Abstract:
A switching amplifying method or a switching amplifier for obtaining one or more than one linearly amplified replicas of an input signal, is highly efficient, and does not have the disadvantage of “dead time” problem related to the class D amplifiers. Said switching amplifying method comprises the steps of: receiving the input signal; pulse modulating the input signal for generating a pulse modulated signal; switching a pulsed current from a direct current (DC) voltage according to the pulse modulated signal; conducting said pulsed current positively or negatively to a filter according to the polarity of the input signal; filtering said pulsed current positively or negatively conducted to the filter for outputting an output signal by the filter.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention is related in general to a power amplifier, and more particularly, to a switching amplifier that can efficiently and linearly amplify an input signal having first and second polarities for obtaining a low-distortion output signal. 
     (2) Description of the Related Art 
     Amplifiers are electronic devices which are used for increasing the power of a signal, and are generally categorized into various classes. The popular amplifiers include class A, class B and class D amplifiers. 
     Reference is made to the exemplary U.S. Patents that disclose various types of amplifiers: U.S. Pat. Nos. 7,952,426; 7,816,985; 7,400,191; 7,286,008; 6,922,101; 6,794,932; 6,563,377; 6,356,151; 5,949,282; 5,805,020; 5,160,896; 5,115,205; 5,014,016; 4,531,096 and 3,629,616. 
     In general, class A amplifiers produce a linearly amplified replica of an input signal, but are inefficient in terms of power usage because the amplifying elements are always biased and conducting, even if there is no input. 
     Class B amplifiers only amplify half of the input wave cycle, thus creating a large amount of distortion, but their efficiency is greatly improved and is much better than class A. A practical circuit using class B elements is the push-pull stage, such as the very simplified complementary pair arrangement. Complementary or quasi-complementary devices are each used for amplifying the opposite halves of the input signal, which is then recombined at the output. This arrangement gives excellent efficiency, but can suffer from the drawback that there is a small mismatch in the cross-over region—at the “joins” between the two halves of the signal, as one output device has to take over supplying power exactly as the other finishes. This is called crossover distortion. 
     In a class D amplifier an input signal is converted to a sequence of higher voltage output pulses. The averaged-over-time power values of these pulses are directly proportional to the instantaneous amplitude of the input signal. The frequency of the output pulses is typically ten or more times the highest frequency in the input signal to be amplified. The output pulses contain inaccurate spectral components (that is, the pulse frequency and its harmonics) which must be removed by a low-pass passive filter. The resulting filtered signal is then a linearly amplified replica of the input. 
     The main advantage of a class D amplifier is power efficiency. Because the output pulses have fixed amplitude, the switching elements are switched either completely on or completely off, rather than operated in linear mode. 
     However, one significant challenge for a driver circuit in class D amplifiers is keeping dead times as short as possible. “Dead time” is the period during a switching transition when both output MOSFETs are driven into Cut-Off Mode and both are “off”. Dead times need to be as short as possible to maintain an accurate low-distortion output signal, but dead times that are too short cause the MOSFET that is switching on to start conducting before the MOSFET that is switching off has stopped conducting. The MOSFETs effectively short the output power supply through themselves, a condition known as “shoot-through”. Driver failures that allow shoot-through result in excessive losses and sometimes catastrophic failure of the MOSFETs. 
     Therefore, the main disadvantage of a class D amplifier is having the “dead time” problem to cause the distortion of the output signal. 
     In summary, class A amplifiers produce a linearly amplified replica of an input signal, but are inefficient in terms of power usage. The push-pull class B amplifiers provide excellent efficiency (compared to class A amplifiers), but introduce crossover distortion. Class D amplifiers are most efficient compared to class A and class B amplifiers, but there is one significant problem for MOSFET driver circuits in class D amplifiers: the “dead time” that cause the distortion of the output signal. 
     Accordingly, in light of current state of the art and the drawbacks to current amplifiers mentioned above. A need exits for a switching amplifier that would continue to be highly efficient, that would efficiently and linearly amplify an input signal for generating low-distortion output signals. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a switching amplifier that produces a linearly amplified replica of an input signal, is highly efficient, and does not have the “dead time” problem related to class D amplifiers. 
