Doherty Amplifier

Abstract

The Doherty amplifier comprises: a first amplifier (9), which amplifies the first signal as an auxiliary amplifier if the frequencies of the first signal and the second signal are respectively the first frequency, and amplifies the first signal as a main amplifier if the frequencies of the first signal and the second signal are respectively the second frequency; a second amplifier (10), which amplifies the second signal as a main amplifier if the frequencies of the first signal and the second signal are respectively the first frequency, and amplifies the second signal as an auxiliary amplifier if the frequencies of the second signal and the second frequency; and a synthesizing circuit (11), which synthesizes the first signal amplified by the first amplifier (9) and the second signal amplified by the second amplifier (10). Furthermore, the second amplifier (10) is an amplifier having a saturated output power greater than that of the first amplifier (9). When the first amplifier (9) amplifies the first signal as a main amplifier and the second amplifier (10) amplifies the second signal as an auxiliary amplifier, the synthesizing circuit (11) changes the output impedance of the first amplifier (9) in such a way that an imaginary component in the output impedance of the first amplifier (9) is reduced.

Description

Technical Field

[0001] The present invention relates to a Doherty amplifier. Background Art

[0002] The Doherty amplifier disclosed in the following Patent Document 1 includes a distribution circuit, a carrier amplifier, a peak amplifier, a 90-degree line, and a synthesizing circuit. The saturated output power of the peak amplifier is greater than the saturated output power of the carrier amplifier.

[0003] In the Doherty amplifier, the saturated output power of the peak amplifier is greater than the saturated output power of the carrier amplifier, so the output reflection coefficient of the carrier amplifier during the compensation operation is increased compared to the case where the saturated output powers of the peak amplifier and the carrier amplifier are equal. In the Doherty amplifier, the efficiency during the compensation operation is improved by the amount by which the output reflection coefficient of the carrier amplifier is increased compared to the case where the saturated output powers of the peak amplifier and the carrier amplifier are equal.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-115760 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the Doherty amplifier disclosed in Patent Document 1, if the frequency of the amplification target signal provided to the distribution circuit is a frequency at which the electrical length of the output side line of the carrier amplifier becomes 90 degrees through the 90-degree line (hereinafter referred to as the "first frequency"), the efficiency during the compensation operation is improved. However, in the case where a signal having a second frequency different from the first frequency is provided to the distribution circuit, the electrical length of the output side line of the carrier amplifier becomes an electrical length different from 90 degrees. The electrical length of the output side line of the carrier amplifier becomes an electrical length different from 90 degrees, thereby increasing the imaginary component in the output impedance of the carrier amplifier. Therefore, there is the following problem: when the frequency of the amplification target signal provided to the distribution circuit is the second frequency, the efficiency during the compensation operation is reduced.

[0009] The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to obtain a Doherty amplifier capable of suppressing a decrease in efficiency during a compensation operation when the frequency of a signal is a second frequency.

[0010] Means for solving problems

[0011] The Doherty amplifier of the present invention comprises: a first amplifier, which amplifies the first signal as an auxiliary amplifier if the frequencies of the first signal and the second signal are respectively the first frequency, and amplifies the first signal as a main amplifier if the frequencies of the first signal and the second signal are respectively the second frequency; a second amplifier, which amplifies the second signal as a main amplifier if the frequencies of the first signal and the second signal are respectively the first frequency, and amplifies the second signal as an auxiliary amplifier if the frequencies of the second signal and the second signal are respectively the second frequency; and a synthesizing circuit, which synthesizes the first signal amplified by the first amplifier and the second signal amplified by the second amplifier, the second amplifier being an amplifier having a saturated output power greater than the saturated output power of the first amplifier, and when the first amplifier amplifies the first signal as the main amplifier and the second amplifier amplifies the second signal as the auxiliary amplifier, the synthesizing circuit changes the output impedance of the first amplifier in such a way as to reduce the imaginary component in the output impedance of the first amplifier.

[0012] Effects of the Invention

[0013] According to the present invention, it is possible to suppress a decrease in efficiency during the compensation operation when the frequency of the signal is the second frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 1 is a diagram showing the structure of a Doherty amplifier according to the first embodiment.

[0015] Figure 2 It is an explanatory diagram showing impedance when the frequency f is the first frequency f1 and the output power of each of the first amplifier 9 and the second amplifier 10 is the saturated output power.

[0016] Figure 3 It is an explanatory diagram showing impedance when compensation is performed when the frequency f is the first frequency f1 and the first amplifier 9 is stopped.

[0017] Figure 4 1 is an explanatory diagram showing the compensation amount BF of the second amplifier 10 .

[0018] Figure 5 It is an explanatory diagram showing impedance when the frequency f is the second frequency f2 and the output power of each of the first amplifier 9 and the second amplifier 10 is the saturated output power.

[0019] Figure 6 1 is an explanatory diagram showing impedance when the frequency f is the second frequency f2 and compensation of the second amplifier 10 is stopped.

[0020] Figure 7 It is an explanatory diagram showing the compensation amount BF of the first amplifier 9.

[0021] Figure 8It is an explanatory diagram showing impedance when compensation is performed when the frequency f is the third frequency f3 and the first amplifier 9 is stopped.

[0022] Fig. 9 1 is an explanatory diagram showing the compensation amount BF of the second amplifier 10 .

[0023] Fig.10 1 is an explanatory diagram showing simulation results of power efficiency corresponding to output power of the Doherty amplifier.

[0024] Fig.11 1 is an explanatory diagram showing simulation results of compensation efficiency corresponding to the frequency f of each of the first signal and the second signal.

[0025] Fig.12 1 is a diagram showing the structure of a Doherty amplifier according to a third embodiment.

[0026] Fig.13 1 is a diagram showing the structure of a Doherty amplifier according to a fourth embodiment.

[0027] Fig.14 1 is a diagram showing the structure of another Doherty amplifier according to the fourth embodiment.

[0028] Fig.15 1 is a diagram showing a configuration of an example of a synthesizing circuit 11 having lumped constant elements. DETAILED DESCRIPTION

[0029] Hereinafter, in order to explain the present invention in more detail, a mode for carrying out the present invention will be described with reference to the accompanying drawings.

[0030] Implementation Method 1

[0031] Figure 1 1 is a diagram showing the structure of a Doherty amplifier according to the first embodiment.

[0032] exist Figure 1 In the process, the amplification target signal is provided to the input terminal 1.

[0033] The input matching circuit 2 is implemented by, for example, a circuit having a lumped constant element, a circuit having a distributed constant line, a circuit combining a lumped constant element and a distributed constant line, a matching circuit combining an inductor and a capacitor, or a quarter-wavelength line.

[0034] One end of the input matching circuit 2 is connected to the input terminal 1 , and the other end of the input matching circuit 2 is connected to the input side of the distributor 3 .

[0035] The input matching circuit 2 performs impedance matching between the input terminal 1 and the distributor 3 .

