The relationship between USB3.1 data transfer rate and frequency bandwidth

Bandwidth: To put it simply, it is the expressway we build. If one lane is a bandwidth, if there are several lanes, multiply the corresponding lanes to get the bandwidth that can run. This is generally written in professional books, and the channel can be different. The frequency range of the distorted transmission signal, the transmission media designed for different applications have different channel qualities, and the supported bandwidth is different. Channel capacity: the maximum amount of signal that the channel can transmit in a unit time, indicating the transmission capacity of the channel , the channel capacity is sometimes expressed as the number of binary bits that can be transmitted per unit time (called the data transmission rate of the channel, bit rate), expressed in the form of bits/second (b/s), abbreviated as bps, in books Write too deep.

Speed: When driving on the highway, there are many factors for how fast you can run. The main factor is whether the lane design is reasonable. A Maserati sports car designed to run 300 yards is useless if you go to our country roads. The quality of the car itself is also very important. , the conductor and characteristic design of the wire will be directly affected. You can refer to the previous high-frequency course, the courseware on the relationship between high-frequency data lines and the control of manufacturing process parameters. When introducing professional books, it is generally written like this. The maximum number of bits transmitted, channel capacity and channel bandwidth have a proportional relationship: the larger the bandwidth, the greater the capacity. The formula for theoretically calculating 4M broadband is: 4*1024/8 = 512K/s, that is to say, 4M broadband in theory The download speed can reach up to 512k/s

Frequency: One of the parameters that is often confused at present, the RF series coaxial cable is the most cited frequency, video signal transmission generally adopts direct modulation technology, in the form of baseband frequency (about 8MHz bandwidth), the most commonly used transmission medium is coaxial Coaxial cable, coaxial cable is specially designed to transmit video signals, its frequency loss, image distortion, and image attenuation are relatively small, and it can complete the task of transmitting video signals very well, but now the twisted version is also used It can solve the problem of audio and video transmission, so in many occasions, the twisted pair version will be considered in terms of cost. For the transmission line of the differential pair, the transmission rate or bandwidth (Mbps) = clock frequency (MHz) * bit width * number of channels * each Clock transmission data group number (cycle), 480Mbps=240MHz*1*1*2, data is transmitted twice per clock cycle (this is related to the encoding method, USB is NRZI), that is, when the transmission rate is 480Mbps, the corresponding clock The frequency is 240MHz, and this 240MHz clock frequency is obtained by multiplying the crystal oscillator in the USB chip. The actual USB crystal oscillator has 12MHz, 24MHz, 48MHz, etc. So now everyone knows that frequency and transmission rate are completely two concepts. For differential signals Transmission line.

In modern network technology, people always use "bandwidth" to represent the data transmission rate of the channel. "Bandwidth" and "rate" have become almost synonymous. There is a clear relationship between the maximum transmission rate of the communication channel and the channel bandwidth, so People can use "bandwidth" to replace "rate". For example, people often express the "high data transmission rate" of the network with the "high bandwidth" of the network. Therefore, "bandwidth" and "rate" are almost the same in the discussion of network technology. became a synonym.

USB 3.0 was the USB community’s response and provided users with the ability to move data at rates up to 450MB/s while retaining backward compatibility with USB2.0；Now, with the continued trend for more bandwidth driven by larger and faster storage solutions,higher resolution video, and broader use of USB as an external expansion/docking solution, USB3.1 extends the performance range of USB up to 1GB/s by doubling the SuperSpeed USB clock rate to 10Gbps and enhancing data encoding efficienc.

Although the nominal interface rate of USB 3.1 is 10Gbps, it still reserves some bandwidth to support other functions, so its actual effective bandwidth is about 7.2Gbps, and the theoretical transmission speed should reach 900MB/s. , the current USB 3.1 interface still has a lot of room for improvement, at least it should reach the level of 800MB/s, the following are the parameters measured by the manufacturer. This red font) From the above test results, the actual performance of the USB 3.1 interface is much higher than that of the USB 3.0, the continuous read and write speed is around 500MB/s to 600MB/s, and the highest score can even exceed 700MB/s , and the USB 3.0 interface, its continuous read and write rate is about 300MB/s to 400MB/s.