Patent Publication Number: US-2019181526-A1

Title: Dual-band system and diplexer thereof

Description:
FIELD OF THE INVENTION 
     The present invention relates to a microwave system and a component, and more particularly to a dual-band system and a diplexer thereof. 
     BACKGROUND OF THE INVENTION 
     In a wireless networking technology, a dual-band system uses two different standard frequencies to transmit signals. For example, a dual-band router is used in a dual-band WiFi system to support the 2.4G frequency band and the 5G frequency band. The term 2.4G denotes the frequency of 2.4 GHz. The term 5G denotes the frequency of 5 GHz. 
       FIG. 1  schematically illustrates a conventional dual-band system. As shown in  FIG. 1 , the dual-band system comprises a dual-band IC  10 , a first band antenna  12  and a second band antenna  14 . The dual-band IC  10  has a first terminal “a” and a second terminal “b”. The first band antenna  12  is connected with the first terminal “a”. The second band antenna  14  is connected with the second terminal “b”. 
     A first band signal is transmitted through a first band signal path between the first terminal “a” of the dual-band IC  10  and the first band antenna  12 . A second band signal is transmitted through a second band signal path between the second terminal “b” of the dual-band IC  10  and the second band antenna  14 . 
     In a dual-band WiFi system, the first terminal “a” is a 2.4G terminal, and the second terminal “b” is a 5G terminal. That is, the first band antenna  12  is a 2.4G antenna, and the second band antenna  14  is a 5G antenna. 
     Since the first band antenna  12  and the second band antenna  14  of the dual-band system as shown in  FIG. 1  are respective antennas, the mass production cost of the dual-band system is high. Moreover, the first band signal and the second band signal interfere with each other through the antenna radiation. 
       FIG. 2  schematically illustrates another conventional dual-band system. As shown in  FIG. 2 , the dual-band system comprises a dual-band IC  20 , an active switch  22  and a dual-band antenna  24 . The dual-band IC  20  has a first terminal “a”, a second terminal “b” and a control terminal “c”. The active switch  22  has a first terminal t 1 , a second terminal t 2 , a third terminal t 3  and a control terminal ctrl. The first terminal t 1  of the active switch  22  is connected with the first terminal “a” of the dual-band IC  20 . The second terminal t 2  of the active switch  22  is connected with the second terminal “b” of the dual-band IC  20 . The third terminal t 3  of the active switch  22  is connected with the dual-band antenna  24 . The control terminal “c” of the dual-band IC  20  is connected with the control terminal ctrl of the active switch  22 . 
     In a dual-band WiFi system, the first terminal “a” is a 2.4G terminal, and the second terminal “b” is a 5G terminal. That is, the dual-band antenna  24  is a 2.4G/5G antenna. 
     In the dual-band system of  FIG. 2 , one of a first band signal path and a second band signal path of the active switch  22  is selected according to a control signal from the control terminal “c” of the dual-band IC  20 . 
     Obviously, the dual-band IC  20  needs an additional control pin to provide the control signal to operate the active switch  22 . In addition, the first band signal path and the second band signal path cannot be used simultaneously. Since the first band signal path and the second band signal path are employed according to time allocation, the utilization efficiency is impaired. Moreover, the active switch  22  requires extra power consumption, and the active switch  22  is not cost-effective. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a diplexer. The diplexer has a first terminal, a second terminal and a third terminal. The diplexer includes a first filter and a second filter. The first filter is connected between the first terminal and the third terminal. A first band signal is operated in a first frequency band and transmitted through a first path between the first terminal and the third terminal. The second filter is connected between the second terminal and the third terminal. A second band signal is operated in a second frequency band and transmitted through a second path between the second terminal and the third terminal. The first filter is a first band-rejection filter for stopping the second band signal. 
