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Transmission Line Delay Calculator
Estimate signal propagation delay for PCB traces, coaxial cables, twisted pairs, and custom transmission media. Use it for timing budget checks, length matching, differential pair skew review, and high-speed interface layout planning.
Input Parameters
Results
Equations Used
Velocity Factor: VF ≈ 1 / √εeff. For custom cable modes, VF is entered directly.
Propagation Speed: v = c × VF, where c ≈ 299,792,458 m/s.
Delay: t = length / v
Skew: skew = mismatch length / v
For FR-4 microstrip this tool uses a simple effective dielectric estimate; exact delay requires PCB stackup and field-solver data.
Frequently Asked Questions (FAQ)
Q1: What is transmission line delay?
It is the time a signal edge takes to travel through a PCB trace, cable, or controlled-impedance interconnect.
Q2: How much delay does FR-4 usually add?
A common board-level estimate is roughly 150–180 ps/in, but the exact value depends on dielectric constant, stackup, trace geometry, and frequency.
Q3: Why does velocity factor matter?
Velocity factor shows how fast a signal travels compared with light in vacuum. Lower velocity factor means higher delay for the same length.
Q4: Can I use this for differential pair length matching?
Yes, use the skew length field to estimate timing mismatch from length difference. Actual differential skew also depends on routing asymmetry and glass weave.
Q5: Is this exact for high-speed PCB design?
No. It is an engineering estimate. Critical DDR, PCIe, USB, HDMI, or RF designs should use stackup data and SI simulation.