[0036] The distributor 3 is implemented by, for example, a Wilkinson distributor or a hybrid circuit.

[0037] The distributor 3 distributes the amplification target signal propagated through the input matching circuit 2 into two.

[0038] The distributor 3 outputs one of the distributed signals as a first signal to the phase correction circuit 4 .

[0039] The distributor 3 outputs the other signal after distribution to the input matching circuit 6 as a second signal.

[0040] The phase correction circuit 4 is implemented by, for example, a circuit having a lumped constant element, a circuit having a distributed constant line, a circuit combining a lumped constant element and a distributed constant line, a matching circuit combining an inductor and a capacitor, or a quarter-wavelength line.

[0041] One end of the phase correction circuit 4 is connected to one output side of the distributor 3 , and the other end of the phase correction circuit 4 is connected to one end of the input matching circuit 5 .

[0042] The phase correction circuit 4 corrects the electrical length of the path through the first amplifier 9 so that the electrical length of the path through the first amplifier 9 and the electrical length of the path through the second amplifier 10 of the two paths from the distributor 3 to the output combining point 14 become the same electrical length.

[0043] The input matching circuit 5 is realized by, for example, a circuit having a lumped constant element, a circuit having a distributed constant line, a circuit combining a lumped constant element and a distributed constant line, a matching circuit combining an inductor and a capacitor, or a quarter-wavelength line.

[0044] One end of the input matching circuit 5 is connected to the other end of the phase correction circuit 4 , and the other end of the input matching circuit 5 is connected to the input side of the first amplifier 9 .

[0045] The input matching circuit 5 matches the input impedance of the first amplifier 9 .

[0046] The input matching circuit 6 is implemented by, for example, a circuit having a lumped constant element, a circuit having a distributed constant line, a circuit combining a lumped constant element and a distributed constant line, a matching circuit combining an inductor and a capacitor, or a quarter-wavelength line.

[0047] One end of the input matching circuit 6 is connected to the other output side of the distributor 3 , and the other end of the input matching circuit 6 is connected to the input side of the second amplifier 10 .

[0048] The input matching circuit 6 matches the input impedance of the second amplifier 10 .

[0049] The bias terminal 7 is supplied with a bias voltage of the first amplifier 9 .

[0050] When the frequency f of the first signal is the first frequency f1, a bias voltage for biasing the input side of the first amplifier 9, i.e., the gate terminal 9a, to Class C is supplied to the bias terminal 7. The first frequency f1 is, for example, a fundamental frequency. The bias voltage for Class C is a voltage lower than the threshold voltage of the first amplifier 9.

[0051] When the frequency f of the first signal is the second frequency f2, a bias voltage for biasing the gate terminal 9a of the first amplifier 9 to AB class is supplied to the bias terminal 7. The second frequency f2 is, for example, twice the frequency of the fundamental frequency. The bias voltage for biasing to AB class is a voltage greater than the threshold voltage of the first amplifier 9.

[0052] The bias terminal 8 is supplied with a bias voltage of the second amplifier 10 .

[0053] When the frequency f of the second signal is the first frequency f1, a bias voltage for biasing the input side of the second amplifier 10, namely the gate terminal 10a, to AB class is supplied to the bias terminal 8. The bias voltage for AB class is a voltage equal to or higher than the threshold voltage of the second amplifier 10.

[0054] When the frequency f of the second signal is the second frequency f2, a bias voltage for biasing the gate terminal 10a of the second amplifier 10 to class C is supplied to the bias terminal 8. The bias voltage for biasing to class C is a voltage lower than the threshold voltage of the second amplifier 10.

[0055] The first amplifier 9 is realized by, for example, a FET (Field Effect Transistor), an HBT (Heterojunction Bipolar Transistor), or a HEMT (High Electron Mobility Transistor).

[0056] When the frequency f of the first signal is the first frequency f1 , a bias voltage biased to a C class is applied to the gate terminal 9 a of the first amplifier 9 .

[0057] When the frequency f of the first signal is the second frequency f2, a bias voltage biased to AB class is applied to the gate terminal 9a of the first amplifier 9.

[0058] When the frequency f of the first signal is the first frequency f1 and the first signal propagated through the input matching circuit 5 is equal to or higher than the first level, the first amplifier 9 amplifies the first signal as an auxiliary amplifier.

[0059] When the frequency f of the first signal is the second frequency f2 , the first amplifier 9 amplifies the first signal as a main amplifier regardless of the signal level of the first signal propagated through the input matching circuit 5 .

[0060] 21 is an example of an output equivalent circuit of the first amplifier 9 . The output equivalent circuit 21 of the first amplifier 9 is represented by a current source 22 and a capacitor 23 .

[0061] The second amplifier 10 is realized by, for example, FET, HBT, or HEMT.

[0062] When the frequency f of the second signal is the first frequency f1, a bias voltage biased to AB class is applied to the gate terminal 10 a of the second amplifier 10 .

[0063] When the frequency f of the second signal is the second frequency f2, a bias voltage biased to class C is applied to the gate terminal 10 a of the second amplifier 10 .

[0064] The saturated output power P of the second amplifier 10 is S2 Greater than the saturated output power P of the first amplifier 9 S1 .

[0065] When the frequency f of the second signal is the first frequency f1 , the second amplifier 10 amplifies the second signal as a main amplifier regardless of the signal level of the second signal propagated through the input matching circuit 6 .

[0066] When the frequency f of the second signal is the second frequency f2 and the second signal propagated through the input matching circuit 6 is equal to or higher than the second level, the second amplifier 10 amplifies the second signal as an auxiliary amplifier.

[0067] 24 is an example of an output equivalent circuit of the second amplifier 10 . The output equivalent circuit 24 of the second amplifier 10 is represented by a current source 25 and a capacitor 26 .

[0068] The combining circuit 11 includes a first output circuit 12 and a second output circuit 13 .

[0069] The synthesizing circuit 11 synthesizes the first signal amplified by the first amplifier 9 and the second signal amplified by the second amplifier 10 .

[0070] The synthesizing circuit 11 outputs a synthesized signal of the amplified first signal and the amplified second signal to the output matching circuit 15 .

[0071] When the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the synthesizing circuit 11 changes the output impedance of the second amplifier 10 so as to reduce the imaginary component in the output impedance of the second amplifier 10.

[0072] That is, when the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the synthesizing circuit 11 changes the output impedance of the second amplifier 10, thereby increasing the output reflection coefficient of the second amplifier 10. The increase in the output reflection coefficient is greater than the saturated output power P of the first amplifier 9. S1 and the saturated output power P of the second amplifier 10 S2 The difference ΔP S This is accompanied by a reduction in the output reflection coefficient of the second amplifier 10.

[0073] When the first amplifier 9 amplifies the first signal as a main amplifier and the second amplifier 10 amplifies the second signal as an auxiliary amplifier, the synthesizing circuit 11 changes the output impedance of the first amplifier 9 so as to reduce the imaginary component in the output impedance of the first amplifier 9.

