Read retry operations where likelihood value assignments change sign at different read voltages for each read retry

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.