What's Good About PCB PI Discontinuity Modeling? See For Yourself in SPB16.3!

The current Allegro PCB Power Integrity (PI) tool is fast, but not accurate enough in the high frequency band due to the effect of discontinuities. This feature uses a discontinuity model in the PI analysis. With discontinuity model integration, PI analysis is more accurate and allows you to control the target impedance more efficiently.

A plane pair can be simulated by an equivalent circuit of a grid of transmission lines. The low-frequency equivalent components of the planes can be derived from a quasistatic model. The S-parameters for discontinuities are extracted by MoM and integrated into an equivalent circuit of the plane pair.

Read on for more information …

Transmission Line Model of a Plane Pair

After the plane pair is divided into rectangular meshes, each mesh is modeled by four transmission lines. The following figure shows the star-type equivalent transmission line circuit for one mesh cell in the SPB16.2 release.

 
In the SPB 16.3 release of PCB PI, a ring-type equivalent transmission line circuit has been adopted to integrate the discontinuity model. The following figure gives the equivalent circuit for the internal mesh cell. The node positions have been changed and the center node in the previous release has been removed.

 
To connect with the discontinuity model represented by an S-parameter subcircuit, the equivalent circuit for the mesh cell at the plane/void edge is a little different with the internal mesh cell, as shown below.

 
 
The multiple transmission lines between the same two nodes are merged to improve the performance, as shown below.

 
 
Discontinuity Modeling

Two types of PDN discontinuities are modeled:
      
Split Plane Overlay

Plane Edge Overlay

Mesh on PCB SI Canvas

Since the new mesh algorithm has changed, the node locations are now at the intersection of the mesh lines. In previous releases, they were located inside each mesh cell.

SPB16.2

SPB16.3
    

 

Please share your experiences using this capability.

Jerry "GenPart" Grzenia