Power switch circuit capable of reducing leakage current

This non-provisional application claims priority of U.S. provisional application No. 62/832,853, filed on Apr. 11, 2019, included herein by reference in its entirety.

1. Field of the Invention

The present invention is related to a power switch circuit, and more particularly, to a power switch circuit capable of reducing leakage current.

2. Description of the Prior Art

As the functions of electronic circuits become more and more complicated, the electronic circuits may require different levels of voltages for performing different operations. For example, the non-volatile memory circuit may use the system voltage for reading operation, and will use a higher voltage for programming operation. In this case, a power switch circuit will be applied to provide the required voltages on demand.

In the prior art, the power switch circuit is designed to output the highest input voltages. However, the high voltage used for program operation is usually generated by a charge pump, and the charge pump needs some time to pump the voltage to the target level. Therefore, if the input voltages received by the power switch circuit are at similar levels during the voltage pumping process of the charge pump, the power switch circuit would be stocked in an unstable status, producing a significant amount of leakage current.

One embodiment of the present invention discloses a power switch circuit. The power switch circuit includes an output terminal, a voltage selection unit, a first level shift circuit, a second level shift circuit, and a leakage control unit.

The output terminal outputs an output voltage. The voltage selection unit receives a first variable voltage and a second variable voltage, and outputs a greater one of the first variable voltage and the second variable voltage as an operation voltage. The first level shift circuit is coupled to the voltage selection unit, and outputs a first control signal according to a first input signal. The second level shift circuit is coupled to the voltage selection unit, and outputs a second control signal according to a second input signal.

The first transistor has a first terminal for receiving the first variable voltage, a second terminal coupled to the output terminal of the power switch circuit, and a control terminal coupled to the first level shift circuit for receiving the first control signal. The second transistor has a first terminal for receiving the second variable voltage, a second terminal coupled to the output terminal of the power switch circuit, and a control terminal coupled to the second level shift circuit for receiving the second control signal.

The leakage control unit has a first terminal coupled to the first terminal of the first transistor and/or the first terminal of the second transistor, a second terminal coupled to the control terminal of the second transistor, and a control terminal for receiving the operation voltage. The leakage control unit establishes an electrical connection between the first terminal and the second terminal of the leakage control unit according to the operation voltage.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

FIG. 1 shows a power switch circuit according to one embodiment of the present invention.

FIG. 2 shows a power switch circuit according to another embodiment of the present invention.

FIG. 3 shows a power switch circuit according to another embodiment of the present invention.

FIG. 4 shows a power switch circuit according to another embodiment of the present invention.

FIG. 5 shows a power switch circuit according to another embodiment of the present invention.

FIG. 1 shows a power switch circuit 100 according to one embodiment of the present invention. The power switch circuit 100 includes an output terminal OUT, a voltage selection unit 110 , a first level shift circuit 120 , a second level shift circuit 130 , a first transistor M 1 A, a second transistor M 2 A, and a first leakage control unit 140 .

The voltage selection unit 110 can receive a first variable voltage VV 1 and a second variable voltage VV 2 , and output a greater one of the first variable voltage VV 1 and the second variable voltage VV 2 as an operation voltage VOP.

In FIG. 1 , the voltage selection unit 110 can include an output terminal, a third transistor M 3 A, and a fourth transistor M 4 A. The output terminal of the voltage selection unit 110 can output the operation voltage VOP. The third transistor M 3 A has a first terminal for receiving the first variable voltage VV 1 , a second terminal coupled to the output terminal of the voltage selection unit 110 , and a control terminal for receiving the second variable voltage VV 2 . The fourth transistor M 4 A has a first terminal for receiving the second variable voltage VV 2 , a second terminal coupled to the output terminal of the voltage selection unit 110 , and a control terminal for receiving the first variable voltage VV 1 .

