Abstract:
A charge pump system includes a charge pump, a ring oscillator, a comparing circuit and a discharge circuit. When an output voltage of the charge pump is relatively low, the comparing circuit turns on the ring oscillator to make the ring oscillator provide an oscillation output to the charge pump to raise the output voltage of the charge pump. When the output voltage of the charge pump is relatively high, the comparing circuit turns off the ring oscillator to stop the ring oscillator from providing the oscillation output to the charge pump, the comparing circuit also makes the discharge circuit provide a discharge path to the charge pump to quickly reduce the output voltage of the charge pump.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a charge pump system, especially refers to a charge pump system having function of voltage detection. 
     2. Description of the Prior Art 
     Charge pumps are widely used in electronic circuitry. Please refer to  FIG. 1 ,  FIG. 1  shows a prior art charge pump system  100 . The charge pump system  100  includes a charge pump  14 , an oscillator  16 , a comparator  18 , a first resistor  11  and a second resistor  12 . The charge pump  14  is coupled to an input voltage V DD  and receives signals from the oscillator  16  for providing an output voltage V OUT . The charge pump system  100  generates a second resistor voltage V R2  via a current flowing through the first resistor  11  and the second resistor  12  to control the operation of the oscillator  16  by comparing the second resistor voltage V R2  with a reference voltage V ref . 
     However, the first resistor  11  and the second resistor  12  may cause the charge pump system  100  to generate a leakage current, dropping and making the output voltage V OUT  unstable. A common method for solving the above problems is to increase the resistance of the first resistor  11  and the second resistor  12 . However, the increase of the resistance of the first resistor  11  and the second resistor  12  may cause delay to the output voltage V OUT . Thus the charge pump system  100  cannot achieve a desirable performance. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a charge pump system including a charge pump, a ring oscillator, a comparing circuit and a discharge circuit. The charge pump includes an output end for providing an output voltage. The ring oscillator includes an output end coupled to a control end of the charge pump for providing an oscillation output to the charge pump. The comparing circuit includes a first impedance, a second impedance and a comparator. The first impedance has a first end coupled to the output end of the charge pump. The second impedance has a first end coupled to a second end of the first impedance, and a second end coupled to ground. The comparator includes a first input end coupled to the second end of the first impedance, a second input end for receiving a reference voltage, and an output end. The discharge circuit includes a first switch, a second switch and a third impedance. The first switch has a first end coupled to the output end of the charge pump, and a control end coupled to the output end of the comparator. The second switch has a first end coupled to a second end of the first switch, and a second end coupled to the ground. The third impedance has a first end coupled to the output end of the charge pump, and a second end coupled to a control end of the second switch. 
     Another embodiment of the present invention provides a charge pump system including a charge pump, a ring oscillator, a comparing circuit and a charge circuit. The charge pump includes an output end for providing an output voltage. The ring oscillator includes an output end coupled to a control end of the charge pump for providing an oscillation output to the charge pump. The comparing circuit includes a first impedance, a second impedance and a comparator. The first impedance has a first end coupled a bias voltage source. The second impedance has a first end coupled to a second end of the first impedance, and a second end coupled to the output end of the charge pump. The comparator includes a first input end coupled to the second end of the first impedance, a second input end for receiving a reference voltage, and an output end. The charge circuit includes a first switch, a second switch and a third impedance. The first switch has a first end coupled to the bias voltage source. The second switch has a first end coupled to a second end of the first switch, a control end coupled to the output end of the comparator, and a second end coupled to the output end of the charge pump. The third impedance has a first end coupled to a control end of the first switch, and a second end coupled to the output end of the charge pump. 
     The charge pump systems of the present invention can charge/discharge quickly and reduce leakage currents. Further, they can provide stable output voltages with little time delay. 
     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 
         FIG. 1  shows a prior art charge pump system. 
         FIG. 2  shows the charge pump system of the first embodiment of the present invention. 
         FIG. 3  shows the charge pump system of the second embodiment of the present invention. 
         FIG. 4  shows the charge pump system of the third embodiment of the present invention. 
