75Ω Stripline Calculator
Controlled Impedance | FR-4 (Er=4.5) | IPC-2141
For 75Ω stripline on FR-4 with 0.2mm dielectric:
Impedance Parameters
MOD: IMP_CAL_V1Impedance Check
Understanding 75Ω Stripline Impedance
75Ω impedance is standard for video transmission and broadcast equipment, matching coaxial cable impedance. To achieve 75Ω characteristic impedance using a striplinetrace on standard FR-4 material (Er=4.5) with 0.2mm dielectric height, you need a trace width of approximately 0.050mm (2.0 mil). This calculation follows the IPC-2141 standard and Hammerstad equations for accurate impedance control.
Key Parameters for 75Ω Design
- Target Impedance: 75Ω (characteristic impedance Z₀)
- Trace Type: Stripline (centered between two ground planes)
- Required Width: 0.050mm (2.0 mil)
- Dielectric Constant: 4.5 (FR-4 standard)
- Dielectric Height: 0.2mm (layer spacing)
- Copper Thickness: 35µm (1oz copper)
- Effective Er: 4.500
- Propagation Delay: 7.076 ps/mm
Stripline vs Microstrip for 75Ω
Stripline traces are embedded between two ground planes, completely surrounded by dielectric material. This provides better EMI shielding and more consistent impedance but requires wider traces for the same impedance value. Stripline is ideal for sensitive signals requiring maximum isolation.
Common 75Ω Applications
75Ω impedance is required by the following standards and interfaces:
75Ω Standard Applications
IPC-2141 Impedance Formula
For stripline, the impedance calculation is simpler as the trace is fully embedded in the dielectric. The formula uses: Z₀ = (60/√Er) × ln(4b / (0.67π(0.8W + T))) where b is the total dielectric thickness and W is the trace width. This provides better impedance consistency compared to microstrip.
Frequently Asked Questions
How tight should my 75Ω trace width tolerance be?
Most high-speed interfaces require ±10% impedance tolerance. For a 75Ω target, this means67.5Ω to 82.5Ω is acceptable. Specify controlled impedance to your PCB manufacturer and expect trace width tolerance of ±0.5-1 mil to achieve this.
Does copper thickness affect 75Ω impedance?
Yes, thicker copper slightly lowers impedance due to increased effective trace width. For precision designs, always include copper thickness in your impedance calculations. Our calculator uses35µm (1oz) as the standard.
What if my PCB uses different dielectric than FR-4?
High-speed designs often use low-loss materials like Rogers 4350B (Er=3.48) or Megtron 6 (Er=3.4). Lower Er requires wider traces for the same impedance. Use our full calculator above to input your specific material properties.
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Complete Your PCB Design
After calculating 75Ω stripline trace width, use our other free tools to complete your high-speed PCB design. Calculate trace current capacity and via sizing for your power delivery network.