Patent Publication Number: US-2023134242-A1

Title: Differential amplifying apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2021-179219 filed on Nov. 2, 2021. The content of this application is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present disclosure relates to a differential amplifying apparatus. 
     2. Description of the Related Art 
     A differential amplifying apparatus used as a power amplifying apparatus for wireless communication or the like has been known (for example, Japanese Unexamined Patent Application Publication No. 2014-155171). The differential amplifying apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2014-155171 includes an amplifier circuit for a low power mode (hereinafter referred to as LPM) and an amplifier circuit for a high power mode (hereinafter referred to as HPM). The amplifier circuit for LPM and the amplifier circuit for HPM are switched and used according to the power mode. 
     However, according to Japanese Unexamined Patent Application Publication No. 2014-155171, the amplifier circuit for LPM is required in addition to the amplifier circuit for HPM, and it is difficult to reduce the size of the differential amplifying apparatus. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     The present disclosure has been made in view of the above, and it is a possible benefit of the present disclosure to provide a differential amplifying apparatus capable of switching power modes and realizing miniaturization of the apparatus. 
     According to an aspect of the present disclosure, in order to solve above-described problems and achieve the possible benefit, there is provided a differential amplifying apparatus including: an input terminal; an input balun to which a signal inputted to the input terminal is input; an output terminal; an output balun that outputs a signal to the output terminal; first and second amplifiers provided in parallel between the input balun and the output balun and configured to output a differential signal; a first diode provided between a reference potential and a path between the input balun and the first amplifier; a second diode provided between a reference potential and a path between the input balun and the second amplifier; and a bias circuit that applies a bias to the first diode and the second diode, in which a cathode of the first diode and a cathode of the second diode are connected to the reference potential. 
     According to the present disclosure, it is possible to realize miniaturization of a differential amplifying apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating an example of a differential amplifying apparatus according to a first embodiment of the present disclosure; 
         FIG.  2    is a diagram focusing on an input matching circuit, an amplifier, and the like according to the first embodiment of the present disclosure; 
         FIG.  3    is a diagram illustrating an example of a differential amplifying apparatus according to a second embodiment of the present disclosure; 
         FIG.  4    is a diagram illustrating an example of a differential amplifying apparatus according to a third embodiment of the present disclosure; 
         FIG.  5    is a diagram illustrating an example of a differential amplifying apparatus according to a fourth embodiment of the present disclosure; 
         FIG.  6    is a diagram illustrating an example of a differential amplifying apparatus according to a fifth embodiment of the present disclosure; 
         FIG.  7    is a diagram illustrating an example of a differential amplifying apparatus according to a sixth embodiment of the present disclosure; and 
         FIG.  8    is a diagram illustrating an example of a differential amplifying apparatus according to a seventh embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description of each embodiment, the same reference numerals are given to the same or equivalent components as those in other embodiments, and the description thereof will be simplified or omitted. The present disclosure is not limited to the embodiments. The constituent elements of each of the embodiments include those that can be easily replaced by a person skilled in the art or those that are substantially the same. Note that the configurations described below can be combined as appropriate. In addition, the configuration can be omitted, replaced, or changed without departing from the gist of the disclosure. 
     First Embodiment 
     Configuration 
       FIG.  1    is a diagram illustrating an example of a differential amplifying apparatus according to a first embodiment of the present disclosure. A differential amplifying apparatus  1  illustrated in  FIG.  1    includes an input terminal  201 , an input matching circuit MN 1 , an amplifier  11  serving as a first amplifier and an amplifier  12  serving as a second amplifier that form a differential amplifier circuit, an output matching circuit MN 2 , and an output terminal  202 . The input matching circuit MN 1  includes a capacitor  30 , an inductor  111 , and an inductor  112 . The output matching circuit MN 2  includes an inductor  121 , an inductor  122 , and a matching circuit  200 . 
