Abstract:
A satellite broadcast receiver including a pre-amplifier to amplify and output a received satellite broadcast signal, a power division part to split the amplified satellite broadcase signal into first and second signals having first and second powers, respectively, using a Wilkinson power divider, a tuner to receive the first signal, and to tune and demodulate a signal of a certain frequency band, and a loopthrough part to output the second signal to the outside.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally concerns a satellite broadcast receiver. More specifically, the present invention concerns a satellite broadcast receiver for receiving a broadcast signal emitted from an artificial satellite.  
         [0003]     2. Description of the Related Art  
         [0004]     Satellite broadcasting is accomplished through a geostationary satellite relaying a satellite broadcast signal, such as a broadcast signal for a television or a radio, transmitted from an earth station to enable an individual recipient or subscribers on a wide area to receive the signal. A satellite broadcast receiver receives the satellite broadcast signal emitted from the satellite.  
         [0005]     In general, the satellite broadcast receiver tunes and receives the recipient&#39;s desired signal of a frequency band among satellite broadcast signals emitted from the satellite, and restores video and audio signals by demodulating the received signal. Furthermore, the satellite broadcast receiver bypasses and outputs the received signal to outside without incurring a loss, which is referred to as a loopthrough function.  
         [0006]      FIG. 1  is a block diagram of a conventional satellite broadcast receiver. Referring to  FIG. 1 , the satellite broadcast receiver includes an antenna  10 , a receiver  20 , a pre-amplifier  30 , an impedance matching network  40 , a signal divider  45 , a tuner  50 , and a loopthrough part  60 .  
         [0007]     The antenna  10  receives the satellite broadcast signal in a frequency ranging from several GHz to tens of GHz from the satellite. The receiver  20  converts the received signal of the antenna  10  to a frequency of 950 MHz˜2150 MHz and outputs the converted signal to the pre-amplifier  30 .  
         [0008]     According to a specification on a power of the loopthrough, a power of the output signal bypassed through the loopthrough part  60  has to be ±3 dB of that of the input signal. To this end, the pre-amplifier  30  is employed, and is connected to an output port of the receiver  20 . The pre-amplifier  30  amplifies and outputs the signal received from the receiver  20 .  
         [0009]     When an output port of one network is connected to an input port of another network, impedance matching is required to reduce reflection due to an impedance difference between the two different connection ports. In general, an impedance matching network is inserted between the two connection ports, and thus compensates the impedance difference of the connection ports. Impedances on the left and on the right based on the input port of the pre-amplifier  30  have to be matched, and impedances on the left and on the right based on the output port of the pre-amplifier  30  have to be matched.  
         [0010]     The impedance matching network  40  is inserted between the output port of the pre-amplifier  30  and the input port of the tuner  50  and the loopthrough part  60 , to obtain the impedance matching at the output port of the pre-amplifier  30 .  
         [0011]     The power of the satellite broadcast signal output from the impedance matching network  40  is divided into the tuner  50  and the loopthrough part  60  by the signal divider  45 . It is not necessary to divide the power into halves. A signal with a power within 3 dB of the power of the input signal of the pre-amplifier  30  is input to the loopthrough part  60 , and the rest is input to the tuner  50 . Commonly, the signal divider  45  is constructed such that one line is split into two lines.  
         [0012]     The conventional satellite broadcast receiver amplifies the received satellite broadcast signal at the pre-amplifier  30  and distributes the amplified signal into the tuner  50  and the loopthrough part  60  at the signal divider  45  through a T-junction. The output port of the pre-amplifier  30  is connected to the impedance matching network  40  for the impedance matching at the output port of the pre-amplifier  30 . However, it is difficult to obtain the impedance matching by inserting the impedance matching network  40 , since the satellite broadcast signal has a broadband characteristic. If the impedance matching is not suitably performed, the signals split into the tuner  50  and the loopthrough part  60  bring about interference, and the signal may be distorted.  
       SUMMARY OF THE INVENTION  
       [0013]     To address the above and/or other problems of the conventional arrangement, an aspect of the present invention provides a satellite broadcast receiver dividing and outputting a power of a satellite broadcast signal into a tuner and a loopthrough part by use of a Wilkinson power divider.  
