Unplug your hard drive, it's disturbing my Bluetooth!

Citations

Copper foil wrapping to shield interference is one of the most common measures in EMC rectification. The high conductivity of copper foil will reflect high-frequency radiation interference. For example, the camera or screen in the mobile phone often has a large area of ​​copper foil wrapping, as shown in the figure below (it has both shielding and heat dissipation functions), or there is a shielding cover on the motherboard, which can play a good shielding role.

During debugging, when there is a suspected interference source, we will try to wrap the interference source with copper foil to test whether it can reduce the interference.

This analysis comes from Intel's debugging summary. It is the RF interference of USB3.0 that affects the 2.4HGz Bluetooth wireless device. The copper foil shielding effect can be seen qualitatively and quantitatively.

Reply to the official account backend: USB shield You can get the full PDF original text.

environment

The figure below is a system working block diagram. USB3.0 peripherals are connected to the power supply through USB cables. USB cables will radiate interference, which will generate noise after being received by the PC's wireless devices.

The figure below shows the test environment. The near-field probe is placed near the USB device (hard disk). The interference collected by the near-field probe is pre-amplified and then analyzed by the spectrum analyzer.

The figure below is the result of the analysis. The gray curve is the situation when there is no USB device connected, and the red curve is the situation after the USB device is connected. It can be seen that the noise level is only about -118dB when there is no USB connection, and after the USB device is connected, the noise level near 2.4GHz reaches -100dB, which is an increase of about 20dB.

Next, the USB device hard disk is copper-clad. As shown in the figure below, there are 4 levels of copper-clad treatment, from case 1 to case 4, the wrapping is getting tighter and tighter. If the gap is large, interference will still leak out.

result

The figure below shows the measurement results after copper foil wrapping. Overall, it can be seen that the tighter the wrapping, the smaller the interference, which is reduced by nearly 12dB.

In order to further reduce interference, the connector is shielded. The figure below shows the result after shielding. The gray curve is when there is no USB device connected, and the noise level is the lowest. The red curve is the highest noise level after USB connection, and the green curve is the result after the connector and cable are shielded, and the interference is effectively suppressed.

Summarize

In summary, shielding has a good effect on suppressing high-frequency interference and is a very effective means for EMC rectification. Reply to the official account backend: USB shielding to obtain the full PDF original text . However, if it is low frequency, it is another way to play.

From Intel