EMI Suppression Filters (EMC and Noise Suppression)Noise Suppression for USB4 (4)

Contents

17Signal Waveform Check: Eye Pattern Measurement Procedure

Because a common mode choke coil is used as a noise suppression measure on the signal line, its effect on signal quality was also checked. The signal for Thunderbolt 3 was checked.
A Thunderbolt 3 test pattern was output from the DUT, and the signal quality after passing through the CMCC was checked.

18Signal Waveform Check: Eye Pattern Measurement

We checked whether use of the common mode choke coil has any effect on signal quality.
A Thunderbolt 3 test pattern was output from the DUT, and the signal quality after passing through the CMCC was checked.
Even if a common mode choke coil is used, the signal waveform quality is identical to that before the filter was inserted, and the Thunderbolt 3 compliance test was passed.
Because USB4 also uses the same signal speed (Max. 20 Gbps), the waveform test is expected to be passed.

Our recommended common mode choke coils

Noise suppression can be implemented using a compact, slim type having a size of 0.65×0.50×0.30 mm with dimensional error of ±0.05 mm without affecting the signal waveform of the high-speed differential transmission line.

19Conclusion

  • Radiated Noise
    • A USB4 operating environment was simulated for conducting a noise assessment.
    • In the 30 to 1000 MHz and the 1 to 18 GHz range, there was no problem with radiated noise.
  • Wi-Fi Reception Sensitivity
    • The Wi-Fi reception sensitivity was reduced when PCI Express, DisplayPort 1.4, and Thunderbolt 3 were operating.
    • In particular, noise in the 2.4 GHz band was found from the board wires when USB 3.1 Gen 2 was operating.
    • The same noise is expected to be generated during USB4 operation.
    • Use of a common mode choke coil eliminated the drop in Wi-Fi sensitivity.
  • Signal Quality
    • The following recommended components can be used to implement noise suppression measures without affecting the signal quality.

Our recommended common mode choke coils

Because the cutoff frequency is high, the effect on high-speed signals is low, and the attenuation characteristics peak is deep, which enables superior noise suppression characteristics.