What makes a high speed USB cable high speed?

Question

I was shopping around for USB 2.0 cables.

Some manufacturers claim their cables are "high speed".

My understanding is that the electronics on the device determine the speed, not the cable.

I understand that the length of the cable has an effect on the speed (but probably negligible, like nanoseconds).

So, what makes a USB 2.0 cable, high speed? (One can search the internet for "high speed usb 2.0 cable" to find instances.)

What is the average speed difference between a high speed cable and a cable not high speed?

Answer 1

USB is defined at several data rates.

12 Mbps is called "Full Speed"

480 Mbps is called "High Speed"

5 Gbps is called "SuperSpeed"

10 Gbps is called "SuperSpeed+"

A USB product marketed as "High Speed" should be conforming to at least the USB 2.0 specification, and capable of carrying a 480 Mbps USB High Speed signal.

Some of the specifications that are related to the bandwidth capability of the cable include

• Characteristic impedance
• Attenuation
• Propagation delay
• (Intra-pair) skew

There are also requirements on things like the diameter of the wires, placement of the USB logo on the connectors, etc.

Answer 2

The cable is extremely important for being able to support the required bitrate on the Data Lines and other requirements of the specification.

As speed requirements increase, impedance matching, attenuation, shielding, cross-talk become important, these are specifications used by the cable designer to choose a design and materials to produce their product. The USB Consortium determines the specifications to be considered a compliant cable.

Looking briefly at the USB Cable and Connector Specification has some more information. This document is incomplete for our purposes but has some useful information.

As an example of what kind of cable specific paramaters are critical for this cable

Presumably, the requirements for the higher speed grades are even tighter.

As an aside, USB Compliance tests the entire cable assembly as a whole, so some of these requirements impact the choice of connector and materials there as well as the cable itself.

Answer 3

USB cables may have different construction (shielded and non-shielded), and may have different materials for wire jacket making the signal to attenuate differently at different data speeds.

For example, many initial USB 1.1 cables used for LS(1.5 Mbps) transmission rate were unshielded.

More recent USB cables are using shielded cable assemblies, and marked as "FS/HS cables".

To make a cable designated as "HS", (480 Mbps rate), the cable must meet certain quality requirements such as be reasonably uniform at 90 Ohm differential impedance along the entire cable, and have decent soldering fan-out inside cable's overmold, where the cable is soldered to connector contact. Not all cables are made equal, and if the cable doesn't pass several certification tests (like valid eye diagram at far end of the cable), it can't be called "HS" cable.

Some cables can have differential impedance outside the 90+-20 Ohm window, and will likely fail with USB HS devices/hubs. So a manufacturer of such cable wouldn't risk to put "HS" label on their production. The difference between "HS" and non-HS cable is not in frequency they can pass through, but would it work in HS mode without errors or not.

In no case you should trust the manufacturer designation unless the cable has USB-IF certification logo, in this case just like this one,

A good cable manufacturer would also provide USB-IF Test ID for the cable. In all other cases it is a gamble with signal fidelity and potential intermittent failure in communication.

Answer 4

The speed of the cable depends on the tolerance of the construction and the materials used. A high speed cable has lower loss insulation and better control of the spacing between the conductors in order to minimize the total loss between the source and destination.

At very high speeds such as 10Gbps, different higher cost materials such as Teflon must be used so that the signal is not reduced by losses associated with the insulation.

USB 2.0 cables are really not all that high speed anymore.

Answer 5

As other answers have said, the difference between the cables is in their construction, and therefore the electrical properties.

The reason for this, is that eventually your digital data will be carried by an analog signal. The analog signal is distorted as it is carried along the cable. If it is distorted too much, the electronics at the receiving end will not be able to to recover the information from the signal. (Such as when a radio signal is too weak for you to make out anything intelligible from it.)

The characteristics of the cable listed in other answers, such as impedance and skew, determine how the signal is distorted as it travels.

Typically, the higher the frequency, the more sensitive to distortion the signal is. Higher bitrates (USB 'speed') require higher frequencies in your analog signal. Accordingly, the cable must be made to finer tolerances.

The length of the cable affects speed, but not because of the 'delay' through the cable, but rather the longer the signal travels through the cable, the more it is distorted. The better the cable matches the ideal properties, the less distorted the signal is per length, and the longer the cable can be and still work.

Answer 6

The cable characteristics determines the speed of the transmission line.

• Cable impedance (characteristics impedance) vs frequency.
• Cable reactance vs frequency.
• Resistance component.
• Interpair and intrapair skew and airgap. Generally, airgap will not be the issue for cable.

USB 2.0 operating speed is 480 Mbps and USB 3.0 is 5-6 Gbps. To transmit data at these speeds, the characteristic impedances must be maintained for signal integrity.