Abstract:
A low-voltage power switch includes a gate-controlled circuit and a switch. The gate-controlled circuit generates a control voltage lower than the voltage of ground according to a control signal. The switch includes a first end, a second end, and a control end. The first end of the switch is coupled to a power supply of a low voltage, the control end of the switch is coupled to the gate-controlled circuit for receiving the gate-controlled signal, and the second end of the switch couples the first end of the switch when the switch receives the gate-controlled signal for outputting the power supply of the low voltage.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a power switch for a power source of low voltage, and more particularly, to a power switch for transmitting a power source of low voltage between regular mode and deep-power-down mode. 
         [0003]    2. Description of the Prior Art 
         [0004]    In electronic devices applied with power sources of low voltage, generally a main power source V DD  (providing a voltage V DD ) and an internal chip power source V CC  (providing a voltage V CC ) are provided. Under the condition that the power consumption is not critical, normally the main power source V DD  is directly connected to the internal chip power source V CC . That is, the voltage V DD  equals the voltage V CC , thereby keeping the internal chips having the maximum operating voltage and operating at the fastest speed. 
         [0005]    However, for portable electronic devices such as cellular phones, the power consumption is critical, and therefore the internal components such as memories and control chips have to be able to function under low power condition. Consequently deep-power-down mode is utilized for reducing power consumption of the portable electronic devices. The deep-power-down mode means that under the condition that the portable electronic device is not turned off, the internal chip power source is turned off. More particularly, in deep-power-down mode, the main power source V DD  is still turned on and keeps providing the voltage V DD  and the internal chip power source V CC  is turned off to stop providing the voltage V CC . In this way, the power consumption of the internal chips of the portable electronic device can be reduced when the portable electronic device is in the sleep mode. 
         [0006]    Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a diagram illustrating a conventional power switch Q P1  for achieving the deep-power-down mode.  FIG. 2  is a timing diagram illustrating the control signal for the conventional power switch Q P1 . As shown in  FIG. 1 , the power switch Q P1  is a P channel Metal Oxide Semiconductor (PMOS) transistor. The first end (source) of the power switch Q P1  is coupled to the main power source V DD , the control end (gate) of the power switch Q P1  receives a gate control signal S GP , and the second end (drain) of the power switch Q P1  outputs the power source V CC  according to the gate control signal S GP . The power source V DD  can be the main power source of the portable electronic device, and the power source V CC  can be the internal chip power source for providing voltage V CC  to the internal chips of the portable electronic device. As shown in  FIG. 2 , the voltage of the gate control signal S GP  falls between the voltages V DD  and V SS  (ground). Generally, when the power switch Q P1  is to be turned on (the first end of the power switch Q P1  is coupled to the second of the power switch Q P1  for outputting the voltage V CC ), the voltage of the gate control signal S GP  has to fall to the voltage V SS ; on the other hand, when the power switch Q P1  is to be turned off (the first end of the power switch Q P1  is not coupled to the second of the power switch Q P1  and consequently the voltage V CC  is not outputted), the voltage of the gate control signal S GP  has to rise to the voltage V DD . In this way, the internal chip power source can be switched between the regular mode and the deep-power-down mode of the portable electronic device for meeting the requirement of the high speed in the regular mode and the power saving in the deep-power-down mode. 
         [0007]    Generally, when the main power source V DD  is high enough, the voltage drop between the voltages V DD  and V CC  is ignorable. However, when the main power source V DD  provides a lower voltage (such as 1.8 volts or lower than that), the voltage drop between the voltages V DD  and V CC  cannot be ignorable. Since the gate control signal S GP  cannot have the power switch Q P1  turn on completely, causing considerable resistance on the power switch Q P1 , the voltage V CC  would be much lower than the voltage V DD  and it possibly effects the normal operations of the chips. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a power switch for transmitting a power source providing a low voltage between regular mode and deep-power-down mode. The power switch comprises a first gate control circuit and a first switch. The first gate control circuit is disposed for generating a first gate control signal according to a control signal. Voltage of the first gate control signal is lower than ground. The first switch comprises a first end, coupled to the power source, a control end coupled to the first gate control circuit for receiving the first gate control signal, and a second end for outputting the power source. The first end of the first switch is coupled to the second end of the first switch when the first switch receives the first gate control signal. 
         [0009]    The present invention further provides a power switch for transmitting a power source providing a low voltage between regular mode and deep-power-down mode. The power switch comprises a first gate control circuit and a first switch. The first gate control circuit is disposed for generating a first gate control signal according to a control signal. Voltage of the first gate control signal is higher than the low voltage. The first switch comprises a second end coupled to the power source, a control end coupled to the first gate control circuit for receiving the first gate control signal, and a first end for outputting the power source. The first end of the first switch is coupled to the second end of the first switch when the first switch receives the first gate control signal. 
