Abstract
In the present generation, internet with instant data access brings up the demands of high speed Ethernet. Development of 400G Ethernet is currently underway. There are two common coding schemes: non-return-to-zero (NRZ) and pulse-amplitude modulation 4-Level (PAM4). Because NRZ needs signaling in higher Nyquist frequency, which results in higher channel dependent loss, PAM4 has become a popular solution.
In this paper, we use 85 Ohm differential signal to explore a way to improve performance in the aspects of insertion loss, return loss and crosstalk for 112Gbps PAM4 application. A 12 layer substrate with low-loss dielectric of ABF-GL102 is used for the study. We scan the gap size of via pad which contributes the impedance discontinuity thus impacts signal integrity. Die bump and BGA pin assignments are the other two key factors in cause of crosstalk.
