Determination of memory read reference and programming voltages
AssigneeSeagate Technology LLC
InventorsArvind Sridharan, Ara Patapoutian
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Abstract
Symmetrical or asymmetrical noise distributions for voltages corresponding to symbols that can be stored in multi-level memory cells (MLCs) of a memory device are used to determine read reference and/or programming voltages. The read reference voltages and/or programming voltages for the MLCs are jointly determined using the symmetrical distributions and a maximum likelihood estimation (MLE) and/or by determining at least one of the read reference voltages and the programming voltages using the asymmetrical distributions.
Claims20
A method of operating a memory device, comprising:
- using symmetrical or asymmetrical noise distributions for voltages corresponding to symbols that can be stored in multi-level memory cells (MLCs) of the memory device;
- determining at least one of read reference voltages and programming voltages for the MLCs including:
- jointly determining the read reference voltages and programming voltages using the symmetrical distributions and a maximum likelihood estimation (MLE);
- and
- determining at least one of the read reference voltages and the programming voltages using the asymmetrical distributions;
- and
- performing at least one of programming the MLCs using the programming voltages and reading the MLCs using the read reference voltages.
A method of operating a memory device, comprising:
- using noise distributions for voltages corresponding to symbols that can be stored in multi-level memory cells (MLCs) of the memory device, each noise distribution comprising a first noise distribution for voltages above a target signal value and a second noise distribution, different from the first noise distribution, for voltages below the target signal value;
- determining at least one of read reference voltages and programming voltages for the MLCs using the first and second noise distributions;
- and
- performing at least one of programming the MLCs using the programming voltages and reading the MLCs using the read reference voltages.
An apparatus, comprising:
- a controller capable of being coupled to a memory device, the controller configured to
- use symmetrical or asymmetrical noise distributions for symbols corresponding to voltage levels capable of being stored in multi-level memory cells (MLCs) of the memory device;
- and
- jointly determine read reference voltages and programming voltages for the MLCs using the symmetrical noise distributions and a maximum likelihood estimation or determine at least one of the read reference voltages and the programming voltages using the symmetrical or the asymmetrical distributions.
The apparatus of claim 15, wherein each of the asymmetrical noise distributions includes first and second noise distributions comprising at least one of:
- a first Gaussian noise distribution having a first standard deviation, σl, and a second the second Gaussian noise distribution function having a second standard deviation, σ2, where σ1≠σ2;
- a first triangular noise distribution having a first base, b1, and a second first triangular noise distribution having a second base, b2, where b1≠b2;
- and
- a first exponential noise distribution having a first rate of change, al and second exponential noise distribution having a second rate of change, α2, where α1≠α2.
The apparatus of claim 16, wherein:
- the MLCs are arranged as a physical page of the memory device, the physical page configured to store a least significant bit (LSB) page comprising LSBs of the MLCs and a most significant bit (MSB) page comprising MSBs of the MLCs in the physical page;
- and
- the controller is configured to determine at least one of the read reference voltages and programming voltages for the MLCs using the first and second noise distribution functions so that a bit error rate of the MSB page and a bit error rate of the LSB page are about equal.
Dependencies are inferred from the claim text.