Time: Mar, 2016
Talker: Michael Ossmann
Michael is a well-known RF engineer and educator, famous for his popular HackerRF One SDR kit. He shares his insights of designing practical RF circuits that don’t require a PhD to understand. The goal is to make it easy for people to design RF (black magic) circuits with a few very simple guidelines.
The typical 4-layer PCB stack-up RF layer -> ground plane -> power plane -> signal layer works well for most RF circuits.
Even though 2-layer design seems sufficient sometimes, it is just easier to do 4-layer design which doesn’t cost much more (from PCB house such as OSH Park) but is less error-prone.
Don’t break ground plane and power plane for signal routing. Use more layers (e.g., 6-layer stack) instead.
Nowadays various integrated RF components with quality metrics are readily available through vendors and distributors. Examples are amplifiers, filters (Michael likes SAW filters a lot), switches, transceivers (something like nRF24L01), impedance transformers (e.g., balun), connectors, etc.
Michael’s favorite filter design tool is Digikey’s parameter search page :)
Those RF ICs reduce the learning curve and complexity of building application circuits, and make the design more robust. Also, they often save board area.
Therefore, use those monolithic RF ICs as often as possible.
50-Ohm design is almost the norm, so make all RF interfaces 50-Ohm compatibile.
This involves impedance calculating tools to calculate the microstrip width, but those tools are easy to find on the Internet.
Pay attention to the PCB dielectric and stack spacing when changing PCB fab house. Those may have an impact on the impedance.
For components that don’t have 50 Ohm interface (such as antenna pinouts on a transceiver IC), use the reference design from the component manufacturer. Do the impedance matching as close to the component as possible.
Sometimes, it is even better: you can find a RF IC to match the impedance instead of using standalone inductors and capacitors. For example, Michael is able to find a balun IC to match the antenna interface for nRF24L01+ transceiver.
Michael demonstrates 3 examples following the above 5 rules. He uses RF ICs as many as possible. Watch the video above.
A: Most components including transceivers are pretty low power those days. But watch out for amplifiers which can draw lots of power. When using amplifiers, be aware of its linearities (1dB power compression point, 3rd order intercept point).
A: If the devices are sellable, FCC certification (equipment authorization to be specific) is a must. However, if the devices are test equipments, FCC certification can be exempted. Be sure to follow manufacturer’s rules in design to pass FCC certification.
A: For PCB antenna and external antenna, it is low cost (PCB) VS performance (external), and low cost (PCB) VS flexibility (external). In terms of PCB antenna and chip antenna, the latter gives better performance per board area (more compact).