     Another embodiment of the present invention provides a dual-band system. The dual-band system includes a dual-band IC, a diplexer, a first matching circuit, a second matching circuit and a dual-band antenna. The dual-band IC has a first terminal and a second terminal. The diplexer has a third terminal, a fourth terminal and a fifth terminal. The diplexer includes a first filter and a second filter. The first filter is connected between the third terminal and the fifth terminal. A first band signal is operated in a first frequency band and transmitted through a first path between the third terminal and the fifth terminal. The second filter is connected between the fourth terminal and the fifth terminal. A second band signal is operated in a second frequency band and transmitted through a second path between the fourth terminal and the fifth terminal. The first matching circuit is connected between the first terminal and the third terminal. The second matching circuit is connected between the second terminal and the fourth terminal. The dual-band antenna is connected with the fifth terminal. The first filter is a first band-rejection filter for stopping the second band signal. 
     Numerous objects, features and advantages of the present invention will be readily apparent upon a reading of the following detailed description of embodiments of the present invention when taken in conjunction with the accompanying drawings. However, the drawings employed herein are for the purpose of descriptions and should not be regarded as limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  (prior art) schematically illustrates a conventional dual-band system; 
         FIG. 2  (prior art) schematically illustrates another conventional dual-band system; 
         FIG. 3  schematically illustrates the architecture of a dual-band system according to a first embodiment of the present invention; 
         FIG. 4A  schematically illustrates a first exemplary diplexer of the dual-band system according to the first embodiment of the present invention; 
         FIG. 4B  schematically illustrates a second exemplary diplexer of the dual-band system according to the first embodiment of the present invention; 
         FIG. 5  is a schematic circuit diagram illustrating the second exemplary diplexer of the dual-band system according to the first embodiment of the present invention; 
         FIG. 6  schematically illustrates the architecture of a dual-band system according to a second embodiment of the present invention; and 
         FIG. 7  is a schematic circuit diagram illustrating the diplexer, the first matching circuit and the second matching circuit of the dual-band system according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 3  schematically illustrates the architecture of a dual-band system according to a first embodiment of the present invention. In this embodiment, the dual-band system comprises a dual-band IC  30 , a diplexer  32  and a dual-band antenna  34 . The dual-band IC  30  has a first terminal “a” and a second terminal “b”. The diplexer  32  has a first terminal t 1 , a second terminal t 2  and a third terminal t 3 . The first terminal t 1  of the diplexer  32  is connected with the first terminal “a” of the dual-band IC  30 . The second terminal t 2  of the diplexer  32  is connected with the second terminal “b” of the dual-band IC  30 . The third terminal t 3  of the diplexer  32  is connected with the dual-band antenna  34 . 
     The diplexer  32  comprises a first filter  36  and a second filter  38 . The first filter  36  is connected between the first terminal t 1  and the third terminal t 3  of the diplexer  32 . The second filter  38  is connected between the second terminal t 2  and the third terminal t 3  of the diplexer  32 . A first band signal is transmitted through a first band signal path between the first terminal “a” of the dual-band IC  30  and the dual-band antenna  34 . A second band signal is transmitted through a second band signal path between the second terminal “b” of the dual-band IC  30  and the dual-band antenna  34 . 
     Various examples of the combination of the first filter and the second filter in the diplexer  32  will be described as follows. 
       FIG. 4A  schematically illustrates a first exemplary diplexer of the dual-band system according to the first embodiment of the present invention. In this embodiment, the first filter of the diplexer  32  is a low pass filter  46 , and the second filter of the diplexer  32  is a high pass filter  48 . The low pass filter  46  is connected between the first terminal t 1  and the third terminal t 3  of the diplexer  32 . The high pass filter  48  is connected between the second terminal t 2  and the third terminal t 3  of the diplexer  32 . 
     In a dual-band WiFi system, the first terminal “a” is a 2.4G terminal, and the second terminal “b” is a 5G terminal. That is, the dual-band antenna  34  is a 2.4G/5G antenna. The cut-off frequency of the low pass filter  46  is in the range between 2.4 GHz and 5 GHz. The cut-off frequency of the high pass filter  48  is in the range between 2.4 GHz and 5 GHz. 
