SRAM cell with separate read and write ports

• US 7,660,149 B2
• Filed: 12/07/2006
• Issued: 02/09/2010
• Est. Priority Date: 12/07/2006
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: Liaw, Jhon-Jhy
• Primary Examiner(s): Zarabian; Amir
• Assistant Examiner(s): TRAN, ANTHAN
• Application Number:
  US11/636,014
• Publication Number:
  US 20080137440A1
• Time in Patent Office: 1,160 Days
• Field of Search: 365/154, 365/230.05
• US Class Current: 365/154
• CPC Class Codes: G11C 11/412 using field-effect transistors only

Abstract

This invention discloses a dual port static random access memory (SRAM) cell, which comprises at least one inverter coupled between a positive supply voltage (Vcc) and a complementary low supply voltage (Vss) and having an input and an output terminals, at least one PMOS transistor with its gate, source and drain connected to the output terminal, Vcc and input terminal, respectively, a write port connected to the input terminal and having a write-word-line, a write-enable and a write-bit-line, and a read port connected to either the input or output terminal and having a read-word-line and a read-bit-line.

Claims

1. A dual port static random access memory (SRAM) cell comprising:

at least one inverter coupled between a positive supply voltage (Vcc) and a complementary low supply voltage (Vss) and having an input and output terminals;

at least one PMOS transistor with its gate, source and drain connected to the output terminal, Vcc and input terminal, respectively;

a write port connected to the input terminal and having a write-word-line, a write-enable and a write-bit-line, wherein the write port further comprises a first switching device and a second switching device connected in series between the input terminal and the write-bit-line; and

a read port connected to either the input or output terminal and having a read-word-line and a read-bit-line, wherein the read port further comprises a first MOS transistor and a second MOS transistor connected in series between the read-bit-line and a supply voltage, wherein a gate of the first MOS transistor is connected to the read-word-line and a gate of the second MOS transistor is directly connected to the input or output terminal, and

wherein the dual port SRAM cell is made of no more than seven transistors to reduce its cell size.

2. The dual port SRAM cell of claim 1, wherein a first control terminal of the first switching device is connected to the write-word-line and a second control terminal of the second switching device that is connected to the write-enable.

3. The dual port SRAM cell of claim 2, wherein the first switching device is a P-type or a N-type metal-oxide-semiconductor (PMOS or NMOS) transistor with its gate as the first control terminal.

4. The dual port SRAM cell of claim 2, wherein the second switching device is a PMOS or NMOS transistor with its gate as the second control terminal.

5. The dual port SRAM cell of claim 2, wherein the first switching device is connected to the input terminal while the second switching device is connected to the write-bit-line.

6. The dual port SRAM cell of claim 2, wherein the first switching device is connected to the write-bit-line while the second switching device is connected to the input terminal.

7. The dual port SRAM cell of claim 1, the first and second MOS transistors are N-type MOS transistors.

8. The dual port SRAM cell of claim 1, wherein the supply voltage is Vss or Vcc.

9. The dual port SRAM cell of claim 1, wherein the first MOS transistor is a first PMOS transistor with its gate connected to the read-word-line.

10. The dual port SRAM cell of claim 1, wherein the second MOS transistor is a second PMOS transistor with its gate connected to the input or output terminal.

11. The dual port SRAM cell of claim 1, wherein the first MOS transistor is connected to the read-bit-line while the second MOS transistor is connected to the supply voltage.

12. The dual port SRAM cell of claim 1, wherein the write-word-line and the read-word-line are a common word-line.

13. A dual port static random access memory (SRAM) cell comprising:

at least one inverter coupled between Vcc and Vss and having an input and output terminals;

at least one PMOS transistor with its gate, source and drain connected to the output terminal, Vcc and input terminal, respectively;

a write-word-line, a write-enable and a write-bit-line;

a first and a second switching devices connected in series between the input terminal and the write-bit-line, wherein a first control terminal of the first switching device is connected to the write-word-line and a second control terminal of the second switching device is connected to the write-enable;

a read-word-line and a read-bit-line; and

a third and a fourth switching devices connected in series between a supply voltage and the read-bit-line, wherein a third control terminal of the third switching device is connected to the read-word-line and a fourth control terminal of the fourth switching device is connected to either the input or output terminal, wherein the third and fourth switching devices are MOS transistors whose gates are directly connected to the read-word-line and the input or output terminal, respectively, and

wherein the dual port SRAM cell is made of no more than seven transistors to reduce its cell size.

14. The dual port SRAM cell of claim 13, wherein the first switching device is a P-type or a N-type metal-oxide-semiconductor (PMOS or NMOS) transistor with its gate as the first control terminal.

15. The dual port SRAM cell of claim 13, wherein the second switching device is a P-type or a N-type metal-oxide-semiconductor (PMOS or NMOS) transistor with its gate as the second control terminal.

16. The dual port SRAM cell of claim 13, wherein the first switching device is connected to the input terminal while the second switching device is connected to the write-bit-line.

17. The dual port SRAM cell of claim 13, wherein the first switching device is connected to the write-bit-line while the second switching device is connected to the input terminal.

18. The dual port SRAM cell of claim 13, wherein the supply voltage is Vss or Vcc.

19. The dual port SRAM cell of claim 13, wherein the third switching device is an NMOS or a PMOS transistor with its gate as the third control terminal.

20. The dual port SRAM cell of claim 13, wherein the fourth switching device is an NMOS or a PMOS transistor with its gate as the fourth control terminal.

21. The dual port SRAM cell of claim 13, wherein the third switching device is connected to the read-bit-line while the fourth switching device is connected to the supply voltage.

22. The dual port SRAM cell of claim 13, wherein the write-word-line and the read-word-line are a common word-line.