Abstract:
Provided are a power amplifier and a method thereof. The power amplifier power amplifier includes: a main amplifying unit receiving power; an auxiliary amplifying unit connected in parallel to the main amplifying unit; and a balloon transformer combined with the main amplifying unit and the auxiliary amplifying unit. Respectively different bias voltages are applied to the main amplifying unit and the auxiliary amplifying unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2011-0121476, filed on Nov. 21, 2011, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention disclosed herein relates to a power amplifier and an amplification method thereof. 
         [0003]    Due to the recent development of wireless communication system techniques, an integrated design system that integrates a plurality of systems into one device is generally used. In such devices, many components operate and consume power simultaneously. Thus, a highly efficient power amplifier is required to increase the efficient use of power. Moreover, since a digital modulated signal used in a wireless communication system has a high peak-to-average power ratio, power amplifiers require both high efficiency and excellent linearity. 
         [0004]    In order to maintain power amplifier linearity, a back off method is generally used. The back off method allows a power amplifier to operate at an output of about 10 dB less than the maximum output. To implement this, an amplifier must be designed that dynamically changes the loads of some components in order to have high efficiency at a lower-than-maximum output. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a power amplifier having high efficiency and excellent linearity by using a transformer and an amplification method thereof. 
         [0006]    Embodiments of the present invention provide power amplifiers including: a main amplifying unit receiving power; an auxiliary amplifying unit connected in parallel to the main amplifying unit; and a balloon transformer combined with the main amplifying unit and the auxiliary amplifying unit, wherein different bias voltages are applied to the main amplifying unit and the auxiliary amplifying unit. 
         [0007]    In some embodiments, the balloon transformer may have a transformation ratio of 1:1. 
         [0008]    In other embodiments, a voltage input to the main amplifying unit and the auxiliary amplifying unit may be distributed by the balloon transformer. 
         [0009]    In still other embodiments, a bias condition of the main amplifying unit may be class AB. 
         [0010]    In even other embodiments, a bias condition of the auxiliary amplifying unit may be class C. 
         [0011]    In yet other embodiments, the main amplifying unit may include a first main amplifier and a second main amplifier; and different bias voltages may be input to the first main amplifier and the second main amplifier. 
         [0012]    In further embodiments, the auxiliary amplifying unit may include a first auxiliary amplifier and a second auxiliary amplifier; and different bias voltages may be input to the first auxiliary amplifier and the second auxiliary amplifier. 
         [0013]    In still further embodiments, an offset line may be connected to the auxiliary amplifying unit. 
         [0014]    In other embodiments of the present invention, power amplifying methods include: distributing an input voltage as first and second input voltages; applying the first and second input voltages to first and second amplifiers having different bias conditions, respectively; combining voltages output from the first and second amplifiers by using a balloon transformer; and outputting the combined voltages as an output voltage by using the balloon transformer. 
         [0015]    In some embodiments, the balloon transformer may have a transformation ratio of 1:1. 
         [0016]    In other embodiments, each of the first and second amplifiers may include an offset line. 
         [0017]    In still other embodiments, a bias condition of the first amplifier may be class AB. 
         [0018]    In even other embodiments, a bias condition of the second amplifier may be class C. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings: 
           [0020]      FIG. 1  is a block diagram illustrating a power amplifier according to an embodiment of the present invention; 
           [0021]      FIG. 2  is a graph illustrating output voltages with respect to output voltages of a main amplifier and an auxiliary amplifier; 
           [0022]      FIG. 3  is a graph illustrating currents with respect to input voltages of a main amplifier and an auxiliary amplifier; 
           [0023]      FIG. 4  is a graph illustrating all operations of the power amplifier of  FIG. 1 ; 
           [0024]      FIG. 5  is a view of a power amplifier according to an embodiment of the present invention; 
           [0025]      FIG. 6  is a detailed view when a load is added on the power amplifier of  FIG. 5 ; 
           [0026]      FIG. 7  is a graph illustrating efficiency of a typical power amplifier and efficiency of a power amplifier suggested from the present invention; and 
           [0027]      FIG. 8  is a flowchart illustrating a power amplifying method of a power amplifier according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0028]    Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. 
