A 100+ Meter 12 Gb/s/Lane Copper Cable Link Based on Clock-Forwarding

Active and passive copper cables for data rates exceeding 10 Gb/s are typically limited to less than 20 m. Optical fiber on the other hand offers superior performance for run length greater than 100 m, but is costly. Although 100 m copper link is demonstrated for 10GBASE-T, it utilizes complex symbols at a lower symbol rate across multiple signaling lanes and dissipates substantial power for DSP. In this paper, we propose a 12 Gbps/lane active cable link that extends copper cables ${>}$ 100 meters using low power and area clocked repeaters powered through the cable that could potentially be embedded in the cable. The quality of the clock in such repeaters is the key component in maintaining a clean signal propagation through long distances. This paper introduces an FIR phase filtering technique in combination with an MDLL to deliver a low jitter forward clock. The total jitter at the end of the cable is 4.4 ps RMS. The link has repeating distances of 8 and 16 meters for data and clock, respectively. Each repeater occupies 1 mm $^2$ of area in a 65-nm CMOS technology and dissipates 48 mW.