Doherty amplifier

Abstract

A Doherty amplifier according to the present disclosure comprises a main amplifier, an auxiliary amplifier, a distribution circuit that distributes signals to the main amplifier and the auxiliary amplifier, and a phase compensation circuit. The main amplifier has a first input matching circuit and a plurality of main amplification stages. The auxiliary amplifier has a second input matching circuit and a plurality of auxiliary amplification stages. The distribution circuit has a first line connected to the first input matching circuit and a second line connected to the second input matching circuit. The electrical length of the first line is such that the input impedance of the first line is higher than the characteristic impedance of the first line and the imaginary component is less than 10% of the real component when a small signal is input. The electrical length of the second line is such that the input impedance of the second line is higher than the characteristic impedance of the second line and the imaginary component is less than 10% of the real component when a small signal is input. The phase compensation circuit is provided in an inter-stage matching circuit of the plurality of main amplification stages or the plurality of auxiliary amplification stages.

Description

Doherty amplifier

[0001] The present disclosure relates to a Doherty amplifier.

[0002] Patent Document 1 discloses a Doherty amplifier provided with an active bias circuit. In the active bias circuit, an average power detection means detects a voltage value indicating the average power of an input signal. An envelope detection means detects the envelope of the input signal. A threshold operation means calculates a threshold of the envelope according to the average power voltage value. A voltage limiting means limits the envelope to a value or less. Thereby, the active bias circuit applies a bias voltage according to the average power of the input signal.

[0003] Japanese Patent Application Laid-Open No. 2008-78847

[0004] In wireless communication, a digital modulation signal having a large PAPR (Peak to Average Ratio) is used to support high-speed and high-capacity communication. Even for such a modulation signal having a large PAPR, a Doherty amplifier is widely used as a circuit for amplifying a signal with low distortion and high efficiency.

[0005] In a Doherty amplifier, a main amplifier biased in class AB and an auxiliary amplifier biased in class C are connected in parallel by a distribution circuit and a combining circuit. A Wilkinson distribution circuit is widely used for the distribution circuit. The auxiliary amplifier can achieve both high efficiency and a large saturation output power by actively modulating the load of the main amplifier while supplying output power to the combining circuit. However, in reality, since the gain of the auxiliary amplifier is biased in class C, it is lower than that of the main amplifier, and complete load modulation is not achieved, resulting in a decrease in the saturation output power.

[0006] Regarding this problem, Patent Document 1 proposes a circuit for dynamically optimizing the gate bias voltage of the auxiliary amplifier with respect to the input power. However, in the circuit of Patent Document 1, the circuit design becomes complicated, and there is a risk of increased cost and size.

[0007] An object of the present disclosure is to obtain a Doherty amplifier that can obtain good RF characteristics while suppressing circuit complexity.

[0008] The Doherty amplifier according to this disclosure comprises a main amplifier, an auxiliary amplifier, a distribution circuit configured to distribute a signal from an input terminal to the main amplifier and the auxiliary amplifier at a branching point, a combining circuit configured to combine the signal from the main amplifier and the signal from the auxiliary amplifier and output it from an output terminal, and a phase compensation circuit whose electrical length is set such that the electrical length of the path from the input terminal through the main amplifier to the output terminal is the same as the electrical length of the path from the input terminal through the auxiliary amplifier to the output terminal, the main amplifier having a first input matching circuit connected to the distribution circuit, and a plurality of main amplification stages connected in series to the output side of the first input matching circuit, the auxiliary amplifier having a second input matching circuit connected to the distribution circuit, and a plurality of auxiliary amplification stages connected in series to the output side of the second input matching circuit, and the distribution circuit having a first transmission line connected between the branching point and the first input matching circuit The phase compensation circuit is provided in the interstage matching circuits of the plurality of main amplification stages or the plurality of auxiliary amplification stages. The characteristic impedance of the first line is the same as the input impedance of the first input matching circuit when a large signal with power that saturates the main amplifier and the auxiliary amplifier is input, and the first line has an electrical length such that when a small signal with lower power than the large signal is input, the input impedance of the first line is lower than the characteristic impedance of the first line and the imaginary component is less than 10% of the real component, and the characteristic impedance of the second line is the same as the input impedance of the second input matching circuit when a large signal is input, and the second line has an electrical length such that when a small signal is input, the input impedance of the second line is higher than the characteristic impedance of the second line and the imaginary component is less than 10% of the real component, and the phase compensation circuit is provided in the interstage matching circuits of the plurality of main amplification stages or the interstage matching circuits of the plurality of auxiliary amplification stages.

