A 16 Gb/s/Link, 64 GB/s Bidirectional Asymmetric Memory Interface

This paper describes a bidirectional, differential, 16 Gb/s per link memory interface that includes a Controller and an emulated DRAM physical interface (PHY) designed in 65 nm CMOS. To achieve high data rate, the interface employs the following technology ingredients: asymmetric equalization, asymmetric timing calibration, asymmetric link margining, inductor based (LC) PLLs, multi-phase error correction, and a data dependent regulator. At 16 Gb/s, this interface achieves a unit-interval to inverter FO4 ratio of 2.8 (Controller) and 1.4 (DRAM) and operates in a channel with 15 dB loss at Nyquist. Under such bandwidth limitations on and off chip, the Controller and DRAM PHYs consume 13 mW/Gb/s and 8 mW/Gb/s, respectively. Using PRBS 2$^{11}-$1, the link achieves a timing margin of 0.19 UI at a BER of 1e-12 for both read and write operations.