         FIG. 5  shows the charge pump system of the fourth embodiment of the present invention. 
         FIG. 6  shows the charge pump system of the fifth embodiment of the present invention. 
         FIG. 7  shows the charge pump system of the sixth embodiment of the present invention. 
         FIG. 8  shows the charge pump system of the seventh embodiment of the present invention. 
         FIG. 9  shows the charge pump system of the eighth embodiment of the present invention. 
         FIG. 10  shows the charge pump system of the ninth embodiment of the present invention. 
         FIG. 11  shows the charge pump system of the tenth embodiment of the present invention. 
         FIG. 12  shows the charge pump system of the eleventh embodiment of the present invention. 
         FIG. 13  shows the charge pump system of the twelfth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 2 .  FIG. 2  shows a charge pump system  200  of the first embodiment of the present invention. The charge pump system  200  includes a charge pump  24 , a ring oscillator  26 , a comparing circuit  250  and a discharge circuit  260 . The charge pump  24  includes an input end  20  for receiving an input voltage V DD , and an output end  222  for providing an output voltage V OUT . An output end  223  of the ring oscillator  26  is coupled to a control end  221  of the charge pump  24  for providing an oscillation output to the charge pump  24 . The comparing circuit  250  includes a first impedance  21 , a second impedance  22  and a comparator  28 . The first impedance  21  has a first end coupled to the output end  222  of the charge pump  24 . The second impedance  22  has a first end coupled to a second end of the first impedance  21 , and a second end coupled to ground. The comparator  28  includes a first input end  211 , a second input end  212  and an output end  213 . The first input end  211  is coupled to the second end of the first impedance  21 . The second input end  212  is used for receiving a reference voltage V ref . The output end  213  of the comparator  28  is coupled to an input end  224  of the ring oscillator  26 . The discharge circuit  260  includes a first switch  201 , a second switch  202  and a third impedance  203 . The first switch  201  has a first end coupled to the output end  222  of the charge pump  24 , and a control end coupled to the output end  213  of the comparator  28 . The second switch  202  has a first end coupled to the second end of the first switch  201 , and a second end coupled to ground. The second switch is an NMMOS transistor and is always turned on. The third impedance  203  has a first end coupled to the output end  222  of the charge pump  24 , and a second end coupled to a control end of the second switch  202 . The third impedance  203  is used for providing a voltage drop so as to reduce the voltage at the control end of the second switch  202 . The first impedance  21  and the second impedance  22  are both resistors, capacitors, NMOS transistors or PMOS transistors. The third impedance  203  is a resistor, a capacitor or a diode. 
     When the charge pump  24  pulls up the output voltage V OUT  of the output end  222  to a high voltage level, the voltage at the first input end  211  of the comparator  28  will exceed the reference voltage V ref , thus the output end  213  of the comparator  28  will output a high voltage, turning on the first switch  201 . When the output end  213  of the comparator  28  outputs a high voltage, the operation of the ring oscillator  26  will be stopped, stopping the charge pump  24  from pulling up the output voltage V OUT  of the output end  222  so as to save power consumption of the charge pump system  200 . On the other hand, when the first switch  201  is turned on, the output voltage V OUT  will discharge through the first switch  201  until the voltage at the first input end  211  is lower than the reference voltage V ref . When the voltage at the first input end  211  is lower than the reference voltage V ref , the output end  213  of the comparator  28  will output a low voltage to turn off the first switch  201  and turn on the ring oscillator  26  to pull up the output voltage V OUT  at the output end  222  of the charge pump  24  again. 
