PAM-4 Eye Diagram Analysis and Its Monitoring Technique for Adaptive Pre-Emphasis for Multi-valued Data Transmissions

To address the ever-increasing demand for highseed interconnectivity between VLSI systems, the emerging IEEE 802.3bs and CEI-56G standards support a maximum data rate of 400Gb/s. A significant challenge at these data rates is overcoming the bit errors caused by intersymbol interference (ISI) in bandwidth-limited legacy channels. To reduce the bandwidth limitation by half, 4-level pulse amplitude modulation (PAM-4) signaling, which transmits two bits per symbol at a slower symbol rate, is employed. However, compared to that of binary non-return-to-zero (NRZ) signaling, PAM-4 signaling has four distinct levels and significantly more complex data transitions. In this paper, we explore the properties of PAM-4 eye diagrams to realize an adaptive pre-emphasis method for PAM-4 data transmissions. Moreover, we extend conventional eye opening monitoring techniques for NRZ signaling to PAM-4 signaling based on folding the histogram of the probability density function of each level.