Definition

Impedance is the total opposition to alternating current, combining resistance, inductance, and capacitance. In PCB design, controlled impedance transmission lines are essential for high-speed signals to prevent reflections and signal degradation. Common values are 50Ω single-ended and 90-100Ω differential. Impedance depends on trace width, dielectric thickness, dielectric constant, and copper thickness. Fabricators typically guarantee ±10% impedance tolerance, achieved through controlled material selection and trace width compensation.