Power switch circuit capable of reducing leakage currents

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 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 circuit, a level shift circuit, and a transistor. The output terminal outputs an output voltage. The voltage selection circuit includes a main selection unit, a first re-comparison unit, and a second re-comparison unit. The main selection unit has a first voltage terminal for receiving a first variable voltage, a second voltage terminal for receiving a second variable voltage, and an output terminal for outputting a greater one of the first variable voltage and the second variable voltage as an operation voltage. The first re-comparison unit adjusts the operation voltage according to a greater one of the operation voltage and the first variable voltage, and the second re-comparison unit adjusts the operation voltage according to a greater one of the operation voltage and the second variable voltage.

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

Another embodiment of the present invention discloses a voltage selection circuit. The voltage selection circuit includes a main selection unit, a first re-comparison unit, and a second re-comparison unit.

The main selection unit has a first voltage terminal for receiving a first variable voltage, a second voltage terminal for receiving a second variable voltage, and an output terminal for outputting a greater one of the first variable voltage and the second variable voltage as an operation voltage. The first re-comparison unit adjusts the operation voltage according to a greater one of the operation voltage and the first variable voltage, and the second re-comparison unit adjusts the operation voltage according to a greater one of the operation voltage and the second variable 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 voltage selection 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 circuit 110 , a level shift circuit 120 , and a transistor M 1 A.

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.

The voltage selection circuit 110 includes a main selection unit 112 , a first re-comparison unit 114 , and a second re-comparison unit 116 . The main selection unit 112 has a first voltage terminal for receiving the first variable voltage VV 1 , a second voltage terminal for receiving the second variable voltage VV 2 , and an output terminal for outputting a greater one of the first variable voltage VV 1 and the second variable voltage VV 2 as an operation voltage VOP.

The level shift circuit 120 can be coupled to the voltage selection circuit 110 , and can output a control signal SIG ctrl1 according to the input signal SIG IN1 .

In some embodiments, the transistor M 1 A can be a P-type transistor. The 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 level shift circuit 120 for receiving the control signal SIG ctrl1 . In this case, the power switch circuit 100 can be used to output the first variable voltage VV 1 as the output voltage Vout through the output terminal OUT of the power switch circuit 100 according to the input signal SIG IN1 .

For example, when the power switch circuit 100 is used to output the first variable voltage VV 1 as the output voltage Vout, the input signal SIG IN1 would be at a first reference voltage VSS. In some embodiments, the first reference voltage VSS can be the ground voltage of the system. In this case, the level shift circuit 120 will keep the control signal SIG ctrl1 to be at the first reference voltage VSS, thereby turning on the transistor M 1 A for outputting the first variable voltage VV 1 as the output voltage Vout. However, when the input signal SIG IN1 is at a second reference voltage VDD, the control signal SIG ctrl1 would be raised to the operation voltage VOP by the level shift circuit 120 , and the level shift circuit 120 will turn off the transistor M 1 A. Consequently, the power switch circuit 100 will not output the first variable voltage VV 1 as the output voltage Vout.

Furthermore, in some embodiments, although the main selection unit 112 is used to output the operation voltage VOP by selecting the greater one of the first variable voltage VV 1 and the second variable voltage VV 2 , the main selection unit 112 may become instable if the first variable voltage VV 1 becomes substantially equal to the second variable voltage VV 2 . For example, the first variable voltage VV 1 may be generated by a charge pump while the second variable voltage VV 2 can be the same as the second reference voltage VDD already existing in the system. In this case, if the second variable voltage VV 2 has reached to a steady level before the charge pump that generates the variable voltage VV 1 is enabled, the first variable voltage VV 1 may be at a voltage smaller than the second variable voltage VV 2 . However, after the charge pump is enabled, the first variable voltage VV 1 can be increased from being smaller than the second variable voltage VV 2 to being greater than the second variable voltage VV 2 .