     One end of the capacitor  30  is connected to the input terminal  201 . The other end of the capacitor  30  is connected to one end of the inductor  111 . The capacitor  30  is a capacitor for cutting a direct current. The other end of the inductor  111  is connected to a reference potential. The reference potential is exemplified by a ground potential, but the present disclosure is not limited thereto. The same applies to the following description. Note that although the capacitor  30  is provided on the side of the amplifiers  11  and  12  with respect to the input terminal  201 , the present disclosure is not limited thereto. For example, the capacitor  30  may be provided on the side opposite to the amplifiers  11  and  12  with respect to the input terminal  201 . 
     The inductor  111  is electromagnetic field coupled to the inductor  112  to form a transformer  110 . Here, one end of the inductor  111  is connected to the input terminal  201 , and the other end thereof is connected to the reference potential. In addition, one end of the inductor  112  is connected to the input of the amplifier  11 , and the other end of the inductor  112  is connected to the input of the amplifier  12 . The transformer  110  operates as an input balun that performs unbalanced-to-balanced conversion for a signal of the inductor  111  serving as a primary winding. The signal inputted to the inductor  111  is converted by the transformer  110  to generate a differential signal in the inductor  112 . The electromagnetic field coupling is defined as either or both of magnetic field coupling and electric field coupling. 
     The output of the input matching circuit MN 1  is connected to one end of a capacitor  31  and one end of a capacitor  32 . The other end of the capacitor  31  is connected to the input of the amplifier  11 . The capacitor  31  is a capacitor for cutting a direct current. The other end of capacitor  32  is connected to the input of the amplifier  12 . The output of the amplifier  11  is connected to one end of the inductor  121 . The output of the amplifier  12  is connected to the other end of the inductor  121 . The capacitor  32  is a capacitor for cutting a direct current. 
     The inductor  121  is electromagnetic field coupled to the inductor  122  to form a transformer  120 . One end of the inductor  122  is connected to the input of the matching circuit  200 . The other end of the inductor  122  is connected to a reference potential. The transformer  120  operates as an output balun that performs balanced-to-unbalanced conversion. The output of the matching circuit  200  is connected to the output terminal  202 . 
       FIG.  2    is a diagram focusing on the input matching circuit MN 1 , the amplifiers  11  and  12 , and the like according to the first embodiment of the present disclosure. As illustrated in  FIG.  2   , a diode D 1  serving as a first diode is provided in a path between the transformer  110  serving as an input balun and the amplifier  11 . The diode D 1  is connected between one end of the inductor  112  and a reference potential GND. The cathode of the diode D 1  is connected to the reference potential GND. In addition, a diode D 2  serving as a second diode is provided in a path between the transformer  110  serving as the input balun and the amplifier  12 . The diode D 2  is connected between the other end of the inductor  112  and the reference potential GND. The cathode of the diode D 2  is connected to the reference potential GND. The diodes D 1  and D 2  are connected in parallel to the amplifiers  11  and  12 . Note that the reference potential GND is a reference potential of the amplifiers  11  and  12 . 
     A bias b 11  outputted from a bias circuit  21  is applied to the anode of the diode D 1 . The bias b 11  outputted from the bias circuit  21  is applied via a bias line  71 . The bias line  71  is connected to a secondary winding of the transformer  110  serving as the input balun. A parallel resonance circuit  41  is connected to the bias line  71 . The parallel resonance circuit  41  includes a capacitor  331  and an inductor  341  connected in parallel with each other. Note that two diodes D 1  may be provided to form a two-stage configuration. However, from the viewpoint of reducing the size of the apparatus, it is desirable to use only one diode D 1  (that is, a one-stage configuration). The bias b 11  may be a voltage for turning on one diode D 1 . 
     A bias b 12  outputted from the bias circuit  21  is applied to the anode of the diode D 2 . The bias b 12  outputted from the bias circuit  21  is applied via a bias line  72 . The bias line  72  is connected to the secondary winding of the transformer  110  serving as the input balun. A parallel resonance circuit  42  is connected to the bias line  72 . The parallel resonance circuit  42  includes a capacitor  332  and an inductor  342  connected in parallel with each other. Note that two diodes D 2  may be provided to form a two-stage configuration. However, from the viewpoint of reducing the size of the apparatus, it is desirable to use only one diode D 2  (that is, a one-stage configuration). The bias b 12  may be a voltage for turning on one diode D 2 . 
