EMI Suppression Filters (EMC and Noise Suppression)Noise Suppression Measures for Wi-Fi 6 (2)

Contents

4Anticipated Noise Issues and Measures①

Noise Entry in the 5 GHz Band

Wi-Fi 6 is compatible with the 2.4 GHz band and 5 GHz band, but when noise (DC-DC converter switching noise, etc.) in the 0.1 GHz to 1 GHz range is applied to the front end of the 2.4 GHz band, third-order intermodulation distortion that interferes with the 5 GHz band occurs.
Communication disturbances occur if this is transmitted to the front end of the 5 GHz band through power lines, etc.
If using a base unit, communication with devices that use a 2.4 GHz band Wi-Fi may be the reason. For wireless units, simultaneous use with Bluetooth® may be the reason.

Examples of Interference to the 5 GHz Band Due to Third-order Intermodulation Distortion

Examples of Interference to the 5 GHz Band Due to Third-order Intermodulation Distortion

Measures Applying Noise Filters That Support the 5 GHz Band

A noise filter that supports the 5 GHz band is applied to prevent noise entry in the 5 GHz band. The BLF03VK is a noise filter that was designed for effective removal of noise in the 5 GHz band.
Inserting the BLF03VK series into the power line can prevent third-order intermodulation distortion from flowing into the front end of the 5 GHz band.

BLF03VK Series

BLF03VK Series Dimensions
BLF03VK Series Impedance-Frequency characteristics

BLF03VK Series Specification Chart

Murata
Part Number
Impedance@5GHz(ohm) Rated Current
(mA) @85℃
Rated Current
(mA) @125℃
DC Resistance
(ohm max.)
220 +/- 40% 800 500 0.155
60 +/- 40% 1200 780 0.065

Noise Filter Recommended by Murata

A compact (0.6 x 0.3 mm) noise filter that specializes in noise suppression in 5 GHz band which is one of the communication frequencies of Wi-Fi (wireless LAN).

This BLF03VK series is the first noise filter with specifications that guarantee impedance values for the 5 GHz band.

5Anticipated Noise Issues and Measures②

Noise That Interferes with Wi-Fi from High Speed Interfaces

Equipping high speed interfaces can also lead to reception sensitivity deterioration.
As Wi-Fi communication becomes faster, the speed of internal data transmission interfaces will also increase, and frequencies that will interfere with Wi-Fi signals will also be processed.
For this reason, PCI Express signals are radiated and the 2.4 GHz band Wi-Fi reception sensitivity deteriorates.
Also, due to the popularity of USB Type-C connectors, support for USB 3.1 has progressed, and due to the USB 3.1 having a signal frequency close to the 2.4 GHz band, there are examples that lead to Wi-Fi reception sensitivity deterioration.

Examples PCI Express Signals Affect Wi-Fi Sensitivity

Examples PCI Express Signals Affect Wi-Fi Sensitivity

Inserting a noise filter in the signal line,
one that does not affect the signal waveform must be used

A noise filter is to be inserted on the interface signal line to eliminate noise that interferes with Wi-Fi from high speed interfaces.
However, since these interfaces use high speed signals, you are required to select those that do not affect signal waveforms.
In principle, common mode choke coils/common mode noise filters (CMCC) do not affect differential signals, but since there are differential mode impedances in actual products to some extent, you are required to select applicable parts.

Examples of Radiation Noise from High Speed Interfaces

No CMCC

Examples of Radiation Noise from High Speed Interfaces No CMCC

Enables checking of radiation noise (red portion)

With CMCC

Examples of Radiation Noise from High Speed Interfaces With CMCC

Insert CMCCs after the TX (transmitter) coupling capacitor

Recommended Noise Filter

For 2.4 GHz

(PCI Express gen3, USB3.1 gen1, HDMI2.1 etc.)

For 5 GHz

(PCI Express gen3, USB3.1 gen2, HDMI2.1 etc.)

Feature

  • Greatly effective in target noise frequencies
  • Does not apply adverse effects on signal waveforms
  • Obtained recommendations from several IC makers

6Conclusion

The 1024QAM modulation method applied on Wi-Fi 6 is easily influenced by noise

Since Wi-Fi 6 is a dual band structure with 2.4 GHz and 5 GHz bands, along with the third-order intermodulation distortion that occurs in the 2.4 GHz band, this results in the deterioration of the reception sensitivity of the 5 GHz band

⇒Measures can be taken by inserting the BLF03VK series to the power line

Wi-Fi sensitivity decrease occurs if high speed interfaces are installed

⇒Measures can be taken by using common mode choke coils/common mode noise filters that support high speed signals on the high speed interface signal line

Noise Filter for Third-order Intermodulation Distortion Measures

BLF03VK Series
Stock Check Impedance (@5GHz) Rated current (@85℃) Rated current (@125℃) DC resistance (max)
220±40% 800 500 0.155
60±40% 1200 780 0.065

Noise Filter for High Speed Interface Noise Suppression Measures

For 2.4 GHz Band Noise Suppression Measures
Stock Check CM Impedance (@100MHz) Rated current DC resistance (@max) DC resistance (Rdc)
28 130 2.375 1.9±25%
35 120 2.875 2.3±25%
15 100 3.125 2.5±25%
For 5 GHz Band Noise Suppression Measures
Stock Check CM Impedance (@100MHz) Rated current DC resistance (@max) DC resistance (Rdc)
12 160 1.5 1.2±25%
12 150 2 1.6±25%
5 100 1.625 1.3±25%