400G PAM4 Testing

Fiber in 400G network

400G PAM4 Testing


Overcoming 400G measurement challenges

The rapid worldwide growth in cloud computing is driving massive demand for high-performance datacenter infrastructure. To keep pace with this relentless demand, developers are transitioning to 400G technologies enabling smaller, faster, lower cost-per-bit solutions.

There are several core technologies that are enabling 400G, including the use of higher order modulation and higher data rates up to 56 GBaud. This new modulation scheme provides four-level pulse amplitude modulation (PAM4), which transmits two bits per symbol, doubling the data rate compared to conventional NRZ.

PAM4 signals, having a lower signal-to-noise ratio and 1/3 of the amplitude of equivalent NRZ, require more advanced tools and features for successful validation.

Accelerate 400G product development

Developing 400G products is challenging. PAM4 signals require more sophisticated tools and features in order to evaluate them successfully. The DPO7OE series optical probe with a DPO70000 real-time scope provides superior features, trigger and debug capabilities to effectively troubleshoot and measure PAM4 signals up to 56 GBaud.

Tektronix Real-time solutions give you the ability to efficiently validate your technology advances and rapidly debug and validate 400G technology complementing the low-noise of a sampling oscilloscope.

Comparison of pulse amplitude modulation (PAM4) versus NRZ shows the increased complexity

The transition from NRZ to PAM4 has increased the complexity of testing optical signals.

Validate faster and increase yield

One of the greatest challenges is keeping test cost per device as low as possible while meeting required specifications. With PAM4 signals increasing the number of tests needed to conduct versus NRZ signals by a factor greater than 10, solutions providing measurements quickly for optimized tuning, with the lowest noise to maximize production yields are required.

The Tektronix sampling solutions include the DSA8300 and the 80C20/21 optical module to provide the highest bandwidth, highest sensitivity, and shortest test time when testing up to 56 GBaud. This solution enables you to effectively balance performance and testing costs.

TDECQ is one of the PAM4 measurements

The TDECQ measurement shows the testing complexity of a PAM4 signal.

Facing challenges in other wired communication applications?


Optical Bandwidth Requirements for NRZ and PAM4 Signaling

Until recently, both optical and electrical bandwidth produced similar results but this is no longer the case with the recent IEEE spec change. This paper clarifies these terms, mathematically shows how they are related, and provides the basis to understand and confidently calculate optical and electrical bandwidth for an optical channel.


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