The USB-Implementers Forum (USB-IF) officially released the USB4  specification on September 3, 2019. The main update is to supplement the existing USB3.2 and USB2.0 architectures to build a new generation of USB.  The architecture of USB4  is based on the Thunderbolt  protocol specification (contributed by Intel to the USBPromoter Group). The maximum transfer rate is 20Gbps (10G x2) from the original USB3.2, which is doubled to 40Gbps (20G x2) and can be transmitted simultaneously.

  Multiple data and images.

From the above characteristics, it is not difficult to find that the logical architecture of USB4  is very similar to the network architecture.  A fixed frame and a physical layer carry different protocol packets, which can include data and image packets, and each packet is marked with an Address to ensure correct transmission.  Therefore, USB4  gradually gets rid of the functional limitations of traditional USB Host and USB Device. USB4  uses a point-to-point transmission method.  This design reserves great flexibility for further increasing transmission speed and functions in the future.

USB4 new features 3 key points

1. USB4 only uses USB Type-C connector.  USB4 signal adopts dual-channel transmission.  In the past, connectors such as USB Type-A or Micro-B only supported single-channel transmission, but could not support USB4.

2. The fastest USB transmission speed supports 40G (20Gbps x2), and can simultaneously display DisplayPort video and audio.  Designed to combine multiple protocols into a single physical interface, the overall speed and performance of the USB4 architecture can be dynamically shared.

3. Backward compatible with USB 2.0 and USB 3.2 and support Thunderbolt 3

USB4 connector and cable 3 key points

1. USB4 only uses USB Type-C connector.

2. USB4Cable passive cable, the supported passive cable length is reduced from 1 meter of USB 3.2 Gen2 to 0.8 meter of USB4 Gen3.

3. For longer cables, such as connecting large screens, or VR applications, use active cables.  USB4 active cables are cables containing Repeater components (such as active components such as Re-timer, Re-driver), and fiber optic cables.  The maximum length of active cable that can be supported is 5 meters, and the maximum length of fiber-optic cables is 50 meters.

It can be known from the above characteristics that the USB4 interface is complex and the bandwidth is doubled, and it also supports up to 100W power supply.  In addition to the differences in product design between USB4 and previous USB3 products, and the attenuation of high-frequency signals on PCBs and connectors, more attention must be paid to high-frequency impedance matching to ensure the quality of transmitted signals during the development stage.  In order to achieve the pursuit of product quality and make products more compatible and ready to enter the market, the test link is particularly important. Compared to the USB3 series cables or connectors, USB4 has added new test items for signal quality to ensure that  Cables and connectors are better and more compatible.