In this case, during the transition of the first variable voltage VV 1 when the first variable voltage VV 1 becomes substantially equal to the second variable voltage VV 2 , the operation voltage VOP may be lower than the first variable voltage VV 1 by a threshold voltage of the transistor P 1 A. Consequently, the level shift circuit 120 will not be able to raise the control signal SIG ctrl1 for turning off the transistor M 1 A effectively, and the leakage currents will be induced.

To reduce the leakage currents caused by the instable operation voltage VOP, the first re-comparison unit 114 and the second re-comparison unit 116 can be used to adjust the operation voltage VOP. The first re-comparison unit 114 can adjust the operation voltage VOP according to a greater one of the operation voltage VOP and the variable voltage VV 1 , and the second re-comparison unit 116 can adjust the operation voltage VOP according to a greater one of the operation voltage VOP and the second variable voltage VV 2 . In this case, whenever the operation voltage VOP is not stable and becomes lower than the first variable voltage VV 1 and the second variable voltage VV 2 , the first re-comparison unit 114 and the second re-comparison unit 116 will adjust the operation voltage VOP to the first variable voltage VV 1 or the second variable voltage VV 2 so that the transistor M 1 A can be firmly turned off, reducing the leakage currents.

In FIG. 1 , the main selection unit 112 includes P-type transistors P 1 A and P 2 A. The P-type transistor P 1 A has a first terminal coupled to the first voltage terminal of the main selection unit 112 , a second terminal coupled to the output terminal of the main selection unit 112 , and a control terminal coupled to the second voltage terminal of the main selection unit 112 . The P-type transistor P 2 A has a first terminal coupled to the second voltage terminal of the main selection unit 112 , a second terminal coupled to the output terminal of the main selection unit 112 , and a control terminal coupled to the first voltage terminal of the main selection unit 112 .

In this case, if the first variable voltage VV 1 is greater than the second variable voltage VV 2 , the P-type transistor P 1 A will be turned on and the P-type transistor P 2 A will be turned off. Therefore, the main selection unit 112 will output the first variable voltage VV 1 as the operation voltage. However, if the first variable voltage VV 1 is smaller than the second variable voltage VV 2 , the P-type transistor P 1 A will be turned off and the P-type transistor P 2 A will be turned on. Therefore, the main selection unit 112 will output the second variable voltage VV 2 as the operation voltage.

The first re-comparison unit 114 includes P-type transistors P 3 A and P 4 A. The P-type transistor P 3 A has a first terminal coupled to the first voltage terminal of the main selection unit 112 , a second terminal coupled to the output terminal of the main selection unit 112 , and a control terminal coupled to the output terminal of the main selection unit 112 . The P-type transistor P 4 A has a first terminal coupled to the output terminal of the main selection unit 112 , a second terminal coupled to the output terminal of the main selection unit 112 , and a control terminal coupled to the first voltage terminal of the main selection unit 112 .

In this case, if the operation voltage VOP is smaller than the first variable voltage VV 1 , the P-type transistor P 3 A will be turned on and the P-type transistor P 4 A will be turned off. Consequently, the first re-comparison unit 114 can raise the operation voltage VOP according to the first variable voltage VV 1 .

Similarly, the second re-comparison unit 116 includes P-type transistors P 5 A and P 6 A. The P-type transistor P 5 A has a first terminal coupled to the second voltage terminal of the main selection unit 112 , a second terminal coupled to the output terminal of the main selection unit 112 , and a control terminal coupled to the output terminal of the main selection unit 112 . The P-type transistor P 6 A has a first terminal coupled to the output terminal of the main selection unit 112 , a second terminal coupled to the output terminal of the main selection unit 112 , and a control terminal coupled to the second voltage terminal of the main selection unit 112 .

In this case, if the operation voltage VOP is smaller than the second variable voltage VV 2 , the P-type transistor P 5 A will be turned on and the P-type transistor P 6 A will be turned off. Consequently, the second re-comparison unit 116 can raise the operation voltage VOP according to the second variable voltage VV 2 .