         [0010]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram illustrating a conventional power switch for achieving the deep-power-down mode. 
           [0012]      FIG. 2  is a timing diagram illustrating the control signal for the conventional power switch. 
           [0013]      FIG. 3  is a diagram illustrating a power switch according to a first embodiment of the present invention. 
           [0014]      FIG. 4  is a timing diagram illustrating the control signal for the power switch according to the first embodiment of the present invention. 
           [0015]      FIG. 5  is a diagram illustrating a power switch according to a second embodiment of the present invention. 
           [0016]      FIG. 6  is a timing diagram illustrating the control signal for the power switch according to the second embodiment of the present invention. 
           [0017]      FIG. 7  is a diagram illustrating a power switch according to a third embodiment of the present invention. 
           [0018]      FIG. 8  is a timing diagram illustrating the control signal for the power switch according to the third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  is a diagram illustrating a power switch SW 1  according to a first embodiment of the present invention.  FIG. 4  is a timing diagram illustrating the control signal for the power switch SW 1  according to the first embodiment of the present invention. As shown in  FIG. 3 , the power switch SW 1  comprises a switch Q P2  and a gate control circuit GC 1 . The switch Q P2  is a PMOS transistor. The first end (source) of the switch Q P2  is coupled to a main power source V DD , the control end (gate) of the switch Q P2  receives a gate control signal S GP , and the second end (drain) of the switch Q P2  outputs the power source V CC  according to the gate control signal S GP . The gate control circuit GC 1  is coupled to the control end of the switch Q P2  for outputting the gate control signal S GP  according to a control signal S 1 . As shown in  FIG. 4 , the voltage of the gate control signal S GP  falls between the voltage V DD  and a voltage V A  which is lower than the voltage V SS . When the switch Q P2  is to be turned on (the first end of the switch Q P2  is coupled to the second of the switch Q P2  for outputting the voltage V CC ), the control signal S 1  is outputted to the gate control circuit GC 1  so that the voltage of the gate control signal S GP  falls to the voltage V A  which is below the voltage V SS  for completely turning on the switch Q P2 ; on the other hand, when the switch Q P2  is to be turned off (the first end of the switch Q P2  is not coupled to the second of the switch Q P2  and consequently the voltage V CC  is not outputted), the control signal S 1  is not outputted to the gate control circuit GC 1  so that the voltage of the gate control signal S GP  rises to the voltage V DD . Since when the switch Q P2  is turned on by the gate control signal S GP  whose voltage is lower than the voltage V SS , the switch Q P2  is turned on completely and the resistance of the switch Q P2  is reduced. Consequently the voltage drop on the switch Q P2  is reduced and the difference between the voltages V DD  and V CC  is reduced as well. Therefore, the problem generated by the conventional power switch is solved and the internal chips can still function well. Furthermore, in order to reduce the body effect of the MOS transistor, the body (the third end) of the switch Q P2  is coupled to the first end of the switch Q P2 . Additionally, the gate control circuit GC 1  can be realized with a charge pump. 
         [0020]    Please refer to  FIG. 5  and  FIG. 6 .  FIG. 5  is a diagram illustrating a power switch SW 2  according to a second embodiment of the present invention.  FIG. 6  is a timing diagram illustrating the control signal for the power switch SW 2  according to the second embodiment of the present invention. As shown in  FIG. 5 , the power switch SW 2  comprises a switch Q N2  and a gate control circuit GC 2 . The switch Q N2  is an N channel Metal Oxide Semiconductor (NMOS) transistor. The second end (drain) of the switch Q N2  is coupled to a main power source V DD , the control end (gate) of the switch Q N2  receives a gate control signal S GN , and the first end (source) of the switch Q N2  outputs the power source V CC  according to the gate control signal S GN . The gate control circuit GC 2  is coupled to the control end of the switch Q N2  for outputting the gate control signal S GN  according to a control signal S 1 . As shown in  FIG. 6 , the voltage of the gate control signal S GN  falls between the Voltage V SS  and a voltage V B  which is higher than the voltage V DD . When the switch Q N2  is to be turned on (the first end of the switch Q N2  is coupled to the second of the switch Q N2  for outputting the voltage V CC ), the control signal S 1  is outputted to the gate control circuit GC 2  so that the voltage of the gate control signal S GN  rises to the voltage V B  which is above the voltage V DD  for completely turning on the switch Q N2 ; on the other hand, when the switch Q N2  is to be turned off (the first end of the switch Q N2  is not coupled to the second of the switch Q N2  and consequently the voltage V CC  is not outputted), the control signal S 1  is not outputted to the gate control circuit GC 2  so that the voltage of the gate control signal S GN  falls to the voltage V SS . Since when the switch Q N2  is turned on by the gate control signal S GN  whose voltage is higher than the voltage V DD , the switch Q N2  is turned on completely and the resistance of the switch Q N2  is reduced. Consequently the voltage drop on the switch Q N2  is reduced and the difference between the voltages V DD  and V CC  is reduced as well. Therefore, the problem generated by the conventional power switch is solved and the internal chips can still function well. Furthermore, in order to reduce the body effect of the MOS transistor, the body (the third end) of the switch Q N2  is coupled to the first end of the switch Q N2 . Additionally, the gate control circuit G C2  can be realized with a charge pump. 
