Non-volatile memory and method with control gate compensation for source line bias errors
Source line bias is an error introduced by a non-zero resistance in the ground loop of the read/write circuits. During sensing the source of a memory cell is erroneously biased by a voltage drop across the resistance and results in errors in the applied control gate and drain voltages. This error is minimized when the applied control gate and drain voltages have their reference point located as close as possible to the sources of the memory cells. In one preferred embodiment, the reference point is located at a node where the source control signal is applied. When a memory array is organized in pages of memory cells that are sensed in parallel, with the sources in each page coupled to a page source line, the reference point is selected to be at the page source line of a selected page via a multiplexor.
1. In a non-volatile memory device having individual pages of memory cells to be sensed in parallel, each memory cell having a source, a drain, a charge storage unit and a control gate for controlling a conduction current along said drain and source, a method of sensing a page of memory cells, comprising:
providing an aggregate node coupling a source voltage control circuit to the source of each memory cell of said page;
coupling the control gate of each memory cell of said page to a word line;
providing a predetermined word line voltage to the word line of each memory cell of said page, wherein said predetermined word line voltage is referenced with respect to said aggregate node so as not to be affected by any voltage differences between said aggregate node and a ground reference.
coupling the drain of each memory cell of said page to an associated bit line; and
providing a predetermined bit line voltage to the associated bit line of each memory cell of said page for sensing operation, wherein each said predetermined bit line voltage is referenced with respect to said aggregate node so as not to be affected by any voltage differences between the aggregate node and a ground reference.
2. The method of sensing as in claim 1 , wherein said aggregate node is at a higher potential than said ground reference.
3. The method of sensing as in claim 1 , wherein said source voltage control circuit is referenced with respect to said ground reference.
4. The method of sensing as in claim 1 , wherein said providing a predetermined word line voltage further comprises:
providing a regulated reference voltage;
providing a DAC-controlled potential divider; and
generating the predetermined word line voltage by dividing said regulated reference voltage using the DAC-controlled potential divider.
5. The method as in any one of claims 1 - 4 , wherein each of said memory cells stores one bit of data.
6. The method as in any one of claims 1 - 4 , wherein each of said memory cells stores more than one bit of data.
7. A non-volatile memory device having individual pages of memory cells to be sensed in parallel, each memory cell having a source, a drain, a charge storage unit and a control gate for controlling a conduction current along said drain and source, comprising:
a source voltage control circuit;
an aggregate node coupling said source voltage control circuit to the source of each memory cell of said page;
a word line coupling to the control gate of each memory cell of said page;
a word line voltage supply for providing a predetermined word line voltage to the word line of each memory cell of said page, wherein said predetermined word line voltage is referenced with respect to said aggregate node so as not to be affected by any voltage differences between said aggregate node and a ground reference;
an associated bit line coupled to the drain of each memory cell of said page; and
a bit line voltage supply for providing a predetermined bit line voltage to the associated bit line of each memory cell of said page for sensing operation, wherein each said predetermined bit line voltage is referenced with respect to said aggregate node so as not to be affected by any voltage differences between said aggregate node and a ground reference.
8. The memory device as in claim 7 , wherein said aggregate node is at a higher potential than said ground reference.
9. The memory device as in claim 7 , wherein said source voltage control circuit is referenced with respect to said ground reference.
10. The memory device as in claim 7 , wherein said word line voltage supply further comprises:
a regulated reference voltage;
a DAC-controlled potential divider; and
an output predetermined word line voltage given by dividing said regulated reference voltage using the DAC-controlled potential divider.
11. The memory device as in any one of claims 7 - 10 , wherein each of said memory cells stores one bit of data.
12. The memory device as in any one of claims 7 - 10 , wherein each of said memory cells stores more than one bit of data.