Signal Integrity
Controlled Impedance
In plain English
Carefully sizing the copper wires so fast signals travel smoothly without bouncing back — like keeping a pipe an even width so water flows without banging.
The technical version
Controlled impedance is the practice of engineering trace geometry and dielectric so a signal line meets a target characteristic impedance, such as 50 ohm single-ended or 100 ohm differential. It depends on trace width, dielectric height, Dk, and copper weight, making it a stackup-level decision. Impedance coupons measured by TDR verify the result.