Apparatuses and methods for setting a signal in variable resistance memory
An example of a method reads a spin torque transfer (STT) memory cell, and writes the STT memory cell using information obtained during the reading of the STT memory cell to set a pulse to write the STT memory cell. An example of an apparatus includes a STT memory cell and read/write circuitry coupled to the STT memory cell to determine a read current (I READ ) through the STT memory cell and to set a pulse to write the STT memory cell using I READ . Additional embodiments are disclosed.
1. An apparatus, comprising:
a data line;
an access device;
a magnetic tunnel junction (MTJ) cell coupled between the data line and the access device, wherein the access device is configured to control a cell current (I CELL ) flowing through the MTJ; and
a comparator configured to compare current flowing through the data line to a reference current set specifically for the cell, and to cause the data line to be deselected responsive to the current flowing through the data line being greater than or equal to the reference current.
2. The apparatus of claim 1 , further comprising a reference current calculator configured to calculate a generated reference current value using a sensed value of a current flowing through the MTJ during a read pulse.
3. The apparatus of claim 2 , further comprising a look-up table, wherein the reference current calculator is configured to calculate the generated reference current value using the sensed value and a value looked up in the look-up table.
4. The apparatus of claim 3 , wherein the access device comprises a transistor and wherein the apparatus is configured to apply a ramped potential on an access line coupled to a gate of the transistor, wherein the ramped potential increases the current flowing through the data line until the data line is deselected responsive to the current flowing through the data line being greater than or equal to the reference current.
5. The apparatus of claim 4 , further comprising a dummy data line configured to conduct current attributable to parasitic capacitance (I DUMMY ) on the dummy data line, and an I DUMMY current mirror coupled to the dummy line to mirror the I DUMMY , wherein a value of the reference current comprises the generated reference value offset by the value of I DUMMY .
6. The apparatus of claim 5 , further comprising:
a regulator coupled to the data line and to the dummy data line and configured to provide a regulated potential to the data line; and
a source, wherein the access device is coupled between the MTJ and the source.
7. The apparatus of claim 5 , further comprising read/write circuitry coupled to the data line and the access line, the read/write circuitry including:
a read/write pulse generator;
a sampler to sample a signal on the data line during the read pulse; and
the reference current calculator, wherein the reference current calculator is configured to calculate the generated reference current value based on the sampled signal on the data line.
8. The apparatus of claim 3 , wherein the looked up value is a function of data to be written into the memory cell.
9. The apparatus of claim 3 , wherein the looked up value is a function of a temperature.
10. The apparatus of claim 3 , wherein the looked up value is a function of a process corner.
11. The apparatus of claim 3 , wherein the looked up value is a function of a power supply voltage.
12. The apparatus of claim 3 , wherein the looked up value is a function of a topological location of the memory cell.
13. An apparatus, comprising:
a data line;
an access device;
a magnetic tunnel junction (MTJ) cell coupled between the data line and the access device, wherein the access device is configured to control a cell current (I CELL ) flowing through the MTJ; and
a comparator configured to compare current flowing through the data line to a reference current set specifically for the cell, and to cause the data line to be deselected responsive to the current flowing through the data line being greater than or equal to the reference current,
wherein the apparatus is configured to write the memory cell using a current ramp up to the reference current.
14. The apparatus of claim 13 , wherein the apparatus is configured to apply a ramp potential on an access line coupled to a gate of the access device, compare the cell current (I CELL ) flowing through a data line coupled to the cell to the reference current, and deselect the data line responsive to the I CELL being equal to or greater than the reference current.
15. The apparatus of claim 14 , wherein the comparator is configured to use a current mirror to compare the I CELL to the reference current.
16. The apparatus of claim 14 , wherein the apparatus is configured to compensate the reference current for data line capacitance.
17. The apparatus of claim 16 , further the apparatus includes a dummy data line, and the apparatus is configured to use the dummy line to compensate the reference current for the data line capacitance.
18. An apparatus, comprising:
a data line;
an access device;
a magnetic tunnel junction (MTJ) cell coupled between the data line and the access device, wherein the access device is configured to control a cell current (I CELL ) flowing through the MTJ;
a comparator configured to compare current flowing through the data line to a reference current set specifically for the cell, and to cause the data line to be deselected responsive to the current flowing through the data line being greater than or equal to the reference current, the comparator being configured to use a current mirror to compare the I CELL to the reference current; and
a dummy data line, and the apparatus is configured to use the dummy line to compensate the reference current for data line capacitance.
19. The apparatus of claim 18 , further comprising:
a reference current calculator configured to calculate a generated reference current value using a sensed value of a current flowing through the MTJ during a read pulse; and
a look-up table, wherein the reference current calculator is configured to calculate the generated reference current value using the sensed value and a value looked up in the look-up table.
20. The apparatus of claim 18 , wherein the access device comprises a transistor and wherein the apparatus is configured to apply a ramped potential on an access line coupled to a gate of the transistor, wherein the ramped potential increases the current flowing through the data line until the data line is deselected responsive to the current flowing through the data line being greater than or equal to the reference current.