Patent Publication Number: US-10784557-B2

Title: Signal processing circuit, signal processing module, and communication apparatus

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present Application is a Continuation Application of U.S. patent application Ser. No. 15/554,870 filed Aug. 31, 2017, which is a 371 National Stage Entry of International Application No. PCT/JP2016/057739, filed on Mar. 11, 2016, which in turn claims priority from Japanese Application No. 2015-065744, filed on Mar. 27, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present technology relates to a signal processing circuit, a signal processing module, and a communication apparatus, and particularly to a signal processing circuit, a signal processing module, and a communication apparatus that are capable of achieving desired coupler characteristics using a microstrip line having an arbitrary line length. 
     BACKGROUND ART 
     In a wireless communication device, a directional coupler is provided, for example, between an amplifier of a transmission signal and an antenna. The directional coupler is configured by disposing two microstrip lines constituting a coupled line on a dielectric substrate. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2013-247675 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     In order to ensure a certain level or more of coupler characteristics, a length of a transmission/reception signal wavelength λ/4 is required as the line length of the microstrip line. For example, in the case where the line width of the microstrip line is 1.6 mm and the line interval of the microstrip line is 1.0 mm, the line length needs to be not less than 30 mm depending on the characteristics of the dielectric substrate. 
     Meanwhile, along with the miniaturization of the wireless communication device, it is also desired to miniaturize the directional coupler. In order to achieve miniaturization of the directional coupler, it is necessary to reduce the line length of the microstrip line. However, even when the line length is simply reduced, it may be impossible to ensure desired coupler characteristics. 
     The present technology has been made in view of the above circumstances to make it possible to achieve desired coupler characteristics by using a microstrip line having an arbitrary line length. 
     Solution to Problem 
     A signal processing circuit according to an aspect of the present technology includes: a directional coupler having a main line as a transmission path of an RF signal and a sub-line constituting a coupled line together with the main line; a termination part including a plurality of devices connectable between a first port and ground, the first port being one of ports on both ends of the sub-line; and a control unit that switches, depending on a frequency of the RF signal, the plurality of devices of the termination part to be connected to the first port, a phase of a return signal of a signal input as a coupling signal corresponding to the RF signal to the termination part via the first port being opposite to a phase of an isolation signal supplied to a second port, the second port being the other port of the sub-line and connected to an output port of the coupling signal. 
     The control unit may switch on/off of switches provided between a plurality of capacitors of the termination part and the first port and between a plurality of resistors of the termination part and the first port. 
     The first port may be connected to the output port via a first switch, and the second port may be connected to the output port via a second switch. In this case, the signal processing circuit may further include a different termination part including a plurality of devices connectable between the second port and the ground. 
     When outputting the coupling signal corresponding to a traveling wave component of the RF signal from the output port, the control unit may turn off the first switch, turn on the second switch, and switch the plurality of devices of the termination part to be connected to the first port. 
     When outputting the coupling signal corresponding to a reflected wave component of the RF signal from the output port, the control unit may turn off the second switch, turn on the first switch, and switch the plurality of devices of the different termination part to be connected to the second port. 
     An attenuation part and a filter part may be provided between the second port and the output port, and the control unit may control paths of the coupling signal in the attenuation part and paths of the coupling signal in the filter part. 
     A path to which an inductor is connected in series and a path bypassing the inductor may be provided in parallel between the second port and the output port, and the control unit may switch paths of the coupling signal depending on the frequency of the RF signal. 
     A capacitor having one electrode connected to the ground may be provided in parallel between the second port and the output port via a switch, and the control unit may switch on/off of the switch of the capacitor depending on the frequency of the RF signal. 
     A path to which a resistor is connected in series and a path bypassing the resistor may be provided in parallel between the second port and the output port, and the control unit may switch paths of the coupling signal depending on the frequency of the RF signal. 
     The directional coupler may include a first sub-line and a second sub-line as the sub-line constituting the coupled line together with the main line, the first sub-line having the same line length as that of the main line, the second sub-line having a line length shorter than that of the main line, the termination part may be provided on a side of the first sub-line, and the termination part may be provided on a side of the second sub-line. In this case, the control unit may output the coupling signal to be transmitted through the first sub-line or the coupling signal to be transmitted through the second sub-line depending on the frequency of the RF signal. 
     The control unit may switch connection of the devices of the termination part on the side of the first sub-line to the first port and outputs the coupling signal to be transmitted through the first sub-line when the frequency of the RF signal is lower than a threshold value, and switch connection of the devices of the termination part on the side of the second sub-line to the first port and outputs the coupling signal to be transmitted through the second sub-line when the frequency of the RF signal is higher than the threshold value. 
     In an aspect of the present technology, depending on a frequency of the RF signal, the plurality of devices of the termination part to be connected to the first port is switched, a phase of a return signal of a signal input as a coupling signal corresponding to the RF signal to the termination part via the first port being opposite to a phase of an isolation signal supplied to a second port, the second port being the other port of the sub-line and connected to an output port of the coupling signal. 
     Advantageous Effects of Invention 
     In accordance with the present technology, it is possible to achieve desired coupler characteristics by using a microstrip line having an arbitrary line length. 
     It should be noted that the effect described here is not necessarily limitative and may be any effect described in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a first configuration example of a coupler module. 
         FIG. 2  is a diagram showing the directionality of a coupler. 
         FIG. 3  is a diagram showing an example of the operation of the coupler module. 
         FIG. 4  is a diagram showing an example of table information. 
         FIG. 5  is a diagram showing an example of characteristics of a CF signal and an ISO signal. 
