Xilinx delivers 58G serdes and showcases a 112G test chip
Tuesday, July 24, 2018 at 8:56PM In the first of two articles, electrical input-output developments are discussed, focussing on Xilinx’s serialiser-deserialiser (serdes) work for its programmable logic chips. In Part 2, the IMEC nanoelectronics R&D centre’s latest silicon photonics work to enable optical I/O for chips is detailed.
Part 1: Electrical I/O
Processor and memory chips continue to scale exponentially. The electrical input-output (I/O) used to move data on and off such chips scales less well. Electrical interfaces are now transitioning from 28 gigabit-per-second (Gbps) to 56Gbps and work is already advanced to double the rate again to 112Gbps. But the question as to when electrical interfaces will reach their practical limit continues to be debated.
Gilles Garcia“Some two years ago, talking to the serdes community, they were seeing 100 gigabits as the first potential wall,” says Gilles Garcia, communications business lead at Xilinx. “In two years, a lot of work has happened and we can now demonstrate 112 gigabits [electrical interfaces].”
The challenge of moving to higher-speed serdes is that the reach shortens with each doubling of speed. The need to move greater amounts of data on- and off-chip also has power-consumption implications, especially with the extra circuitry needed when moving from non-return-to-zero signalling to the more complex 4-level pulse-amplitude modulation (PAM-4) scheme.
PAM-4 is already used for 56-gigabit electrical I/O for such applications as 400 Gigabit Ethernet optical modules and by the leading edge 12.8-terabit capacity switch chips. Having 112-gigabit serdes at least ensures one further generation of switch chips and optical modules but what comes after that is still to be determined. Even if more can be squeezed out of copper, the trace lengths will shorten and optics will continue to get closer to the chip.
