PAM4 (4 Pulse Amplitude Modulation) is the modulation technology that fits for high-speed signal interconnection in the next-generation data center, which paves the way to 400G Ethernet in data centers.
PAM4 signaling refers to 4-level pulse-amplitude modulation, which is one kind of PAM modulation. For PAM4 modulation, one baud rate transmit two bits per transmission interval. The two bits can be either 00, 01, 10 or 11 as shown in the following figure.
PAM realizes more data on the existing fiber, which, in other words, suggests it is feasible to increase bandwidth by using advanced modulation PAM4 technology to increase the data rate without having to configure the data center with more fibers.
Actually, PAM4 signal was taken as the alternative modulation type when making the 100G Ethernet.
However, it was not put into use due to the higher cost and technique immaturity. PAM4 at 25Gbaud and 50Gbaud are in the market now for new intro data center applications.