         [0029]      FIG. 1  is a block diagram illustrating a power amplifier according to an embodiment of the present invention. Referring to  FIG. 1 , the power amplifier  10  includes a main amplifier  11 , an auxiliary amplifier  12 , an input impedance converter  13 , an output impedance converter  14 , and a load  15 . That is, the power amplifier  10  is configured through the Doherty method. Once an input voltage Vin is input to the power amplifier  10 , it is distributed into the main amplifier  11  and the auxiliary amplifier  12  through a voltage distributor (not shown). Voltages, which are amplified by the main amplifier  11  and the auxiliary amplifier  12  of the power amplifier  10 , are combined and then delivered to the load  15 . 
         [0030]    The main amplifier  11  has a wide range of linearity. For this, the main amplifier  11  may operate under a bias condition of class A, class B, or class AB. In relation to the bias condition applied to the main amplifier  11 , the class A has more excellent linearity but somewhat less efficiency than the class B. In this embodiment, the main amplifier  11  operates under a bias condition of the class AB having an average property of the class A and the class B. 
         [0031]    The auxiliary amplifier  12  has limited linearity (i.e., only operating under a high voltage condition) but high efficiency. For this, the auxiliary amplifier  12  may operate under the bias condition of the class C. In relation to a bias condition applied to the auxiliary amplifier  12 , it means that the class C only operates under a high input voltage condition in which a bias of class A, class B, or class AB is saturated. 
         [0032]    The input impedance converter  13  is inserted to compensate for a phase difference between the main amplifier  11  and the auxiliary amplifier  12 . The input impedance converter  13  may be implemented with a microstrip line. In this embodiment, the input impedance converter  13  is a microstrip line having a phase delay of 90°. 
         [0033]    The output impedance converter  14  is inserted for impedance matching between the amplifiers and the load  15 . The output impedance converter  14  serves to change output impedances from the main amplifier  11  and the auxiliary amplifier  12  when an input voltage changes. The output impedance converter  14  may be implemented with a microstrip line. 
         [0034]      FIGS. 2 and 3  are graphs illustrating operations of the main amplifier  11  and the auxiliary amplifier  12  of  FIG. 1  in more detail. Referring to  FIGS. 2 and 3 , the main amplifier  11  operates linearly until an input voltage becomes V in     —     max /2. At this point, V in     —     max /2 is the maximum input voltage at which an output voltage is unsaturated. The main amplifier  11  is saturated at an input voltage higher than that. 
         [0035]    On the contrary, the auxiliary amplifier  12  does not operate at a low input voltage, i.e., an input voltage less than V in     —     max /2. Furthermore, the auxiliary amplifier  12  operates linearly until V in     —     max /2 becomes V in     —     max . 
         [0036]      FIG. 4  is a graph illustrating all operations of the power amplifier  10  of  FIG. 1 . Only the main amplifier  11  operates linearly in a low voltage interval. The auxiliary amplifier  12  is in an off-state, and operates like an open circuit. As voltage becomes increased, i.e., an input voltage is equal to or more than V in     —     max /2, the main amplifier  11  is saturated. Moreover, the auxiliary amplifier  12  operates linearly. If an input voltage becomes equal to or more than V in     —     max , both the main amplifier  11  and the auxiliary amplifier  12  are saturated. At this point, the power amplifier  10  has the maximum output. 
         [0037]    All operations of the power amplifier  10  include operations of the main amplifier  11  and the auxiliary amplifier  12 . Accordingly, the power amplifier  10  maintains linearity in a wider range than an amplifier having one bias condition. That is, the linearity criteria P 1 dB of the power amplifier  10  is improved by about 3 dB than when there is only one amplifier. Additionally, the auxiliary amplifier  12  does not operate under a low power condition. That is, the auxiliary amplifier  12  does not consume DC power, so that the power amplifier  10  becomes highly efficient. 
         [0038]    However, the power amplifier  10  has an issue related to an output impedance change because the auxiliary amplifier  12  changes into an on or off state. Moreover, the auxiliary amplifier  12  is ideally supposed to operate as an open circuit when it is in an off state, but does not operate as the open circuit actually. In addition, a parasite capacitance exists at an output terminal of a transistor. The parasite capacitance lowers an output impedance of a transistor to a very low level. Due to this, there is another issue related to an RF gain change. 
