Differential Routing Basics You Need to Know

Single-ended signaling refers to transmitting a signal on a trace and then using a common reference for the signal’s return path. When we route a bunch of traces on the board and the ground plane provides the path for the signal returns, that is single-ended signaling. This is how most of the PCB nets are routed. 

However, as the signal frequencies increase, single-ended signaling can be victimized by some problems, including the noise of Crosstalk and electromagnetic interference (EMI). Here is where differential signaling can help.

Differential signaling is a method of sending the same information over two traces. It uses two complementary signals to transmit one data signal; the second signal is inverted from the first. The signal receiver uses the difference between the inverted and non-inverted signals to generate the differential output.

Some advantages of differential signaling are

• Resistance to incoming EMI and Crosstalk
• Reduction of outgoing EMI and Crosstalk
• Lower-Voltage operation
• Effective increase in signal-to-noise ratio (SNR)

The Cadence PCB Design tool, Allegro PCB Editor, offers the creation, rule setup, and interactive routing of differential pairs. It supports two types of differential pairs: Model-defined differential pairs and User-defined differential pairs. Multiple checks such as Gather Control, Primary Gap and Width, Neck Gap and Width, Length Matching, and Static and Dynamic Phase Control can be set in Constraint Manager to trigger the differential pair rule checking and analysis DRCs.

Team PCBTech

Cadence Design Systems