[0074] That is, when the first amplifier 9 amplifies the first signal as the main amplifier and the second amplifier 10 amplifies the second signal as the auxiliary amplifier, the synthesizing circuit 11 changes the output impedance of the first amplifier 9, thereby reducing the output reflection coefficient of the first amplifier 9. The reduction in the output reflection coefficient is less than the difference ΔP S The amount of amplification of the output reflection coefficient of the first amplifier 9 is associated therewith.

[0075] exist Figure 1 In the Doherty amplifier shown in FIG. 1 , the synthesizing circuit 11 has a first output circuit 12 and a second output circuit 13. However, this is only an example. Fig.15 As shown in FIG. 1 , the synthesizing circuit 11 may further include lumped constant elements in addition to the first output circuit 12 and the second output circuit 13. As the lumped constant elements, a series inductor, a parallel inductor, a series capacitor, a parallel capacitor, or a combination thereof are assumed for the first output circuit 12. In addition, a series inductor, a parallel inductor, a series capacitor, a parallel capacitor, or a combination thereof are assumed for the second output circuit 13.

[0076] Fig.15 1 is a diagram showing a configuration of an example of a synthesizing circuit 11 having lumped constant elements.

[0077] exist Fig.15 In the shown synthesis circuit 11 , a series inductor 51 , a parallel inductor 52 , and a series capacitor 53 are provided for the first output circuit 12 , and a series inductor 54 , a parallel capacitor 55 , and a series capacitor 56 are provided for the second output circuit 13 .

[0078] One end of the first output circuit 12 is connected to the output side of the first amplifier 9 , and the other end of the first output circuit 12 is connected to the output combining point 14 .

[0079] The first output circuit 12 is a circuit that changes the output load for the first amplifier 9 .

[0080] When the frequency f of the first signal is the first frequency f1, the first output circuit 12 has an electrical length shorter than 90 degrees, and when the frequency f of the first signal is the second frequency f2, the first output circuit 12 has an electrical length of 90 degrees. When the frequency f of the first signal is the second frequency f2, the electrical length of the first output circuit 12 is not strictly limited to 90 degrees, and may deviate from 90 degrees within a range that does not cause practical problems.

[0081] One end of the second output circuit 13 is connected to the output side of the second amplifier 10 , and the other end of the second output circuit 13 is connected to the output combining point 14 .

[0082] The second output circuit 13 is a circuit that changes the output load for the second amplifier 10 .

[0083] When the frequency f of the second signal is the first frequency f1, the second output circuit 13 has an electrical length longer than 90 degrees, and when the frequency f of the second signal is the second frequency f2, the second output circuit 13 has an electrical length of 180 degrees. When the frequency f of the second signal is the second frequency f2, the electrical length of the second output circuit 13 is not strictly limited to 180 degrees, and may deviate from 180 degrees within a range that does not cause any practical problems.

[0084] As the electrical lengths of the first output circuit 12 and the second output circuit 13 , the following specific examples are assumed.

[0085] When the frequency f of each of the first signal and the second signal is the first frequency f1, the first output circuit 12 has an electrical length of 52.2 degrees, and the second output circuit 13 has an electrical length of 104.4 degrees.

[0086] Furthermore, when the frequency f of each of the first signal and the second signal is the second frequency f2, the first output circuit 12 has an electrical length of 90 degrees, and the second output circuit 13 has an electrical length of 180 degrees.

[0087] The output combining point 14 is a connection point between the other end of the first output circuit 12 and the other end of the second output circuit 13 .

[0088] The output matching circuit 15 is realized by, for example, a circuit having a lumped constant element, a circuit having a distributed constant line, a circuit combining a lumped constant element and a distributed constant line, a matching circuit combining an inductor and a capacitor, or a quarter-wavelength line.

[0089] One end of the output matching circuit 15 is connected to the output combining point 14 , and the other end of the output matching circuit 15 is connected to one end of the load 16 .

[0090] The output matching circuit 15 is a circuit that matches the impedance of the output combining point 14 with the impedance of the load 16 .

[0091] The load 16 is the external load of the Doherty amplifier.

[0092] One end of the load 16 is connected to the other end of the output matching circuit 15 , and the other end of the load 16 is grounded.

[0093] Next, Figure 1 The operation of the Doherty amplifier shown will be described.

[0094] First, the operation when the frequency f of each of the first signal and the second signal is the first frequency f1 will be described. Here, it is assumed that the first frequency f1 is a basic frequency.

[0095] When the frequency f of the first signal is the first frequency f1, a bias voltage for biasing the gate terminal 9a of the first amplifier 9 to Class C is supplied to the bias terminal 7, whereby the first amplifier 9 operates as an auxiliary amplifier.

[0096] When the frequency f of the second signal is the first frequency f1, a bias voltage for biasing the gate terminal 10a of the second amplifier 10 to AB class is supplied to the bias terminal 8, whereby the second amplifier 10 operates as a main amplifier.

[0097] The saturated output power P of the second amplifier 10 is S2 Greater than the saturated output power P of the first amplifier 9 S1 That is, the size of the second amplifier 10 is larger than the size of the first amplifier 9 .

[0098] The first amplifier 9 and the second amplifier 10 have different sizes. Therefore, when the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the output reflection coefficient of the second amplifier 10 is reduced according to the size ratio of the first amplifier 9 to the second amplifier 10. In addition, the output reflection coefficient of the second amplifier 10 is reduced, thereby reducing the compensation amount BF of the second amplifier 10.

[0099] When the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the synthesizing circuit 11 changes the output impedance of the second amplifier 10 to increase the output reflection coefficient of the second amplifier 10 .

[0100] exist Figure 1 In the Doherty amplifier shown in the figure, the electrical lengths of the first output circuit 12 and the second output circuit 13 are designed so that the amount of increase in the output reflection coefficient achieved by the synthesizing circuit 11 is larger than the amount of reduction in the output reflection coefficient caused by the size ratio of the first amplifier 9 to the second amplifier 10. If the synthesizing circuit 11 further includes a lumped constant element in addition to the first output circuit 12 and the second output circuit 13, the electrical lengths and lumped constant elements are designed so that the amount of increase in the output reflection coefficient achieved by the synthesizing circuit 11 is larger than the amount of reduction in the output reflection coefficient caused by the size ratio.

[0101] Therefore, in Figure 1 In the Doherty amplifier shown, when the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the compensation amount BF of the second amplifier 10 is increased, thereby improving the efficiency of the compensation operation.

[0102] Figure 2 It is an explanatory diagram showing impedance when the frequency f is the first frequency f1 and the output power of each of the first amplifier 9 and the second amplifier 10 is the saturated output power.

[0103] exist Figure 2 In the example, the output power of the first amplifier 9 is assumed to be the saturated output power P S1 The optimal load impedance of the first amplifier 9 is Ropt_1, and the output power of the second amplifier 10 is the saturated output power P S2 The optimal load impedance of the second amplifier 10 at this time is Ropt_2.

