Optimization of reference voltages in a non-volatile memory (NVM)

An apparatus comprising:

• a non-volatile memory (NVM) comprising semiconductor memory cells;
• a read circuit configured to read a programmed state of the memory cells responsive to application of a first of read voltages thereto;
• and
• a read voltage manager circuit configured to perform a first calibration operation to generate the first set of read voltages, accumulate the first set of read voltages into a history distribution comprising additional sets of read voltages obtained by the read voltage manager circuit from a time-ordered sequence of previously performed calibration operations, select a second set of read voltages based on the history distribution, and perform a second calibration operation upon the memory cells by incrementally adjusting the second set of read voltages to arrive at a third set of read voltages that provide an error rate that meets predetermined criteria, the read circuit thereafter using the third set of read voltages during a subsequent read operation after a conclusion of the calibration operation, the read voltage manager circuit appending the third set of read voltages to the history distribution for use during subsequent calibration operations.

A data storage device, comprising:

• a flash memory comprising flash memory cells arranged into garbage collection units (GCUs) each allocated and erased as a unit;
• a controller circuit configured to transfer user data sets between the GCUs and an external client device;
• and
• a read voltage manager circuit configured to accumulate read voltages applied by the controller circuit to successfully retrieve the user data sets into a population distribution, to select an initial calibration set of read voltages based on a shape of the population distribution, to perform a calibration operation upon a calibration group of the memory cells to derive a final calibration set of read voltages based on the initial calibration set of read voltages, to implement subsequent read operations using the final calibration set of read voltages, and to add the final calibration set of read voltages to the population distribution for use during a subsequent calibration operation, the population distribution comprising previously obtained calibration sets of read voltages generated from corresponding calibration operations upon the flash memory cells prior to generation of the final calibration set of read voltages.