     One aspect of the present invention provides a method of obtaining an output signal, wherein the output signal is a linearly amplified replica of an input signal having first and second polarities, comprising the steps of: receiving the input signal; pulse modulating the input signal for generating a pulse modulated signal; switching a pulsed current according to the pulse modulated signal; conducting said pulsed current positively or negatively to a filter according to the polarity of the input signal; filtering said pulsed current positively or negatively conducted to the filter for outputting the output signal by the filter. 
     Yet another aspect of the present invention provides a method of obtaining one or more than one slave output signals that are linearly amplified replicas of the input signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present general inventive concept will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is an exemplary block and circuit diagram illustrating a first embodiment of a switching amplifier in accordance with present invention, wherein the pulsed current supply unit using an inductor. 
         FIG. 2  are exemplary waveform diagrams illustrating the various waveforms at input and output points of a switching control unit of various figures in accordance with the present invention. 
         FIG. 3  is an exemplary block and circuit diagram illustrating an embodiment of the amplifier control unit integrating an input signal and a negative feedback signal in  FIGS. 1, 4 and 5  in accordance with the present invention. 
         FIG. 4  is an exemplary block and circuit diagram illustrating a second embodiment of a switching amplifier in accordance with present invention, wherein the pulsed current supply unit using a flyback transformer comprising an output winding. 
         FIG. 5  is an exemplary block and circuit diagram illustrating a third embodiment of a switching amplifier in accordance with present invention, wherein the pulsed current supply unit using a flyback transformer comprising two output windings. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The detailed description set forth below in connection with the appended drawings is intended as a description of presently preferred embodiments of the invention and is not intended to represent the only forms in which the present invention may be constructed and or utilized. 
       FIG. 1  is an exemplary block and circuit diagram illustrating a first embodiment of a switching amplifier  100  in accordance with present invention, wherein the pulsed current supply unit  102  using an inductor  102 F. 
     As illustrated in  FIG. 1 , the switching amplifier  100  of the present invention for amplifying an input signal  106  having positive and negative polarities is comprised of: a pulsed current supply unit  102  comprising a plurality of switches for switching a pulsed current from a direct current (DC) voltage  109 ; a switching power transmitting unit  104  comprising a plurality of switches and coupled to the pulsed current supply unit  102  for conducting the pulsed current from the pulsed current supply unit  102  positively or negatively to a filter unit  107 ; an amplifier control unit  105  for receiving the input signal  106  and coupled to the switches of the pulsed current supply unit  102  and the switching power transmitting unit  104  to control their switching according to the input signal  106 ; the filter unit  107  to obtain an output signal  108  corresponding to the input signal  106  by filtering the output of the switching power transmitting unit  104  and outputting the output signal  108 . 
     The switching amplifier  100  according to present invention, wherein the pulsed current supply unit  102  comprises: an inductance means  102 F; a first switching unit comprising two switches  102 A,  102 B coupled to the inductance means for switching a current from a direct current (DC) voltage  109  to the inductance means  102 F; a second switching unit comprising a switch  102 C and two diode  102 D,  102 E coupled between the inductance means  102 F and the direct current (DC) voltage  109  for switching a current from the inductance means  102 F to the direct current (DC) voltage  109 . 
     The switching amplifier  100  according to present invention, wherein the switching power transmitting unit  104  comprises: a diode  104 A for preventing a current flow from the filter unit  107  to the pulsed current supply unit  102 ; switches  104 B,  104 C,  104 D, and  104 E for transmitting a current from the switching power transmitting unit  104  to the filter unit  107  positively or negatively. 
     The switching amplifier  100  according to present invention, wherein the filter unit  107  is a low pass filter 
     In this non-limiting exemplary embodiment, the input signal  106  is an analog signal. And it should be noted that it is obvious for a corresponding embodiment of a switching amplifier in accordance with this invention for an input signal which is a discrete time signal. 
     As further illustrated in  FIG. 1 , the amplifier control unit  105  comprises an input unit  105 A for receiving the input signal  106  and having an analog to digital converter for converting the input signal  106  to a discrete time input signal x [n]
 
