Pulse amplitude modulation (PAM) is a signal encoding scheme where the data is represented by varying the amplitude of regular carrier pulses. In high-speed digital links like PCIe or Ethernet, PAM4 uses four distinct voltage levels to transmit two bits per symbol. This doubles the data rate over standard binary signaling without increasing the baud rate, though it shrinks the noise margin.
The new backplane design struggles with eye closure on the PAM4 signals due to excessive insertion loss.
Related terms
Modulate
To vary a property of a carrier signal in order to transmit information.
Eye pattern
An oscilloscope display that overlaps multiple digital signal transitions to evaluate signal integrity.
SerDes
A functional block that converts parallel data streams into a single high-speed serial stream and back.