Controlling Impedance

An ideal transmission line has a characteristic impedance along the entire trace. If the characteristic impedance of the matched transmission line is perfectly maintained, the full signal exists at the end of the trace without reflection or signal attenuation.

To control impedance, you need to control three features of the circuit’s geometry:

The trace width.
The spacing between the signal return path and the signal trace.
The dielectric coefficient of the material surrounding the trace.

You can calculate these values using a trace impedance calculator. Work with your PCB manufacturer during your PCB layout design for these impedance calculations.

Additionally:

Use 40 ±10% for all single-ended signals.
Use 80 Ω ±10% for all differential signals.
Route high-speed signals using a minimum number of vias and corners to reduce signal reflections and impedance changes.
To route a 90° turn, use two 135° turns or an arc instead of a single 90° turn. This method reduces reflections on the signal by minimizing impedance discontinuities.