EMI Suppression Filters (EMC and Noise Suppression)Noise Suppression for USB4 (1)

Contents

1USB4 Standard and Its Adoption

USB (Universal Serial Bus) is widely used worldwide as a differential interface standard for data transmission primarily between hosts, such as computers, and devices.
The needs for high-capacity data transmission over high-speed communication routes and integration of various existing differential interface standards in the market led to the development of the new USB4 standard in September 2019.
USB4 is expected to become widely adopted in computers and their peripherals in coming years.

※ With the defining of the USB4 standard, the names of previous standards were changed.

2Integration of USB and Thunderbolt

Thunderbolt 3 adopted the USB Type-C connector so that a Thunderbolt 3 port could also be used as a USB 3.1 port.
The USB4 standard was defined for complete compatibility with Thunderbolt 3.
Most of the electrical specifications for USB4 are based on Thunderbolt 3.

3Specifications and Comparison of Thunderbolt 3 and USB4

USB4 has the same maximum data transfer speed as Thunderbolt 3.
Although there are some slight differences in the signal amplitude and other specifications, the basic specifications are identical, and so USB4 will have the same noise issues arising from data signals and require the same signal quality care as Thunderbolt 3.

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Thunderbolt 3 USB4
Data transmission rate (per lane) 20Gbps
※Max:40Gbps (20Gbps x2lane)
20Gbps
※Max40Gbps (20Gbps x2lane)
Number of data lanes 2 data lanes 2 data lanes
Connector, cable Connector: USB Type-C connector
Cable: Special-purpose cable
Connector: USB Type-C connector
Cable: Special-purpose cable
Characteristic impedance of
transmission line
Differential: 90Ω±5% Single-ended: 42.5Ω(typical)
Available interface DisplayPort, PCI Express USB, DisplayPort, PCI Express

4Anticipated Noise Issues with USB

During USB4 communication, care must be provided for two types of noise issues. The first is radiation noise that radiates from the board or cable to the outside and affects external devices. The second is intrasystem EMC noise that interferes with other circuits inside the device, resulting in malfunctions and reduced performance.

Noise issues during USB4 communication: 1

  • Radiated emissions

Noise issues where noise radiates from USB4 device or cable.

Noise issues during USB4 communication: 2

  • Intrasystem EMC (drop in Wi-Fi reception sensitivity)

Noise issue where noise arising from data signals interferes with the Wi-Fi antenna inside the device during USB4 communication, resulting in lower Wi-Fi communication sensitivity.

※Devices capable of USB4 communication are still not available (as of February 2020).
For this reason, noise assessments were conducted using devices capable of communication by Thunderbolt 3, which has virtually the same electrical characteristics as USB4.