     In  FIG. 2 , the first input end  211  of the comparator  28  is a positive input end, the second input end  212  of the comparator  28  is a negative input end, and the first switch  201  is an NMOS transistor. Please refer to  FIG. 3 .  FIG. 3  shows a charge pump system  300  of the second embodiment of the present invention. The difference between the charge pump system  300  and the charge pump system  200  lies in that the first input end  311  of the comparator  38  is a negative input end, the second input end  312  of the comparator  38  is a positive input end, and the first switch  301  is a PMOS transistor. In  FIG. 3 , when the charge pump  24  pulls up the output voltage V OUT  of the output end  222  to a high voltage level, the voltage at the first input end  211  will exceed the reference value V ref , thus the output end  313  of the comparator  38  will output a low voltage, turning on the first switch  201 . When the output end  313  of the comparator  38  outputs a low voltage, the operation of the ring oscillator  26  will be stopped, stopping the charge pump  24  from pulling up the output voltage V OUT  at the output end  222  to save power consumption of the charge pump system  300 . On the other hand, when the first switch  301  is turned on, the output voltage V OUT  will discharge through the first switch  301  until the voltage at the first input end  311  is lower than the reference voltage V ref . When the voltage at the first input end  311  is lower than the reference voltage V ref , the output end  313  of the comparator  38  will output a high voltage level, turning on the ring oscillator  26  to pull up the output voltage V OUT  at the output end  222  of the charge pump  24  again 
     Please refer to  FIG. 4 .  FIG. 4  shows a charge pump system  400  of the third embodiment of the present invention. The difference between the charge pump system  400  and the charge pump system  200  lies in that the charge pump system  400  further comprises a fourth impedance  204 . The fourth impedance  204  has a first end coupled to the second end of the third impedance  203 , and a second end coupled to ground. The third impedance  203  and the fourth impedance  204  provide a voltage drop so as to reduce the voltage at the control end of the second switch  202 . The third impedance  203  and the fourth impedance  204  are both resistors, capacitors or diodes. In the third embodiment, when the third impedance  203  and the fourth impedance  204  are both capacitors, the leakage current flowing through the third impedance  203  and the fourth impedance  204  to ground can be avoided. 
     Please refer to  FIG. 5 .  FIG. 5  shows a charge pump system  500  of the fourth embodiment of the present invention. The difference between the charge pump system  500  and the charge pump system  200  is that the ring oscillator  26  of the charge pump system  500  is not coupled to the output end  213  of the comparator  28 . Though the charge pump system  200  can save power by turning off the ring oscillator  26 , the ring oscillator  26  requires a delay time to resume working. Through utilizing the configuration of the charge pump system  500 , the output voltage V OUT  at the output end  222  of the charge pump  24  can avoid the delay time due to the continuous operation of the ring oscillator  26 . 
     In the first embodiment to the fourth embodiment, when the first impedance  21  and the second impedance  22  are both capacitors, the current flowing from the output end  222  of the charge pump  24  to ground through the first impedance  21  and the second impedance  22  can be avoided, thus stabilizing the output voltage V OUT . 
     Please refer to  FIG. 6 .  FIG. 6  shows a charge pump system  600  of the fifth embodiment of the present invention. The charge pump system  600  includes a charge pump  64 , a ring oscillator  66 , a comparing circuit  650  and a charge circuit  660 . The charge pump  64  includes an input end  60  for receiving an input voltage V DD , and an output end  622  for providing an output voltage −V OUT . An output end  623  of the ring oscillator  66  is coupled to a control end  621  of the charge pump  64  for providing an oscillation output to the charge pump  64 . The comparing circuit  650  includes a first impedance  61 , a second impedance  62  and a comparator  68 . The first impedance  61  has a first end coupled to a bias voltage source V bias . The second impedance  62  has a first end coupled to a second end of the first impedance  61 , and a second end coupled to the output end  622  of the charge pump  64 . The comparator  68  includes a first input end  611 , a second input end  612  and an output end  613 . The first input end  611  is coupled to the second end of the first impedance  61 . The second input end  612  is used for receiving a reference voltage V ref . The output end  613  of the comparator  68  is coupled to an input end  624  of the ring oscillator  66 . The charge circuit  660  includes a first switch  601 , a second switch  602  and a third impedance  603 . The first switch  601  has a first end coupled to the bias voltage source V bias , and the first switch  601  is a PMOS transistor and is always turned on. The second switch  602  has a first end coupled to the second end of the first switch  601 , a control end coupled to the output end  613  of the comparator  68 , and a second end coupled to the output end  622  of the charge pump  64 . The third impedance  603  has a first end coupled to the control end of the first switch  601 , and a second end coupled to the output end  622  of the charge pump  64 . The third impedance  603  is used for providing a voltage drop so as to reduce the voltage at the control end of the first switch  601 . The first impedance  61  and the second impedance  62  are both resistors, capacitors, NMOS transistors or PMOS transistors. The third impedance  603  is a resistor, a capacitor or a diode. 
