Memory sense amplifiers and memory verification methods
Memory sense amplifiers and memory verification methods are described. According to one aspect, a memory sense amplifier includes a first input coupled with a memory element of a memory cell, wherein the memory element has different memory states at different moments in time, a second input configured to receive a reference signal, modification circuitry configured to provide a data signal at the first input from the memory element having a plurality of different voltages corresponding to respective ones of different memory states of the memory cell at the different moments in time, and comparison circuitry coupled with the modification circuitry and configured to compare the data signal and the reference signal at the different moments in time and to provide an output signal indicative of the memory state of the memory cell at the different moments in time as a result of the comparison to implement a plurality of verify operations of the memory states of the memory cell at the different moments in time.
1. A memory sense amplifier comprising:
a first input coupled with a memory element of a memory cell, wherein the memory element has different memory states at different moments in time;
a second input configured to receive a reference signal;
modification circuitry configured to provide a data signal at the first input from the memory element having a plurality of different voltages corresponding to respective ones of the different memory states of the memory element at the different moments in time, wherein the modification circuitry comprises a plurality of transistors individually coupled with one of the first and the second inputs;
supply circuitry configured to provide different bias signals to the transistors, the different bias signals corresponding to the different memory states of the memory element to be verified at the different moments in time; and
comparison circuitry coupled with the modification circuitry and configured to compare the data signal and the reference signal at the different moments in time and to provide an output signal indicative of the memory states of the memory element at the different moments in time as a result of the comparison to implement a plurality of verify operations of the memory states of the memory element at the different moments in time.
2. The amplifier of claim 1 wherein the modification circuitry is configured to provide the reference signal having a plurality of different voltages corresponding to respective ones of the different memory states of the memory element at the different moments in time.
3. The amplifier of claim 1 wherein the transistors comprise parallel cascode transistors and the comparison circuitry comprises a current mirror.
4. A memory sense amplifier comprising:
a first input coupled with a memory element of a memory cell, wherein the memory element has different memory states at different moments in time:
a second input configured to receive a reference signal;
modification circuitry configured to provide a data signal at the first input from the memory element having a plurality of different voltages corresponding to respective ones of the different memory states of the memory element at the different moments in time;
comparison circuitry coupled with the modification circuitry and configured to compare the data signal and the reference signal at the different moments in time and to provide an output signal indicative of the memory states of the memory element at the different moments in time as a result of the comparison to implement a plurality of verify operations of the memory states of the memory element at the different moments in time; and
wherein the modification circuitry comprises parallel cascode transistors individually coupled with one of the first and second inputs, and further comprising supply circuitry configured to provide different voltage biases to a gate of one of the cascode transistors to provide the data signal having the different voltages.
5. A memory sense amplifier comprising:
a first input coupled with a memory element of a memory cell, wherein the memory element has different memory states at different moments in time;
a second input configured to receive a reference signal;
modification circuitry configured to provide a data signal at the first input from the memory element having a plurality of different voltages corresponding to respective ones of the different memory states of the memory element at the different moments in time;
comparison circuitry coupled with the modification circuitry and configured to compare the data signal and the reference signal at the different moments in time and to provide an output signal indicative of the memory states of the memory element at the different moments in time as a result of the comparison to implement a plurality of verify operations of the memory states of the memory element at the different moments in time; and
wherein the modification circuitry comprises parallel cascode transistors individually coupled with one of the first and second inputs, and further comprising supply circuitry configured to provide a first voltage bias to one of the cascode transistors corresponding to a first of the different memory states and to provide a second voltage bias to the one of the cascode transistors corresponding to a second of the different memory states.
6. The amplifier of claim 5 wherein the memory element has an increased electrical resistance in the first memory state compared with the second memory state, and the first voltage bias is greater than the second voltage bias.
7. The amplifier of claim 1 further comprising a control circuit configured to determine a plurality of target memory states to which the memory cell is to be programmed to at the different moments in time, and to use the determined target memory states to control the provision of the data signal having the different voltages at the different moments in time.
8. The amplifier of claim 1 further comprising reference circuitry configured to provide the reference signal comprising different characteristics corresponding to the different memory states of the memory element at the different moments in time.
