Create Your Own PCB / Differential Pairs Routing
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Create Your Own PCB

Differential Pairs Routing

In our drone's PCB, there is a USB differential pair that also needs to be routed. Routing of differential pairs is similar to routing single traces but uses a separate tool named Interactive Differential Pair Routing. You can access this tool using the Active Bar or by selecting Route > Interactive Differential Pair Routing from the main menus. Let’s route our differential pair.

Tip: The differential pair can be defined in the schematic by using the Place > Directives sub-menu using the nets naming scheme *_P/*_N, or in the PCB panel in Differential Pairs Editor mode.

Choose Route > Interactive Differential Pair Routing from the main menus. We need to start routing from pins 70 and 71 of the U12 component. Click on either of the pins to start differential routing. 

Differential pairs routing
Fig. 1 - Differential pairs routing

We need to connect this differential pair to the CN1 component located at the bottom of the PCB, so make a via transition using the - on the number keypad. The completed differential routing is shown in the figure below.

Completed differential pair routing
Fig. 2 - Completed differential pair routing

For your routing to be perfect, there are basic rules that will help you avoid signal integrity problems.

  • Differential pairs should be routed as symmetrically as possible relative to each other. Any divergence in symmetry breaks the tracks coupling, leads to impedance discontinuity, and negates the differential pair usage benefits. Wrong tracks can be moved taking this rule into account or retraced if necessary.
Example of symmetric and asymmetric differential pair routing
Fig. 3 - Example of symmetric and asymmetric differential pair routing
  • Avoid straight and sharp angles during track placement. It is highly recommended to use 45 degree angle routing mode. Incorrectly angled tracks cause negative changes in signal quality. This can be easily corrected by using the Gloss feature. Select the entire track then choose Route > Gloss Selected from the main menus to automatically improve the route quality for the placed track by reducing the overall length and number of corners. You can also place the new track above the already placed track to replace it with the new routing style.
Example of poor routing and good routing quality
Fig. 4 - Example of poor routing and good routing quality

You now have all the basic skills you need to finish the routing of this PCB. Show your imagination and complete the routing. Don’t forget to use the Show/Hide connections option. If you have difficulties, you can refer to the figures below. Don't worry if you cannot connect all the GND pins as they will be connected by a polygon in the next chapters.

Tip: If you need to move the component with relevant routing, enable the Component re-route option on the PCB Editor - Interactive Routing page of the Preferences dialog.
Completed routing for the Top Layer
Fig. 5 - Completed routing for the Top Layer
Completed routing for Inner Layer 3 [3] L3
Fig. 6 - Completed routing for Inner Layer 3 [3] L3
Completed routing for Inner Layer 4 [4] L4
Fig. 7 - Completed routing for Inner Layer 4 [4] L4
Completed routing for the Bottom Layer
Fig. 8 - Completed routing for the Bottom Layer
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