Abstract:
After coupling a first voltage source to a voltage supply circuit, a second voltage source having a same electrical level but an opposite electrical pole with said first voltage source is generated. An audio amplifier is then driven by both the first voltage source and the second voltage source, where said audio amplifier requires a pair of voltage sources having the same electrical level but opposite electrical poles to be driven. The voltage supply circuit generates the second voltage source from the first voltage source by simultaneously switching two sets of switches, where said both sets of switches have non-synchronous statuses in switching.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an audio amplifier and a related voltage supply circuit, and more particularly, to an audio amplifier driven by a single voltage source and a related voltage supply circuit. 
   2. Description of the Prior Art 
   Current audio amplifiers are popularly implemented with Class D amplifiers. A conventional Class AB amplifier generates linear signals whereas a Class D amplifier generates pulse width modulation (PWM) signals, which primarily includes audio signals, pulse width modulation signals, and harmonic waves. While a Class D amplifier operates, an output stage metal oxide semiconductor field-effect transistor (MOSFET) of said Class D amplifier is required to be biased with a pair of voltage sources, one of which is a positive voltage source whereas the other one is a negative voltage source, where said pair of voltage sources is mutually opposite in views of electrical pole and is equivalent in aspects of electrical level, for driving said Class D amplifier. In the prior art, the positive voltage source from the pair of voltage sources is coupled to a positive bias terminal of the output stage MOSFET of the Class D amplifier, whereas the negative voltage source from said pair of voltage sources is coupled to a negative bias terminal of the output stage MOSFET of said Class D amplifier, for biasing said Class D amplifier. That is, a port has to be further added on each of the positive bias terminal and the negative bias terminal of the output stage MOSFET of the Class D amplifier for receiving the positive voltage source and the negative voltage source respectively, and for driving the Class D amplifier. 
   SUMMARY OF THE INVENTION 
   The claimed invention provides an audio amplifier driven by single voltage source. The audio amplifier comprises a voltage supply circuit and an audio amplifier set. The voltage supply circuit comprises a first voltage source, a first switch having a first terminal coupled to the first voltage source, a second switch having a first terminal coupled to a second terminal of the first switch, and a second terminal coupled to ground, a first capacitor having a first terminal coupled to the second terminal of the first switch, and a second terminal, a third switch having a first terminal coupled to the second terminal of the first capacitor and a second terminal coupled to ground, a fourth switch having a first terminal coupled to the second terminal of the first capacitor and a second terminal, and a second capacitor having a first terminal coupled to the second terminal of the third switch and a second switch coupled to the second terminal of the fourth switch. The audio amplifier set comprises a plurality of sub-audio amplifiers, each of which having a positive voltage input terminal coupled to the first voltage source and a negative voltage input terminal coupled to the second terminal of the second capacitor. 
   The claimed invention also provides a voltage supply circuit. The voltage supply circuit comprises a first voltage source, a first switch, a second switch, a first capacitor, a third switch, a fourth switch, and a second capacitor. The first switch has a first terminal coupled to the first voltage source. The second switch has a first terminal coupled to a second terminal of the first switch, and a second terminal coupled to ground. The first capacitor has a first terminal coupled to the second terminal of the first switch, and a second terminal. The third switch has a first terminal coupled to the second terminal of the first capacitor, and a second terminal coupled to ground. The fourth switch has a first terminal coupled to the second terminal of the first capacitor, and a second terminal. The second capacitor has a first terminal coupled to the second terminal of the third switch, and a second terminal coupled to the second terminal of the fourth switch. 
   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  is a block diagram of an audio amplifier of the present invention. 
       FIG. 2  is a diagram of the power supply circuit shown in  FIG. 1 , and illustrates a first stage of generating the second voltage source having the electrical level of −VCC. 
       FIG. 3  illustrates a second stage of generating the second voltage source having the electrical level of −VCC according to the power supply circuit shown in  FIG. 2 . 
       FIG. 4  is a diagram of the sub-audio amplifier shown in  FIG. 1  according to a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention provides an audio amplifier of biasing an output stage MOSFET with a pair of voltage sources having opposite electrical poles and a same electrical level, where said pair of voltage sources includes a positive voltage source and a negative voltage source and is generated from a single voltage source. Note that the audio amplifier of the present invention may be a Class D amplifier. 
   Please refer to  FIG. 1 , which is a block diagram of an audio amplifier  100  of the present invention. As shown in  FIG. 1 , the audio amplifier  100  includes a voltage supply circuit  200  and a sub-audio amplifier set  300 . The sub-audio amplifier set  300  includes a plurality of sub-audio amplifiers  400 . A positive voltage with an electrical level VCC is outputted from a positive output terminal of the voltage supply circuit  200  to each sub-audio amplifier  400  in the sub-audio amplifier set  300 , whereas a negative voltage with an electrical level −VCC is also outputted from a negative output terminal of the voltage supply circuit  200  to each sub-audio amplifier  400  in the sub-audio amplifier set  300 . 
   Please refer to  FIG. 2 , which is a diagram of the power supply circuit  200  shown in  FIG. 1 . As shown in  FIG. 2 , the power supply circuit  200  includes a first voltage source VCC, a first switch  202 , a second switch  204 , a first capacitor  206 , a third switch  208 , a fourth switch  210 , and a second capacitor  212 . The first switch  202  has a first terminal coupled to the first voltage source VCC. The second switch  204  has a first terminal coupled to a second terminal of the first switch  202 , and a second terminal coupled to ground. The first capacitor  206  has a first terminal coupled to the second terminal of the first switch  202 . The third switch  208  has a first terminal coupled to a second terminal of the first capacitor  206 , and a second terminal coupled to ground. The fourth switch  210  has a first terminal coupled to the second terminal of the first capacitor  206 . The second capacitor  212  has a first terminal coupled to the second terminal of the third switch  208 , and a second terminal coupled to a second terminal of the fourth switch  210 . 