[0009] The Doherty amplifier according to this disclosure allows for a large change in the power distribution ratio in response to changes in input power, thereby achieving good RF characteristics. Furthermore, the Doherty amplifier according to this disclosure does not require a complex circuit for changing the gate bias voltage. Therefore, circuit complexity can be suppressed.

[0010] This figure shows the configuration of a Doherty amplifier according to Embodiment 1. This figure shows the configuration of a Doherty amplifier according to a comparative example. This figure shows the calculation results of the dependence of input impedance on input power in the comparative example. This figure shows the calculation results of input impedance when the electrical length of the second transmission line is changed in the comparative example. This figure shows the calculation results of the dependence of power distribution ratio on input power in the comparative example. This figure shows the calculation results of the dependence of RF characteristics on the electrical length of the second transmission line in the comparative example. This figure shows the dependence of PAE on the gate voltage of the first main amplification stage in the comparative example. This figure shows the dependence of small signal gain on the gate voltage of the first main amplification stage in the comparative example. This figure shows the dependence of saturation output power on the gate voltage of the first main amplification stage in the comparative example. This figure shows the calculation results of input impedance when the gate voltage of the first main amplification stage in the comparative example is close to the Class B bias condition. This figure shows the dependence of power distribution ratio on input power in the comparative example. This figure shows the calculation results of input impedance when the electrical length of the first transmission line is changed in Embodiment 1. This figure shows the dependence of power distribution ratio on input power in Embodiment 1. This figure shows the dependence of PAE on the gate voltage of the first main amplification stage in Embodiment 1. This figure shows the dependence of the small-signal gain on the gate voltage of the first-stage main amplifier in Embodiment 1. This figure shows the dependence of the saturated output power on the gate voltage of the first-stage main amplifier in Embodiment 1. This figure shows the dependence of the input reflection on the input power in Embodiment 1. This figure shows an example of a lumped-element circuit according to Embodiment 2. This figure shows an example of a lumped-element circuit according to Embodiment 2. This figure shows an example of a lumped-element circuit according to Embodiment 2. This figure shows an example of a lumped-element circuit according to Embodiment 2.

[0011] The Doherty amplifiers according to each embodiment will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repetition of the description may be omitted.

[0012] Embodiment 1. Figure 1 shows the configuration of a Doherty amplifier 100 according to Embodiment 1. The Doherty amplifier 100 is, for example, a power amplifier for wireless communication. The Doherty amplifier 100 includes a main amplifier 20 and an auxiliary amplifier 40 connected in parallel between an input terminal 11 and an output terminal 12. A signal is input from the input terminal 11 and output from the output terminal 12. The distribution circuit 60 is configured to distribute the signal from the input terminal 11 to the main amplifier 20 and the auxiliary amplifier 40 at a branching point 64. The combining circuit 70 is configured to combine the signal from the main amplifier 20 and the signal from the auxiliary amplifier 40 and output it from the output terminal 12.

[0013] The main amplifier 20 has an input matching circuit 31 connected to the distribution circuit 60, and a plurality of main amplification stages 21 and 22 connected in series to the output side of the input matching circuit 31. Figure 1 shows an example in which the main amplifier 20 is a two-stage amplifier. An interstage matching circuit 32 is connected between the first main amplification stage 21 and the final main amplification stage 22. An output matching circuit 33 is connected to the output side of the main amplification stage 22.

