8.3.6.1 De-Emphasis Equalization

De-emphasis of the differential output is provided as a form of continuous-time linear equalization that imposes a high-pass frequency response onto the output signal to compensate for frequency-dependent attenuation as the signal propagates through the channel to the receiver. In the time-domain, the de-emphasis appears as the bit transition transient followed by an immediate reduction in the differential amplitude, as shown in Figure 32. The characteristic appearance of the waveform changes with differential amplitude and the magnitude of de-emphasis applied. The serial lane rate determines the available period of time during which the de-emphasis transient settles. However, the lane rate does not affect the settling behavior of the applied de-emphasis. The de-emphasis value is measured as the ratio (in units of [dB]) between the peak voltage after the signal transition to the settled voltage value in one bit period. The data rate for this measurement is 1 Gb/s to allow settling of the de-emphasis transient.

Figure 32. De-emphasis of the Differential Output Signal