     When the charge pump  64  pulls down the output voltage −V OUT  of the output end  622  to a low voltage level, the voltage at the first input end  611  of the comparator  68  will be lower than the reference voltage V ref , thus the output end  613  of the comparator  68  will output a high voltage, turning on the second switch  602 . When the output end  613  of the comparator  68  outputs the high voltage, the operation of the ring oscillator  66  will be stopped, stopping the charge pump  64  from pulling down the output voltage −V OUT  of the output end  622  so as to save power consumption of the charge pump system  600 . On the other hand, when the second switch  602  is turned on, the bias voltage source V bias  will charge the output voltage −V OUT  through the first switch  601  and the second switch  602  until the voltage at the first input end  611  is greater than the reference voltage V ref . When the voltage at the first input end  611  is greater than the reference voltage V ref , the output end  613  of the comparator  68  will output a low voltage to turn off the second switch  602  and turn on the ring oscillator  66  to pull down the output voltage −V OUT  at the output end  622  of the charge pump  64  again. 
     In  FIG. 6 , the first input end  611  of the comparator  68  is a negative input end, the second input end  612  of the comparator  68  is a positive input end, and the second switch  602  is an NMOS transistor. Please refer to  FIG. 7 .  FIG. 7  shows a charge pump system  700  of the sixth embodiment of the present invention. The difference between the charge pump system  700  and the charge pump system  600  lies in that the first input end  711  of the comparator  78  is a positive input end, the second input end  712  of the comparator  78  is a negative input end, and the second switch  702  is a PMOS transistor. In  FIG. 7 , when the charge pump  64  pulls down the output voltage −V OUT  of the output end  622  to a low voltage level, the voltage at the first input end  711  will be lower than the reference voltage V ref , thus the output end  713  of the comparator  78  will output a low voltage, turning on the second switch  702 . When the output end  713  of the comparator  78  outputs a low voltage, the operation of the ring oscillator  66  will be stopped, stopping the charge pump  64  from pulling down the output voltage −V OUT  at the output end  622  to save power consumption of the charge pump system  700 . On the other hand, when the second switch  702  is turned on, the bias voltage source V bias  will charge the output voltage −V OUT  through the first switch  601  and the second switch  702  until the voltage at the first input end  711  is greater than the reference voltage V ref . When the voltage at the first input end  711  is greater than the reference voltage V ref , the output end  713  of the comparator  78  will output a high voltage, turning on the ring oscillator  66  to pull down the output voltage −V OUT  at the output end  622  of the charge pump  64  again. 
     Please refer to  FIG. 8 .  FIG. 8  shows a charge pump system  800  of the seventh embodiment of the present invention. The difference between the charge pump system  800  and the charge pump system  600  lies in that the charge pump system  800  further comprises a fourth impedance  604 . The fourth impedance  604  has a first end coupled to the bias voltage source V bias , and a second end coupled to the first end of the third impedance  603 . The third impedance  603  and the fourth impedance  604  provide a voltage drop so as to reduce the voltage at the control end of the first switch  601 . The third impedance  603  and the fourth impedance  604  are both resistors, capacitors or diodes. In the seventh embodiment, when the third impedance  603  and the fourth impedance  604  are both capacitors, the leakage current flowing through the third impedance  603  and the fourth impedance  604  to ground can be avoided. 
     Please refer to  FIG. 9 .  FIG. 9  shows a charge pump system  900  of the eighth embodiment of the present invention. The difference between the charge pump system  900  and the charge pump system  600  is that the ring oscillator  66  of the charge pump system  900  is not coupled to the output end  613  of the comparator  68 . Though the charge pump system  600  can save power by turning off the oscillator  66 , the oscillator  66  requires a delay time to resume working. Through utilizing the configuration of the charge pump system  900 , the output voltage −V OUT  at the output end  622  of the charge pump  64  can avoid the delay time due to the continuous operation of the ring oscillator  66 . 