Also, in FIG. 1 , the third transistor M 3 A and the fourth transistor M 4 A can be P-type transistors. In this case, when the first variable voltage VV 1 is greater than the second variable voltage VV 2 , the third transistor M 3 A will be turned on and the fourth transistor M 4 A will be turned off. Therefore, the voltage selection unit 110 will output the first variable voltage VV 1 as the operation voltage VOP through the output terminal of the voltage selection unit 110 . However, if the second variable voltage VV 2 is greater than the first variable voltage VV 1 , then the third transistor M 3 A will be turned off and the fourth transistor M 4 A will be turned on. In this case, the voltage selection unit 110 will output the second variable voltage VV 2 as the operation voltage VOP.

The first level shift circuit 120 is coupled to the voltage selection unit 110 , and can output a first control signal SIG ctrl1 according to the first input signal SIG IN1 . Similarly, the second level shift circuit 130 is coupled to the voltage selection unit 110 , and can output a second control signal SIG ctrl2 according to a second input signal SIG IN2 .

In FIG. 1 , the first level shift circuit 120 and the second level shift circuit 130 can have the same structures. For example, the first level shift circuit 120 includes P-type transistors P 1 and P 2 , and N-type transistors N 1 and N 2 . The P-type transistor P 1 has a first terminal coupled to the voltage selection unit 110 for receiving the operation voltage VOP, a second terminal for outputting the first control signal SIG ctrl1 , and a control terminal. The P-type transistor P 2 has a first terminal coupled to the voltage selection unit 110 for receiving the operation voltage VOP, a second terminal coupled to the control terminal of the P-type transistor P 1 , and a control terminal coupled to the second terminal of the P-type transistor P 1 . The N-type transistor N 1 has a first terminal coupled to the second terminal of the P-type transistor P 1 , a second terminal for receiving a system voltage VS, and a control terminal for receiving a first complementary input signal SIG IN1C complementary with the first input signal SIG IN1 . The N-type transistor N 2 has a first terminal coupled to the second terminal of the P-type transistor P 2 , a second terminal for receiving the system voltage VS, and a control terminal for receiving the first input signal SIG IN1 .

Similarly, the second level shift circuit 130 can include P-type transistors P 3 and P 4 , and N-type transistors N 3 and N 4 . In this case, the control terminal of the N-type transistor N 4 can receive the second input signal SIG IN2 , and the control terminal of the N-type transistor N 3 can receive a second complementary input signal SIG IN2C complementary with the second input signal SIG IN2 . Also, the second terminal of the P-type transistor P 3 will output the second control signal SIG ctrl2 . However, in some other embodiments, the first level shift circuit 120 and the second level shift circuit 130 may also be implemented by some different structures.

In FIG. 1 , the first transistor M 1 A has a first terminal for receiving the first variable voltage VV 1 , a second terminal coupled to the output terminal OUT of the power switch circuit 100 , and a control terminal coupled to the first level shift circuit 120 for receiving the first control signal SIG ctrl1 . The second transistor M 2 A has a first terminal for receiving the second variable voltage VV 2 , a second terminal coupled to the output terminal OUT of the power switch circuit 100 , and a control terminal coupled to the second level shift circuit 130 for receiving the second control signal SIG ctrl2 . In FIG. 1 , the first transistor M 1 A and the second transistor M 2 A can be P-type transistors.

Also, in some embodiments, the input signals SIG IN1 and SIG IN2 can be complementary so that only one of the first transistor M 1 A and the second transistor M 2 A will be turned on at a time for outputting the second variable voltage VV 2 or the first variable voltage VV 1 as required. For example, when the power switch circuit 100 is used to output the second variable voltage VV 2 , the first input signal SIG IN1 would be at the second variable voltage VV 2 and the second input signal SIG IN2 would be at a system voltage VS smaller than the second variable voltage VV 2 . In this case, the first control signal SIG ctrl1 would be raised to the operation voltage VOP by the first level shift circuit 120 while the second control signal SIG ctrl2 may remain at the system voltage VS. Consequently, the first transistor M 1 A will be turned off, the second transistor M 2 A will be turned on, and the power switch circuit 100 will output the second variable voltage VV 2 as the output voltage Vout through the output terminal OUT.

In some embodiments, the power switch circuit 100 can output the first variable voltage VV 1 and the second variable voltage VV 2 as the output voltage Vout for performing the read operation and the program operation of a memory cell. However, in some other embodiments, the power switch circuit 100 may be adopted in other application for providing the operation voltage VOP required.

