Patent Publication Number: US-2016233915-A1

Title: Communication device and electronic device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/114,248, filed on Feb. 10, 2015, and further claims the benefit of U.S. Provisional Application No. 62/153,613, filed on Apr. 28, 2015, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The disclosure generally relates to a communication device, and more particularly, to a communication device which can support communication in multiple frequency components/sub-ranges or the field of carrier aggregation. 
     2. Description of the Related Art 
     To meet LTE-A (Long Term Evolution-Advance) requirements, support of wider transmission bandwidths is required than the 20 MHz bandwidth specified in 3GPP (3rd Generation Partnership Project) Release 8/9. The preferred solution to this is carrier aggregation, which is one of the most distinctive features of 4G LTE-A. Carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth. 
     However, the technology of carrier aggregation requires multiple frequency bands or sub-ranges and wide frequency bandwidth. It has become a critical challenge for engineers to design such an antenna system to meet the requirements of carrier aggregation. 
     BRIEF SUMMARY OF THE INVENTION 
     In one exemplary embodiment, the disclosure is directed to a communication device including an antenna, a frequency dividing circuit, and at least one variable impedance circuit. The frequency dividing circuit has a common port coupled to the antenna and at least one output port. The frequency dividing circuit is configured to divide a frequency range received from the common port into a plurality of frequency sub-ranges and output at least one of the frequency sub-ranges respectively at the at least one output port. Each variable impedance circuit is coupled between a corresponding one of the at least one output port of the frequency dividing circuit and a respective first reference voltage. Each variable impedance circuit provides a respective variable impedance value switched between different respective impedance values. 
     In some embodiments, the antenna switches between the different respective impedance values in at least one of the frequency sub-ranges independently from the other one or more frequency sub-ranges. 
     In some embodiments, the first reference voltage is a ground voltage. 
     In some embodiments, the frequency dividing circuit is a passive element. 
     In some embodiments, the frequency dividing circuit is an active element. 
     In some embodiments, a range of at least one of the at least one of the frequency sub-ranges respectively output at the at least one output port is dynamically changed. 
     In some embodiments, each output port of the frequency dividing circuit is coupled to a respective one of the at least one variable impedance circuit. 
     In some embodiments, at least one output port of the frequency dividing circuit is not coupled to any of the at least one variable impedance circuit. 
     In some embodiments, the at least one output port of the frequency dividing circuit not coupled to any of the at least one variable impedance circuit is float, short to a second reference voltage different or the same as the first reference voltage, or coupled to a loading element. 
     In some embodiments, the frequency dividing circuit includes a low-pass filter, a high-pass filter, a band-pass filter, a diplexer, duplexer, tri-plexer, quad-plexer, or a combination thereof. 
     In some embodiments, at least one of the at least one variable impedance circuit includes: a first terminal, a second terminal, a plurality of loading elements, and a switch element. The first terminal is coupled to the first reference voltage. The second terminal coupled to one of the at least one output port of the frequency dividing circuit. The loading elements are coupled to one of the first terminal and the second terminal, and have different impedances. The switch element is coupled to the other one of the first terminal and the second terminal and switching between the loading elements. 
     In some embodiments, the switch element includes a first terminal and a second terminal. The first terminal is coupled to the output port of the frequency dividing circuit. The second terminal is switchably coupled to one of the loading elements. 
     In some embodiments, at least one of the loading elements includes one or more inductors, one or more variable capacitors, one or more fixed capacitors, or a combination thereof. 
     In some embodiments, at least one of the at least one variable impedance circuit includes a tuner. The tuner is coupled to the first reference voltage and generating different impedance values. 
     In some embodiments, the communication device further includes a processor. The processor receives communication information directly or indirectly from the antenna, and generates at least one control signal according to the communication information. An impedance value of each of the at least one variable impedance circuit is determined according to one of the at least one control signal. 
     In some embodiments, the communication device further includes a coupler. The coupler is coupled between the antenna and the processor, and provides the communication information from the antenna to the processor. 
