Introduction
As an EMC consultant, I understand the importance of maximizing emission from your product. While many designers are already familiar with these techniques, it's always helpful to have a refresher. In this article, I will share the ten best ways to maximize emission from your product, allowing you to become more proficient in the EMC business.
1. Start with the clock
The clock is a crucial element in maximizing emission. Choose the highest frequency clock with the fastest rise time possible. Clock frequencies above 50 MHz and rise times less than one nanosecond are particularly desirable. Additionally, ensure that the clock routing is optimized by making the trace as long as possible and keeping it far away from ground planes and power planes.
2. Utilize slots in ground and power planes
By incorporating slots in your ground and power planes, you can reduce the weight of your PCBs while increasing the impedance of the ground plane. This increased ground impedance will elevate the ground voltage that excites the cables connected to the board, thereby increasing their radiation.
3. Route high frequency traces across isolated ground planes
If you have isolated ground planes, it's crucial to route high frequency clock traces or other high frequency signals across the slot between the planes. This forces the ground return currents to flow in large loops, increasing the impedance and maximizing emission.
4. Implement decoupling capacitors
To provide high frequency decoupling for digital logic ICs, place a single 0.1 uF capacitor (or a 0.01 uF capacitor if necessary) near the IC. This tried-and-true decoupling method has been effective for over forty years, ensuring proper functionality and emission control.
5. Avoid common-mode filters on unshielded I/O cables
Unshielded I/O cables should not have any common-mode filters or ferrite chokes. However, if you do use filters, ensure that the PCB layout maximizes the parasitics to optimize their effectiveness in controlling emission.
6. Optimize shielded cables
If using shielded cables for I/O signals, terminate the cable shield using a long pigtail. A three to four-inch pigtail is sufficient, but a six to eight-inch pigtail can be even more effective. Alternatively, consider not terminating the cable shield at all to reduce manufacturing costs.
7. Connect logic ground to the chassis
To maximize cable radiation, it's important to connect the logic ground to the chassis. This can be achieved by connecting the edge of the PCB farthest from the I/O cables to the chassis, ensuring a significant ground voltage drop that excites the cables and enhances radiation.
8. Optimize metal enclosures
If your product is housed in a metal enclosure, there are several steps you can take to maximize radiation. Ensure that all seams are covered with a nonconductive paint or, if using a conductive finish, prevent electrical contact between the surfaces. Increase the number and length of seams, and consider incorporating large cooling holes.
9. Consider AC power line filter placement
If you use an AC power line filter, mount it away from where the AC power line enters the enclosure. Run the power cord via a circuitous route to the filter inside the enclosure and use a long, heavy gauge wire for the ground connection. Avoid direct connection of the filter's metal case to the chassis.
10. Additional design considerations
There are many other techniques you can incorporate into the design process to maximize emission. However, the ten listed above are an excellent starting point, capable of increasing the emission from your product by at least 20 to 30 dB.
While these techniques are valuable, it's important to note that if you wish to sell your product, you may need to address regulatory compliance EMC tests. Consider seeking the help of EMC consulting services to ensure your product meets the necessary standards.
By implementing these strategies, you can significantly enhance the emission from your product, ensuring it performs optimally in the market.
Remember that successful product design involves careful consideration of all aspects, including emission control. Happy designing!