A 128Gb/s PAM-4 Transmitter with Edge-Boosting Pulse Generator and Pre-Emphasis Asymmetric Fractional-Spaced FFE in 28nm CMOS

The demand for ever-increasing throughput has impelled the development of wireline TXs operating at higher data rates. In recent years, TXs have adopted the PAM-4 signaling and achieved data rates of more than 100Gb/s [2]–[6]. PAM-4 demonstrates twice the bandwidth efficiency compared to NRZ. However, due to the different edge-transition times between the middle and top/bottom eyes, PAM-4 eyes exhibit unequal switching jitter (SWJ), leading to a decrease in the horizontal eye-opening and a deterioration of signal integrity. The UI-spaced FFE used in TXs only provides loss compensation at the Nyquist frequency, making it incapable of handling SWJ in PAM-4 eyes. The fractional-spaced FFE (FS-FFE) provides an extended compensation range beyond the Nyquist frequency and reduces the SWJ in PAM-4 eyes [2], but it is unable to handle the unequal SWJ in PAM-4 eyes.