[0014] The auxiliary amplifier 40 has an input matching circuit 51 connected to the distribution circuit 60, and a plurality of auxiliary amplification stages 41 and 42 connected in series to the output side of the input matching circuit 51. Figure 1 shows an example in which the auxiliary amplifier 40 is a two-stage amplifier. Between the first auxiliary amplification stage 41 and the final auxiliary amplification stage 42, an interstage matching circuit 52, a phase compensation circuit 53, and an interstage matching circuit 54 are connected in series. An output matching circuit 55 is connected to the output side of the auxiliary amplification stage 42. The transistors constituting the main amplification stages 21 and 22 and the auxiliary amplification stages 41 and 42 are, for example, GaN-HEMT (High Electron Mobility Transistor) or Si-LDMOS (Laterally Diffused Metal Oxide Semiconductor).

[0015] The electrical length of the phase compensation circuit 53 is set so that the electrical length of the path from the input terminal 11 through the main amplifier 20 to the output terminal 12 is the same as the electrical length of the path from the input terminal 11 through the auxiliary amplifier 40 to the output terminal 12. For example, a lumped-element circuit as shown in Figures 18A-18D can be used as the phase compensation circuit 53. The capacitance and inductance values ​​of the phase compensation circuit 53 are set so that the electrical length of the path from the input terminal 11 through the main amplifier 20 to the output terminal 12 is the same as the electrical length of the path from the input terminal 11 through the auxiliary amplifier 40 to the output terminal 12. In this embodiment, the phase compensation circuit 53 is provided in the interstage matching circuits of multiple auxiliary amplifier stages 41 and 42. As will be described later, the phase compensation circuit 53 may also be provided in the interstage matching circuits of multiple main amplifier stages 21 and 22.

[0016] The distribution circuit 60 has a first line 61 connected between the branching point 64 and the input matching circuit 31, and a second line 62 connected between the branching point 64 and the input matching circuit 51. The first line 61 and the second line 62 are both microstrip lines. The first line 61 and the second line 62 may be formed on a printed circuit board, or they may be composed of an MMIC (Monolytic Microwave Integrated Circuit). The combining circuit 70 has a λ / 4 line 71 and an impedance transformation circuit 72 provided between the combining point 74 and the output terminal 12.

[0017] Node 65 is an input terminal of the input matching circuit 31. Let ZM1 be the input impedance seen from node 65 to the input matching circuit 31. Node 66 is an input terminal of the first transmission line 61. Let ZM2 be the input impedance seen from node 66 to the first transmission line 61. Node 67 is an input terminal of the input matching circuit 51. Let ZA1 be the input impedance seen from node 67 to the input matching circuit 51. Node 68 is an input terminal of the second transmission line 62. Let ZA2 be the input impedance seen from node 68 to the second transmission line 62. Also, let ZIN be the input impedance seen from input terminal 11 to branch point 64.

[0018] In Doherty amplifiers, it is common practice to make the gate width of the transistors in the final auxiliary amplification stage 42 larger than the gate width of the transistors in the final main amplification stage 22 in order to improve efficiency. Below, we will explain the case where the Doherty amplifier 100 is an asymmetric Doherty amplifier in which, for example, the gate width of the auxiliary amplification stage 42 is twice the gate width of the main amplification stage 22.

[0019] Figure 2 shows the configuration of a Doherty amplifier 800 according to a comparative example. In order to explain the features of the Doherty amplifier 100 of this embodiment, the configuration of the comparative example will be described first. The Doherty amplifier 800 according to the comparative example is provided with a first transmission line 861 and a second transmission line 862 instead of the first transmission line 61 and the second transmission line 62. The first transmission line 861 and the second transmission line 862 are microstrip transmission lines. In addition, only an interstage matching circuit 54 is provided instead of an interstage matching circuit 52, a phase compensation circuit 53, and an interstage matching circuit 54. The other configurations are the same as those of the first embodiment.

[0020] The design and operation of the distribution circuit 60 of the Doherty amplifier 800 in the comparative example will be described below. In the following, a signal with power that causes the main amplifier 20 and the auxiliary amplifier 40 to saturate will be called a large signal. A signal with less power than a large signal will be called a small signal. Specifically, a small signal is a signal with power that causes the gain of the auxiliary amplifier 40, which is biased to Class C, to be less than 0 dB.

