Creating Hierarchical Designs

You can use any network as a subnetwork within another network to create a hierarchical design. There are two ways to create a subnetwork:

• Use the Create Hierarchy command (Edit > Component > Create Hierarchy) and specify a portion of an existing design to be copied to its own design file for use as a subnetwork.
• Create a new design consisting of a network you want to use as a subnetwork.

  Hint To view design hierarchy in the current project, choose View > Design Hierarchies from the Main window.

To access a design in one project for use as a subnetwork in a design in another project, create a hierarchical project (File > Include/Remove, in the Main window). For details, refer to Creating a Hierarchical Project under the section on Managing Projects and Designs.

Note The Update Component Definitions command (Edit > Component) enables you to explicitly update component definitions (that you have changed) throughout the current design. If you select the Update Component Definitions in Subnetwork option, the design hierarchy will be traversed (downward) and components will be updated throughout the hierarchy.)

Creating a Subnetwork from an Existing Design

The Create Hierarchy command copies the selected portion of your design to another file, saves that new file, deletes the selected items in the original file and replaces them with a default symbol representing the deleted items.

Hint You can create a custom symbol to use in place of the default symbol. For details on symbols, refer to Working with Symbols.

The example used to illustrate this command is based on a simple, 3-resistor attenuator that is part of a larger design. In this example, the main design is named main_design and the file created using the Create Hierarchy command (containing the 3-resistor attenuator) is named my_atten.

To create a subnetwork from an existing design:

1. Select the items you want to include in the subnetwork (represented here inside the box drawn with a dashed line).
   
2. Choose Edit > Component > Create Hierarchy and a dialog box appears.
3. Provide a name for the new file, in this example, my_atten, and click OK (The name you supply is the filename for the subnetwork as well as part of the annotation for the symbol when you place it in a design-however, no annotation is displayed in this example.)
   The selected items disappear from your original design and are replaced by a default symbol (in this example, a 2-port symbol). Wires are redrawn to reconnect the remainder of the design to the symbol.
4. Save the file. The design used in this example appears as shown next.
   

If you want to use this network as a parametric subnetwork in a hierarchical design, you must open this newly created file (my_atten.dsn) and define the parameters that you want to be passed from the subnetwork to the network.

To define parameters for an existing subnetwork:

1. Open the file containing the subnetwork design.
2. Choose File > Design Parameters and a dialog box appears.
3. Supply a parameter name (not to exceed 8 characters), and select the appropriate characteristics for that parameter.
4. When you are through assigning characteristics to that parameter, click Add and the newly defined parameter is added to the Parameters list box.
5. Continue in this manner until you have assigned all the desired parameters for this network and click OK.
   For a more detailed discussion on defining parameters, refer to the section titled, Defining Parameters.

Creating a Parametric Subnetwork

Any network can serve as a parametric subnetwork. A parametric subnetwork is any network for which you define the control parameters that pass through to the network into which you place the subnetwork. Once you have defined the parameters, your subnetwork can serve as a template enabling you to assign parameter values each time you place it in a design. You can construct whole libraries of re-usable subnetworks in this manner.
The details of this process are presented using a simple design consisting of a capacitor and a resistor in series and two ports. This subnetwork is called series_r_c and is represented by the default 2-port symbol.

Creating the Subnetwork

You can create the subnetwork first, or define parameters and then create the subnetwork. In this example, the subnetwork is created first.

To create the subnetwork:

1. Choose File > New Design in the Schematic window and assign a name, in this example, series_r_c. This name becomes part of the annotation for the symbol representing the subnetwork when you place it within another design.
2. Select Analog/RF Network as the Type of Network and click OK.
3. Click the Library button and select a category, in this example, Lumped Components.
4. Select a component, in this example, C (Capacitor).
5. Place the capacitor in the Schematic window. Note the component parameter C is set equal to the default value of 1.0 pF. Click the End Command button.
   
6. Click the capacitance value to invoke the on-screen editor and use the Back Space key to erase the 1.0 pF.
7. Type C and press Return. The parameter now reads C=C (This C parameter will be defined in the Design Parameters dialog box in a later step and serves as a variable here.) The parameter C (capacitance) of this component will now pass through to the network in which it is placed.
8. Place the next element, in this example, R (Resistor), accepting the default values. Connect it to pin 2 of the capacitor symbol.
9. Add ports and click the End Command button. The subnetwork should resemble the following illustration.
   

Defining Design Characteristics

Design characteristics include elements such as the name of the symbol used to represent the subnetwork and a library from which the subnetwork can be accessed. In some cases you may find the default design characteristics acceptable (default symbol and default current project as the library, for example). If this is the case, proceed to the next section, Defining Parameters.

To alter the default characteristics:

1. Choose File > Design Parameters and a dialog box appears. In the General tab, the current design name is reflected in the Name field at the top of the dialog box.
2. The Description field also displays the current design name by default. You can change this to a more helpful label defining the purpose of the network design. The label you provide here will be displayed, together with the design name, as a component to place from the designated library (Library Name field).
   Optionally, add a description, in this example, cap and res.
   
3. The Component Instance Name default is X. The text in this field is used as a prefix in building a unique name (ID) for every item. This prefix becomes part of the annotation displayed with the symbol representing the parametric subnetwork when you place it in a design.
   Optionally, assign a unique name, in this example, para_sub.
   
4. Notice that the Symbol Name field reads SYM_2Port. This is the default symbol for a 2-port design. In this example, we are using the default symbol, but you can select one of the other symbols from the drop-down list, or click More Symbols to select one by clicking an icon from the appropriate category. For more information, refer to Working with Symbols.
5. In the Library Name field, specify the name of the library in which you want the subnetwork stored. This library name is the name that appears in the Component Library enabling you to select the subnetwork and place it in a design. There are several ways to specify a library name:
   • Accept the default Library Name – an asterisk ( * ). This means the design will be available in the Component Library through the current project
   • Type any name to create a new library
   • Enter the name of any of the supplied libraries
   • Select the name of any library you created previously
     Create a new library name, in this example, my_subnetworks.
     
6. Turn on or off the following options, as required by your design.
   
   • Allow Only One Instance - Specifies whether or not the subnetwork can be placed more than once in a design. The default is off, meaning the subnetwork can appear more than once in a design. Change to on if you want to restrict placement of the subnetwork to once per design (seldom done).
   • Include in BOM - Specifies whether or not the details of this design are included when a Bill Of Materials (BOM) is generated. Without this option, only the top level design information is included in the BOM.
   • Layout Object - Analog/RF designs only. Defines the design as an object. Layout objects have no parameters and are used to assign artwork to new elements or designs with no default artwork. For details, refer to the Layout Library documentation.
   • Simulate from Layout (SimLay) - Analog/RF designs only. The netlist required for simulation is generated from either the Schematic or the Layout. Select this option to generate the netlist from the Layout. The SimLay portion of this label will appear in the Status panel of the Schematic and Layout windows if you select this option; the default is to simulate from the Schematic, and the Status panel reflects SimSchem.
7. Layout only - select the appropriate Simulation method:
   
   • Select Subnetwork, to use a schematic symbol you have created
   • Select Built-in Component, to use a supplied simulator item.
     • Simulate As - Select a component name from the drop-down list, or type the name of any component.
     • Copy Component's Parameters - Select this option to copy the parameters of the selected component to use as a starting point.
   • Select Not Simulated, to create layout-or schematic-only non-simulated items
8. Analog/RF layout designs only - select the appropriate artwork Type.
   
9. Click Save AEL file to save the information defined so far (This is done automatically when you save the design file.)
   

Defining Parameters

When you define parameters for a network, the network serves as a template, enabling you to assign new parameter values each time you use the network. This is useful when a portion of the network is used several times in a design with certain element value differences, or in constructing libraries of reusable networks.
Parameters of the network are generally referenced as variables by the elements of the network. You can define the parameters before or after creating these variable references.
Each parameter has characteristics that determine how it is handled when the network is reused. These include the name and label displayed in the Item Parameters dialog box, the unit of the parameter, the type of value assigned to the parameter, the default value, and certain control attributes.

To define the parameters that should be passed to the upper-level network:

1. Click the Parameters tab.
2. Optionally (Analog/RF designs only), you can click Copy Parameters From as a shortcut for defining parameters, if one of the supplied components has a number of parameters in common. You can then cut any unwanted parameters, as well as modify the characteristics of the remaining parameters.
3. The Parameter Name field contains the parameter name that will be referenced in the subnetwork schematic. Parameter names become part of the annotation of the symbol representing the parametric subnetwork when you place it in a design.
   Supply a Parameter Name (not to exceed 8 characters), in this example, C.
   
4. Select a Value Type from the drop-down list, in this example, Real.
   
5. Specify a Default Value, in this example, 5. This value can be changed at the time you place the subnetwork.
   

   Hint If you do not specify a scale factor along with the default value, the current setting in the Preferences dialog box is used (Options > Preferences > Unit/Scale), based on the Parameter Type.

6. Optionally, select a Parameter Type for this parameter, in this example, Capacitance. This can be a dimensional unit or a string for the parameter, if one is needed (String is used for assigning SMT artwork in layout.)
   
7. Optionally, supply a Parameter Description.
8. Select any of all of the following options, as they apply. Note that some options are desensitized depending on the current Value Type.
   
