Universal Serial Bus (USB) is probably one of the most versatile interfaces in the world. It was originally initiated by Intel and Microsoft and features as hot plug and play as possible. Since the introduction of USB interface in 1994, after 26 years of development, through USB 1.0/1.1, USB2.0, USB 3.x, finally developed to the present USB4; The transmission rate has also increased from 1.5Mbps to the latest 40Gbps. At present, not only the newly launched smart phones basically support Type-C interface, but also notebook computers, digital cameras, smart speakers, mobile power supplies and other devices have begun to adopt TYPE-C specification USB interface, which has been successfully introduced into the automotive field. Instead of USB-A, Tesla’s new Model 3 has usB-C ports, and Apple has completely converted its macBooks and AirPods Pro to pure USB Type-C ports for data transfer and charging. In addition, according to the requirements of the eu, apple will also use USB type-c interface in the future iPhone15, and it is no doubt that USB4 will be the main product interface in the future market.
Requirements for USB4 cables
The biggest change in the new USB4 is the introduction of the Thunderbolt protocol specification that Intel shared with usb-if. Running over dual links, the bandwidth is doubled to 40Gbps, and Tunnelling supports multiple data and display protocols. Examples include PCI Express and DisplayPort. In addition, USB4 maintains good compatibility with the introduction of the new underlying protocol, being backward compatible with USB3.2/3.1/3.0/2.0, as well as Thunderbolt 3. As a result, USB4 has become the most complex USB standard to date, requiring designers to understand USB4, USB3.2, USB2.0, USB Type-C and USB Power Delivery specifications. In addition, designers must understand the PCI Express and DisplayPort specifications, as well as the HIGH-DEFINITION content protection (HDCP) technology that is compatible with the USB4 DisplayPort mode, and the cables and connectors we are familiar with have higher requirements to meet the electrical performance requirements of the USB4 cable finished products.
A coaxial version of USB4 came out of nowhere
In the USB3.1 10G era, many manufacturers adopted coaxial structure to meet the requirements of high frequency performance. Coaxial version was not applied in USB series before, its application scenarios are mainly Notebook, mobile phone, GPS, measuring instrument, Bluetooth technology, etc. General application of cable description is medical coaxial line, teflon coaxial electronic line, Radio frequency coaxial wire, etc., with the market bulk cost control requirements, in the USB3.1 era of stranding to meet the performance of the product quickly occupy the market, but with the USB4 market for high-frequency transmission requirements more and more rigorous, and high-speed transmission needs wire has a strong anti-interference ability and electrical performance stability, In order to ensure the stability of high frequency transmission, the current mainstream USB4 is still the main coaxial version, coaxial production and manufacturing process is a complex process, to solve the high frequency and high speed application requires appropriate production equipment and mature and stable production process. In the production of the product, material selection, process parameters and process control, the electrical parameters of specialized laboratory tests play a key role, throughout the development bottleneck of the coaxial structure, in addition to your (material cost, processing cost expensive) other are good, but the development of the market always revolve around how to achieve the biggest batch price, Pair of twist version has always been in the gap of coaxial development research and development and breakthrough.
It can be seen from the structure of the coaxial line, from inside to outside, respectively: central conductor, insulating layer, outer conductive layer (metal mesh), wire skin. Coaxial cable is a composite composed of two conductors. The central wire of coaxial cable is used to transmit signals. The metal shielding net plays two roles: one is to provide the current loop for the signal as the common ground, and the other is to suppress the interference of electromagnetic noise to the signal as a shielding net. The center wire and the shielding network between the semi-foaming polypropylene insulation layer, the insulation layer determines the transmission characteristics of the cable, and effectively protect the middle wire, expensive have expensive reason.
USB4 twisted pair version coming?
As electronic circuits operate at higher frequencies, the electrical characteristics of electronic components become more difficult to master. When the component size or the whole circuit size compared to the wavelength of the operating frequency is greater than one, the circuit inductance capacitance value, or components the parasitic effect of material properties and so on, even when we were using the wire pair structure, basic frequency parameters testing is cannot meet the requirements of customers, and flexible than the coaxial version of the structure and its diameter is far, Why can I not apply the pair USB in batches? In general, the higher the frequency of cable usage, the shorter the wavelength of the signal, and the smaller the skew pitch, the better the balance effect. However, too small splicing pitch will bring low production efficiency and sprain of insulated core wire. The pitch of the line pair is very small, the number of torsion is many, and the torsion stress on the section is concentrated seriously, resulting in serious deformation and damage of the insulation layer, and finally causing the distortion of electromagnetic field, affecting some electrical indicators such as SRL value and attenuation. When insulation eccentricity exists, the distance between conductors changes periodically due to the revolution and rotation of insulating single line, which brings periodic fluctuation of impedance. The fluctuation period is relatively long. In high frequency transmission, this slow change can be detected by electromagnetic waves and affect the return loss value. The USB4 pair version cannot be used in batches.
Not to the ground, but don’t want to use your death coaxial, so people began to verify difference USB4 shielding ways to do the product, to wring the biggest drawback is easily twisted conductor, and the difference with parallel packet directly for homework, avoid conductor sprain, as we all know, currently USES the difference of the SAS, SFP + etc are used in high speed line, Enough to show that its performance must be higher than the stranded version, an important role of high frequency data line is to transmit data signals, but when we use it around may appear all kinds of messy interference information. Let’s think about if these interference signals enter the inner conductor of the data line and superimpose on the original transmitted signal, is it possible to interfere or change the original transmitted signal, thus causing useful signal loss or problems? And difference of aluminum foil layer is to transfer information to us to play the role of a protective and shielding, used to reduce the interference of outside independent signals for transmission, the main package belt material and aluminum foil pull is use aluminum foil sealing and shielding, one-sided or two-sided coating on the plastic film, lu: su composite foil that is used as the shield of the cable. Cable foil requires less oil on the surface, no holes and high mechanical properties. The process of wrapping is to gather two insulated core wires and ground wires together through wrapping machine. At the same time, a layer of aluminum foil and a layer of self-adhesive polyester tape on the outer bread are used to shield the wire pair and stabilize the structure of wrapping core wires. This process is having important effect to wire property, include impedance, delay difference, attenuation, because this must produce strictly by craft requirement, undertake testing to electric property, in order to ensure wrap core wire is accord with requirement. Of course, not all data lines have two layers of shielding. Some have multiple layers, some have only one layer, or none at all. Shielding is a metallic separation between two spatial regions to control the induction and radiation of electric, magnetic and electromagnetic waves from one region to the other. To be specific, the conductor core is surrounded by a shielding body to prevent them from being affected by the external electromagnetic field/interference signal, and to prevent the interference electromagnetic field/signal from spreading outward. USB differential pair high frequency signal testing can be comparable to coaxial, differential pair USB4 cable is coming.
Post time: Aug-16-2022
