Carrier Board Design Guide for SOM-9X35 Module
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Each segment of a differential pair connection needs to be matched individually. A connection can be
segmented by a connector, serial coupling capacitors or vias. The two bends in the following figure would
compensate each other. Since the vias divide the differential pair into two segments, the bends need to be
compensated individually. This makes sure that the positive and negative signals are propagated synchronously
through the vias. The violation of this rule might need to be checked manually as the DRC may only check the
length difference over the whole connection.
Figure 24: Length differences need to be compensated in each segment
The signal speed is not equal for different layers. Since the difference is hard to estimate, it is preferable to
route signals on the same layer if they need to be matched. For example, the MIPI display interface requires
tight matching between the signal pairs and the clock pair.
It is preferable to route all data and clock signals of a MIPI DSI channel on the same layer.
Figure 25:
Pairs within same Interface should be routed preferable on same layer
Whenever possible, a symmetric breakout of differential pair signal is preferred in order to avoid the need of
serpentine traces.
Figure 26:
Preferred symmetrical breakout
