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Design Notes

Double Stub-Extraction Through Hierarchy

This is a simple example demonstrating extraction through hierarchy concepts.   The concepts will be explained by building a double stub network using a single stub design twice through hierarchy.    

Overview

In the first release of the extraction flow in the AWRDE, you were required to have an EXTRACT block at the hierarchy level where you were performing the simulation.   The extraction process would then extract any element configured to extract from that level and any level below.  The extraction flow has been enhanced to allow EXTRACT blocks at any level of hierarchy. How this affects the top level extraction and simulation are controlled by a new Hierarchy parameter on the EXTRACT block.  

The basic building block for this example is a simple single stub using simple microstrip models.   The end of the stub is INTENTIONALLY left open (typically we would use an MOPEN model) to show an obvious simulation difference between a schematic simulation and an EM simulation. 

This example will walk you through various ways you can use extraction and help you understand what the Hierarchy parameter does.   For each case, there are additional schematics or EM structures and graphs to show you exactly what is being simulated during the extraction process. 

Extraction Setup

The three microstrip models in the “single_stub” schematic are set to extract using the group name of EM_Extract.   You can verify this by double clicking on any of these models and clicking on the Model Options tab.   There are EXTRACT blocks (that are disabled to start) in both schematics that configure the EM_Extract  group to simulate with AXIEM.  The STACKUP element in the Global Definitions specifies the physical properties (dielectric layers, metal properties, etc) for the generated EM structures.

Step 1 - No Extraction

This is the starting point.   The “single_stub” schematic is  the basic single stub network.   The “double_stub” schematic uses two of the “single_stub subcircuits.  See the “Insertion_Loss” graph to see both structures have a resonance at about 11 GHz.  

Step 2 - Extraction at Lower Level Only

Enable the EXTRACT block in the single_stub schematic (select the EXTRACT block, right mouse click, and select Toggle Enable) and simulate.   Notice a new EM structure named “1stub” was generated and  the change on the “Insertion_Loss” graph.   Also, notice that the Hierarchy parameter on the EXTRACT block is set to Off.  

The elements used when simulating the “single_stub” schematic are extracted using AXIEM and the results are used in this schematic.   To prove this, please see the “Compare_1” graph that shows the simulations results from the “single_stub schematic and the “Reference_single_stub” EM structure.   These results are identical.   

The “double_stub” schematic results do not include any results from EM simulation.   Said another way, the extracted results from the “single_stub schematic do not apply for the “double_stub” simulation.   To prove this, please see the “Compare_2” graph that shows the simulation results from the “double_stub” schematic and the “Reference_No_EM” schematic.   These results are identical.    This is the correct result  because the Hierarchy parameter on the EXTRACT block in the “single_stub” schematic is set to Off.   

Step 3 -Lower Level Extraction used at Top Level

Change the Hierarchy parameter on the EXTRACT block in the “single_stub” schematic to On and simulate.   Notice the change on the” Insertion_Loss” graph. 

In this situation, nothing has changed for the “single_stub” schematic simulation.  You can verify this from the “Compare_1” graph. 

The extraction results from the “single_stub” schematic are now used for the “double_stub” schematic.  See the “Compare_2” graphs to see that the “double_stub” results no longer match the results with no EM.  See the” Compare_3” graph which shows the results from the “double_stub” schematic are equivalent to cascading two instances of an EM result together.   The “Reference_two_single_stubs” schematic uses two subcircuits of the “Reference_single_stub” EM structure. 

Step 4 -Lower Level Skipped at Top Level

Enable the EXTRACT block in the “double_stub” schematic and simulate.   Notice in this case there is no change in any answers.   This is because all elements that could extract are being extracted in the “single_stub” schematic and so there is nothing left to extract in the “double_stub” schematic.  

Step 5-Lower Level Extracted at Top Level

Change the Hierarchy parameter on the EXTRACT block in the “single_stub” schematic to Off and simulate.   Notice an EM structure named 2stub was generated and the change on the “Insertion_Loss” graph.  

In this situation, separate EM structures are generated for each level of hierarchy.   You can verify this again with the “Compare_1” graph for the “single_stub schematic and the “Compare_4” graph for the “double_stub” schematic, which compares against the “Reference_double_stub” EM structure.  These results are identical.  

Discussion

By setting the Hierarchy parameter to Off, you will have the identical behavior to the previous implementation of extraction in hierarchy, where the EXTRACT block at the hierarchical level you are simulating is the only one that will control extraction at this level.  

A common situation to set the Hierarchy parameter to On, is when you want to EM some section of your design and have the EM results used anytime this schematic is used in hierarchy.   This would be equivalent to creating an EM structure and then using the EM structure as a subcircuit in your design.   The only difference is now that the schematic layout can be used to generate the layout for your EM simulation.   

Schematic - double_stub

Schematic - single_stub

Schematic Layout - double_stub

Graph - Insertion_Loss