Hierarchical common source line structure in NAND flash memory
View Patent ↗Each memory cell string in a generic NAND flash cell block connects to a Common Source Line (CLS). A value for applying to the CSL is centrally generated and distributed to a local switch logic unit corresponding to each NAND flash cell block. For source-line page programming, the distribution line may be called a Global Common Source Line (GCSL). In an array of NAND flash cell blocks, only one NAND flash cell block is selected at a time for programming. To reduce power consumption, only the selected NAND flash cell block receives a value on the CSL that is indicative of the value on the GCSL. Additionally, the CSLs of non-selected NAND flash cell blocks may be disabled through an active connection to ground.
1. A local switch logic unit for reducing power consumption from source-line page programming in a memory device which comprises a plurality of NAND Flash memory blocks,
wherein each one of said plurality of NAND Flash memory blocks is coupled to one of said local switch logic unit and connected to a local common source line, said local switch logic unit comprising:
a first semiconductor switch for selectively allowing passage of a signal received on a global common source line to said one of said plurality of NAND Flash blocks on said local common source line; and
a second semiconductor switch for selectively placing a predetermined voltage on said local common source line.
2. The local switch logic unit of claim 1 wherein said first semiconductor switch is an n-type Metal Oxide Semiconductor (NMOS) transistor.
3. The local switch logic unit of claim 2 wherein said second semiconductor switch is an n-type Metal Oxide Semiconductor (NMOS) transistor.
4. The local switch logic unit of claim 1 further comprising a first input line for receiving a voltage level indicative of selection of said one of said plurality of NAND flash memory blocks.
5. The local switch logic unit of claim 1 further comprising a second input line for receiving a voltage level indicative of said one of said plurality of NAND flash memory blocks not having been selected.
6. The local switch logic unit of claim 1 wherein said predetermined voltage is ground.
7. A method of reducing power consumption from source-line page programming in a memory device which comprises a plurality of NAND Flash memory blocks,
wherein each one of said plurality of NAND Flash memory blocks is coupled to a local switch logic unit and connected to a local common source line, said method comprising:
receiving an indication of selection of said one of said plurality of NAND flash memory blocks;
responsive to receiving said indication of selection, permitting passage of a signal received on a global common source line to said one of said plurality of NAND flash memory blocks on said local common source line;
receiving an enable indication; and
responsive to receiving said enable indication, isolating said local common source line from a predetermined voltage.
8. The method of claim 7 wherein said predetermined voltage is ground.
9. A method of reducing power consumption from source-line page programming in a memory device which comprises a plurality of NAND Flash memory blocks,
wherein each one of said plurality of NAND Flash memory blocks is coupled to a local switch logic unit and connected to a local common source line, said method comprising:
receiving an indication that said one of said plurality of NAND flash memory blocks has not been selected;
responsive to receiving said indication, isolating a global common source line from said local common source line of said one of said plurality of NAND flash memory blocks;
receiving a disable indication; and
responsive to receiving said disable indication, connecting said local common source line to a predetermined voltage.
10. The method of claim 9 wherein said predetermined voltage is ground.
11. A memory array comprising:
a plurality of NAND Flash memory blocks, each one of said plurality of NAND Flash memory blocks including a plurality of NAND Flash memory strings, each plurality of NAND Flash memory strings coupled to a local switch logic unit and connected to a local common source line;
the local switch logic unit including:
a first semiconductor switch for selectively allowing passage, on said local common source line, of a signal to said plurality of NAND flash memory strings in said one of said plurality of NAND flash memory blocks, wherein said signal is received on a global common source line; and
a second semiconductor switch for selectively placing a predetermined voltage on said local common source line.
12. The memory array of claim 11 wherein said first semiconductor switch is an n-type Metal Oxide Semiconductor (NMOS) transistor.
13. The memory array of claim 12 wherein said second semiconductor switch is an n-type Metal Oxide Semiconductor (NMOS) transistor.
14. The memory array of claim 11 wherein said local switch logic further comprises a first input line for receiving a voltage level indicative of selection of said one of said plurality of NAND Flash memory blocks.
15. The memory array of claim 14 further comprising, associated with said one of said plurality of NAND Flash memory blocks, a row decoder adapted to receive row pre-decoded signals and, based on said row pre-decoded signals, provide, on said first input line, said voltage level indicative of selection of said one of said plurality of NAND Flash memory blocks.
16. The memory array of claim 15 wherein said local switch logic further comprises a second input line for receiving a voltage level indicative of said one of said plurality of NAND Flash memory blocks not having been selected.
17. The memory array of claim 16 further comprising, associated with said one of said plurality of NAND Flash memory blocks, a local charge pump adapted to receive, from said row decoder, a latch signal, and, based on said latch signal, provide, to said second input line, said voltage level indicative of selection of said one of said plurality of NAND Flash memory blocks not having been selected.
18. The memory array of claim 17 wherein said local switch logic unit further includes a third semiconductor switch for selectively allowing passage, on a ground select line, of a ground select signal to said plurality of NAND Flash memory strings in said one of said plurality of NAND Flash memory blocks.
19. The memory array of claim 18 wherein said passage of said ground select signal is based on said latch signal on said second input line.
20. The memory array of claim 11 wherein said predetermined voltage is ground.