scaa059a1 AC-Coupling AC-coupling is used to change the common-mode voltage level when interconnecting different physical layers. A simple example is shown in Figure 1. VOH = 1.4 V VOL = 1 V VOH = Vterm + 0.2 V VOL = Vterm - 0.2 V Vterm Figure 1. AC-Coupling to Shift Common-Mode Voltage The capacitor in Figure 1 removes the dc component of the signal (common-mode voltage), while the ac component (voltage swing) is passed on. The resistor to Vterm in Figure 1 represents the biasing structure used to set the common-mode voltage on the receiver side of the ac-coupling capacitor. Throughout this document the biasing structure is either part of the internal biasing of the receiver or an external resistor pullup and/or pulldown network. In high-speed applications, ac-coupling is only recommended for……