4.2.3.1.1 PAM4 Signaling

PAM4 stands for Pulse Amplitude Modulation 4-levels. It is a signaling mechanism where 4 levels (2 bits) are encoded in same Unit Interval (UI) resulting in 3 eyes, as shown in § Figure 4-24.
翻译： PAM4代表4电平脉冲幅度调制。它是一种在同一单位间隔（UI）内编码4个电平（2个比特）的信令机制，从而产生3个眼图（Eyes），如图4-24所示。