     In some embodiments, the antenna includes a feeding point, one or more radiation elements, and a tuning point. The feeding point is coupled to a signal source. One of the one or more radiation elements is coupled to the feeding point. The tuning point is coupled through the frequency dividing circuit and the at least one variable impedance circuit to the first reference voltage. 
     In some embodiments, the antenna further includes a ground/reference plane. The ground/reference plane provides the first reference voltage. 
     In some embodiments, the antenna further includes one or more reference points. Each of the one or more reference points is coupled to a second reference voltage which is the same or different from the first reference voltage and a corresponding one of the one or more radiation elements. 
     In another exemplary embodiment, the disclosure is also directed to An electronic device in a communication device, comprising: an antenna terminal, configured to be coupled to an antenna; a frequency dividing circuit, having a common port coupled to the antenna terminal and at least one output port, and configured to divide a frequency range received from the common port into a plurality of frequency sub-ranges and output at least one of the frequency sub-ranges respectively at the at least one output port; and at least one variable impedance circuit, each coupled between a corresponding one of the at least one output port of the frequency dividing circuit and a respective first reference voltage, and providing a respective variable impedance value switched between different respective impedance values. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a diagram of a communication device according to an embodiment of the invention; 
         FIG. 2A  is a diagram of a communication device according to an embodiment of the invention; 
         FIG. 2B  is a diagram of a communication device according to an embodiment of the invention; 
         FIG. 3A  is a diagram of a communication device according to an embodiment of the invention; 
         FIG. 3B  is a diagram of a communication device according to an embodiment of the invention; 
         FIG. 3C  is a diagram of a diplexer according to an embodiment of the invention; 
         FIG. 4A  is a diagram of a variable impedance circuit according to an embodiment of the invention; 
         FIG. 4B  is a diagram of a variable impedance circuit according to an embodiment of the invention; 
         FIG. 4C  is a diagram of a variable impedance circuit according to an embodiment of the invention; 
         FIG. 4D  is a diagram of a variable impedance circuit according to an embodiment of the invention; 
         FIGS. 5A to 5I  are diagrams of communication devices according to some embodiments of the invention; 
         FIG. 5J  is a diagram of a variable impedance circuit according to an embodiment of the invention; 
         FIG. 6  is a diagram of a communication device according to an embodiment of the invention; 
         FIG. 7  is a diagram of a communication device according to an embodiment of the invention; and 
         FIG. 8  is a diagram of return loss of an antenna of a communication device according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to illustrate the purposes, features and advantages of the invention, the embodiments and figures of the invention will be described in detail as follows. 
       FIG. 1  is a diagram of a communication device  100  according to an embodiment of the invention. For example, the communication device  100  may be a smartphone, a tablet computer, or a notebook computer. The communication device  100  can support the technology of carrier aggregation in the field of LTE-A (Long Term Evolution-Advance). As shown in  FIG. 1 , the communication device  100  includes an antenna  110 , a frequency dividing circuit  120 , and at least one variable impedance circuit  130 . The frequency dividing circuit  120  has a common port  115  coupled to the antenna  110 , and at least one output port  125 , each coupled to one of the at least one variable impedance circuit  130 . More specifically, in the implementation shown in  FIG. 1 , one output port  125  is coupled to the variable impedance circuit  130 . In other implementations where the frequency dividing circuit  120  has multiple output ports  125 , one or more of the output ports  125  may be coupled to one or more variable impedance circuits  130 , respectively. The frequency dividing circuit  120  is configured to divide a frequency range received from the common port  115  into multiple frequency sub-ranges, and is configured to output at least one of the respective frequency sub-ranges respectively at the at least one output port  125 . More specifically, in the implementation shown in  FIG. 1 , one of the frequency sub-ranges is output at the output port  125 . In other implementations where the frequency dividing circuit  120  has multiple output ports  125 , one or more of the frequency sub-ranges may be output at one or more of the output ports, respectively. Each of the at least one variable impedance circuit  130  can provide a respective variable impedance value switched between different respective impedance values. 
