Comparative analysis of sensing schemes for multilevel non-volatile memories

Reading multilevel non-volatile memories is a very demanding task. Three sensing techniques (the parallel scheme, the binary-serial scheme and the mixed parallel-serial scheme) are considered here. Their operation principles are described and a comparative evaluation in terms of both access time and circuit complexity is carried out. The parallel approach is the most suitable for 4-level-cell memories (2 bit per cell). The mixed approach seems to be the most attractive for a large number of programmable levels (at least 16 levels per cell). In this case, the sensing area overhead is limited to less than 1% of the memory array while access time penalty is less than 50%.