Non-volatile static memory cell
View Patent ↗A static memory cell comprising a pair of cross-coupled inverters ( 10, 12 ) which is “shadowed” with non-volatile memory elements ( 14, 16 ) so that data written in the static memory can be stored in the non-volatile cell, but also can be recalled later. The non-volatile cells ( 14, 16 ) are programmed with opposite data to increase the robustness of the retrieval process, and they are cross-coupled to the internal nodes (A, B) of the static memory cell, one the non-volatile cells ( 14 ) having a control gate connected to B and its source to A, and the other non-volatile element ( 16 ) having a control gate connected to A and its source to B. The drain of each non-volatile element ( 14, 16 ) is connected by means of a respective pMOS transistor ( 18, 20 ) to a program supply means.
1. A memory device comprising, in a single integrated circuit package:
a static memory means defining at least first and second nodes communicatively connected with read and/or write data lines, wherein the static memory means comprises a pair of cross-coupled inverters, each of the cross-coupled inverters including first and second transistors that are connected in series, sources of the first transistors of the cross-coupled inverters being connected to each other; and
at least one non-volatile memory means associated with said static memory means, and writing data stored therein to said static memory means; said non-volatile memory means comprising a first non-volatile element having a control gate connected to a first node and a source connected to a second node, and a second non-volatile element having a control gate connected to the second node and a source connected to the first node, the drain of each non-volatile element being connected by means of a respective transistor to a supply means; characterized in that said respective transistors are arranged to isolate the drains of the first and second non-volatile elements from the supply means during a program cycle of the memory device, the drains of the first and second non-volatile elements being connected to drains of the respective transistors, the supply means being connected to sources of the respective transistors, the sources of the respective transistors being also connected to the sources of the first transistors of the cross-coupled inverters.
2. A memory device according to claim 1 , wherein said non-volatile memory elements comprise embedded flash or EEPROM elements.
3. A memory device according to claim 1 , wherein said non-volatile memory elements comprise double or single poly floating gate type memory cells.
4. A memory device according to claim 1 , wherein said non-volatile memory elements comprise devices which can be programmed and erased by means of tunneling of charges.
5. A memory device according to claim 1 , wherein the non-volatile memory elements are programmed with opposite data.
6. A memory device according to claim 1 , wherein one or more respective selection transistors are provided, by means of which the nodes are communicatively coupled to the read and/or write lines.
7. A memory device according to claim 1 , including one or more isolation transistors.
8. A reconfigurable programmable logic device including a memory device according to claim 1 .
9. A field programmable gate array including a memory device according to claim 1 .
10. A memory device according to claim 1 , wherein gates of the respective transistors are connected together to receive a common signal.