     In one embodiment, the range of the frequency sub-ranges respectively output at the at least one output port  125  are fixed. In other embodiments, the range of at least one of the frequency sub-ranges respectively output at the output port  125  is dynamically changed. In some embodiments, the frequency dividing circuit  120  is a passive element. In alternative embodiments, the frequency dividing circuit  120  is an active element. For example, the frequency dividing circuit  120  may include a low-pass filter, a high-pass filter, a band-pass filter, a diplexer, duplexer, tri-plexer, quad-plexer, or a combination thereof. 
     Each of the variable impedance circuits  130  can be coupled between a corresponding output port  125  of the frequency dividing circuit  120  and a respective reference voltage, such as VREF 1 . It is noted that in implementation, the variable impedance circuits  130  may be coupled to the same reference voltage VREF 1  or respective reference voltages VRE 1 s have the same or different voltage levels. In some embodiments, each output port  125  of the frequency dividing circuit  120  is coupled to a respective variable impedance circuit  130 . In some embodiments, at least one output port  125  of the frequency dividing circuit  120  is not coupled to any of the variable impedance circuits  130 . In some embodiments where at least one output port  125  of the frequency dividing circuit  120  is not coupled to any of the variable impedance circuits  130 , the output port  125  of the frequency dividing circuit  120  that is not coupled to any of the variable impedance circuits  130  is float, short to a second reference voltage VREF 2  different or the same as the first reference voltage VREF 1 , or coupled to a loading element. 
     Generally speaking, the antenna  110  operates in multiple frequency bands by using the frequency dividing circuit  120  and the variable impedance circuit  130 . With the cooperation of the frequency dividing circuit  120  and the at least one variable impedance circuit  130 , the antenna  110  can switch between the different respective impedance values in at least one of the frequency sub-ranges independently from the other frequency sub-ranges. In addition, the frequency dividing circuit  120  can be configured to suppress harmonic interference in the antenna  110 . Please refer to the following embodiments for detailed descriptions. 
       FIG. 2A  is a diagram of a communication device  200 A according to an embodiment of the invention. In the embodiment of  FIG. 2A , the frequency dividing circuit of the communication device  200 A is a low-pass filter  220 A, and the reference voltage VREF 1  is a ground voltage VSS but is not limited thereto. The low-pass filter  220 A can pass low-frequency signals and block high-frequency signals. With such a design, the high frequency sub-range and the low frequency sub-range are separated into different signal paths without tending to interfere with each other and the low frequency sub-range is output from the output port of the frequency dividing circuit. Accordingly, the antenna  110  can switch between the different respective impedance values of the variable impedance circuit  130  in the low frequency sub-ranges independently from the high frequency sub-range. 
       FIG. 2B  is a diagram of a communication device  200 B according to an embodiment of the invention. In the embodiment of  FIG. 2B , the frequency dividing circuit of the communication device  200 B is a high-pass filter  220 B, and the reference voltage VREF 1  is a ground voltage VSS. The high-pass filter  220 B can pass high-frequency signals and block low-frequency signals. With such a design, the high frequency sub-range and the low frequency sub-range are separated into different signal paths without tending to interfere with each other and the high frequency sub-range is output from the output port of the frequency dividing circuit. Accordingly, the antenna  110  can switch between the different respective impedance values of the variable impedance circuit  130  in the high frequency sub-ranges independently from the low frequency sub-range. 