         [0039]    Furthermore, a Complementary Metal-Oxide Semiconductor (CMOS) power amplifier is mainly implemented in the form of a differential cascode structure. However, a power amplifier in a recent developing Wibro system requires a high Peak-to-Average Power Ratio (PAPR) and high output power. 
         [0040]    In order to resolve the above issues, another embodiment of the present invention provides a method of combining voltages by using a balloon transformer in a plurality of power amplifiers. Through this, a balloon transformer may be used in an improved CMOS voltage amplifier without an additional circuit. 
         [0041]      FIG. 5  is a view of a power amplifier according to an embodiment of the present invention. Referring to  FIG. 5 , the power amplifier  100  includes a main amplifying unit  110 , an auxiliary amplifying unit  120 , and a balloon transformer  130 . The power amplifier  100  may be a CMOS power amplifier used for terminals such as a mobile phone, a portable computer, a PDA, a radio, and a pager. An input voltage RF_in input in the power amplifier  100  is applied to the main amplifying unit  110  and the auxiliary amplifying unit  120  through a voltage distributor (not shown). The voltage distributor may be configured using a balloon transformer. 
         [0042]    The main amplifying unit  110  and the auxiliary amplifying unit  120  have different bias conditions. The bias condition is input through bias applying resistances Rm and Rp. The main amplifying unit  110  and the auxiliary amplifying unit  120  may amplify and output the distributed voltage. The balloon transformer  130  combines voltages output from the main amplifying unit  110  and the auxiliary amplifying unit  120 . Additionally, the balloon transformer  130  outputs the combined voltage RF_out. 
         [0043]      FIG. 6  is a detailed view when a load is added on the power amplifier  100  of  FIG. 5 . Referring to  FIG. 6 , the power amplifier  200  includes a main amplifying unit  210 , an auxiliary amplifying unit  220 , a balloon transformer  230 , and a load  240 . An input voltage RF_in input to the power amplifier  200  is applied to the main amplifying unit  210  and the auxiliary amplifying unit  220  through a voltage distributor (not shown). 
         [0044]    The main amplifying unit  210  includes at least one main amplifier  211  to  21   n.  The main amplifying unit  210  has a wide range of linearity. For this, the main amplifying unit  210  may operate under class A, class B, or class AB. The bias is applied through bias applying resistances Rm 1  to Rmn. In this embodiment, the main amplifying unit  210  operates under a bias condition of the class AB having an average property of the class A and class B. 
         [0045]    The auxiliary amplifying unit  220  includes at least one auxiliary amplifier  221  to  22   n.  The auxiliary amplifying unit  220  has limited linearity (i.e., only operating under a high voltage condition) but high efficiency. For this, the auxiliary amplifying unit  220  may operate under the bias condition of the class C. The bias is applied through bias applying resistances Rp 1  to Rpn. 
         [0046]    The balloon transformer  230  is combined with the output terminals of the main amplifying unit  210  and the auxiliary amplifying unit  220 . The balloon transformer  230  may receive differential outputs of the main amplifying unit  210  and the auxiliary amplifying unit  220 . In this embodiment, a transformation ratio of the balloon transformer  230  is 1:1. However, the transformation ratio may vary. The balloon transformer  230  combines the outputs of the main amplifying unit  210  and the auxiliary amplifying unit  220 . Also, the balloon transformer  230  delivers the combined power RF_out to the load  240 . 
         [0047]    Hereinafter, operations of the power amplifier  200  in a low power state, for example, before a 6 dB back off state, will be described below. The main amplifying unit  210  in a low power state is in a linear operation state. An output of the main amplifying unit  210  is combined by the balloon transformer  230  and then is delivered to the load  240 . Accordingly, a load impedance seen from the main amplifying unit  210  is modulated by the balloon transformer  230 . For example, let&#39;s assume in this embodiment that a voltage input to each main amplifying unit  210  is same. Then, a load impedance seen from the main amplifying unit  210  is reduced to 1/n. Due to this load modulation property, the main amplifying unit  210  linearly operates until a 6 dB back off point. 
