https://www.edn.com/electronics-blogs/rowe-s-and-columns/4460291/NRZ-is-dead–but-not-everywhere
PAM4 modulation is everywhere.
“Five years ago, PAM4 was a concept”
“PAM4 is being deployed everywhere except in short-reach links.”
“DSP is enabling PAM4 optical channels”
PAM4 has won the battle in fiber-optic and other medium and long-reach applications.
2 Comments
Tomi Engdahl says:
The fundamentals of PAM4
https://www.edn.com/design/systems-design/4441212/The-fundamentals-of-PAM4?utm_source=Aspencore&utm_medium=EDN&utm_campaign=social
As our society’s hunger for data grows—not only more data, but more data delivered faster—older modulation schemes based on NRZ-type encoding grow increasingly inadequate.
For quite some time, NRZ-type encoding has been the mainstay modulation scheme for data transmission
We need a way to double the bit rate in the channel without doubling the required bandwidth, and that’s where PAM4 enters the picture. PAM4 takes the L (Least Significant Bit) signal, divides it in half, and adds it to the M (Most Significant Bit) signal. The result is four signal levels instead of two, with each signal level corresponding to a two-bit symbol.
The PAM4 signal looks like trace M+L/2
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.
Tomi Engdahl says:
Home> Test-and-measurement Design Center > How To Article
PAM4: A new measurement science
https://www.edn.com/design/test-and-measurement/4440925/PAM4–A-new-measurement-science