x={x[n]}, 0&lt;n&lt;∞;
 
a pulse modulation unit  105 B for getting a pulse modulated signal from pulse modulating the discrete time input signal x[n]; and a switching control unit  105 C coupled to the switches  102 A,  102 B, and  102 C of the pulsed current supply unit  102 , the switches  104 B,  104 C,  104 D and  104 E of the switching power transmitting unit  104  to control their switching according to the pulse modulated signal from the pulse modulation unit  105 B.
 
     In this non-limiting exemplary embodiment  100 , the amplifier control unit  105  is a digital signal processing circuit. And it is obvious for a corresponding embodiment of an analog signal processing circuit for the amplifier control unit  105  in accordance with this invention by using an input unit for receiving an analog input signal and a pulse modulator for pulse modulating said analog input signal. 
       FIG. 2  are exemplary waveform diagrams illustrating the various waveforms at input and output points of switching control units in the circuits of various figures in accordance with the present invention. 
     As illustrated in  FIG. 2 , a non-limiting exemplary waveform for the pulse modulated signal from the pulse modulation unit  105 B is illustrated in  FIG. 2(A) , since the input signal  106  has first and second polarities; therefore, the pulse modulated signal also has first and second polarities. According to the pulse modulated signal illustrated in  FIG. 2(A) , a non-limiting exemplary waveform of switching control signals from the switching control unit  105 C to the switches  102 A and  102 B for controlling their switching are illustrated in  FIG. 2(B) ; a non-limiting exemplary waveform of switching control signal from the switching control unit  105 C to the switch  102 C for controlling its switching is illustrated in  FIG. 2(C) . Also according to the pulse modulated signal illustrated in  FIG. 2(A) , non-limiting exemplary waveforms of switching control signals from the switching control unit  105 C to the switches  104 B,  104 D and  104 C,  104 E are illustrated in  FIG. 2(D)  and  FIG. 2(E) , respectively. 
     Accordingly, as illustrated in  FIG. 1  and  FIG. 2 , when the input signal  106  is zero, the switches  104 B,  104 C,  104 D,  104 E of the switching power transmitting unit  104  are all switched off. The switches  102 A,  1028  and  102 C switch on and off alternately to charge and discharge the inductor  102 F to regulate current of the inductor  102 F: when the switches  102 A,  102 B switch on and  102 C switches off, the inductor  102 F is charging energy from the direct current (DC) voltage  109 ; and when the switches  102 A,  102 B switch off and  102 C switches on, the energy contained in the inductor  102 F is discharged back to the direct current (DC) voltage  109 . Therefore, at steady state, for approximately equal charging and discharging time, the energy flow in and out of the inductor  102 F are equal during each switching, therefore, this switching keeps the energy stored in the inductor  102 F constant. For the inductance of the inductor  102 F is large enough and the switching frequency of the switches  102 A,  1028  and  102 C is fast enough, the current flow through the inductor  102 F keeps approximately constant since its variation is small enough. 
     When the input signal  106  is not zero, as illustrated in  FIG. 1  and  FIG. 2(A) ˜ 2 (E), the switches  102 A,  102 B,  102 C and the switching power transmitting unit  104  switch alternately to keep the energy stored in the inductor  102 F constant, therefore when the switching power transmitting unit  104  is switched on, the current from the inductor  102 F to the filter  107  keeps constant. 
     As illustrated in  FIG. 1  and  FIG. 2(A), 2(D), 2(E)  the switches  104 B˜ 104 E switch for conducting the current from the inductor  102 F to the filter unit  107 . For the polarity of the pulse modulated signal  FIG. 2(A)  is positive, the switches  104 B,  104 D switch on to conduct the current from the inductor  102 F to the filter unit  107  positively; otherwise, for the polarity of the pulse modulated signal  FIG. 2(A)  is negative, the switches  104 C and  104 E switch on to conduct the current from the inductor  102 F to the filter unit  107  negatively. 
     As further illustrated in  FIG. 1 , the filter unit  107  is a low pass filter to obtain the output signal  108  corresponding to the input signal  106  by filtering the output of the switching power transmitting unit  104  and outputting the output signal  108 . 
     As further illustrated in  FIG. 1  and  FIG. 2 , the level of the output signal  108  can be adjusted by control the current level of the inductor  102 F. Based on the current level feedback signal  110  representing a current flow through the inductor  102 F, the switching control unit  105 C can adjust the current flow through the inductor  102 F by changing the duty ratio between the charging and discharging periods of the inductor  102 F according to the current level feedback signal  110 . 
     As further illustrated in  FIG. 1 , the switching amplifier  100  further comprises a negative feedback signal generator  111  to generate a negative feedback signal corresponding to the output signal  112 , wherein the amplifier control unit  105  integrates the input signal  106  and the negative feedback signal  112 . 
       FIG. 3  is an exemplary block and circuit diagram illustrating an embodiment of the amplifier control unit  105  integrating the input signal  106  and a negative feedback signal  112  in  FIG. 1  in accordance with the present invention. 
     As illustrated in  FIG. 3  and  FIG. 1 , the input unit  105 A has an analog to digital converter  301  and further comprises a linear digital transformer  302  and a negative feedback controller  303 . Wherein the analog to digital converter  301  receives the input signal  106  and converts the input signal  106  to a discrete time input signal:
 
x={x[n]}, 0&lt;n&lt;∞;
 
     The linear digital transformer  302  transforms the discrete time input signal x[n] by multiplying a gain G to the discrete time input signal (the default value of the gain G is 1):
 
 X[n]={G×x[n ]}), 0&lt; n&lt;∞ 
 
to get a compensated discrete time signal X[n] and sends the compensated discrete time signal X[n] to pulse modulation unit  105 B.
 
