4: What if my spiral isn't square?
A: This calculator assumes square spirals. For circular or hexagonal spirals, different formulas may be needed.

Q5: How do I calculate average diameter?
A: Average diameter is (d_outer + d_inner)/2, where d_outer is the outer diameter and d_inner is the inner diameter.