         [0014]     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
         [0015]     To achieve the above and/or other aspects and features of the present invention, the satellite broadcast receiver comprises a pre-amplifier to amplify and output a received satellite broadcast signal; a power division part to split the amplified satellite broadcast signal into first and second signals having first and second powers, respectively, using a Wilkinson power divider; a tuner to receive the first signal, and to tune and demodulate a signal of a certain frequency band; and a loopthrough part to output the second signal to outside.  
         [0016]     The power division part may comprise a power division controller to determine a power division ratio of the first and second powers.  
         [0017]     The power division controller may comprises a first resistor connected between a first output port of the Wilkinson power divider and the tuner; and a second resistor connected between a second output port of the Wilkinson power divider and the loopthrough part.  
         [0018]     The Wilkinson power divider may be a microstrip type.  
         [0019]     The pre-amplifier may comprise an amplifier to amplify the received satellite broadcast signal according to a predetermined gain using a transistor; an impedance matching part to match an input impedance of the amplifier to a predetermined impedance; and a power supplier to supply a power to the amplifier.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:  
         [0021]      FIG. 1  is a block diagram of a conventional satellite broadcast receiver;  
         [0022]      FIG. 2  is a block diagram of a satellite broadcast receiver dividing a power of a satellite broadcast signal by use of a Wilkinson power divider according to an embodiment of the present invention;  
         [0023]      FIG. 3  is a view of the Wilkinson power divider of  FIG. 2 ; and  
         [0024]      FIG. 4  is a circuit diagram of the satellite broadcast receiver of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the drawings.  
         [0026]      FIG. 2  is a block diagram of a satellite broadcast receiver which divides a power of a satellite broadcast signal by use of a Wilkinson power divider according to an embodiment of the present invention. Referring to  FIG. 2 , the satellite broadcast receiver includes an antenna  110 , a receiver  120 , a pre-amplifier  130 , a Wilkinson power division part  140 , a tuner  150 , and a loopthrough part  160 .  
         [0027]     The antenna  110  receives the satellite broadcast signal in a frequency ranging from several GHz to tens of GHz from a satellite. The receiver  120  down-converts the received signal of the antenna  10  to a frequency of approximately 950 MHz˜2150 MHz and outputs the converted signal to the pre-amplifier  130 . The pre-amplifier  130  amplifies and outputs the satellite broadcast signal received from the receiver  120 .  
         [0028]     A power of the satellite broadcast signal amplified in the pre-amplifier  130  is divided and output to the tuner  150  and the loopthrough part  160  through the Wilkinson power division part  140 .  FIG. 3  depicts the Wilkinson power division part  140  of  FIG. 2 , which is described in detail below.  
         [0029]     A power divider divides a power, that is, splits a single power signal into two or more power signals. The power divider is a kind of a coupler.  
         [0030]     A simple T-junction power divider, which is used for a high frequency signal, divides the power into two paths, in which three ports are not completely matched. This is because there is no solution to compensate or convert any impedance difference between ports since the power divider having the T-junction line alone is a lossless structure. In addition, a lossless-loop may be generated, which may bring about oscillation as the frequency becomes higher.  
         [0031]     To address the oscillation, a resistor is inserted between the two paths. In order to obtain a superior power division in a high frequency signal, an impedance balance between ports has to be maintained by realizing a power divider which produces a loss of signal power. The Wilkinson power divider is designed in consideration of the property of the high frequency signal. The Wilkinson power divider is in a microstrip form on a printed circuit board (PCB), and is used for the realization of the power divider.  
         [0032]     Referring to  FIG. 3 , the Wilkinson power divider divides the power using a T-junction transmission line. A characteristic impedance of an incoming line is Z 0 , and that of a split line is √{square root over (2)}Z 0 . A length of the split line is λ/4, and a register having a resistance of 2Z 0  is inserted between the output ports for the impedance matching. The Wilkinson power divider divides the power of the input signal into halves in  FIG. 3 , but the ratio of the power division is adjustable by connecting resistors having different resistance to the split lines, respectively.  
         [0033]     Referring back to  FIG. 2 , the tuner  150  tunes a satellite broadcast signal of a certain frequency band among the satellite broadcast signals received from the Wilkinson power division part  140 , demodulates the satellite broadcast signal of the tuned frequency band, and therefore, extracts a video signal and an audio signal. The loopthrough part  160  receives the portion of the satellite broadcast signal from the Wilkinson power division part  140  that bypasses the tuner  150 , and outputs this signal portion as it is.  