         FIG. 6  is a diagram showing a second configuration example of the coupler module. 
         FIG. 7  is a diagram showing an example of the operation of the coupler module shown in  FIG. 6 . 
         FIG. 8  is a diagram showing another example of the operation of the coupler module shown in  FIG. 6 . 
         FIG. 9  is a diagram showing a third configuration example of the coupler module. 
         FIG. 10  is a diagram showing a fourth configuration example of the coupler module. 
         FIG. 11  is a diagram showing a fifth configuration example of the coupler module. 
         FIG. 12  is a diagram showing an example of level equalization of the CF signal. 
         FIG. 13  is a diagram showing a sixth configuration example of the coupler module. 
         FIG. 14  is a diagram showing a seventh configuration example of the coupler module. 
         FIG. 15  is a diagram showing characteristics of the CF signal and an ISO signal. 
         FIG. 16  is a diagram showing an eighth configuration example of the coupler module. 
         FIG. 17  is a diagram showing a ninth configuration example of the coupler module. 
         FIG. 18  is a circuit diagram showing a configuration example of a switch. 
         FIG. 19  is another circuit diagram showing a configuration example of the switch. 
         FIG. 20  is still another circuit diagram showing a configuration example of the switch. 
         FIG. 21  is a diagram showing an example of a structure of the coupler module. 
         FIG. 22  is a block diagram showing a configuration example of a communication apparatus. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the present technology will be described with reference to the drawings. Note that descriptions will be made in the following order.
     1. First Embodiment (example of performing adjustment of termination condition)   2. Second Embodiment (example of performing adjustment of termination condition and level adjustment of CF signal)   3. Others   

     1. First Embodiment 
     &lt;1-1. First Configuration Example of Coupler Module&gt; 
       FIG. 1  is a diagram showing a first configuration example of a coupler module  1  according to an embodiment of the present technology. 
     The coupler module  1  shown in  FIG. 1  is mainly includes a controller  11 , a coupler  21 , and a termination part  22 . The coupler  21  provided in the coupler module  1  shown in  FIG. 1  is a single directional coupler that outputs, from a coupling port, a coupling signal corresponding to the traveling wave component of an RF signal. 
     The coupler module  1  is mounted on a wireless communication apparatus together with other modules. In a module outside the coupler module  1 , various kinds of processing are performed on signals output from the coupler module  1 . 
     The controller  11  controls switching (on/off) of switches provided in respective units of the coupler module  1 . Information relating to the frequency of an RF signal input to the coupler module  1  and the like are supplied to the controller  11  from an external controller provided in the wireless communication apparatus. 
     The coupler  21  has a microstrip line  21 A that is a main line and a microstrip line  21 B that is a sub-line. The microstrip line  21 A and the microstrip line  21 B constitute a coupled line. The line lengths of the microstrip line  21 A and the microstrip line  21 B are the same. 
     The left end of the microstrip line  21 A is connected to a port P 1  that is an input port of an RF signal, and the right end of the microstrip line  21 A is connected to a port P 3  that is an output port of the RF signal. For example, an antenna is provided ahead of the port P 3 . 
     Meanwhile, both ends of the microstrip line  21 B are connected to ports P 2  and P 4 . The port P 2  is connected to an output port P 11  for a coupling signal, and the port P 4  is connected to the ground via the termination part  22 . 
       FIG. 2  is a diagram showing the directionality of the coupler  21 . 
     In the case where an RF signal is input to the port P 1 , a CF (Coupling Factor) signal, which is a coupling signal corresponding to the traveling wave component of the RF signal, is supplied to the port P 2  as indicated by an arrow A 1 . Further, as indicated by an arrow A 2 , an ISO (Isolation) signal, which is a coupling signal corresponding to the reflected wave component of the RF signal, is supplied to the port P 2 . 
     The difference between the CF signal and the ISO signal is the directivity representing the performance of the coupler  21 . The directivity needs to have a certain value or more (dB). The signal supplied to the port P 2  is output to the outside from the output port P 11 , and various kinds of processing are performed on the output signal, in the circuit in the subsequent stage. 
     A switch  23  connected to the ground is connected to a contact a between the port P 2  and the output port P 11  shown in  FIG. 1 . 
     The termination part  22  connected to the port P 4  includes a plurality of passive devices. In  FIG. 1 , resistors  32 - 1  and  32 - 2  and capacitors  32 - 3  and  32 - 4  are shown. 
     The resistor  32 - 1  is connected to the port P 4  via a switch  31 - 1 , and the resistor  32 - 2  is connected to the port P 4  via a switch  31 - 2 . The capacitor  32 - 3  is connected to the port P 4  via a switch  31 - 3 , and the capacitor  32 - 4  is connected to the port P 4  via a switch  31 - 4 . The switches  31 - 1  to  31 - 4  are each formed of a FET (Field Effect Transistor), for example. The respective sides of the resistors  32 - 1  and  32 - 2  and the capacitors  32 - 3  and  32 - 4  opposite to the switches are connected to the ground. 
     As described above, a plurality of resistors and a plurality of capacitors are connected in parallel to the port P 4  via switches. Although only four devices are shown in the example shown in  FIG. 1 , five or more devices may be provided in the termination part  22 . 
       FIG. 3  is a diagram showing an example of the operation of the coupler module  1 . 
     In the case where an RF signal is input to the port P 1 , the controller  11  controls the termination part  22  to connect a predetermined device of the termination part  22  to the port P 4 . As a result, at least one of the termination resistor and the termination capacitor on the port P 4  side changes. In the example shown in  FIG. 3 , the switch  31 - 3  is turned on and the capacitor  32 - 3  is connected to the port P 4 . 
     Which device of the termination part  22  is to be connected to the port P 4  is determined by the frequency of the RF signal. The controller  11  has table information representing combinations of the frequency of the RF signal and the device of the termination part  22  to be connected to the port P 4 . The table information is stored in a memory in the controller  11 , for example. 
       FIG. 4  is a diagram showing an example of the table information. 
     In the example shown in  FIG. 4 , in the case where the frequency of the RF signal is a frequency f 1 , only a resistor R 1  (resistor  32 - 1 ) is connected to the port P 4 . Further, in the case where the frequency of the RF signal is a frequency f 2 , the resistor R 1  and a capacitor C 1  (capacitor  32 - 3 ) are connected to the port P 4 . In the case where the frequency of the RF signal is a frequency f 3 , only a resistor R 2  (resistor  32 - 2 ) is connected to the port P 4 . In the case where the frequency of the RF signal is a frequency f 4 , the resistor R 2  and a capacitor C 2  (capacitor  32 - 4 ) are connected to the port P 4 . 
     As described above, the termination condition (the termination resistor and the termination capacitor) of the port P 4  is switched depending on the frequency of the RF signal. The termination condition of the port P 4  represents that the phase of a return signal of the signal supplied to the port P 4  becomes opposite to the phase of an ISO signal in response to the input of the RF signal as indicated by an arrow A 3  in  FIG. 3 . 
     That is, the controller  11  has in advance information on the termination condition in which the phase of the return signal becomes opposite to the phase of the ISO signal, for each frequency of the RF signal, and causes the termination part  22  to operate on the basis of the information. 
     As the phase of the return signal becomes opposite to the phase of the ISO signal, the ISO signal is canceled by the return signal. 
       FIG. 5  is a diagram showing an example of characteristics of the CF signal and the ISO signal. 
     A curve L 1  shows the characteristics of the CF signal and a curve L 2  shows the characteristics of the ISO signal. The horizontal axis shows the frequency and the vertical axis shows dB. 
     For example, in the case where the frequency of the RF signal is 2.3 GHz, by optimizing the termination condition and generating an attenuation pole of the ISO signal in the vicinity of 2.3 GHz, it is possible to increase the difference between the CF signal and the ISO signal indicated by an outlined arrow, i.e., directivity. The attenuation pole of the ISO signal is generated by canceling the ISO signal by the return signal. 
     As described above, by optimizing the termination condition depending on the frequency of the RF signal, it is possible to improve the directivity. 
     Since the attenuation pole of the ISO signal can be generated at a position of an arbitrary frequency, it is possible to realize a broadband module capable of handling RF signals of various frequencies. 
     Further, by generating the attenuation pole of the ISO signal at a position of an arbitrary frequency, it is possible to improve the directivity regardless of the line length of the microstrip lines  21 A and  21 B. That is, it is possible to achieve desired coupler characteristics even with an arbitrary line length without requiring the line length of the wavelength λ/4 generally required for coupler design. 
     Because it is possible to achieve desired coupler characteristics even in the case where the line lengths of the microstrip lines  21 A and  21 B are each set to an arbitrary length, e.g., not more than 20 mm, it is possible to achieve miniaturization of the entire coupler module  1 . 
     &lt;1-2. Second Configuration Example of Coupler Module&gt; 
       FIG. 6  is a diagram showing a second configuration example of the coupler module  1 . 
     In the configuration shown in  FIG. 6 , the same reference symbols are given to the same components as those shown in  FIG. 1 . Overlapping explanations are omitted as appropriate. The same applies to  FIG. 7  and subsequent figures. 
     The coupler  21  provided in the coupler module  1  shown in  FIG. 6  is a dual directional coupler capable of outputting a coupling signal corresponding to the traveling wave component of the RF signal and a coupling signal corresponding to the reflected wave component. In the case of outputting a coupling signal corresponding to the traveling wave component, the CF signal and the ISO signal are supplied to the port P 2  (forward (FWD)). Meanwhile, in the case of outputting a coupling signal corresponding to the reflected wave component, the CF signal and the ISO signal are supplied to the port P 4  (reverse (REV)). 
     The port P 4  is connected to the output port P 11  via a switch  41 A. A termination part  22 A is connected to a contact b between the port P 4  and the switch  41 A. 
     The configuration of the termination part  22 A is similar to that of the termination part  22  shown in  FIG. 1 . A resistor  32 - 1 A is connected to the contact b via a switch  31 - 1 A, and a resistor  32 - 2 A is connected to the contact b via a switch  31 - 2 A. A capacitor  32 - 3 A is connected to the contact b via a switch  31 - 3 A, and a capacitor  32 - 4 A is connected to the contact b via a switch  31 - 4 A. The respective sides of the resistors  32 - 1 A and  32 - 2 A and the capacitors  32 - 3 A and  32 - 4 A opposite to the switches are connected to the ground. 
     Meanwhile, the port P 2  is connected to the output port P 11  via a switch  41 B. A termination part  22 B is connected to a contact c between the port P 4  and the switch  41 A. 
     The configuration of the termination part  22 B is also similar to that of the termination part  22 . A resistor  32 - 1 B is connected to the contact c via a switch  31 - 1 B, and a resistor  32 - 2 B is connected to the contact c via a switch  31 - 2 B. A capacitor  32 - 3 B is connected to the contact c via a switch  31 - 3 B and a capacitor  32 - 4 B is connected to the contact c via a switch  31 - 4 B. The respective sides of the resistors  32 - 1 B and  32 - 2 B and the capacitors  32 - 3 B and  32 - 4 B opposite to the switches are connected to the ground. 
