Ethernet Opens Door to PAM4

By EETimes

June 18, 2015

The relatively new and complex PAM4 modulation scheme has been adopted for some aspects of the 400 Gbit/second Ethernet standard, setting a direction for new silicon development.

Modulation formats have been hotly debated over the last 6-12 months in the IEEE P802.3bs group setting a standard for for 400 Gigabit Ethernet (400GbE). Decisions to adopt PAM4 optical modulation schemes at the recent IEEE May meeting will have significant implications on the technology direction of the industry moving forward.

The 400 GbE project includes electrical interfaces to address chip-to-chip and chip-to-module applications as well as optical interfaces for 100 meter multimode fiber (MMF), 500m single-mode fiber (SMF), 2km SMF, and 10km SMF. Initially, the group was able to make fast decisions on some 16-wide interfaces for both electrical and optical MMF, adopting 16x25 Gbit/second with traditional NRZ modulation. These proposals strongly leverage the existing 25 Gbit/s signaling technology developed initially for the 100 GbE market which is seeing wide development and implementation today.

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