     Consequently, the 2.4G band signal can pass the low pass filter  46 , but the 5G band signal cannot pass the low pass filter  46 . Moreover, the 5G band signal can pass the high pass filter  48 , but the 2.4G band signal cannot pass the high pass filter  48 . In other words, the 2.4G band signal is transmitted through the 2.4G band signal path between the first terminal “a” of the dual-band IC  30  and the dual-band antenna  34 , and the 5G band signal is transmitted through the 5G band signal path between the second terminal “b” of the dual-band IC  30  and the dual-band antenna  34 . 
       FIG. 4B  schematically illustrates a second exemplary diplexer of the dual-band system according to the first embodiment of the present invention. In this embodiment, the first filter of the diplexer  32  is a first band-rejection filter  56 , and the second filter of the diplexer  32  is a second band-rejection filter  58 . The first band-rejection filter  56  is connected between the first terminal t 1  and the third terminal t 3  of the diplexer  32 . The second band-rejection filter  58  is connected between the second terminal t 2  and the third terminal t 3  of the diplexer  32 . The band-stop frequency of the first band-rejection filter  56  is in the range of the second band frequency. Consequently, the second band signal is stopped by the first band-rejection filter  56 . The band-stop frequency of the second band-rejection filter  58  in the range of the first band frequency. Consequently, the first band signal is stopped by the second band-rejection filter  58 . 
     In a dual-band WiFi system, the first terminal “a” is a 2.4G terminal, and the second terminal “b” is a 5G terminal. That is, the dual-band antenna  34  is a 2.4G/5G antenna. That is, the 2.4G band signal is stopped by the second band-rejection filter  58 , and the 5G band signal is stopped by the first band-rejection filter  56 . In other words, the 2.4G band signal is transmitted through the 2.4G band signal path between the first terminal “a” of the dual-band IC  30  and the dual-band antenna  34 , and the 5G band signal is transmitted through the 5G band signal path between the second terminal “b” of the dual-band IC  30  and the dual-band antenna  34 . 
     The above two exemplary diplexers are presented herein for purpose of illustration and description only. That is, other types of filters may be combined together as the diplexer of the present invention. 
     In a third exemplary diplexer  32 , the first filter is a band-rejection filter, and the second filter is a high pass filter. The 5G band signal is stopped by the first filter, but the 2.4G band signal is transmitted through the first filter. The 5G band signal is transmitted through the second filter, but the 2.4G band signal is not transmitted through the second filter. 
     In a fourth exemplary diplexer  32 , the first filter is a low pass filter, and the second filter is a band-rejection filter. The 2.4G band signal is transmitted through the first filter, but the 5G band signal is not transmitted through the first filter. The 2.4G band signal is stopped by the second filter, but the 5G band signal is transmitted through the second filter. 
       FIG. 5  is a schematic circuit diagram illustrating the second exemplary diplexer of the dual-band system according to the first embodiment of the present invention. The first band-rejection filter  56  of the diplexer  32  comprises a first inductor La and a first capacitor Ca, which are connected with each other in parallel. The second band-rejection filter  58  of the diplexer  32  comprises a second inductor Lb and a second capacitor Cb, which are connected with each other in parallel. 
     The band-stop frequency of the first band-rejection filter  56  is in the range between 4 GHz and 6 GHz. Consequently, the 5G band signal is stopped by the first band-rejection filter  56 , but the 2.4G band signal is not stopped by the first band-rejection filter  56 . The inductance of the first inductor La and the capacitance of the first capacitor Ca are suitably selected to form the first band-rejection filter  56 . For example, the inductance of the first inductor La is in the range between 1 nH and 10 nH, and the capacitance of the first capacitor Ca is in the range between 0.1 pF and 2 pF. 
