Using Differential Pairs in Allegro PCB Editor
February 9, 2012 11 Product Version 16.5
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.
Let's consider an example. Assume that the Dynamic Phase constraints are set as follows:
When the DRC is updated, it shows the following:
The beginning of the yellow pseudo line (closest to driver) is where the Differential Pair
initially goes out of Phase (beyond the 20 mil tolerance). The DRC marker D-Y is placed
at the initial 'out of phase spec' location as measured from the Driver Pins.
Notes:
• There can only be 1 DRC marker on a differential pair, even though there may be
multiple violation zones.
• It is assumed that the designer will correct the phase issues working from the
Drivers to the Receivers.
