17. November 2020

400G Technology Info Graphics

High Speed Meets Bandwidth

Download now our 400G Technology Info Graphics and get an overview of the bandwidth of optical networks in time, interesting facts about optical transceiver modules and the advantages and technical specifications of PAM4. Ideal for looking up and printing.




400G Technology Info Graphics

Development of Bandwidth

The global demand for higher bandwidth and the constant increase regarding the needed volume of data requires new technologies in order to be able to follow this trend. Wheras 1G was the benchmark in 1999, 21 years later we have reached 400 times this data volume. In order to meet the requirements of applications such as 5G, Internet of Things (IoT) or cloud data centres, the new 400G technology is the next level to keep pace with this development.

ETH standard development until 2020

QSFP-DD – One Form Factor, Many Possible Uses

Among the 400G modules, the QSFP-DD has prevailed as the most popular form factor against the CFP8 and OSFP modules. It is characterized by its small size and above all by its low power consumption of a maximum of 15 Watts.
There are different variants to cover certain applications or to support the different types of fibres. The following table shows an overview of the different QSFP-DD modules and their different characteristics:

Overview of the different QSFP-DD modules

PAM4 - Pulse Amplitude Modulation

Due to the constantly growing demand for higher data rates the NRZ coding (Non Return to Zero) which has been the norm up to now reached its limits. Pulse Amplitude Modulation or in short PAM4, is therefore used in 400G modules.

Comparison of NRZ & PAM4

With the NRZ coding there are only two discrete amplitude values. The signal can be either “High” or “Low”. As a result, only one information bit can be transmitted per symbol. In contrast, with Pulse Amplitude Modulation, 4 discrete amplitude values can be used. This means that with PAM4 coding twice the number of information bits can be transmitted per time unit.

Comparison of the NRZ and PAM4 modulation

Signal Methods: Eye Diagram

By using Pulse Amplitude Modulation, the limits of Non Return to Zero coding can be overcome. As described, the decisive difference lies in the different amplitude values of the PAM4 coding. When looking at the signals of the two types of modulation on the oscilloscope, the difference can be made clear easily. This leads to the formation of the so-called eye patterns:

If we are looking at the signals of the NRZ Modulation, we see the characteristic formation of a single eye opening with 2 fixed amplitude values and one rising and one falling edge for each symbol.

In comparison, there are 3 characteristic features in PAM4 Eye openings with 4 discrete amplitude values. This allows 2 bits per symbol and thus twice the data rate per time unit.

Signal of NRZ Coding and PAM4 Coding
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Jörg Elsäßer
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