     A bias b 21  outputted from a bias circuit  22  is applied to the input of the amplifier  11 . The bias b 21  outputted from the bias circuit  22  is applied to the input of the amplifier  11  via a resistance element  51 . Thus, a bias is applied to the transistor in the amplifier  11 . A bias b 22  outputted from a bias circuit  22  is applied to the input of the amplifier  12 . The bias b 22  outputted from the bias circuit  22  is applied to the input of the amplifier  12  via a resistance element  52 . Thus, a bias is applied to the transistor in the amplifier  12 . Operation 
     A signal inputted to the input terminal  201 , for example, an input signal RFin of a radio frequency (RF) is divided into two signals having phases different from each other by approximately 180° via the transformer  110 , and then inputted to the amplifiers  11  and  12 . The two signals amplified by the amplifiers  11  and  12  are combined via the output matching circuit MN 2  and outputted to the output terminal  202  as an output signal RFout. 
     Here, the gain of the differential amplifying apparatus  1  can be adjusted by turning on or off the diode D 1  connected to the input side of the amplifier  11  and the diode D 2  connected to the input side of the amplifier  12 . 
     To be specific, by turning on the diodes D 1  and D 2  by the biases b 11  and b 12  applied from the bias circuit  21 , a part of the input signal flows to the reference potential GND through the diodes D 1  and D 2 . As a result, the gain can be reduced and the LPM can be realized. 
     On the other hand, the diodes D 1  and D 2  are turned off by the biases b 11  and b 12  applied from the bias circuit  21 . At this time, the parallel resonance circuits  41  and  42  are adjusted so as to be open (i.e., having infinite impedance) at an operating frequency. Therefore, the gain is not affected. Thus, the HPM can be realized without reducing the gain. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     When a diode is connected to a preceding stage (specifically, between the input terminal  201  and the transformer  110 ) of the transformer  110  serving as the input balun, since the impedance of the preceding stage of the transformer  110  is relatively high and the voltage amplitude of a signal becomes large, there is a possibility that the diode is turned on unintentionally. On the other hand, as in the first embodiment, by connecting the diodes D 1  and D 2  to a subsequent stage of the transformer  110  serving as the input balun (specifically, between the transformer  110  and the amplifiers  11  and  12 ), the input voltage amplitude of the signal can be reduced by using the fact that the impedance of the subsequent stage of the transformer  110  is lower than the impedance of the preceding stage of the transformer  110 , and the diode can be prevented from being turned on unintentionally. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus. 
     Second Embodiment 
     Configuration 
       FIG.  3    is a diagram illustrating an example of a differential amplifying apparatus la according to a second embodiment of the present disclosure.  FIG.  3    is a diagram focusing on the input matching circuit MN 1 , the amplifiers  11  and  12 , and the like according to the second embodiment. Also in the second embodiment, the diodes D 1  and D 2  are connected to the subsequent stage of the transformer  110  serving as the input balun. 
     As illustrated in  FIG.  3   , in the second embodiment, unlike the first embodiment, the bias line  70  is connected to a midpoint P 21  of the inductor  112  serving as the secondary winding of the input balun. The midpoint P 21  is a virtual ground point of the high frequency signal. The midpoint in the present disclosure does not mean a position at which the inductance value of the secondary winding of the transformer is half, but is defined as a half of the primary winding within a range of manufacturing variation of the secondary winding of the transformer. Note that the bias line  70  may be connected to any portion of the inductor  112  and does not necessarily need to be connected to the midpoint P 21  of the inductor  112 . 
     The midpoint P 21  of the secondary winding of the transformer  110  is connected to the bias circuit  21  via a parallel resonance circuit  40 . The parallel resonance circuit  40  includes a capacitor  330  and an inductor  340  connected in parallel with each other. The parallel resonance circuit  40  is adjusted so as to be open (i.e., having infinite impedance) at the operating frequency. 
     Operation 
     In  FIG.  3   , a bias is applied to the diodes D 1  and D 2  via the parallel resonance circuit  40 . Similar to the differential amplifying apparatus according to the first embodiment described with reference to  FIG.  2   , the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. In particular, by connecting the diodes D 1  and D 2  to the subsequent stage of the transformer  110  serving as the input balun, the input voltage amplitude can be reduced due to low impedance. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus. 
