Tech Primer
USB (Universal Serial Bus) is a common communication interface standard. USB supports hot-swap, which means it can be installed and removed without rebooting computers. This advantage makes it become the most popular connection standard for the consumer devices such as PCs, digital cameras, printers and media players. With the development of USB technology, its data transfer rate has increased from 1.5Mbit/s to 480Mbit/s. Additionally, the emergence of USB OTG (On-The-Go) technology makes it possible to realize communication between devices without any host, thus increasing the flexibility of USB applications.
However, the limit on transfer distance of USB narrows its applications: the maximum cable length of USB1.1 is 5 meter for full speed. Even the USB 2.0 permits several levels of USB hubs in a long chain, the distance can’t be longer than 100 meters. Fiber-optic transmission supports long distance at high speed with low loss. Therefore, the addition of a USB-to-fiber converter can extend the transmission distance of USB far beyond the limit of USB standard. This converter allows users control remote cameras, printers, scanners, storage devices, and other USB devices on a computer through optical fiber.
The USB-to-fiber converter is made up of USB physical interface, optical transceiver module and control module, as well as power supply and auxiliary circuit. USB interface converts USB differential signal into normal signal that can be processed by FPGA. Usually, a USB transceiver is used to achieve this function. Optical transceiver implements conversion between optical and electronic signals, and then sends out the converted signals. Control module is a FPGA chip used for packing the data from optical transceiver and unpacking the data from USB transceiver.
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