PCB Trace Impedance Calculator
Use this free online PCB impedance calculator to determine microstrip and stripline trace impedance for your high-speed digital and RF circuits. Calculate single-ended and differential impedance instantly based on your stackup parameters.
Why Controlled Impedance Matters in PCB Design
In high-speed PCB design, maintaining a specific trace impedance is critical for signal integrity. Mismatched impedance along a transmission line can lead to signal reflections, crosstalk, and electromagnetic interference (EMI). Common routing configurations include:
Microstrip: Our microstrip impedance calculator handles traces routed on the outer layers of the PCB with a single ground reference plane below.
Stripline: Traces routed on inner layers between two solid reference planes. They provide excellent EMI shielding and more consistent impedance for dense boards.
Edge-Coupled (Differential Pair): Used for high-speed differential signals like USB, PCIe, and HDMI. The differential impedance depends heavily on the spacing (S) and coupling between the two parallel traces.
Common Target Impedances for High-Speed Interfaces
| Protocol / Interface | Single-Ended (Z₀) | Differential (Zdiff) | Standard Tolerance |
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Frequently Asked Questions (FAQ)
What is controlled impedance in PCB design?
Controlled impedance is the characteristic impedance of a transmission line formed by a PCB trace and its associated reference planes. It ensures high-speed digital and RF signals travel from the driver to the receiver without distortion or reflection.
Why is 50 ohms the standard for PCB impedance?
50 ohms provides an excellent balance between power handling capacity and signal loss. Originally established as a standard in the RF/microwave industry, it is now widely adopted for most single-ended high-speed digital signals.
What happens if my PCB trace impedance is wrong?
Impedance mismatches cause signal reflections, ringing, and crosstalk. This can severely degrade signal integrity, lead to data transmission errors, and increase electromagnetic interference (EMI) emissions.
How does trace width affect impedance?
Trace impedance is inversely proportional to trace width. Increasing the trace width decreases the impedance, while decreasing the trace width increases the impedance. You can test this by adjusting the (W) value in our calculator.
What is the difference between a microstrip and a stripline?
A microstrip is routed on the outer layer of a PCB with only one reference plane below it. A stripline is routed on an inner layer, sandwiched between two solid reference planes, providing better EMI shielding and more consistent impedance.
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