     In addition, in the differential amplifying apparatus according to the first embodiment described with reference to  FIG.  2   , a parallel resonance circuit is provided for each of the two diodes D 1  and D 2 , whereas in a second embodiment, only one parallel resonance circuit may be provided. Therefore, the circuit scale can be made smaller than that in the first embodiment. 
     Third Embodiment 
     Configuration 
       FIG.  4    is a diagram illustrating an example of a differential amplifying apparatus  1   b  according to a third embodiment of the present disclosure.  FIG.  4    is a diagram focusing on the input matching circuit MN 1 , the amplifiers  11  and  12 , and the like according to the third embodiment. As illustrated in  FIG.  4   , also in the third embodiment, the diodes D 1  and D 2  are connected to the subsequent stage of the transformer  110  serving as the input balun. As in the second embodiment, the bias line  70  is connected to the midpoint P 21  of the inductor  112 . 
     In the differential amplifying apparatus according to the second embodiment described with reference to  FIG.  2   , a bias is applied via the parallel resonance circuit  40 . On the other hand, the differential amplifying apparatus according to the third embodiment does not use a parallel resonance circuit. 
     Since the midpoint P 21  of the inductor  112  serving as the secondary winding of the transformer  110  serving as the input balun becomes a virtual ground point of a high frequency signal, there is no problem in principle even when a parallel resonance circuit is not provided. When the parallel resonance circuit is omitted in this manner, the circuit scale can be further reduced. 
     Operation 
     When the diodes D 1  and D 2  are turned on by a bias b 1  applied from the bias circuit  21 , a part of the input signal flows to the reference potential GND through the diodes D 1  and D 2 . As a result, the gain can be reduced and the LPM can be realized. 
     On the other hand, the diodes D 1  and D 2  are turned off by the bias b 1  applied from the bias circuit  21 . Thus, a part of the input signal does not flow to the reference potential GND through the diodes D 1  and D 2 , and the HPM can be realized without reducing the gain. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus. 
     Fourth Embodiment 
     Configuration 
       FIG.  5    is a diagram illustrating an example of a differential amplifying apparatus  1   c  according to a fourth embodiment of the present disclosure.  FIG.  5    is a diagram focusing on the input matching circuit MN 1 , the amplifiers  11  and  12 , and the like according to the fourth embodiment. 
     In the fourth embodiment illustrated in  FIG.  5   , the cathodes of the diodes D 1  and D 2 , which are shunt diodes, are connected to each other and connected to the reference potential via a resistance element  53 . At this time, when the resistance value of the resistance element  53  is increased to some extent, a secondary distortion inputted to the amplifiers  11  and  12 , which are a differential pair, can be reduced. Other configurations of the fourth embodiment illustrated in  FIG.  5    are the same as those of the first embodiment described with reference to  FIG.  2   . 
     Operation 
     When the diodes D 1  and D 2  are turned on by the biases b 11  and b 12  applied from the bias circuit  21 , a part of the input signal flows to the reference potential GND through the diodes D 1  and D 2 . As a result, the gain can be reduced and the LPM can be realized. 
     On the other hand, the diodes D 1  and D 2  are turned off by the biases b 11  and b 12  applied from the bias circuit  21 . Thus, a part of the input signal does not flow to the reference potential GND through the diodes D 1  and D 2 , and the HPM can be realized without reducing the gain. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus. 
     Fifth Embodiment 
     Configuration 
       FIG.  6    is a diagram illustrating an example of a differential amplifying apparatus  1   d  according to a fifth embodiment of the present disclosure.  FIG.  6    is a diagram focusing on the input matching circuit MN 1 , the amplifiers  11  and  12 , and the like according to the fifth embodiment. Also in the fifth embodiment, the diodes D 1  and D 2  are connected to the subsequent stage of the transformer  110  serving as the input balun. 
     In the fifth embodiment illustrated in  FIG.  6   , a bias line  73  is connected to the midpoint P 21  of the inductor  112 . The midpoint P 21  is a virtual ground point of the high frequency signal. The bias line  73  is provided with a series resonance circuit including an inductor  61  and a capacitor  33 . One end of the inductor  61  and one end of the capacitor  33  are connected in series. The other end of the inductor  61  is connected to the midpoint of the inductor  112  serving as the secondary winding of the transformer  110 . The other end of the capacitor  33  is connected to the inductor  111  serving as the primary winding and the reference potential. The bias b 1  is applied to a connection point between the inductor  61  and the capacitor  33 . Note that the inductor  61  may be replaced with a signal line. 
     Operation 
     When the diodes D 1  and D 2  are turned on by the bias b 1  applied from the bias circuit  21 , a part of the input signal flows to the reference potential GND through the diodes D 1  and D 2 . As a result, the gain can be reduced and the LPM can be realized. 
     On the other hand, the diodes D 1  and D 2  are turned off by the bias b 1  applied from the bias circuit  21 . Thus, a part of the input signal does not flow to the reference potential GND through the diodes D 1  and D 2 , and the HPM can be realized without reducing the gain. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     In addition, the midpoint of the secondary winding of the input matching circuit MN 1  and the reference potential of the primary winding are connected via the series resonance circuit. By matching the resonant frequency of the series resonance circuit with the frequency to be removed, for example, a second harmonic component having a frequency twice as high as the fundamental frequency can be removed. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus. 
     Sixth Embodiment 
     Configuration 
       FIG.  7    is a diagram illustrating an example of a differential amplifying apparatus le according to a sixth embodiment of the present disclosure.  FIG.  7    illustrates an example of a configuration including two stages of amplifiers between the input matching circuit MN 1  and the output matching circuit MN 2  of the first embodiment. The two-stage amplifiers are in cascading connection via electromagnetic field coupling by a transformer so that the output of the preceding stage becomes the input of the subsequent stage. 
     As illustrated in  FIG.  7   , the differential amplifying apparatus le according to the sixth embodiment includes a transformer TR 1  in the subsequent stage of amplifiers  11 - 1  and  12 - 1 . In addition, the differential amplifying apparatus le according to the sixth embodiment includes amplifiers  11 - 2  and  12 - 2  in the subsequent stage of the transformer TR 1 . Further, the differential amplifying apparatus le according to the sixth embodiment includes the output matching circuit MN 2  in the subsequent stage of the amplifiers  11 - 2  and  12 - 2 . The transformer TR 1  includes an inductor  141 - 1  serving as the primary winding and an inductor  142 - 1  serving as the secondary winding. 
     The differential amplifying apparatus le according to the sixth embodiment includes capacitors  31 - 1  and  31 - 2 . The capacitors  31 - 1  and  31 - 2  correspond to the capacitor  31  in  FIG.  2   . The differential amplifying apparatus le according to the sixth embodiment includes capacitors  32 - 1  and  32 - 2 . The capacitors  32 - 1  and  32 - 2  correspond to the capacitor  32  in  FIG.  2   . 
     The differential amplifying apparatus le according to the sixth embodiment includes resistance elements  51 - 1  and  51 - 2 . The resistance elements  51 - 1  and  51 - 2  correspond to the resistance element  51  in  FIG.  2   . The differential amplifying apparatus le according to the sixth embodiment includes resistance elements  52 - 1  and  52 - 2 . The resistance elements  52 - 1  and  52 - 2  correspond to the resistance element  52  in  FIG.  2   . 
     The differential amplifying apparatus le according to the sixth embodiment has the diodes D 1  and D 2  only in the first stage. The bias b 11  outputted from the bias circuit  21  is applied to the anode of the diode D 1 . The bias b 11  outputted from the bias circuit  21  is applied via the bias line  71 . The parallel resonance circuit  41  is connected to the bias line  71 . The parallel resonance circuit  41  includes the capacitor  331  and the inductor  341 . 
     The bias b 12  outputted from the bias circuit  21  is applied to the anode of the diode D 2 . The bias b 12  outputted from the bias circuit  21  is applied via the bias line  72 . The parallel resonance circuit  42  is connected to the bias line  72 . The parallel resonance circuit  42  includes the capacitor  332  and the inductor  342 . 
