Determination of optimum threshold voltage to read data values in memory cells

摘要

An adaptive search scheme leads to threshold voltages that have lower bit error rates over initial values. An initial reference voltage is used and data is measured for set steps in voltage about the initial value sufficient to fit a polynomial curve. A minimum is used to determine the lowest bit error rate and corresponding optimum threshold voltage. This voltage is adopted as the new threshold voltage for reading the given data.

主权项

1. A method of operating a memory device, comprising:
determining respective bit error rates affecting memory cells of a solid-state, non-volatile memory for shifted threshold voltages used to read the data values in the memory cells, the shifted threshold voltages comprising an initial threshold voltage shifted by each of at least three voltage steps; applying a polynomial fit to the respective bit error rates as a function of the at least three voltage steps; determining, in response to the polynomial fit, an optimal bit error rate having an associated optimal threshold voltage; and applying the optimal threshold voltage to read the data values in the cells.