Murata Noise Suppression for Thunderbolt™ 3

Figure 1. Comparison of data transfer rates of different interfaces

Alternate Method for Evaluation of Thunderbolt 3 Noise
Murata says it is difficult to obtain materials for the evaluation of Thunderbolt 3 noise, so the noise situation and noise suppression methods are estimated based on the data for USB 3.1 Gen 2, which is an interface that uses technology similar to Thunderbolt 3.

Measurement of USB 3.1 radiation noise (Gen1 & Gen2)

Communication is performed using a USB 3.1-compatible SSD connected to a host PC, and the radiation noise is measured. (Measurement is performed in both the Gen1 and Gen2 operating modes.)

The noise level when an NFP0QHB542HS2 common mode choke noise filter is inserted into the USB Tx line as noise suppression is also checked. (Figure 2, below)

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

Figure 2. USB 3.1 Gen 1 and Gen 2 noise measurement results and confirmation of filter insertion effects

USB 3.1 Gen 1 communication: Narrowband noise (second-order harmonics) was observed at 5GHz, which is twice the signal fundamental frequency of 2.5GHz

USB 3.1 Gen 2 communication: Narrowband noise (second-order harmonics) was observed at 10 GHz, which is twice the signal fundamental frequency of 5GHz

Considerations regarding Thunderbolt 3

It is expected second-order harmonics of the communication signal frequency will be observed as narrowband common mode noise in Thunderbolt 3 communication, in the same manner as USB 3.1.

Thunderbolt 3 supports data transfer rates of 10Gbps/lane and 20Gbps/lane, so it is speculated that 10GHz and 20GHz common mode noise will occur with Thunderbolt 3.

Like USB 3.1, a common mode noise filter is effective.

Figure 3. Radiation noise expected for Thunderbolt 3

Effects of noise filters on Thunderbolt 3 signals

Signal integrity
Murata 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 NFP0QHB542HS2 common mode choke coil was used, the eye pattern is maintained at a level that satisfied the standard.

This shows that when using noise filters with Thunderbolt 3, conventional filters should not be used, and products that support higher frequency signals should be chosen.

Figure 4. Effect of different filters on signal waveforms

Summary

Thunderbolt 3 is expected to become widespread due to its adoption in USB 4.0. Murata speculates Thunderbolt 3 noise will be similar to that of USB 3.1 Gen 1 and Gen 2 and that the key to Thunderbolt 3 noise suppression is to eliminate second-order harmonic common mode noise. Thunderbolt 3 uses high-speed signals, and sufficient care is needed so the filters used do not adversely affect the signal quality. Murata's NFP0QHB542HS2 common mode noise filter is commercialized for high-speed signals and can effectively eliminate second-order harmonic 10GHz and 20GHz common mode noise without a significant adverse effect on Thunderbolt 3 signal quality.

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