Comments on: NRZ is dead, but not everywhere | EDN https://www.epanorama.net/blog/2018/02/08/nrz-is-dead-but-not-everywhere-edn/ All about electronics and circuit design Sun, 19 Apr 2026 21:53:56 +0000 hourly 1 http://wordpress.org/?v=3.9.14 By: Tomi Engdahl https://www.epanorama.net/blog/2018/02/08/nrz-is-dead-but-not-everywhere-edn/comment-page-1/#comment-1581254 Thu, 08 Feb 2018 20:20:27 +0000 http://www.epanorama.net/newepa/?p=63192#comment-1581254 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

]]> By: Tomi Engdahl https://www.epanorama.net/blog/2018/02/08/nrz-is-dead-but-not-everywhere-edn/comment-page-1/#comment-1581253 Thu, 08 Feb 2018 20:19:42 +0000 http://www.epanorama.net/newepa/?p=63192#comment-1581253 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.

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