     Note that the bias b 21  outputted from the bias circuit  22  is applied to the input side of the amplifier  11 - 1  via the resistance element  51 - 1 . The bias b 22  outputted from the bias circuit  22  is applied to the input side of the amplifier  12 - 1  via the resistance element  52 - 1 . A bias b 31  outputted from the bias circuit  22  is applied to the input side of the amplifier  11 - 2  via the resistance element  51 - 2 . A bias b 32  outputted from the bias circuit  22  is applied to the input side of the amplifier  12 - 2  via the resistance element  52 - 2 . 
     Operation 
     The output of the differential amplifier circuit formed by the amplifiers  11 - 1  and  12 - 1  is inputted to the differential amplifier circuit formed by the amplifiers  11 - 2  and  12 - 2  via the transformer TR 1 . The output of the differential amplifier circuit formed by the amplifiers  11 - 2  and  12 - 2  is outputted to the output terminal  202  via the output matching circuit MN 2 . 
     Also in the sixth embodiment, by turning on the diodes D 1  and D 2  by the biases b 11  and b 12  applied from the bias circuit  21 , a part of the input signal flows to the reference potential GND through the diodes D 1  and D 2 . As a result, the gain can be reduced and the LPM can be realized. 
     On the other hand, the diodes D 1  and D 2  are turned off by the biases b 11  and b 12  applied from the bias circuit  21 . At this time, the parallel resonance circuits  41  and  42  are adjusted so as to be open (i.e., having infinite impedance) at an operating frequency. Therefore, the gain is not affected. Thus, the HPM can be realized without reducing the gain. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     Note that in the seventh embodiment, two stages of amplifiers are provided in the configuration of the first embodiment, but the two stages of amplifiers may be provided in any one of the configurations of the second embodiment, the third embodiment, the fourth embodiment, and the fifth embodiment. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus. 
     Seventh Embodiment 
     Configuration 
       FIG.  8    is a diagram illustrating an example of a differential amplifying apparatus if according to a seventh embodiment of the present disclosure.  FIG.  8    illustrates an example of a configuration including N stages (N is an integer of 2 or more, the same applies hereinafter) of amplifiers between the input matching circuit MN 1  and the output matching circuit MN 2  of the first embodiment. The N-stage amplifiers are in cascading connection via electromagnetic field coupling by a transformer so that the output of the preceding stage becomes the input of the subsequent stage. 
     As illustrated in  FIG.  8   , the differential amplifying apparatus if according to the seventh embodiment includes the transformer TR 1  in the subsequent stage of the first stage amplifiers  11 - 1  and  12 - 1 . In addition, the differential amplifying apparatus if according to the seventh embodiment includes the second stage amplifiers  11 - 2  and  12 - 2  in the subsequent stage of the transformer TR 1 . Further, the differential amplifying apparatus if according to the seventh embodiment includes a transformer TR 2  in the subsequent stage of the amplifiers  11 - 2  and  12 - 2 . Similarly, the differential amplifying apparatus if according to the seventh embodiment includes N-th stage amplifiers  11 -N and  12 -N in the subsequent stage of the transformer TR 2 . The differential amplifying apparatus if according to the seventh embodiment includes the output matching circuit MN 2  in the subsequent stage of the N-th stage amplifiers  11 -N and  12 -N. The transformer TR 1  includes the inductor  141 - 1  serving as the primary winding and the inductor  142 - 1  serving as the secondary winding. The transformer TR 2  includes an inductor  141 - 2  serving as the primary winding and an inductor  142 - 2  serving as the secondary winding. 
     The differential amplifying apparatus if according to the seventh embodiment includes capacitors  31 - 1 ,  31 - 2 , . . . , and  31 -N. The capacitors  31 - 1 ,  31 - 2 , . . . , and  31 -N correspond to the capacitor  31  in  FIG.  2   . The differential amplifying apparatus if according to the seventh embodiment includes capacitors  32 - 1 ,  32 - 2 , . . . , and  32 -N. The capacitors  32 - 1 ,  32 - 2 , . . . , and  32 -N correspond to the capacitor  32  in  FIG.  2   . 
