PCB and Transmission Lines
Model class: Standard approximation
Differential microstrip impedance
Estimate differential microstrip impedance from single-ended impedance and the spacing-to-height ratio.
Interactive engine
Start with the stated conditions.
Values stay in this browser. Choose a representative scenario, then calculate deliberately.
Example ready
Calculate to inspect the result.
The result will identify the direct answer, assumptions, and any warning that changes the next decision.
Assumptions to check
- The entered differential-microstrip values represent the stated operating condition.
- This standard approximation is evaluated in the declared lumped or first-pass model.
- A differential-microstrip calculation is not a component qualification or safety approval.
What this differential-microstrip calculation establishes
Estimate differential microstrip impedance from single-ended impedance and the spacing-to-height ratio. The useful result is the stated electrical quantity and the decision it supports, not an unstated claim about a finished product. This engine keeps the governing relationship visible so an input, unit, condition, or model boundary can be reviewed before a value becomes a component or layout choice.
Differential impedance uses the documented coupled-microstrip approximation Zdiff = 2Z0(1 - 0.48e^(-0.96 s/h)). Treat the number as a first-pass result for the declared operating point. When a source, load, temperature, frequency, waveform, component tolerance, or measurement condition changes, repeat the calculation at the relevant corner rather than assuming the nominal answer persists.
Worked decision context
Using this documented approximation, Z0 = 50 Ω and s/h = 2 give a differential impedance of 92.96 Ω. That example verifies the equation and illustrates the scale of the result, but it does not select a part by itself. Compare the result with available values, ratings, tolerance bands, and the receiving circuit or physical environment before implementation.
Use the primary output to identify the binding constraint. If it leaves little margin, document which input dominates and use selected-part data, a higher-fidelity model, simulation, or measurement. This is especially important when a small numerical difference changes a thermal, timing, noise, or reliability decision.
Limits and validation handoff
This approximation is valid over its published s/h range only. Verify against the specific stackup's field-solver result before locking a fabrication spec. The calculation does not silently include omitted parasitics, installation conditions, manufacturing variation, or product policy. Those conditions can be decisive even when the arithmetic is exact for the selected model.
Record inputs, units, model assumptions, and the intended decision with the result. Verify the leading risk against the selected component data sheet and a representative measurement when the circuit has consequential energy, high voltage, safety, compliance, or reliability requirements.
Common mistakes
- Treating the differential-microstrip result as a guaranteed operating limit rather than a first-pass standard approximation estimate.
- Mixing a data-sheet value measured under one condition with this differential-microstrip calculation performed at another.
- Selecting a component before checking the boundary this calculation names: this approximation is valid over its published s/h range only. Verify against the specific stackup's field-solver result before locking a fabrication spec.
Model limit and handoff
Keep the entered differential-microstrip conditions with the calculation, then validate the binding limit using the selected component, physical implementation, and representative operating corner.
FAQs
Is this differential-microstrip result sufficient to approve a design?
No. It applies standard approximation reasoning to the entered differential-microstrip values and names the checks that still need selected-part data, a higher-fidelity model, or measurement. This approximation is valid over its published s/h range only. Verify against the specific stackup's field-solver result before locking a fabrication spec.
What does this differential-microstrip calculator assume that could make the result wrong?
Differential impedance uses the documented coupled-microstrip approximation Zdiff = 2Z0(1 - 0.48e^(-0.96 s/h)). If the entered values do not match the real operating condition, the result no longer describes the actual circuit.
Where should this differential-microstrip result go next?
Compare this differential-microstrip result with Controlled-impedance handoff, then use the stated next decision below the calculator to move from this first-pass number toward an implementation.