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Background reference positioning and local reference positioning using threshold voltage shift read

  • US 10,157,677 B2
  • Filed: 07/20/2017
  • Issued: 12/18/2018
  • Est. Priority Date: 07/28/2016
  • Status: Active Grant
First Claim
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1. A nonvolatile memory controller comprising:

  • a status circuit configured to determine a usage characteristic of a nonvolatile memory device; and

    a background reference positioning circuit coupled to the status circuit and configured to perform, upon the occurrence of one or more of an endurance event, a retention timer event and a read disturb event at a closed block, background reads of representative pages of each page group of the closed block by sending threshold voltage shift read instructions to the nonvolatile memory device, the threshold voltage shift read instructions representative of offsets to each threshold voltage that is required for reading the representative pages of each page group of the closed block to identify a set of updated threshold voltage offset values for each page group of the closed block;

    a read circuit coupled to the status circuit and to the background reference positioning circuit and configured to determine whether the usage characteristic meets a usage characteristic threshold and when the usage characteristic is determined to meet the usage characteristic threshold, the read circuit is configured to perform all subsequent host-requested reads of pages of the closed block by sending threshold voltage shift read instructions to the nonvolatile memory device, the threshold voltage shift read instructions using the set of updated threshold voltage offset values corresponding to the page group of the page being read;

    wherein the status circuit is operable to determine a number of reads for each closed block of the nonvolatile memory device and the background reference positioning circuit is configured to determine that the read disturb event has occurred each time that the number of reads reaches a read disturb threshold; and

    wherein the status circuit is operable to determine closed block retention time for each closed block of the nonvolatile memory device, and wherein the background reference positioning circuit is configured to determine that the retention timer event has occurred when the closed block retention time reaches a threshold retention time.

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