Dynamic threshold schemes for multi-level non-volatile memories

In non-volatile memories, reading stored data is typically done through the use of predetermined fixed thresholds. However, due to problems commonly affecting such memories, including voltage drift, overwriting, and inter-cell coupling, fixed threshold usage often results in significant asymmetric errors. To combat these problems, the notion of dynamic thresholds was introduced and applied to the reading of binary sequences. In this paper, we explore the use of dynamic thresholds for multi-level cell (MLC) memories. We provide a general scheme to compute and apply dynamic thresholds and derive performance bounds. We show that the proposed scheme compares favorably with the best-possible thresholding scheme. Finally, we develop asymmetric limited magnitude error-correction codes tailored to take advantage of dynamic thresholds.