Method and apparatus for integrated circuit with DRAM
Various aspects of an integrated circuit having a DRAM are disclosed. In one embodiment an integrated circuit includes a DRAM that (1) pre-charges the bit lines to a voltage that is biased toward a weaker one of two memory cell logic states, (2) selectively stores data in an inverted form that reduces the power needed to refresh such data (in at least one embodiment), (3) retains data in the sense/latch circuits and use such circuits as a form of cache to reduce the frequency that memory cells are accessed and thereby reduce memory access time, and (4) supplies a reference (e.g., V PP ) from a circuit that employs an alternate, lower power, operating mode (e.g., if the DRAM is in standby).
1. A dynamic random access memory (DRAM) that comprises a read mode having a pre-charge state, the DRAM comprising:
a memory space having a plurality of memory cells, at least a subset of the memory cells being capable of storing signals corresponding to a first logic state or a second logic state, wherein one of the logic states is weaker than the other logic state;
a plurality of logic circuits, at least one of which comprises CMOS logic;
a plurality of bit lines for reading and writing data to the at least a subset of the memory cells; and
a circuit to, in the pre-charge state, pre-charge at least a first one of the bit lines to a predetermined voltage biased toward the weaker logic state, wherein the weaker logic state is a low logic state, and wherein the circuit to pre-charge comprises a pull down transistor coupled between the first one of the bit lines and a first supply voltage, wherein the pull down transistor is a P channel FET.
2. The DRAM of claim 1 , wherein the circuit to pre-charge is further adapted to, in the pre-charge state, pre-charge at least a second one of the bit lines to a second predetermined voltage biased toward a second weaker logic state, wherein the second weaker logic state is a logic high state, and wherein the circuit to pre-charge comprises a pull up transistor coupled between the second one of the bit lines and a second supply voltage.
3. The DRAM of claim 1 , wherein the plurality of combinatorial logic circuits comprises a decoder circuit for indicating one or more of the memory cells, and wherein the pull down transistor comprises a control input coupled to the decoder circuit, and being connected between one of the indicated memory cells and one of the plurality of bit lines.
4. The DRAM of claim 1 , wherein the predetermined voltage is substantially equal to V SS .
5. The DRAM of claim 1 , further comprising a sense circuit that is coupled to the plurality of bit lines and outputs a signal that indicates the logic state of the memory cell being read.
6. The DRAM of claim 5 , wherein the sense circuit comprises CMOS logic.
7. The DRAM of claim 1 , wherein the memory space is arranged as a matrix of rows and columns.
8. The DRAM of claim 1 , wherein the memory space comprises reference cells.
9. An integrated circuit comprising an embedded DRAM such as recited in claim 1 .
10. The integrated circuit of claim 9 , further comprising a digital information processor.
11. A battery powered device having an integrated circuit such as recited in claim 9 .
12. The battery powered device of claim 11 , wherein the integrated circuit further comprises a digital information processor.
13. A dynamic random access memory (DRAM) that comprises a read mode having a pre-charge state, the DRAM comprising:
a memory space having a plurality of memory cells, at least a subset of the memory cells being capable of storing signals corresponding to a first logic state or a second logic state, wherein one of the logic states is weaker than the other logic state;
a plurality of logic circuits, at least one of which comprises CMOS logic;
a plurality of bit lines for reading and writing data to the at least a subset of the memory cells; and
means for pre-charging at least a first one of the bit lines to a predetermined voltage biased toward the weaker logic state in the pre-charge state, wherein the weaker logic state is a low logic state, and wherein the means for pre-charging comprises a pull down transistor coupled between the first one of the bit lines and a first supply voltage, wherein the pull down transistor is a P channel FET.
14. The DRAM of claim 13 , wherein the means for pre-charging is further adapted to, in the pre-charge state, pre-charge at least a second one of the bit lines to a second predetermined voltage biased toward a second weaker logic state, wherein the second weaker logic state is a logic high state, and wherein the means for pre-charging comprises a pull up transistor coupled between the second one of the bit lines and a second supply voltage.
15. The DRAM of claim 13 , wherein the plurality of combinatorial logic circuits comprises a decoder circuit for indicating one or more of the memory cells, and wherein the pull down transistor comprises a control input coupled to the decoder circuit, and being connected between one of the indicated memory cells and one of the plurality of bit lines.
16. The DRAM of claim 13 , wherein the predetermined voltage is substantially equal to V SS .
17. The DRAM of claim 13 , further comprising a sense circuit that is coupled to the plurality of bit lines and outputs a signal that indicates the logic state of the memory cell being read.
18. The DRAM of claim 13 , wherein the sense circuit comprises CMOS logic.
19. The DRAM of claim 13 , wherein the memory space is arranged as a matrix of rows and columns.
20. The DRAM of claim 13 , wherein the memory space comprises reference cells.
21. A method for use in a CMOS DRAM having a memory space having a plurality of memory cells, at least a subset of the memory cells being capable of storing signals corresponding to a first logic state or a second logic state, wherein one of the logic states is weaker than the other logic state, and further having a plurality of bit lines for reading and writing data to the at least a subset of the memory cells, the CMOS DRAM including a read mode having a pre-charge state, the method comprising:
pre-charging at least a first one of the bit lines to a predetermined voltage biased toward the weaker logic state in the pre-charge state, wherein the weaker logic state is a low logic state, and wherein pre-charging the at least a first one of the bit lines comprises turning on a pull down transistor coupled between the first one of the bit lines and a first supply voltage, wherein the pull down transistor is a P channel FET.
22. The method of claim 21 , further comprising pre-charging at least a second one of the bit lines to a second predetermined voltage biased toward a second weaker logic state in the pre-charge state, wherein the second weaker logic state is a logic high state, and wherein pre-charging the at least a second one of the bit lines comprises turning on a pull up transistor coupled between the second one of the bit lines and a second supply voltage, the first supply voltage having a higher potential than the second supply voltage.
23. The method of claim 21 , wherein if the predetermined voltage is substantially equal to V SS .
24. The method of claim 21 , further comprising sensing a signal on the first one of the bit lines and providing a signal that indicates the logic state of the memory cell being read.
25. The method of claim 21 , wherein sensing comprises supplying the first one of the bit lines to at least one CMOS logic circuit.
26. The method of claim 21 , wherein the memory space is arranged as a matrix of rows and columns.
27. The method of claim 21 , wherein the memory space comprises reference cells.