EMI Suppression Filters (EMC and Noise Suppression)Noise suppression for Thunderbolt3

Contents

1What is Thunderbolt3?

  • Thunderbolt is a high-speed digital interface developed by Intel Corporation that achieves communication speeds as high as 40 Gbps.
  • Thunderbolt was developed from technology based on PCI-Express, and has been successively revised to Thunderbolt3.
  • Thunderbolt3 was adopted as the standard specification for USB4.0 in 2019, and is expected to spread as a high-speed general-purpose interface.
  • We examined the Thunderbolt3 noise situation and noise filters suitable for noise suppression.
Figure 1

Figure 1. Comparison of data transfer rates of different interfaces

2Alternate method for evaluation of Thunderbolt3 noise

It is difficult to obtain materials for evaluation of Thunderbolt3 noise, so the noise situation and noise suppression methods were estimated based on the data for USB3.1 Gen2, which is an interface that uses technology similar to Thunderbolt3.

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Comparison of technical requirements for Thunderbolt3 and USB 3.1 Gen2
Thunderbolt3 (evaluation case)
USB3.1 Gen2
Transfer Data Rate 20Gbps x1lane
※Max:40Gbps(20Gbps x2lane)
10Gbps x1lane
Number of Data lanes Data 2lane Data 1lane
Connector, Cable Connector: USB Type-C
Cable: dedicated cable
Connecter: USB Type-C
Cable: dedicated cable
Receiver EQ Must Must
Characteristic Impedance
of transmission line
90ohm plus minus 5% Cable:
90ohm plus or minus 5ohm
Connector:
90ohm plus or minus10ohm
(transmission line no Regulation)
Third party certification exam required Voluntary restraint

3USB3.1 noise situation

  • Measurement of USB3.1 radiation noise (Gen1 & Gen2)

Communication was performed using a USB3.1 compatible SSD connected to a host PC, and the radiation noise was measured.
(Measurement was performed in both the Gen1 and Gen2 operating modes.)
The noise level when a NFP0QHB542HS2 common mode choke noise filter is inserted to the USB Tx line as noise suppression was also checked.

Figure 2

Figure 2.
USB3.1 Gen1 & Gen2 noise measurement results and confirmation of filter insertion effects

USB3.1 Gen1 communication: Narrow band noise (second-order harmonics) was observed at 5 GHz, which is twice the signal fundamental frequency of 2.5 GHz.

USB3.1 Gen2 communication: Narrow band noise (second-order harmonics) was observed at 10 GHz, which is twice the signal fundamental frequency of 5 GHz.

The main component of this noise is thought to be the common mode, so large suppression effects for the noise observed at 5 GHz and 10 GHz were obtained by inserting a NFP0QHB542HS2 common mode noise filter to the Tx line.

4Considerations regarding Thunderbolt3

  • Radiation noise expected for Thunderbolt3

It is expected that second-order harmonics of the communication signal frequency will be observed as narrow band common mode noise in Thunderbolt3 communication, in the same manner as USB3.1.

Thunderbolt3 supports data transfer rates of 10 Gbps/lane and 20 Gbps/lane, so it is speculated that 10 GHz and 20 GHz common mode noise will occur with Thunderbolt3. 

Figure 3

Figure 3. Radiation noise expected for Thunderbolt3

Like USB3.1, a common mode noise filter is effective.

5Effects of noise filters on Thunderbolt3 signals

  • Signal integrity
Figure 4

Figure 4. Effect of different filters on signal waveforms

We examined the effect of noise filters on Thunderbolt3 signals.
When a conventional noise filter was used, the eye pattern of the signal collapsed and did not satisfy the standard.
When the newly developed NFP0QHB542HS2 common mode choke coil was used, the eye pattern was maintained at a level that satisfied the standard.

This showed that when using noise filters with Thunderbolt3, conventional filters should not be used, and instead products that support higher frequency signals should be selected.

6Summary

Recommended noise suppression products for Thunderbolt™3. Can eliminate high frequency common mode noise. Have little effect on high-speed signals.