Storage system and method for decision-based memory read threshold calibration
A read threshold voltage can vary over time due to process variation, data retention issues, and program disturb conditions. A storage system can calibrate the read threshold voltage using data from a decoded codeword read from a wordline in the memory. For example, the storage system can use the data instead of syndrome weight in a bit error rate estimate scan (BES). As another example, the storage system can use the data to generate a bit error rate distribution, which can be used instead of a cell voltage distribution histogram. Using these techniques can help reduce latency and power consumption, increase throughput, and improve quality of service.
1. A storage system comprising:
a memory; and
a controller coupled to the memory and configured to:
decode a codeword read from a wordline in the memory;
determine that a bit error rate in the decoded codeword is above a threshold; and
in response to determining that the bit error rate in the decoded codeword is above the threshold:
designate the wordline as a candidate for read threshold calibration;
store data from the decoded codeword; and
cause read threshold calibration to be performed using the data from the decoded codeword instead of syndrome weight in a bit error rate estimate scan (BES).
2. The storage system of claim 1 , wherein the read threshold calibration is performed upon determining that the bit error rate is above the threshold.
3. The storage system of claim 1 , wherein the codeword is read during a sequential read operation.
4. The storage system of claim 1 , wherein the read threshold calibration is performed during a maintenance operation.
5. The storage system of claim 1 , wherein the data from the decoded codeword is stored in the controller.
6. The storage system of claim 1 , wherein the data from the decoded codeword is stored in a complementary metal-oxide-semiconductor (CMOS) bonded array (CBA).
7. The storage system of claim 1 , wherein the codeword is read during a maintenance operation.
8. The storage system of claim 1 , wherein the read threshold calibration is performed in the memory.
9. The storage system of claim 1 , wherein the read threshold calibration is performed in a complementary metal-oxide-semiconductor (CMOS) bonded array (CBA).
10. The storage system of claim 1 , wherein the memory comprises a three-dimensional memory.
11. In a storage system comprising a controller and a memory, a method comprising:
sending, from the controller to the memory, a decision-based valley search command for a wordline in the memory;
decoding a codeword read from the wordline;
passing data from the decoded codeword to latches in the memory;
reading the wordline;
generating a bit error rate distribution by performing an exclusive-or operation on data read from the wordline and the data from the decoded codeword; and
performing a read threshold calibration by finding minima in the bit error rate distribution.
12. The method of claim 11 , wherein the minima are found in the bit error rate distribution instead of a cell voltage distribution histogram.
13. The method of claim 11 , wherein the read threshold calibration is performed in the memory.
14. The method of claim 11 , wherein the read threshold calibration is performed in a complementary metal-oxide-semiconductor (CMOS) bonded array (CBA).
15. The method of claim 11 , wherein the data from the decoded codeword is stored in the controller.
16. The method of claim 11 , wherein the data from the decoded codeword is stored in a complementary metal-oxide-semiconductor (CMOS) bonded array (CBA).
17. The method of claim 11 , wherein the read threshold calibration comprises a valley search operation.
18. The method of claim 11 , further comprising sending a result of the read threshold calibration to a controller in the storage system.
19. A storage system comprising:
a memory;
means for decoding a codeword read from a wordline in the memory;
means for determining that a bit error rate in the decoded codeword is above a threshold; and
means for performing the following in response to determining that the bit error rate in the decoded codeword is above the threshold:
designating the wordline as a candidate for read threshold calibration;
storing data from the decoded codeword; and
causing read threshold calibration to be performed using the data from the decoded codeword instead of syndrome weight in a bit error rate estimate scan (BES).