Abstract:
A power supply device for driving an amplifier includes a power generator for providing a first voltage for a first power reception end of the amplifier, a power conversion unit coupled to the power generator, for converting the first voltage into a second voltage, a charge pump coupled between the power conversion unit and a second power reception end of the amplifier, for generating a third voltage for the amplifier according to the second voltage, and a control unit coupled to the power conversion unit, for controlling the power conversion unit, so as to adjust the second voltage to make the third voltage equal to a specific multiple of the first voltage.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a division of application Ser. No. 11/610,483, filed Dec. 13, 2006, which claims the benefit of U.S. Provisional Application No. 60/822,084, filed Aug. 11, 2006, the entirety of which is incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a power supply device for driving an amplifier, and more particularly, to a power supply device capable of reducing power consumption of an amplifier and enlarging an output range of the amplifier. 
   2. Description of the Prior Art 
   An amplifier is an electronic device used in a variety of electronic products, which can amplify signal amplitudes. The amplifier appears in many types and structures, which can be simply composed of a bipolar junction transistor (BJT) or a metal oxide semiconductor (MOS) transistor, or be integrated by complicated circuits such as OP 741. 
   The amplifier is widely used in many applications. For example, U.S. Pat. No. 7,061,327 discloses a headset using a single voltage supply to drive an operational amplifier of the headset via a charge pump. Furthermore, U.S. Pat. No. 5,289,137 discloses an integrated circuit using a single power supply and a charge pump for driving an operational amplifier. Both of the U.S. Pat. Nos. 7,061,327 and 5,289,137 use single power supplies with charge pumps for driving the amplifier. However, shortcomings of these two patents are power consumption and restriction of output ranges. The details are described as bellows. Please refer to  FIG. 1 , which reveals a schematic diagram of signals corresponding to an amplifier in FIG. 4 of the U.S. Pat. No. 7,061,327. Voltages V DD  and V SS  respectively represent a positive voltage and a negative voltage for driving the amplifier. Since the U.S. Pat. No. 7,061,327 uses single power supply with a charge pump, the voltage V DD  can keep a relation by V SS =−V DD . In addition, the charge pump is substantially composed of capacitors and thereby, generates the Voltage V SS  via charging and discharging of the capacitors. Under this circumstance, the voltage V SS  performs as an unstable linear curve rippling as the capacitors are charged and discharged. Since amplitudes of output signals of the amplifier must be restricted between the voltages V DD  and V SS , negative amplitude of the amplifier may be curtailed as a variation range of the voltage V SS  becomes large. In order to solve the problem, the prior art can increase the voltage V DD  so that the output range of the amplifier can be enlarged, or increase capacitance of the capacitors in the charge pump. However, increasing the voltage V DD  represents increasing power consumption, while increasing capacitance of the capacitors in the charge pump represents increasing the capacitor size. 
   Therefore, using a single power supply with a charge pump for driving an amplifier results in a restriction of an output range of the amplifier, and power consumption cannot be efficiently reduced. Besides, if a single power supply is used for driving multiple amplifiers, current variation produced by switching transistors of a certain amplifier may cause malfunction of the power supply, and reduces system efficiency. 
   SUMMARY OF THE INVENTION 
   It is therefore a primary objective of the claimed invention to provide a power supply device for driving an amplifier. 
   The present invention discloses a power supply device for driving an amplifier, which comprises a power generator for providing a first voltage for a first power reception end of the amplifier, a power conversion unit coupled to the power generator, for converting the first voltage into a second voltage, a charge pump coupled between the power conversion unit and a second power reception end of the amplifier, for generating a third voltage for the amplifier according to the second voltage, and a control unit coupled to the power conversion unit, for controlling the power conversion unit, so as to adjust the second voltage to make the third voltage equal to a specific multiple of the first 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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a schematic diagram of signals corresponding to an amplifier according to a FIG. 4 of the U.S. Pat. No. 7,061,327. 
       FIG. 2  depicts a schematic diagram of a power supply device for driving an amplifier according to a first embodiment of the present invention. 
       FIG. 3  depicts a schematic diagram of signal waveforms corresponding to the amplifier in  FIG. 2  in a power saving mode. 
       FIG. 4  depicts a schematic diagram of signal waveforms corresponding to the amplifier in  FIG. 2  in a normal mode. 
       FIG. 5  depicts a schematic diagram of the power supply device for driving two amplifiers in  FIG. 2 . 
       FIG. 6  depicts a schematic diagram of a power supply device for driving an amplifier according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 2 , which is a schematic diagram of a power supply device  10  for driving an amplifier  12  according to an embodiment of the present invention. The amplifier  12  receives driving power through a positive power reception end  120  and a negative power reception end  122 , amplifies a signal V IN  received by a signal reception end  124 , and outputs a signal V OUT  from a signal output end  126 . The power supply device  10  includes a first power generator  100 , a second power generator  102 , a charge pump  104 , and a control unit  106 . The first power generator  100  and the second power generator  102  generate voltages CV DD  and CV CC  for a positive power reception end  120  of the amplifier  12  and the charge pump  104 . The charge pump  104  converts the voltage CV CC  provided by the second power generator  102  into a negative voltage CV SS , CV SS =(−n 2 )×CV CC , and outputs the voltage CV SS  to the negative power reception end  122  of the amplifier  12 . Thus, positive and negative powers driving the amplifier  12  are provided by different power generators. The control unit  106  controls the voltage CV CC  of the second power generator  102 , so as to adjust the voltage CV SS  to make the voltage CV DD  equal to a multiple of the voltage CV SS , or CV SS =(−n)×CV DD . 
