# Patent

## Title
Power supply device for driving an amplifier

## Abstract

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

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/822,084, filed on Aug. 11, 2006 and entitled “DUAL (OR MULTI) SUPPLY OPERATIONAL AMPLIFIER/HEADPHONE DRIVER AND CHARGE PUMP” the contents of which are incorporated herein 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. No. 7,061,327 and U.S. Pat. No. 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 VDD and VSS 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 VDD can keep a relation by VSS=−VDD. In addition, the charge pump is substantially composed of capacitors and thereby, generates the Voltage VSS via charging and discharging of the capacitors. Under this circumstance, the voltage VSS 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 VDD and VSS, negative amplitude of the amplifier may be curtailed as a variation range of the voltage VSS becomes large. In order to solve the problem, the prior art can increase the voltage VDD 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 VDD 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. The power supply device includes a first power generator, a second power generator, a charge pump and a control unit. The first power generator is used for providing a first voltage for a first power reception end of the amplifier. The second power generator is used for providing a second voltage. The charge pump is coupled between the second power generator and a second power reception end of the amplifier and is used for generating a third voltage for the amplifier according to the second voltage. The control unit is coupled to the second power generator and is used for controlling the second power generator, so as to adjust the second voltage to make the third voltage equal to a multiple of the first voltage.
The present invention further discloses a power supply device for driving an amplifier. The power supply device includes a power generator, a power conversion unit, a charge pump and a control unit. The power generator is used for providing a first voltage for a first power reception end of the amplifier. The power conversion unit is coupled to the power generator and is used for converting the first voltage into a second voltage. The charge pump is coupled between the power conversion unit and a second power reception end of the amplifier, and is used for generating a third voltage for the amplifier according to the second voltage. The control unit is coupled to the power conversion unit and is used 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 VIN received by a signal reception end 124, and outputs a signal VOUT 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 CVDD and CVCC for a positive power reception end 120 of the amplifier 12 and the charge pump 104. The charge pump 104 converts the voltage CVCC provided by the second power generator 102 into a negative voltage CVSS, CVSS=(−n2)×CVCC, and outputs the voltage CVSS 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 CVCC of the second power generator 102, so as to adjust the voltage CVSS to make the voltage CVDD equal to a multiple of the voltage CVSS, or CVSS=(−n)×CVDD.
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 VOUT 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 VOUT 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 CVSS 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 CVSS is 1.5 times the voltage CVDD, 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 VIN1, VIN2 received from signal reception ends 524, 532, and then output signals VOUT1, VOUT2 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 VIN received by a signal reception end 624, and outputs a signal VOUT 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 CVDD 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 CVDD into a voltage CVCC and outputs the voltage CVCC to the charge pump 604. The charge pump 604 converts the voltage CVCC provided by the power conversion unit 602 into a negative voltage CVSS (CVSS=(−n2)×CVCC) and outputs the voltage CVSS to the negative power reception end 622 of the amplifier 62. Besides, the control unit 606 controls the voltage CVCC of the power conversion unit 602, so as to adjust the voltage CVSS to make the voltage CVDD equal to a multiple of the voltage CVSS, or CVSS=(−n)×CVDD.
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 VOUT 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 VOUT of the amplifier 62 has a greater amplitude, so that n can be set larger than 1. In this way, even if the voltage CVSS 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 CVSS is 1.5 times the voltage CVDD, 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.

## Claims

1. A power supply device for driving an amplifier comprising:
a first power generator for providing a first voltage for a first power reception end of the amplifier;
a second power generator for providing a second voltage;
a charge pump coupled between the second power generator 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 second power generator, for controlling the second power generator, so as to adjust the second voltage to make the third voltage equal to a multiple of the first voltage.

2. The power supply device of claim 1, wherein the amplifier is used for amplifying audio signals.

3. The power supply device of claim 1, wherein the amplifier is an operational amplifier.

4. The power supply device of claim 1, wherein the control unit controls the second power generator to make the third voltage smaller than the first voltage when the amplifier operates in a power saving mode.

5. The power supply device of claim 1, wherein the control unit controls the second power generator to make the third voltage greater than the first voltage when the amplifier operates in a wide output range mode.