串行/解串器与铜质千兆连接
Copper cable data links have been evolving for many years. They have transitioned from very low data rate links to links running at multiple gigabits per second. With advances in serdes /gigabit transceiver technology (serializer and de-serializer), we are likely to see optical data link implementations relegated to its traditional optical networking arenas such as SONET, optical GbE and Fibre-Channel standards compliant applications. Copper cable-based data links are likely to replace optical implementations especially for short distance (<10 meters), high-speed links within proprietary-natured applications that tend to be non-standards based.
Historical Perspective:
For early gigabit link adopters, the lack of semiconductor physical layer device advances prevented copper-based gigabit data link implementation. At the time, optical was the only choice available for achieving gigabit serial link performance. Additionally, optical provided system designers with easy solutions to solve difficult problems, i.e., gigabit serial data communications. This solution came at the expense of higher implementation costs. The high cost of optical modules, fiber, test equipment and the hard-to-find expertise often made end-products more expensive to build, test and support. For these reasons, designers typically avoided optical serial implementations and used familiar methods such as wider-parallel copper buses running at slower, but more manageable line rates.
This brute-force method using numerous parallel links, however, had limitations. As the aggregate data rate moves higher, the designer must add more parallel lines in order to scale with the data rate. At some point, depending on the design, the large number of parallel links becomes unmanageable. In addition, these implementations demand valuable board space and consume vast amounts of power. Beyond a certain number of parallel links, designers also have to carefully mange the channel skew between the copper lines to maintain signal integrity. In today’s low-power, low-cost and small form- factor driven markets, optical and parallel gigabit copper solutions do not meet a designer’s requirements who is "pushing the envelope" in gigabit data rate applications.
The birth of Serdes
With no optimal solution available, systems designers began to demand answers from semiconductors vendors. At the time, few companies could make a solid business case for investing in the serialization/de-serialization (Serdes) and clock data recovery (CDR) technologies addressing these issues. However, with communications equipment, consumer electronics and industrial automation equipment explosion, applications requiring the serdes technology increased. Thus, semiconductor vendors could justify developing the serdes technology that would eventually foster the gigabit serdes. Even with the advent of the new gigabit serdes technology, many systems designers still questioned its "robustness" for transmitting gigabit-per-second payloads over copper media while maintaining target bit error rates (BER). Over time, as the engineering community understood the underlying concepts of CDR/PLL technology, gigabit serdes became a powerful tool.
