Reading and Writing Flash Memory Using Delta Sigma Modulation

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Electrical Engineering


Electrical and Computer Engineering

Major Advisor

R. Jacob Baker


The state of a flash memory cell, whether it is a logic high or low, is determined by sensing the current through the cell.[1-3] Today's common design practice is to convert the current to a voltage and then use a differential amplifier or latch to determine whether the flash memory cell has been programmed or erased.[1-9] The differential amplifier or latch scheme for data sensing has a major shortcoming; it is sensitive to process variations and noise, demanding wide threshold voltage margins between the programmed and erased memory cell states. As a result, programming and erase times are long, and it is difficult to store more than one bit of data per memory cell.[10]

This thesis presents a new and improved sense amplifier design based on delta sigma modulation. Flash cell current is converted from analog to digital using a one-bit ΔΣ modulator. The delta sigma modulator cancels out noise and outputs an accurate measurement of average cell current. The data conversion circuitry is simple and less sensitive to noise and process variations, with less margin required between programmed and erased states. This new design approach leads to both more precise sensing and more economical memory chips.

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