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Spirent: PAM4: The New Modulation Standard for High-Speed Ethernet Serdes

2018-03-28  |  White Papers

 

PAM4: The New Modulation Standard for High-Speed Ethernet Serdes



Spirent PAM4 Unequalized vs Equalized Eye

Through two decades of evolution of Ethernet from Fast (100Mbps) to Gigabit Ethernet, then to 10GbE and 100GbE, more attention traditionally has been paid to block encoding, in which data bits are grouped into blocks from MAC to PHY, prior to being sent to the PHY. Line coding, performed by a serializer to prepare for transmission on a physical medium, has relied on a simple two-level code scheme called Non-Return to Zero (NRZ). In contrast to 10MbE’s use of direct Manchester encoding, all Ethernet rates of 100Mbps and higher required a simple voltage change to turn a logic level in code space into a signal for transmission over a medium.



NRZ was chosen for its efficiency over alternatives such as Return to Zero (RZ) and Encoded NRZ (ENRZ). Block codes often were chosen in the context of existing line codes – for example, the use of Manchester 8B/10B as the input block code for a serdes can maintain an accurate clock for NRZ. Nevertheless, NRZ was considered the obvious choice of line code for an Ethernet PHY design. To address NRZ requirements Spirent has the only quint speed series of products in the industry supporting 100/50/40/25/10GbE on the same test module. The flexibility to offer quint speed and support for NRZ across several ethernet speeds makes these test modules a popular choice.


Download the white-paper to continue reading.


Spirent PAM4 White Paper



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