BoardSurfers: Training Insights: RF PCB Design Flow Using Allegro Editors

Allegro® RF PCB solution provides you with a unified design solution for complex mixed-signal projects. From schematic to layout and manufacturing, a total front-to-back design flow helps you streamline your entire RF design process. You lay RF design areas on your board using discrete functions for component creation and placement as well as routing. You can use the conventional back-to-front flow to backannotate RF component changes from the layout in the layout editor to the schematic in the schematic editor. Changes to parameter values, reference designators, and connectivity are all supported for backannotation. The layout-driven backannotation is an enhancement to the conventional back-to-front flow in the schematic editor. This enhancement lets you backannotate more changes made in the back-end RF portion of the design in a structural process.

In this blog, you will see how to create an RF schematic using the schematic editor and then how to create an RF layout for an existing schematic using the layout editor. So, let’s get started.

Creating an RF Schematic in Schematic Editor

Before you start placing the components in the schematic, you must make sure that you have included the rf_comp_lib library in your project setup. This is the schematic library that contains all the RF components.

Also, this library is fully documented in the Cadence Help system just in case you need any helping hand. Just browse through Allegro RF PCB Library Reference in the Allegro PCB Editor section in Cadence Help, and here you see all the documentation for RF components.

While placing the RF components into the schematic, you can use the property editor window to change the parameters according to the need of your schematic.

Now that you have included the required library and you have the support of the documentation for RF components, you can easily create an RF schematic by placing and connecting the RF components according to the need of your design.

To learn in detail about this flow, watch the Creating an RF Schematic using Allegro Design Entry HDL training byte on the Cadence Support portal. Click the training byte link now or visit Cadence Support and search for this training byte under Video Library.

Creating an RF Layout in Layout Editor

To create an RF layout, run the packager on the schematic that you have created to generate a netlist that you can load into the layout editor. To do this, choose File – Export Physical in the schematic editor. This command packages the logic design, produces a netlist, and loads it into the layout editor. This command also annotates the schematic with the packaging properties, such as reference designators.

To load the netlist into the layout editor, browse to the empty board file in the Input Board File section and specify the output board file in the Output Board File section. Enable the Create user-defined properties check box. This is an important option that ensures that all RF properties pass over into the layout editor when packaging the schematic. Click OK after applying all the desired settings.

After completing the packaging, exit the schematic editor and start the layout editor. Ensure to enable the Analog/RF option in the Product Choices dialog to access the RF-PCB menu in the layout editor.

You can do auto placement of the components in the layout editor using RF PCB commands. Choose RF-PCB – Autoplace to perform auto placement. This command allows you to work with a group of components that are grouped based upon the connectivity in the schematic that you have just loaded. To speed up the placement process for discrete components, turn on the Enable relative rotation for non RF check box.

Click Start to initiate the auto placement or select individual groups. The selected group attaches to the mouse pointer. Left-click the design canvas to place the attached group.

You can modify the placement by moving components or by changing their properties. In the following image, you see how to optimize the placement using RF commands:

To edit the RF component parameters in the layout, choose RF-PCB – Edit – Change. You can resize a selected RF component, edit its parameters, and pin-to-net assignments using the GUI as shown in the following image:

You can also use the RF-PCB – Add Connect command to route RF traces with different bend types directly within the layout editor. Each trace and bend is considered an RF component. As you route a trace, you can insert other RF components conveniently.

Once through with RF layout design, you can also backannotate the changes to the schematic. Open the schematic editor and choose File – Import Physical. In the Import Physical dialog, select RF PCB Options and enable RF PCB Import.

Click OK in the Import Physical dialog to bring the changes in from the RF layout through the packager and update the schematic. This completes the backannotation process.

To learn in detail about this flow, watch the Creating an RF Layout using Allegro PCB Editor training byte on the Cadence Support portal. Click the training byte link now or visit Cadence Support and search for this training byte under Video Library.

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