Patent Document

BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a signal processing device.  
         [0003]     2. Description of the Related Art  
         [0004]     A related art dual band terminal includes a diplexer capable of receiving two respectively different frequencies (1900 MHz band (PCS) and 800 MHz (DCN))) through one antenna. However, the latest dual band terminal further includes a global position system (GPS) function, and thus uses a triple band terminal. The triple band terminal processes three frequency bands (PCS: 1850 to 1990 MHz, GPS: 1574.42 to 1576.42 MHz, and DCN: 824 to 894 MHz).  
         [0005]     That is, current mobile communication terminals basically are equipped with a GPS function. For example, the FCC&#39;s E911 rules require a location tracking function (radio location determination) through a GPS satellite to provide precise location information of the mobile communication terminal.  
         [0006]      FIG. 1  is a block diagram of components in a related art triple band mobile communication terminal  10 .  
         [0007]     Referring to  FIG. 1 , the related art triple band mobile communication terminal  10  includes an active switch  11 , a DCN signal processing unit  12 , a PCS signal processing unit  13 , a GPS signal processing unit  14 , and controller  15 .  
         [0008]     The active switch  11  performing a triplexer function receives respective signals of a DCN band, a PCS band, and a GPS bans through an antenna, and transmits signals of the DCN band and the PCS band.  
         [0009]     The DCN signal processing unit  12  processes the signal of the DCN band separated from the active switch  11 .  
         [0010]     Moreover, the PCS signal processing unit  13  processes the signal of the DCN as a call signal, and the GPS signal processing unit  14  demodulates the signal of the GPS band to generate three-dimensional ground location determination information.  
         [0011]     The controller  15  outputs the transmitted signal from the DCN signal processing unit  12  or the PCS signal processing unit  13  as a voice, transmits the received signal to the DCN processing unit  12  or the PCS signal processing unit  13 , or processes the inputted ground location determination information from the GPS signal processing unit  14 .  
         [0012]     At this point, the antenna includes a dual band antenna and a GPS antenna. The dual band antenna transmits and receives signals in synchronization with the DCN/PCS signals. It is possible to realize the triple band using only one antenna through a triplexer that is not a single pole three throw (SP3T).  
         [0013]     A related art triplexer can be realized as one chip using more than  10  lumped elements. However, problems can occur as follows.  
         [0014]     First, as the number of receiving modes increase, a frequency interval between the receiving modes becomes closer. Thus, it is difficult to manufacture a filter for simultaneously filtering various signals. Especially, when a frequency interval in the GPS mode and the PCS mode becomes 280 MHz, it is very hard to manufacture a triplexer to separate signals, and also many lumped elements are necessary.  
         [0015]     Second, since many lumped elements are necessary, it is difficult to minimize the product.  
         [0016]     Third, when the triplexer is realized using the many lumped elements, the insertion loss occurs due to a high frequency, and also the ripples in a pass band increase according to the increase of the frequency band.  
         [0017]     Accordingly, it is necessary to improve a structure of the related art triplexer to realize a high quality call service and miniaturization.  
       SUMMARY OF THE INVENTION  
       [0018]     Accordingly, the present invention is directed to a signal processing device that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0019]     An object of the present invention is to provide a signal processing device minimizing the number of lumped elements.  
         [0020]     Another object of the present invention is to provide a signal processing device maintaining stably each frequency band signal without a cross-talk effect by preventing a leakage current between adjacent circuits.  
         [0021]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0022]     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a signal processing device including: a diplexer unit separating a first signal from signals that are received from an antenna to transmit the first signal to a first signal processing unit; a band pass filter unit transmitting a second signal in received signals from the diplexer unit to a second signal processing unit; and an LC tank unit cutting-off the transmitted second signal, and transmitting a third signal in the received signals from the diplexer unit to a third signal processing unit.  
         [0023]     In another aspect of the present invention, there is provided a signal processing device including: a diplexer unit separating a first signal, a second signal, and a third signal in received signals from an antenna; a first signal processing unit processing the first signal separated from the diplexer unit; a band pass filter unit passing the second signal and cutting-off the third signal in the second and third signals separated from the diplexer unit; a second signal processing unit connected to the band pass filter unit to process the second signal; an LC tank unit passing the third signal and cutting-off the second signal in the second and third signals separated from the diplexer unit; and a third signal processing unit connected to the LC tank unit to process the third signal.  