Accordingly, for the switching amplifier  100  further comprises the negative feedback signal generator  111  to generate the negative feedback signal corresponding to the output signal  112  and the amplifier control unit  105  integrates the input signal  106  and the negative feedback signal  112 , the pulse modulation unit  105 B receives the compensated discrete time signal X[n].
 
     As further illustrated in  FIG. 3 , the negative feedback controller  303  receives the discrete time input signal from the analog to digital converter  301  and compares it to the negative feedback signal  112 , therefore to adjust the gain G of the linear digital transformer  302  according to the comparison. For example, if the negative feedback signal  112  corresponding to the output signal  108  shows that the output signal  108  is below a required level, then the negative feedback controller  303  will increase the gain G of the linear digital transformer  302  to increase the output signal  108 , wherein said required level is obtained according to the discrete time input signal. 
     In this non-limiting exemplary embodiment  100 , the amplifier control unit  105  is a digital signal processing circuit. And it is obvious for a corresponding embodiment of an analog signal processing circuit for the amplifier control unit  105  in accordance with this invention by using an analog input unit for receiving an analog input signal, a programmable gain amplifier for amplifying the an analog input signal and a pulse modulator for pulse modulating said amplified analog signal. 
       FIG. 4  is an exemplary block and circuit diagram illustrating a second embodiment of a switching amplifier  400  in accordance with present invention. 
     As illustrated in  FIG. 4 , the switching amplifier  400  of the present invention for amplifying an input signal  106  having positive and negative polarities is comprised of: a pulsed current supply unit comprising a plurality of switches  402  for switching a pulsed current from a direct current (DC) voltage  109 ; a switching power transmitting unit  404  comprising a plurality of switches and coupled to the pulsed current supply unit for conducting the pulsed current positively or negatively to a filter unit  407 ; an amplifier control unit  105  for receiving the input signal  106  and coupled to the switches  402  of the pulsed current supply unit and the switching power transmitting unit  404  to control their switching according to the input signal  106 ; the filter unit  407  to obtain an output signal  408  corresponding to the input signal  106  by filtering the output of the switching power transmitting unit  404  and outputting the output signal  408 . 
     The switching amplifier  400  of the present invention, wherein its pulsed current supply unit comprises: a flyback transformer  401 ; a first switching unit  402 A coupled to the flyback transformer  401  for switching a current from a direct current (DC) voltage  109  to the flyback transformer  401 ; a second switching unit  402 B coupled between the flyback transformer  401  and the direct current (DC) voltage  109  for switching a current from the flyback transformer  401  to the direct current (DC) voltage  109 ; wherein the pulsed current supply unit outputs a pulsed current when the switches of the first switching unit  402 A and the second switching unit  402 B are all switched off. A diode means  402 C is for preventing a current flow from the direct current (DC) voltage  109  to the secondary winding  401 B. 
     The switching amplifier  400  of the present invention, wherein the flyback transformer  401  comprises: a primary winding  401 A coupled to the first switching unit  402 A for charging energy to the flyback transformer from the direct current (DC) voltage  109 ; a secondary winding  401 B coupled to the second switching unit  402 B for discharging energy stored in the flyback transformer  401  to the direct current (DC) voltage  109 ; an output winding unit comprising an output winding  401 C for discharging energy stored in the flyback transformer to the output signal  408 . 
     The switching amplifier  400  of the present invention, wherein the switching power transmitting unit  404  comprises: a diode means unit  404 A for preventing a current flow from the filter unit  407  to the pulsed current supply unit; a plurality of switches  404 B,  404 C,  404 D,  404 E for transmitting a current from the pulsed current supply unit to the filter unit  407  positively or negatively. 
       FIG. 2  are exemplary waveform diagrams illustrating the various waveforms at input and output points of switching control units in the circuits of various figures in accordance with the present invention. 
