3 Levels of Impedance Control
The importance of controlled impedance in a printed circuit board can depend on many variables, including the PCB’s unique characteristics and how the board will be used. Typically, printed circuit boards are available with three levels of impedance control service.
Impedance control is the most often used in high-end designs with a tight tolerance or unusual configuration. There are a number of different types of controlled impedance. The most common is referred to as characteristic impedance. Other types include wave impedance, image impedance, and input impedance.
The board is manufactured and then tested via a Time Domain Reflectometry (TDR) test to determine if impedance specifications are met; changes can be made if needed. It will be necessary to work closely with your circuit board supplier on impedance control specifications to achieve the best results.
This refers to compatibility in impedance. The impedance control trace will be indicated on the design. Width of the trace and height of the dielectric can be adjusted as needed. If necessary, a TDR test can be performed to check that impedance is correct. However, this does add some additional cost.
No Impedance Control
Because the impedance tolerances in the design are not tight, correct impedance can be achieved by conforming to standard specifications without impedance control. The printed circuit board manufacturer can provide accurate impedance without extra steps, which makes this the most cost-effective level.