Noise suppression technologies/case study introduction (Consumer)

Noise suppression for Thunderbolt™3

07/22/2019

INDEX

What is Thunderbolt™3？
Alternate method for evaluation of Thunderbolt™3 noise
USB3.1 noise situation
Considerations regarding Thunderbolt™3
Effects of noise filters on Thunderbolt™3 signals
Summary

1. What is Thunderbolt ™ 3？

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 Thunderbolt™3.
Thunderbolt™3 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 Thunderbolt™3 noise situation and noise filters suitable for noise suppression.

Figure 1. Comparison of data transfer rates of different interfaces

2. Alternate method for evaluation of Thunderbolt ™ 3 noise

It is difficult to obtain materials for evaluation of Thunderbolt™3 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 Thunderbolt™3.

Comparison of technical requirements for Thunderbolt^™3 and USB 3.1 Gen2

	Thunderbolt^™3	(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

3. USB3.1 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 NFG0QHB542HS2 common mode choke noise filter is inserted to the USB Tx line as noise suppression was also checked.

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 NFG0QHB542HS2 common mode noise filter to the Tx line.

4. Considerations regarding Thunderbolt ™ 3

Radiation noise expected for Thunderbolt™3

It is expected that second-order harmonics of the communication signal frequency will be observed as narrow band common mode noise in Thunderbolt™3 communication, in the same manner as USB3.1.

Thunderbolt™3 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 Thunderbolt™3.

Figure 3. Radiation noise expected for Thunderbolt™3

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

5. Effects of noise filters on Thunderbolt ™ 3 signals

Signal integrity

Figure 4. Effect of different filters on signal waveforms

We examined the effect of noise filters on Thunderbolt™3 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 NFG0QHB542HS2 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 Thunderbolt™3, conventional filters should not be used, and instead products that support higher frequency signals should be selected.

6. Summary

Thunderbolt™3 is expected to become widespread due to its adoption in USB4.0.
It is speculated that Thunderbolt™3 noise will be similar to that of USB3.1 Gen1 and Gen2.
The key to Thunderbolt™3 noise suppression will be to eliminate second-order harmonic common mode noise.
Thunderbolt™3 uses high-speed signals, so sufficient care must be taken so that the filters used do not adversely affect the signal quality.
The NFG0QHB542HS2 common mode noise filter was commercialized for high-speed signals, and can effectively eliminate second-order harmonic 10 GHz and 20 GHz common mode noise without a significant adverse effect on Thunderbolt™3 signal quality.