       FIG. 3A  is a diagram of a communication device  300 A according to an embodiment of the invention. In the embodiment of  FIG. 3A , the frequency dividing circuit of the communication device  300 A is a diplexer  320 A, and the number of variable impedance circuits  130  of the communication device  300 A is one. The diplexer  320 A has a first terminal (serving as the common port of the frequency dividing circuit) coupled to the antenna  110 , a second terminal (serving as one output port of the frequency dividing circuit) coupled to the variable impedance circuit  130 , and a third terminal (serving as another output port of the frequency dividing circuit) kept floated. The variable impedance circuit  130  is coupled between the second terminal of the diplexer  320 A and a reference voltage VREF 1  (e.g., a ground voltage VSS). The diplexer  320 A performs the function of frequency division. For example, the inner structure of the diplexer  320 A may be displayed in  FIG. 3C .  FIG. 3C  is a diagram of the diplexer  320 A according to an embodiment of the invention. In the embodiment of  FIG. 3C , the diplexer  320 A includes a low-pass filter  220 A and a high-pass filter  220 B. The low-pass filter  220 A is coupled between the antenna  110  and the variable impedance circuit  130  (i.e., coupled between the first terminal and the second terminal of the diplexer  320 A). The high-pass filter  220 B is coupled to the antenna  110  (i.e., coupled between the first terminal and the third terminal of the diplexer  320 A). The low-pass filter  220 A and the high-pass filter  220 B are configured to collectively divide low-frequency signals and high-frequency signals into different signal paths. Therefore, the high frequency sub-range and the low frequency sub-range are separated into different signal paths without tending to interfere with each other and output from different output ports of the frequency dividing circuit, respectively. Accordingly, the antenna  110  can switch between the different respective impedance values of the variable impedance circuit  130  in the low frequency sub-range independently from the high frequency sub-range. In alternative embodiments, the low-pass filter  220 A and the high-pass filter  220 B are interchanged with each other, and the antenna  110  can therefore switch between the different respective impedance values of the variable impedance circuit  130  in the high frequency sub-ranges independently from the low frequency sub-range so as to meet different design requirements. 
       FIG. 3B  is a diagram of a communication device  300 B according to an embodiment of the invention. In the embodiment of  FIG. 3B , the frequency dividing circuit of the communication device  300 B is a diplexer  320 A, and the number of variable impedance circuits  130  and  140  of the communication device  300 B is two. The diplexer  320 A has a first terminal (serving as a common port of the frequency dividing circuit) coupled to the antenna  110 , a second terminal (serving as one output port of the frequency dividing circuit) coupled to the variable impedance circuit  130 , and a third terminal (serving as another output port of the frequency dividing circuit) coupled to the variable impedance circuit  140 . The variable impedance circuit  130  is coupled between the second terminal of the diplexer  320 A and a reference voltage VREF 1  (e.g., a ground voltage VSS). The variable impedance circuit  140  is coupled between the third terminal of the diplexer  320 A and the reference voltage VREF 1  or a reference voltage VREF 2  (e.g., the ground voltage VSS, or other different bias voltage). The diplexer  320 A performs the function of frequency division. For example, the inner structure of the diplexer  320 A may be displayed in  FIG. 3C . The diplexer  320 A may include a low-pass filter  220 A and a high-pass filter  220 B. The low-pass filter  220 A is coupled between the antenna  110  and the variable impedance circuit  130  (i.e., coupled between the first terminal and the second terminal of the diplexer  320 A). The high-pass filter  220 B is coupled between the antenna  110  and the variable impedance circuit  140  (i.e., coupled between the first terminal and the third terminal of the diplexer  320 A). In alternative embodiments, the low-pass filter  220 A and the high-pass filter  220 B are interchanged with each other. With such a design, the high frequency sub-range and the low frequency sub-range are separated into different signal paths without tending to interfere with each other and output from different output ports of the frequency dividing circuit, respectively. Accordingly, the antenna  110  can switch between the different respective impedance values of the variable impedance circuit  130  in the high frequency sub-range independently from the low frequency sub-range, and also can switch between the different respective impedance values of the variable impedance circuit  140  in the low frequency sub-range independently from the high frequency sub-range. 
     The above variable impedance circuit  130  (or  140 ) may be implemented with a variety of circuit structures. Please refer to the following embodiments. It should be understood that these embodiments are just exemplary, rather than limitations of the invention. 