9. The amplifier of claim 1 further comprising equalization and pre-charge circuitry configured to equalize and pre-charge the memory sense amplifier for different lengths of time corresponding to verification of the different memory states of the memory element.
10. A memory sense amplifier comprising:
a cascode transistor configured to define a voltage of a data signal from a memory cell; and
supply circuitry configured to provide a first voltage bias to a gate of the cascode transistor corresponding to a first of a plurality of memory states of the memory cell to be verified at a first moment in time and a second voltage bias to the gate of the cascode transistor corresponding to a second of the memory states to be verified at a second moment in time.
11. The amplifier of claim 10 wherein the cascode transistor provides the data signal at a first voltage as a result of the provision of the first voltage bias and provides the data signal at a second voltage as a result of the provision of the second voltage bias, and wherein the first and second voltages are different.
12. The amplifier of claim 11 further comprising a current mirror configured to compare the voltage signal with a reference signal at the first and second moments in time and to provide an output signal indicative of the memory state of the memory cell at the different moments in time as a result of the comparison.
13. The amplifier of claim 10 wherein the memory cell has an increased electrical resistance in the first memory state, and the first voltage bias is greater than the second voltage bias.
14. The amplifier of claim 10 further comprising a control circuit configured to determine the first and the second memory states of the memory cell to be verified at the first and second moments in time, and to use the determined first and second memory states to control the provision of the first and second voltage biases to the gate of the cascode transistor at the first and second moments in time.
15. A memory verification method comprising:
accessing a plurality of target data values indicative of a plurality of memory states of the memory cell at different moments in time;
accessing a data signal from the memory cell at the different moments in time;
modifying the data signal differently corresponding to respective ones of the different memory states of the memory cell at the different moments in time; and
using the modified data signal, verifying the memory states of the memory cell at the different moments in time.
16. The method of claim 15 wherein the modifying comprises providing the data signal having different voltages at the different moments in time corresponding to the different target data values.
17. The method of claim 16 wherein the modifying comprises modifying using a cascode transistor.
18. The method of claim 17 wherein the modifying comprises applying different bias voltages to a gate of the cascode transistor corresponding to the different memory states.
19. The method of claim 16 wherein the data signal has a smaller current corresponding to a first of the memory states of the memory cell compared with a second of the memory states of the memory cell, and wherein the modifying comprises modifying the data signal to an increased voltage corresponding to the first of the memory states compared with the second of the memory states of the memory cell.
20. The method of claim 19 wherein the memory cell has different electrical resistances corresponding to the different memory states including an increased electrical resistance in the first of the memory states compared with the second of the memory states.
21. The method of claim 16 wherein the verifying comprises:
comparing the modified data signal to a reference signal; and
as a result of the comparing, providing an output signal indicative of the memory states of the memory cell at the different moments in time.
22. The method of claim 21 further comprising, before the comparing, providing the reference signal having different voltages at the different moments in time corresponding to the different target data values.
23. The method of claim 15 wherein the modifying comprises modifying using a sense amplifier, and further comprising, before the verifying, equalizing and pre-charging the sense amplifier for different lengths of time corresponding to the different memory states of the memory cell.
24. A memory verification method comprising:
accessing one of a plurality of target data values to be written to a memory cell;
attempting to write the one target data value to the memory cell; and
using the one target data value, performing a verification operation of a memory state of the memory cell comprising:
accessing a data signal from the memory cell;
selecting one of a plurality of modifications of the data signal corresponding to the one target data value;
converting the data signal using the one modification; and
using the modified data signal, determining whether the memory state of the memory cell corresponds to the one target data value.
25. The method of claim 24 wherein the plurality of modifications comprise providing the data signal at different voltages.
26. The method of claim 24 wherein the converting comprises converting the data signal using a cascode transistor.
27. The method of claim 26 wherein the converting comprises applying different bias voltages to a gate of the cascode transistor corresponding to different ones of the target data values.
28. The method of claim 26 wherein the determining comprises comparing the modified data signal to a reference signal using a current mirror.
29. The method of claim 28 further comprising, using the one target data value, selecting the reference signal from a plurality of reference signals.
30. The method of claim 28 further comprising, using the one target data value, selecting one of a plurality of different configurations of the current mirror.