   • Display parameter on schematic - Select this option to display, on the schematic, the parameter being defined.
   • Optimizable - Select this option to allow this parameter to be optimized.
   • Allow Statistical Distribution - Select this option to allow post-production tuning for this parameter during yield analysis.
   • Not edited - Select this option to prevent this parameter from appearing in the Component Parameters dialog box for editing and always use the default value assigned here instead.
   • Not netlisted - Select this option to prevent a parameter from being considered in simulation, but still be recognized for artwork generation.
9. Click Add to add the newly defined parameter to the Select Parameter list box. The parameter C is added to the Parameters list box.
   
   • Use Add to add a new parameter to the list
   • Use Cut to delete parameters
   • Use Cut and Paste buttons to rearrange the order of the parameters.

     Hint You can position these user-defined parameters to display somewhere other than the default location of supplied parameters. For details refer to Positioning Parameters for Your Symbol under the section on Working with Symbols.

10. Optionally (Analog/RF designs only), you can click Add Multiplicity Factor (_M) to enable simulation of this subnetwork as though it were x number of these subnetworks - connected in parallel - where x is the value you assign to the parameter _M.
11. Click OK to dismiss the dialog box and choose File > Save Design.

Placing the Subnetwork in a Design

Now you can place the subnetwork you just created into another network. The parameter you assigned (capacitance in this example) will pass through to the network.

To place a subnetwork:

1. Open the file containing the network in which you want to place the subnetwork (in this example, main_network - not shown).
2. Click the Library button (or choose Insert > Component > Component Library).
3. In the Component Library window, locate and select the library containing the design, in this example, my_subnetworks.
4. Select the subnetwork, in this example, series_r_c, and place it in the drawing area. Click End Command.
   Notice that C = 5 F. This 5 is the value from the Default Value field (for the parameter C) in the Design Definition dialog box. Because we did not specify a scale factor, the default F (Farads), from the Preferences dialog box is used (Options > Preference > Unit/Scale).
5. Using the on-screen editor, change the default capacitance value to the desired value for the current design, in this example, 2. Press Return.
   

Modifying a Subnetwork Design

If you make changes to a subnetwork that affect the component definition (any changes in the Design Parameters dialog box-information that is saved in the .ael file), that serves as a subnetwork in a higher-level design, you need to explicitly update the higher-level design to recognize those changes.

To update a higher-level design that contains a modified subnetwork:

1. From the higher-level design, choose Edit > Component > Update Component Definitions.
2. To traverse the hierarchy (downward) in search of any subnetwork designs whose component definitions have been changed, select the option Update Component Definitions in Subnetwork and click OK. Changes to any subnetwork designs are now reflected in the instance(s) in the main design.

Viewing the Network Represented by a Symbol

Whenever your design contains a symbol that represents a network, you can view the actual network being represented by the symbol by using the Push Into Hierarchy command.

To push into and then pop out of an item:

1. Select the item.
2. Choose View > Push Into Hierarchy. The network represented by the symbol is displayed.
   The Pop Out of Hierarchy command is the reverse of pushing, and only works if a design has been pushed into.
3. When you are through viewing the network, choose Pop Out of Hierarchy and you are brought back to the item (or design containing the item).

Editing a Hierarchical Design

In the Layout window, you can edit the actual artwork represented by a component without pushing down into the hierarchy. This feature is particularly helpful is some cases such as when you need to position items in the subnetwork to align with items in the main design. For details on pushing into a hierarchical design to edit it, refer to Pushing Into or Popping Out of Hierarchy under the section on Creating a Layout.

Use the following steps to edit a hierarchical design without pushing into the hierarchy.

1. Select the component representing the design.
2. Choose Edit > Edit In Place > Push Into to enter the edit mode for the network represented by the symbol.
3. Use the editing commands and tools to make the desired modifications. The few commands that are disabled when you edit a hierarchical design are as follows. The Schematic window excludes the same commands as the Layout window. Schematic window commands that don't have an equivalent command in the Layout window are not disabled.

   Main Window > File Menu	ALL COMMANDS DISABLED. EXCEPT: New Design, Open Design, and Copy Design
   Main Window > Tools Menu	Playback Macro
   Layout Window > File Menu	Close Design, Revert to Saved Design, Save Design As, Delete Design, Import, Export, Exit Advanced Design System
   Layout Window > Edit Menu	Component > Create Hierarchy
   Layout Window > Tools Menu	DRC: Width Spacing, DRC: Custom Rules
   Layout Window > Schematic Menu	All commands in menu

Edit in Place Hints/Tips

• You cannot use Push Into after you use Edit in Place, but you can use Edit in Place after you use Push Into.
• Edit in Place will not edit AEL artwork macros.
• Edit in Place will not work if Layout Units/Precision is different from the top level.
• Parametric subnetworks use default values defined in Design Parameters.
• You can snap to pin of ports but not to edges/vertices using Edit in Place.
• Edit > Edit In Place > Push Into will not work if the design is open in multiple windows or if it is being Edited in Place in another window.