1. What is PCB Impedance?

Definition: Characteristic impedance is the resistance to current flow in a transmission line when a voltage is applied, crucial for signal integrity in PCBs.

Purpose: Proper impedance matching prevents signal reflections and ensures maximum power transfer between components in high-speed circuits.

2. How Does the Impedance Calculator Work?

The calculator uses the formula:

Where:

• \( Z \) — Characteristic impedance (ohms)
• \( L \) — Inductance per unit length (Henrys/meter)
• \( C \) — Capacitance per unit length (Farads/meter)

Explanation: The square root of the inductance to capacitance ratio determines the characteristic impedance of the transmission line.

3. Importance of Impedance Control

Details: Controlled impedance is critical for high-speed digital circuits, RF applications, and any design where signal integrity matters.

4. Using the Calculator

Tips: Enter the distributed inductance (L) in H/m and distributed capacitance (C) in F/m. Typical values range from 200-400 nH/m for L and 50-150 pF/m for C.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical impedance value for PCBs?
A: Common values are 50Ω for RF systems, 75Ω for video, and 90-100Ω for differential pairs in digital circuits.

Q2: How do I measure L and C for my PCB trace?
A: Use field solvers, empirical formulas, or measure with TDR (Time Domain Reflectometry) equipment.

Q3: What affects PCB trace impedance?
A: Trace width, thickness, dielectric constant, and height above ground plane are primary factors.

Q4: Why is impedance matching important?
A: Mismatched impedance causes signal reflections, leading to data corruption in digital systems and power loss in RF systems.

Q5: How accurate is this calculator?
A: It provides theoretical values. For precise results, use specialized PCB design tools that account for all geometric factors.