       FIG. 7  is a diagram showing an example of the operation of the coupler module  1  in the case of outputting a coupling signal corresponding to the traveling wave component of the RF signal. 
     In this case, the controller  11  turns off the switch  41 A and turns on the switch  41 B. A CF signal, which is a coupling signal corresponding to the traveling wave component of the RF signal, is supplied to the port P 2  as indicated by the arrow A 1 , and an ISO signal, which is a coupling signal corresponding to the reflected wave component, is transmitted to the port P 2  as indicated by the arrow A 2 . 
     Further, the controller  11  controls the termination part  22 A provided on the opposite side to the port P 2  as the port to which the coupling signal is to be supplied, and connects a predetermined device of the termination part  22 A to the port P 4 . In the example shown in  FIG. 7 , the switch  31 - 3 A is turned on and the capacitor  32 - 3 A is connected to the port P 4 . 
     The controller  11  has in advance information on the termination condition for each frequency of the RF signal in which the phase of the return signal becomes opposite to the phase of the ISO signal for the case of outputting a coupling signal corresponding to the traveling wave component of the RF signal and the case of outputting a coupling signal corresponding to the reflected wave component. The controller  11  controls the termination part  22 A or the termination part  22 B on the basis of the information that the controller  11  has in advance. 
     By switching the termination condition of the port P 4  depending on the frequency of the RF signal, the phase of the return signal of the signal supplied to the port P 4  in response to the input of the RF signal becomes opposite to the phase of the ISO signal, as indicated by the arrow A 3 . 
     As described above, by optimizing the termination condition on the port P 4  side depending on the frequency of the RF signal, it is possible to improve the directivity in the case of outputting a coupling signal corresponding to the traveling wave component of the RF signal. 
       FIG. 8  is a diagram showing another example of the operation of the coupler module  1  in the case of outputting a coupling signal corresponding to a reflected wave component of an RF signal. 
     In this case, the controller  11  turns on the switch  41 A and turns off the switch  41 B. A CF signal, which is a coupling signal corresponding to the reflected wave component of the RF signal, is supplied to the port P 4  as indicated by an arrow A 11 , and an ISO signal, which is a coupling signal corresponding to the traveling wave component, is transmitted to the port P 4  as indicated by an arrow A 12 . 
     Further, the controller  11  controls the termination part  22 B provided on the opposite side to the port P 4  as the port to which a coupling signal is to be supplied, and connects a predetermined device of the termination part  22 B to the port P 2 . In the example shown in  FIG. 8 , the switch  31 - 4 B is turned on and the capacitor  32 - 4 B is connected to the port P 2 . 
     By switching the termination condition of the port P 2  depending on the frequency of the RF signal, the phase of the return signal of the signal supplied to the port P 2  in response to the input of the RF signal becomes opposite to the phase of the ISO signal, as indicated by an arrow A 13 . 
     As described above, by optimizing the termination condition on the port P 2  side depending on the frequency of the RF signal, it is possible to improve the directivity in the case of outputting a coupling signal corresponding to the reflected wave component of the RF signal. 
     &lt;1-3. Third Configuration Example of Coupler Module&gt; 
       FIG. 9  is a diagram showing a third configuration example of the coupler module  1 . 
     The coupler  21  provided in the coupler module  1  shown in  FIG. 9  is a dual directional coupler. In the coupler module  1  shown in  FIG. 9 , processing is performed by sharing one termination part for the case of outputting a coupling signal corresponding to the traveling wave component of the RF signal and the case of outputting a coupling signal corresponding to the reflected wave component. 
     On the port P 4  side, a switch  51 A is provided between the contact b and the termination part  22 . Meanwhile, on the port P 2  side, a switch  51 B is provided between the contact c and the termination part  22 . 
     In the case of outputting a coupling signal corresponding to the traveling wave component of the RF signal, the controller  11  turns off the switch  41 A and turns on the switch  41 B. Further, the controller  11  turns on the switch  51 A and turns off the switch  51 B. A CF signal, which is a coupling signal corresponding to the traveling wave component of the RF signal, and an ISO signal, which is a coupling signal corresponding to the reflected wave component, are supplied to the port P 2 . 
     The controller  11  controls the termination part  22  to switch the termination condition on the port P 4  side depending on the frequency of the RF signal. By switching the termination condition of the port P 4 , the phase of the return signal of the signal supplied to the port P 4  becomes opposite to the phase of the ISO signal. 
     Meanwhile, in the case of outputting a coupling signal corresponding to the reflected wave component of the RF signal, the controller  11  turns on the switch  41 A and turns off the switch  41 B. Further, the controller  11  turns off the switch  51 A and turns on the switch  51 B. A CF signal, which is a coupling signal corresponding to the reflected wave component of the RF signal, and an ISO signal, which is a coupling signal corresponding to the traveling wave component, are supplied to the port P 4 . 
     The controller  11  controls the termination part  22  to switch the termination condition on the port P 2  side depending on the frequency of the RF signal. By switching the termination condition of the port P 2 , the phase of the return signal of the signal supplied to the port P 2  becomes opposite to the phase of the ISO signal. 
     As described above, by using one termination part in common for the case of outputting a coupling signal corresponding to the traveling wave component of the RF signal and the case of outputting the coupling signal corresponding to the reflected wave component, it is possible to reduce the size of the circuit. 
     &lt;1-4. Fourth Configuration Example of Coupler Module&gt; 
       FIG. 10  is a diagram showing a fourth configuration example of the coupler module  1 . 
     The coupler  21  provided in the coupler module  1  shown in  FIG. 10  is a dual directional coupler. A filter part  61  and an attenuation part  62  are provided between the output port P 11  and a contact d on the output side of the switch  41 A and the switch  41 B. 
     The filter part  61  has three paths connected in parallel. An inductor  71  is provided in the upper stage path, and a capacitor  73  is provided between a switch  72  and a switch  74  in the middle stage path. On the input side of the capacitor  73 , a capacitor  75  having one electrode connected to the ground is provided. On the output side of the capacitor  73 , a capacitor  76  having one electrode connected to the ground is provided. In the lower stage path, a capacitor  78  is provided between a switch  77  and a switch  79 . 
     The attenuation part  62  has two paths connected in parallel. A capacitor  83  connected to the ground is provided between a switch  81  and a switch  82  in the upper stage path. In the lower stage path, an attenuator  85  is provided between a switch  84  and a switch  86 . 
     The controller  11  controls on/off of the switches  41 A and  41 B and the termination conditions of the ports P 2  and P 4  as described with reference to FIGS.  6  to  8 . Further, the controller  11  controls the impedance of the preceding stage of the output port P 11  by switching the paths of the filter part  61  through which the CF signal is transmitted and switching the paths of the attenuation part  62  through which the CF signal is transmitted. As a result, the controller  11  is capable of further optimizing the directivity. 
     It is also possible to provide the coupler  21  as a single directional coupler and to provide the filter part  61  and the attenuation part  62  between the coupler  21  and the output port P 11 . 
     2. Second Embodiment 
     Next, a coupler module provided with a circuit configuration for equalizing the level (power) of the CF signal in each frequency band will be described. 
     &lt;2-1. Fifth Configuration Example of Coupler Module&gt; 
       FIG. 11  is a diagram showing a fifth configuration example of the coupler module  1 . 
     The coupler  21  provided in the coupler module  1  shown in  FIG. 11  is a single directional coupler. Between the coupler  21  and the output port P 11 , there are provided an upper stage path provided with a switch  101  and a lower stage path provided with an inductor  103  between a switch  102  and a switch  104 . 
     For example, in the case where the frequency of the CF signal is lower than a threshold value (the CF signal is a low band signal), the controller  11  turns on the switch  101  and turns off the switch  102  and the switch  104 . The CF signal is transmitted through the upper stage path bypassing the inductor  103 , and output from the output port P 11 . 
     Meanwhile, in the case where the frequency of the CF signal is higher than the threshold value (the CF signal is a high band signal), the controller  11  turns off the switch  101  and turns on the switch  102  and the switch  104 . The CF signal is transmitted through the lower stage path to which the inductor  103  is connected in series, and output from the output port P 11 . 
     By using a path to which an inductor is connected in series as a transmission path of the CF signal, it is possible to reduce the level of the high band CF signal to close to the level of the low band CF signal. 
     By providing a plurality of paths having different loads and switching the transmission path depending on the frequency of the CF signal, it is possible to equalize the level of the CF signal in each frequency band. 
       FIG. 12  is a diagram showing an example of level equalization of the CF signal. 
     In the case where the level of the CF signal is raised as indicated by an outlined arrow on the graph on the left side by, for example, adjusting the characteristics of the coupler  21 , the level of the CF signal rises over the entire frequency band. The coupling degree of the coupler  21  is higher as the frequency of the RF signal is higher. Therefore, the higher the frequency of the RF signal is, the higher the level of the CF signal is. 
     As shown in the graph on the right side of  FIG. 12 , by lowering the level of the CF signal for each frequency band by, for example, switching the path, it is possible to achieve level equalization of the CF signal. In the case of the example shown in  FIG. 12 , although there is a difference of 5 dB between the low band CF signal and the high band CF signal, it is adjusted so as to be within a difference of 2 dB. 
     As described above, the level equalization of the CF signal may make signal processing in a circuit provided at the subsequent stage of the coupler module  1  easy. 
     &lt;2-2. Sixth Configuration Example of Coupler Module&gt; 
       FIG. 13  is a diagram showing a sixth configuration example of the coupler module  1 . 
     Between the coupler  21  of the coupler module  1  and the output port P 11  shown in  FIG. 13 , a capacitor  112  having one electrode connected to the ground is provided in parallel via a switch  111 . The other configuration is similar to the configuration shown in  FIG. 11 . 
     For example, in the case where the frequency of the CF signal is lower than a threshold value, the controller  11  turns off the switch  111 . Meanwhile, in the case where the frequency of the CF signal is higher than the threshold value, the controller  11  turns on the switch  111 . 
     Also by providing a capacitor in parallel as shown in  FIG. 13 , it is possible to equalize the level of the CF signal for each frequency band. 
     &lt;2-3. Seventh Configuration Example of Coupler Module&gt; 
       FIG. 14  is a diagram showing a seventh configuration example of the coupler module  1 . 
     The configuration of the coupler module  1  shown in  FIG. 14  is different from the configuration shown in  FIG. 11  in that a resistor  123  is provided instead of the inductor  103 . 
     That is, between the coupler  21  and the output port P 11 , there are provided an upper stage path provided with a switch  121  and a lower stage path provided with the resistor  123  between a switch  122  and a switch  124 . 
     For example, in the case where the frequency of the CF signal is lower than a threshold value, the controller  11  turns on the switch  121  and turns off the switch  122  and the switch  124 . The CF signal is transmitted through the upper stage path bypassing the resistor  123 , and output from the output port P 11 . 
     Meanwhile, in the case where the frequency of the CF signal is higher than the threshold value, the controller  11  turns off the switch  121  and turns on the switch  122  and the switch  124 . The CF signal is transmitted through the lower stage path to which the resistor  123  is connected in series, and output from the output port P 11 . 
     By using the path to which the resistor  123  is connected in series as the transmission path of the CF signal, it is possible to lower the level of the high band CF signal to close to the level of the low band CF signal. 
     In the examples shown in  FIGS. 11, 13, and 14 , although the coupler  21  provided in the coupler module  1  is a single directional coupler, the coupler  21  may be a dual directional coupler. 
       FIG. 15  is a diagram showing an example of characteristics of the CF signal and the ISO signal whose levels are equalized. 
     Part A of  FIG. 15  is a diagram showing the characteristics in the case where the configuration shown in  FIG. 13  in which a capacitor is provided in parallel at the front stage of the output port P 11  is employed. A curve L 11  shows the characteristics of the CF signal and a curve L 12  shows the characteristics of the ISO signal. The difference between the levels of the high band side and the low band side in the level of the CF signal shown by the curve L 11  is smaller than that in the level of the CF signal shown by the curve L 1  shown in  FIG. 5 . 
     Part B of  FIG. 15  is a diagram showing the characteristics in the case where the configuration shown in  FIG. 14  in which a resistor is provided in series at the front stage of the output port P 11  is employed. A curve L 21  shows the characteristics of the CF signal and a curve L 22  shows the characteristics of the ISO signal. Also the difference between the levels of the high band side and the low band side in the level of the CF signal shown by the curve L 21  is smaller than that in the level of the CF signal shown by the curve L 1  shown in  FIG. 5 . 
     &lt;2-4. Eighth Configuration Example of Coupler Module&gt; 
       FIG. 16  is a diagram showing an eighth configuration example of the coupler module  1 . 
     The coupler module  1  shown in  FIG. 16  adjusts the level of the CF signal without using passive devices. 
     The configuration on the upper side of  FIG. 16  connected to the port P 2  and the port P 4  of the microstrip line  21 B is the same as the configuration described with reference to  FIG. 1  except that the switch  41 A is provided on the port P 4  side and the switch  41 B is provided on the port P 2  side. In the example shown in  FIG. 16 , the same configuration as the upper configuration is provided on the lower side with the coupler  21  disposed therebetween. 
     The coupler  21  is provided with a microstrip line  21 C in addition to the microstrip line  21 B, as a sub-line with the microstrip line  21 A as a main line. The microstrip line  21 A and the microstrip line  21 C also constitute a coupled line. The line length of the microstrip line  21 C is shorter than the line length of the microstrip line  21 A. 
     As described above, the coupling degree of the coupler  21  is higher as the frequency of the RF signal is higher. In the case where assumption is made that the line length of the main line and the line length of the sub-line are fixed, the higher the frequency of the RF signal is, the higher the level of the CF signal is. Meanwhile, in the case where assumption is made that the frequency of the RF signal is fixed, the level of the CF signal flowing through the sub-line having the same line length as that of the main line is higher than the level of the CF signal flowing through the sub-line having a line length shorter than the main line. 
     The coupler module  1  shown in  FIG. 16  adjusts the level of the CF signal by switching the configuration used for signal processing depending on the frequency of the RF signal. That is, the configuration on the upper side connected to the microstrip line  21 B having the same line length as that of the microstrip line  21 A is used in the case where the RF signal is a low band signal. The configuration on the lower side connected to the microstrip line  21 C having a line length shorter than that of the microstrip line  21 A is used when the RF signal is a high band signal. 
     Ports P 5  and P 6  are connected to both ends of the microstrip line  21 C. The port P 5  is connected to an output port P 12  via a switch  131 B, and the port P 6  is connected to an output port P 12  via a switch  131 A. The output port P 11  and the output port P 12  may be the same port. 
     A termination part  132  is connected to a contact e between the port P 6  and the switch  131 A. The configuration of the termination part  132  is also similar to that of the termination part  22  shown in  FIG. 1 , for example. A resistor  152 - 1  is connected to the contact e via a switch  151 - 1 , and a resistor  152 - 2  is connected to the contact e via a switch  151 - 2 . A capacitor  152 - 3  is connected to the contact e via a switch  151 - 3 , and a capacitor  152 - 4  is connected to the contact e via a switch  151 - 4 . The respective sides of the resistors  152 - 1  and  152 - 2  and the capacitors  152 - 3  and  152 - 4  opposite to the switches are connected to the ground. 
     A switch  133  having one electrode connected to the ground is connected to a contact f on the path between the ports P 5  and P 6  and the output port P 12 . 
     For example, in the case where the frequency of the CF signal is lower than a threshold value, the controller  11  turns off the upper switch  41 A, turns on the upper switch  41 B, and turns off the lower switches  131 A and  131 B. The controller  11  switches the termination condition of the port P 4  by controlling the termination part  22 , and outputs a low band CF signal. 
     Meanwhile, in the case where the frequency of the CF signal is higher than the threshold value, the controller  11  turns off the upper switches  41 A and  41 B, turns off the lower switch  131 A, and turns on the lower switch  131 B. The controller  11  switches the termination condition of the port P 6  by controlling the termination part  132 , and outputs a high band CF signal. 
     Accordingly, even in the case where the frequency of the RF signal is high, it is possible to output, from the output port P 12 , a CF signal having a level close to the CF signal output from the output port P 11  when the frequency of the RF signal is low. In the case where the level of the CF signal is adjusted by using a device, although the loss between the port P 1  and the port P 3  becomes large, it is possible to suppress such loss. 
     The coupler  21  shown in  FIG. 16  can also be a dual directional coupler. 
     3. Others 
       FIG. 17  is a diagram showing an eighth configuration example of the coupler module  1 . 
     As shown in  FIG. 17 , it is also possible to provide a resistor  161  and a switch  162  connected in series between the port P 2  and the port P 4  of the coupler  21 . By switching on/off of the switch  162 , the controller  11  is capable of further adjusting the termination condition by the amount corresponding to the resistor  161 . 
     &lt;3-1. Configuration Example of Switch&gt; 
       FIG. 18  is a circuit diagram showing a configuration example of a switch. 
     Although each switch provided in the coupler module  1  is a simple switch shown in Part A of  FIG. 18  in the above description, it is also possible to employ the configuration shown in Part B of  FIG. 18 . The switch shown in Part B of  FIG. 18  has a configuration in which a resistor is connected to a gate terminal of a FET. 
     It is also possible to connect a plurality of switches shown in Part B of  FIG. 18  in series as shown in Part C of  FIG. 18 . Increasing the number of stages of the switch makes it possible to enhance the resistance to electrostatic discharge (ESD: Electro Static Discharge). The configuration shown in Part C of  FIG. 18  can be used for any of the switch connected in series and the switch connected in shunt. 
       FIG. 19  is another circuit diagram showing a configuration example of the switch. 
     Each of the above-described switches can be realized by a circuit configuration as shown in  FIG. 19 . 
     The switch circuit shown in  FIG. 19  has a structure in which two FETs  11  and  12  are connected in series to a signal path (signal input terminal to signal output terminal) and a FET  13  is connected in shunt from a connection midpoint between the FET  11  and the FET  12 . The FET  11  and the FET  12  are simultaneously turned on or off by control voltage applied to a control terminal CTL 1 . The FET  13  is turned on or off complementarily to the FET  11  and the FET  12  by control voltage applied to a control terminal CTL  2 . 
       FIG. 20  is still another circuit diagram showing a configuration example of the switch. In the configuration shown in  FIG. 20 , the same reference symbols are given to the same components as those shown in  FIG. 19 . 
     In the example shown in  FIG. 20 , a resistor R 4  is provided between a source terminal of the FET  11  and a ground GND, and a resistor R 5  is provided between a drain terminal of the FET  11  and the ground GND. Further, the resistor R 5  is provided between a source terminal of the FET  12  and the ground GND, and the resistor R 6  is provided between a drain terminal of the FET  12  and the ground GND. The resistors R 4 , R 5 , and R 6  are resistors for biasing. By keeping the drain region and the source region of each FET at the same potential as the ground GND, there is no need to externally apply bias to the drain region and the source region, and the mounting area can be reduced. 
     It is also possible to mount each switch in the form of an SOI (Silicon On Insulator) in which a silicon layer is formed on an insulating layer. 
     &lt;3-2. Module Structure&gt; 
       FIG. 21  is a diagram showing an example of the structure of the coupler module  1 . 
     It is possible not only to mount the configuration of the coupler module  1  shown in  FIG. 1  and the like on a single substrate but also to divide it into a ceramic substrate  201  and an IC chip  202  and mount the ceramic substrate  201  and the IC chip  202  as shown in Part A of  FIG. 21 . The IC chip  202  is formed by disposing various devices on a silicon substrate. 
     For example, in the configuration shown in  FIG. 1 , the coupler  21  is mounted on the ceramic substrate  201 , and the termination part  22  is mounted on the ceramic substrate  201 . The combination of the configuration mounted on the ceramic substrate  201  and the configuration mounted on the IC chip  202  can be arbitrarily set. For example, the coupler module  1  is obtained by laminating and arranging the IC chip  202  on the ceramic substrate  201 . 
     Further, it is also possible to mount all the configurations of the coupler module  1  on the IC chip  202  as shown in Part B of  FIG. 21 . 
     By providing a coupler, each switch, a termination part, and the like in the IC chip  202 , it is possible to reduce the number of parts. 
     &lt;3-3. Example of Communication Apparatus&gt; 
       FIG. 22  is a block diagram showing a configuration example of a communication apparatus on which the coupler module  1  is mounted. 
     A CPU (Central Processing Unit)  301 , a ROM (Read Only Memory)  302 , and a RAM (Random Access Memory)  303  are connected to each other via a bus  304 . 
     Further, an input/output interface  305  is connected to the bus  304 . An input unit  306  including a keyboard, a mouse, and the like, and an output unit  307  including a display, a speaker, and the like are connected to the input/output interface  305 . Further, to the input/output interface  305 , a storage unit  308  including a hard disk or a non-volatile memory, a communication unit  309  that is a wireless communication module, and a drive  310  for driving a removable medium  311  are connected. 
     An antenna  309 A is provided in the communication unit  309 . The coupler module  1  is provided inside the communication unit  309  so as to be connected to the antenna  309 A. 
     &lt;3-3. Others&gt; 
     Although the controller  11  is provided inside the coupler module  1  in the above description, but it may be provided outside the coupler module  1 . 
     Although the number of couplers provided in the coupler module  1  is one, it is also possible to provide a plurality of couplers. The plurality of couplers may be any of a single directional coupler and a dual directional coupler. 
     The combination of the configurations can be arbitrarily set. For example, it is also possible to provide the filter part  61  and the attenuation part  62  shown in  FIG. 10  in the coupler module  1  having another configuration such as those shown in  FIG. 1 ,  FIG. 6 , and the like. It is also possible to provide the configuration used for adjusting the level of the CF signal at the front stage of the output port P 11  shown in  FIG. 11 ,  FIG. 13 , and  FIG. 14  in the coupler module  1  having another configuration. 
     Embodiments of the present technology are not limited to the above-mentioned embodiments and examples, and various modifications can be made without departing from the essence of the present technology. 
     The effects described herein are merely examples and not limited, and another effect may be exerted. 
     Combination Example of Configurations 
     It should be noted that the present technology may take the following configurations. 
     (1) 
     A signal processing circuit, including: 
     a directional coupler having a main line as a transmission path of an RF signal and a sub-line constituting a coupled line together with the main line; 
     a termination part including a plurality of devices connectable between a first port and ground, the first port being one of ports on both ends of the sub-line; and 
     a control unit that switches, depending on a frequency of the RF signal, the plurality of devices of the termination part to be connected to the first port, a phase of a return signal of a signal input as a coupling signal corresponding to the RF signal to the termination part via the first port being opposite to a phase of an isolation signal supplied to a second port, the second port being the other port of the sub-line and connected to an output port of the coupling signal. 
     (2) 
     The signal processing circuit according to (1) above, in which 
     the control unit switches on/off of switches provided between a plurality of capacitors of the termination part and the first port and between a plurality of resistors of the termination part and the first port. 
     (3) 
     The signal processing circuit according to (1) or (2) above, further including 
     a different termination part including a plurality of devices connectable between the second port and the ground, wherein 
     the first port is connected to the output port via a first switch, and 
     the second port is connected to the output port via a second switch. 
     (4) 
     The signal processing circuit according to (3) above, in which 
     when outputting the coupling signal corresponding to a traveling wave component of the RF signal from the output port, the control unit turns off the first switch, turns on the second switch, and switches the plurality of devices of the termination part to be connected to the first port. 
     (5) 
     The signal processing circuit according to (3) above, in which 
     when outputting the coupling signal corresponding to a reflected wave component of the RF signal from the output port, the control unit turns off the second switch, turns on the first switch, and switches the plurality of devices of the different termination part to be connected to the second port. 
     (6) 
     The signal processing circuit according to any one of (1) to (5) above, in which 
     an attenuation part and a filter part are provided between the second port and the output port, and 
     the control unit controls paths of the coupling signal in the attenuation part and paths of the coupling signal in the filter part. 
     (7) 
     The signal processing circuit according to any one of (1) to (5) above, in which 
     a path to which an inductor is connected in series and a path bypassing the inductor are provided in parallel between the second port and the output port, and 
     the control unit switches paths of the coupling signal depending on the frequency of the RF signal. 
     (8) 
     The signal processing circuit according to any one of (1) to (5) above, in which 
     a capacitor having one electrode connected to the ground is provided in parallel between the second port and the output port via a switch, and 
     the control unit switches on/off of the switch of the capacitor depending on the frequency of the RF signal. 
     (9) 
     The signal processing circuit according to any one of (1) to (5) above, in which 
     a path to which a resistor is connected in series and a path bypassing the resistor are provided in parallel between the second port and the output port, and 
     the control unit switches paths of the coupling signal depending on the frequency of the RF signal. 
     (10) 
     The signal processing circuit according to any one of (1) to (9) above, in which 
     the directional coupler includes a first sub-line and a second sub-line as the sub-line constituting the coupled line together with the main line, the first sub-line having the same line length as that of the main line, the second sub-line having a line length shorter than that of the main line, 
     the termination part is provided on a side of the first sub-line, and the termination part is provided on a side of the second sub-line, and 
     the control unit outputs the coupling signal to be transmitted through the first sub-line or the coupling signal to be transmitted through the second sub-line depending on the frequency of the RF signal. 
     (11) 
     The signal processing circuit according to (10) above, in which 
     the control unit
         switches connection of the devices of the termination part on the side of the first sub-line to the first port and outputs the coupling signal to be transmitted through the first sub-line when the frequency of the RF signal is lower than a threshold value, and   switches connection of the devices of the termination part on the side of the second sub-line to the first port and outputs the coupling signal to be transmitted through the second sub-line when the frequency of the RF signal is higher than the threshold value.       

     (12) 
     A signal processing module, including: 
     a directional coupler having a main line as a transmission path of an RF signal and a sub-line constituting a coupled line together with the main line; 
     a termination part including a plurality of devices connectable between a first port and ground, the first port being one of ports on both ends of the sub-line; and 
     a control unit that switches, depending on a frequency of the RF signal, the plurality of devices of the termination part to be connected to the first port, a phase of a return signal of a signal input as a coupling signal corresponding to the RF signal to the termination part via the first port being opposite to a phase of an isolation signal supplied to a second port, the second port being the other port of the sub-line and connected to an output port of the coupling signal. 
     (13) 
     A communication apparatus, including: 
     a signal processing module mounted on the communication apparatus, the signal processing module including
         a directional coupler having a main line as a transmission path of an RF signal and a sub-line constituting a coupled line together with the main line,   a termination part including a plurality of devices connectable between a first port and ground, the first port being one of ports on both ends of the sub-line, and   a control unit that switches, depending on a frequency of the RF signal, the plurality of devices of the termination part to be connected to the first port, a phase of a return signal of a signal input as a coupling signal corresponding to the RF signal to the termination part via the first port being opposite to a phase of an isolation signal supplied to a second port, the second port being the other port of the sub-line and connected to an output port of the coupling signal.       

     REFERENCE SIGNS LIST 
     
         
         
           
               1  coupler module 
               11  controller 
               21  coupler 
               22  termination part