High resolution analog storage EPROM and flash EPROM
First Claim
1. A method for reading a threshold voltage of a memory cell, comprising:
- connecting the memory cell, a cascoding device, and a first transistor in series between a voltage supply and ground, wherein the first transistor has a gate coupled to its drain;
biasing the memory cell in the linear region;
connecting a load and a second transistor in series between the voltage supply and ground, wherein a gate of the second transistor is connected to the gate of the first transistor so that current through the second transistor mirrors current through the first transistor; and
measuring at a first terminal of the load a voltage that indicates the threshold voltage of the memory cell.
3 Assignments
0 Petitions
Accused Products
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.
256 Citations
14 Claims
-
1. A method for reading a threshold voltage of a memory cell, comprising:
-
connecting the memory cell, a cascoding device, and a first transistor in series between a voltage supply and ground, wherein the first transistor has a gate coupled to its drain; biasing the memory cell in the linear region; connecting a load and a second transistor in series between the voltage supply and ground, wherein a gate of the second transistor is connected to the gate of the first transistor so that current through the second transistor mirrors current through the first transistor; and measuring at a first terminal of the load a voltage that indicates the threshold voltage of the memory cell. - View Dependent Claims (2, 3)
-
-
4. A method for reading a threshold voltage of a memory cell, comprising:
-
coupling a drain/source of the memory cell through a high impedance load to a reference voltage; applying a bias voltage to a control gate of the memory cell; ramping a voltage of a source/drain of the memory cell from the reference voltage to the bias voltage, wherein the ramping is done at a rate which initially operates the memory cell in the linear region and prevents channel hot electrons from disturbing the threshold voltage of the memory cell; and sensing the voltage at the drain/source to determine the threshold voltage of the memory cell. - View Dependent Claims (5, 6, 7)
-
-
8. A method for reading a threshold voltage of a memory cell, comprising:
-
ramping a control gate voltage of the memory cell between a first voltage and a second voltage; sensing when the memory cell transitions between non-conducting and conducting; and reading the control gate voltage when the memory cell transitions. - View Dependent Claims (9, 10, 11, 12, 13, 14)
-
Specification