ESD arrays for USB / Ethernet
Useful when the differential pair estimate is part of a protected high-speed I/O path.
High-speed PCB calculatorClose to target
PCB Differential Impedance Calculator
Estimate differential microstrip impedance quickly from trace width, spacing, dielectric height, copper thickness, and dielectric constant.
Use this lightweight page to estimate a differential pair quickly, compare it against your target impedance, and decide whether width or spacing needs the next small adjustment.
Geometry snapshot
Edge-coupled microstrip differential pair
Stack-up inputs
Enter the main physical dimensions and dielectric constant. Values are converted internally before the impedance estimate runs.
Estimated output
Close to targetDifferential impedance
100.6 Ohm
This geometry estimates 100.6 Ohm against a target of 100 Ohm, leaving about 626.8 mOhm of error. The smallest likely next move is to decrease spacing slightly.
Target impedance
100 Ohm
Single-ended impedance
57.1 Ohm
Target mismatch
0.6%
Next small tweak
decrease spacing slightly
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Turn the impedance target into sourcing work
After the stack-up estimate, continue into connectors, ESD protection, common-mode chokes, or RFQ workflows tied to your high-speed interface.
Suggested query
100 ohm differential pair connector ESD common mode choke
Escalate to sourcing
Need the full interface BOM reviewed?
Move from line geometry into BOM upload or RFQ when the routing decision also impacts protection, connectors, and signal integrity support parts.
Interface Protection
Common-mode chokes
Helpful for EMI cleanup on high-speed differential channels after the routing target is confirmed.
Board connectors and cable headers
Good next step when the impedance target is tied to a specific connector family or channel topology.
Impedance tuning reference
What does a differential impedance calculator estimate?
A differential impedance calculator gives a fast first-pass estimate of how trace width, spacing, dielectric height, and dielectric constant influence the impedance of a coupled pair. It is most useful when you need a quick geometry sanity check before sending the stack-up to a field solver or fabricator.
For a high-speed PCB team, this kind of estimate is practical during early routing, connector selection, and stack-up tradeoff work. It helps answer whether the next adjustment should come from wider traces, tighter gaps, or a different dielectric height.
Differential microstrip formula and practical limits
Approximation used on this page
Z_{diff} \approx 2 Z_0 \left(1 - 0.48 e^{-0.96 s/h}\right)
| Target class | Width trend | Spacing trend | Practical note |
|---|---|---|---|
| Lower Zdiff | Wider trace | Smaller gap | Use when the current geometry is too high in impedance. |
| Higher Zdiff | Narrower trace | Larger gap | Use when the pair is coupling too strongly or the trace is too wide. |
| Keep copper loss moderate | Avoid very narrow lines | Adjust gap second | Manufacturing tolerance can dominate when the geometry gets too aggressive. |
FAQ
Frequently asked questions about differential impedance
Is this calculator for microstrip or stripline?
This page is tuned for a simple edge-coupled microstrip estimation, where the pair runs above a reference plane.
Should I change width or spacing first?
If the pair is close to target, a small width adjustment is often the easiest first move. Spacing becomes the stronger lever when coupling needs a clearer shift.
Can this replace the board shop impedance calculation?
No. It is a fast engineering estimate and should be followed by fabricator or field-solver confirmation before release.