   The aim of the present invention is generating a second voltage source with an electrical level of −VCC at the first terminal of the second capacitor  212  by inputting the first voltage source with an electrical level of VCC to the voltage supply circuit  200 , where the second voltage source with the electrical level of −VCC has the same electrical level but an opposite electrical pole with the first voltage source having the electrical level of VCC. Two stages are described in generating the second voltage source having the electrical level of −VCC. In a first stage, as illustrated in  FIG. 2 , both the first switch  202  and the third switch  208  are switched to be short-circuited, whereas both the second switch  204  and the fourth switch  210  are switched to be open-circuited. At this time, a voltage difference with an electrical level of VCC is generated across the first capacitor  206 , where the electrical level at the first terminal of the first capacitor  206  is higher than the second terminal of the first capacitor  206 . Please proceed to  FIG. 3 , which illustrates a second stage of generating the second voltage source having the electrical level of −VCC. As shown in  FIG. 3 , both the first switch  202  and the third switch  208  are switched to be open-circuited, whereas both the second switch  204  and the fourth switch  210  are switched to be short-circuited. At this time, the abovementioned voltage difference across the first capacitor  206  is maintained. Since both the first terminal of the first capacitor  206  and the first terminal of the second capacitor  212  are coupled to ground at the same time, therefore in the second stage, a voltage difference with the same electrical level with the voltage difference across the first capacitor  206  is generated across the second capacitor  212 , and an electrical level at the second terminal of the second capacitor  212  thus becomes −VCC. At last, the second voltage source having the electrical level −VCC is thus generated as shown in  FIG. 3 . 
   With both the abovementioned first stage and second stage, the first voltage source having the electrical voltage VCC and the second voltage source having the electrical voltage −VCC are generated simultaneously in the power supply circuit  200  illustrated in both  FIG. 2  and  FIG. 3 , for driving each sub-audio amplifier  400  in the sub-audio amplifier set  300  shown in  FIG. 1 . 
   Please refer to  FIG. 4 , which is a diagram of the sub-audio amplifier  400  shown in  FIG. 1  according to a preferred embodiment of the present invention. As shown in  FIG. 4 , the sub-audio amplifier  400  includes a comparator  402 , a preceding driver  404 , a transistor set  406 , an inductor  408 , a third capacitor  410 , and a speaker  412 . The comparator  402  has a positive input terminal coupled to a sawtooth signal source, and a negative input terminal coupled to an audio signal source AUDIO IN as shown in  FIG. 4 . With the aid of the sawtooth signal source, audio signals from the audio signal source AUDIO IN are transformed into pulse width modulation signals at an output terminal of the comparator  402 . The preceding driver  404  has an input terminal coupled to the output terminal of the comparator  402 , for receiving the pulse width modulation signals. The transistor set  406  has an input terminal coupled to an output terminal of the preceding driver  404 , and includes a first transistor  414  and a second transistor  416 . The first transistor  414  has a source coupled to the first voltage source having the electrical level of VCC, a gate coupled to the input terminal of the transistor set  406 , and a drain coupled to an output terminal of the transistor set  406 . The second transistor  416  has a drain coupled to the output terminal of the transistor set  406 , a gate coupled to the input terminal of the transistor set  406 , and a source coupled to the second terminal of the second capacitor  212  shown in  FIG. 2 , i.e., to the generated second voltage source having the electrical level of −VCC. The inductor  408  has a first terminal coupled to the output terminal of the transistor set  406 . The third capacitor  410  has a first terminal coupled to a second terminal of the inductor  408 , and a second terminal coupled to ground. The speaker  412  has a first input terminal coupled to the first terminal of the third capacitor  410 , and a second input terminal coupled to the second terminal of the third capacitor  410 . That is, the speaker  412  is parallel-coupled to the third capacitor  410 , and therefore, the speaker  412  is driven by a voltage difference stored across the third capacitor  410 . 
   Note that in the present invention, the sub-audio amplifier  400  shown in  FIG. 1  is not necessarily implemented as illustrated in  FIG. 4 . It indicates a fact that the sub-audio amplifier  400  shown in  FIG. 1  may also be replaced with other circuits required to be biased with a pair of voltage sources having a same electrical level but opposite electrical poles, and there are also embodiments of the present invention relating to the indicated fact. Besides, both the first transistor  414  and the second transistor  416  in the transistor set  406  may also be replaced by other elements capable of implementing an output stage in said transistor set  406 , and such replacements should also be classified as embodiments of the present invention. 
   The present invention discloses an audio amplifier capable of biasing an output stage with single voltage source. In the disclosed audio amplifier, the single voltage source is coupled to a voltage supply circuit for generating another voltage source having a same electrical level but an opposite electrical pole with the coupled single voltage source, and for utilizing both the coupled voltage source and the generated voltage source to drive the disclosed audio amplifier. Note that the disclosed amplifier may be a Class D amplifier. With the aid of dispositions in the present invention, only one port is required to be added for biasing an output stage MOSFET of the disclosed audio amplifier instead of utilizing two ports for biasing an output stage MOSFET of an audio amplifier in the prior art. That is, an amount of ports utilized for biasing an output stage MOSFET of an audio amplifier is thus decreased or saved. 
   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.