Best read reference voltage search of 3D NAND memory

A memory system, comprising:

• a semiconductor memory device;
• and
• a memory controller comprising circuitry configured to:
• determine a first best read offset of a first best read reference voltage with respect to a first default read reference voltage;
• determine an anchor read reference voltage having a same offset as the first best read offset with respect to a second default read reference voltage, wherein the first default read reference voltage and the second default read reference voltage are set for reading a page from a set of multi-level cells (MLCs) in the semiconductor memory device;
• determine a first scan range based on the anchor read reference voltage, wherein an upper limit of the first scan range is the anchor read reference voltage plus an upper limit offset, and a lower limit of the first scan range is the anchor read reference voltage plus a lower limit offset, the upper limit offset and the lower limit offset being a positive voltage value or a negative voltage value;
• and
• determine a second best read offset of a second best read reference voltage with respect to the second read reference voltage based on the first scan range.

A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause the processor to perform a method, the method comprising:

• determining a first best read offset of a first best read reference voltage with respect to a first default read reference voltage;
• determining an anchor read reference voltage having a same offset as the first best read offset with respect to a second default read reference voltage, wherein the first default read reference voltage and the second default read reference voltage are set for reading a page from a set of multi-level cells (MLCs) in a semiconductor memory device;
• determining a first scan range based on the anchor read reference voltage, wherein an upper limit of the first scan range is the anchor read reference voltage plus an upper limit offset, and a lower limit of the first scan range is the anchor read reference voltage plus a lower limit offset, the upper limit offset and the lower limit offset being a positive voltage value or a negative voltage value;
• and
• determining a second best read offset of a second best read reference voltage with respect to the second read reference voltage based on the first scan range.