The EMC compliance test is probably one of the most challenging tests, and there are countless ways to fail it. However, in most of the cases, the problem of many products seems to be the lack of proper EMC design techniques. Because of that, I’ve created a list of 7 tips which, if taken into consideration during the product’s design phase, will help you pass the EMC compliance assessment:
1. Pay attention to the RF noise on the cables and reduce it, if necessary.
If you don’t want this to be the reason for your failure, it’s essential to ensure that most, preferably all, of the unintentional noise on the external and internal cabling is removed. To do it, keep in mind the following design rules:
- Minimise the slew rate of the rising and falling edges of the signal on the cables. If the slew rate is high, then the signal will contain more energy at higher frequencies. To lower the slew rate, you can do two things: reduce the drive strength of the driver; pass the signals through a non-populated low-pass filter.
- Be careful when using power supplies and static I/O, and make sure they are clean and don’t produce any RF energy. You can keep the RF noise off cabling by either adding in-line ferrite beads or providing adequate power supply de-coupling at the connector.
2. Be careful with the application of electrostatic discharges on ground connectors.
The amplitude of the discharge pulse depends on your product standard but usually is 4kV or 8kV. In case of negligence, the outcome might be either device resetting or permanent degradation of device performance. To avoid having any issues, you can try to:
- Identify the ESD testing locations and levels
- Choose an appropriate transient suppressor
- Place the ESD protection as close as possible to the area where the discharge event is supposed to happen
- And, project the discharge path correctly.
3. When selecting a power adapter, make sure that the power adapter itself has passed the emissions class that your product needs to pass.
In other words, if your product is class B, don’t use a power adapter of class A. The emissions limits of class B are more stringent than those of class A.
4. While choosing an LVD display, keep in mind that this can have a significant impact on your product’s radiated emissions performance.
Not all LVD displays are the same, and some can have much worse radiated emissions performance than seemingly identical other models. Therefore, if you can, order LVD samples from different manufacturers and do an emissions test on each one.
5. Ensure the compliance of the auxiliary equipment.
To avoid any problems, always use auxiliary equipment of reputable manufacturers whose products you know are tested and compliant.
6. Critical to ensuring a first time EMC test pass is to select a transient device with correct, high enough, rating to deal with the applied disturbances.
If the device rating is too low and not high enough, then the product won’t be able to cope with the pulse applied. To ensure your product’s success during the EMC testing, try to find out what test levels the test lab is going to apply to your product.
7. Make sure that any sensitive analog/RF circuitry is protected with a well-grounded conductive shield.
By protecting any sensitive circuitry that your product’s design has, you can be quite sure that no measurement errors, outside of the general product specifications, will show up during the examination.