The cables also include ground connections, buried components such as bypass capacitors, and cable ID circuits. It is easier to match lengths in this type of wire, and it will probably be the more popular of the two alternatives. One coax carries the signal, and the other carries a negative copy of the same signal.Īnother implementation of the pair of data lines is twinaxial (twinax), where both the positive and the negative copies of the signal share the same shield. Two matched micro-coax cables create a single high-speed differential data line. They have an insulating jacket, and inside is a braided shield that hides another insulated wire. The micro-coax cables could easily be mistaken for ordinary wires. It describes many possible cables, including specialized cables for USB 2.0, HDMI, high-speed data, and power-only.
The USB specification is freely available from usb.org. There are two dedicated ground wires, and ground current also flows in the coaxial shields. New versions remove one of these and provide Vconn instead, which can provide more power. In earlier versions of the specification, there were two configuration wires. Configuration happens on the Config Channel. The power wire Vbus can carry up to 3 Amps of current and 20 Volts. For example, analog headphone connections are possible. There are also two wires for a sideband, which can be another type of communication. A legacy USB 2.0 interface is also included. These high data rates require length-matching and impedance control. The lines are differential, providing 4 lanes of digital signals, with 2 in each direction. The USB-C cable has 8 coax or 4 twinax high speed data connections. Cable length is also limited by the application, due to both power loss and signal attenuation at high data rates. High current applications require thicker gauge copper. Each cable is tailored for its application, and electronically identified. There is not a single standardized USB-C cable. To reach the potential of this interface, first understand how the cables and connectors influence the PC Board layout requirements. Power delivery in USB-C coexists with SuperSpeed digital data.
USB-C: Cables, Connectors, and Circuit boards
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