Differential Microstrip Impedance Calculator

The Formula

The formula for calculating differential microstrip impedance is complex and typically involves numerical methods or approximations. A simplified version is:

\[Z_{diff} \approx 2Z_0\left(1 - 0.48e^{-0.96\frac{s}{h}}\right)\]

Where:

• Z_diff: Differential impedance
• Z_0: Single-ended impedance of each trace
• s: Spacing between the traces
• h: Height of the substrate

Calculation Steps

1. Calculate the single-ended impedance (Z_0) for each trace
2. Determine the s/h ratio
3. Apply the differential impedance formula
4. Adjust for more accurate results using field solver software if necessary

Example Calculation

For a differential microstrip with:

• Trace width (W) = 0.3 mm
• Trace spacing (S) = 0.3 mm
• Substrate height (H) = 0.254 mm
• Dielectric constant (εr) = 4.4

Assuming Z_0 ≈ 50Ω (calculated separately):

\[Z_{diff} \approx 2 * 50\Omega \left(1 - 0.48e^{-0.96\frac{0.3}{0.254}}\right) \approx 93.4\Omega\]

Visual Representation

This visual shows a cross-section of the differential microstrip structure with the calculated impedance based on our example.