[0104] The saturated output power P of the second amplifier 10 is S2 Greater than the saturated output power P of the first amplifier 9 S1 , therefore, if Ropt_1 is set to β×Ropt_2, β is a value greater than 1.

[0105] At this time, as shown in the following equation (1), the impedance RL viewed from the output combining point 14 toward the load 16 becomes a value obtained by connecting the optimum load impedance Ropt_1 of the first amplifier 9 and the optimum load impedance Ropt_2 of the second amplifier 10 in parallel.

[0106]

[0107] β is a value greater than 1. Therefore, as shown in the following equation (2), the impedance RL viewed from the output combining point 14 toward the load 16 is greater than 0.5 times the optimal load impedance Ropt_2.

[0108] RL>0.5×Ropt_2 (2)

[0109] Figure 3 It is an explanatory diagram showing impedance when compensation is performed when the frequency f is the first frequency f1 and the first amplifier 9 is stopped.

[0110] Figure 4 1 is an explanatory diagram showing the compensation amount BF of the second amplifier 10 .

[0111] During compensation, the first amplifier 9 is stopped, so the second amplifier 10 occupies the output load of the output combining point 14. Therefore, the impedance Γ1 (=RL) from the output combining point 14 to the load 16 side is greater than 0.5 times Ropt_2.

[0112] If it is assumed that the size of the first amplifier 9 is equal to the size of the second amplifier 10, the impedance Γ1 becomes 0.5 times Ropt_2. Figure 1 In the Doherty amplifier shown, the second amplifier 10 is larger than the first amplifier 9, so the impedance Γ1 is smaller than that of a general Doherty amplifier in which the first amplifier 9 and the second amplifier 10 are equal in size. That is, the compensation amount BF is reduced.

[0113] During compensation, the first amplifier 9 stops, so the output impedance of the first amplifier 9 becomes an open circuit. Since the output impedance of the first amplifier 9 becomes an open circuit, when the first amplifier 9 is viewed from the output combining point 14, the first output circuit 12 functions as a virtual open stub.

[0114] The first output circuit 12 functions as an open stub, so the impedance Γ1 from the output synthesis point 14 to the load 16 side becomes the impedance Γ2. The impedance Γ1 becomes the impedance Γ2, and thus, Figure 4 As shown in , the compensation amount BF is enlarged. Figure 4 As shown, impedance Γ2 has a reactance component, namely an imaginary component.

[0115] exist Figure 1 In the Doherty amplifier shown in FIG. 1 , the size of the second amplifier 10 is larger than the size of the first amplifier 9. Therefore, during compensation, Figure 4 As shown, according to the size ratio between the first amplifier 9 and the second amplifier 10, the compensation amount BF of the second amplifier 10 is reduced.

[0116] In addition, Figure 1 In the Doherty amplifier shown in FIG. 1 , the second output circuit 13 is used as shown in FIG. Figure 4 As shown in FIG. 1 , the impedance Γ2 becomes Γ3 on the real axis. That is, the imaginary component of the impedance Γ2 is reduced by the second output circuit 13 .

[0117] exist Figure 1 In the Doherty amplifier shown in Figure 4As shown, the amount of increase in the compensation amount BF achieved by the synthesizing circuit 11 is greater than the amount of decrease in the compensation amount BF corresponding to the size ratio between the first amplifier 9 and the second amplifier 10 .

[0118] The impedance Γ3 is greater than the impedance 2×Rout_2 of a general Doherty amplifier with a compensation amount BF of 6 dB. Therefore, Figure 1 The Doherty amplifier shown obtains a larger compensation amount BF than a general Doherty amplifier.

[0119] In addition, the impedance Γ3 is changed on the real axis, so that Figure 1 The Doherty amplifier shown does not cause the reduction in efficiency associated with the output impedance of the second amplifier 10 having an imaginary component.

[0120] Next, the operation when the frequency f of each of the first signal and the second signal is the second frequency f2 will be described. Here, it is assumed that the second frequency f2 is twice the frequency of the basic frequency.

[0121] When the frequency f of the first signal is the second frequency f2, a bias voltage for biasing the gate terminal 9a of the first amplifier 9 to AB class is supplied to the bias terminal 7, whereby the first amplifier 9 operates as a main amplifier.

[0122] When the frequency f of the second signal is the second frequency f2, a bias voltage for biasing the gate terminal 10a of the second amplifier 10 to Class C is supplied to the bias terminal 8, whereby the second amplifier 10 operates as an auxiliary amplifier.

[0123] The first amplifier 9 and the second amplifier 10 have different sizes. Therefore, when the first amplifier 9 amplifies the first signal as a main amplifier and the second amplifier 10 amplifies the second signal as an auxiliary amplifier, the output reflection coefficient of the first amplifier 9 is increased according to the size ratio of the first amplifier 9 to the second amplifier 10. In addition, the output reflection coefficient of the first amplifier 9 is increased, thereby increasing the compensation amount BF of the first amplifier 9.

[0124] When the first amplifier 9 amplifies the first signal as a main amplifier and the second amplifier 10 amplifies the second signal as an auxiliary amplifier, the synthesizing circuit 11 changes the output impedance of the first amplifier 9 to reduce the output reflection coefficient of the first amplifier 9 .

[0125] exist Figure 1In the Doherty amplifier shown in the figure, the electrical lengths of the first output circuit 12 and the second output circuit 13 are designed so that the reduction amount of the output reflection coefficient achieved by the combining circuit 11 is smaller than the increase amount of the output reflection coefficient caused by the size ratio of the first amplifier 9 to the second amplifier 10. If the combining circuit 11 further includes a lumped constant element in addition to the first output circuit 12 and the second output circuit 13, the electrical lengths and lumped constant elements are designed so that the reduction amount of the output reflection coefficient achieved by the combining circuit 11 is larger than the increase amount of the output reflection coefficient caused by the size ratio.

[0126] Therefore, in Figure 1 In the Doherty amplifier shown, when the first amplifier 9 amplifies the first signal as a main amplifier and the second amplifier 10 amplifies the second signal as an auxiliary amplifier, the compensation amount BF of the first amplifier 9 is increased, thereby improving the efficiency of the compensation operation.

[0127] Figure 5 It is an explanatory diagram showing impedance when the frequency f is the second frequency f2 and the output power of each of the first amplifier 9 and the second amplifier 10 is the saturated output power.

[0128] exist Figure 5 In the example, the output power of the first amplifier 9 is assumed to be the saturated output power P S1 The optimal load impedance of the first amplifier 9 is Ropt_1, and the output power of the second amplifier 10 is the saturated output power P S2 The optimal load impedance of the second amplifier 10 at this time is Ropt_2.

