Abstract:
Provided is a power amplifier device. The power amplifier device includes: a cutoff unit cutting off a direct current (DC) component of a signal delivered from a signal input terminal; a circuit protecting unit connected to the cutoff unit and stabilizing a signal delivered from the cutoff unit; and an amplification unit connected to the circuit protecting unit and amplifying a signal delivered from the circuit protecting unit, wherein the amplification unit comprises a plurality of transistors connected in parallel to the circuit protecting unit and the circuit protecting unit comprises resistors connected to between bases of the plurality of transistors.

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. 10-2009-0120101, filed on Dec. 4, 2009, 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 device, and more particularly, to a power amplifier device realized with a transistor. 
         [0003]    As demands on terminals and communication devices are increased according to recent expansions of communication markets, they need to be small and lightweight. In this case, power consumed in the terminals and communication devices accounts for a vital part of product performance. 
         [0004]    A power amplifier device for amplifying power at a transmit output terminal is built in a communication device such as a wire or wireless phone or a mobile phone. This power amplifier device is mainly realized using a transistor. In case of this power amplifier device, a power amplifier circuit with transistors arranged in parallel is typically used to increase an amplification rate. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a power amplification circuit having a high power gain and stability. 
         [0006]    Embodiments of the present invention provide power amplifier devices including: a cutoff unit cutting off a direct current (DC) component of a signal delivered from a signal input terminal; a circuit protecting unit connected to the cutoff unit and stabilizing a signal delivered from the cutoff unit; and an amplification unit connected to the circuit protecting unit and amplifying a signal delivered from the circuit protecting unit, wherein the amplification unit includes a plurality of transistors connected in parallel to the circuit protecting unit and the circuit protecting unit includes resistors connected to between bases of the plurality of transistors. 
         [0007]    In some embodiments, when a bias operating point of the plurality of transistors is different, the resistors connected to between the bases of the plurality of transistors may form a negative feedback loop. 
         [0008]    In other embodiments, the cutoff unit may include a plurality of capacitors connected in parallel to the signal input terminal. 
         [0009]    In still other embodiments, the plurality of capacitors may reduce a reflection coefficient with respect to a signal delivered from the signal input terminal. 
         [0010]    In even other embodiments, the circuit protecting unit may further include resistors connected to between each capacitor of the cutoff unit and each transistor of the amplification unit. 
         [0011]    In yet other embodiments, the power amplifier devices may further include an amplification adjusting unit connected to the circuit protecting unit and adjusting a voltage level of a bias signal delivered from a bias input terminal. 
         [0012]    In further embodiments, the amplification adjusting unit may include a plurality of resistors connected in parallel to the bias input terminal. 
         [0013]    In still further embodiments, collectors of the plurality of transistors may be connected to a common matching circuit. 
         [0014]    In even further embodiments, the plurality of transistors may be a Heterojunction Bipolar Transistor (HBT). 
         [0015]    In yet further embodiments, the plurality of transistors may be a GaAs HBT. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    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: 
           [0017]      FIG. 1  is a circuit diagram illustrating a unit cell of a power amplifier according to an embodiment of the present invention; 
           [0018]      FIG. 2  is a circuit diagram illustrating a power amplifier according to an embodiment of the present invention; 
           [0019]      FIG. 3A  is a circuit diagram illustrating a bias circuit according to an embodiment of the present invention; 
           [0020]      FIG. 3B  is a circuit diagram illustrating a bias circuit according to another embodiment of the present invention; 
           [0021]      FIG. 4A  is a circuit diagram illustrating a matching circuit according to an embodiment of the present invention; and 
           [0022]      FIG. 4B  is a circuit diagram illustrating a matching circuit according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0023]    Hereinafter, 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. 
         [0024]      FIG. 1  is a circuit diagram illustrating a unit cell of a power amplifier according to an embodiment of the present invention. 
         [0025]    Referring to  FIG. 1 , the unit cell of the power amplifier includes a capacitor C 1 , a plurality of resistors R 1  to R 3 , and a transistor Q 1 . In more detail, a base of the first transistor Q 1  is connected in series to the first and second resistors R 1  and R 2 . One end of the third resistor R 3  is connected to between the first and second resistors R 1  and R 2 . The first capacitor C 1  is connected in series to the first resistor R 1 . 
         [0026]    According to an embodiment of the present invention, the unit cell of the power amplifier receives a DC bias voltage through a bias input terminal  1   a . The unit cell of the power amplifier receives an RF signal through a signal input terminal  1   b . That is, the unit cell of the power amplifier may be divided into a Direct Current (DC) bias path and a Radio Frequency (RF) signal path. 
         [0027]    In the DC bias path, a DC bias voltage is applied to the base of the first transistor Q 1  through the second and third resistors R 2  and R 3 . In this case, the sum of the second and third resistors R 2  and R 3  allows the unit cell of the power amplifier to be electrically stable. That is, when current is increased by the reduction of built-in potential due to a temperature rise, the sum of the second and third resistors R 2  and R 3  forms a negative feedback that reduces a base-emitter voltage Vv2 of the first transistor Q 1 . Accordingly, the unit cell of the power amplifier becomes electrically stable. 
