Far-end crosstalk cancellation using via stub for DDR4 memory channel

This paper presents a new methodology to cancel the far-end crosstalk in DDR4 memory channel. By utilizing the long via stub, the far end crosstalk is greatly reduced without increasing the routing area. To further demonstrate the crosstalk cancellation impacts on the memory channel margin, DDR4 DQ topology was simulated at the speed of 2133MT/s, 2400MT/s, and 2677MT/s, respectively. From the DDR4 channel simulation, we successfully demonstrated that the eye height and width at the data rates of 2677MT/s were improved by the amount of 30.03% and 22.84%, respectively, after adding the via stubs. The simulation also confirmed that the via stub does not affect the eye diagram at all when there is no any aggressor. It also demonstrates that, as the via-to-via spacing is decreased from 40mil to 25mil, the eye height and width at 2667MT/s are increased 11.12% and 10.82%, respectively. 12 layer test board is also implemented and the good correlation is achieved under 10GHz.