Program and verify word-line voltage regulator for multilevel Flash memories

This paper presents a word-line voltage generator for multilevel (ML) Flash memory programming. The required voltages are provided by a regulator supplied by an on-chip charge-pump voltage multiplier. A feedback loop including a digitally programmable resistive divider generates the staircase-shaped waveform needed for adequate ML programming accuracy as well as the read/verify voltage required for read and verify operations. A high-swing controlled-discharge circuit minimizes the settling time when switching from program to verify phases and vice versa. The same generator is used to provide the voltage required in read and in program mode, thus saving silicon area and minimizing current consumption. Experimental results of the proposed circuit integrated in a 4-level-cell 64-Mb NOR-type Flash memory are presented.