       FIG. 4A  is a diagram of a variable impedance circuit  430 A according to an embodiment of the invention. In the embodiment of  FIG. 4A , the variable impedance circuit  430 A includes a switch element  440  and multiple inductors  451  to  454 . The inductors  451  to  454  are coupled to a reference voltage VREF 1 , and they have different inductances. The switch element  440  can switch between the inductors  451  to  454 , so that the variable impedance circuit  430 A can provide different impedance values (i.e., inductance values of inductors  451 - 454 ) for the antenna  110 . 
       FIG. 4B  is a diagram of a variable impedance circuit  430 B according to an embodiment of the invention. In the embodiment of  FIG. 4B , the variable impedance circuit  430 B includes a switch element  440 , multiple inductors  451  to  453 , and a variable capacitor  460 . The inductors  451  to  453  are coupled to a reference voltage VREF 1 , and they have different inductances. The variable capacitor  460  is also coupled to the reference voltage VREF 1 , and it is configured to generate a variety of capacitances. The switch element  440  can switch between the variable capacitor  460  and the inductors  451  to  453 , so that the variable impedance circuit  430 B can provide different impedance values (i.e., capacitance values of capacitor  460  and inductance values of inductors  451 - 454 ) for the antenna  110 . 
       FIG. 4C  is a diagram of a variable impedance circuit  430 C according to an embodiment of the invention. In the embodiment of  FIG. 4C , the variable impedance circuit  430 C includes a variable capacitor  460 . The variable capacitor  460  is coupled to a reference voltage VREF 1 , and it is configured to generate a variety of capacitances, so that the variable impedance circuit  430 C can provide different impedance values (variable capacitance value of variable capacitor  460 ) for the antenna  110 . 
       FIG. 4D  is a diagram of a variable impedance circuit  430 D according to an embodiment of the invention. In the embodiment of  FIG. 4D , the variable impedance circuit  430 D includes a tuner  470 . The tuner  470  is coupled to a reference voltage VREF 1 , and it is configured to generate a variety of impedance values, so that the variable impedance circuit  430 D can provide different impedance values for the antenna  110 . 
       FIGS. 5A to 5I  are diagram of communication devices  500 A to  5001  according to some exemplary embodiments of the invention. In the embodiments of  FIGS. 5A to 5I , the frequency dividing circuits of  FIGS. 2A to 3C  are respectively implemented in cooperation with the variable impedance circuits of  FIG. 4A to 4D , so as to form the communication devices  500 A to  5001 . It should be noted that the frequency dividing circuit has one or more output ports (P 1  and/or P 2 ), which are respectively coupled to one or more variable impedance circuits. The output ports are arranged for separately output the frequency sub-ranges, e.g., the low/medium/high-frequency sub-ranges. 
       FIG. 5J  is a diagram of at least one variable impedance circuit  530  according to an embodiment of the invention. Generally speaking, the variable impedance circuit  530  includes a first terminal, a second terminal, multiple loading elements  551  to  554 , and a switch element  540 . The first terminal of the variable impedance circuit  530  is coupled to a reference voltage VREF 1  (e.g., a ground voltage VSS). The second terminal of the variable impedance circuit  530  is coupled to one of the output ports  125  of the frequency dividing circuit  120  (not shown). The loading elements  551  to  554  are coupled to one of the first terminal and the second terminal, and they have different impedance values. The switch element  540  is coupled to the other one of the first terminal and the second terminal, and it switches between the loading elements  551  to  554 . The switch element  540  has a first terminal coupled to the output port  125  of the frequency dividing circuit  120 , and a second terminal switchably coupled to one of the loading elements  551  to  554 . At least one of the loading elements  551  to  554  includes one or more inductors, one or more variable capacitors, one or more fixed capacitors, or a combination thereof. 
