Method and apparatus for low voltage write in a static random access memory
View Patent ↗An integrated circuit memory includes a plurality of memory cells, where each of the plurality of memory cells comprises a first storage node and a second storage node. Each of the plurality of memory cells comprises a transistor coupled between the first and second storage nodes and responsive to an equalization signal. An equalization control circuit provides the equalization signal to selected memory cells of the plurality of memory cells. The equalization control circuit is for equalizing a voltage between the first and second storage nodes to enable to a write operation of the selected memory cells. During the write operation a data signal is provided to a first bit line that swings between a logic high voltage equal to a power supply voltage and a logic low voltage equal to ground potential. The transistor and the equalization control circuit enables reliable memory operation at low power supply voltages.
1. A method for writing to a memory cell, the memory cell having a first storage node and a second storage node, the first storage node coupled to a first bit line and the second storage node coupled to a second bit line, the method comprising:
providing a power supply voltage to the memory cell;
decoupling the first and second storage nodes from the first and second bit lines;
equalizing a voltage between the first and second storage nodes;
coupling the first storage node to the first bit line through a first transistor and coupling the second storage node to the second bit line through a second pass transistor; and
providing a data signal to the first storage node on the first bit line and the second bit line to write logic states, wherein the data signal is applied at a voltage substantially equal to the power supply voltage to the first bit line and a voltage substantially equal to ground potential to the second bit line to write a first logic state.
2. The method of claim 1 , wherein the power supply voltage is equal to or less than one volt.
3. The method of claim 1 further comprising a range of power supply voltages, and wherein when the power supply voltage is greater than or equal to a predetermined voltage within the range of power supply voltages, the voltage between the first and second storage nodes is not equalized.
4. The method of claim 1 , wherein equalizing a voltage between the first and second storage nodes comprises providing a transistor having a first current electrode coupled to the first storage node, a second current electrode coupled to the second storage node, and a control electrode for receiving a bit equalization signal.
5. The method of claim 1 , wherein equalizing a voltage between the first and second storage nodes further comprises:
providing a first transistor having a first current electrode coupled to the first storage node, a second current electrode, and a control electrode for receiving a bit equalization signal; and
providing a second transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode coupled to the second storage node, and a control electrode for receiving a enable signal.
6. The method of claim 1 , wherein the method is implemented in a data processor having a memory array.
7. An integrated circuit memory comprising:
a plurality of memory cells, each of the plurality of memory cells for receiving a first power supply voltage comprising a first storage node and a second storage node, the first storage node coupled to a first bit line through a first pass transistor and the second storage node coupled to a second bit line through a second pass transistor in response to an asserted word line, each of the plurality of memory cells comprising an equalization transistor coupled between the first and second storage nodes and responsive to an equalization signal;
an equalization control circuit for providing the equalization signal to equalization transistors of selected memory cells of the plurality of memory cells, the equalization transistors for equalizing a voltage between the first and second storage nodes to enable a write operation of the selected memory cells; and,
column logic means for, during the write operation, providing a data signal at a first logic state by applying to the first bit line substantially the power supply voltage and to the second bit line substantially ground potential and at a second logic state by applying to the second bit line substantially the power supply voltage and to the first bit line substantially ground potential.
8. The integrated circuit memory of claim 7 , wherein the power supply voltage is equal to or less than one volt.
9. The integrated circuit memory of claim 7 wherein when the power supply voltage is greater than or equal to a predetermined voltage the equalization control circuit does not provide the equalization signal.
10. The integrated circuit memory of claim 7 wherein the equalization transistor further comprises a first current electrode coupled to the first storage node, a second current electrode, and a control electrode for receiving the equalization signal.
11. The integrated circuit memory of claim 10 further comprising a second transistor having a first current electrode coupled to the second current electrode of the transistor, a second current electrode coupled to the second storage node, and a control electrode for receiving an enable signal.
12. The integrated circuit memory of claim 7 wherein the integrated circuit memory is a portion of a data processor.
13. An integrated circuit memory comprising a plurality of memory cells, each memory cell of the plurality of memory cells comprising:
a first inverter having an input terminal coupled to a first storage node and an output terminal coupled to a second storage node for being powered by a power supply voltage;
a second inverter having an input terminal coupled to the second storage node and an output terminal coupled to the first storage node for being powered by the power supply voltage;
a first transistor having a first current electrode coupled to the first storage node, a second current electrode coupled to a first bit line, and a control electrode for receiving an address signal;
a second transistor having a first current electrode coupled to the second storage node, a second current electrode coupled to a second bit line, and a control electrode for receiving the address signal;
a third transistor having a first current electrode coupled to the first storage node, a second current electrode, and a control electrode for receiving an equalization signal;
a fourth transistor having a first current electrode coupled to the second current electrode of the third transistor, a second current electrode coupled to the second storage node, and a control electrode for receiving a enable signal; and
column logic means for, during a write operation, providing a data signal at a first logic state by applying to the first bit line substantially the power supply voltage and to the second bit line substantially ground potential and at a second logic state by applying to the second bit line substantially the power supply voltage and to the first bit line substantially ground potential.
14. The integrated circuit memory of claim 13 , further comprising an equalization control circuit for providing the equalization signal to selected memory cells of the plurality of memory cells, the equalization control circuit for equalizing a voltage between the first and second storage nodes to enable a write operation of the selected memory cells.
15. The integrated circuit memory of claim 14 , wherein when the power supply voltage is greater than or equal to a predetermined voltage the equalization control circuit does not provide the equalization signal.
16. The integrated circuit memory of claim 15 , wherein the predetermined voltage is equal to or less than one volt.
17. The integrated circuit memory of claim 13 , wherein the plurality of memory cells are implemented as one of either a register file or a random access memory in a data processor.
18. A method for writing to a memory cell powered by a power supply voltage, the memory cell having a first storage node and a second storage node, the first storage node coupled to a first bit line and the second storage node coupled to a second bit line in response to a word line becoming active, the method comprising:
equalizing the storage nodes;
causing the word line to become active in response to the step of equalizing;
applying data on the first and second bit lines while the word line is active and during the step of equalizing, wherein the data is applied as a first logic state by applying to the first bit line substantially the power supply voltage and to the second bit line substantially ground potential and as a second logic state by applying to the second bit line substantially the power supply voltage and to the first bit line substantially ground potential;
terminating the step of equalizing in response to the step of causing the word line to become active; and
terminating the step of applying data after the step of terminating the step of equalizing.