Multi-level signaling in high-density, high-speed electrical links

We present an analysis comparing multi-level signaling to standard NRZ signaling for module-to-module on-board electrical interconnects. To study on-board electrical performance, duobinary and PAM4 I/O models were created and compared to NRZ signaling in behavioral link-level simulations. A great variety of high-density, high-speed on-board module-to-module electrical links were analyzed, and specific interconnect channels were validated experimentally with programmable equalization transceiver chips communicating through a set of fabricated test structures. Link performance was measured with on-chip eye monitoring circuits and an oscilloscope. Simulation results show that NRZ signaling with FFE and DFE equalization offers the best electrical performance.