     In the fifth embodiment to the eighth embodiment, when the first impedance  61  and the second impedance  62  are both capacitors, the current flowing through the first impedance  61  and the second impedance  62  to the output end  622  of the charge pump  64  can be avoided, thus stabilizing the output voltage −V OUT . 
     Please refer to  FIG. 10 .  FIG. 10  shows a charge pump system  1000  of the ninth embodiment of the present invention. The charge pump  1000  implements the first impedance  21  and the second impedance  22  of the charge pump system  200  with a first NMOS transistor  1001  and a second NMOS transistor  1002  respectively. As shown in  FIG. 10 , when the first impedance  21  and the second impedance  22  are implemented with the first NMOS transistor  1001  and the second NMOS transistor  1002  respectively, the drain of the first NMOS transistor  1001  is coupled to the gate of the first NMOS transistor  1001 , and the drain of the second NMOS transistor  1002  is coupled to the gate of the second NMOS transistor  1002 . The drain of the first NMOS transistor  1001  is coupled to the output end  222  of the charge pump  24 , the drain of the second NMOS transistor  1002  and a source of the first NMOS transistor  1001  are both coupled to the first input end  211  of the comparator  28 . And the source of the second NMOS transistor  1002  is coupled to ground. In the ninth embodiment, since the first NMOS transistor  1001  and the second NMOS transistor  1002  are smaller, the size of the charge pump  1000  can be effectively reduced. 
     Please refer to  FIG. 11 .  FIG. 11  shows a charge pump system  1100  of the tenth embodiment of the present invention. The charge pump  1100  implements the first impedance  61  and the second impedance  62  of the charge pump system  600  with a first NMOS transistor  1101  and a second NMOS transistor  1102  respectively. As shown in  FIG. 11 , when the first impedance  61  and the second impedance  62  are implemented with the first NMOS transistor  1101  and the second NMOS transistor  1102  respectively, the drain of the first NMOS transistor  1101  is coupled to the gate of the first NMOS transistor  1101 , and the drain of the second NMOS transistor  1102  is coupled to the gate of the second NMOS transistor  1102 . The drain of the first NMOS transistor  1101  is coupled to the bias voltage source V bias , a source of the first NMOS transistor  1101  and the drain of the second NMOS transistor  1101  are both coupled to the first input end  611  of the comparator  68 , and a source of the second NMOS transistor  1102  is coupled to the output end  622  of the charge pump  64 . In the tenth embodiment, due to the volumes of the first NMOS transistor  1101  and the second NMOS transistor  1102  are smaller, the volume of the charge pump  1100  can be effectively reduced. 
     Please refer to  FIG. 12 .  FIG. 12  shows a charge pump system  1200  of the eleventh embodiment of the present invention. The charge pump  1200  implements the first impedance  21  and the second impedance  22  of the charge pump system  200  with a first PMOS transistor  1201  and a second PMOS transistor  1202  respectively. As shown in  FIG. 12 , when the first impedance  21  and the second impedance  22  are implemented with the first PMOS transistor  1201  and the second PMOS transistor  1202  respectively, the drain of the first PMOS transistor  1201  is coupled to the gate of the first PMOS transistor  1201 , and the drain of the second PMOS transistor  1202  is coupled to the gate of the second PMOS transistor  1202 . A source of the first PMOS transistor  1201  is coupled to the output end  222  of the charge pump  24 , a source of the second PMOS transistor  1202  and the drain of the first PMOS transistor  1201  are both coupled to the first input end  211  of the comparator  28 . And the drain of the second PMOS transistor  1202  is coupled to ground. In the ninth embodiment, due to the volumes of the first PMOS transistor  1201  and the second PMOS transistor  1202  are smaller, the volume of the charge pump  1200  can be effectively reduced. 
