Sense amplifier local feedback to control bit line voltage
View Patent ↗Methods for precharging bit lines using closed-loop feedback are described. In one embodiment, a sense amplifier may include a bit line precharge circuit for setting a bit line to a read voltage prior to sensing a memory cell connected to the bit line. The bit line precharge circuit may include a first transistor in a source-follower configuration with a first gate and a first source node electrically coupled to the bit line. By applying local feedback from the first source node to the first gate, the bit line settling time may be reduced. In some cases, a first voltage applied to the first gate may be determined based on a first current drawn from the first bit line. Thus, the first voltage applied to the first gate may vary over time depending on the conductivity of a selected memory cell connected to the bit line.
1. A system, comprising:
a plurality of memory cells, the plurality of memory cells includes a first memory cell and a second memory cell; and
one or more managing circuits in communication with the plurality of memory cells, the one or more managing circuits configured to cause a first sense amplifier to be coupled to a first bit line, the first bit line is connected to the first memory cell, the first sense amplifier includes a first precharge circuit, the first precharge circuit includes a first transistor, the first transistor includes a first gate and a first source node, the first source node is connected to the first bit line, the one or more managing circuits configured to cause the first bit line to be precharged to a read voltage using the first precharge circuit, the first precharge circuit configured to set the first gate to a first bias voltage based on feedback from the first bit line, the one or more managing circuits configured to cause a second sense amplifier to be coupled to a second bit line, the second bit line is connected to the second memory cell, the second sense amplifier includes a second precharge circuit, the second precharge circuit includes a second transistor, the second transistor includes a second gate and a second source node, the second source node is connected to the second bit line, the one or more managing circuits configured to cause the second bit line to be precharged to the read voltage using the second precharge circuit, the second precharge circuit configured to set the second gate to a second bias voltage based on feedback from the second bit line, the second bias voltage is different from the first bias voltage, the one or more managing circuits configured to cause the first memory cell to be sensed using the first sense amplifier and the second memory cell to be sensed using the second sense amplifier.
2. The system of claim 1 , further comprising:
a replica circuit configured to generate a source bias voltage, the first precharge circuit configured to set the first gate to the first bias voltage based on feedback from the first bit line and the source bias voltage, the second precharge circuit configured to set the second gate to a second bias voltage based on feedback from the second bit line and the source bias voltage.
3. The system of claim 2 , wherein:
the source bias voltage is less than the read voltage, the first bias voltage is greater than the read voltage, the second bias voltage is greater than the read voltage.
4. The system of claim 1 , wherein:
the system includes a non-volatile memory including the first memory cell and the second memory cell, the non-volatile memory is monolithically formed in one or more physical levels of arrays of memory cells having an active area disposed above a silicon substrate, the system includes circuitry associated with the operation of the first memory cell and the second memory cell.
5. A method, comprising:
generating a source bias voltage;
coupling a first sensing circuit to a first bit line, the first bit line is connected to a first memory cell, the first sensing circuit includes a first transistor, the first transistor includes a first gate and a first source node, the first source node is coupled to the first bit line;
regulating the first bit line to a read voltage using the first transistor, the first gate is set to a first bias voltage based on the source bias voltage and feedback from the first source node;
coupling a second sensing circuit to the second bit line, the second bit line is connected to a second memory cell, the second sensing circuit includes a second transistor, the second transistor includes a second gate and a second source node, the second source node is coupled to the second bit line;
regulating the second bit line to the read voltage using the second transistor, the second gate is set to a second bias voltage different from the first bias voltage based on the source bias voltage and feedback from the second source node;
sensing a first current through the first memory cell using the first sensing circuit subsequent to the regulating the first bit line; and
sensing a second current through the second memory cell using the second sensing circuit subsequent to the regulating the second bit line.
6. The method of claim 5 , wherein:
the generating a source bias voltage includes generating the source bias voltage using a replica circuit that biases a dummy bit line connected to a dummy memory cell to the read voltage.
7. The method of claim 5 , wherein:
the generating a source bias voltage includes generating the source bias voltage using a temperature dependent reference, the source bias voltage generated by the temperature dependent reference is inversely proportional to temperature.
8. The method of claim 5 , wherein:
the source bias voltage is less than the read voltage, the first bias voltage is greater than the read voltage, the second bias voltage is greater than the read voltage.
9. The method of claim 5 , wherein:
the regulating the first bit line includes setting the first gate to the first bias voltage using a third transistor, the third transistor includes a third gate, the third gate is connected to the first source node.
10. A method, comprising:
connecting a first sense amplifier to a first bit line, the first bit line is connected to a first memory cell, the first sense amplifier includes a first precharge circuit, the first precharge circuit includes a first transistor, the first transistor includes a first gate and a first source node, the first source node is connected to the first bit line;
precharging the first bit line to a first voltage using the first precharge circuit, the precharging the first bit line includes setting the first gate to a first bias voltage based on feedback from the first bit line;
connecting a second sense amplifier to a second bit line, the second bit line is connected to a second memory cell, the second sense amplifier includes a second precharge circuit, the second precharge circuit includes a second transistor, the second transistor includes a second gate and a second source node, the second source node is connected to the second bit line;
precharging the second bit line to the first voltage using the second precharge circuit, the precharging the second bit line includes setting the second gate to a second bias voltage based on feedback from the second bit line, the second bias voltage is different from the first bias voltage;
sensing the first memory cell using the first sense amplifier subsequent to the precharging the first bit line; and
sensing the second memory cell using the second sense amplifier subsequent to the precharging the second bit line.
11. The method of claim 10 , further comprising:
generating a source bias voltage, the precharging the first bit line includes setting the first gate to the first bias voltage based on feedback from the first bit line and the source bias voltage, the precharging the second bit line includes setting the second gate to the second bias voltage based on feedback from the second bit line and the source bias voltage.
12. The method of claim 11 , wherein:
the generating a source bias voltage includes generating the source bias voltage using a replica circuit that biases a dummy bit line connected to a dummy memory cell to the read voltage.
13. The method of claim 11 , wherein:
the first voltage comprises a read voltage.
14. The method of claim 13 , wherein:
the source bias voltage is less than the read voltage.
15. The method of claim 13 , wherein:
the first bias voltage is greater than the read voltage and the second bias voltage is greater than the read voltage.
16. The method of claim 10 , wherein:
the precharging the second bit line is performed while the first bit line is being precharged to the first voltage.
17. The method of claim 10 , wherein:
the precharging the first bit line includes setting the first gate to the first bias voltage using a third transistor, the third transistor includes a third gate, the third gate is connected to the first source node.
18. The method of claim 11 , wherein:
the generating a source bias voltage includes generating the source bias voltage such that the first precharge circuit precharges the first bit line to the first voltage over a range of temperatures.
19. The method of claim 10 , wherein:
the first memory cell is part of a monolithic three-dimensional memory array, the monolithic three-dimensional memory array includes the first memory cell and a third memory cell, the first memory cell is located above the third memory cell, the third memory cell is located above a substrate, the first memory cell and the third memory cell are formed above the substrate without any intervening substrates between the first memory cell and the third memory cell.
20. The method of claim 10 , wherein:
the first memory cell is part of a non-volatile memory, the non-volatile memory is monolithically formed in one or more physical levels of arrays of memory cells having an active area disposed above a silicon substrate.