         [0024]     In a further another aspect of the present invention, there is provided a signal processing device including: a diplexer unit including two types of band stop filters connected in parallel, one type passing a first signal and cutting-off a second signal and a third signal in received signals from an antenna, the other type passing a second signal and a third signal and cutting-off a first signal in the received signals from the antenna; a first signal processing unit processing the first signal separated from the diplexer unit; a bans pass filter passing the second signal and cutting-off the third signal in the second and third signals separated from the diplexer unit; a second signal processing unit connected to the band pass filter unit to process the second signal; an LC tank unit passing the third signal and cutting-off the second signal in the second and third signals separated from the diplexer unit; and a third signal processing unit connected to the LC tank unit to process the third signal.  
         [0025]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0027]      FIG. 1  is a block diagram of components in a related art triple band mobile communication terminal;  
         [0028]      FIG. 2  is a circuit diagram of components in a signal processing device according to an embodiment of the present invention;  
         [0029]      FIG. 3  is a smith chart of an input impedance characteristic in a band pass filter according to an embodiment of the present invention;  
         [0030]      FIG. 4  is a view of a circuit configuration in an LC tank according to an embodiment of the present invention;  
         [0031]      FIG. 5  is a view of another diplexer in a signal processing device according to an embodiment of the present invention; and  
         [0032]      FIG. 6  is view of signal transfer characteristics in a signal processing device according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.  
         [0034]      FIG. 2  is a circuit diagram of components in a signal processing device according to an embodiment of the present invention.  
         [0035]     Referring to  FIG. 2 , a triplexer  100  includes a diplexer  120 , a PSN (phase shift network), a band pass filter  150 , and an LC tank  170 .  
         [0036]     An input terminal of the diplexer  120  is connected to an antenna  110 . Additonally, output terminals of the diplexer  120 , the band pass filter  150 , and the LC tank  170  are, respectively, connected to a DCN signal processing unit  130 , a GPS signal processing unit  160 , and a PCS signal processing unit  180 .  
         [0037]     The triplexer  100  transmits and receives frequency signals (i.e., a DCN signal, a GPS signal, and a PCS signal) in a triple band through an antenna.  
         [0038]     The diplexer  120  includes a high pass filter (HPF) and a low pass filter (LPF) with integrated passive devices, and applies a frequency division multiplex method to divide entire signals (mixed various frequency signals) into two frequency bands in which a frequency spectrum is not overlapped.  
         [0039]     The HPF passes a GPS signal and a PCS signal of a high band in entire signals that are inputted from the antenna  110 , and the LPF passes a DCN signal of a low band.  
         [0040]     When the signals are divided, the diplexer  120  transmits the divided DCN signal into the DCN signal processing unit  130 . Then, the DCN signal processing unit  130  processes the DCN signal and outputs a voice.  
         [0041]     The PSN  140  and the LC tank  120  are connected in parallel to the diplexer  120 . Additionally, the PSN  140  is connected in series to the band pass filter  150  and the GPS signal processing unit  160 .  
         [0042]     When the GPS signal and the PCS signal separated from the DCN signal flow into the PSN  140  and the LC tack  170 , current becomes reduced, and also signal characteristics are distorted. Thus, the transmitting and receiving quality can be deteriorated.  
         [0043]     That is, since the signals passing through the diplexer  100  to be separated from the DCN signal include the GPS signal and the PCS signal, a corresponding signal needs to be filtered to input, respectively, the GPS signal and the PCS signal into the GPS signal processing unit  160  and the PCS signal processing unit  180  without leakage.  
         [0044]     For this, the PSN  140  allows impedance of the band pass filter  150  to operate as an open circuit in a PCS band.  
         [0045]      FIG. 5  is a view of another diplexer in a signal processing device according to an embodiment of the present invention.  
         [0046]     A diplexer  220  includes a DCN band stop filter having an LC circuit to cut-off a DCN signal, and a PCS&amp;GPS band stop filter having an LC circuit to cut-off the PCS and GPS signals. The DCN band stop filter and the PCS&amp;GPS band stop filter are connected in parallel.  
