State Dependent Sensing For Wordline Interference Correction
First Claim
1. An apparatus, comprising:
- a plurality of memory cells; and
a sense circuit configured to determine a condition of a first unselected memory cell adjacent to a selected memory cell prior to sensing for the selected memory cell;
a read circuit configured to perform for the selected memory cell a plurality of sense operations for a plurality of states, the plurality of sense operations for a particular state of the selected memory cell corresponding to different conditions of the first unselected memory cell; and
a compensation circuit configured to adjust a pass bias applied to the first unselected memory cell during each of the plurality of sense operations, the pass bias including a first pass voltage for a first condition of the first unselected memory cell during sensing for a first state and a second pass voltage for the first condition during sensing for a second state that is different from the first state, the first pass voltage is greater than the second pass voltage.
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Accused Products
Abstract
A variable compensation pass bias based on a state being sensed in non-volatile memory based is provided. Shifts in the apparent charge stored by a memory cell can occur because of coupling based on charge stored by adjacent cells. To account for the shift, compensations can be applied to an adjacent word line when reading based on the different possible conditions of an adjacent cell. The effects of coupling may be more pronounced for memory cells in lower states corresponding to lower threshold voltages. A compensation pass bias can be reduced as the state being sensed at a selected word line increases to account for the different effects. A compensation pass bias for an adjacent word line may be reduced with the application of larger read reference voltages to a selected word line. Other variations to a compensation pass bias are provided.
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Citations
20 Claims
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1. An apparatus, comprising:
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a plurality of memory cells; and a sense circuit configured to determine a condition of a first unselected memory cell adjacent to a selected memory cell prior to sensing for the selected memory cell; a read circuit configured to perform for the selected memory cell a plurality of sense operations for a plurality of states, the plurality of sense operations for a particular state of the selected memory cell corresponding to different conditions of the first unselected memory cell; and a compensation circuit configured to adjust a pass bias applied to the first unselected memory cell during each of the plurality of sense operations, the pass bias including a first pass voltage for a first condition of the first unselected memory cell during sensing for a first state and a second pass voltage for the first condition during sensing for a second state that is different from the first state, the first pass voltage is greater than the second pass voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus, comprising:
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a plurality of memory cells; a read circuit coupled to the plurality of memory cells, the read circuit reads a selected memory cell by using a first reference voltage for a first state and a second reference voltage for a second state, the first reference voltage is lower than the second reference voltage; and a compensation circuit coupled to the plurality of memory cells, the compensation circuit sequentially applies to a first unselected memory cell adjacent to the selected memory cell a first set of pass voltages for a plurality of sense operations for the first state and a second set of pass voltages for a plurality of sense operations for the second state, the first set of pass voltages includes a first pass voltage that is higher than each pass voltage of the second set. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A method, comprising:
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sensing a selected word line coupled to a plurality of memory cells for a plurality of states; sequentially applying a high pass bias and a low pass bias to an adjacent word line for sensing a first state based on direct look ahead values associated with adjacent memory cells of the adjacent word line; and reducing the high pass bias for sensing each subsequent state that has higher threshold voltages than the first state. - View Dependent Claims (16, 17, 18, 19)
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20. An apparatus, comprising:
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a plurality of memory cells; means for determining a condition of a first unselected memory cell adjacent to a selected memory cell prior to sensing the selected memory cell; means for reading the selected memory cell using a plurality of sense operations for a plurality of states, the plurality of sense operations for a particular state of the selected memory cell corresponding to different conditions of the first unselected memory cell; and means for adjusting a pass voltage applied to the first unselected memory cell during each of the plurality of sense operations, a first pass voltage for a first condition of the first unselected memory cell during sensing for a first state is greater than a second pass voltage for the first condition during sensing for a second state that is associated with higher threshold voltages than the first state.
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Specification