     It is noted that in the embodiments of  FIGS. 4A-4C  and  FIG. 5J , the loading elements are coupled between the switch element  440  and the reference voltage VREF 1 . However, in alternative embodiments, the switch element  440  and the loading elements can have their positions exchanged. Specifically, the switch element can be coupled between the loading elements and the reference voltage VREF 1 . In summary, at least one of the at least one variable impedance circuits can include a first terminal, coupled to the first reference voltage, a second terminal, coupled to one of the at least one output port of the frequency dividing circuit, a plurality of loading elements, coupled to one of the first terminal and the second terminal and having different impedances, and a switch element, coupled to the other one of the first terminal and the second terminal and switching between the loading elements. 
       FIG. 6  is a diagram of a communication device  600  according to an embodiment of the invention. In the embodiment of  FIG. 6 , the communication device  600  includes an antenna  110 , a frequency dividing circuit  120 , at least one variable impedance circuit  130 , a coupler  660 , and a processor  670 . The coupler  660  is coupled between the antenna  110  and the processor  670 , and it provides communication information SA from the antenna  110  to the processor  670 . The communication information SA may include return loss or RSSI (Received Signal Strength Indicator) of the antenna  110 . The coupler  660  may be disposed at any position of the RF (Radio Frequency) path of the communication device  600 . For example, the coupler  660  may be positioned on the antenna  110 , or on a frame of a mobile phone. The processor  670  receives the communication information SA directly or indirectly from the antenna  110 , and generates at least one control signal SC according to the communication information SA. The impedance value of each variable impedance circuit  130  can be determined according to one of the control signals SC. 
       FIG. 7  is a diagram of a communication device  700  according to an embodiment of the invention. In the embodiment of  FIG. 7 , the communication device  700  includes an antenna, a frequency dividing circuit  120 , and at least one variable impedance circuit  130 . The antenna includes a ground/reference plane  710 , and one or more radiation elements  720 . The ground/reference plane  710  and the one or more radiation elements  720  may be made of metal materials, such as silver, copper, aluminum, iron, or their alloys. The ground/reference plane  710  and the radiation elements  720  may be disposed on a dielectric substrate (not shown), such as a printed circuit board or an FR4 (Flame Retardant 4) substrate. For example, the ground/reference plane  710  may substantially have a rectangular shape, and one of the radiation elements  720  may substantially have a straight-line shape. A feeding point  721  of one of the radiation elements  720  is coupled to a positive electrode of a signal source  790 . A negative electrode of the signal source  790  is coupled to the ground/reference plane  710 . The ground/reference plane  710  provides a reference voltage VREF 1  (e.g., a ground voltage VSS). The grounding point  722  of one of the radiation elements  720  can be directly coupled to the ground/reference plane  710 . The tuning point  723  of one of the radiation elements  720  is coupled through the frequency dividing circuit  120  and the variable impedance circuit  130  to the reference voltage VREF 1 . In some embodiments, the grounding point  722 , the feeding point  721 , and the tuning point  723  are arranged in a straight line. The feeding point  721  may be positioned between the grounding point  722  and the tuning point  723 . In some embodiments, the antenna further includes one or more reference points. Each of the reference points is coupled to a reference voltage VREF 2 , which is the same or different from the reference voltage VREF 1 , and is further coupled to a corresponding radiation element  720 . 
     The antenna can operate in multiple frequency sub-ranges without interference therebetween. For example, a first current path  724  from the feeding point  721  to the left open end of the radiation element  720  may be excited to generate a medium/high-frequency sub-range, and a second current path  725  from the feeding point  721  to the right open end of the radiation element  720  may be excited to generate a low-frequency sub-range. In some embodiments, the frequency dividing circuit  120  is a diplexer for separating medium/high-frequency sub-ranges to obtain the low-frequency sub-range, so that they do not tend to negatively affect each other. In such a manner, the second current path  725  can be completely separated from the first current path  724  by the frequency dividing circuit  120 , and the harmonic interference between high/medium/low frequency sub-ranges in the communication device  700  can be effectively suppressed. 
