Design Considerations and Simulation for RF Components

Events
1

Watch our webinar with EMA Design Automation on design considerations and simulation of RF components!

Webinar agenda:

  • Typical component placement challenges in radio-frequency circuits
  • Active RF component considerations
    • o Selecting the right RF amplifier
    • o Ensuring frequency stability with oscillators
    • o Using mixers for frequency conversion
  • Passive RF component considerations
  • Effects of component parasitics on circuit performance
  • Techniques to achieve uniform impedance in RF layouts
  • Selecting high-frequency connectors
  • Managing heat from power amplifiers: Thermal vias and heatsinks

Missed the webinar? Click the link below to watch the recording.

2

See the Q&A:

Question Answer
When I transition to and from stripline to microstrip, I put gnd vias close to the transition. How important is it to stitch the ground planes together at other locations? Why? As you pointed out, the importance of stitching ground planes together depends largely on the frequency of operation.

The farther away the stitching vias are from the transition, the less impact they have on the circuit’s performance. A useful way to think about this is in terms of wavelength. Ground vias are most effective when they are placed within approximately one-sixth of the wavelength of the operating frequency.

So, if you’re working in the gigahertz range, where the wavelength is about 6 inches per nanosecond, ground stitching within roughly 1 inch of the transition would have the most effect. Beyond that distance, the impact on signal integrity and return current continuity diminishes significantly.
Have you seen a difference in RF performance using different types of flux? We don’t perform functional testing, so I can’t comment directly on performance differences between flux types. However, many of our customers prefer to use no-clean flux and then clean it afterward using solutions such as Kyzen in our in-line washing system.
Do you recommend any surface finishes above 20GHz? For frequencies above 20 GHz, surface finishes such as Immersion Silver, ENIG/ENEPIG, or Hard Gold are recommended. These finishes offer excellent signal integrity and surface smoothness suitable for high-frequency applications.
What’s the difference between using Cadence AWR office or something like ADS, SystemVue, or HFSS for microwave analysis? We can match the capabilities of tools like ADS, SystemVue, or HFSS within Cadence AWR Microwave Office itself or by linking it with other Cadence simulation tools such as Clarity and Axiom.

In terms of differences, many users find AWR Microwave Office easier to use for design work. Additionally, when dealing with very complex structures, AWR often provides faster simulation speeds compared to ADS.

That’s why we encourage customers to perform evaluations to experience the differences firsthand in terms of ease of use and simulation performance.
I’ve simulated and designed numerous RF-Front Ends, but have never had clarity on how to begin thermal simulations from a PCB layout, besides prayer. When it comes to starting thermal simulations from a PCB layout, Cadence provides several integrated approaches using the same simulation environment.

For example, if you’re performing signal integrity or RF analysis, you might use tools like Sigrity (which uses Clarity as the 3D simulation engine) or AWR for RF design. Both can feed into Celsius, Cadence’s thermal simulation tool, for thermal analysis.

Essentially, whether you’re approaching it from a full-board perspective or focusing on heat generated by specific RF circuits, the process converges within the same simulation framework—linking your electrical and thermal analyses for accurate, layout-based thermal modeling.
I’m using Altium Designer. Do you think their solver is accurate, like configuring the impedances of traces width and spaces for stripline, microstrip for single-ended and differential pair? The simple answer is that Altium’s impedance calculator works well for basic calculations but is not a full electromagnetic simulator. These calculators are based on simplified forms of Maxwell’s equations and provide good approximations for most standard cases.

However, Sierra Circuits’ impedance calculator offers higher accuracy and can handle more complex trace geometries and refined cross-sectional shapes.
Sorry, I was late due to an internet connection issue. How would this tool help if I am working with frequency only up to 2.2GHz? Is it worth getting it? Yes, 2.2 GHz definitely falls within the RF design range.

At that frequency, you can still benefit from using RF design tools, as they provide accurate closed-form models for traces, components, and interconnects. For lower frequencies like 2.2 GHz, these models are usually sufficient for reliable simulations.

It’s especially valuable if you’re working on RF circuits such as filters, bandpass filters, or power amplifiers, where precise modeling and tuning can significantly improve performance.
When dealing with active components, such as amplifiers, how does AWR calculate the effects of DC? AWR includes a DC calculation mode that sets the operating points for active components. These operating points can then be back-annotated to the schematic.

All AC simulations are performed based on these established DC operating points, meaning the tool fully accounts for DC effects during analysis.