ERROR INDICATOR FROM ECC DECODER
The subject disclosure provides a method for generating a read-level error signal, comprising, correcting a plurality of bits read from a flash memory, determining a first error rate of a first error type corrected in the bits and determining a second error rate of a second error type corrected in the bits. In certain aspects, methods of the subject technology further provides steps for comparing the first error rate with the second error rate and generating a read-level error signal based on the comparison of the first error rate and the second error rate. A decoder and flash storage device are also provided.
1 . A method for generating a read-level error signal, comprising:
correcting a plurality of bits read from a flash memory;
determining a first error rate of a first error type corrected in the bits;
determining a second error rate of a second error type corrected in the bits;
comparing the first error rate with the second error rate; and
generating a read-level error signal based on the comparison of the first error rate and the second error rate.
2 . The method of claim 1 , wherein the first error type is a programmed logical ‘0’ incorrectly read as a logical ‘1.’
3 . The method of claim 1 , wherein the second error type is a programmed logical ‘1’ incorrectly read as a logical ‘0.’
4 . The method of claim 1 , further comprising:
comparing a number of corrected bits with a threshold, wherein the read-level error signal is generated if the number of corrected bits exceeds a threshold.
5 . The method of claim 1 , wherein the read-level error signal comprises a sign and a value, wherein the sign indicates a direction of the read-level error and the value indicates a degree of the read-level error.
6 . The method of claim 1 , wherein the plurality of bits are read from a LSB page in the flash memory.
7 . The method of claim 1 , wherein a number of the plurality of bits read from the flash memory having a logical value of ‘0’ is equal to a number of the plurality of bits read from the flash memory having a logical value of ‘1.’
8 . The method of claim 1 , further comprising:
adjusting a read level of the flash memory based on the read-level error signal.
9 . A decoder configured to generate a read-level error signal, the decoder configured to perform operations comprising:
decoding a code word read from a flash memory;
determining a number of bits corrected in the decoded code word;
determining an error type for each corrected bit; and
generating a read-level error signal based on the determined number of corrected bits and the determined error types.
10 . The decoder of claim 9 , further comprising:
comparing a number of corrected bits with a threshold, wherein the read-level error signal is generated if the number of corrected bits exceeds a threshold.
11 . The decoder of claim 9 , wherein the read-level error signal comprises a sign and a value, wherein the sign indicates a direction of the read-level error and the value indicates a degree of the read-level error.
12 . The decoder of claim 9 , wherein the code word is read from a LSB page in the flash memory.
13 . The decoder of claim 9 , wherein a number of code word bits read from the flash memory having a logical value of ‘0’ is equal to a number of code word bits read from the flash memory having a logical value of ‘1.’
14 . A flash storage device, comprising:
a flash memory array;
a controller configured to store encoded bits in the flash memory array and to read encoded bits from the flash memory array; and
a decoder coupled to the flash memory array and the controller, wherein the decoder is configured to perform operations for:
decoding a plurality of encoded bits, read from the flash memory array, to generate a plurality of decoded bits;
determining a first error rate and a second error rate based on the decoding of the encoded bits;
calculating an error bias based the first error rate and the second error rate; and
providing, to the controller, a read-level error signal indicating a read-level error in the flash memory based on the calculated error bias.
15 . The flash storage device of claim 14 , wherein the first error rate is based on a number of bits programmed as logical ‘0’ and incorrectly read as a logical ‘1.’
16 . The flash storage device of claim 14 , wherein the first error rate is based on a number of bits programmed as logical ‘1’ and incorrectly read as a logical ‘0.’
17 . The flash storage device of claim 14 , wherein providing the read-level error signal is based on whether a difference between the first error rate and the second error rate exceeds a threshold.
18 . The flash storage device of claim 14 , wherein the read-level error signal comprises a sign and a value, wherein the sign indicates a direction of the read-level error and the value indicates a degree of the read-level error.
19 . The flash storage device of claim 14 , wherein the plurality of encoded bits are read from a LSB page in the flash memory array.
20 . The flash storage device of claim 14 , wherein a number of encoded bits read from the flash memory array having a logical value of ‘0’ is equal to a number of encoded bits read from the flash memory having a logical value of ‘1.’
21 . The flash storage device of claim 14 , wherein the error bias is calculated based on a difference between a proportion of total errors for the first error rate and a proportion of total errors for the second error rate.