Variable sweep at top-level hierarchy of circuit schematics in AWR

It is a common issue encountered in AWR that any variations made at subcircuit level do not show its effect at the top level in hierarchy. Here we discusses the solution to this issue by presenting a case study. Figure 1 shows the design of Power Amplifier, which has a hierarchy and consists of Class AB amplifier and Class C amplifier. PA is at the top level in the hierarchy and the Class AB amplifier and Class C amplifier are subcircuits in the schematic.

                                                                             Figure 1: PA at top-level schematic

If  the Gate bias V1 (Gate voltage) of the Class C amplifier is swept from -5V to -2.5V, the change in the Output Power vs. Input Power plot of the Class C amplifier (subcircuit level) is observed but not at the top-level schematic, as shown in Figure 2.

                         Figure 2: Variations observed in Class C amplifier (subcircuit level)

Figure 3 shows that this issue can be resolved by performing three steps at the top-level schematic. These steps are: (a) add sweep variable box, (b) declare V1 as "variable" by right-clicking and selecting Properties, and (c) add the V1 variable to the Class C amplifier.

                                              Figure 3: Changes to be made at top-level schematic

Figure 4 shows that this issue can be resolved by performing two steps at the subcircuit level (lower in the hierarchy). These steps are: (a) disable sweep variable box and (b) declare V1<<-3 as "parameter" by right-clicking and selecting properties.

                                            Figure 4: Changes to be made at lower-level schematic in hierarchy

After these changes are made at the top-level schematic and subcircuit level (lower in the hierarchy), the variation in the results can be observed at the top-level schematic, as shown in the Figure 5.

                               Figure 5: Variations observed in PA (top level in hierarchy)

Now that you have read the article, just think about these:

• What is hierarchy in circuit schematics? Why do we need it?

• What are advantages of having hierarchy?

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 Team SimTech