Semiconductor device including sense amplifier having enhanced sensing margin and method of controlling the same

1. A semiconductor device comprising:

a first switch coupling a first power source and a first node according to a first control signal;

a sense amplifier coupled between the first node and a second node and performing a sensing operation;

a second switch coupling a second power source and the second node according to a second control signal; and

a sense amplifier control circuit providing the first control signal and the second control signal,

wherein the sense amplifier control circuit controls the second control signal, so that a voltage of the second node reaches a shift voltage higher than a voltage of the second power source during a first sensing period of the sensing operation and a bias current flows through the second node during a second sensing period of the sensing operation, the second sensing period being subsequent to the first sensing period,

wherein the sense amplifier further performs an offset cancelling operation before the sensing operation, and

wherein the sense amplifier control circuit controls the second control signal so that the voltage of the second node reaches the shift voltage during the offset cancelling operation.

2. The semiconductor device of claim 1 , wherein the second switch includes a first metal-oxide-silicon (MOS) transistor having a source and a drain that are coupled between the second node and the second power source and a gate that receives the second control signal, and

wherein the sense amplifier control circuit controls the second control signal so that a voltage difference between the source and the drain of the first MOS transistor reaches the shift voltage.

3. The semiconductor device of claim 2 , wherein the first MOS transistor is an NMOS transistor and the sense amplifier control circuit controls the second control signal to have a first voltage during the first sensing period and a second voltage during the second sensing period, the second voltage being higher than the first voltage.

4. The semiconductor device of claim 1 , further comprising a third switch coupling the second node and the second power source according to a third control signal,

wherein the sense amplifier control circuit controls the second control signal and the third control signal, so that the voltage of the second node reaches the shift voltage during the first sensing period and the bias current flowing through the second node increases during the second sensing period.

5. The semiconductor device of claim 4 , wherein the second switch includes a second MOS transistor having a source and a drain that are coupled between the second node and the second power source and a gate that receives the second control signal,

wherein the third switch includes a third MOS transistor having a source and a drain that are coupled between the second node and the second power source and a gate that receives the third control signal, and

wherein the sense amplifier control circuit controls the second control signal so that a voltage difference between the source and the drain of the second MOS transistor reaches the shift voltage during the first sensing period, and controls the third control signal so that the bias current flowing through the second node increases during the second sensing period.

6. The semiconductor device of claim 5 , wherein the second MOS transistor and the third MOS transistor are NMOS transistors, and

wherein the sense amplifier control circuit controls the second control signal to have a first voltage during the first sensing period and the second sensing period, and controls the third control signal to have a second voltage during the first sensing period and a third voltage during the second sensing period, the third voltage being higher than the second voltage.

7. The semiconductor device of claim 6 , wherein a channel width of the third MOS transistor is greater than a channel width of the second MOS transistor.

8. The semiconductor device of claim 4 ,

wherein the sense amplifier control circuit controls the second control signal and the third control signal so that the voltage of the second node reaches the shift voltage during the offset cancelling operation.

9. The semiconductor device of claim 8 , further comprising a cell capacitor configured to be coupled to a first bit line according to a word line signal,

wherein the first bit line is coupled to the cell capacitor at a specific time after the offset cancelling operation and before the sensing operation.

10. The semiconductor device of claim 9 , wherein the sense amplifier comprises:

a first inverter coupled between the first node and the second node;

a second inverter coupled between the first node and the second node;

a first NMOS transistor coupling an input node and an output node of the first inverter according to an offset cancelling control signal;

a second NMOS transistor coupling an input node and output node of the second inverter according to the offset cancelling control signal;

a third NMOS transistor coupling the input node of the first inverter and the first bit line according to an input control signal; and

a fourth NMOS transistor coupling the input node of the second inverter and a second bit line according to the input control signal.

11. A semiconductor device comprising:

a first switch coupling a first power source and a first node according to a first control signal;

a sense amplifier coupled between the first node and a second node and performing a sensing operation;

a second switch coupling a second power source and the second node according to a second control signal; and

a sense amplifier control circuit providing the first control signal and the second control signal,

wherein the sense amplifier control circuit controls the second control signal, so that a voltage of the second node reaches a shift voltage higher than a voltage of the second power source during a first sensing period of the sensing operation and a bias current flows through the second node during a second sensing period of the sensing operation, the second sensing period being subsequent to the first sensing period, and

wherein a metastable point of the sense amplifier is substantially in the middle of a voltage of the first power source and the voltage of the second power source.

12. A method of controlling a semiconductor device, wherein the semiconductor device comprising a first switching device coupled between a first power source and a first node, a second switching device coupled between a second power source and a second node, and a sense amplifier coupled between the first and second nodes, the method comprising:

providing a first control signal to the first switching device, the first control signal having a first voltage during a first sensing period of a sensing operation;

providing a second control signal to the second switching device, the second control signal having a second voltage during the first sensing period of the sensing operation, the second control signal having a third voltage during a second sensing period of the sensing operation subsequent to the first period, the third voltage being higher than the second voltage; and

performing an offset canceling operation before the sensing operation,

wherein the second control signal has the second voltage during the offset canceling operation.

13. The method of claim 12 , wherein the second voltage of the second control signal is greater than a voltage of the second power source.

14. The method of claim 13 , wherein the third voltage of the second control signal is sufficiently high to fully turn on the second switching device.

15. The method of claim 12 , wherein the first sensing period is in a range from 0.15 ns to 0.25 ns.

16. The method of claim 12 , wherein the semiconductor device further comprises a third switching device coupled between the second node and the second power source, the method further comprising:

providing a third control signal to the third switching device, the third control signal having a fourth voltage during the offset canceling operation and during the first sensing period and the second sensing period of the sensing operation.

17. The method of claim 12 , further comprising:

causing a voltage of the second node to reach a shift voltage during the first sensing period of the sensing operation according to the second voltage of the second control signal, the shift voltage being higher than a voltage of the second power source.

18. The method of claim 17 , wherein a voltage of the second power source is a ground voltage, the method further comprising:

shifting a metastable point of the sense amplifier substantially to a half of a voltage of the first power source.