Dynamic detection for flash memory

Abstract

A method of decoding data stored in non-volatile memory in which each memory cell stores data by adopting one of a plurality of storage states. The method comprises using a threshold for determining a physical property of the memory cells to distinguish between at least two storage states, reading a data codeword from a plurality of the memory cells using the threshold and determining a bit error rate for the data codeword read using the threshold, repeatedly modifying said threshold and re-reading said data codeword using said modified threshold and determining a modified bit error rate for the data codeword read using the modified threshold, selecting the one of the modified thresholds for which the mutual information content between the stored data input and the read data is maximised based on the bit error rate for the data codeword read using the threshold and the bit error rate for the data codeword read using the modified threshold, determining a log likelihood ratio of a quantisation interval bounded by the threshold and the selected threshold generating soft decoded data by performing soft decoding of the data using said log likelihood ratio and outputting the soft decoding data.