   Therefore, in the power supply device  10 , levels of positive and negative powers of the amplifier  12  may be different for applying to different situations. For example, please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  is a schematic diagram of signal waveforms corresponding to the amplifier  12  in a condition of n=0.5, while  FIG. 4  is a schematic diagram of signal waveforms corresponding to the amplifier  12  in a condition of n=1.5. In  FIG. 3 , the output voltage V OUT  of the amplifier  12  has a small amplitude when operating in a power saving mode, such as an idle mode, so that setting n smaller than 1 can reduce quiescent current and power consumption. On the contrary, in  FIG. 4 , the output voltage V OUT  of the amplifier  12  has a greater amplitude when operating in a normal mode, so that n can be set larger than 1. In this way, even if the voltage CV SS  varies with charging and discharging capacitors of the charge pump  104 , signals outputted from the amplifier  12  can be prevented from being curtailed since the voltage CV SS  is 1.5 times the voltage CV DD , meaning that the amplifier  12  has a wider output range in the negative polarity. Thus, the capacitors in the charge pump  104  can be replaced with capacitors of less capacitance, so that a size of the charge pump  104  can be reduced. 
   Note that, the power supply device  10  shown in  FIG. 2  is an exemplary embodiment of the present invention, and those skills in the art can make modification, such as driving a plurality of amplifiers, not just one. Please refer to  FIG. 5 , which is a schematic diagram of the power supply device  10  for driving amplifiers  500 ,  502  according to the present invention. The amplifiers  500 ,  502  receive driving power from positive reception ends  520 ,  528  and negative reception ends  522 ,  530 , amplify signals V IN   1 , V IN   2  received from signal reception ends  524 ,  532 , and then output signals V OUT   1 , V OUT   2  to a load circuit  504 , such as a stereo headphone or a loudspeaker, through signal output ends  526 ,  534 . 
   In addition, the present invention can also accomplish the same performance by one power generator. Please refer to  FIG. 6 , which is a schematic diagram of a power supply device  60  for driving an amplifier  62  according to a second embodiment of the present invention. The amplifier  62  receives driving power from a positive power reception end  620  and a negative power reception end  622 , amplifies a signal V IN  received by a signal reception end  624 , and outputs a signal V OUT  through a signal output end  626 . The power supply device  60  includes a power generator  600 , a power conversion unit  602 , a charge pump  604  and a control unit  606 . The power generator  600  provides a voltage CV DD  for a positive power reception end  620  of the amplifier  62  and the power conversion unit  602 . The power conversion unit  602  converts the voltage CV DD  into a voltage CV CC  and outputs the voltage CV CC  to the charge pump  604 . The charge pump  604  converts the voltage CV CC  provided by the power conversion unit  602  into a negative voltage CV SS  (CV SS =(−n 2 )×CV CC ) and outputs the voltage CV SS  to the negative power reception end  622  of the amplifier  62 . Besides, the control unit  606  controls the voltage CV CC  of the power conversion unit  602 , so as to adjust the voltage CV SS  to make the voltage CV DD  equal to a multiple of the voltage CV SS , or CV SS =(−n)×CV DD . 
   Therefore, in the power supply device  60 , levels of positive and negative powers of the amplifier  62  may be different for applying to different situations. In a power saving mode (as shown in  FIG. 3 ), the output voltage V OUT  of the amplifier  62  has a small amplitude, so that setting n smaller than 1 can reduce quiescent current to reduce power consumption. On the contrary, in a normal mode (as shown in  FIG. 4 ), the output voltage V OUT  of the amplifier  62  has a greater amplitude, so that n can be set larger than 1. In this way, even if the voltage CV SS  varies with charging and discharging capacitors of the charge pump  604 , signals outputted from the amplifier  62  can be prevented from being curtailed since the voltage CV SS  is 1.5 times the voltage CV DD , meaning that the amplifier  62  has a wider output range in the negative polarity. Thus, the capacitors in the charge pump  604  can be replaced with capacitors of less capacitance, so that a size of the charge pump  604  can be reduced. 
   In summary, in the present invention power supply device, levels of the positive and negative powers of the amplifier can be different. In the power saving mode, the present invention can set n smaller than 1 for reducing quiescent current and saving power. In the normal mode, the present invention can set n larger than 1, so that the amplifier has a wider output range in the negative polarity. Under this circumstance, the capacitors in the charge pump can be replaced by capacitors of less capacitance, so that the size of the charge pump can be further reduced. In addition, due to two power generators driving multiple amplifiers, the present invention can prevent current variation generated by switching transistors from affecting system operations. 
   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.