Pipeline sensing using voltage storage elements to read non-volatile memory cells
View Patent ↗Various embodiments are generally directed to a method and apparatus for carrying out a pipeline sensing operation. In some embodiments, a read voltage from a first memory cell is stored in a voltage storage element (VSE) and compared to a reference voltage to identify a corresponding memory state of the first memory cell while a second read voltage from a second memory cell is stored in a second VSE. In other embodiments, bias currents are simultaneously applied to a first set of memory cells from the array while read voltages generated thereby are stored in a corresponding first set of VSEs. The read voltages are sequentially compared with at least one reference value to serially output a logical sequence corresponding to the memory states of the first set of memory cells while read voltages are stored for a second set of memory cells in a second set of VSEs.
1. A method comprising:
storing a read voltage from a first memory cell in a voltage storage element (VSE);
comparing the read voltage to a reference voltage to identify a corresponding memory state of the first memory cell; and
storing a second read voltage from a second memory cell in a second VSE during the comparing step to carry out a pipeline sensing operation upon the first and second memory cells.
2. The method of claim 1 , wherein the first storing step comprises applying a bias current to the first memory cell and coupling the VSE to the first memory cell to store the read voltage therefrom.
3. The method of claim 1 , wherein the comparing step comprises coupling the VSE to a first sense input of a sense amplifier, applying the reference voltage to a second sense input of the sense amplifier, and operating the sense amplifier to output a logical value indicative of the memory state of the first memory cell in relation to the first and second sense inputs.
4. The method of claim 1 , wherein a plurality of read voltages from a first set of memory cells are simultaneously stored in respective VSEs during the first storing step, and wherein said plurality of read voltages are sequentially sensed by a sense amplifier during the comparing step.
5. The method of claim 4 , wherein a second plurality of read voltages from a second set of memory cells are simultaneously stored in respective VSEs during the comparing step for subsequent sensing by said sense amplifier.
6. The method of claim 1 , wherein the reference voltage of the comparing step is supplied from an external reference source.
7. The method of claim 1 , wherein the reference voltage of the comparing step is stored in a third VSE.
8. The method of claim 1 , wherein the first and second VSEs each comprise a capacitor coupled to a bit line adjacent the respective memory cells.
9. The method of claim 1 , wherein the respective memory cells each comprise a magnetic tunneling junction (MTJ).
10. An apparatus comprising a memory array of semiconductor memory cells, and a control circuit which carries out a pipeline sense operation to read data from the array by simultaneously applying bias currents to a first set of memory cells from the array while storing read voltages generated thereby in a corresponding first set of voltage storage elements (VSEs), and then sequentially comparing the read voltages stored in said first set of VSEs with at least one reference value to serially output a logical sequence corresponding to the memory states of the first set of memory cells.
11. The apparatus of claim 10 , wherein the control circuit further operates to simultaneously apply bias currents to a second set of memory cells from the array and store read voltages generated thereby in a second set of VSEs during said sequential comparison of the read voltages stored in the first set of VSEs.
12. The apparatus of claim 11 , wherein the control circuit further operates to sequentially compare the read voltages stored in said second set of VSEs with at least one reference value to serially output a logical sequence corresponding to the memory states of the second set of memory cells.
13. The apparatus of claim 10 , wherein the control circuit comprises a sense amplifier which carries out said sequential comparison.
14. The apparatus of claim 10 , further comprising an external reference source which generates the at least one reference voltage.
15. The apparatus of claim 10 , wherein the at least one reference voltage is stored in a separate VSE.
16. The apparatus of claim 10 , wherein once the read voltage stored in a selected VSE is read, the control circuit further operates to transfer the read voltage from the VSE back to the bit line to assist in pre-bitline charging for a read operation on a different memory cell in the array.
17. The apparatus of claim 10 , wherein the respective memory cells each comprise a magnetic tunneling junction (MTJ).
18. A method comprising:
storing a read data value from a first memory cell in a first voltage storage element (VSE);
comparing the read data value to a reference value to identify a corresponding memory state of the first memory cell; and
storing a second read data value from a second memory cell in a second VSE during the comparing step to carry out a pipeline sensing operation upon the first and second memory cells.
19. The method of claim 18 , wherein the first and second VSEs are each characterized as a capacitor.
20. The method of claim 18 , wherein the respective memory cells each comprise a magnetic tunneling junction (MTJ).