Reference cell with various load circuits compensating for source side loading effects in a non-volatile memory

• US 6,754,106 B1
• Filed: 09/16/2002
• Issued: 06/22/2004
• Est. Priority Date: 09/16/2002
• Status: Active Grant

• Current Assignee: Infineon Technologies Batam PT (Infineon Technologies AG)
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Yang, Jean, Li, Jiang, Wu, Yider
• Primary Examiner(s): Mai, Son
• Application Number:
  US10/245,146
• Time in Patent Office: 645 Days
• Field of Search: 365/185.2, 365/185.21, 365/185.24
• US Class Current: 365/185.2
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/28 using differential sensing or reference cells, e.g. dummy cells
• CPC Class Codes: G11C 2211/5634 Reference cells

Abstract

A load circuit for compensating for source side loading effects in a non-volatile memory. Specifically, embodiments of the present invention describe a reference cell that is coupled to a plurality of load circuits. At least one of the plurality of load circuits, an m^th load circuit, comprises a select transistor coupled to m resistors that are coupled in series. The m^th load circuit matches a source side loading effect of a corresponding m^th memory cell located m memory cells away from a source line node on a source line coupling source regions in memory cells of a row of memory cells.

Claims

1. A load circuit comprising:

a select transistor of an m^th load circuit in a plurality of load circuits; and

m resistors coupled in series, said m resistors coupled to said m^th load circuit, said m^th load circuit for matching a source side loading effect of a corresponding m^th memory cell located m memory cells away from a source line node on a source line coupling source regions in memory cells of a row of memory cells by reducing in series current contributions of a voltage associated with said source line node.

2. The load circuit as described in claim 1, wherein said plurality of load circuits are coupled to a reference cell, said reference cell for providing a reference current for a non-volatile memory comprising a plurality of memory cells, said reference cell approximately identical to at least one of said plurality of memory cells.

3. The load circuit as described in claim 2, wherein each of said plurality of load circuits reduces said reference current equal to a reduction in current of a corresponding memory cell due to source side loading effects.

4. The load circuit as described in claim 2, wherein said m^th load circuit, when selected, reduces said reference current equal to a reduction in current of said corresponding m^th memory cell due to said source side loading effects.

5. The load circuit as described in claim 2, wherein said plurality of load circuits are coupled in parallel to a source region in said reference cell.

6. The load circuit as described in claim 1, further comprising:

a switching circuit coupled to said plurality of load circuits for selecting respective load circuits.

7. The load circuit as described in claim 1, wherein said source side loading effect of said m^th memory cell is approximately equal to m multiplied by a unit source side load value, said unit load value equal to resistance values for each of said m resistors.

8. The load circuit as described in claim 1, further comprising:

a differential amplifier coupled to said load circuit and to a source line of said row of memory cells, said differential amplifier for comparing a reference current, reduced by said m^th load circuit, against current read from said source line from said m^th memory cell.

9. A load circuit comprising:

a reference cell for providing a reference current for a non-volatile memory comprising a plurality of memory cells, said reference cell approximately identical to at least one of said plurality of memory cells; and

a plurality of load circuits coupled to said reference cell, wherein at least one of said plurality of load circuits comprises a select transistor coupled to a plurality of resistors that are coupled in series for matching a source side loading effect of a corresponding memory cell in said non-volatile memory by reducing in series current contributions from a source line voltage coupled to said reference cell.

10. The load circuit as described in claim 9, further comprising:

a logic circuit for selecting between each of said plurality of selection circuits for matching source side loads associated with memory cells being read in a row of memory cells of said non-volatile memory.

11. The load circuit as described in claim 10, wherein said select transistor when selected by said logic circuit, turns on said select transistor for reducing said reference current with said plurality of resistors.

12. The load circuit as described in claim 9, wherein said reference cell and each of said plurality of memory cells is a floating gate memory cell comprising:

a control gate;

a floating gate separated from said control gate by a dielectric layer; and

an oxide layer separating said floating gate from a channel region separating a source region and a drain region in a substrate.

13. The load circuit as described in claim 9, wherein said plurality of load circuits are coupled in parallel to a source region of said reference cell.

14. The load circuit as described in claim 9, wherein said plurality of load circuits comprises N load circuits corresponding to N memory cells in a row of memory cells of said non-volatile memory, and wherein an m^th resistor circuit in said plurality of load circuits comprises:

a select transistor coupled to m resistors, said m resistors coupled in series, said m^th resistor circuit corresponding to an m^th memory cell located m memory cells away from a source line node on a source line coupled to said row of memory cells, said source line coupling in series source regions in said row of memory cells.

15. The load circuit as described in claim 14, wherein each of said memory cells in said row of memory cells has an associated source side load value equal to a unit source side load value multiplied by the number of memory cells away from said source line node said associated source side load value is measured from, said unit source side load value approximately identical to load values for each of said plurality of resistors.

16. The load circuit as described in claim 9, wherein said non-volatile memory comprises:

at least one array of memory cells from said plurality of memory cells arranged in a plurality of rows and a plurality of columns, each of said memory cells in said array comprising a source region and a drain region, and capable of storing a respective bit;

a plurality of word lines coupled to respective rows of said memory cells;

a plurality of bit lines coupled to respective columns of said memory cells; and

a plurality of source lines wherein at least one of said plurality of source lines corresponds to a respective row of memory cells in said plurality of rows, and couples in series source regions of memory cells in said respective row.

17. A method for matching source side loading effects in a non-volatile memory comprising:

creating a plurality of load circuits for matching source side loads associated with memory cells being read in a row of memory cells of a non-volatile memory;

coupling said plurality of load circuits in parallel to a source region in a reference cell to reduce in series current contributions of a voltage associated with a source line node as from said source side loads, said reference cell for providing a reference current; and

selecting between said plurality of load circuits depending on which memory cell in said row of memory cells is being read.

18. The method as described in claim 17, wherein said creating said plurality of load circuits further comprises:

creating an m^th load circuit comprising a select transistor coupled to m resistors that are coupled in series, said m^th load circuit for matching a source side loading effect of a corresponding m^th memory cell located m memory cells away from a source line node on a source line coupling source regions in memory cells of said row of memory cells.

19. The method as described in claim 17, further comprising:

comparing said reference current against current from a memory cell being read in said non-volatile memory.

20. The method as described in claim 17, wherein said non-volatile memory comprises:

at least one array of memory cells from said plurality of memory cells arranged in a plurality of rows and a plurality of columns, each of said memory cells in said array comprising a source region and a drain region, and capable of storing a respective bit;

a plurality of word lines coupled to respective rows of said memory cells;

a plurality of bit lines coupled to respective columns of said memory cells; and

a plurality of source lines wherein at least one of said plurality of source lines corresponds to a respective row of memory cells in said plurality of rows, and couples in series source regions of memory cells in said respective row.

21. The method as described in claim 17, wherein said selecting between said plurality of load circuits is performed with a logic circuit.

22. The method as described in claim 18, wherein said selecting between said plurality of load circuits reduces said reference current approximately equal to a reduction in current of a corresponding memory cell being read due to source side loading effects.

23. The method as described in claim 17, further comprising:

coupling a differential amplifier to said reference cell and to a source line of said row of memory cells, said differential amplifier for comparing said reference current, reduced by a corresponding load circuit, against current read from said source line from a corresponding memory cell.