Evolving USB technology meets aerospace needs

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Evolving Universal Serial Bus (USB) 3.x specifications, along with the new Type-C connectors, will enable the simultaneous transfer of data and video with fast power charging between electronic devices. USB is poised for growth in a number of markets including civilian and defense aerospace industries. According to a report by Allied Market Research, USB is expected to surpass other major data transfer types by 2022, including CAT5/CAT6, DVI, VGA, HDMI and others. Table 1: Evolution of USB versions and data rates.

First released in 1996, the USB standard established specifications for cables, connectors and protocols between PCs and peripheral devices. To date, there have been three generations of USB specifications: USB 1.x, USB 2.0 and USB 3.x (see Table 1).

Note that USB 3.2 preserves existing USB 3.1 SuperSpeed and SuperSpeed+ data modes while introducing two new SuperSpeed+ transfer modes over the USB-C connector, with data rates of 10 and 20 Gbit/s (1,250 and 2,500 MB/s).

USB 2 vs. USB 3

Specifications for USB 2.0 and 3.x differ in many respects. For example, the data transfer rate of 2.0 is 480 Mbps while 3.0 runs more than 10 times faster at 5 Gbps. The actual transfer rate depends upon the device in use plus the bus type, USB ports and cables.

The next notable difference is the addition of a new physical interface with twice as many wires in the USB connector and cables to accommodate the more than double data rate increase. To accommodate this increase in wires, B Male and Micro B Male have new connectors. These connector types are larger than the existing 2.0 versions and cannot be used with 2.0 ports.

The final difference between 2.0 and 3.x lies with the available power, power efficiency (via idle states and shut down modes) and power management system. The former provided up to 500 mA, whereas the newer versions provide up to 900 mA. This increase in available current enables devices to charge faster from the bus.

Fast charging, signal integrity and the ability to recover from common errors are features of 3.x that appeal to mission applications in civilian and defense aerospace where flight and ground crews must have immediate access to vital information with no signal interruptions.

Another unique application of USB technology in aerospace and military applications is in electronic flight bags (EFBs). Traditional, paper-laden flight bags are being replaced with an electronic version that not only greatly reduces weight, but also improves operational efficiency (see Figure 1).

Figure 1: The touch screen of an electronic flight bag. Source: NASA

What about the cables?

Cables are the critical interface providing data and power between systems.

As noted earlier, in order to achieve a faster data transfer rate of 4.8 Gbps and higher power transfer of 900 mA, USB 3.1 uses two additional high-speed data wires than its predecessor USB 2.0 (see Figures 2A and 2B).

Figure 2A: Data cable wiring for USB 3.1. Source: PIC Wire & Cable

Figure 2B: Data cable wiring for USB 2.0. Source: PIC Wire & Cable

Users should also pay attention to the physical and electrical properties of the cable. Robust cables are engineered to provide strong shielding protection against EMI to ensure signal integrity and system reliability, which will allow the cable to run at longer distances. Good cables feature tape-wrapped jackets for applications requiring light weight and flexibility. A wrapped jacket also enables laser marking for easy identification – especially for massive cable installations in main avionic applications.

Connectors

In addition to a slightly thicker cable, users can differentiate the high-speed USB 3.x from the lower-speed USB 2.0 versions by the blue interior color of the 3.x connectors. Such visual aids are necessary, as any device that uses the different connectors cannot use the 2.0 equivalent cables. In addition, while the 2.0 B connectors physically fit into the 3.0 B ports, the different wiring configuration does not allow proper data transfer. The A connectors still work properly, however, so any 2.0 device with a 2.0 cable can be used with 3.0 ports or hubs.

To clarify:

• If USB 2.0 cables are used with USB 3.0 ports, then the transfer rate will fall back to 2.0.
• If USB 3.0 cables are used in both a USB 2.0 device and port (assuming the connectors fit), then the device will perform at the slower USB 2.0 speeds.
• USB 3.0 devices require 3.0 cables to work at 3.0 and 3.1 speeds.
• USB Type-C connectors are needed for the fastest USB 3.2 speeds.

Summary

USB connectors and cables have undergone significant changes within the latest 3.X specifications. These changes enable significant increases in data speed and device charging times, which are essential features needed in both civilian and defense aerospace applications. For more on USB cable technology, go to PIC Wire & Cable.