Methods and circuits for single-memory dynamic cell multivalue data storage
First Claim
1. A multivalue dynamic random access memory (DRAM) cell comprising:
- first circuitry operable for sensing a least significant bit (LSB) of a stored data value, said first circuitry having first and second nodes operable for coupling to a respective one of a complementary bitline pair;
a first storage element operable for storing a reference voltage coupled to said first node wherein said reference voltage is independent of a precharge voltage on said bitline pair;
a second storage element operable for storing said reference voltage coupled to said second node;
second circuitry operable for sensing a most significant bit (MSB) and having third and fourth nodes for coupling to a respective one of said complementary bitline pair;
a first cross-coupling element coupled to said first storage element and said fourth node to form a dynamic voltage divider with said first storage element, said first cross-coupling element operable for providing a signal for offsetting said reference signal in response to said MSB; and
a second cross-coupling element coupled to said second storage element and said third node to form a dynamic voltage divider with said second storage element, said second cross-coupling element operable for providing a signal for offsetting said reference signal in response to said MSB.
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Abstract
A multivalue dynamic random access memory cell and method therefor are provided. Sense circuitry for sensing a most significant bit (MSB) and a least significant bit (LSB) of a binary data value are coupled to an unsegmented complementary bitline pair. The binary data is represented by a multilevel voltage stored on a storage element in the DRAM cell. A reference signal is provided to the sense circuitry, wherein the reference signal is independent of a precharge on the bitline pair. Cross-coupling elements offset the reference signal in response to the sensing of the MSB, whereby the voltage levels corresponding to the LSB are sensed. Following a read, the multilevel data value is restored on the storage element by a restore/write unit including a programmable voltage supply. The detected MSB/LSB pair are input to the restore/write unit which outputs the corresponding voltage level to the DRAM cell. A write is effected using the same restore/write unit with the binary datum to be stored input to the restore/write unit.
394 Citations
16 Claims
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1. A multivalue dynamic random access memory (DRAM) cell comprising:
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first circuitry operable for sensing a least significant bit (LSB) of a stored data value, said first circuitry having first and second nodes operable for coupling to a respective one of a complementary bitline pair; a first storage element operable for storing a reference voltage coupled to said first node wherein said reference voltage is independent of a precharge voltage on said bitline pair; a second storage element operable for storing said reference voltage coupled to said second node; second circuitry operable for sensing a most significant bit (MSB) and having third and fourth nodes for coupling to a respective one of said complementary bitline pair; a first cross-coupling element coupled to said first storage element and said fourth node to form a dynamic voltage divider with said first storage element, said first cross-coupling element operable for providing a signal for offsetting said reference signal in response to said MSB; and a second cross-coupling element coupled to said second storage element and said third node to form a dynamic voltage divider with said second storage element, said second cross-coupling element operable for providing a signal for offsetting said reference signal in response to said MSB. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A random access memory comprising:
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an array of rows and columns of memory cells; plurality of bitlines, each associated with a one of said plurality of columns, wherein each of said memory cells comprises; first circuitry operable for sensing a most significant bit (MSB) of a stored data value, said first circuitry coupled to a corresponding one of said plurality of bitlines; second circuitry operable for sensing a least significant bit (LSB) of a stored data value, said first circuitry coupled to said corresponding one of said plurality of bitlines, wherein said MSB and said LSB are output on said corresponding bitline; a data storage element operable for coupling to said corresponding bitline; and a write/restore unit coupled to said plurality of bitlines, said write/restore unit including a programmable voltage supply operable for receiving a multibit binary data value and, in response thereto, outputting a multilevel stored data value for storage in said data storage element. - View Dependent Claims (11, 12, 13)
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14. A method of storing a plurality of data bits in a random access memory cell comprising:
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for a write to said memory cell; providing said plurality of data bits to a programmable voltage supply, said programmable voltage supply outputting a preselected voltage representing said plurality of data bits; storing said preselected voltage in a storage element in said cell; for a read operation; sensing a most significant bit (MSB) of said data bits in response to said preselected voltage in said storage element; sensing a least significant bit (LSB) of said data bits in response to said preselected voltage in said storage element and said MSB; following a read operation, restoring said preselected voltage in said storage element, said step of restoring comprising; providing said MSB and said LSB to said programmable voltage source; and outputting said preselected voltage in response to said MSB and said LSB. - View Dependent Claims (15, 16)
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Specification