         [0021]    Please refer to  FIG. 7  and  FIG. 8 .  FIG. 7  is a diagram illustrating a power switch SW 3  according to a third embodiment of the present invention.  FIG. 8  is a timing diagram illustrating the control signal for the power switch SW 3  according to the third embodiment of the present invention. As shown in  FIG. 7 , the power switch SW 3  comprises two switches Q P2  and Q N2 , and two gate control circuits GC 1  and GC 2 . The switch Q P2  is a PMOS transistor, and the switch Q N2  is an NMOS transistor. The first end (source) of the switch Q P2  is coupled to a main power source V DD , the control end (gate) of the switch Q P2  receives a gate control signal S GP , and the second end (drain) of the switch Q P2  outputs the power source V CC  according to the gate control signal S GP . The second end (drain) of the switch Q N2  is coupled to the main power source V DD , the control end (gate) of the switch Q N2  receives a gate control signal S GN , and the first end (source) of the switch Q N2  outputs the power source V CC  according to the gate control signal S GN . The gate control circuits GC 1  and GC 2  are respectively coupled to the control end of the switch Q P2  and the control end of the switch Q N2  for outputting the gate control signals S GP  and S GN  according to a control signal S 1 . As shown in  FIG. 8 , the voltage of the gate control signal S GP  falls between the voltage V DD  and a voltage V A  which is lower than the voltage V SS , and the voltage of the gate control signal S GN  falls between the voltage V SS  and a voltage V B  which is higher than the voltage V DD . When the switch Q P2  is to be turned on (the first end of the switch Q P2  is coupled to the second of the switch Q P2  for outputting the voltage V CC ) and the switch Q N2  is to be turned on (the first end of the switch Q N2  is coupled to the second of the switch Q N2  for outputting the voltage V CC ), the control signal S 1  is outputted to the gate control circuits GC 1  and G C2  SO that the voltage of the gate control signal S GP  falls to the voltage V A  which is below the voltage V SS  for completely turning on the switch Q P2  and the voltage of the gate control signal S GN  rises to the voltage V B  which is above the voltage V DD  for completely turning on the switch Q N2 ; on the other hand, when the switch Q P2  is to be turned off (the first end of the switch Q P2  is not coupled to the second of the switch Q P2  and consequently the voltage V CC  is not outputted) and the switch Q N2  is to be turned off (the first end of the switch Q N2  is not coupled to the second of the switch Q N2  and consequently the voltage V CC  is not outputted), the control signal S 1  is not outputted to the gate control circuits GC 1  and GC 2  so that the voltage of the gate control signal S GP  rises to the voltage V DD  and the voltage of the gate control signal S GN  falls to the voltage V SS . Since when the switch Q P2  is turned on by the gate control signal S GP  whose voltage is lower than the voltage V SS , and the switch Q N2  is turned on by the gate control signal S GN  whose voltage is higher than the voltage V DD , the switch Q P2  is turned on completely and the resistance of the switch Q P2  is reduced, and the switch Q N2  is turned on completely and the resistance of the switch Q N2  is reduced. Consequently the voltage drop on the switches Q P2  and Q N2  are reduced and the difference between the voltages V DD  and V CC  is reduced as well. Therefore, the problem generated by the conventional power switch is solved and the internal chips can still function well. Furthermore, in order to reduce the body effect of the MOS transistor, the body (the third end) of the switch Q P2  is coupled to the first end of the switch Q P2 , and the body (the third end) of the switch Q N2  is coupled to the first end of the switch Q N2 . The advantage of the power switch SW 3  is that the outputted power source V CC  is still stable when the main power source V DD  varies since the switches Q P2  and Q N2  are complementary to each other. 
         [0022]    To sum up, the power switch of the present invention for transmitting power sources of low voltage utilizes gate control circuits to reduce the voltage drop on the power switch. Therefore, when the main power source provides a low voltage, in regular mode, the internal chip power source still provides almost same voltage as the voltage provided from the main power source to the internal chips so as to allow the internal chips to operate normally, and in deep-power-down mode, the internal chip power source can be effectively turned off, providing great convenience. 
         [0023]    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.