     As illustrated in  FIG. 2 , a non-limiting exemplary waveform for the pulse modulated signal from the pulse modulation unit  105 B is illustrated in  FIG. 2(A) , since the input signal  106  has first and second polarities; therefore, the pulse modulated signal also has first and second polarities. According to the pulse modulated signal illustrated in  FIG. 2(A) , a non-limiting exemplary waveform of switching control signals from the switching control unit  105 C to the switch  402 A for controlling its switching is illustrated in  FIG. 2(B) ; a non-limiting exemplary waveform of switching control signal from the switching control unit  105 C to the switch  402 B for controlling its switching is illustrated in  FIG. 2(C) . Also according to the pulse modulated signal illustrated in  FIG. 2(A) , non-limiting exemplary waveforms of switching control signals from the switching control unit  105 C to the switches  404 B,  404 D and  404 C,  404 E are illustrated in  FIG. 2(D)  and  FIG. 2(E) , respectively. 
     Accordingly, as illustrated in  FIG. 4  and  FIG. 2 , when the input signal  106  is zero, the switches  404 B,  404 C,  404 D,  404 E of the switching power transmitting unit  404  are all switched off. The switches  402 A and  402 B switch on and off alternately to charge and discharge the flyback transformer  401  to regulate current of the flyback transformer  401 : when the switch  402 A switches on and  402 B switches off, the flyback transformer  401  is charging energy from the direct current (DC) voltage  109 ; and when the switch  402 A switches off and  402 B switches on, the energy contained in the flyback transformer  401  is discharged back to the direct current (DC) voltage  109 . Therefore, at steady state, for approximately equal charging and discharging time, the energy flow in and out of the flyback transformer  401  are equal during each switching, therefore, this switching keeps the energy stored in the flyback transformer  401  constant. For the inductance of the primary winding  401 A is large enough and the switching frequency of the switches  402 A and  402 B is fast enough, the current flow through the flyback transformer  401  keeps approximately constant since its variation is small enough. 
     When the input signal  106  is not zero, as illustrated in  FIG. 4  and  FIG. 2(A) ˜ 2 (E), the switches  402 A,  402 B and the switching power transmitting unit  404  switch alternatively to keep the energy stored in the flyback transformer  401  constant, therefore when the switching power transmitting unit  404  is switched on, the current from the flyback transformer  401  to the filter  407  keeps constant. 
     As illustrated in  FIG. 4  and  FIG. 2(A), 2(D), 2(E)  the switches  404 B˜ 404 E switch for conducting the current from the flyback transformer  401  to the filter unit  407 . For the polarity of the pulse modulated signal  FIG. 2(A)  is positive, the switches  404 B,  404 D switch on for conducting the current from the flyback transformer  401  to the filter unit  407  positively; otherwise, for the polarity of the pulse modulated signal  FIG. 2(A)  is negative, the switches  404 C and  404 E switch on for conducting the current from the flyback transformer  401  to the filter unit  407  negatively. 
     As further illustrated in  FIG. 4 , the filter unit  407  is a low pass filter to obtain the output signal  408  corresponding to the input signal  106  by filtering the output of the switching power transmitting unit  404  and outputting the output signal  408 . 
     As further illustrated in  FIG. 4  and  FIG. 2 , the level of the output signal  408  can be adjusted by control the current level of the flyback transformer  401 . Based on the current level feedback signal  410  representing a current flow through the flyback transformer  401 , the switching control unit  105 C can adjust the current flow through the flyback transformer  401  by changing the duty ratio between the charging and discharging periods of the flyback transformer  401  according to the current level feedback signal  410 . 
     As further illustrated in  FIG. 4 , the switching amplifier  400  further comprises a negative feedback signal generator  111  to generate a negative feedback signal corresponding to the output signal  112 , wherein the amplifier control unit  105  integrates the input signal  106  and the negative feedback signal  112 . 
       FIG. 3  is an exemplary block and circuit diagram illustrating an embodiment of the amplifier control unit  105  integrating the input signal  106  and a negative feedback signal  112  in  FIG. 4  in accordance with the present invention. 
     As illustrated in  FIG. 3  and  FIG. 4 , the input unit  105 A has an analog to digital converter  301  and further comprises a linear digital transformer  302  and a negative feedback controller  303 . Wherein the analog to digital converter  301  receives the input signal  106  and converts the input signal  106  to a discrete time input signal:
 
x={x[n]}), 0&lt;n&lt;∞;
 
     The linear digital transformer  302  transforms the discrete time input signal x[n] by multiplying a gain G to the discrete time input signal (the default value of the gain G is 1):
 
 X[n]={G×x[n ]}), 0 &lt;n&lt;∞ 
 
to get a compensated discrete time signal X[n] and sends the compensated discrete time signal X[n] to pulse modulation unit  105 B.
 
