Nonvolatile semiconductor memory device
View Patent ↗Provided is a nonvolatile semiconductor memory device which reads out a memory cell at high speed. A minute current source ( 105 ) is connected to a clamp NMOS transistor ( 103 ) for clamping a drain voltage of a memory cell ( 101 ), and a minute current is caused to flow through the clamp NMOS transistor ( 103 ). When the current does not flow through the memory cell ( 101 ), by causing the minute current to flow through the clamp NMOS transistor ( 103 ), the drain voltage of the memory cell ( 101 ) is prevented from rising. A bias voltage (BIAS) to be input to the clamp NMOS transistor ( 103 ) can be set high and the drain voltage of the memory cell ( 101 ) can also be high, and hence a current value of the memory cell ( 101 ) becomes larger and speed of sensing a current of a sense amplifier circuit ( 104 ) is improved.
1. A semiconductor memory device, comprising:
a memory cell;
a clamp NMOS transistor connected between the memory cell and an input of a sense amplifier circuit; and
a minute current source connected to a source of the clamp NMOS transistor and configured to cause a minute current flow from the source of the clamp NMOS transistor to a ground terminal, the minute current source comprising an NMOS transistor that comprises a drain connected to the source of the clamp NMOS transistor.
2. The semiconductor memory device of claim 1 , further comprising a selection NMOS transistor connected between the clamp NMOS transistor and the memory cell.
3. A semiconductor memory device, comprising:
a memory cell;
a clamp NMOS transistor connected between the memory cell and an input of a sense amplifier circuit; and
a minute current source connected to a source of the clamp NMOS transistor and configured to cause a minute current flow from the source of the clamp NMOS transistor to a ground terminal, the minute current source comprising one of a resistance element, a bipolar transistor, and a PN diode.
4. The semiconductor memory device of claim 3 , further comprising a bias voltage generating circuit configured to provide a bias voltage to a gate of the clamp NMOS transistor.
5. The semiconductor memory device of claim 3 , the bias voltage circuit comprising:
a constant current source comprising a source terminal connected to the gate of the clamp transistor;
a first NMOS transistor comprising a drain and a gate connected to the gate of the clamp NMOS transistor; and
a second NMOS transistor comprising:
a drain and a gate connected a source of the first NMOS transistor and to the minute current source; and
a source connected to the ground terminal.
6. The semiconductor memory device of claim 3 , where the minute current source comprises an NMOS transistor comprising:
a drain connected to the source of the clamp NMOS transistor; and
a gate connected to the drain and gate of the second NMOS transistor and to the source of the first NMOS transistor.
7. The semiconductor memory device of claim 5 , where the first NMOS transistor and the clamp NMOS transistor each comprising threshold values that are substantially the same.
8. The semiconductor memory device of claim 6 , where the threshold value of each of the first NMOS transistor and the clamp NMOS transistor are lower than a threshold value of the second NMOS transistor and a threshold value of the memory cell.
9. A semiconductor memory device, comprising:
a memory cell;
a clamp NMOS transistor connected between the memory cell and an input of a sense amplifier circuit; and
a minute current source connected to a source of the clamp NMOS transistor and configured to cause a minute current flow from the source of the clamp NMOS transistor to a ground terminal;
where the clamp NMOS transistor comprises a threshold value that is lower than a threshold value of the memory cell.
10. The semiconductor memory device of claim 1 , where the minute current source comprises a current value that is less than a reference current of the sense amplifier circuit connected to the clamp NMOS transistor.
11. A semiconductor memory device, comprising:
a memory cell;
a clamp NMOS transistor connected between the memory cell and a sense amplifier circuit, the clamp NMOS transistor comprising:
a gate connected to a bias voltage generating circuit that provides a bias voltage to the gate of the clamp NMOS transistor; and
a source; and
a minute current source connected to the source of the clamp NMOS transistor and configured to cause a minute current flow from the source of the clamp NMOS transistor to a ground terminal such that a drain voltage of the memory cell is prevented from rising when the memory cell is read out while having no current flowing therethrough.
12. The semiconductor memory device of claim 11 , further comprising a selection NMOS transistor connected between the clamp NMOS transistor and the memory cell.
13. The semiconductor memory device of claim 11 , the minute current source comprising an NMOS transistor that comprises:
a drain connected to the source of the clamp NMOS transistor; and
a source connected to the ground terminal.
14. The semiconductor memory device of claim 11 , where the clamp NMOS transistor comprises a threshold value that is lower than a threshold value of the memory cell.
15. The semiconductor memory device of claim 11 , where the minute current source comprises a current value that is less than a reference current of the sense amplifier circuit connected to the clamp NMOS transistor.
16. The semiconductor memory device of claim 11 , the minute current source comprising one of a resistance element, a bipolar transistor, and a PN diode.