A 0.54 pJ/b 20 Gb/s Ground-Referenced Single-Ended Short-Reach Serial Link in 28 nm CMOS for Advanced Packaging Applications

High-speed signaling over high density interconnect on organic package substrates or silicon interposers offers an attractive solution to the off-chip bandwidth limitation problem faced in modern digital systems. In this paper, we describe a signaling system co-designed with the interconnect to take advantage of the characteristics of this environment to enable a high-speed, low area, and low-power die to die link. Ground-Referenced Signaling (GRS) is a single-ended signaling system that eliminates the problems traditionally associated with single-ended design by using the ground plane as the reference and signaling above and below ground. This design employs a novel charge pump driver that additionally eliminates the issue of simultaneous switching noise with data independent current consumption. Silicon measurements from a test chip implementing two 16-lane links, with forwarded clocks, in a standard 28nm process demonstrate 20Gb/s operation at 0.54pJ/bit over 4.5mm organic substrate channels at a nominal 0.9V power supply voltage. Timing margins at the receiver are >0.3UI at a BER of <10^-12 . We estimate BER < 10^-25 at the eye center.