100 Ohm Differential Impedance Calculator

100 Ohm Differential Impedance Equation:

\[ Z_{diff} = 2 \times Z_0 \times (1 - 0.48 \times \exp(-0.96 \times S / H)) \]

Differential Impedance (Zdiff):

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1. What is 100 Ohm Differential Impedance?

Differential impedance refers to the impedance between two signal lines in a differential pair. The 100 ohm standard is widely used in high-speed digital communications (like USB, Ethernet, HDMI) to maintain signal integrity and minimize electromagnetic interference.

2. How Does the Calculator Work?

The calculator uses the differential impedance equation:

\[ Z_{diff} = 2 \times Z_0 \times (1 - 0.48 \times \exp(-0.96 \times S / H)) \]

Where:

\( Z_{diff} \) — Differential impedance (ohms)
\( Z_0 \) — Single-ended impedance (ohms)
\( S \) — Spacing between conductors (units)
\( H \) — Height above reference plane (units)

Explanation: This equation calculates the characteristic impedance of a differential microstrip transmission line, accounting for the coupling effects between the two conductors.

3. Importance of Differential Impedance Calculation

Details: Accurate impedance matching is crucial for high-speed signal integrity. Mismatched impedance causes signal reflections, leading to data errors, reduced noise immunity, and electromagnetic compatibility issues in high-frequency circuits.

4. Using the Calculator

Tips: Enter single-ended impedance in ohms, spacing and height in consistent units (e.g., mils or mm). All values must be positive numbers. The calculator will compute the resulting differential impedance.

5. Frequently Asked Questions (FAQ)

Q1: Why is 100 ohms a common differential impedance standard?
A: 100 ohms provides a good balance between signal integrity, power consumption, and noise immunity for most high-speed digital applications.

Q2: What factors affect differential impedance?
A: Trace width, spacing between traces, dielectric constant, height above ground plane, and copper thickness all influence the final impedance value.

Q3: When should I use differential signaling?
A: Differential signaling is preferred for high-speed data transmission, long-distance communication, and environments with high electromagnetic interference.

Q4: How accurate is this calculation method?
A: This equation provides a good approximation for microstrip configurations, but for precise designs, use professional PCB design tools with more sophisticated models.

Q5: What are typical units for S and H parameters?
A: Typically mils (thousandths of an inch) or millimeters are used, but any consistent unit system will work as long as both S and H use the same units.