What is phase tolerance?
The phase tolerance is used to accommodate physical issues in a board layout that would prevent two nets in a pair from being routed at exactly the same length. These issues can include placement issues or issues regarding routing blockages in the design.
How do you define a differential pair?
Differential Pairs can be defined as an Electrical CSet or a Physical CSet. You can define Min Line Spacing, Primary Gap, Primary Width, Neck Gap, Neck Width, + and – Tolerance as either a Physical or Electrical CSet.
What is differential pair impedance?
Differential impedance is defined as impedance between the two lines when the line pair is driven differentially. This definition effectively makes it equal to twice the odd mode impedance. Common mode impedance is defined as impedance between the two lines when the line pair is driven with common mode stimulus.
Are RX and TX differential pairs?
Thus the Rx and Tx channels are largely independent on the bit-interval scale. As result there is no restrictions on delays between Rx and Tx lanes, and there is no need in trace length matching between differential pairs. However the trace length within each differential pair should be matched as best as you can.
What is length matching in PCB design?
PCB trace length matching is exactly as its name suggests: you are matching the lengths of two or more PCB traces as they are routed across a board. These traces could be one of the following: Multiple single-ended traces routed in parallel. Each end of a differential pair.
How do you calculate differential pair impedance?
The differential impedance value that is returned from most calculators is equal to the sum of the impedance from each trace (including contributions from coupling). Taking this value and dividing by 2 gives you the odd-mode impedance value of each trace.
What is 3W rule in PCB?
If you’ve ever wondered how far you need to keep your traces from each other to minimize coupling, then use the 3W rule. It states that the separation between traces must be three times the width of a single trace when measured from center to center.
How is phase tolerance applied to a differential pair?
You are partially correct in your first statement; phase tolerance IS a property that is applied to the differential pair, but Allegro will break the individual nets of the differential pair into pin pairs according to their PINUSE configuration.
Where does phase tolerance get applied in cm?
Phase Tolerance property gets applied to the differential pair (i.e. the diff pair object in CM and gets applied to the “whole” net not pin pairs, I think) so I am not sure what you mean by ” would like to set phase tolerance to say 5mils and see the property on pin pairs from A-B and A-C though I could live with B-C being created as well.”
How to define differential pairs-parallel systems?
Min Line Width 0.2mm for outer layers, 0.15mm for inner layers. Primary Gap 0.2mm for outer layers, 0.15mm for inner layers. +/- Tolerance 0.05mm for all layers. Min Line Space 0.15mm for outer layers, 0.1mm for inner layers.
How does Allegro configure net / diff pin pairs?
The issue that I am having with this is that Allegro configures the pin pairs associated with a given net/diff pair based upon the PINUSE property (and apparently the part CLASS, though I haven’t seen this affect anything in my situation.)