Accordingly, for the switching amplifier  400  further comprises the negative feedback signal generator  111  to generate the negative feedback signal corresponding to the output signal  112  and the amplifier control unit  105  integrates the input signal  106  and the negative feedback signal  112 , the pulse modulation unit  105 B receives the compensated discrete time signal X[n].
 
     As further illustrated in  FIG. 3 , the negative feedback controller  303  receives the discrete time input signal from the analog to digital converter  301  and compares it to the negative feedback signal  112 , therefore to adjust the gain G of the linear digital transformer  302  according to the comparison. For example, if the negative feedback signal  112  corresponding to the output signal  508  shows that the output signal  508  is below a required level, then the negative feedback controller  303  will increase the gain G of the linear digital transformer  302  to increase the output signal  508 , wherein said required level is obtained according to the discrete time input signal. 
     In this non-limiting exemplary embodiment  400 , the amplifier control unit  105  is a digital signal processing circuit. And it is obvious for a corresponding embodiment of an analog signal processing circuit for the amplifier control unit  105  in accordance with this invention by using an analog input unit for receiving an analog input signal, a programmable gain amplifier for amplifying the an analog input signal and a pulse modulator for pulse modulating said amplified analog signal. 
     The switching amplifier  400  according to the present invention further comprising: a rectifying and smoothing unit comprising a full bridge rectifier  415  and a capacitor  413  to rectify and smooth an alternating current (AC) voltage  416  and to provide the direct current (DC) voltage  109 . 
     The switching amplifier  400  according to the present invention further comprising: isolator circuits  417 ,  418  coupled between the switches  402 A,  402 B of the pulsed current supply unit and the amplifier control unit  105  to provide electric isolation between them. 
     The switching amplifier  400  according to the present invention further comprising: isolator circuits  419 ,  420  coupled between the switching power transmitting unit  404  and the amplifier control unit  105  to provide electric isolation between them. 
     The switching amplifier  400  according to the present invention further comprising: isolator circuits  421  coupled between the negative feedback signal generator  111  and the amplifier control unit  105  to provide electric isolation between them. 
     The switching amplifier  400  according to the present invention further comprising: the flyback transformer further comprising one or more than one slave output winding units that each slave winding unit comprises a slave output winding  401 D; one or more than one switching power transmitting units  422  and their corresponding filters  425  coupled to the slave output winding units of the flyback transformer  401  for getting or more than one slave output signals  423  corresponding to the input signal. 
     The switching amplifier  400  according to the present invention further comprising: isolator circuits coupled between the switching power transmitting units  422  and the amplifier control unit  105  to provide electric isolation between the switching power transmitting units  422  and the amplifier control unit  105 . 
       FIG. 5  is an exemplary block and circuit diagram illustrating a second embodiment of a switching amplifier  500  in accordance with present invention. 
     As illustrated in  FIG. 5 , the switching amplifier  500  of the present invention for amplifying an input signal  106  comprising positive and negative polarities is comprised of: a pulsed current supply unit comprising a plurality of switches  502  for switching a pulsed current from a direct current (DC) voltage  109 ; a switching power transmitting unit  504  comprising a plurality of switches and coupled to the pulsed current supply unit for conducting the pulsed current positively or negatively to a filter unit  507 ; an amplifier control unit  105  for receiving the input signal  106  and coupled to the switches  502  of the pulsed current supply unit and the switching power transmitting unit  504  to control their switching according to the input signal  106 ; the filter unit  507  to obtain an output signal  508  corresponding to the input signal  106  by filtering the output of the switching power transmitting unit  504  and outputting the output signal  508 . 
     The switching amplifier  500  of the present invention, wherein its pulsed current supply unit comprises: a flyback transformer  501 ; a first switching unit  502 A coupled to the flyback transformer  501  for switching a current from a direct current (DC) voltage  109  to the flyback transformer  501 ; a second switching unit  502 B coupled between the flyback transformer  501  and the direct current (DC) voltage  109  for switching a current from the flyback transformer  501  to the direct current (DC) voltage  109 ; wherein the pulsed current supply unit outputs a pulsed current when the switches of the first switching unit  502 A and the second switching unit  502 B are all switched off. A diode means  502 C is for preventing a current flow from the direct current (DC) voltage  109  to the secondary winding  501 B. 
     The switching amplifier  500  of the present invention, wherein the flyback transformer  501  comprises: a primary winding  501 A coupled to the first switching unit  502 A for charging energy to the flyback transformer from the direct current (DC) voltage  109 ; a secondary winding  501 B coupled to the second switching unit  502 B for discharging energy stored in the flyback transformer  501  to the direct current (DC) voltage  109 ; an output winding unit comprising two output windings  501 C,  501 D for discharging energy stored in the flyback transformer to the output signal  508 . 
