Why move from NRZ to PAM-4 - Tutorial Series on the 400G / PAM-4 Challenges – Part 1

Blog Post created by stmichel Employee on Mar 14, 2017

PAM-4 PAM4 signal, eye diagram


The disruptive switch to PAM-4  (or PAM4) signaling used in 400 Gb Ethernet, 64G Fibre Channel and other standards comes along with new questions. It’s time to find answers with this new video tutorial series that provides quick insights.



This first tutorial starts with the basic question: why do data centers need PAM-4 at all? It also answers which design challenges and measurement requirements the PAM-4 adopters will have.

This video explains how PAM-4 enables higher data throughput compared to NRZ. It also delves into the implications on signal quality.

Throughout the next episodes in this tutorial series on PAM-4 (PAM4), the evolving optical and electrical standards using this modulation format will be reviewed. You’ll also find a practical example of typical Ethernet implementations. PAM-4 brings new test needs and test patterns as well as new test parameters such as transmitter and dispersion eye closure for PAM-4 (TDECQ) will be discussed in detail. Furthermore, transmitter and dispersion penalty (TDP) will be explained.

The tutorial series will also cover the additional complexity of clock recovery.

You will learn about the new key optical and electrical PAM-4 measurements for characterizing transmitter outputs. This includes retrieving parameters like the output waveform, the transmitter linearity, the signal to noise and distortion ratio (SNDR), symbol error ratio (BER and SER), eye symmetry mask width (ESMW) and different types of jitter.

Of course, new characterization measurements on PAM-4 receiver inputs will also be discussed. These comprise stressed input and input linearity tests.