     Moreover, the first inductor La contains a parasitic capacitor. Consequently, in another embodiment, the first band-rejection filter  56  comprises the first inductor La only. For example, the inductance of the first inductor La is 5.6 nH, and the parasitic capacitance of the first inductor La is 0.2 pF. Consequently, the band-stop frequency of the first band-rejection filter  56  is about 5 GHz. In other words, the first band-rejection filter  56  with the first inductor La is feasible. 
     The band-stop frequency of the second band-rejection filter  58  is in the range between 2.2 GHz and 2.6 GHz. Consequently, the 2.4G band signal is stopped by the second band-rejection filter  58 , but the 5G band signal is not stopped by the second band-rejection filter  58 . The inductance of the second inductor Lb and the capacitance of the second capacitor Cb are suitably selected to form the second band-rejection filter  58 . For example, the inductance of the second inductor Lb is in the range between 1 nH and 10 nH, and the capacitance of the second capacitor Cb is in the range between 0.1 pF and 5 pF. 
     In other words, the 2.4G band signal is transmitted through the 2.4G band signal path between the first terminal “a” of the dual-band IC  30  and the dual-band antenna  34 , and the 5G band signal is transmitted through the 5G band signal path between the second terminal “b” of the dual-band IC  30  and the dual-band antenna  34 . 
       FIG. 6  schematically illustrates the architecture of a dual-band system according to a second embodiment of the present invention. In this embodiment, the dual-band system comprises a dual-band IC  30 , a diplexer  32 , a dual-band antenna  34 , a first matching circuit  62  and a second matching circuit  64 . The dual-band IC  30  has a first terminal “a” and a second terminal “b”. The diplexer  32  has a first terminal t 1 , a second terminal t 2  and a third terminal t 3 . 
     In comparison with the first embodiment, the dual-band system of this embodiment further comprises the first matching circuit  62  and the second matching circuit  64 . The first matching circuit  62  is connected between the first terminal “a” of the dual-band IC  30  and the first terminal t 1  of the diplexer  32 . The second matching circuit  64  is connected between the second terminal “b” of the dual-band IC  30  and the second terminal t 2  of the diplexer  32 . In case that both of the first matching circuit  62  and the second matching circuit  64  are conducting wires, the dual-band system of this embodiment is identical to the dual-band system of the first embodiment. The examples of the diplexer  32  used in the dual-band system of the first embodiment are also applied to the dual-band system of this embodiment. 
       FIG. 7  is a schematic circuit diagram illustrating the diplexer, the first matching circuit and the second matching circuit of the dual-band system according to the second embodiment of the present invention. The circuitry of the diplexer is similar to that of  FIG. 5 , and is not redundantly described herein. 
     The first matching circuit  62  comprises an inductor Lc and a capacitor Cc. The inductor Lc is connected between a ground terminal and the first terminal t 1  of the diplexer  32 . The capacitor Cc is connected between the first terminal “a” of the dual-band IC  30  and the first terminal t 1  of the diplexer  32 . For example, the inductance of the inductor Lc is about 9.1 nF, and the capacitance of the capacitor Cc is about 1 pF. 
     The second matching circuit  64  comprises an inductor Ld and a capacitor Cd. The inductor Ld is connected between the second terminal “b” of the dual-band IC  30  and the second terminal t 2  of the diplexer  32 . The capacitor Cd is connected between the second terminal “b” of the dual-band IC  30  and the ground terminal. For example, the inductance of the inductor Ld is about 1 nF, and the capacitance of the capacitor Cd is about 0.2 pF. 
     The circuitry structures of the first matching circuit  62  and the second matching circuit  64  are not restricted. It is noted that numerous modifications and alterations of the first matching circuit and the second matching circuit may be made while retaining the teachings of the invention. 
     From the above descriptions, the present invention provides a dual-band system and a diplexer of the dual-band system. The diplexer of the dual-band system comprises at least one band-rejection filter. Since the band-rejection filter is composed of simple electronic components, the band-rejection filter is cost-effective. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.