Furthermore, in some embodiments, the first variable voltage VV 1 can be generated by a charge pump, and the second variable voltage VV 2 can be an existing system voltage. In this case, when the charge pump is disabled, the first variable voltage VV 1 may be smaller than the second variable voltage VV 2 . However, after the charge pump is enabled, the first variable voltage VV 1 may be increased from being smaller than the second variable voltage VV 2 to being greater than the second variable voltage VV 2 .

Therefore, before the first variable voltage VV 1 reaches the targeted level, the first variable voltage VV 1 may become substantially equal to the second variable voltage VV 2 for a period of time. In this case, the operation voltage VOP generated by the voltage selection unit 110 would be smaller than second variable voltage VV 2 by a threshold voltage of the fourth transistor M 4 A. Consequently, when the power switch circuit 100 is used to output the first variable voltage VV 1 , the first input signal SIG IN1 would be at the system voltage VS and the second input signal SIG IN2 would be at a second variable voltage VV 2 . Correspondingly, the first control signal SIG ctrl1 remains at the system voltage VS while the second control signal SIG ctrl2 would be raised to the operation voltage VOP. However, since the operation voltage VOP is equal to the second variable voltage VV 2 minus the threshold voltage of the fourth transistor M 4 A, the operation voltage VOP would be smaller than the first variable voltage VV 1 . Therefore, the second transistor M 2 A may not be turned off as expected, and the first transistor M 1 A and the second transistor M 2 A may be turned on at the same time, causing a significant leakage current flowing from the first terminal of the first transistor M 1 A through the first transistor M 1 A and the second transistor M 2 A to the first terminal of the second transistor M 2 A. Furthermore, the leakage current may be a huge burden to the charge pump, and the charge pump may not be able to further increase the first variable voltage VV 1 . Consequently, the first variable voltage VV 1 will never reach its target value, resulting in operation fail.

In some embodiments, the first leakage control unit 140 can be used to reduce the leakage current aforementioned. In FIG. 1 , the first leakage control unit 140 has a first terminal coupled to the first terminal of the second transistor M 2 A, a second terminal coupled to the control terminal of the second transistor M 2 A, and a control terminal for receiving the operation voltage VOP. The first leakage control unit 140 can establish an electrical connection between the first terminal and the second terminal of the first leakage control unit 140 according to the operation voltage VOP.

For example, the first leakage control unit 140 can establish the electrical connection when the first variable voltage VV 1 is substantially equal to the second variable voltage VV 2 . Therefore, in the case that the power switch circuit 100 needs to output the first variable voltage VV 1 while the operation voltage VOP is lower than the second variable voltage VV 2 , the first leakage control unit 140 can raise the voltage of the control terminal of the second transistor M 2 A to the second variable voltage VV 2 so that the second transistor M 2 A can be turned off, reducing the leakage current.

In FIG. 1 , the first leakage control unit 140 includes a fifth transistor M 5 A. The fifth transistor M 5 A has a first terminal coupled to the first terminal of the first leakage control unit 140 , a second terminal coupled to the second terminal of the first leakage control unit 140 , and a control terminal coupled to the control terminal of the first leakage control unit 140 . Also, the fifth transistor M 5 A can be a P-type transistor.

In this case, when the second control signal SIG ctrl2 is raised to the operation voltage VOP while the operation voltage VOP is lower than the second variable voltage VV 2 , the fifth transistor M 5 A will be turned on. Consequently, the voltage of the control terminal of the second transistor M 2 A can be raised to the second variable voltage VV 2 through the fifth transistor M 5 A so the second transistor M 2 A can be turned off as required.

Since the fifth transistor M 5 A is used to raise the voltage of the control terminal of the second transistor M 2 A without requiring a large current, the size of the fifth transistor M 5 A can be smaller than the size of the first transistor M 1 A, and the size of the fifth transistor M 5 A can be smaller than the size of the second transistor M 2 A. Consequently, the leakage current caused during the pumping process of the first variable voltage VV 1 can be reduced with only small additional circuit area.