       FIG. 8  is diagram of return loss of the antenna of the communication device  700  according to an embodiment of the invention. The horizontal axis represents operation frequency (MHz) of the antenna, and the vertical axis represents the return loss (dB) of the antenna. The curves CC 1  to CC 4  represent different operating states of the respective variable impedance circuit  130 . For example, referring to the embodiments of  FIG. 4A , when the switch element  440  switches to the inductors  451  to  454 , the corresponding return loss of the antenna may be displayed as the curves CC 1  to CC 4 , respectively. In the embodiment of  FIG. 8 , the frequency dividing circuit  120  of the communication device  700  is a low-pass filter or a diplexer for frequency division. It is noted that not all output port(s) are illustrated. With such a design, when the variable impedance circuit  130  performs a switching operation, only the low-frequency current path is affected, and it has almost no impact on the medium/high-frequency current paths. According to the measurement of  FIG. 8 , during the switching operation of the variable impedance circuit  130 , the return loss of the antenna operating in the medium/high-frequency bands is almost the same, and only the return loss of the antenna operating in the low-frequency sub-range is changed accordingly. Since the signal paths of different frequency sub-ranges do not tend to negatively affect each other, the harmonic interference in the communication device  700  is significantly improved. 
     In one embodiment, an electronic device for use in a communication device such as the communication device is also disclosed. The electronic device may include an antenna terminal, configured to be coupled to an antenna such as antenna  110 , a frequency dividing circuit such as the frequency dividing circuit  120 , and at least one variable impedance circuit such as the frequency dividing circuit  130 . The frequency dividing circuit can have a common port coupled to the antenna terminal and at least one output port, and configured to divide a frequency range received from the common port into a plurality of frequency sub-ranges and output at least one of the frequency sub-ranges respectively at the at least one output port. Each of the at least one variable impedance circuit can be coupled between a corresponding one of the at least one output port of the frequency dividing circuit and a respective first reference voltage, and can provide a respective variable impedance value switched between different respective impedance values. More details can be analogized from the descriptions in connection to the above embodiments. 
     The embodiments in disclosure propose a novel communication device with a frequency dividing circuit or a frequency dividing mechanism. The frequency dividing circuit may be implemented with a low-pass filter, a high-pass filter, a band-pass filter, a diplexer, duplexer, tri-plexer, quad-plexer, or a combination thereof. With such a design, low/medium/high-frequency components or sub-ranges do not tend to negatively affect each other, and harmonic interference in the communication device can be effectively eliminated. In comparison to the conventional design, the embodiments can provide at least the following advantages: (1) widening the bandwidth of a communication device for carrier aggregation, (2) suppressing the harmonic interference in the communication device, (3) simplifying the structure of the control circuits of the communication device, and (4) reducing the manufacturing cost of the communication device. 
     The above embodiments are just exemplary, rather than limitations of the invention. It should be understood that the communication device is not limited to the configuration of  FIGS. 1 to 8 . The invention may merely include any one or more features of any one or more embodiments of  FIGS. 1 to 8 . In other words, not all of the features shown in the figures should be implemented in the communication device of the invention. 
     The above terms “at least one” or “one or more” mean any positive integer which is greater than one or is equal to one. The number of elements in  FIGS. 1 to 8  is not a limitation of the invention. For example, in the embodiments of  FIG. 3B , although there are exactly two variable impedance circuits  130  and  140  displayed in the figure, it should be understood that any positive number of variable impedance circuits, such as 2, 3, 4, 5, or more, may be used and respectively coupled to the output ports of the diplexer  320 A. For example, in the embodiments of  FIG. 4A , although there are exactly four inductors displayed in the figure, it should be understood that any positive number of inductors, such as 2, 3, 4, 5, or more, may be used for providing different inductances. 
     Use of ordinal terms such as “first”, “second”, “third”, etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having the same name (but for use of the ordinal term) to distinguish the claim elements. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.