4-Slot, 8-Drop Impedance-Matched Bidirectional Multidrop DQ Bus With a 4.8-Gb/s Memory Controller Transceiver

Abstract

In this paper, we introduce an impedance-matched bidirectional multidrop (IMBM) DQ bus, together with a 4.8-Gb/s transceiver for a memory controller that supports this bus. Reflective ISI is eliminated at each stub of the IMBM DQ bus by resistive unidirectional impedance matching. A prototype memory controller transceiver is designed and fabricated in a 0.13- $\mu{\rm m}$ CMOS process and operates with a 1.2-V supply voltage. Its effectiveness is shown on various multidrop channel configurations. At 4.8 Gb/s, this transceiver with a 4-slot, 8-drop IMBM DQ bus has an eye opening of 0.39 UI in TX mode and 0.58 UI in RX mode, at a threshold of $10^{-9}$ BER, whereas a comparable transceiver with a conventional 4-slot, 8-drop stub series terminated logic has no timing margin under the same test conditions. Our transceiver consumes 14.25 mW/Gb/s per DQ in TX mode, and 13.69 mW/Gb/s per DQ in RX mode.