Memory device with sense amplifier and self-timed latch

• US 20040202014A1
• Filed: 04/11/2003
• Published: 10/14/2004
• Est. Priority Date: 04/11/2003
• Status: Active Grant

• Current Assignee: Progressive Semiconductor Solutions LLC (Acacia Research Corporation)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Pelley, Perry H. III, Palmer, Jeremiah T. C.
• Granted Patent: US 6,862,208 B2
• Time in Patent Office: Days
• US Class Current: 365/154
• CPC Class Codes: G11C 11/419 Read-write [R-W] circuits

Abstract

A memory device (201) includes a plurality of memory cells (203), bit lines, word lines, a sense amplifier (314), and a self-timed latch (215). The sense amplifier (314), responsive to a sense enable signal, is for sensing and amplifying a voltage on the bit lines corresponding to a stored logic state of a selected one of the plurality of memory cells. An isolation circuit (306, 308) is coupled between the bit lines (205 and 207) and the sense amplifier (314). The isolation circuit (306, 308) is for decoupling the selected one of the plurality of memory cells from the sense amplifier (314) at about the same time that the sense enable signal is asserted. A self-timed latch (215) is coupled to the sense amplifier (314). The self-timed latch (215) does not receive a clock signal and is responsive to only the amplified voltage.

Claims

1. A memory device, comprising:

a plurality of memory cells, each of the plurality of memory cells coupled to a bit line;

a sense amplifier for amplifying a data signal from a selected one of the plurality of memory cells via the bit line to provide an amplified data signal in response to asserting a sense enable signal;

an isolation circuit, coupled between the bit line and the sense amplifier, the isolation circuit for decoupling the selected one of the plurality of memory cells from the sense amplifier at about the same time as the assertion of the sense enable signal; and

a self-timed storage device, coupled to the sense amplifier, for storing data corresponding to the amplified data signal only in response to the amplified data signal.

2. The memory device of claim 1, wherein the memory device is implemented on an integrated circuit.

3. The memory device of claim 1, wherein the memory device is characterized as being a static random access memory (SRAM).

4. The memory device of claim 1, wherein:

the data signal is a differential data signal;

the amplified data signal is an amplified differential data signal;

the sense amplifier comprises a pair of cross-coupled inverters, the pair of cross-coupled inverters being coupled to amplify the differential data signal to provide the amplified differential data signal in response to the sense enable signal.

5. The memory device of claim 1, wherein the self-timed storage device comprises:

a first transistor having a first current electrode, a second current electrode coupled to a power supply voltage terminal, and a control electrode coupled to a first data line;

a second transistor having a first current electrode, a second current electrode coupled to the power supply voltage terminal, and a control electrode coupled to a second data line;

a first inverter having an input coupled to the first current electrode of the first transistor, and an output coupled to the first current electrode of the second transistor; and

a second inverter having an input coupled to the first current electrode of the second transistor and an output coupled to the first current electrode of the first transistor.

6. The memory device of claim 1, wherein the sense amplifier comprises:

a first transistor having a first current electrode coupled to a first power supply voltage terminal, a second current electrode coupled to a first data line, and a control electrode;

a second transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode, and a control electrode coupled to the control electrode of the first transistor;

a third transistor having a first current electrode coupled to the first power supply voltage terminal, a second current electrode coupled to the control electrode of the first transistor and to a second data line, and a control electrode coupled to the second current electrode of the first transistor;

a fourth transistor having a first current electrode coupled to the second current electrode of the third transistor, a second current electrode, and a control electrode coupled to the control electrode of the third transistor; and

a fifth transistor having a first current electrode coupled to the second current electrodes of both the second and fourth transistors, a second current electrode coupled to a second power supply voltage terminal, and a control electrode for receiving the sense enable signal.

7. The memory device of claim 1, wherein the data signal is a differential data signal provided on a first bit line and a second bit line, and the isolation circuit further comprising:

a first isolation transistor for selectively coupling the first bit line to a first data line; and

a second isolation transistor for selectively coupling the second bit line to a second data line.

8. The memory device of claim 7 wherein the sense amplifier is coupled to the first data line and the second data line, the first isolation transistor for selectively coupling the first bit line to the sense amplifier, the second isolation transistor for selectively coupling the second bit line to the sense amplifier.

9. The memory device of claim 7, further comprising:

a precharge circuit coupled to the first and second data lines, the precharge circuit for precharging the first and second data lines prior to the assertion of the sense enable signal.

10. The memory device of claim 7, further comprising:

a first inverter having an input coupled to the first data line and an output coupled to a first input of the self-timed storage device;

a second inverter having an input coupled to the second data line and an output coupled to a second input of the self-timed storage device.

