A Multi-Gigabit Transceiver (MGT) is a SerDes capable of operating at serial bit rates above 1 Gigabit/second. MGTs are used increasingly for data communications because they can run over longer distances, use fewer wires, and thus have lower costs than parallel interfaces with equivalent data throughput.
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Functions
Like other SerDes, the primary function of the MGT is to transmit parallel data as stream of serial bits, and convert the serial bits it receives to parallel data. The most basic performance metric of an MGT is its serial bit rate, or line rate, which is the number of serial bits it can transmit or receive per second. Although there is no strict rule, MGTs can typically run at line rates of 1 Gigabit/second or more. MGTs have become the 'data highways' for data processing systems that demand a high in/out raw data input and output (e.g. video processing applications). They are becoming very common on FPGA - such programmable logic devices being especially well fitted for parallel data processing algorithms.
Beyond serialization and deserialization, MGTs must incorporate a number of additional technologies to allow them to operate at high line rates. Some of these are listed below:
Signal integrity and jitter
Signal Integrity is critical for MGTs due to their high line rates. The quality of a given high-speed link is characterized by the Bit Error Ratio (BER) of the connection (the ratio of bits received in error to total bits received), and jitter.
BER and jitter are functions of the entire MGT connection, including the MGTs themselves, their serial lines, their reference clocks, their power supplies, and the digital systems that create and consume their parallel data. As a result, MGTs are often measured by how little jitter they transmit (Jitter Transfer/Jitter Generation), and how much jitter they can tolerate before their BER is too high (Jitter Tolerance). These measurements are commonly taken using a BERT, and analyzed using an Eye diagram.
Other considerations
Some other metrics for MGTs include:
Protocols that use MGTs
MGTs are used in the implementation of the following serial protocols: