Stripline PCB Differential Impedance Calculator

Differential Pair Impedance in Stripline Geometry

Input Fields

Single-Ended Impedance

Z₀

Ω

Single-ended characteristic impedance of one stripline

Spacing Between Lines

s

mm

Distance between the centers of the differential pair traces

Substrate Height

h

mm

Distance from the trace to the reference plane

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Differential Impedance

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Stripline Differential Impedance Formula

$$Z_{\text{diff}} = 2Z_0 \cdot \left( 1 – 0.347 \cdot e^{-2.9 \cdot \left( \frac{s}{h} \right)} \right)$$

Where:

• $$Z_{\text{diff}}$$ = differential impedance (Ω)
• $$Z_0 $$= single-ended impedance (Ω)
• $$s$$ = spacing between the pair traces (mm)
• $$h$$ = distance from trace to ground plane (mm)

This empirical formula is widely used for symmetric stripline configurations with identical reference planes.

Stripline Differential Impedance – Calculation Example

Given:

• $$Z_0$$ = 50 Ω
• $$s$$ = 0.15 mm
• $$h$$ = 0.2 mm

Calculation:

1. $$\frac{s}{h} = \frac{0.15}{0.2} = 0.75$$
2. $$e^{-2.9 \cdot 0.75} ≈ e^{-2.175} ≈ 0.1138$$
3. $$Z_{\text{diff}} = 2 \cdot 50 \cdot \left( 1 – 0.347 \cdot 0.1138 \right ) ≈ 100 \cdot (1 – 0.0395) ≈ 96.05~\Omega$$

Differential pairs in stripline configurations are commonly used in high-speed digital interfaces due to their noise immunity and precise impedance control. This calculator helps engineers estimate the impedance of tightly coupled traces routed on internal PCB layers. Proper impedance matching minimizes reflection and ensures signal integrity in data links such as LVDS, USB, or Ethernet.