     Please refer to  FIG. 13 .  FIG. 13  shows a charge pump system  1300  of the twelfth embodiment of the present invention. The charge pump  1300  implements the first impedance  61  and the second impedance  62  of the charge pump system  600  with a first PMOS transistor  1301  and a second PMOS transistor  1302  respectively. As shown in  FIG. 13 , when the first impedance  61  and the second impedance  62  are implemented with the first PMOS transistor  1301  and the second PMOS transistor  1302  respectively, the drain of the first PMOS transistor  1301  is coupled to the gate of the first PMOS transistor  1301 , and the drain of the second PMOS transistor  1302  is coupled to the gate of the second PMOS transistor  1302 . A source of the first PMOS transistor  1301  is coupled to the bias voltage source V bias , the drain of the first PMOS transistor  1301  and a source of the second PMOS transistor  1301  are both coupled to the first input end  611  of the comparator  68 , and the drain of the second PMOS transistor  1302  is coupled to the output end  622  of the charge pump  64 . In the tenth embodiment, due to the volumes of the first PMOS transistor  1301  and the second PMOS transistor  1302  are smaller, the volume of the charge pump  1300  can be effectively reduced. 
     Although the first impedance  21  and the second impedance  22  of the charge pump system  200  are implemented with the first NMOS transistor  1001  and the second NMOS transistor  1002  in the ninth embodiment, and are implemented with the first PMOS transistor  1201  and the second PMOS transistor  1202  in the eleventh embodiment. However, the first impedance  21  and the second impedance  22  of the charge pump system  200  can also be implemented with typical diodes. Similarly, although the first impedance  61  and the second impedance  62  of the charge pump system  600  are implemented with the first NMOS transistor  1101  and the second NMOS transistor  1102  in the tenth embodiment, and are implemented with the first PMOS transistor  1301  and the second PMOS transistor  1302  in the twelfth embodiment. However, the first impedance  61  and the second impedance  62  of the charge pump system  600  can also be implemented with typical diodes. 
     The present invention utilizes the discharge circuit  260  in the charge pump systems  200 ,  300 ,  400 ,  500 ,  1000  and  1200  to discharge the output voltage V OUT  quickly. When the first impedance  21  and the second impedance  22  are both capacitors, the current flowing through the first impedance  21  and the second impedance  22  to ground can be effectively reduced, stabilizing the output voltage V OUT . In the charge pump system  500 , the ring oscillator  26  is not coupled to the output end  213  of the comparator  28 , thus can avoid the delay of the ring oscillator  26  caused by repeatedly turning on and off the ring oscillator  26 . In the charge pump system  1000 , the first impedance  21  and the second impedance  22  are implemented with the first NMOS transistor  1001  and the second NMOS transistor  1002  respectively, thus effectively reducing the volume of the charge pump system  1000 . In the charge pump system  1200 , the first impedance  21  and the second impedance  22  are implemented with the first PMOS transistor  1201  and the second PMOS transistor  1202  respectively, thus effectively reducing the volume of the charge pump system  1200 . 
     The present invention utilizes the charge circuit  660  in the charge pump systems  600 ,  700 ,  800 ,  900 ,  1100  and  1300  to charge the output voltage −V OUT  quickly. When the first impedance  61  and the second impedance  62  are both capacitors, the current flowing through the first impedance  61  and the second impedance  62  to the output end  622  of the charge pump  64  can be effectively reduced, stabilizing the output voltage −V OUT . In the charge pump system  900 , the ring oscillator  66  is not coupled to the output end  613  of the comparator  68 , thus can avoid the delay of the ring oscillator  66  caused by repeatedly turning on and off the ring oscillator  66 . In the charge pump system  1100 , the first impedance  61  and the second impedance  62  are implemented with the first NMOS transistor  1101  and the second NMOS transistor  1102  respectively, thus effectively reducing the volume of the charge pump system  1100 . In the charge pump system  1300 , the first impedance  61  and the second impedance  62  are implemented with the first PMOS transistor  1301  and the second PMOS transistor  1302  respectively, thus effectively reducing the volume of the charge pump system  1300 . 
     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.