System and method for correcting errors in data using a compound code

摘要

Storage of digital data in non-volatile media such as NAND FLASH needs to take account of the errors in data retrieved from the memory. The error rate tends to increase with the number of write/erase cycles of a cell of memory and with the time that the data has been stored. To achieve a very low uncorrected bit error rate (UBER) a substantial amount of redundancy data needs to be stored for error correction purposes. A method and apparatus is disclosed where a first redundancy data is represented by a second redundancy data computed from the first redundancy data. The first redundancy data may not be stored and is reconstructed from the stored data using a same generation procedure as previously used. The reconstructed estimate of the first redundancy data is corrected by the second redundancy data, and is used to correct the underlying data.

主权项

1. An apparatus to correct data errors, comprising:
a processor configured to use an error correcting code (ECC); and a memory configured to store data, the data including ECC data; wherein the ECC is used by the processor to identify a number of error bits in the data read from the memory and to correct the identified error bits; a counter that stores the number of identified error bits by using the ECC; a first limit of error bits that can be corrected by using the ECC; a second limit of error bits that can be identified by using the ECC but cannot be corrected by using the ECC; wherein the processor is configured to invert the identified error bits identified by using the ECC when the ECC is unable to be used to correct the identified error bits; and wherein the processor is further configured to invert the error bits identified by using the ECC when the number of identified error bits is more than the first limit and less than the second limit; and subsequently, the ECC is used to correct the data with the inverted bits.