Semiconductor memory system including selection transistors
A semiconductor memory system comprising a memory matrix including a plurality of memory cells arranged in rows and columns and connected to a plurality of column lines, each memory cell of the same column having a first and a second terminal connected to a first and a second column line respectively. Furthermore, the memory system comprises a first and a second conduction line which can be connected to said first and second column lines, and generating means provided with at least a first and a second output line, making available a first and a second reading/writing voltage to said first and second terminal respectively. The memory system also comprises at least a first and a second selection transistor connected to the same command line and having corresponding operative terminals connected directly to the first and to the second output lines respectively and corresponding cell terminals connected directly to the first and to the second conduction lines respectively.
1. Semiconductor memory system comprising:
a memory matrix including a plurality of memory cells arranged in rows and columns and connected to a plurality of column lines, each memory cell of the same column having a first and a second terminal connected to a first and a second column line respectively,
a plurality of conduction lines which can be selectively connected to the plurality of column lines and including a first and a second conduction line which can be connected to said first and second column lines,
generating means provided with a plurality of output lines including at least a first and a second output line to make available a first and a second reading/writing voltage respectively to be supplied to said first and second terminal,
groups of selection transistors which can be activated/deactivated to/from conduction by means of command lines to selectively connect the plurality of output lines to the plurality of conduction lines,
wherein each group of transistors comprises at least a first and a second transistor connected to the same command line, said first and second transistors having corresponding operative terminals connected directly to the first and to the second output lines respectively, and corresponding cell terminals connected directly to the first and to the second conduction lines respectively.
2. Memory system according to claim 1 , in which said memory matrix can be divided into a plurality of sub-matrices each of which can be accessed by means of a respective group of conduction lines, and each group of transistors is associated to a respective sub-matrix to selectively connect the plurality of output lines to a group of conduction lines.
3. Memory system according to claim 2 , comprising a decoder provided with input lines to receive address signals and with an output bus including said plurality of command lines, the decoder enabling selection of the command lines on the basis of said address signals to activate/deactivate to/from conduction each group of transistors.
4. Memory system according to claim 2 , in which said sub-matrices have at least two conduction lines in common and are, therefore, linked.
5. Memory system according to claim 1 , comprising further groups of selection transistors to connect/disconnect said plurality of conduction lines to/from the column lines.
6. Memory system according to claim 5 , in which said first and second conduction lines can be connected to said first and second column lines by means of two respective selection transistors belonging to said further groups of transistors.
7. Memory system according to claim 6 , in which during a reading/writing operation of a pre-established memory cell connected to said first or second column lines, said first or second output lines are connected to said first or second column lines by means of a conductive path for an electric current associated with said first and second reading/writing voltages not including other transistors besides the pre-established cell, the first and second transistor and said two selection transistors, such as to reduce the total impedance along the conductive path.
8. Memory system according to claim 1 , in which said generating means are such as to leave at least one output line of said plurality of output lines floating, and are such as to also generate an erasure voltage of cells of the memory matrix.
9. Memory system according to claim 8 , in which said generating means further comprise a third and a fourth output lines to make available at least one biasing voltage to be supplied to a further column line distinct from said first and second column lines, during reading of a first cell connected to them.
10. Memory system according to claim 9 , in which the generating means are such as to distribute, on said plurality of output lines, the first and the second reading/writing voltages, said erasing voltage and said biasing voltage depending on the address signals which identify said first cell.
11. Memory system according to claim 2 , in which each group of conduction lines associated with a respective sub-matrix comprises four conduction lines.
12. Memory system according to claim 2 , in which each group of transistors associated with the respective sub-matrix comprises four transistors connected to a common command line.
13. Memory system according to claim 3 , in which the decoder, making it possible to activate/deactivate each group of transistors to/from conduction, enables reading, writing and erasing operations only of predetermined sub-matrices of the memory matrix.
14. Memory system according to claim 4 , in which said predetermined sub-matrices may or may not be linked.
15. Memory system according to claim 1 , in which said plurality of memory cells includes non volatile NROM type cells and dual bit.
16. Memory system according to claim 1 , comprising a sense amplifier to perform current type reading of at least one data element contained in each cell, said amplifier being provided with an input terminal to receive a reading current correlated to the data element and a reference terminal to receive a reference current to be compared to said reading current.
17. Memory system according to claim 16 , comprising a commutator provided with:
a plurality of inputs each connected to a respective output line of the plurality of generating means,
an output selectively connectable to the plurality of inputs on the basis of the address signals, said output being connected to the input terminal of the sense amplifier.
18. Memory system according to claim 3 , comprising a plurality of pre-decoding blocks to decode external address signals, obtaining said address signals in the form of a sequence of numerical signals.
19. Memory system according to claim 1 , comprising a voltage regulator connectable to command terminals of memory cells belonging to a row of said matrix.
20. Memory system according to claim 1 , in which said memory matrix is associated with a less significant bit of a memory word, said system comprising at least one further memory matrix associated with another bit of the memory word, the decoder enabling parallel reading of said bits.
21. A memory, comprising:
a word line;
a command line;
first and second main column lines;
first and second electric output lines;
a nonvolatile memory cell having a control terminal coupled to the word line and having first and second conduction terminals respectively coupled to the first and second main column lines;
a first selection switch having a control terminal coupled to the command line and having first and second conduction terminals respectively coupled to the first main column line and to the first electric output line; and
a second selection switch having a control terminal coupled to the command line and having first and second conduction terminals respectively coupled to the second main column line and to the second electric output line.
22. The memory of claim 21 , further comprising an address decoder operable to access the memory cell by activating the first and second selection switches via the command line.
23. The memory of claim 21 , further comprising a function generator coupled to the first and second electric output lines and operable to generate a read voltage on one of the lines and a ground voltage on the other one of the lines.
24. The memory of claim 21 , further comprising a function generator coupled to the first and second electric output lines and operable to generate a program voltage on one of the lines and a reference voltage on the other one of the lines.
25. The memory of claim 21 , further comprising a function generator coupled to the first and second electric output lines and operable to generate an erase voltage on one of the lines and to electrically float the other one of the lines.
26. The memory of claim 21 , further comprising:
a first access transistor operable to couple the first conduction terminal of the memory cell to the first main column line; and
a second access transistor operable to couple the second conduction terminal of the memory cell to the second main column line.
27. The memory of claim 21 wherein the first and second selection switches respectively comprise first and second selection transistors.
28. The memory of claim 21 wherein the memory cell comprises a dual-bit memory cell.
29. An electronic system, comprising:
a memory, comprising,
a word line,
an command line,
first and second main column lines,
first and second electric output lines,
a nonvolatile memory cell having a control terminal coupled to the word line and having first and second conduction terminals respectively coupled to the first and second main column lines,
a first selection switch having a control terminal coupled to the command line and having first and second conduction terminals respectively coupled to the first main column line and to the first electric output line, and
a second selection switch having a control terminal coupled to the command line and having first and second conduction terminals respectively coupled to the second main column line and to the second electric output line.