         [0028]    In the RF signal path, an RF signal is applied to the base of the first transistor Q 1  through the first capacitor C 1  and the first and second resistors R 1  and R 2 . In this case, the first capacitor C 1  serves as to cut off a DC component applied through the signal input terminal  1   b.  The sum of the first and second resistors R 1  and R 2  allows the unit cell of the power amplifier to be electrically stable. 
         [0029]    As mentioned above, the unit cell of the power amplifier according to an embodiment of the present invention is divided into the DC bias path and the RF signal path. Accordingly, the unit cell of the power amplifier may become electrically stable. Additionally, the third resistor R 3  is connected in parallel to between the first and second resistors R 1  and R 2 . Since a value of the third resistor R 3  is properly set, a gain of the unit cell of the power amplifier may be adjusted with an appropriate value. 
         [0030]    Moreover, according to an embodiment of the present invention, a Bipolar Junction Transistor (BJT) is used as the first transistor Q 1 . For example, a Heterojunction Bipolar Transistor (HBT) may be used as the first transistor Q 1 . As another example, a GaAs HBT may be used as the first transistor Q 1 . However, this should be understood as an exemplary one. For example, the first transistor Q 1  may be a Metal-Oxide-Silicon (MOS) transistor. 
         [0031]    Furthermore, the power amplifier according to an embodiment of the present invention has a structure in which the unit cells of the amplifier of  FIG. 1  is repeatedly connected in parallel. This will be described in more detail with reference to  FIG. 2 . 
         [0032]      FIG. 2  is a circuit diagram illustrating a power amplifier according to an embodiment of the present invention. 
         [0033]    Referring to  FIG. 2 , the power amplifier  100  includes a cutoff unit  10 , an amplification adjusting unit  20 , a circuit protecting unit  30 , and an amplification unit  40 . 
         [0034]    The cutoff unit  10  is connected to between a signal input terminal  1   b  and the amplification adjusting unit  20 . The cutoff unit  10  includes a plurality of capacitors C 1  to Cn. The cutoff unit  10  serves to cut off a DC component applied from the signal input terminal  1   b.    
         [0035]    The amplification adjusting unit  20  is connected to between a bias input terminal  1   a  and the circuit protecting unit  30 . The amplification adjusting unit  20  includes a plurality of resistors R 31  to R 3   n . More specifically, one ends of the resistors R 31  to R 3   n  of the amplification adjusting unit  20  are connected to the bias input terminal  1   a.  The other ends of the resistors R 31  to R 3   n  of the amplification adjusting unit  20  are connected to between the resistors R 11  to R 1   n  and the resistors R 21  to R 2   n  of the circuit protecting unit  30 . The amplification adjusting unit  20  delivers a DC bias voltage from the bias input terminal  1   a  to the circuit protecting unit  30 . 
         [0036]    According to an embodiment of the present invention, the resistors R 31  to R 3   n  of the amplification adjusting unit  20  may be set with a proper value to prevent gain reduction and power loss. Accordingly, a DC bias voltage level delivered to the circuit protecting unit  30  may be set with a proper value. 
         [0037]    The circuit protecting unit  30  is connected to the cutoff unit  10 , the amplification adjusting unit  20 , and the amplification unit  40 . The circuit protecting unit  30  includes a plurality of resistors R 11  to R 1   n , R 21  to R 2   n , and R 41  to R 4   n.    
         [0038]    Specifically, the resistors R 11  to R 1   n  and the resistors R 11  to R 1   n  of the circuit protecting unit  30  are connected in series to each other. The resistors R 11  to R 1   n  of the circuit protecting unit  30  are connected in series to the capacitors C 1  to Cn of the cutoff unit  10 , respectively. Nodes N 11  to N 1   n  between the resistors R 11  to R 1   n  and the resistors R 21  to R 2   n  of the circuit protecting unit  30  are connected to the resistors R 31  to R 3   n  of the amplification adjusting unit  20 , respectively. Nodes N 21  to N 2   n  between the resistors R 21  and R 2   n  and the resistors R 41  and R 4   n  of the circuit protecting unit  30  are connected to bases of the transistors Q 1  to Qn, respectively. 
         [0039]    The circuit protecting unit  30  delivers a signal from the cutoff unit  10  to the amplification unit  40 . The resistors R 11  to R 1   n  and the resistors R 21  to R 2   n  of the circuit protecting unit  30  stabilize a signal from the cutoff unit  10  and output the stabilized signal. 
         [0040]    According to an embodiment of the present invention, the resistors R 41  to R 4   n  of the circuit protecting unit  30  are respectively connected to between the bases of the transistors Q 1  to Qn. For example, the resistor R 41  is connected to between a node N 21  and a node N 22 . Accordingly, when a bias operating point of each of the transistors Q 1  to Qn is different, the resistors R 41  to R 4   n  of the circuit protecting unit  30  stabilize the power amplifier  100  through negative feedback effect. 
