Today’s data center infrastructure is continuously optimized to address bandwidth capacity growth, power, reach and service differentiation. Higher transmission rates, more transmission lanes and new multi-level data formats like PAM-4 address the increased transmission bandwidth demand for the next generation data center interconnects. The latest revisions of #IEEE 802.3 bs and #OIF CEI-56G implementation agreements define PAM-4 and NRZ interfaces for electrical chip-to-chip, chip-to-module, backplane connections and #optical interfaces for up to 400 Gbit/s bandwidth. R&D and validation labs who need to characterize receivers for data center interconnects with PAM-4 or NRZ signal formats and data rates up to #64 Gbaud are facing new test challenges, such as tighter timing margins, channel loss, non-linearity, level interference and crosstalk effects, making test efficiency and accuracy essential. Channel loss and reflections in electrical interconnects like #chip-to-chip, #chip-to-module interfaces and #backplanes, create more and more challenges with increasing symbol rates for the design and test of transmitters and receivers. One commonly used technique to overcome the channel loss dilemma is the use of digital pre-distortions in the transmitter and equalization in the receivers.
Equalization in the receivers helps to reopen closed eyes by removing the intersymbol interference (ISI). The amount of ISI depends on the physical distance, the material of the PC board trace or cable, the symbol rate and the transmitted patterns. The ability to adjust the amount of equalization to the real channel conditions is therefore mandatory. The new #M8040A is the latest member of the modular AXIe based M8000 series of BER test solutions. It is a highly integrated BERT that supports #PAM-4 signals up to #64 Gbaud and NRZ signals up to #64 Gbit/s. The pattern generator module provides built-in de-emphasis, jitter injection and an optional second channel. Engineers and designers can select PAM-4 and NRZ in the user interface, eliminating the need for external combiners, cabling and deskew to provide PAM-4 signals. For best signal quality, remote heads reduce the distance to the device under test. The analyzer module provides true PAM-4 #error analysis in real-time for long PRBS and QPRBS patterns. The built-in and adjustable equalizer is a new option of the analyzer that helps to open closed eyes on the loopback channel. The analyzer now also supports symbol rates up to 64 Gbaud for NRZ signals. This ensures proofing even low bit error ratios and symbol error ratios with the required confidence. Users can control the M8040A from a graphical and remote control interface.
Adjustable equalization in the error analyzer helps to re-open closed eyes caused by the loss of the loopback channel. The image illustrates channel loss over frequency. Depending on NRZ or PAM-4 coding and the Nyquist frequency of the received pattern the maximum range of the available equalization can vary.
More information about the Keysight M8040A 64 GBaud BERT: