Patent Publication Number: US-2021184328-A1

Title: Directional coupler

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of International Application No. PCT/JP2019/033515 filed on Aug. 27, 2019 which claims priority from Japanese Patent Application No. 2018-161719 filed on Aug. 30, 2018. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a directional coupler including a main line and a sub-line that are electromagnetically coupled to each other. 
     Directional couplers including main lines and sub-lines that are electromagnetically coupled to each other are used to extract power (that is, traveling waves) of radio-frequency signals that are propagated on the lines in a forward direction. In such a directional coupler, a termination resistor is connected to one end of the sub-line (for example, refer to Patent Document 1). 
     Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-27617 
     BRIEF SUMMARY 
     However, the directional coupler disclosed in Patent Document 1, in which the termination resistor is connected to one end of the sub-line, has a problem in that the resistance value of the termination resistor is varied not to achieve stable directivity. The directivity is a value indicating the capability to discriminate between the traveling waves and reflected waves, which are extracted by the directional coupler. In the directional couplers, for example, the directional coupler disclosed in Patent Document 1, the frequency at which the directivity is maximized is varied for each directional coupler. 
     In order to resolve the above problem, use of a variable termination circuit capable of varying the resistance value as the termination resistor and correction of the impedance of the variable termination circuit are considered. However, in this case, there is a problem in that the impedance at the other end of the sub-line (that is, output impedance) is varied due to the difference in the amount of correction for each directional coupler not to achieve stable return loss. The return loss is a reciprocal of the ratio of the reflected waves with respect to incident waves (that is, the reciprocal of a reflection coefficient) and indicates the degree of matching. 
     The present disclosure provides a directional coupler capable of achieving the directivity and the return loss more stable than those of directional couplers in related art. 
     A directional coupler according to an embodiment of the present disclosure includes a main line and a sub-line electromagnetically coupled to each other, a variable termination circuit that is connected to one end of the sub-line and that has a variable impedance, a variable matching circuit that is connected to the other end of the sub-line and that has a variable impedance or a variable attenuator that has a variable attenuation, and a control circuit that controls the impedance of the variable termination circuit and that controls the impedance of the variable matching circuit or the attenuation of the variable attenuator. The control circuit includes a non-volatile memory and controls the impedance of the variable termination circuit in accordance with data stored in the memory. 
     The present disclosure provides a directional coupler capable of achieving the directivity and the return loss more stable than those of directional couplers in the related art. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the configuration of a directional coupler according to an embodiment. 
         FIG. 2  is a diagram illustrating an example of a variable termination circuit according to a modification of the present embodiment. 
         FIG. 3  is a diagram illustrating a detailed circuit example of a variable matching circuit illustrated in  FIG. 1 . 
         FIGS. 4A and 4B  include diagrams illustrating a detailed circuit example of a variable attenuator illustrated in  FIG. 1 . 
         FIGS. 5A and 5B  include diagrams illustrating a detailed circuit example of a variable filter illustrated in  FIG. 1 . 
         FIG. 6  is a block diagram illustrating a detailed configuration example of a control circuit illustrated in  FIG. 1 . 
         FIG. 7A  is a flowchart indicating an example of how to store data (data for controlling the capacitance value of the variable termination circuit) in a memory in the directional coupler according to the present embodiment. 
         FIG. 7B  is a flowchart indicating an example of how to store data (data for controlling the resistance value of the variable termination circuit) in the memory in the directional coupler according to the present embodiment. 
         FIG. 8  is a flowchart illustrating an example of how to adjust the directional coupler according to the present embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will herein be described in detail with reference to the drawings. All the embodiments described below indicate specific examples of the present disclosure. Numerical values, shapes, materials, components, the positions where the components are arranged, the connection mode of the components, steps, the order of the steps, and so on, which are indicated in the embodiments described below, are only examples and are not intended to limit the present disclosure. Among the components in the embodiments described below, the components that are not described in the independent claims indicating the highest-level concepts of the present disclosure are described as optional components. In addition, the drawings are not necessarily strictly indicated. The same reference numerals are used in the respective drawings to identify substantially the same components and a duplicated description of such components may be omitted or simplified. 
       FIG. 1  is a block diagram illustrating the configuration of a directional coupler  10  according to an embodiment. The directional coupler  10  is a bidirectional coupler capable of selectively extracting traveling waves and reflected waves on a line (the power of radio-frequency signals propagated on the line in the opposite directions). The directional coupler  10  includes a main line  11 , a sub-line  12 , a switch circuit  13 , a variable termination circuit  14 , a variable matching circuit  15 , a variable attenuator  16 , a variable filter  17 , a coupling port  18 , and a control circuit  19 . 
     The main line  11  is a line connected in series to the line from which the traveling waves and the reflected waves are extracted. Here, on the main line  11 , the power travelling from a left-side terminal Pin to a right-side terminal Pout in  FIG. 1  is referred to as the traveling waves and the power travelling in the opposite direction is referred to as the reflected waves. 
     The sub-line  12  is a line that is electromagnetically connected to the main line  11  and that extracts the traveling waves or the reflected waves. 
     The switch circuit  13  is a circuit to switch between the extraction of the traveling waves and the extraction of the reflected waves using the directional coupler  10 . The switch circuit  13  is composed of two switch elements  13   a  and  13   b  controlled by the control circuit  19  or an external circuit (that is, a circuit placed outside the directional coupler  10 ). The traveling waves are extracted by the directional coupler  10  when common terminals are connected to left-side terminals (“FWD”) in  FIG. 1  in the two switch elements  13   a  and  13   b , and the reflected waves are extracted by the directional coupler  10  when the common terminals are connected to right-side terminals (“REV”) in  FIG. 1  in the two switch elements  13   a  and  13   b.    
     The switch elements  13   a  and  13   b  are radio-frequency switches that are turned on or off in response to a control signal that is externally input. Each of the switch elements  13   a  and  13   b  is, for example, a field effect transistor (FET) The same applies to all the switch elements described below. 
     The variable termination circuit  14  is a circuit that is connected to one end of the sub-line  12  via the switch circuit  13  and that has a variable impedance. The impedance of the variable termination circuit  14  can be controlled in response to the control signals supplied from the control circuit  19  and the external circuit. In the present embodiment, the variable termination circuit  14  includes multiple impedance elements  14   a  to  14   f  and switch elements  14   g  to  14   j  connected to the four impedance element  14   a ,  14   b ,  14   e , and  14   f , respectively, among the multiple impedance elements  14   a  to  14   f . Although the case is illustrated in  FIG. 1  in which the variable termination circuit  14  includes the multiple switch elements, it is sufficient for at least one switch element to be provided. In other words, it is sufficient for the variable termination circuit  14  to include the switch element connected to at least one impedance element, among the multiple impedance elements  14   a  to  14   f.    
     More specifically, the multiple impedance elements  14   a  to  14   f  include multiple capacitances (the impedance elements  14   a  to  14   c ) connected in parallel to each other, and the multiple switch elements  14   g  to  14   j  include the multiple switch elements  14   g  and  14   h  that are connected in parallel to each other and that are connected in series to the multiple capacitances (the impedance element  14   a  and impedance elements  14   b ), respectively. The multiple impedance elements  14   a  to  14   f  include multiple resistors (the impedance elements  14   d  to  14   f ) connected in parallel to each other, and the multiple switch elements  14   g  to  14   j  include the multiple switch elements  14   i  and  14   j  that are connected in parallel to each other and that are connected in series to the multiple resistors (the impedance elements  14   e  and  14   f ), respectively. The impedance elements  14   a  to  14   f  may be not only lumped constant circuit elements but also distributed constant circuit elements. 
     The multiple switch elements  14   g  to  14   j  include the switch elements (for example, the switch elements  14   g  and  14   i ) that are turned on or off under the control of the control circuit  19 , which is based on data stored in a memory  19   a , (that is, for trimming) and the switch elements (for example, the switch elements  14   h  and  14   j ) that are turned on or off under the control of the control circuit  19  and the external circuit, which is not based on the data stored in the memory  19   a , (that is, for tuning). Each of the switch elements for tuning (for example, the switch elements  14   h  and  14   j ) is an example of a controlled unit that varies the impedance of the variable termination circuit  14  under the control that is not based on the data stored in the memory  19   a . The control of the variable termination circuit  14 , which is not based on the data stored in the memory  19   a , means control of the variable termination circuit  14  based on information other than the data stored in the memory  19   a  and is, for example, dynamic adjustment of the impedance of the variable termination circuit  14 , which is matched with the frequency band of the radio-frequency signal propagated on the main line  11 . 
     Although the multiple switch elements  14   g  to  14   j  are connected to the impedance elements composed of the capacitances and the resistors in the present embodiment, the connection mode of the multiple switch elements  14   g  to  14   j  is not limited to this. The multiple switch elements  14   g  to  14   j  may be connected only to the impedance elements composed of the capacitances or may be connected only to the impedance elements composed of the resistors. In addition, the mixture of the capacitances and the resistors is not limitedly used as the impedance elements included in the variable termination circuit  14 . Only the capacitances may be used as the impedance elements included in the variable termination circuit  14  or only the resistors may be used as the impedance elements included in the variable termination circuit  14 . 
     The variable matching circuit  15  is a circuit that is connected to the other end of the sub-line  12  via the switch circuit  13  and that has a variable impedance. In other words, the signal extracted on the sub-line  12  is input into the variable matching circuit  15 . The variable matching circuit  15  is provided to improve the loss caused by the reflected waves from the coupling port  18  by adjusting output impedance at the coupling port  18 . The impedance of the variable matching circuit  15  can be controlled in response to the control signals from the control circuit  19  and the external circuit. 
     The variable attenuator  16  is an attenuator that is connected to the other end of the sub-line  12  and that has a variable attenuation. In the present embodiment, the variable attenuator  16  is connected to the other end of the sub-line  12  via the switch circuit  13  and the variable matching circuit  15 . In other words, the signal extracted from the variable matching circuit  15  is input into the variable attenuator  16 . The variable attenuator  16  is provided to enable adjustment of the degree of coupling of the directional coupler  10 . The attenuation of the variable attenuator  16  can be controlled in response to the control signals from the control circuit  19  and the external circuit. The degree of coupling means the ratio between the power propagated on the line in the forward direction and the power extracted at the coupling port  18 . 
     The variable filter  17  is a filter that is connected to the other end of the sub-line  12  via the switch circuit  13 , the variable matching circuit  15 , and the variable attenuator  16  and that has a variable pass band. In other words, the signal output from the variable attenuator  16  is input into the variable filter  17 . The variable filter  17  is, for example, a low pass filter having a variable pass band and is provided to reduce the frequency dependence of the degree of coupling of the directional coupler  10 . The pass band of the variable filter  17  can be controlled in response to the control signals from the control circuit  19  and the external circuit. 
     The coupling port  18  is a terminal from which the signal extracted by the directional coupler  10  is output. 
     The control circuit  19  is an example of a control circuit that controls the impedance of the variable termination circuit  14  and that controls the impedance of the variable matching circuit  15  or the attenuation of the variable attenuator  16 . The control circuit  19  includes the memory  19   a  and a detection circuit  19   b . In the present embodiment, the control circuit  19  controls (performs trimming of) the impedance of the variable termination circuit  14 , the impedance of the variable matching circuit  15 , the attenuation of the variable attenuator  16 , and the pass band of the variable filter  17  in accordance with the data stored in the memory  19   a . For example, the control circuit  19  short-circuits or opens the switch elements  14   g  to  14   j  in accordance with the data stored in the memory  19   a  to control the impedance of the variable termination circuit  14 . Specifically, the control circuit  19  may be realized by a logic circuit, such as the one described below ( FIG. 6 ), may include a communication circuit communicating with the external circuit, or may include a microcomputer incorporating programs. 
     The memory  19   a  is a non-volatile memory. Specifically, in the present embodiment, the memory  19   a  is a storage unit composed of multiple memory devices, such as electrical fuses, capable of performing writing only once and stores data that has been written in advance. The memory device capable of performing writing only once is a write-once memory device and is a memory device of a type in which deletion and modification of the data that has been written are disabled. In the present embodiment, data corresponding to the control of the impedance of the variable termination circuit  14 , the impedance of the variable matching circuit  15 , the attenuation of the variable attenuator  16 , and the pass band of the variable filter  17  (that is, data corresponding to the trimming) is stored in the memory  19   a  in advance. 
     The detection circuit  19   b  is an example of a circuit that detects the impedance of the variable termination circuit  14  to generate the data to be stored in the memory  19   a  based on the detected impedance. The detection circuit  19   b  includes, for example, a replica of the variable termination circuit  14  (that is, a circuit imitating the variable termination circuit  14 ) and indirectly detects the impedance of the variable termination circuit  14  using the replica. In the manufacturing stage of the directional coupler  10 , the impedance of the variable termination circuit  14  is detected by the detection circuit  19   b , data used for adjusting the impedance of the variable termination circuit  14  to a desired value (that is, data for the trimming) is generated by the control circuit  19  or the external circuit based on the detected impedance, and the generated data is written to the memory  19   a.    
     After the manufacturing (after the data is stored in the memory  19   a ), the detection of the impedance of the variable termination circuit  14  by the detection circuit  19   b  may also be used for the adjustment of the impedance of the variable termination circuit  14 , the impedance of the variable matching circuit  15 , the attenuation of the variable attenuator  16 , and the pass band of the variable filter  17  by the control circuit  19  or the external circuit (that is, for the tuning, which is dynamic adjustment in the use of the directional coupler  10  after the manufacturing). 
     Although the variable termination circuit  14  is the circuit in which the multiple series circuits of the impedance elements and the switch elements are connected in parallel to each other in  FIG. 1 , the configuration of the variable termination circuit  14  is not limited to this configuration.  FIG. 2  is a diagram illustrating a configuration example of a variable termination circuit according to a modification of the present embodiment. The variable termination circuit according to the present modification includes multiple resistors  141   a  to  141   c  connected in series to each other as the multiple impedance elements and includes multiple switch elements  141   d  to  141   f  connected in parallel to the multiple resistors  141   a  to  141   c , respectively, as the multiple switch elements. Such a variable termination circuit may be included as the whole or part of the variable termination circuit  14  according to the above embodiment. In other words, in the variable termination circuit  14  according to the present embodiment, all or part of the multiple impedance elements may be connected in series to each other or all or part of the multiple switch elements may be connected in parallel to the corresponding impedance elements. This enables the value of the impedance of the variable termination circuit, which is determined by the combination of turning-on and turning-off the respective switch elements, to be further varied. 
     Although the case is illustrated in  FIG. 2  in which the multiple switch elements are provided, it is sufficient for at least one switch element to be provided. In other words, it is sufficient for the variable termination circuit according to the modification of the present embodiment to include one switch element connected in parallel to at least one impedance element, among the multiple impedance elements (the resistors  141   a  to  141   c ). 
       FIG. 3  is a diagram illustrating a detailed circuit example of the variable matching circuit  15  illustrated in  FIG. 1 . The variable matching circuit  15  is a circuit capable of varying the impedance using multiple capacitances and multiple inductors. The variable matching circuit  15  is composed of five capacitances  15   a  to  15   e  connected between a path between an input terminal IN and an output terminal OUT and ground, inductors  15   f  and  15   g  provided on the path, and switch elements  15   h  to  15   n  provided for the capacitances  15   a  to  15   e  and the inductors  15   f  and  15   g , respectively. 
     In the present embodiment, the switch elements  15   h  to  15   n  include the switch elements (for example, the switch elements  15   h  to  15   j ,  15   m , and  15   n ) that are turned on or off under the control of the control circuit  19 , which is based on the data stored in the memory  19   a , (that is, for trimming) and the switch elements (for example, the switch elements  15   k  and  15   l ) that are turned on or off under the control of the control circuit  19  and the external circuit, which is not based on the data stored in the memory  19   a , (that is, for tuning). Each of the switch elements for tuning (for example, the switch elements  15   k  and  15   l ) is an example of a controlled unit that varies the impedance of the variable matching circuit  15  under the control that is not based on the data stored in the memory  19   a . The control of the variable matching circuit  15 , which is not based on the data stored in the memory  19   a , means control of the variable matching circuit  15  based on information other than the data stored in the memory  19   a  and is, for example, dynamic adjustment of the impedance of the variable matching circuit  15 , which is matched with the frequency band of the radio-frequency signal propagated on the main line  11 . 
       FIGS. 4A and 4B  include diagrams illustrating a detailed circuit example of the variable attenuator  16  illustrated in  FIG. 1 . The variable attenuator  16  is a circuit that can vary the attenuation of the signal using multiple resistors.  FIG. 4A  illustrates the variable attenuator  16  composed of variable resistors  16   a  to  16   c  connected in one T-shaped pattern and three switch elements  16   g  to  16   i  for connecting or disconnecting part of the variable resistors  16   a  to  16   c .  FIG. 4B  illustrates three resistors  161   a  to  163   a  connected in series to each other and switch elements  164   a  to  166   a  connected in parallel to the respective resistors as an example of the variable resistor  16   a  included in the variable attenuator  16 . The three resistors  161   a  to  163   a  have, for example, different resistance values. The variable resistor  16   a  illustrated in  FIG. 4B  is applicable to the variable resistors  16   b  and  16   c . The three resistors  161   a  to  163   a  may have, for example, the same resistance value. 
     In the present embodiment, for example, the switch elements  164   a  to  166   a  are the switch elements that are turned on or off under the control of the control circuit  19 , which is based on the data stored in the memory  19   a , (that is, for trimming) and the switch elements  16   g  to  16   i  are the switch elements that are turned on or off under the control of the control circuit  19  and the external circuit, which is not based on the data stored in the memory  19   a , (that is, for tuning). Each of the switch elements for tuning (for example, the switch elements  16   g  to  16   i ) is an example of a controlled unit that varies the attenuation of the variable attenuator  16  under the control that is not based on the data stored in the memory  19   a . The control of the variable attenuator  16 , which is not based on the data stored in the memory  19   a , means control of the variable attenuator  16  based on information other than the data stored in the memory  19   a  and is, for example, dynamic adjustment of the attenuation of the variable attenuator  16 , which is matched with the frequency band of the radio-frequency signal propagated on the main line  11 . 
       FIGS. 5A and 5B  include diagrams illustrating a detailed circuit example of the variable filter  17  illustrated in  FIG. 1 . The variable filter  17  is a low pass filter capable of varying its pass band.  FIG. 5A  illustrates the variable filter  17  composed of four capacitances  17   a  to  17   d  connected between the path from the input terminal IN to the output terminal OUT and the ground, two capacitances  17   e  and  17   f  and one inductor  17   g  connected on the path or connected in parallel to the path, and switch elements  17   h  to  17   j  connected in series to the capacitances  17   a  and  17   d  and the capacitance  17   f , respectively. The capacitances  17   b ,  17   c , and  17   e  are variable capacitances.  FIG. 5B  illustrates three capacitances  171   e  to  173   e  connected in parallel to each other and switch elements  174   e  to  176   e  connected in series to the respective capacitances as an example of the capacitance  17   e . The three capacitances  171   e  to  173   e  have, for example, different capacitance values. The configuration of the variable capacitance illustrated in  FIG. 5B  is applicable to the capacitances  17   b  and  17   c.    
     In the present embodiment, the switch elements  174   e  to  176   e  are the switch elements that are turned on or off under the control of the control circuit  19 , which is based on the data stored in the memory  19   a , (that is, for trimming) and the switch elements  17   h  to  17   j  are the switch elements that are turned on or off under the control of the control circuit  19  and the external circuit, which is not based on the data stored in the memory  19   a , (that is, for tuning). 
     Each of the switch elements for tuning (for example, the switch elements  17   h  to  17   j ) is an example of a controlled unit that varies the pass band of the variable filter  17  under the control that is not based on the data stored in the memory  19   a . The control of the variable filter  17 , which is not based on the data stored in the memory  19   a , means control of the variable filter  17  based on information other than the data stored in the memory  19   a  and is, for example, dynamic adjustment of the pass band of the variable filter  17 , which is matched with the frequency band of the radio-frequency signal propagated on the main line  11 . 
       FIG. 6  is a block diagram illustrating a detailed configuration example of the control circuit  19  illustrated in  FIG. 1 . The memory  19   a  in the control circuit  19  and a circuit for outputting the control signals corresponding to the data stored in the memory  19   a  are illustrated here. The illustration of the detection circuit  19   b  is omitted in  FIG. 6 . 
     As illustrated in  FIG. 6 , the memory  19   a  is composed of electrical fuses  19   a   1  to  19   a   3 , which are multiple memory devices. The multiple electrical fuses  19   a   1  to  19   a   3  are conducted or blown out (that is, data is written to the electrical fuses  19   a   1  to  19   a   3 ) based on whether the corresponding switch elements for trimming of the variable termination circuit  14  (for example, the switch elements  14   g  and  14   i ), the corresponding switch elements for trimming of the variable matching circuit  15  (for example, the switch elements  15   h  to  15   j ,  15   m , and  15   n ), the corresponding switch elements for trimming of the variable attenuator  16  (for example, the switch elements  164   a  to  166   a ), and the corresponding switch elements for trimming of the variable filter  17  (for example, the switch elements  174   e  to  176   e ) are turned on or off. 
     In addition, as illustrated in  FIG. 6 , the control circuit  19  includes level shifters  191  to  193  corresponding to the multiple electrical fuses  19   a   1  to  19   a   3 , respectively, in the memory  19   a . The level shifters  191  to  193  are direct current-direct current (DC-DC) converters that increase or decrease the voltages occurring based on the states (conducted or blown out) of the corresponding electrical fuses  19   a   1  to  19   a   3  to voltages suitable to control the corresponding switch elements for trimming. The control circuit  19  outputs the voltages that are increased or decreased, which are output from the level shifters  191  to  193 , to the corresponding switch elements for trimming to control (perform trimming of) the impedance of the variable termination circuit  14 , the impedance of the variable matching circuit  15 , the attenuation of the variable attenuator  16 , and the pass band of the variable filter  17 . 
     When the FETs are used for the above respective switch elements, the respective switch elements are controlled in response to application of the voltages output from the level shifters  191  to  193 , that is, the voltages occurring based on the states of the electrical fuses  19   a   1  to  19   a   3  to the gate electrodes of the respective FETs. 
     The state (conducted or blown out) of each electrical fuse and the state (short-circuited or opened) of the corresponding switch element for trimming have the following correspondence. Typically, the blown-out of the electrical fuse generates High voltage and the switch element for trimming is short-circuited in response to the High voltage output from the level shifter. In contrast, the conduction of the electrical fuse generates Low voltage and the switch element for trimming is opened in response to the Low voltage output from the level shifter. However, the opposite correspondence may be established depending on selection of the conductivity type (P type or N type) of the peripheral circuit connected to the electrical fuse and the switch element. 
     Examples of how to store data in the memory  19   a  in the directional coupler  10  according to the present embodiment, which is configured in the above manner, (that is, trimming examples) will now be described. 
       FIG. 7A  is a flowchart indicating an example of how to store data (data for controlling the capacitance value of the variable termination circuit  14  here) in the memory  19   a  in the directional coupler  10  according to the present embodiment. 
     First, a capacitance component (capacitance value) in the impedance of the variable termination circuit  14  is compared with the desired value (S 10 ). 
     If it is determined that the capacitance component (capacitance value) in the impedance of the variable termination circuit is lower than the desired value (“lower than desired value” in S 10 ), the data is written to the memory  19   a  so as to increase the capacitance value in the variable termination circuit (S 11 ). For example, in the variable termination circuit  14 , the data is written to the memory  19   a  so that the number of the switch elements that short-circuit the impedance elements composed of the capacitances is greater than the number of the switch elements that open the impedance elements composed of the capacitances. Specifically, when the switch element  14   h  is the switch element for trimming, in addition to the switch element  14   g , in the variable termination circuit  14  illustrated in  FIG. 1 , the data is written to the memory  19   a  with a writing circuit placed outside the directional coupler  10  or a writing circuit (not illustrated) incorporated in the control circuit  19  or the like in the control circuit  19  so that all the switch elements  14   g  and  14   h  for trimming are short-circuited. In this case, for example, if the capacitance component (capacitance value) in the impedance of the variable termination circuit  14  after mass production is varied toward a direction lower than the desired value, performing the trimming to increase the capacitance component (capacitance value) in the impedance of the variable termination circuit  14  enables the variation to be corrected. 
     If it is determined that the capacitance component (capacitance value) in the impedance of the variable termination circuit is higher than the desired value (“higher than desired value” in S 10 ), the data is written to the memory  19   a  so as to decrease the capacitance value in the variable termination circuit (S 12 ). For example, in the variable termination circuit  14 , the data is written to the memory  19   a  so that the number of the switch elements that short-circuit the impedance elements composed of the capacitances is smaller than the number of the switch elements that open the impedance elements composed of the capacitances (S 13 ). Specifically, when the switch element  14   h  is the switch element for trimming, in addition to the switch element  14   g , in the variable termination circuit  14  illustrated in  FIG. 1 , the data is written to the memory  19   a  with the writing circuit placed outside the directional coupler  10  or the writing circuit (not illustrated) incorporated in the control circuit  19  or the like in the control circuit  19  so that all the switch elements  14   g  and  14   h  for trimming are opened. In this case, for example, if the capacitance component (capacitance value) in the impedance of the variable termination circuit  14  after mass production is varied toward a direction higher than the desired value, performing the trimming to decrease the capacitance component (capacitance value) in the impedance of the variable termination circuit  14  enables the variation to be corrected. 
     If it is determined that the capacitance component (capacitance value) in the impedance of the variable termination circuit is equal to the desired value (“equal to desired value” in S 10 ), the capacitance value is not particularly adjusted. 
     The data may be written to the memory  19   a  with the writing circuit placed outside the directional coupler  10  or the writing circuit (not illustrated) incorporated in the control circuit  19  or the like in the control circuit  19  so that both the switch elements to be short-circuited and the switch elements to be opened exist in the variable termination circuit  14  depending on the detected impedance of the variable termination circuit  14 . For example, when the switch element  14   h  is the switch element for trimming, in addition to the switch element  14   g , in the variable termination circuit  14  illustrated in  FIG. 1 , the data may be written to the memory  19   a  so that the switch element  14   g  is short-circuited and the switch element  14   h  is opened, among the switch elements  14   g  and  14   h  for trimming. In this case, for example, combination of the adjustment to decrease the impedance of the variable termination circuit  14  after mass production with the adjustment to increase the impedance of the variable termination circuit  14  after mass production may enable the correction of the variation with higher accuracy. 
     As an example, when half of all the switch elements for trimming in the variable termination circuit  14  is short-circuited and the remaining half of them is opened, the number, the kind, the connection mode, and so on of the impedance elements and the switch elements for trimming are designed so that the impedance of the variable termination circuit  14  has a median within a variable range and a target value. This enables the variation to be corrected in many cases, for example, if the impedance of the variable termination circuit  14  after mass production is varied. 
     Although the trimming example for the capacitance component in the impedance of the variable termination circuit  14  is indicated in  FIG. 7A , data to increase or decrease the resistance value of the variable termination circuit  14  may be written to the memory  19   a  so as to suppress the variation in accordance with a result of comparison between a resistance value that is detected and a desired value, also for the resistance component in the impedance of the variable termination circuit  14 , as indicated in a flowchart in  FIG. 7B .  FIG. 7B  is a flowchart indicating an example of how to store data (data for controlling the resistance value of the variable termination circuit  14  here) in the memory  19   a  in the directional coupler  10  according to the present embodiment. Steps S 10   a , S 11   a , and S 12   a  in  FIG. 7B  correspond to Steps S 10 , S 11 , and S 12  illustrated in  FIG. 7A  and the same processing as in  FIG. 7A  is performed in  FIG. 7B  except that the “capacitance value” is replaced with the “resistance value”. However, in the switch elements for trimming connected in series to the resistors in the variable termination circuit  14 , the resistance value is decreased with the increasing number of the switch elements to be short-circuited and the resistance value is increased with the increasing number of the switch elements to be opened. 
     An example of how to adjust the directional coupler  10  according to the present embodiment will now be described. 
       FIG. 8  is a flowchart illustrating an example of how to adjust the directional coupler  10  according to the present embodiment. 
     If the impedance (that is, at least one of the resistance value and the capacitance value) of the variable termination circuit  14  is to be adjusted (Yes in S 20 ), at least the attenuation of the variable attenuator  16  is adjusted (S 21 ). If the impedance of the variable termination circuit  14  is not to be adjusted (No in S 20 ), the attenuation of the variable attenuator  16  is not adjusted. 
     For example, when the trimming to adjust the impedance of the variable termination circuit  14  based on the data stored in the memory  19   a  is performed, the control circuit  19  performs the trimming to adjust the attenuation of the variable attenuator  16  based on the data stored in the memory  19   a  by the control circuit  19  or performs the tuning to adjust the attenuation of the variable attenuator  16  not based on the data stored in the memory  19   a  (for example, in accordance with the frequency band of the signal propagated on the main line  11 ) by the control circuit  19  or the external circuit. 
     When the attenuation of the variable attenuator  16  is adjusted, it is determined whether the impedance at the coupling port  18  side of the directional coupler  10  (the output impedance of the directional coupler  10 ) after the adjustment of the attenuation is varied by a predetermined amount from that before the adjustment of the attenuation (S 22 ). If the impedance at the coupling port  18  side of the directional coupler  10  (the output impedance) is varied by a predetermined amount (Yes in S 22 ), the impedance of the variable matching circuit  15  is adjusted (S 23 ). If the impedance at the coupling port  18  side of the directional coupler  10  (the output impedance) is not varied by a predetermined amount (No in S 22 ), the impedance of the variable matching circuit  15  is not adjusted. 
     For example, when the output impedance of the directional coupler  10  is varied by a predetermined amount as the result of the adjustment of the attenuation of the variable attenuator  16 , the control circuit  19  performs the trimming to adjust the impedance of the variable matching circuit  15  based on the data stored in the memory  19   a  by the control circuit  19  or performs the tuning to adjust the impedance of the variable matching circuit  15  not based on the data stored in the memory  19   a  (for example, in accordance with the frequency band of the signal propagated on the main line  11 ) by the control circuit  19  or the external circuit. 
     Performing the adjustment of the variable attenuator  16  or the variable matching circuit  15  in accordance with the state of the variable termination circuit  14  or the state of the output impedance in the above manner enables the output impedance of the directional coupler  10 , which is varied due to the adjustment of the variable termination circuit  14 , to be returned to a desired value. As a result, it is possible to stabilize the directivity and the return loss of the directional coupler  10 . 
     As described above, the directional coupler  10  according to the present embodiment includes the main line  11  and the sub-line  12  electromagnetically coupled to each other, the variable termination circuit  14  that is connected to one end of the sub-line  12  and that has a variable impedance, the variable matching circuit  15  that is connected to the other end of the sub-line  12  and that has a variable impedance or the variable attenuator  16  that has a variable attenuation, and the control circuit  19  that controls the impedance of the variable termination circuit  14  and that controls the impedance of the variable matching circuit  15  or the attenuation of the variable attenuator  16 . The control circuit  19  includes the non-volatile memory  19   a  and controls the impedance of the variable termination circuit  14  in accordance with the data stored in the memory  19   a.    
     With the above configuration, since the impedance of the variable termination circuit  14  is adjusted by the control circuit  19  in accordance with the data stored in the memory  19   a  at one end side of the sub-line  12 , the variation in the directivity of the directional coupler  10  is suppressed. In addition, since the impedance of the variable matching circuit  15  or the attenuation of the variable attenuator  16  is adjusted by the control circuit  19  for the output impedance at the other end side of the sub-line  12 , which occurs in association with the adjustment of the impedance of the variable termination circuit  14 , the variation in the return loss of the directional coupler  10  is also suppressed. Accordingly, the directional coupler  10  capable of achieving the directivity and the return loss more stable than those of directional couplers in the related art is realized. 
     Here, the memory  19   a  includes a memory device capable of performing writing only once. 
     With the above configuration, since the data is not modified after the data corresponding to the adjustment of the impedance of the variable termination circuit  14  is written to the memory  19   a , the adjustment of the impedance of the variable termination circuit  14  is stably continued. 
     The memory device is, for example, an electrical fuse. 
     With the above configuration, since the electrical fuse, which is relatively easily manufactured and the manufacturing cost of which is low, is used as the memory device of the memory  19   a , the directional coupler  10  is easily manufactured. 
     The control circuit  19  controls the impedance of the variable matching circuit  15  or the attenuation of the variable attenuator  16  in accordance with the data stored in the memory  19   a.    
     With the above configuration, not only the impedance of the variable termination circuit  14  but also the impedance of the variable matching circuit  15  or the attenuation of the variable attenuator  16  are adjusted by the control circuit  19  in accordance with the data stored in the memory  19   a . Accordingly, the trimming to ensure the stable directivity and return loss of the directional coupler  10  is enabled with the data stored in the memory  19   a.    
     The variable termination circuit  14  includes the multiple impedance elements  14   a  to  14   f  and the switch elements  14   g  to  14   j  respectively connected to at least one or more impedance elements  14   a ,  14   b ,  14   e , and  14   f , among the multiple impedance elements  14   a  to  14   f . The control circuit  19  short-circuits or opens the switch elements  14   g  and  14   i  in accordance with the data stored in the memory  19   a  to control the impedance of the variable termination circuit  14 . 
     With the above configuration, short-circuiting or opening the switch elements corresponding to the respective multiple impedance elements composing the variable termination circuit  14  in accordance with the data stored in the memory  19   a  to enable or disable the respective impedance elements enables the impedance of the variable termination circuit  14  to be adjusted. 
     The multiple impedance elements  14   a  to  14   f  include the multiple capacitances (the impedance elements  14   a  and  14   b ) connected in parallel to each other, and the switch elements  14   g  and  14   h  are connected in series to at least one capacitance, among the multiple capacitances (the impedance elements  14   a  and  14   b ). 
     With the above configuration, since the capacitances connected in parallel are capable of being selected as the components of the variable termination circuit  14 , the adjustment of the capacitance components in the impedance of the variable termination circuit  14  is enabled. 
     The multiple impedance elements include the resistors  141   a  to  141   c  connected in series to each other. The switch elements  141   d  to  141   f  are connected in parallel to at least one resistor, among the multiple resistors. 
     With the above configuration, since the resistors connected in series are capable of being selected as the components of the variable termination circuit  14 , the adjustment of the resistance components in the impedance of the variable termination circuit  14  is enabled. 
     The multiple impedance elements  14   a  to  14   f  include the multiple resistors (the impedance elements  14   e  and  14   f ) connected in parallel to each other. The switch element  14   i  and  14   j  are connected in series to at least one resistor, among the multiple resistors (the impedance elements  14   e  and  14   f ). 
     With the above configuration, since the resistors connected in parallel are capable of being selected as the components of the variable termination circuit  14 , the adjustment of the resistance components in the impedance of the variable termination circuit  14  is enabled. 
     The variable matching circuit  15  and the variable attenuator  16  are connected in series to the other end of the sub-line  12 . 
     With the above configuration, since the adjustment of both the impedance of the variable matching circuit  15  and the attenuation of the variable attenuator  16  is enabled at the other end side of the sub-line  12 , the variation in the directivity and the return loss of the directional coupler  10  is reliably suppressed. 
     The directional coupler  10  includes the variable attenuator  16 . When the control circuit  19  adjusts (controls) the impedance of the variable termination circuit  14 , the control circuit  19  adjusts (controls) at least the attenuation of the variable attenuator  16 . 
     With the above configuration, since the adjustment corresponding to the adjustment of the impedance of the variable termination circuit  14  connected to one end side of the sub-line  12  is capable of being performed at the other end side of the sub-line  12 , the variation in the directivity and the return loss of the directional coupler  10  is reliably suppressed. 
     The variable termination circuit  14  further includes the controlled unit that varies the impedance of the variable termination circuit  14  under control that is not based on the data stored in the memory  19   a.    
     With the above configuration, the impedance of the variable termination circuit  14  is capable of being subjected to not only the trimming in accordance with the data stored in the memory  19   a  but also the tuning, which is dynamic adjustment depending on the frequency band or the like of the signal propagated on the main line  11 , to improve the directivity of the directional coupler  10 . 
     The control circuit  19  further includes the detection circuit  19   b  that detects the impedance of the variable termination circuit  14  and that generates data to be stored in the memory  19   a  based on the detected impedance. 
     With the above configuration, since the detection circuit  19   b  in the directional coupler  10  is capable of being used to determine the data to be stored in the memory  19   a , the trimming is capable of being finished without necessarily preparing a suitable measurement device. 
     The directional coupler  10  includes the variable matching circuit  15 . The variable matching circuit  15  further includes the controlled unit that varies the impedance of the variable matching circuit  15  under control that is not based on the data stored in the memory  19   a.    
     With the above configuration, the impedance of the variable matching circuit  15  is capable of being subjected to the tuning, which is the dynamic adjustment depending on the frequency band or the like of the signal propagated on the main line  11  to more appropriately match the output impedance of the directional coupler  10 . 
     The directional coupler  10  includes the variable attenuator  16 . The variable attenuator  16  further includes the controlled unit that varies the attenuation of the variable attenuator  16  under control that is not based on the data stored in the memory  19   a.    
     With the above configuration, the attenuation of the variable attenuator  16  is capable of being subjected to the tuning, which is the dynamic adjustment depending on the frequency band or the like of the signal propagated on the main line  11 , to more appropriately set the degree of coupling of the directional coupler  10 . 
     The directional coupler  10  includes the variable filter  17  connected to the other end of the sub-line  12 . 
     With the above configuration, the frequency characteristics of the directional coupler  10  are capable of being appropriately adjusted. 
     Although the directional coupler  10  according to the present disclosure is described above based on the embodiment and the modification, the present disclosure is not limited to the embodiment and the modification. Aspects realized by making various changes supposed by the person skilled in the art to the embodiment and the modification within the spirit and scope of the present disclosure and other aspects build by combining part of the components in the embodiment and the modification are also included in the scope of the present disclosure. 
     For example, although the directional coupler  10  according to the above embodiment includes the switch circuit  13 , the switch circuit  13  is not necessarily provided. The variable termination circuit  14  may be fixedly connected to one end of the sub-line  12  and the variable matching circuit  15 , the variable attenuator  16 , and the variable filter  17  may be fixedly connected to the other end thereof. Since the variable termination circuit  14  and at least one of the variable matching circuit  15  and the variable attenuator  16  are controlled by the control circuit  19  even in a case in which the directional coupler  10  is a unidirectional coupler that fixedly extracts one of the traveling waves and the reflected waves on the line, the directional coupler capable of achieving the stable directivity and return loss is realized. 
     Although the directional coupler  10  according to the above embodiment is provided with the variable matching circuit  15 , the variable attenuator  16 , and the variable filter  17  at the other end side of the sub-line  12 , all of these components may not be necessarily provided. With at least one of the variable matching circuit  15  and the variable attenuator  16 , the output impedance at the other end side of the sub-line  12 , which occurs in association with the adjustment of the impedance of the variable termination circuit  14 , can be adjusted using at least one of the variable matching circuit  15  and the variable attenuator  16 . 
     If at least one of the variable matching circuit  15  and the variable attenuator  16  is provided at the other end side of the sub-line  12 , the other of the variable matching circuit  15  and the variable attenuator  16  may be of a fixed type, instead of a variable type. Similarly, the variable filter is an arbitrary component and the frequency band of the variable filter may be of a fixed type. In addition, the order of connection of the variable matching circuit  15 , the variable attenuator  16 , and the variable filter  17  is not limited to the order in the above embodiment, and the variable matching circuit  15 , the variable attenuator  16 , and the variable filter  17  may be connected in an arbitrary order. 
     Although the directional coupler  10  according to the above embodiment includes the detection circuit  19   b , the detection circuit  19   b  is not necessarily provided. It is possible to generate the data to be stored in the memory  19   a , which is used for trimming of the variable termination circuit  14 , using a device that measures the impedance of the variable termination circuit  14 , which is provided separately from the directional coupler  10 . 
     Although the variable termination circuit  14  includes the switch elements for trimming and the switch elements for tuning in the directional coupler  10  according to the above embodiment, the variable termination circuit  14  may not necessarily include the switch elements for tuning. Since the impedance of the variable termination circuit  14  is adjusted by the control circuit  19  in accordance with the data stored in the memory  19   a  when the variable termination circuit  14  includes the switch elements for trimming, the variation in the directivity of the directional coupler is suppressed. In addition, the variable termination circuit  14  may include an inductor as a passive element. 
     Similarly, although the variable matching circuit  15 , the variable attenuator  16 , and the variable filter  17  include the switch elements for trimming and the switch elements for tuning in the directional coupler  10  according to the above embodiment, the variable matching circuit  15 , the variable attenuator  16 , and the variable filter  17  may not necessarily include these switch elements. Since at least one of the impedance of the variable matching circuit  15  and the attenuation of the variable attenuator  16  is adjusted by the control circuit  19  or the external circuit in association with the trimming of the variable termination circuit  14  when at least one of the variable matching circuit  15  and the variable attenuator  16  includes the switch elements for trimming or tuning, the variation in the directivity and the return loss of the directional coupler is suppressed. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is usable as the directional coupler that extracts the power of the traveling waves of the radio-frequency signal propagated on the line, particularly, as the directional coupler capable of achieving the stable directivity and return loss over the mass-produced product. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  directional coupler 
               11  main line 
               12  sub-line 
               13  switch circuit 
               13   a ,  13   b  switch element 
               14  variable termination circuit 
               14   a  to  14   f  impedance element 
               14   g  to  14   j  switch element 
               141   a  to  141   c  resistor 
               141   d  to  141   f  switch element 
               15  variable matching circuit 
               15   a  to  15   e  capacitance 
               15   f ,  15   g  inductor 
               15   h  to  15   n  switch element 
               16  variable attenuator 
               16   a  to  16   c  variable resistor 
               161   a  to  163   a  resistor 
               16   g  to  16   i ,  164   a  to  166   a  switch element 
               17  variable filter 
               17   a  to  17   f ,  171   e  to  173   e  capacitance 
               17   g  inductor 
               17   h  to  17   j ,  174   e  to  176   e  switch element 
               18  coupling port 
               19  control circuit 
               19   a  memory 
               19   a   1  to  19   a   3  electrical fuse 
               19   b  detection circuit 
               191  to  193  level shifter