A Single-Loop SS-LMS Algorithm with Single-Ended Integrating DFE Receiver for Multi-Drop DRAM Interface

Abstract

A 3.8 Gb/s multi-drop single-ended integrating DFE (IDFE) receiver is implemented in a 0.18 um CMOS by using a single-loop LMS-algorithm to find the DFE coefficients automatically. Initially, a preamble input data pattern ('1101') is applied to the main IDFE circuit to determine the DFE coefficients, while a fixed input data pattern ('1111') is applied to the replica IDFE circuit. The difference between the outputs of the two IDFE circuits is used in the feedback loop to determine the DFE coefficients. The reference voltage (Vref) of preamplifier is generated inside chip by a Vref loop to reduce the effect of the external noise and the input offset voltage of preamplifier and IDFE circuits and also to track the mid-level of the input data swing in spite of process variations of TX chips. An integrating deskew scheme with a minimum overhead is introduced. 2-drop and 4-drop DRAM channels are tested. The maximum data rate was increased from 1.0 Gb/s to 2.6 Gb/s by DFE in the heavily loaded 4-drop interface, from 3.5 Gb/s to 3.8 Gb/s by DFE in the 2-drop interface.