[0129] The saturated output power P of the second amplifier 10 is S2 Greater than the saturated output power P of the first amplifier 9 S1 , therefore, if Ropt_2 is set to α×Ropt_1, α is a value smaller than 1.

[0130] At this time, as shown in the following equation (3), the impedance RL viewed from the output combining point 14 toward the load 16 becomes a value obtained by connecting the optimum load impedance Ropt_1 of the first amplifier 9 and the optimum load impedance Ropt_2 of the second amplifier 10 in parallel.

[0131]

[0132] α is a value smaller than 1. Therefore, as shown in the following equation (4), the impedance RL viewed from the output combining point 14 toward the load 16 is smaller than 0.5 times the optimal load impedance Ropt_1.

[0133] RL<0.5×Ropt_1 (4)

[0134] Figure 3 1 is an explanatory diagram showing impedance when the frequency f is the second frequency f2 and compensation of the second amplifier 10 is stopped.

[0135] Figure 7 It is an explanatory diagram showing the compensation amount BF of the first amplifier 9.

[0136] During compensation, the second amplifier 10 is stopped, so the first amplifier 9 occupies the output load of the output combining point 14. Therefore, the impedance Γ4 (=RL) from the output combining point 14 to the load 16 side is less than 0.5 times Ropt_1.

[0137] If it is assumed that the size of the first amplifier 9 is equal to the size of the second amplifier 10, the impedance Γ4 becomes 0.5 times Ropt_1. Figure 1 In the Doherty amplifier shown, the second amplifier 10 is larger than the first amplifier 9, so the impedance Γ4 is increased compared to a general Doherty amplifier in which the first amplifier 9 and the second amplifier 10 are equal in size. That is, the compensation amount BF is increased.

[0138] During compensation, the second amplifier 10 stops, so the output impedance of the second amplifier 10 becomes an open circuit. In addition, the electrical length of the second output circuit 13 is 180 degrees. Therefore, the impedance Γ4 is not changed by the second output circuit 13.

[0139] The impedance Γ4 is not changed by the second output circuit 13, and therefore the impedance Γ5 viewed from the first output circuit 12 toward the output combining point 14 is the same as the impedance Γ4, and the compensation amount BF does not change.

[0140] Here, the electrical length of the second output circuit 13 is 180 degrees, so the impedance Γ4 is not changed by the second output circuit 13, and the compensation amount BF does not change. However, this is just an example, and the second output circuit 13 may also have a lumped constant element, for example, to change the impedance Γ4 to reduce the compensation amount BF.

[0141] exist Figure 1 In the Doherty amplifier shown in FIG. 1 , the size of the second amplifier 10 is larger than the size of the first amplifier 9. Therefore, during compensation, Figure 7 As shown, according to the size ratio between the first amplifier 9 and the second amplifier 10, the compensation amount BF of the first amplifier 9 is enlarged.

[0142] In addition, Figure 1 In the Doherty amplifier shown in FIG. 1 , through the first output circuit 12, as shown in FIG. Figure 7 As shown, impedance Γ5 becomes Γ6 on the real axis.

[0143] exist Figure 1 In the Doherty amplifier shown in Figure 7 As shown, the reduction amount of the compensation amount BF achieved by the synthesizing circuit 11 is smaller than the increase amount of the compensation amount BF corresponding to the size ratio of the first amplifier 9 to the second amplifier 10.

[0144] The impedance Γ6 is greater than the impedance 2×Rout_2 of a general Doherty amplifier with a compensation amount BF of 6 dB. Therefore, Figure 1 The Doherty amplifier shown obtains a larger compensation amount BF than a general Doherty amplifier.

[0145] In addition, the impedance Γ6 is changed on the real axis, so that Figure 1 The Doherty amplifier shown does not cause a decrease in efficiency associated with the output impedance of the first amplifier 9 having an imaginary component.

[0146] In the above-mentioned first embodiment, the Doherty amplifier is configured to include: a first amplifier 9, which amplifies the first signal as an auxiliary amplifier when the frequencies of the first signal and the second signal are the first frequency, and amplifies the first signal as a main amplifier when the frequencies of the first signal and the second signal are the second frequency; a second amplifier 10, which amplifies the second signal as a main amplifier when the frequencies of the first signal and the second signal are the second frequency, and a synthesizing circuit 11, which synthesizes the first signal amplified by the first amplifier 9 and the second signal amplified by the second amplifier 10. In addition, the second amplifier 10 is an amplifier having a saturated output power greater than the saturated output power of the first amplifier 9, and when the first amplifier 9 amplifies the first signal as the main amplifier and the second amplifier 10 amplifies the second signal as the auxiliary amplifier, the synthesizing circuit 11 changes the output impedance of the first amplifier 9 in such a way that the imaginary component in the output impedance of the first amplifier 9 is reduced. Therefore, the Doherty amplifier can suppress a decrease in efficiency during the compensation operation when the frequency of the signal is the second frequency.

[0147] Implementation Method 2

[0148] In the second embodiment, a Doherty amplifier is described in which, when the frequency f of each of the first signal and the second signal is the third frequency f3, the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier.

[0149] The structure of the Doherty amplifier in the second embodiment is the same as that of the Doherty amplifier in the first embodiment. A structural diagram showing the Doherty amplifier in the second embodiment is shown in FIG. Figure 1 .

[0150] However, in the Doherty amplifier of the second embodiment, when the frequency f of the first signal is the first frequency f1, the first output circuit 12 has an electrical length shorter than 90 degrees, and when the frequency f of the first signal is the second frequency f2, the first output circuit 12 has an electrical length of 90 degrees. In addition, when the frequency f of the first signal is the third frequency f3, the first output circuit 12 has an electrical length of more than 90 degrees.

[0151] When the frequency f of the second signal is the first frequency f1, the second output circuit 13 has an electrical length longer than 90 degrees, and when the frequency f of the second signal is the second frequency f2, the second output circuit 13 has an electrical length of 180 degrees. In addition, when the frequency f of the second signal is the third frequency f3, the second output circuit 13 has an electrical length shorter than 270 degrees.

[0152] The operation when the frequency f of each of the first signal and the second signal is the third frequency f3 will be described. Here, it is assumed that the third frequency f3 is a frequency three times the basic frequency.

[0153] When the frequency f of the first signal is the third frequency f3, a bias voltage for biasing the gate terminal 9a of the first amplifier 9 to Class C is supplied to the bias terminal 7, whereby the first amplifier 9 operates as an auxiliary amplifier.

[0154] When the frequency f of the second signal is the third frequency f3, a bias voltage for biasing the gate terminal 10a of the second amplifier 10 to AB class is supplied to the bias terminal 8, whereby the second amplifier 10 operates as a main amplifier.

[0155] The saturated output power P of the second amplifier 10 is S2 Greater than the saturated output power P of the first amplifier 9 S1 That is, the size of the second amplifier 10 is larger than the size of the first amplifier 9 .