         [0041]    The amplification unit  40  is connected to the circuit protecting unit  30  and an output terminal  2 . The amplification unit  40  amplifies a signal from the circuit protecting unit  30  and then outputs it the output terminal  2 . 
         [0042]    In more detail, the transistors Q 1  to Qn of the amplification unit  40  receive a signal from the signal input terminal  1   b  through their bases. The transistors Q 1  to Qn of the amplification unit  40  receive a bias voltage, delivered from the bias input terminal  1   a  through their bases, to drive the transistors Q 1  to Qn. The transistors Q 1  to Qn of the amplification unit  40  amplify the delivered signal and output it to the output terminal  2 . 
         [0043]    The output terminal  2  is connected to a matching circuit where the power amplifier  100  has the maximum output voltage or gain. The matching circuit typically consists of a combination of an inductor L and a capacitor C. 
         [0044]    The power amplifier  100  according to an embodiment of the present invention has the above-mentioned structure. Hereinafter, a series of operations of the power amplifier will be described in more detail. 
         [0045]    A signal from the signal input terminal  1   b  is delivered to the cutoff unit  10 . The capacitors C 1  to Cn of the cutoff unit  10  cut off a DC component of the delivered signal. Additionally, the capacitors C 1  to Cn of the cutoff unit  10  serve to lower a reflection coefficient at the input side. 
         [0046]    Signals passing through the cutoff unit  10  are delivered to the circuit protecting unit  30 . The resistors R 11  to R 1   n  and the resistors R 21  to R 2   n  of the circuit protecting unit  30  stabilize the delivered signal. Additionally, resistance values of the resistors R 31  to R 3   n  of the amplification adjusting unit  20  are set with a proper value. Accordingly, an input bias of a proper value may be applied to the bases of the transistors Q 1  to Qn. 
         [0047]    Signals passing through the circuit protecting unit  30  are delivered to the transistors Q 1  to Qn of the amplification unit  30 . A bias current passing through the amplification adjusting unit  20  is delivered to the transistors Q 1  to Qn of the amplification unit  30 . The transistors Q 1  to Qn of the amplification unit  30  amplify a signal and a bias current and output them. 
         [0048]    Moreover, the resistors R 41  to R 4   n  of the circuit protecting unit  30  are respectively connected to the bases of the transistors Q 1  to Qn. If a bias operating point of each of the transistors Q 1  to Qn is different, the resistors R 41  to R 4   n  of the circuit protecting unit  30  stabilize the power amplifier  100  through negative feed-back effect. 
         [0049]      FIG. 3A  is a circuit diagram illustrating a bias circuit according to an embodiment of the present invention. A bias output BIAS OUT generated by the bias circuit of  FIG. 3A  is delivered to the bias input terminal  1   a  of  FIG. 2 . 
         [0050]    Referring to  FIG. 3A , the bias circuit  200  includes a resistor  220  and a transistor  210 . A collector of the transistor  210  is connected to the resistor  220  and an emitter of the transistor  210  is connected to a ground. A base of the transistor  210  is connected to the collector. A reference voltage Vref is applied to the transistor  210  through the resistor  220 , and the bias output BIAS OUT is outputted through the base of the transistor  210 . 
         [0051]      FIG. 3B  is a circuit diagram illustrating a bias circuit according to another embodiment of the present invention. The bias circuit  300  of  FIG. 3B  is similar to that  200  of  FIG. 3A . However, the bias circuit  300  of  FIG. 3B  generates a bias output BIAS OUT through a current mirror. 
         [0052]      FIG. 4A  is a circuit diagram illustrating a matching circuit according to an embodiment of the present invention. An input port  3  of the matching circuit  400  of  FIG. 4A  receives an RF signal from the output terminal  2  of  FIG. 2 . 
         [0053]    Referring to  FIG. 4A , the matching circuit  400  includes the input port  3 , output ports  4   a  and  4   b , a plurality of capacitors  411  to  417 , and a plurality of inductors  421  to  423 . 
         [0054]    In a first path, the capacitor  412  and the inductor  421  constitute a parallel resonant circuit. Values of the capacitor  412  and the inductor  421  may be selectively provided in order to allow the parallel resonant circuit to provide a parallel resonant open circuit on RF signals of a predetermined band. In this case, the RF energy of a predetermined band is not delivered to the output port  4   a.    
         [0055]    In a second path, the inductor  423  and the capacitor  417  form a series resonant circuit for providing a short circuit in a predetermined frequency band. The series resonant circuit provides a high reflection to a frequency of a predetermined band so that an RF energy of a predetermined band is not provided to the output port  4   b.    
         [0056]      FIG. 4B  is a circuit diagram illustrating a matching circuit according to another embodiment of the present invention. The matching circuit  500  of  FIG. 4B  is similar to that  400  of  FIG. 4A . However, the capacitor  415  of  FIG. 4A  is replaced with the inductor  524  and the capacitor  517  in the matching circuit  500  of  FIG. 4B . 
         [0057]    According to an embodiment of the present invention, by adding resistors connecting bases of transistors, respectively, a power amplifier circuit having high stability is provided. 
         [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.