ZERO-ONE BALANCE MANAGEMENT IN A SOLID-STATE DISK CONTROLLER

摘要

An SSD controller maintains a zero count and a one count, and/or in some embodiments a zero/one disparity count, for each read unit read from an SLC NVM (or the lower pages of an MLC). In an event that the read unit is uncorrectable in part due to a shift in the threshold voltage distributions away from their nominal distributions, the maintained counts enable a determination of a direction and/or a magnitude to adjust a read threshold to track the threshold voltage shift and restore the read data zero/one balance. In various embodiments, the adjusted read threshold is determined in a variety of described ways (counts, percentages) that are based on a number of described factors (determined threshold voltage distributions, known stored values, past NVM operating events). Extensions of the forgoing techniques are described for MLC memories.

主权项

1. A method, comprising:
scrambling data to be written to a portion of a non-volatile memory to produce scrambled data having a known statistical average number of zero bits and a known statistical average number of one bits; writing the scrambled data to the portion of the non-volatile memory; subsequent to the writing, reading the portion of the non-volatile memory; computing a disparity between a number of zero bits and a number of one bits in data read from the portion of the non-volatile memory; and determining a threshold voltage for a subsequent read of the non-volatile memory based at least in part on the disparity.