     The switching amplifier  500  of the present invention, wherein the switching power transmitting unit  504  comprises: a diode means unit comprising two diodes  504 A,  504 B for preventing a current flow from the filter unit  507  to the pulsed current supply unit; a plurality of switches  504 C,  504 D for transmitting a current from the pulsed current supply unit to the filter unit  507  positively or negatively. 
       FIG. 2  are exemplary waveform diagrams illustrating the various waveforms at input and output points of switching control units in the circuits of various figures in accordance with the present invention. 
     As illustrated in  FIG. 2 , a non-limiting exemplary waveform for the pulse modulated signal from the pulse modulation unit  105 B is illustrated in  FIG. 2(A) , since the input signal  106  has first and second polarities; therefore, the pulse modulated signal also has first and second polarities. According to the pulse modulated signal illustrated in  FIG. 2(A) , a non-limiting exemplary waveform of switching control signals from the switching control unit  105 C to the switch  502 A for controlling its switching is illustrated in  FIG. 2(B) ; a non-limiting exemplary waveform of switching control signal from the switching control unit  105 C to the switch  502 B for controlling its switching is illustrated in  FIG. 2(C) . Also according to the pulse modulated signal illustrated in  FIG. 2(A) , non-limiting exemplary waveforms of switching control signals from the switching control unit  105 C to the switches  504 C and  504 D are illustrated in  FIG. 2(D)  and  FIG. 2(E) , respectively. 
     Accordingly, as illustrated in  FIG. 5  and  FIG. 2 , when the input signal  106  is zero, the switches  504 C,  504 D of the switching power transmitting unit  504  are all switched off. The switches  502 A and  502 B switch on and off alternately to charge and discharge the flyback transformer  501  to regulate current of the flyback transformer  501 : when the switch  502 A switches on and  502 B switches off, the flyback transformer  501  is charging energy from the direct current (DC) voltage  109 ; and when the switch  502 A switches off and  502 B switches on, the energy contained in the flyback transformer  501  is discharged back to the direct current (DC) voltage  109 . Therefore, at steady state, for approximately equal charging and discharging time, the energy flow in and out of the flyback transformer  501  are equal during each switching, therefore, this switching keeps the energy stored in the flyback transformer  501  constant. For the inductance of the primary winding  501 A is large enough and the switching frequency of the switches  502 A and  502 B is fast enough, the current flow through the flyback transformer  501  keeps approximately constant since its variation is small enough. 
     When the input signal  106  is not zero, as illustrated in  FIG. 5  and  FIG. 2(A) ˜ 2 (E), the switches  502 A,  502 B and the switching power transmitting unit  504  switch alternately to keep the energy stored in the flyback transformer  501  constant, therefore when the switching power transmitting unit  504  is switched on, the current from the flyback transformer  501  to the filter  507  keeps constant. 
     As illustrated in  FIG. 5  and  FIG. 2(A), 2(D), 2(E)  the switches  504 C,  504 D switch for conducting the current from the flyback transformer  501  to the filter unit  507 . For the polarity of the pulse modulated signal  FIG. 2(A)  is positive, the switch  504 C switches on for conducting the current from the flyback transformer  501  to the filter unit  507  positively; otherwise, for the polarity of the pulse modulated signal  FIG. 2(A)  is negative, the switch  504 D switches on for conducting the current from the flyback transformer  501  to the filter unit  507  negatively. 
     As further illustrated in  FIG. 5 , the filter unit  507  is a low pass filter to obtain the output signal  508  corresponding to the input signal  106  by filtering the output of the switching power transmitting unit  504  and outputting the output signal  508 . 
     As further illustrated in  FIG. 5  and  FIG. 2 , the level of the output signal  508  can be adjusted by control the current level of the flyback transformer  501 . Based on the current level feedback signal  510  representing a current flow through the flyback transformer  501 , the switching control unit  105 C can adjust the current flow through the flyback transformer  501  by changing the duty ratio between the charging and discharging periods of the flyback transformer  501  according to the current level feedback signal  510 . 
     As further illustrated in  FIG. 5 , the switching amplifier  500  further comprises a negative feedback signal generator  111  to generate a negative feedback signal corresponding to the output signal  112 , wherein the amplifier control unit  105  integrates the input signal  106  and the negative feedback signal  112 . 
       FIG. 3  is an exemplary block and circuit diagram illustrating an embodiment of the amplifier control unit  105  integrating the input signal  106  and a negative feedback signal  112  in  FIG. 5  in accordance with the present invention. 
     As illustrated in  FIG. 3  and  FIG. 5 , the input unit  105 A has an analog to digital converter  301  and further comprises a linear digital transformer  302  and a negative feedback controller  303 . Wherein the analog to digital converter  301  receives the input signal  106  and converts the input signal  106  to a discrete time input signal:
 
x={x[n]}, 0&lt;n&lt;∞;
 