That is, with the re-comparison units 114 and 116 , the operation voltage VOP can be maintained at a solid value, and will not be smaller than the first variable voltage VV 1 or the second variable voltage VV 2 when the first variable voltage VV 1 is equal to the second variable voltage VV 2 . Therefore, the leakage currents caused by instable operation voltage VOP can be reduced.

Furthermore, in some embodiments, the body terminals of the P-type transistors P 1 A, P 2 A, P 3 A, P 4 A, P 5 A and P 6 A can be coupled to the output terminal of the main selection unit 112 for reducing leakage currents. Since the P-type transistors P 3 A, P 4 A, P 5 A and P 6 A are mainly used to adjust the operation voltage VOP without requiring large current loading, the sizes of the P-type transistors P 3 A, P 4 A, P 5 A and P 6 A can be rather small.

In present embodiments, the first terminal of the transistor M 1 A receives the first variable voltage VV 1 , and the power switch circuit 100 can be used to output the first variable voltage VV 1 as the output voltage Vout through the output terminal OUT of the power switch circuit 100 . However, in some other embodiments, the first terminal of the transistor M 1 A may receive the second variable voltage VV 2 , and the power switch circuit 100 can be used to output the second variable voltage VV 2 as the output voltage Vout through the output terminal OUT of the power switch circuit 100 . Since the voltage selection circuit 110 is able to stably output the higher voltage of the first variable voltage VV 1 and the second variable voltage VV 2 as the operation voltage VOP, the leakage current can still be reduced. Furthermore, in some embodiments, the second variable voltage VV 2 can also be generated by a charge pump.

FIG. 2 shows a voltage selection circuit 210 according to another embodiment of the present invention. In some embodiments, the voltage selection circuit 210 can be applied to the power switch circuit 100 and replace the voltage selection circuit 110 . The voltage selection circuit 210 and the voltage selection circuit 110 have similar structures and can be operated with similar principles. However, each of the re-comparison units 214 and 216 can be implemented by a single P-type transistor.

In FIG. 2 , the first re-comparison unit 214 includes a P-type transistor P 3 B. The P-type transistor P 3 B has a first terminal coupled to the first voltage terminal of the main selection unit 212 for receiving the first variable voltage VV 1 , a second terminal coupled to the output terminal of the main selection unit 212 , and a control terminal coupled to the output terminal of the main selection unit 212 . In this case, if the operation voltage VOP is smaller than the first variable voltage VV 1 , the P-type transistor P 3 B will be turned on, and the first re-comparison unit 214 will raise the operation voltage VOP according to the first variable voltage VV 1 .

Also, the second re-comparison unit 216 includes a P-type transistor P 5 B. The P-type transistor P 5 B has a first terminal coupled to the second voltage terminal of the main selection unit 212 for receiving the second variable voltage VV 2 , a second terminal coupled to the output terminal of the main selection unit 212 , and a control terminal coupled to the output terminal of the main selection unit 212 . In this case, if the operation voltage VOP is smaller than the second variable voltage VV 2 , the P-type transistor P 5 B will be turned on, and the second re-comparison unit 216 will raise the operation voltage VOP according to the second variable voltage VV 2 .

Since the leakage currents are mostly induced when the first variable voltage VV 1 is equal to the second variable voltage VV 2 and the operation voltage VOP is smaller than the first variable voltage VV 1 and the second variable voltage VV 2 , the re-comparison units 214 and 216 can adjust the operation voltage VOP with the P-type transistors P 3 B and P 5 B without using the P-type transistors P 4 A and P 6 A of the re-comparison units 114 and 116 respectively. Therefore, the area of the voltage selection circuit 210 can be even smaller than the area of the voltage selection circuit 110 .

In summary, the power switch circuits and the voltage selection circuits provided by the embodiments of the present invention can keep the operation voltage stable by adopting the re-comparison units. Consequently, the leakage currents caused by instable operation voltage can be reduced.

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.