Choosing Your RF Design Environment Flow

You can’t build a house without blueprints. So why do so many RF design flows try to build a board without a schematic? Most often, this crude process comes about due to lack of availability of RF design tools. But the wireless industry is the new cool kid on the block. As a result, electronic design automation (EDA) software vendors are scrambling to disencumber the rigid printed circuit board (PCB) world of tailored processes and streamlined user flows. RF engineers demand freedom from constraints, so EDA vendors are peeling back the layers of traditional PCB design and opening up some truly excellent solutions. But with these solutions, RF engineers are challenged to rethink their request for primitive simplicity and consider a higher-level process.

Traditional DXF-Driven RF Design Flow

To successfully examine the RF design challenge, it is important to first examine a traditional RF design flow. The term “traditional” is meant to convey that the flow is a common solution for many companies on the cutting edge that had no software tools available to help them. It is fair to say that many of these design flows were established many years ago, before software tools gained strength in the RF specialty.

This traditional RF design process is most easily identified in its use of DXF file transfer to bridge the RF and PCB design gap (see Figure 1). But there are very real problems with using primitive shapes in an advanced PCB design software package. Designers often have to “fake out” the software system by copying the primitive objects into component geometries, or by trying to manipulate the shapes as area fill objects.

In addition to these headaches, the primitive shapes can’t be modified very easily. Even if they are modified, Design Rule Checks (DRCs) can’t be fully exercised, introducing instability into the potential success of a design. In short, designers are left trying to use software methods that were never intended for RF design.

While many RF design companies have figured their way through these issues, there is one glaring problem with this design process: there is no schematic. This means that there is next to no control over the connectivity, and the presence of a schematic for the PCB portion of a mixed RF-digital-analog design becomes almost useless since synchronization of the schematic and layout can’t be accomplished without more dangerous workarounds. Some EDA vendors offer reverse engineering solutions to help these issues, but even then, the layout-driven design process can be messy and time-consuming. In the end, designs are difficult to reuse and only partially archived.

The positive response to all these negatives is that the EDA software systems are finally offering an unobstructed path for RF and mixed RF-digital-analog designs. The future of RF design will undoubtedly be reached using these new methods.

Integrated RF Design Flow

As RF designs gained a larger share of the electronics industry, RF engineers and EDA software vendors teamed up to work out exactly what the design process should be. EDA vendors have taken on more of a consulting role, where the needs of the RF community are heard and then steps are taken to try to ease their pain points in the design process. The results are not the same with every vendor, but most are gravitating toward a fully integrated solution with bidirectional data transfer between the RF simulation applications and the schematic and layout tools (see Figure 2).

While this new process is not as simple as the traditional DXF data transfer method, it offers many more advantages. The simulation-to-design cycle is now shortened into direct bidirectional data exchange with the schematic. This means that the RF circuit can be designed and simulated at any time during the PCB design and layout process, and changes are transferred much more quickly. In addition to shortening the design cycle, the schematic has finally entered the picture. Just as building a house requires blueprints, the RF and mixed-signal circuits are now complete “blueprints” that can be reused in new designs, used for future design revisions, and properly documented and archived.