FIG. 2 shows a power switch circuit 100 ′ according to another embodiment of the present invention. The power switch circuit 100 ′ and the power switch circuit 100 have similar structures and can be operated with the same principles. However, the power switch circuit 100 ′ further includes a second leakage control unit 140 ′. The second leakage control unit 140 ′ has a first terminal coupled to the first terminal of the first transistor M 1 A, a second terminal coupled to the control terminal of the first transistor M 1 A, and a control terminal for receiving the operation voltage VOP. The second leakage control unit 140 ′ can establish an electrical connection between the first terminal and the second terminal of the second leakage control unit 140 ′ according to the operation voltage VOP.

The second leakage control unit 140 ′ can have the same structure as the first leakage control unit 140 , and can perform the same function to reduce the leakage current. For example, the second leakage control unit 140 ′ can include a transistor M 5 A′. The transistor M 5 A′ has a first terminal coupled to the first terminal of the second leakage control unit 140 ′, a second terminal coupled to the control terminal of the second leakage control unit 140 ′, and a control terminal coupled to the control terminal of the second leakage control unit 140 ′. Also, the transistor M 5 A′ can be a P-type transistor. In this case, when the control signal SIG ctrl1 is meant to turn off the first transistor M 1 A but is not high enough to fully turn off the first transistor M 1 A, the second leakage control unit 140 ′ can be turned on to raise the voltage of the control terminal of the first transistor M 1 A. Consequently, the first transistor MIA can be turned off and the leakage current can be reduced.

FIG. 3 shows a power switch circuit 200 according to another embodiment of the present invention. The power switch circuit 200 and the power switch circuit 100 have similar structures and can be operated with similar principles. However, the first leakage control unit 240 further includes a sixth transistor M 6 B. The sixth transistor M 6 B has a first terminal coupled to the first terminal of the first transistor M 1 A, a second terminal coupled to the second terminal of the first leakage control unit 240 , and a control terminal coupled to the control terminal of the first leakage control unit 240 . The sixth transistor M 6 B can be P-type transistor.

In this case, when the second control signal SIG ctrl2 is raised to the operation voltage VOP while the operation voltage VOP is lower than the second variable voltage VV 2 , the fifth transistor M 5 A and the sixth transistor M 6 B will both be turned on. Consequently, the voltage of the control terminal of the second transistor M 2 A can be raised to the second variable voltage VV 2 through the fifth transistor M 5 A and the sixth transistor M 6 B so the second transistor M 2 A can be turned off as required.

Since the sixth transistor M 6 B is used to raise the voltage of the control terminal of the second transistor M 2 A without requiring large current, the sixth transistor M 6 B can also be smaller than the first transistor M 1 A and the second transistor M 2 A.

In some embodiments, if the sixth transistor M 6 B can reduce the leakage current effectively, the fifth transistor M 5 A may be omitted.

Also, in some embodiments, the sixth transistor M 6 B may cause leakage current when the power switch circuit 200 is used to output the second variable voltage VV 2 as the output voltage Vout. For example, when the first input signal SIG IN1 is at the second variable voltage VV 2 and the second input signal SIG IN2 is at the system voltage VS, the first control signal SIG ctrl1 would be raised to the operation voltage VOP and second control signal SIG ctrl2 would be at the system voltage VS. Therefore, the first transistor MIA should be turned off and the second transistor M 2 A should be turned on for outputting the second variable voltage VV 2 as the output voltage Vout.

However, in this case, if the first variable voltage VV 1 is substantially equal to the second variable voltage VV 2 , the operation voltage VOP would be lower than the first variable voltage VV 1 by the threshold voltage of the fourth transistor M 4 A, and the sixth transistor M 6 B will be turned on. Consequently, the leakage current may flow from the first terminal of the sixth transistor M 6 B through the N-type transistor N 3 in the second level shift circuit 130 to the ground. The leakage current can be a huge burden to the charge pump, and the charge pump may not be able to further increase the first variable voltage VV 1 . To reduce the leakage current, another transistor may be added.

