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Designing for RF - Tips and Tricks from the PCB Design Pros
This document presents key considerations for designing radio frequency (RF) components, focusing on grounding, materials, and routing practices. It emphasizes the importance of health and safety, as well as the need for proper simulation and implementation to reduce costs and complexity. The document concludes with a reminder that grounding is critical in RF design.
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Designing for RF - Tips and Tricks from the PCB Design Pros
- 1. Orlen Bates Sr. ApplicationEngineer RF Designs the Wave of the Future 9/4/2018 1
- 2. Agenda • What areRF Waves • Design Considerations • Best Practices • Examples • Q&A 9/4/2018 2
- 3. What are RFWaves? Radio frequency (RF) refers to the rate of oscillation of electromagnetic radio waves in the range of 3 kHz to 300 GHz, as well as the alternating currents carrying the radio signals. This is the frequency band that is used for communications transmission and broadcasting. 9/4/2018 3
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- 5. Design Considerations 1. Health andSafety Requirements 2. Environment Conditions 3. Product Lifecycle Expectations 4. PCB Stack-up & Material Usage
- 6. Best Practices RF Ground •Proper grounding is KEY • Connect the ground pins of the RF components to the RF ground plane as short as possible • If the board includes multilayer ground planes, provide many ground vias wherever the signal trace makes a transition from one side of the plane to the other.
- 7. Best Practices RF Ground,RF Ground and say it again RF Ground Consider the use of an RF fence / cover
- 8. Best Practices Plating /Copper • Use gold plating for RF components created from etch • No copper inlands near the RF circuitry • No copper thieving near the RF circuitry • Ground both ends of copper pours, and stitch many vias wherever possible • Separate RF planes from all other planes
- 9. Best Practices SMT vs.Thru Hole • Use SMT parts for RF • If thru-hole is required backdrilling should be used with thru-hole components and vias. This will remove that unwanted antenna.
- 10. Best Practices Stackup /Materials • Multi-layer PCB is best • Always provide continuous grounds under traces • Consider material selection carefully. Standard FR4 may not meet your needs Source: Isola
- 11. Best Practices Vias • Useisolated vias for separate portions of a filter or matching network • Use least number of vias in RF routing, max number of vias in RF grounding
- 12. Best Practices Routing • Orientsensitive traces orthogonally • Use short traces between the crystal and RF device • Keep interconnect traces separated as much as possible • Keep trace lengths to a minimum
- 13. Best Practices Routing, PrintedCircuit/Selection • Adhere to proper corner routing • Use wire-wound inductors whenever possible and avoid using printed down circuit parts unless needed • Place inductors, coils and a planer isolated from each other
- 14. Best Practices Simulation • Simulationis strongly recommended if RF component is being printed / down as part of the board
- 15. Key Takeaways • Ground.Ground. Ground. • Carefully consider RF implementation as design choices will have a significant impact on cost and complexity • Understanding the effects RF circuitry has on your design is half the battle…oh and ground.
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- 17. 9/4/2018 Your PDNGives Your Board Life 17 Thank you for joining us today. Please contact us for more information on OrCAD products, training, and services. 800-813-7494 info@ema-eda.com www.ema-eda.com
Editor's Notes
- #2 My first RF design was with hand taping and an x-acto knife, trimming the bishop graphic tape ordering boards, re-trimming the tape and respinning over and over until we got it correct. I remember the EE saying “RF Design the Wave of the Future”. I believe the future is here, with Wi-Fi needed for just about everything we design.
- #4 The term microwave is a reference to a class of waves, referenced as a microwave range or spectrum of frequencies that the Wi-Fi signal operates. For Example, the Wi-Fi signal from your laptop is often transmitted at 2.4 GHz, a frequency found within the microwave range, or spectrum of 300 MHz to 300 GHz the same frequency as our microwave ovens. The wavelength of an alternating current depends on the frequency.
- #5 The distance between Wi-Fi waves is shorter than that of radio waves but longer than that of microwaves, giving Wi-Fi a unique transmission band that can’t be interrupted by other signals. Wi-Fi waves are about 3 to 5 inches from crest to crest show here in the Wavelength measurement. So, the main difference between radio waves and microwaves is its wavelength and frequency operation. The only difference is the wavelength of the propagation or radiation. Various portions of the electromagnetic spectrum are reserved for specific uses, like radio, short wave radio, television, garage door openers, etc. One example is my garage door opener, half way down my driveway I can open one of the three doors, so all three doors has a different frequency. But as months go by I have to move closer to the garage door to open it. So why is that? The electric field is getting weak, how do I fix that? New battery in the remote. The garage door company I went with has the frequency rotating so it not the same each time, keeping us safe.
- #6 Rf energy in medical treatments has been used for over 75 years. MRI uses RF waves to generate images of the human body. Cauterize of the blood vessels in surgery for year now.
- #7 Vias in the ground pads are the best, we call that via-in-pad. Vias in a signal pad is best if the need is to change layers.
- #8 Shielding is what it is all about.
- #9 Soldermask removed from the RF traces so by having no soldermask where the RF fields are, gives the best transmission and if your board is made by different fabs, you get the most repeatable transmission.
- #10 Stubs on the vias and thru hole padstacks are just as bad as the copper thieving or copper inlands we had just talked about. They become unwanted antennas.
- #11 FR4 might be cheaper material but to respect the wave and its requirements, FR4 can fail in some applications.
- #12 Via for shielding, is a number one requirement.
- #14 If inductors, planar, coils are created as copper parts grounding and shielding for isolation is a must.
- #15 Any serious RF designs should be simulated, we interface with IFF files and DXF files.
- #16 The real issues will start when your RF circuit needs to be added to the digital design. They do not get along grounding is your best defense in this battle.