Abstract: Methods and apparatus are provided for read retry operations that estimate written data based on syndrome weights. One method comprises reading a codeword from a memory multiple times using multiple read reference voltages; obtaining a syndrome weight for each of the readings of the codeword; identifying a given reading of the codeword having a substantially minimum syndrome weight; and estimating a written value of the codeword based on the given reading. Two cell voltage probability distributions of cell voltages are optionally calculated for each possible cell state of the memory, based on the estimated written value and plurality of readings of the codeword. The cell voltage probability distributions are used to (i) dynamically select log likelihood ratio values for a failing page, (ii) determine a read reference voltage that gives a desired log likelihood ratio value, or (iii) dynamically select log likelihood ratio values for the page populations associated with the distributions.

Abstract: Methods and apparatus are provided for read retry operations that estimate written data based on syndrome weights. One method comprises reading a codeword from a memory multiple times using multiple read reference voltages; obtaining a syndrome weight for each of the readings of the codeword; identifying a given reading of the codeword having a substantially minimum syndrome weight; and estimating a written value of the codeword based on the given reading. Two cell voltage probability distributions of cell voltages are optionally calculated for each possible cell state of the memory, based on the estimated written value and plurality of readings of the codeword. The cell voltage probability distributions are used to (i) dynamically select log likelihood ratio values for a failing page. (ii) determine a read reference voltage that gives a desired log likelihood ratio value, or (iii) dynamically select log likelihood ratio values for the page populations associated with the distributions.

Abstract: Read retry operations in a memory employ likelihood value assignments that change sign at different read voltages for a plurality of read retry operations. A method for multiple read retries of a memory comprises reading a codeword using a first read voltage to obtain a first read value; mapping the first read value to first likelihood values based on a first likelihood value assignment that changes sign substantially at the first read voltage; reading the codeword using a second read voltage to obtain a second read value, wherein the second read voltage is shifted from the first read voltage to compensate for an expected change in analog voltages; and mapping the second read value to second likelihood values based on a second likelihood value assignment, wherein the second likelihood value assignment changes sign substantially at the second read voltage. Read data is optionally generated using iterative decoding of the codeword based on the first likelihood values and/or the second likelihood values.

Abstract: Methods and apparatus are provided for read retry operations with read reference voltages ranked for different page populations of a memory. One method comprises obtaining a plurality of rankings of a plurality of read reference voltages for a plurality of page populations, wherein the rankings are based on a predefined performance metric; and reading a codeword from the memory a plurality of times, wherein each of the read operations uses a different one of the plurality of read reference voltages selected based on the rankings of the plurality of read reference voltages. The performance metric comprises, for example, a bit error rate, a bit polarity disparity, a substantially minimal syndrome weight and/or measures of an average system latency or a tail latency. The ranking is optionally based on a size of the page populations that had each of the ranked read reference voltages. Channel estimation is performed separately for each of the plurality of page populations.