[0156] The first amplifier 9 and the second amplifier 10 have different sizes. Therefore, when the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the output reflection coefficient of the second amplifier 10 is reduced according to the size ratio of the first amplifier 9 to the second amplifier 10. In addition, the output reflection coefficient of the second amplifier 10 is reduced, thereby reducing the compensation amount BF of the second amplifier 10.

[0157] When the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the synthesizing circuit 11 changes the output impedance of the second amplifier 10 to increase the output reflection coefficient of the second amplifier 10 .

[0158] In the Doherty amplifier of the second embodiment, the electrical lengths of the first output circuit 12 and the second output circuit 13 are designed so that the amount of increase in the output reflection coefficient achieved by the synthesizing circuit 11 is greater than the amount of decrease in the output reflection coefficient caused by the size ratio of the first amplifier 9 to the second amplifier 10. If the synthesizing circuit 11 further includes a lumped constant element in addition to the first output circuit 12 and the second output circuit 13, the electrical lengths and lumped constant elements are designed so that the amount of increase in the output reflection coefficient achieved by the synthesizing circuit 11 is greater than the amount of decrease in the output reflection coefficient caused by the size ratio.

[0159] Therefore, in the Doherty amplifier of the second embodiment, when the first amplifier 9 amplifies the first signal as an auxiliary amplifier and the second amplifier 10 amplifies the second signal as a main amplifier, the compensation amount BF of the second amplifier 10 is increased, thereby improving the efficiency during the compensation operation.

[0160] The impedance when the frequency f is the third frequency f3 and the output power of each of the first amplifier 9 and the second amplifier 10 is the saturated output power is the same as the impedance when the frequency f is the first frequency f1, which is Figure 2 .

[0161] Figure 8 It is an explanatory diagram showing impedance when compensation is performed when the frequency f is the third frequency f3 and the first amplifier 9 is stopped.

[0162] Fig. 9 1 is an explanatory diagram showing the compensation amount BF of the second amplifier 10 .

[0163] During compensation, the first amplifier 9 stops, so the second amplifier 10 occupies the output load of the output combining point 14. Therefore, the impedance Γ7 (=RL) from the output combining point 14 to the load 16 side is greater than 0.5 times Ropt_2.

[0164] If the size of the first amplifier 9 is equal to the size of the second amplifier 10, the impedance Γ7 becomes 0.5 times Ropt_2. In the Doherty amplifier of the second embodiment, the size of the second amplifier 10 is larger than the size of the first amplifier 9, so the impedance Γ7 is reduced compared with the general Doherty amplifier in which the size of the first amplifier 9 is equal to the size of the second amplifier 10. That is, the compensation amount BF is reduced.

[0165] During compensation, the first amplifier 9 stops, so the output impedance of the first amplifier 9 becomes an open circuit. Since the output impedance of the first amplifier 9 becomes an open circuit, when the first amplifier 9 is viewed from the output combining point 14, the first output circuit 12 functions as a virtual open stub.

[0166] The first output circuit 12 functions as an open stub, so the impedance Γ7 from the output synthesis point 14 to the load 16 side becomes the impedance Γ8. The impedance Γ7 becomes the impedance Γ8, and thus, Fig. 9 As shown in , the compensation amount BF is enlarged. Fig. 9 As shown, impedance Γ8 has a reactance component, namely an imaginary component.

[0167] In the Doherty amplifier of the second embodiment, the size of the second amplifier 10 is larger than the size of the first amplifier 9. Therefore, during compensation, the compensation amount BF of the second amplifier 10 is reduced according to the size ratio between the first amplifier 9 and the second amplifier 10.

[0168] In addition, in the Doherty amplifier of the second embodiment, the second output circuit 13 is used, as shown in FIG. Fig. 9 As shown in FIG. 1 , the impedance Γ8 becomes Γ9 on the real axis. That is, the imaginary component of the impedance Γ8 is reduced by the second output circuit 13 .

[0169] In the Doherty amplifier of embodiment 2, as Fig. 9 As shown, the amount of increase in the compensation amount BF achieved by the synthesizing circuit 11 is greater than the amount of decrease in the compensation amount BF corresponding to the size ratio between the first amplifier 9 and the second amplifier 10 .

[0170] The impedance Γ9 is larger than the impedance 2×Rout_2 of a general Doherty amplifier having a compensation amount BF of 6 dB. Therefore, the Doherty amplifier of the second embodiment obtains a larger compensation amount BF than the general Doherty amplifier.

[0171] Furthermore, since the impedance Γ9 is changed on the real axis, the Doherty amplifier according to the second embodiment does not suffer from a decrease in efficiency due to the output impedance of the second amplifier 10 having an imaginary component.

[0172] Fig.10 1 is an explanatory diagram showing simulation results of power efficiency corresponding to output power of the Doherty amplifier.

[0173] exist Fig.10 In FIG. 1 , the horizontal axis represents the output power (dBm) of the Doherty amplifier according to the second embodiment, and the vertical axis represents the power efficiency (%) of the Doherty amplifier according to the second embodiment.

[0174] Fig.11 1 is an explanatory diagram showing simulation results of compensation efficiency corresponding to the frequency f of each of the first signal and the second signal.

[0175] exist Fig.11 In FIG. 1 , the horizontal axis represents the frequency f of each of the first signal and the second signal, and the vertical axis represents the compensation efficiency (%) of the Doherty amplifier according to the second embodiment.

[0176] like Fig.10 As shown, the Doherty amplifier of Embodiment 2 obtains a compensation amount greater than 6 dB.

[0177] like Fig.11 As shown, the Doherty amplifier of the second embodiment achieves high compensation efficiency not only when the frequency f is the first frequency f1 which is the basic frequency, but also when the frequency f is the second frequency f2 which is twice the frequency and the third frequency f3 which is triple the frequency.

[0178] In the above-mentioned second embodiment, the Doherty amplifier is configured such that, if the frequencies of the first signal and the second signal are each the third frequency, the first amplifier 9 amplifies the first signal as an auxiliary amplifier, and the second amplifier 10 amplifies the second signal as a main amplifier. Furthermore, when the respective frequencies are the third frequency and the first amplifier 9 amplifies the first signal as an auxiliary amplifier, and the second amplifier 10 amplifies the second signal as a main amplifier, the synthesizing circuit 11 changes the output impedance of the second amplifier 10 in such a manner as to reduce the imaginary component in the output impedance of the second amplifier 10. Therefore, the Doherty amplifier can suppress the reduction in efficiency during the compensation operation when the frequency of the signal is the third frequency.

[0179] Implementation 3

[0180] In the third embodiment, a Doherty amplifier is described in which the signal source of the first signal supplied to the first amplifier 33 and the signal source of the second signal supplied to the second amplifier 34 are different signal sources.

[0181] Fig.12 is a diagram showing the structure of a Doherty amplifier in Embodiment 3. Fig.12 In, with Figure 1 The same reference numerals denote the same or corresponding parts, and thus their descriptions are omitted.