     The linear digital transformer  302  transforms the discrete time input signal x[n] by multiplying a gain G to the discrete time input signal (the default value of the gain G is 1):
 
 X[n]={G×x[n ]}), 0&lt; n&lt;∞ 
 
to get a compensated discrete time signal X[n] and sends the compensated discrete time signal X[n] to pulse modulation unit  105 B.
 
Accordingly, for the switching amplifier  500  further comprises the negative feedback signal generator  111  to generate the negative feedback signal corresponding to the output signal  112  and the amplifier control unit  105  integrates the input signal  106  and the negative feedback signal  112 , the pulse modulation unit  105 B receives the compensated discrete time signal X[n].
 
     As further illustrated in  FIG. 3 , the negative feedback controller  303  receives the discrete time input signal from the analog to digital converter  301  and compares it to the negative feedback signal  112 , therefore to adjust the gain G of the linear digital transformer  302  according to the comparison. For example, if the negative feedback signal  112  corresponding to the output signal  508  shows that the output signal  508  is below a required level, then the negative feedback controller  303  will increase the gain G of the linear digital transformer  302  to increase the output signal  508 , wherein said required level is obtained according to the discrete time input signal. 
     In this non-limiting exemplary embodiment  500 , the amplifier control unit  105  is a digital signal processing circuit. And it is obvious for a corresponding embodiment of an analog signal processing circuit for the amplifier control unit  105  in accordance with this invention by using an analog input unit for receiving an analog input signal, a programmable gain amplifier for amplifying the an analog input signal and a pulse modulator for pulse modulating said amplified analog signal. 
     The switching amplifier  500  according to the present invention further comprising: a rectifying and smoothing unit comprising a full bridge rectifier  515  and a capacitor  513  to rectify and smooth an alternating current (AC) voltage  516  and to provide the direct current (DC) voltage  109 . 
     The switching amplifier  500  according to the present invention further comprising: isolator circuits  517 ,  518  coupled between the switches  502 A,  502 B of the pulsed current supply unit and the amplifier control unit  105  to provide electric isolation between them. 
     The switching amplifier  500  according to the present invention further comprising: isolator circuits  519 ,  520  coupled between the switching power transmitting unit  504  and the amplifier control unit  105  to provide electric isolation between them. 
     The switching amplifier  500  according to the present invention further comprising: isolator circuits  521  coupled between the negative feedback signal generator  111  and the amplifier control unit  105  to provide electric isolation between them. 
     The switching amplifier  500  according to the present invention further comprising: the flyback transformer further comprising one or more than one slave output winding units that each slave winding unit comprises two slave output windings  501 E,  501 F; one or more than one switching power transmitting units  522  and their corresponding filters  525  coupled to the slave output winding units of the flyback transformer  501  for getting or more than one slave output signals  523  corresponding to the input signal. 
     The switching amplifier  500  according to the present invention further comprising: isolator circuits coupled between the switching power transmitting units  522  and the amplifier control unit  105  to provide electric isolation between the switching power transmitting units  522  and the amplifier control unit  105 . 
     From the switching amplifiers  100 ,  400  and  500  in accordance with the present invention, one aspect of the present invention provides a switching amplifier that is highly efficient and without the “dead time” problem related to the class D amplifiers. Accordingly, the switches of the switching amplifiers  100 ,  400  and  500  are never short the direct current (DC) voltage through themselves. 
     From the switching amplifiers  100 ,  400  and  500  in accordance with the present invention, another aspect of the present invention provides a switching amplifier that its output signal is completely off when there is no input signal, as illustrated in  FIG. 2 . 
     From the switching amplifiers  100 ,  400  and  500  in accordance with the present invention, yet another aspect of the present invention provides a switching amplifier comprised of an act of comparing an input signal with an output feedback signal for detection and correction of overall system signal processes therefore is substantially immune to DC current source supply and load perturbations, as illustrated in  FIGS. 1, 4 and 5 . 
     It is to be understood that the above described embodiments are merely illustrative of the principles of the invention and that other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention.