Using Differential Pairs in Allegro PCB Editor
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The constraints associated with Differential Pairs now support Static and Dynamic
Phases. The margins of each constraint can be set independently using length or time.
The Max_Length (running skew) constraint for Dynamic Phase is limited to length
only.
Static Phase Tolerance - A onetime check from driver to receiver for comparing
lengths or delays of each member. If a driver cannot be determined, the check is
performed across the longest path of the pair (No change in behavior in 16.3).
Dynamic Phase - Etch length of each member is compared at each bend point interval
across the driver-receiver path of the differential pair. Etch length is always measured
back to the driver pins.
Dynamic Phase Max Length - When specified, the differential pair is permitted to
exceed the phase tolerance constraint for a contiguous etch length of less than or equal
to the value of the specified Max Length constraint. If no compensation is made within
this specified distance, a DRC is reported at the point where the differential pair first
goes out of phase.
Consider an example. Assume that the Dynamic Phase constraints are set as follows:
When the DRC is updated, it shows the following:
