The fundamentals of PAM4 - Part 1: Page 3 of 3

January 25, 2016 //By David Maliniak
The fundamentals of PAM4 - Part 1
David Maliniak, Teledyne LeCroy considers the fundamentals relating to PAM4 tehcnology.
period (or symbol period) is T. However, the opening of each of these three eyes is A/3. For bandwidth requirement, we roll back to 1/T. Thus, this signal, which moves 56 Gb/s, does so using the same amount of bandwidth as did the ML signal that moved 28 Gb/s. But with the SNR related to A/3, we find that our M+L/2 signal is three times m.

We have, in effect, traded off SNR for bandwidth. Many serial links are bandwidth-constrained, as it's difficult to move much more than 28 Gb/s over any length of copper. But when you have some SNR headroom, it may well pay off to consider a PAM4 modulation scheme.

Now that we've covered the basics of PAM4, we'll look next time at real-world application scenarios and consider the test requirements related to each one.

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