|
||||||||||||||||||||||||||||||||||||||||||
|
||||||||||||||||||||||||||||||||||||||||||
Faster imaging using SUPERSPEED USB 3.0 technology
Summary of new features and applicability of USB 3 as a camera interface*
Why is a new standard needed?
While USB 2 has been adequate up until now, the demand for faster data
transmission is ever increasing and this has resulted in the need for
further development of this ubiquitous standard.
The current generation of camera CMOS sensors delivers images with a resolution
of 10 megapixels – and even with a colour depth of 8 bits per pixel
(which is common for USB cameras) USB2 only just manages to transfer four
full frames-per-second. Sensors that can output data with a bit depth
of 10 or 12 bits take use 2 bytes per pixel and so this cuts the maximum
possible frame rate in half. Further trends including the interpolation
to colour data in the camera or simultaneous output of colour and monochrome
data increase the amount of data transferred and so put further pressure
on the bandwidth capability of the interface.
Features that have long been available in powerful GigE cameras were not
feasible in the USB world with its bandwidth of about 40 MB/sec. However,
deploying a GigE camera is not always possible and in embedded applications
where high resolution is required a fast USB3 connection can be especially
useful.
SuperSpeed USB (USB3) is not only interesting because of its higher transmission
speed, this revised and extended USB protocol allows for more efficient,
resource-friendly data transmission. By omitting polling and by supporting
the future use of DMA (Direct Memory Access) USB controllers, it will
be possible to retrieve image data from USB cameras with very little CPU
load.
What did the new standard aim to do?
The aim of the new standard was to improve on the fundamental limitations
of USB2 by:
** Increasing the data rate by a factor of about ten
to reach 5 Gigabits-per-second
** Maintaining and support the existing USB infrastructure
** Optimizing power management of connected devices
** Omitting the polling procedure used in the previous
USB protocol so that peripheral devices can send data on their own
| Essential differences between USB 2.0 and 3.0 | ||
USB 2.0 “Hi-Speed” |
USB 3.0 “SuperSpeed” |
|
| Bandwidth (usable) | 480 Mbps (about 40 MB/sec) | 5 Gbps (about 400 MB/sec) |
| Maximum power supply | 500 mA @ 5 V (2.5 W) | 900 mA @ 5 V (4.5 W) |
| Data transfer | Polling/host-controlled | Asynchronous/device controlled |
| Duplexing | Half-duplex: Unidirectional transfer | Dual simplex: Separate wire pairs for sending/receiving |
| Cable length using standard cables* | 5 metres | 3 metres |
| * A maximum cable length is not specified. These values indicate the estimated maximum length that is possible using standard cables. | ||
Note:
Version 3.0 is not intended to replace the existing standard 2.0.
USB 2.0, devices to date may have been declared as “USB 2.0 compatible”
even if they do not support the high data rate offered by Hi-Speed USB
(USB2) – provided that they otherwise comply with the standard.
In the case of USB 3.0, a device must actually support the SuperSpeed
data rate to be marked as “USB 3.0 compatible.”
| Summary of other differences between USB 2.0 and SuperHigh Speed USB 3.0 | ||
| Backward compatibility | Generally possible to plug USB 2.0 cables into USB 3.0 connectors – but the opposite is not always true | Page 4; section 3.1 |
| Power management | High-power mode: Instead of the previous 500 mA, a SuperSpeed
USB connection now provides up to 900 mA per device. New standby mode: USB 2.0 allows the host to put idle devices into a standby mode with lower power requirements (up to 100 mA). A standalone power management on the device side is not implemented. SuperSpeed USB3 allows the devices to change independently to a different operating mode - four are provided, applied progressively |
Page 6; sections 3.2.1 and 3.2.2. |
| Protocol/Polling/host controller | As with the previous USB standards, all devices connected to a USB3 bus share the available bandwidth based on a host-controlled protocol. Besides higher data transfer speeds, SuperSpeed USB provides new protocol level mechanisms which enable the devices to transfer large data volumes more efficiently. | Page 6; section 3.3 |
| Cables | For USB3, copper lines are still used as they are in USB2, but separate wire pairs transmit the signals in the sending and receiving directions resulting in a full-duplex-capable connection. In contrast to the construction of the USB2 cable, the wire pairs of USB3 must have an additional shield in order to increase the interference resistance of the high-frequency signals. | Page 6; section 3.4.1 |
| Connectors | The USB 3.0 specification defines new connector types
with added pins for the SuperSpeed lines. Detailed explanation and diagrams in White Paper |
Page; section 3.4.2 |
Applications
As well as being appropriate for use in industrial image processing,
the SuperSpeed USB will also be ideally suited for laboratory
or medical systems, where the strict requirements of industrial
environments with respect to cable lengths do not apply.
About iDS Imaging
With their uEye® camera series, IDS Imaging Development Systems GmbH offer a series of modern USB and GigE cameras for image processing in industrial and non-industrial environments.
CMOS and CCD sensors produced by renowned manufacturers provide resolutions from VGA to 10 megapixels and frame rates up to 100 full frames per second.
Using the extensive uEye® SDK software package that is available for free, all cameras, no matter whether they are equipped with a USB or GigE interface, can be integrated with image processing libraries or custom applications. Click to view the iDS range of cameras distributed by Adept Electronic Solutions.
*Summarised from iDS Imaging's white paper: USB 3.0 – Background Factors, New Features and Applicability as a Camera Interface. Click to download White Paper pdf document
Adept Electronic Solutions are "The Machine Vision and Imaging Specialists" and distributor of iDS Imaging Machine Vision products in Australia and New Zealand. To find out more about iDS Imaging or any machine vision product please email us at: adept@adept.net.au or call us at Perth (08) 92425411 / Sydney (02) 99792599 / Melbourne (03) 95555621 or use our online contact us page.
|
If you like this page, please recommend and share it. |
||
| More | ||
