Characteristic impedance
This is a calculator for the characteristic impedance of surface wiring. For high-speed signals, surface mount wiring with low effective dielectric constant (i.e., low loss and delay) is recommended. Single 50Ω: DDR data bus, DDR address bus Differential 75Ω: Analog video signal Differential 85Ω: USB, PCI Express Differential 90Ω: DDR DQS, DDR clock Differential 100Ω: Ether, MDII, LVDS, MIPI
mm
mm
mm
SI prefixes accepted (4k7 / 1M / 10m / 220). Upper-case M = mega, lower-case m = milli
Single-end
49.13ohm
Difference
91.34ohm
Advanced — Cu thickness, Pcb relative permittivity
mm
er
Derived values
- Effective permittivity εeff
- 2.71
- 0.475 × εr + 0.67
- Propagation delay
- 5.49 ps/mm
- Used for length matching
- Capacitance per length
- 0.112 pF/mm
- TD / Z0
- Inductance per length
- 0.27 nH/mm
- TD × Z0
A 1 ns skew corresponds to 182 mm of trace length (length matching rule of thumb).
Allowing the usual ±10% fabrication tolerance, the single-ended value lands between 44.22 and 54.04 Ω.
History
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