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A Shorter, Predictable Design Cycle for Complex PCBs - Dynamic Phase Control

Comments(0)Filed under: PCB Layout and routing, PCB design, DDR3, Allegro, PCB, Allegro 16.3, Constraint-driven PCB Design flow, ECSets, DDR2, XAUI, phase control, dynamic phase control

This is second in a series of blog posts about making your design cycles shorter and more predictable for increasingly complex PCB designs. In my last post I talked about using ECSets and Topology Apply capabilities for high-speed standards based interfaces such as DDRx and PCI Express.

Continuing on that theme, implementing high-speed signals can be a challenge as the delay tolerances shrink and matching requirements increase.

Take the example of differential pairs on advanced standards based interfaces (PCI Express generation two and three). A few years ago, static phase tolerance from driver to receiver was good enough. Now, with newer interfaces, differential pairs cannot be out of phase over a certain length. A requirement like "differential pairs can be out of phase by 20 mils for a running length of no more than 1/2” is common in many designs. To manage such increasingly complex constraints, it is important to arm yourself with a tool that provides “Dynamic Phase Control” to implement fast, sensitive differential pairs.This Dynamic Phase control should be integrated with routing (interactive or automatic) of high speed differential pairs to accelerate correct-by-construction design completion.

Allegro PCB Design XL heads-up display for dynamic phase control accelerates creation of high-speed differential pairs

Speaking of tight tolerances on differential pairs, how do you account for phase skew inside the drivers and receivers for BGA packages? How do you account for delay through vias on a thick PCB?

Accounting for delay through a via is easy, but it should be integrated with the interactive etch editing system to alert you immediately if Z-axis delay through the vias is going to create a problem.

When it comes to accounting for delays on matched signals inside the BGAs, Allegro PCB Design XL suite allows users to manage it couple of ways. Users can import that delay into Constraint Manger and then implement the PCBs. Another way is to annotate such delays on the pins of BGAs when the BGA symbol is created and added to the library.

To learn more about these capabilities, watch this archived webinar – Predictable, Shorter Design Cycles for Dense, Complex PCBs.

Feel free to comment on this or contact me directly via email –

Hemant Shah




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