         [0034]      FIG. 4  is a circuit diagram of the satellite broadcast receiver of  FIG. 2 , and illustrates the pre-amplifier  130 , the Wilkinson power division part  140 , the tuner  150 , and the loopthrough part  160 .  FIG. 4  further illustrates a low noise block down-converter (LNB)-A part  170  and an LNB-B part  180  to determine polarity of the satellite broadcast signal.  
         [0035]     The pre-amplifier  130  includes an F-connector  131 , a capacitor C 59 , an impedance matching part  132 , a power supplier  133 , a bias controller  134 , and a bipolar transistor BFP 420 . The F-connector  131  receives the satellite broadcast signal. The capacitor C 59  blocks a direct current (DC) flowing from the LNB-A part  170  to the pre-amplifier  130 . The impedance matching part  132  includes a capacitor C 60  and a resistor R 39 . The impedance matching part  132  matches the impedances of the output port of the receiver  120  and the input port of the pre-amplifier  130 .  
         [0036]     The power supplier  133  includes a Vcc power, a resistor R 24 , and a capacitor C 37 . The capacitor C 37  is a bypass capacitor for removing noise components from the Vcc power. The bias controller  134  adjusts a voltage applied to a base of the bipolar transistor BFP 420 . The adjusted voltage determines the amplitude of the output signal at a collector of the bipolar transistor BFP 420 . The bipolar transistor BFP 420  is an Rf bipolar transistor which amplifies the input signal, and its gain is 16 dB.  
         [0037]     The Wilkinson power division part  140  includes a Wilkinson power divider  141 , a power division controller  142 , an impedance matching part  143 , and a capacitor C 52 . The capacitor C 52  blocks direct current from flowing to the Wilkinson power divider  141  from the Vcc power. The Wilkinson power divider  141  splits the incoming satellite broadcast signal into separate signals to be respectively sent to the tuner  150  and the loopthrough part  160 . The incoming line of the Wilkinson power divider  141 , which has a characteristic impedance is Z 0 , is split into two lines each having a characteristic impedance of √{square root over (2)}Z 0 . The length of the respective split lines is λ/4. Hence, the characteristic impedances of the A˜B line and the A˜C line are √{square root over (2)}Z 0 , and their length is λ/4, respectively. A resistor R 34  is inserted between the output ports of the Wilkinson power divider  141  for the sake of the impedance matching, and the resistance of the resistor R 34  is 2Z 0 .  
         [0038]     The power division controller  142  includes two resistors R 20  and R 21 . The resistor R 20  is connected between the output port of the Wilkinson power divider  141  and the tuner  150 , and the resistor R 21  is connected between the output port of the Wilkinson power divider  141  and the impedance matching part  143 . The ratio of the resistance values of the resistors R 20  and R 21  determines a power division ratio at which the Wilkinson power divider  141  splits the satellite broadcast signal. Accordingly, it is possible to adjust the ratio of the powers of the satellite broadcast signals to be respectively sent to the tuner  150  and the loopthrough part  160  by adjusting the ratio of the resistance values of the resistors R 20  and R 21 .  
         [0039]     The impedance matching part  143  includes a capacitor C 27  and resistors R 15  and R 17 , and performs the impedance matching at the output port of the Wilkinson power division part  140 . The capacitor C 27  blocks direct current from flowing from an LNB-B  181  to the Wilkinson power division part  140 .  
         [0040]     The LNB-A part  170  includes an LNB-A  171  and a plurality of capacitors C 71  through C 74 . The LNB-A  171  is a circuit which determines the polarity of the satellite broadcast signal.  
         [0041]     The LNB-B part  180  includes the LNB-B  181  and a capacitor C 19 . When the LNB-A part  170  is not in operation, the LNB-B  181  determines the polarity of the satellite broadcast signal input to the loopthrough part  160 .  
         [0042]     In light of the foregoing, the power of the satellite broadcast signal is divided and output to the tuner and the loopthrough part by use of the Wilkinson power divider, and the impedance matching network does not need to be provided at the output ports of the pre-amplifier. Accordingly, it is possible to obtain the impedance matching even though the satellite broadcast signal has the broadband characteristic. The interference of the signals, which arises in the event of the improper impedance matching, is prevented. In addition, the power loss due to the insertion of the impedance matching network is prevented. The power division ratio of the satellite broadcast signal can be easily adjusted by adjusting the ratio of the resistance values of the resistors connected to the output ports of the Wilkinson power divider.  
         [0043]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.