11. The memory device of claim 10, wherein the self-timed storage device comprises:

a first transistor having a first current electrode, a second current electrode coupled to a power supply voltage terminal, and a control electrode coupled to the first data line;

a second transistor having a first current electrode, a second current electrode coupled to the power supply voltage terminal, and a control electrode coupled to the second data line;

a first inverter having an input coupled to the first current electrode of the first transistor, and an output coupled to the first current electrode of the second transistor; and

a second inverter having an input coupled to the first current electrode of the second transistor and an output coupled to the first current electrode of the first transistor.

12. A memory device comprising:

a plurality of memory cells, each of the plurality of memory cells coupled to a first bit line and to a second bit line;

a first data line coupled to the first bit line during at least a portion of a read cycle;

a second data line coupled to the second bit line during at least a portion of the read cycle;

a sense amplifier having a pair of cross-coupled inverters, the pair of cross-coupled inverters being coupled to the first data line and to the second data line for amplifying a data signal from a selected one of the plurality of memory cells in response to asserting a sense enable signal;

a first buffer circuit having an input coupled to the first data line and an output;

a second buffer circuit having an input coupled to the second data line and an output;

a self-timed storage device having a first input coupled to the output of the first buffer circuit and a second input coupled to the output of the second buffer circuit, the self-timed storage device responsive only to a differential voltage between the output of the first buffer circuit and the output of the second buffer circuit.

13. The memory device of claim 12, wherein the plurality of memory cells is characterized as being a plurality of static random access memory (SRAM) cells.

14. The memory device of claim 12, wherein the memory device is part of an integrated circuit.

15. The memory device of claim 12, further comprising:

a first isolation transistor for selectively coupling the first bit line to the first data line; and

a second isolation transistor for selectively coupling the second bit line to the second data line.

16. The memory device of claim 15, wherein the first and second isolation transistors decouple the first and second data lines from the first and second bit lines at about the same time as the assertion of the sense enable signal.

17. The memory device of claim 12, wherein the sense amplifier comprises:

a first transistor having a first current electrode coupled to a first power supply voltage terminal, a second current electrode coupled to the first data line, and a control electrode;

a second transistor having a first current electrode coupled to the second current electrode of the first transistor, a second current electrode, and a control electrode coupled to the control electrode of the first transistor;

a third transistor having a first current electrode coupled to the first power supply voltage terminal, a second current electrode coupled to the control electrode of the first transistor and to the second data line, and a control electrode coupled to the second current electrode of the first transistor;

a fourth transistor having a first current electrode coupled to the second current electrode of the third transistor, a second current electrode, and a control electrode coupled to the control electrode of the third transistor; and

a fifth transistor having a first current electrode coupled to the second current electrodes of both the second and fourth transistors, a second current electrode coupled to a second power supply voltage terminal, and a control electrode for receiving the sense enable signal.

18. The memory device of claim 12, wherein the self-timed storage device comprises:

a first transistor having a first current electrode, a second current electrode coupled to a power supply voltage terminal, and a control electrode coupled to the first data line;

a second transistor having a first current electrode, a second current electrode coupled to the power supply voltage terminal, and a control electrode coupled to the second data line;

a first inverter having an input coupled to the first current electrode of the first transistor, and an output coupled to the first current electrode of the second transistor; and

a second inverter having an input coupled to the first current electrode of the second transistor and an output coupled to the first current electrode of the first transistor.

19. The memory device of claim 12, wherein the first and second buffer circuits are first and second inverters, respectively.

20. The memory device of claim 12, further comprising a precharge circuit coupled to the first and second data lines, the precharge circuit for precharging the first and second data lines prior to the assertion of the sense enable signal.

21. The memory device of claim 12, wherein the sense enable signal is generated from a clock signal.

22. A method for reading a memory cell of a memory device, the memory device comprising a plurality of memory cells, each of the plurality of memory cells coupled to a bit line and to a word line, the method comprising:

selecting at least one of the plurality of memory cells;

sensing and amplifying a voltage on the bit line using a sense amplifier in response to asserting a sense enable signal to produce an amplified data signal, the amplified data signal representative of a logic state stored in the at least one of the plurality of memory cells selected by the selecting;

decoupling the bit line from the sense amplifier at about the same time as the sense enable signal is asserted; and

latching data corresponding to the amplified data signal in a self-timed latch, the self-timed latch latching the data in response to only the amplified data signal.

23. The method of claim 22, wherein the memory device is characterized as being a static random access memory (SRAM).

24. The method of claim 22, wherein the sense enable signal is generated from a clock signal.

25. The method of claim 22, further comprising precharging the first and second data lines prior to the assertion of the sense enable signal.