Methods, and circuits, are disclosed for operating a programmable memory device. One method embodiment includes storing a value as a state in a first memory cell and as a complementary state in a second memory cell. Such a method further includes determining the state of the first memory cell using a first self-biased sensing circuit and the complementary state of the second memory cell using a second self-biased sensing circuit, and comparing in a differential manner an indication of the state of the first memory cell to a reference indication of the complementary state of the second memory cell to determine the value.
1. A method for operating a programmable memory device, comprising:
storing a value as a state in a first memory cell and as a complementary state in a second memory cell;
determining the state of the first memory cell using a first self-biased sensing circuit and the complementary state of the second memory cell using a second self-biased sensing circuit; and
comparing in a differential manner an indication of the state of the first memory cell to a reference indication of the complementary state of the second memory cell to determine the value,
wherein the first memory cell is used in adjusting a reference voltage subsequently used in evaluating programmable states of memory cells of the memory device that do not have an associated complementarily-programmed memory cell.
2. The method of claim 1 , wherein the states are resistance states and wherein one of the first and second memory cells is programmed to have an amorphous programmable resistance state, and the other to have a crystalline programmable resistance state.
3. The method of claim 2 , wherein a resistance of the amorphous programmable resistance state is at least one order of magnitude different than a resistance of the crystalline programmable resistance state.
4. The method of claim 1 , wherein comparing includes driving a logic level signal corresponding to the value based on a differential processing of output signals from the sensing circuits.
5. The method of claim 1 , wherein the reference indication of the complementary state of the second memory cell is only used for comparing to the indication of the state of the first memory cell.
6. The method of claim 5 , wherein the reference indication of the complementary state of the second memory cell is ignored in comparisons involving indications of the state from other than the first memory cell.
7. The method of claim 1 , wherein determining the state of the first and second memory cells occurs before the reference voltage used in evaluating any memory cells of the memory device is adjusted.
8. The method of claim 7 , wherein the indication of the state of the first memory cell is a bias voltage, and the reference indication of the complementary state of the second memory cell is a complementary bias voltage, and the difference between the bias voltage and the reference voltage is greater than the difference between the bias voltage and the complementary bias voltage.
9. A method of operating a memory device, comprising:
programming a first group of programmable cells to states;
programming a second group of programmable cells to complementary states such that particular cells of the second group are programmed to complementary states compared to corresponding cells of the first group; and
sensing a cell of the first group and a corresponding cell of the second group with a pair of self-biased first stage sense circuits and a second stage sense circuit to determine a value stored in the cell of the first group and corresponding cell of the second group,
wherein the first one of the memory cells is operable as a device that uses the fuse in adjusting a reference voltage used in determining states of a number of other memory cells in the array.
10. The method of claim 9 , wherein the complementary states are resistance states, and wherein sensing the cell of the first group does not utilize an external reference voltage signal in determining the resistance state of the cell.
11. A semiconductor device, comprising:
an array of memory cells;
a first self-biased sensing circuit configured to determine a state stored in a first one of the memory cells;
a second self-biased sensing circuit configured to determine a complementary state stored in a second one of the memory cells; and
wherein an indication of the state of the first one of the memory cells to a reference indication of the complementary state of the second other one of the memory cells to determine a value,
wherein the first one of the memory cells is operable as a device that uses the fuse in adjusting a reference voltage used in determining states of a number of other memory cells in the array.
12. The semiconductor device of claim 11 , wherein the first one of the memory cells is operable as a fuse for the array of memory cells.
13. The semiconductor device of claim 11 , wherein the complementary state of the second other one of the memory cells is only used for comparing to the state of the first one of the memory cells.
14. The semiconductor device of claim 11 , wherein each of the self-biased sensing circuits include a bias current source arranged to provide negative feedback to a bias transistor, the bias transistor operable to clamp a memory cell bias voltage to a junction voltage of the bias transistor.
15. The semiconductor device of claim 11 , wherein the state stored in the first one of the memory cells and the state stored in the second other one of the memory cells are programmable resistance states.
16. The circuit of claim 15 , wherein the programmable resistance states are used to adjust a reference voltage used to determine programmable resistance states for other memory cells of the semiconductor device.
17. A programmable resistance memory device, comprising:
an array of memory cells including a first group of cells and a second group of complementary cells; and
sensing circuitry coupled to the array, including:
at least two first stage self-biased sense circuits;
one or more second stage sense circuits coupled to the at least two first stage self-biased sense circuits; and
wherein:
one of the at least two first stage sense circuits is selectively coupled to a cell of the first group;
another one of the at least two first stage sense circuits is selectively coupled to a complementary cell of the second group corresponding to the cell of the first group; and
the second stage sense circuits are configured to compare, in a differential manner, an indication of a state from the cell of the first group to a reference indication of a state from the complementary cell of the second group to determine a stored value,
wherein the at least two first stage self-biased sense circuits and the one or more second stage sense circuits are arranged to determine a reference voltage used in evaluating programmable states of the array of memory cells.
18. The programmable resistance memory device of claim 17 , wherein a cell of the first group stores information corresponding to a reference voltage signal, the sensing circuitry differentially determining the information from the cell with respect to the complementary cell and not with respect to the reference voltage signal.