Also, in some embodiments, the power switch circuit 200 can further include a second leakage control unit having the same structure as the first leakage control unit 240 . The second leakage control unit can be coupled to the first terminal and the control terminal of the first transistor M 1 A and can be controlled by the operation voltage VOP. Therefore, when the control signal SIG ctrl1 is meant to turn off the first transistor M 1 A but is not high enough to fully turn off the first transistor M 1 A, the second leakage control unit can be turned on to raise the voltage of the control terminal of the first transistor M 1 A. Consequently, the first transistor M 1 A can be turned off and the leakage current can be reduced.

FIG. 4 shows a power switch circuit 300 according to another embodiment of the present invention. The power switch circuit 300 and the power switch circuit 100 have similar structures and can be operated with similar principles. However, the first leakage control unit 340 includes a fifth transistor M 5 C and a sixth transistor M 6 C.

The fifth transistor M 5 C has a first terminal coupled to the first terminal of the first transistor M 1 A, a second terminal, and a control terminal for receiving a leakage control signal SIG LC . The sixth transistor M 6 C has a first terminal coupled to the second terminal of the fifth transistor M 5 C, a second terminal coupled to the second terminal of the first leakage control unit 340 , and a control terminal coupled to the control terminal of the first leakage control unit 340 . Also, the fifth transistor M 5 C and the sixth transistor M 6 C can be P-type transistors, and the body terminal of the fifth transistor M 5 C can be coupled to the body terminal of the sixth transistor M 6 C.

In some embodiments, the leakage control signal SIG LC can be generated according to the first input signal SIG IN1 . For example, the leakage control signal SIG LC can be substantially equal to the first input signal SIG IN1 . In this case, when the first input signal SIG IN1 is at the second variable voltage VV 2 and the second input signal SIG IN2 is at the system voltage VS, the fifth transistor M 5 C will be turned off. Consequently, the leakage current caused by the sixth transistor M 6 B when the power switch circuit 200 outputs the second variable voltage VV 2 can be reduced.

Furthermore, in some embodiments, the sizes of the fifth transistor M 5 C and the sixth transistor M 6 C can be smaller than sizes of the first transistor MIA and the second transistor M 2 A.

Also, in some embodiments, the power switch circuit 300 can further include a second leakage control unit having the same structure as the first leakage control unit 340 for reducing the leakage current on the first transistor M 1 A. In this case, the second leakage control unit can be coupled to the first terminal of the second transistor M 2 A and the control terminal of the first transistor M 1 A, and can be controlled by the operation voltage VOP.

FIG. 5 shows a power switch circuit 400 according to another embodiment of the present invention. The power switch circuit 400 and the power switch circuit 300 have similar structures and can be operated with similar principles. However, the first leakage control unit 440 further includes a seventh transistor M 7 D.

The seventh transistor M 7 D has a first terminal coupled to the first terminal of the second transistor M 2 A, a second terminal coupled to the second terminal of the first leakage control unit 440 , and a control terminal coupled to the control terminal of the first leakage control unit 440 . That is, the seventh transistor M 7 D can be used to reduce the leakage current in the power switch circuit 400 as the fifth transistor M 5 A in the power switch circuit 100 . In this case, the seventh transistor M 7 D can be a P-type transistor, and the size of the seventh transistor M 7 D can be smaller than the sizes of the first transistor M 1 A and the second transistor M 2 A.

Also, in some embodiments, the power switch circuit 400 can further include a second leakage control unit having the same structure as the first leakage control unit 440 for reducing the leakage current on the first transistor M 1 A. In this case, the second leakage control unit can be coupled to the control terminal of the first transistor M 1 A and the first terminals of the first transistor M 1 A and the second transistor M 2 A. The second leakage control unit can be controlled by the operation voltage VOP.

In summary, the power switch circuits provided by the embodiments of the present invention can reduce the leakage current with the leakage control unit, allowing the charge pump to pump the voltage to the target level smoothly. Also, since the leakage control unit is mainly used to adjust the voltage at the control terminal of the transistors for outputting the output voltage, the leakage control unit will not induce large current, and the size of the leakage control unit can be rather small.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.