Universal Serial Bus, or more commonly known as USB, is a peripheral connectivity standard that was originally released in 1996. USB 1.0 includes two speed grades, Low Speed and Full Speed, which support data rate of 1.5Mbps and 12Mbps, respectively. USB 1.0 targeted to unify the interface for peripheral connectivity in PC. In 2000, USB 2.0 was released, and it added Hi-Speed USB at 480Mbps. The higher maximum bandwidth addressed the growing storage trend and the larger amount of data being transported between PC and peripherals. To date, there are over 6 billion USB devices in the world, with approximately 2 billion new USB devices sold per year.
The latest addition to the USB family is the USB 3.0 specification, which boosts the maximum data transfer rate to 5Gbps, or just over 600MB/s. The USB 3.0 specification is designed to be fully backward compatible. The new SuperSpeed SSTX+/- and SSRX+/- signals pairs are complemented by the legacy USB 2.0 D+/D- signals. In systems that do not yet fully support USB 3.0, USB 2.0 can be used.
With several products out in the market with USB 3.0 certification, the question really is, how long will it take for mass-market adoption and what will be the key drivers that promote such adoption?
Why USB 3.0?
USB 3.0, code name SuperSpeed, offers several value propositions that greatly benefit mobile handheld devices and consumer electronics. First, the increased data rates of up to 5Gbps or 600MB/s provide ample bandwidth for high performance applications. With the recent popularization of high-definition content and 3D technology, the media file sizes being transferred have also increased drastically. These trends were immediately reflected in the size of the mass storage devices being shipped; new handheld devices are now shipping with embedded and/or removable storage as big as 64GB. This trend is expected to continue as more HD and 3D content is becoming available.
New embedded and removable mass storage standards, eMMC 4.41 and SD 3.0 have defined densities of up to 2TB. In order to keep up with the increasing mass storage densities, the speed to sideload content onto and off a handheld device also needs to be improved. To put things in perspective, one appropriate analogy of using USB 2.0 with next generation storage is like using a small garden hose to fill an Olympic-sized swimming pool; it simply takes too long. Quantitatively, transferring 1 GB of data with USB 2.0 takes about 60 seconds, and it can take upwards of 60 minutes to transfer 64 GB of data. Now, imagine using USB 2.0 to transfer 2TB of data. With SuperSpeed USB 3.0, the transfer speed is increased by 10x, which allows 64 GB of media data to be transferred in just a few minutes’ time.
Battery Life Considerations
The second value proposition for USB 3.0 is its superior power management. USB 3.0 introduces new power modes that allow the USB Link Layer to be independently powered down when a USB connection is established but not active. These new power modes allow for more efficient use of the limited battery that powers mobile devices. In usage cases that require intermittent data access over USB, e.g. video streaming and music playback, this protocol layer improvement, along with the faster USB 3.0 speed, can drive down the overall per-bit power consumption by 80%. Moreover, the low-power Link Layer states are entered and exited automatically, and are designed to be transparent to the higher applications layer. This makes it easy for systems to migrate to USB 3.0.
USB 3.0 has also increased the amount of current that a downstream USB Device can draw from a traditional Host (e.g. PC). This limit is raised from USB 2.0’s 500mA to USB 3.0’s 900mA, which translates into an 80% increase in available power. Not only will this enable higher performance applications, but it also allows mobile handhelds to charge their batteries faster. The shortened charge time is invaluable for end users who are always on the go. For example, to fully charge a drained 1400mAh battery with an assumed 90% efficiency would take over 3 hours with a USB 2.0 Host, but only 1.5 hour with USB 3.0.
The Age of HD and 3D Multimedia
HD camcorders and video-capable mobile phones are becoming increasingly popular and video sharing applications like YouTube now support HD (1080p) formats. To store various formats of compressed and uncompressed HD video formats, we see a corresponding increase in storage densities. Higher storage densities also means the pipe needed to fill it needs to be faster. Users do not have the patience to wait for an hour to sideload video from their device to the PC for editing and sharing. USB 3.0 plays a key role in this new generation of high-definition content creation and consumption.
Figure 1: Video formats and storage requirements
With the value propositions described above, USB 3.0 can enable new usage models as well as improves on existing ones. Apart from the ability to sideload media content at 10x the speed of a USB 2.0 system, one of the early applications identified for USB 3.0 is content/code flashing during manufacturing. The cost to manufacture a mobile handheld device strongly correlates to the amount of time it needs to spend in the manufacturing line, and the most time consuming part of the process is flash programming and preloading content. The flashing process is often done by USB, and today, USB 2.0 is widely used in the production line. Not only will USB 3.0 flash phones at 10x the speed, it can also be used to flash multiple devices at the same time. Ultimately, USB 3.0 can significantly lower manufacturing cost.