     The differential amplifying apparatus if according to the seventh embodiment includes resistance elements  51 - 1 ,  51 - 2 , . . . , and  51 -N. The resistance elements  51 - 1 ,  51 - 2 , . . . , and  51 -N correspond to the resistance element  51  in  FIG.  2   . The differential amplifying apparatus if according to the seventh embodiment includes resistance elements  52 - 1 ,  52 - 2 , . . . , and  52 -N. The resistance elements  52 - 1 ,  52 - 2 , . . . , and  52 -N correspond to the resistance element  52  in  FIG.  2   . 
     The differential amplifying apparatus if according to the seventh embodiment has the diodes D 1  and D 2  only in the first stage. The bias b 11  outputted from the bias circuit  21  is applied to the anode of the diode D 1 . The bias b 11  outputted from the bias circuit  21  is applied via the bias line  71 . The parallel resonance circuit  41  is connected to the bias line  71 . The parallel resonance circuit  41  includes the capacitor  331  and the inductor  341 . 
     The bias b 12  outputted from the bias circuit  21  is applied to the anode of the diode D 2 . The bias b 12  outputted from the bias circuit  21  is applied via the bias line  72 . The parallel resonance circuit  42  is connected to the bias line  72 . The parallel resonance circuit  42  includes the capacitor  332  and the inductor  342 . 
     Note that the bias b 21  outputted from the bias circuit  22  is applied to the input side of the amplifier  11 - 1  via the resistance element  51 - 1 . The bias b 22  outputted from the bias circuit  22  is applied to the input side of the amplifier  12 - 1  via the resistance element  52 - 1 . The bias b 31  outputted from the bias circuit  22  is applied to the input side of the amplifier  11 - 2  via the resistance element  51 - 2 . The bias b 32  outputted from the bias circuit  22  is applied to the input side of the amplifier  12 - 2  via the resistance element  52 - 2 . Similarly, a bias bn 1  outputted from the bias circuit  22  is applied to the input side of the amplifier  11 -N via the resistance element  51 -N. A bias bn 2  outputted from the bias circuit  22  is applied to the input side of the amplifier  12 -N via the resistance element  52 -N. 
     Operation 
     The output of the differential amplifier circuit formed by the amplifiers  11 - 1  and  12 - 1  is inputted to the differential amplifier circuit formed by the amplifiers  11 - 2  and  12 - 2  in the subsequent stage via the transformer TR 1 . The output of the differential amplifier circuit formed by the amplifiers  11 - 2  and  12 - 2  is inputted to the differential amplifier circuit formed by the amplifiers in the subsequent stage via the transformer TR 2 . Similarly, the output is sequentially inputted to the differential amplifier circuit formed by the amplifiers in the subsequent stage. The output of the differential amplifier circuit formed by the amplifiers  11 -N and  12 -N in the N-th stage, which is the final stage, is outputted to the output terminal  202  via the output matching circuit MN 2 . 
     Also in the seventh embodiment, by turning on the diodes D 1  and D 2  by the biases b 11  and b 12  applied from the bias circuit  21 , a part of the input signal flows to the reference potential GND through the diodes D 1  and D 2 . As a result, the gain can be reduced and the LPM can be realized. 
     On the other hand, the diodes D 1  and D 2  are turned off by the biases b 11  and b 12  applied from the bias circuit  21 . At this time, the parallel resonance circuits  41  and  42  are adjusted so as to be open (i.e., having infinite impedance) at the operating frequency. Therefore, the gain is not affected. Thus, the HPM can be realized without reducing the gain. 
     As described above, the LPM can be realized by turning on the diodes D 1  and D 2  and the HPM can be realized by turning off the diodes D 1  and D 2  by the applied bias. 
     Note that in the seventh embodiment, N stages of amplifiers are provided in the configuration of the first embodiment, but the N stages of amplifiers may be provided in any one of the configurations of the second embodiment, the third embodiment, the fourth embodiment, and the fifth embodiment. 
     As described above, by adding a diode and turning on or off the diode by the applied bias, the LPM and HPM can be realized without providing a configuration dedicated to the LPM. Therefore, it is possible to realize miniaturization of the differential amplifying apparatus.