[0182] The input terminal 31 is supplied with a first signal from a first signal source (not shown) provided outside the Doherty amplifier.

[0183] The second signal is supplied from a second signal source (not shown) provided outside the Doherty amplifier to the input terminal 32. The first signal source and the second signal source are different signal sources.

[0184] The first amplifier 33 is realized by, for example, FET, HBT, or HEMT.

[0185] A bias voltage biased to class B is applied to the gate terminal 33 a of the first amplifier 33 . That is, a bias voltage having substantially the same magnitude as the threshold voltage of the first amplifier 33 is applied to the gate terminal 33 a of the first amplifier 33 .

[0186] When the frequency f of the first signal is the first frequency f1 and the power of the first signal is lower than the power of the second signal, the first amplifier 33 amplifies the first signal as an auxiliary amplifier.

[0187] When the frequency f of the first signal is equal to the second frequency f2 and the power of the first signal is greater than the power of the second signal, the first amplifier 33 amplifies the first signal as a main amplifier.

[0188] and Figure 1 Similarly to the first amplifier 9 shown, the output equivalent circuit of the first amplifier 33 is the output equivalent circuit 21 .

[0189] The second amplifier 34 is realized by, for example, FET, HBT, or HEMT.

[0190] A bias voltage biased to class B is applied to the gate terminal 34 a of the second amplifier 34 . That is, a bias voltage having substantially the same magnitude as the threshold voltage of the second amplifier 34 is applied to the gate terminal 34 a of the second amplifier 34 .

[0191] When the frequency f of the second signal is the first frequency f1 and the power of the second signal is greater than the power of the first signal, the second amplifier 34 amplifies the second signal as a main amplifier.

[0192] When the frequency f of the second signal is the second frequency f2 and the power of the second signal is lower than the power of the first signal, the second amplifier 34 amplifies the second signal as an auxiliary amplifier.

[0193] and Figure 1 Similarly to the second amplifier 10 shown, the output equivalent circuit of the second amplifier 34 is the output equivalent circuit 24 .

[0194] Next, Fig.12 The operation of the Doherty amplifier shown will be described.

[0195] exist Fig.12 In the Doherty amplifier shown, when a first signal of a first frequency f1 is supplied from a first signal source to an input terminal 31, a second signal of a first frequency f1 is supplied from a second signal source to an input terminal 32. At this time, the power of the first signal is smaller than the power of the second signal.

[0196] When the first signal source supplies the first signal of the second frequency f2 to the input terminal 31, the second signal source supplies the second signal of the second frequency f2 to the input terminal 32. At this time, the power of the first signal is greater than the power of the second signal.

[0197] Therefore, when the first signal of the first frequency f1 is supplied to the input terminal 31, the first amplifier 33 amplifies the first signal as an auxiliary amplifier. When the first signal of the second frequency f2 is supplied to the input terminal 31, the first amplifier 33 amplifies the first signal as a main amplifier.

[0198] When the second signal of the first frequency f1 is supplied to the input terminal 32, the second amplifier 34 amplifies the second signal as a main amplifier. When the second signal of the second frequency f2 is supplied to the input terminal 32, the second amplifier 34 amplifies the second signal as an auxiliary amplifier.

[0199] As described above, even if the signal source of the first signal supplied to the first amplifier 33 and the signal source of the second signal supplied to the second amplifier 34 are different signal sources, the first amplifier 33 is connected to the second amplifier 34. Figure 1 The first amplifier 9 shown in the figure operates in the same manner, and the second amplifier 34 operates in the same manner as the first amplifier 9 shown in the figure. Figure 1 The second amplifier 10 shown operates in the same manner.

[0200] Fig.12 The synthesis circuit 11 shown is Figure 1 The synthesizing circuit 11 shown operates in the same manner.

[0201] Therefore, with Figure 1 The Doherty amplifier shown is similarly Fig.12 The Doherty amplifier shown can suppress a decrease in efficiency during the compensation operation when the frequency of the signal is the second frequency.

[0202] Furthermore, it is possible to suppress a decrease in efficiency during the compensation operation when the frequency of the signal is the third frequency.

[0203] Implementation 4

[0204] In the fourth embodiment, a Doherty amplifier is described in which the transmission line 41 is connected and the electrical length of the transmission line 41 is an integral multiple of 180 degrees at the frequency f of each of the first signal and the second signal.

[0205] Fig.13 is a diagram showing the structure of a Doherty amplifier in accordance with Embodiment 4. Fig.13 In, with Figure 1 The same reference numerals denote the same or corresponding parts, and thus their descriptions are omitted.

[0206] One end of the transmission line 41 is connected to the output side of the first amplifier.

[0207] The other end of the transmission line 41 is connected to one end of the first output circuit 12 in the combining circuit 11 .

[0208] At the frequency f of each of the first signal and the second signal, the electrical length of the transmission line 41 is an integral multiple of 180 degrees.

[0209] exist Fig.13 In the Doherty amplifier shown, the transmission line 41 is applied to Figure 1 The Doherty amplifier shown in FIG. However, this is only an example, and the transmission line 41 can also be applied to Fig.12 The Doherty amplifier is shown.

[0210] The impedance at one end of the transmission line 41 whose electrical length is an integral multiple of 180 degrees and the impedance at the other end of the transmission line 41 are the same impedance.

[0211] Therefore, even if the transmission line 41 is connected between the output side of the first amplifier 9 and the synthesizing circuit 11, Figure 1 The Doherty amplifier shown operates similarly.

[0212] exist Fig.13 In the Doherty amplifier shown in FIG. 1 , the transmission line 41 is connected between the output side of the first amplifier 9 and the synthesizing circuit 11. However, this is only an example. Fig.14 As shown, a transmission line 42 whose electrical length is an integral multiple of 180 degrees at the frequency f of each of the first signal and the second signal may be connected between the output side of the second amplifier 10 and the synthesizing circuit 11 .

[0213] Fig.14 1 is a diagram showing the structure of another Doherty amplifier according to the fourth embodiment.

[0214] exist Fig.14 In the Doherty amplifier shown, the transmission line 42 is applied to Figure 1 However, this is only an example, and the transmission line 42 can also be applied to Fig.12 The Doherty amplifier is shown.

[0215] Furthermore, the present invention can carry out free combination of the various embodiments, modification of arbitrary components of the various embodiments, or omission of arbitrary components of the various embodiments.

[0216] Industrial Applicability

[0217] The present invention is applicable to a Doherty amplifier.

[0218] Description of symbols

[0219] 1: input terminal; 2: input matching circuit; 3: distributor; 4: phase correction circuit; 5: input matching circuit; 6: input matching circuit; 7: bias terminal; 8: bias terminal; 9: first amplifier; 9a: gate terminal; 10: second amplifier; 10a: gate terminal; 11: synthesis circuit; 12: first output circuit; 13: second output circuit; 14: output synthesis point; 15: output matching circuit; 16: load; 21: output equivalent circuit; 22: current source; 23: capacitor; 24: output equivalent circuit; 25: current source; 26: capacitor; 31, 32: input terminal; 33: first amplifier; 33a: gate terminal; 34: second amplifier; 34a: gate terminal; 41, 42: transmission line; 51: series inductor; 52: parallel inductor; 53: series capacitor; 54: series inductor; 55: parallel inductor; 56: series capacitor.

