Measurement method for reading multi-level memory cell utilizing measurement time delay as the characteristic parameter for level definition

摘要

A method for operating a memory cell in which a variation of the characteristic parameter of the memory cell affects the effective resistance of the memory cell. The method includes measuring a first discharge time of a reference voltage through the memory cell, determining that the first discharge time is less than a minimum discharge time, adding a supplemental capacitor in parallel with the memory cell, adding including coupling the capacitor to the memory cell through a switch, measuring a second discharge time of the reference voltage through the memory cell, storing the second discharge time and determining the value stored in the memory cell based on the second discharge time. Measuring the first and second discharge times includes pre-charging an electronic circuit coupled to the memory cell, activating the memory cell so as to discharge the electronic circuit, at least partially through the memory cell, starting a time measurement when the memory cell is activated, and stopping the time measurement when the voltage level in the electronic circuit falls below a pre-defined reference voltage.