         [0047]     The diplexer  220  of  FIG. 5  includes only four lumped elements, which are less than the number of lumped elements in diplexer  120  of  FIG. 2  having the HPF and the LPF.  
         [0048]      FIG. 3  is a smith chart of an input impedance characteristic in the band pass filter  150  according to an embodiment of the present invention.  
         [0049]     Referring to  FIG. 3 , when load impedance coordinates of a signal are formed on point A in the smith chart, a circuit operates as an open circuit in an aspect of a signal. When load impedance coordinates of a signal are formed on point B in the smith chart, a circuit operates as a short circuit in an aspect of a signal.  
         [0050]     In the PCS band, input impedance coordinates of the band pass filter  150  are formed on point C. Moreover, the load impedance coordinates C of the PCS signal is moved to an opening point A of the band pass filter  150  through the PSN  140 .  
         [0051]     Accordingly, since the band pass filter  150  operates as an open circuit in an aspect of a PCS signal, the PCS signal does not flow into the band pass filter  150 , but flows into the LC tank  170  without a signal loss.  
         [0052]     On the other hand, the GPS signal passing through the PSN  140  flows into the GPS signal processing unit  160  through the band pass filter  150 . Then, the GPS signal processing unit  160  decodes the GPS signal to generate a position information.  
         [0053]     The band pass filter  150  includes a GPS saw filter.  
         [0054]     As described above, since the PSN  140  and the LC tank  170  are connected in parallel to the diplexer  120 , the GPS signal and the PCS signal separated from DCN signal in the diplexer  120  flow into the PSN  140 , the band pass filter  150 , and the LC tank  170 .  
         [0055]     Thus, an impedance matching is performed in the PSN  140  to move impedance coordinates of the PCS signal into an opening point. Accordingly, the LC tank  170  operates as an open circuit in the GPS band to prevent the GPS signal from being leaked to the PCS signal processing unit  180 .  
         [0056]      FIG. 4  is a view of a circuit configuration in the LC tank  170  according to an embodiment of the present invention.  
         [0057]     Referring to  FIG. 4 , The LC tank  170  includes an inductor  174  and a capacitor  172 , which are connected in parallel. The LC tank  170  cuts-off the GPS signal in the GPS signal and the PCS signal flowing from the diplexer  120 .  
         [0058]     Accordingly, the LC tank  170  operates as an open circuit in an aspect of the GPS signal, and most of the GPS signal flow into the band pass filter  150  without a current loss.  
         [0059]     The PCS signal passing through the LC tank  170  is inputted into the PCS signal processing unit  180 , and then the PCS signal processing unit  180  analyzes the signal to output a voice, or processes the signal as data.  
         [0060]      FIG. 6  is view of signal transfer characteristics in a signal processing device according to an embodiment of the present invention.  
         [0061]     A line of a reference numeral  20  represents transmitting characteristics of a signal transmitted from the antenna  110  into the DCN signal processing unit  130 . A line of a reference numeral  21  represents signal transmitting characteristics of a signal transmitted from the antenna  110  into the GPS signal processing unit  160 .  
         [0062]     A line of a reference numeral  22  represents transmitting characteristics of a signal transmitted from the antenna  110  into the PCS signal processing unit  180 . A line of a reference numeral  23  represents transmitting characteristics of a signal transmitted from the antenna  110  into the antenna  110 .  
         [0063]     According to the present invention, an insertion loss of an 849.1 MHz band signal that is transmitted from the antenna  110  into the DCN signal processing unit  130  is −0.257 dB. An insertion loss of a 1.576 GHz band signal that is transmitted from the antenna  110  into the GPS signal processing unit  160  is −1.073 dB. An insertion loss of a 1.85a GHz band signal that is transmitted from the antenna  110  into the PCS signal processing unit  180  is −1.423 dB.  
         [0064]     According to the signal processing unit of the present invention, since a triplexer can be manufactured using the minimum number of lumped elements, miniaturization can be achieved. Additionally, since a leakage current between adjacent circuits is effectively cut off, a transmitting and receiving quality can be improved.  
         [0065]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Category: 5