High resolution analog storage eprom and flash eprom

Abstract

Circuits and processes write and read analog signals in non-volatile memory cells such as EPROM and flash EPROM cells. One read process determines a memory cell's threshold voltage by slowly ramping the control gate voltage and sensing when the cell conducts. Another read process slowly ramps the source voltage of a memory cell and determines the cell's threshold voltage from the drain voltage of the memory cell. Still another read process connects a cascoding device to a memory cell and biases the memory cell in the linear region while the threshold voltage of the memory cell is determined from a voltage across a load which carries a current that mirrors the current through the memory cell. Read processes disclosed for analog memory cells also apply to binary memory cells, multilevel digital memory cells, and other applications which require precise reading of threshold voltages.