Dynamic RAM storage techniques

• US 7,602,634 B2
• Filed: 08/24/2007
• Issued: 10/13/2009
• Est. Priority Date: 03/10/2004
• Status: Expired due to Fees

• Current Assignee: Altera Corporation (Intel Corporation)
• Original Assignee: Altera Corporation (Intel Corporation)
• Inventors: Turner, John
• Primary Examiner(s): AUDUONG, GENE NGHIA
• Application Number:
  US11/844,916
• Publication Number:
  US 20070285979A1
• Time in Patent Office: 781 Days
• Field of Search: 365/149, 365/154, 365/156, 365/63, 365/187, 365/203
• US Class Current: 365/149
• CPC Class Codes: G11C 11/405 with three charge-transfer gates, e.g. MOS transistors, per cell
• CPC Class Codes: G11C 11/406 Management or control of the refreshing or charge-regeneration cycles
• CPC Class Codes: G11C 11/4085 Word line control circuits, e.g. word line drivers, - boosters, - pull-up, - pull-down, - precharge
• CPC Class Codes: G11C 11/4094 Bit-line management or control circuits
• CPC Class Codes: G11C 11/4097 Bit-line organisation, e.g. bit-line layout, folded bit lines
• CPC Class Codes: G11C 2207/104 Embedded memory devices, e.g. memories with a processing device on the same die or ASIC memory designs
• CPC Class Codes: G11C 2211/4065 Low level details of refresh operations
• CPC Class Codes: G11C 5/005 Circuit means for protection against loss of information of semiconductor storage devices
• CPC Class Codes: G11C 7/02 with means for avoiding parasitic signals

Abstract

Dynamic RAM (DRAM) cells are provided. Data can be read from a DRAM cell without draining the stored charge stored in the cell. During a read cycle, current flows between a Read Bit line and a supply voltage, and charge is not drained directly from the DRAM storage node. Each DRAM cell has a small number of transistors. The DRAM cell can be used to store configuration data on a programmable integrated circuits (IC). Pass gates are used on programmable ICs to drive signals across the chip. Data stored in DRAM cells is provided directly to the pass gates at the full supply voltage to prevent signal degradation. A p-channel transistor eliminates all N-type junctions from the storage node reducing the collection of particles that may cause soft errors.

Claims

1. A memory cell, the memory cell comprising:

an n-channel transistor having a gate coupled to a read word line and a drain coupled to a read bit line;

an inverter having an output coupled to a source of the n-channel transistor;

a p-channel transistor coupled between an input of the inverter and a write bit line, a gate of the p-channel transistor being coupled to a write word line; and

a pass gate having a gate directly connected to the source of the n-channel transistor and coupled to the output of the inverter such that a voltage stored on the inverter is operable to drive a gate voltage of the pass gate, wherein the voltage stored on the inverter comprises a data bit of the memory cell.

2. The memory cell according to claim 1, wherein the pass gate is a programmable routing connector that couples interconnect lines on a field programmable gate array.

3. The memory cell according to claim 1, wherein the pass gate is used to configure logic performed by logic circuitry on a field programmable gate array.

4. The memory cell according to claim 1, wherein the pass gate is turned fully on or fully off in order to prevent signal degradation.

5. The memory cell according to claim 1, wherein at least one refresh cycle is used to maintain a voltage stored at an input of the inverter.

6. The memory cell according to claim 1, wherein the inverter is a CMOS inverter.

7. The memory cell according to claim 6, wherein the inverter further includes a second p-channel transistor and a second n-channel transistor.

8. The memory cell according to claim 7, wherein the second p-channel and second n-channel transistor in the inverter store charge between refresh cycles.

9. The memory cell according to claim 1, wherein the input of the inverter is not directly connected to an N-type doped semiconductor region.

10. The memory cell according to claim 1 wherein the voltage stored on the inverter is operable to drive a gate voltage of the pass gate to the full value of a supply voltage.

11. The memory cell according to claim 1 wherein the memory cell comprises a DRAM cell.

12. The memory cell according to claim 1 wherein the output of the inverter is directly connected to the source of the n-channel transistor.

13. A method of operating a memory cell, the method comprising:

applying a first voltage on a write word line to turn on a p-channel transistor within the memory cell, wherein the p-channel transistor is coupled between an input of an inverter and a write bit line;

applying a second voltage on the write bit line coupled to a drain of the p-channel transistor to store a charge at the inverter;

applying a third voltage on the write word line to turn off the p-channel transistor;

applying a fourth voltage on a read word line to turn on a first n-channel transistor, the first n-channel transistor coupled in series with a second n-channel transistor; and

driving a gate voltage of a pass gate using the charge stored on the inverter.

14. The method according to claim 13, further comprising:

sensing a fifth voltage on a read bit line coupled to a drain of the first n-channel transistor.

15. The method according to claim 13, further comprising:

turning the pass gate fully on or fully off in order to prevent signal degradation.

16. The method according to claim 13, further comprising:

using at least one refresh cycle to maintain a voltage stored at an input of the inverter.

17. The method according to claim 13, wherein the driving the gate voltage of a pass gate comprises driving the pass gate to the full value of a supply voltage.

18. A memory cell, the memory cell comprising:

an n-channel transistor having a gate coupled to a read word line and a drain coupled to a read bit line;

a single inverter having an output directly connected to a source of the n-channel transistor, such that a voltage stored on the inverter is operable as a data bit of the memory cell; and

a p-channel transistor coupled between an input of the single inverter and a write bit line, a gate of the p-channel transistor being coupled to a write word line.

19. The memory cell according to claim 18, wherein the output of the inverter is coupled to a pass gate.

20. The memory cell according to claim 19, wherein the pass gate is a programmable routing connector that couples interconnect lines on a field programmable gate array.

21. The memory cell according to claim 19, wherein the pass gate is used to configure logic performed by logic circuitry on a field programmable gate array.

22. The memory cell according to claim 18, wherein the input of the inverter is not directly connected to an N-type doped semiconductor region.

23. The memory cell according to claim 18, further comprising a capacitor coupled to the input of the inverter.

24. The memory cell according to claim 23, wherein the capacitor is one of a planar capacitor and a trench capacitor.

25. The memory cell according to claim 18, further comprising:

a sense amplifier having an input coupled to the read bit line; and

a multiplexer coupled between an output of the sense amplifier and the write bit line.

26. The memory cell according to claim 18, wherein the single inverter further includes a second p-channel transistor and a second n-channel transistor.

27. The memory cell according to claim 18, wherein the single inverter isolates the charge stored at the input terminal of the single inverter from an output terminal of the single inverter.

28. The memory cell according to claim 18 wherein the memory cell comprises a DRAM cell.