Background reference positioning and local reference positioning using threshold voltage shift read
First Claim
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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Accused Products
Abstract
A nonvolatile memory system, a nonvolatile memory controller and a method for reducing latency of a memory controller are disclosed. Upon the occurrence of one or more of an endurance event, a retention timer event and a read disturb event at a closed block, a background reference positioning circuit performs background reads of representative pages of each page group of a closed block at 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. When a usage characteristic is determined to meet a usage characteristic threshold, a read circuit performs subsequent host-requested reads using a threshold voltage shift read instruction and reads of pages of the closed block are performed using the set of updated threshold voltage offset values corresponding to the page group of the page being read.
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Citations
20 Claims
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1. A nonvolatile memory controller comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A nonvolatile memory system comprising:
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a plurality of nonvolatile memory devices; a memory controller coupled to each of the nonvolatile memory devices, the memory controller configured to perform program operations and read operations on memory cells of the nonvolatile memory devices, the nonvolatile memory controller comprising; a status circuit configured to determine at least one usage characteristic of a nonvolatile memory device; 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 to be read, 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; and a read circuit coupled to the status circuit and to the background reference positioning circuit and configured to determine whether a 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 to be read, 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; and 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 a read disturb event has occurred each time that the number of reads for a particular closed block 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 a retention timer event has occurred each time that the closed block retention time reaches a threshold retention time. - View Dependent Claims (13, 14, 15, 16)
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17. A method for reducing latency of a nonvolatile memory controller comprising:
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identifying a plurality of page groups in each block of a nonvolatile memory device; performing background reads of representative pages of each page group of a block using 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 block to identify a set of updated threshold voltage offset values for each page group of the block; storing a local reference positioning table that includes a plurality of local reference positioning correction values; determining the order in which the plurality of local reference positioning correction values are to be applied to decode failures by determining whether a current number of program and erase cycles is near a next endurance threshold, determining whether a current read count is near a next read disturb threshold and determining whether a current retention time is near a next retention time threshold; based on the determined order, adding a first one of the local reference positioning correction values to each of the threshold voltage offset values in the set of updated threshold voltage offset values to obtain a first set of local reference positioning threshold voltage offset values; based on the determined order, adding a second one of the local reference positioning correction values to each of the threshold voltage offset values in the set of updated threshold voltage offset values to obtain a second set of local reference positioning threshold voltage offset values; based on the determined order, adding a third one of the local reference positioning correction values to each of the threshold voltage offset values in the set of updated threshold voltage offset values to obtain a third set of local reference positioning threshold voltage offset values; upon a first decode failure of a read of one of the representative pages, reading the one of the representative pages using the first set of local reference positioning threshold voltage offset values; upon a second decode failure of a read of the one of the representative pages, reading the one of the representative pages using the second set of local reference positioning threshold voltage offset values; and upon a third decode failure of a read of the one of the representative pages, reading the one of the representative pages using the third set of local reference positioning threshold voltage offset values. - View Dependent Claims (18, 19, 20)
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Specification