Claims

1. A Doherty amplifier, characterized in that: The Doherty amplifier has: a first amplifier, wherein if the first signal and the second signal each have a first frequency, the first amplifier amplifies the first signal as an auxiliary amplifier, and if the first signal and the second signal each have a second frequency, the first amplifier amplifies the first signal as a main amplifier; a second amplifier, wherein if the respective frequencies are the first frequencies, the second amplifier amplifies the second signal as a main amplifier, and if the respective frequencies are the second frequencies, the second amplifier amplifies the second signal as an auxiliary amplifier; and a synthesizing circuit that synthesizes the first signal amplified by the first amplifier and the second signal amplified by the second amplifier, The second amplifier is an amplifier having a saturated output power greater than the saturated output power of the first amplifier. When the first amplifier amplifies the first signal as a main amplifier and the second amplifier amplifies the second signal as an auxiliary amplifier, the synthesizing circuit changes the output impedance of the first amplifier so as to reduce an imaginary component in the output impedance of the first amplifier.

2. The Doherty amplifier according to claim 1, characterized in that: When the first amplifier amplifies the first signal as a main amplifier and the second amplifier amplifies the second signal as an auxiliary amplifier, the synthesizing circuit changes the output impedance of the first amplifier, thereby reducing the output reflection coefficient of the first amplifier. The amount of reduction in the output reflection coefficient is smaller than the amount of increase in the output reflection coefficient of the first amplifier associated with the difference between the saturated output power of the first amplifier and the saturated output power of the second amplifier.

3. The Doherty amplifier according to claim 1, characterized in that: When the first amplifier amplifies the first signal as an auxiliary amplifier and the second amplifier amplifies the second signal as a main amplifier, the synthesizing circuit changes the output impedance of the second amplifier so as to reduce an imaginary component in the output impedance of the second amplifier.

4. The Doherty amplifier according to claim 3, characterized in that: When the first amplifier amplifies the first signal as an auxiliary amplifier and the second amplifier amplifies the second signal as a main amplifier, the synthesizing circuit changes the output impedance of the second amplifier, thereby increasing the output reflection coefficient of the second amplifier. The amount of increase in the output reflection coefficient is greater than the amount of decrease in the output reflection coefficient of the second amplifier associated with the difference between the saturated output power of the first amplifier and the saturated output power of the second amplifier.

5. The Doherty amplifier according to claim 3, characterized in that: The synthesis circuit has: a first output circuit, one end of which is connected to the output side of the first amplifier; and a second output circuit, one end of which is connected to the output side of the second amplifier, and the other end of which is connected to the other end of the first output circuit, When the respective frequencies are the first frequencies, the first output circuit has an electrical length shorter than 90 degrees, and when the respective frequencies are the second frequencies, the first output circuit has an electrical length of 90 degrees. When the respective frequencies are the first frequencies, the second output circuit has an electrical length longer than 90 degrees, and when the respective frequencies are the second frequencies, the second output circuit has an electrical length of 180 degrees.

6. The Doherty amplifier according to claim 3, characterized in that: If the respective frequencies are the third frequency, the first amplifier amplifies the first signal as an auxiliary amplifier, and the second amplifier amplifies the second signal as a main amplifier. When the respective frequencies are the third frequencies, the first amplifier amplifies the first signal as an auxiliary amplifier, and the second amplifier amplifies the second signal as a main amplifier, the synthesizing circuit changes the output impedance of the second amplifier in such a manner as to reduce an imaginary component in the output impedance of the second amplifier.

7. The Doherty amplifier according to claim 6, characterized in that: When the respective frequencies are the third frequency, the first amplifier amplifies the first signal as an auxiliary amplifier and the second amplifier amplifies the second signal as a main amplifier, the synthesizing circuit changes the output impedance of the second amplifier, thereby increasing the output reflection coefficient of the second amplifier. The increase amount of the output reflection coefficient is larger than the decrease amount of the output reflection coefficient of the first amplifier associated with the difference between the saturated output power of the first amplifier and the saturated output power of the second amplifier.

8. The Doherty amplifier according to claim 6, characterized in that: The synthesis circuit has: a first output circuit, one end of which is connected to the output side of the first amplifier; and a second output circuit, one end of which is connected to the output side of the second amplifier, and the other end of which is connected to the other end of the first output circuit, When the respective frequencies are the first frequencies, the first output circuit has an electrical length shorter than 90 degrees, when the respective frequencies are the second frequencies, the first output circuit has an electrical length of 90 degrees, and when the respective frequencies are the third frequencies, the first output circuit has an electrical length greater than 90 degrees, When the respective frequencies are the first frequencies, the second output circuit has an electrical length longer than 90 degrees, when the respective frequencies are the second frequencies, the second output circuit has an electrical length of 180 degrees, and when the respective frequencies are the third frequencies, the second output circuit has an electrical length shorter than 270 degrees.

9. The Doherty amplifier according to claim 1, characterized in that: When the respective frequencies are the first frequencies, when a bias voltage lower than a threshold voltage is applied, the first amplifier amplifies the first signal as an auxiliary amplifier, and when the respective frequencies are the second frequencies, when a bias voltage higher than the threshold voltage is applied, the first amplifier amplifies the first signal as a main amplifier, When the respective frequencies are the first frequencies, when a bias voltage higher than the threshold voltage is applied, the second amplifier amplifies the second signal as a main amplifier, and when the respective frequencies are the second frequencies, when a bias voltage lower than the threshold voltage is applied, the second amplifier amplifies the second signal as an auxiliary amplifier.

10. The Doherty amplifier according to claim 1, characterized in that: When the respective frequencies are the first frequencies and the power of the first signal is less than the power of the second signal, the first amplifier amplifies the first signal as an auxiliary amplifier, and when the respective frequencies are the second frequencies and the power of the first signal is greater than the power of the second signal, the first amplifier amplifies the first signal as a main amplifier, When the respective frequencies are the first frequencies and the power of the second signal is greater than the power of the first signal, the second amplifier acts as a main amplifier to amplify the second signal; and when the respective frequencies are the second frequencies and the power of the second signal is less than the power of the first signal, the second amplifier acts as an auxiliary amplifier to amplify the second signal.

11. The Doherty amplifier according to claim 1, characterized in that: The Doherty amplifier has a transmission line connected between the output side of the first amplifier and the synthesis circuit or between the output side of the second amplifier and the synthesis circuit, and the electrical length of the transmission line is an integer multiple of 180 degrees at the respective frequencies of the first signal and the second signal.

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