         [0048]    The auxiliary amplifying unit  220  in a low power state is in an off state. Accordingly, the auxiliary amplifying unit  220  operates as an open circuit. That is, the auxiliary amplifying unit  220  does not consume unnecessary DC power, thereby improving efficiency of the power amplifier  200 . However, the actual auxiliary amplifying unit  220  is not ideally opened. To compensate for this, an offset line (not shown) may be added to the auxiliary amplifying unit  220 . Through this, an electrical length is added to the auxiliary amplifying unit  220 , so that an output impedance of the auxiliary amplifying unit  220  becomes close to an open circuit. Additionally, in order to compensate for the time delay resulting from the added electrical path of the auxiliary amplifying unit  220 , the same offset line may be added to the input terminal of the main amplifying unit  210 . 
         [0049]    Hereinafter, operations of the power amplifier  200  in a high power state, for example, after a 6 dB back off state, will be described below. The main amplifying unit  210  in a high power state is in a saturation state. Accordingly, the main amplifying unit  210  maintains the maximum efficiency characteristic up to the maximum output area, i.e., an area that the auxiliary amplifying unit  220  is saturated. An output of the main amplifying unit  210  is combined by the balloon transformer  230  and then is delivered to the load  240 . 
         [0050]    The auxiliary amplifying unit  220  in a high power state operates in a linear state. An output of the auxiliary amplifying unit  220  is combined by the balloon transformer  230  and then is delivered to the load  240 . 
         [0051]    At this point, when it reaches the maximum output area, i.e., an area that the auxiliary amplifying unit  220  is saturated, both the main amplifying unit  210  and the auxiliary amplifying unit  220  are saturated. At this point, the power amplifier  200  shows the maximum efficiency. If a ratio of amplifiers of the main amplifying unit  210  and the auxiliary amplifying unit  220  is 1:1, each amplifier provides the half of an entire output power. Additionally, it is seen from each amplifier that the load impedance is equally distributed. 
         [0052]      FIG. 7  is a graph illustrating efficiency of a typical power amplifier and efficiency of a power amplifier suggested from the present invention. Referring to  FIG. 7 , it is observed that the power amplifier of the present invention has high efficiency because the auxiliary amplifier does not operate when operating in a lower power in comparison with a typical power amplifier. 
         [0053]      FIG. 8  is a flowchart illustrating a power amplifying method of a power amplifier according to an embodiment of the present invention. First, once an input voltage is applied to the power amplifier, a voltage distributor distributes an input voltage into a first amplifier (e.g., a main amplifying unit) and a second amplifier (e.g., an auxiliary amplifying unit) in operation S 1 . That is, the distributed voltage is input into the main amplifying unit and the auxiliary amplifying unit in operation S 2 . The voltage amplified by the main amplifying unit and the auxiliary amplifying unit is combined through a balloon transformer in operation S 3 . The balloon transformer outputs the combined power in operation S 4 . 
         [0054]    In the above embodiment, the main amplifiers  211  to  21   n  in the main amplifying unit  210  operate under the same bias condition, for example, class AB, but the present invention is not limited thereto. A bias condition may be given gradually between the main amplifiers  211  to  21   n.  This is identically applied to the auxiliary amplifying unit  220 . 
         [0055]    As described above, the power amplifier suggested by the present invention utilizes a balloon transformer for voltage combination. Accordingly, an impedance transformer does not need to be implemented, so that the chip may be miniaturized. Furthermore, a balloon transformer for voltage combination is already implemented in a CMOS, so that no additional circuit is required in a typical amplifier. 
         [0056]    Furthermore, although a structure using an impedance transformer relates to a current combining method, an amplifier suggested by the present invention relates to a voltage combining method. Therefore, loss at an output terminal is relatively small. Moreover, the present invention controls an amplifier without a device such as a switch, so that no loss from that occurs and ease of use is provided. 
         [0057]    As described above, the power amplifier of the present invention can have high efficiency and excellent linearity. 
         [0058]    The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.