State determination in resistance variable memory

An apparatus, comprising:

• an array of resistance variable memory cells;
• and
• a controller coupled to the array and configured to:
• apply an evaluation signal to a resistance variable memory cell in the array of resistance variable memory cells;
• sense three or more responses from the resistance variable memory cell responsive to the evaluation signal at three or more sample points;
• determine a first delta between a first pair of the three or more responses;
• determine a second delta between a second pair of the three or more responses;
• determine an absolute difference between the first delta and the second delta;
• and
• determine whether the resistance variable memory cell changes from an initial data state to a different data state during application of the evaluation signal responsive to the absolute delta.

A method for sensing a memory cell, comprising:

• applying an evaluation signal to a Spin Torque Transfer (STT) memory cell, the evaluation signal sufficient to cause the STT memory cell to switch from a first data state to a second data state at a threshold current, wherein the first data state is one of an anti-parallel state and a parallel state and the second data state is the other of the anti-parallel state and the parallel state;
• sensing responses of the STT memory cell to the evaluation signal by:
• sensing a first response at a first sample point;
• sensing a second response at a second sample point;
• and
• sensing a third response at a third sample point;
• determining a combined response as two times the second response less the first response and less the third response;
• determining that the STT memory cell was in the first data state if the combined response is greater than a predefined threshold;
• and
• determining that the STT memory cell was in the second data state if the combined response is less than the predefined threshold.

An apparatus, comprising:

• an array of resistance variable memory cells;
• and
• a controller coupled to the array and configured to determine a data state of a memory cell in the array of resistance variable memory cells by:
• applying an evaluation signal to the memory cell, the evaluation signal including a current that goes above a threshold current sufficient to cause the memory cell to switch from a first resistance to a second resistance;
• sensing a first response from the memory cell responsive to the evaluation signal at a first sample point;
• sensing a second response from the memory cell responsive to the evaluation signal at a second sample point;
• sensing a third response from the memory cell responsive to the evaluation signal at a third sample point;
• determining a first delta between the first response and the second response;
• determining a second delta between the second response and the third response;
• and
• determining whether the memory cell changes from the first resistance to the second resistance during application of the evaluation signal responsive to a difference between the first delta and the second delta.