The 400 gigabit Ethernet (GE) standards define 4-level PAM (PAM4) multilevel signaling as a recommended modulation format to implement serial 400GE data center interfaces. This is an evolution from the two state non-return-to-zero (NRZ) modulation used in 100GE. PAM4 effectively doubles the data rate for a link bandwidth at the expense of reduced signal to noise ratio (SNR). You require new measurements to characterize impairments that were not an issue in previous NRZ designs. We can help you ensure accurate and repeatable results to accelerate the development of your PAM4 interface components and systems.

PAM4 Design and Simulation

Conventional signal impairments such as jitter, noise, channel loss, and intersymbol interference (ISI) behave differently in PAM4 designs. You need to perform electro-optical-electrical simulation of your 400GE designs to analyze the trade-offs between PAM4 and NRZ. We can help you save significant design time and minimize the effects of unexpected impairments.

Related Product

Circuit Design Software

PAM4 Transmitter and Receiver Test

PAM4 designs are far more susceptible to noise than NRZ designs, since four signal levels are packed into an amplitude swing of two. You must perform new transmitter (Tx) test measurements, such as signal to noise and distortion ratio (SNDR) and output jitter, to characterize your PAM4 transmitter devices. Forward error correction (FEC) is used to correct channel errors in PAM4 links and must be considered in PAM4 receiver (Rx) testing. We can help you address these new PAM4 physical layer test challenges to ensure compliance of your 400GE devices to industry standards.

PAM4 Channel characterization

As the data rate increases using PAM4 multi-level signaling in serial interconnects, the rise time of the data transition from logic zero level to one becomes faster. This faster rise time creates larger reflections at impedance discontinuities and degrades the signal quality at the end of the channel. As a result, you need to account for signal degradation due to physical layer components such as printed circuit board traces, connectors, cables, and integrated circuit (IC) packages when testing the performance of your PAM4 devices. We can help you characterize PAM4 channel effects to ensure the performance of your 400GE devices.

Further Reading

White Papers 2019.09.22

400G and Beyond in the Data Center

400G and Beyond in the Data Center

Data center operators will soon begin migrating their networks to 400 gigabit Ethernet (GE), and research and development into 800G and terabit speeds is under way. New breakthrough technologies, such as four-level pulse amplitude modulation (PAM4) signaling, are the solution to increasing network bandwidth while maintaining the data center footprint.

2019.09.22

Webinar

Addressing FEC Challenges on Your 400G Device

Addressing FEC Challenges on Your 400G Device

Forward error correction (FEC) is a necessity in the 400G world but introduces new test challenges. In this webcast, you will discover tools for debugging and solving your FEC test challenges.

Application Notes 2020.01.28

Error Analysis of PAM4 Signals

Error Analysis of PAM4 Signals

Increasing demands for a connected world continue to drive next generation solutions. Multilevel signaling formats, such as PAM4 are enabling technology to implement 400G. The switch from NRZ to PAM4 is revolutionary.

2020.01.28

Infographics 2018.10.10

400GE FEC Encode/Decode Processing

400GE FEC Encode/Decode Processing

The IEEE 802.3bs Task Group defines specifications for 400 Gigabit Ethernet (GE), where forward error correction (FEC) is mandatory. See how a 400GBASE-R Reed-Solomon RS-544 (KP4 FEC) encode/decode works in operation. Note that FEC encoding/decoding takes place at the binary level before the physical layer.

2018.10.10

Posters 2019.01.10

Ten Things You Need To Know About Data Center Innovation

Ten Things You Need To Know About Data Center Innovation

Emerging technologies such as 5G and IoT generate explosive amounts of data in the network and create new computing, storage, and performance demands in the data center. This poster outlines issues that data center operators need to consider.

2019.01.10

eBooks 2018.08.29

400GE is Revolutionary, Not Evolutionary

400GE is Revolutionary, Not Evolutionary

This ebook outlines the three key challenges that data center operators face as they transition from 100GE to 400GE, and provides detailed information on how to overcome these challenges to increase channel capacity, guarantee quality, and reduce test time and cost.

2018.08.29

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