[0021] The input matching circuit 31 of the main amplifier 20 is designed so that the input impedance ZM1 is 100Ω when a large signal is input, that is, at the input power at which the main amplifier 20 saturates. The input matching circuit 51 of the auxiliary amplifier 40 is designed so that the input impedance ZA1 is 50Ω when a large signal is input, that is, at the input power at which the auxiliary amplifier 40 saturates. On the other hand, the input impedance ZA1 at small signals is different from 50Ω. The reason why the impedance differs depending on the input power is that the bias of the first stage auxiliary amplification stage 41 is set to Class C bias. The nonlinearity of the parasitic capacitance of the transistors in the auxiliary amplification stage 41 causes a change in impedance. In contrast, the input impedance ZM1 of the main amplifier 20, which is biased to Class AB, has little dependence on input power and shows a value close to 100Ω even at small signals.

[0022] Figure 3 shows the calculated dependence of input impedances ZM1 and ZA1 on input power in a comparative example. In Figure 3, the starting point of the arrow indicates the impedance at small signals, and the input power increases in the direction of the arrow. The ending point of the arrow indicates the impedance at large signals. The input impedance ZM1 of the main amplifier 20 shows little change with respect to input power and is approximately 100Ω. In contrast, the input impedance ZA1 of the auxiliary amplifier 40 has a large reactive component at small signals and approaches 50Ω as the input power increases.

[0023] The characteristic impedance of the second transmission line 862 is set to 50Ω, the same as the input impedance ZA1 at large signals. Furthermore, the electrical length θ2 of the second transmission line 862 is set so that the input impedance ZA2 is maximized at small signals. Figure 4 shows the calculation results of the input impedance ZA2 when the electrical length θ2 of the second transmission line 862 is changed in the comparative example. In Figure 4, the input impedance ZA2 when the electrical length θ2 is changed in 25° steps is shown. At θ2 = 50°, the input impedance ZA2 at small signals is maximized. Therefore, in the case of Figure 4, θ2 is set to 50°. Also, from Figure 4, it can be seen that at large signals, the input impedance ZA2 is 50Ω and does not depend on the electrical length θ2.

[0024] Furthermore, the electrical length θ1 of the first transmission line 861 is determined so that the pass-through phase of the main amplifier 20 and the auxiliary amplifier 40 from the branching point 64 to the combination point 74 is the same. The characteristic impedance of the first transmission line 861 is set to the same value as the input impedance ZM1. In the example in Figure 2, the electrical length θ1 of the first transmission line 861 is 10° and the characteristic impedance is 100Ω.

[0025] As described above, by designing the distribution circuit 60, the input impedance ZM2 of the first transmission line 861 is 100Ω regardless of the input power. Also, the input impedance ZA2 of the second transmission line 862 is set to an impedance higher than 50Ω for small signals and 50Ω for large signals. The power distribution ratio in the distribution circuit 60 is determined by the impedance ratio of ZM2 and ZA2. Therefore, when a large signal is input, the auxiliary amplifier 40 receives twice the power of the main amplifier 20, corresponding to the size ratio of the final stage transistors. On the other hand, when a small signal is input, the power distribution ratio to the main amplifier 20 is greater than when a large signal is input, improving the gain of the main amplifier 20. In this way, the power distribution ratio in the distribution circuit 60 can be changed according to the input power. As a result, the gain of the main amplifier 20 is high for small signals, and the gain of the auxiliary amplifier 40 is high for large signals, thus achieving high efficiency and large saturated output power as a Doherty amplifier.

[0026] In the Doherty amplifier 800 of the comparative example, the electrical length θ2 of the second transmission line 862 is important. Figure 5 shows the calculation results of the dependence of the power distribution ratio on the input power in the comparative example. Figure 5 shows the power distribution ratio when the electrical length θ2 is changed. According to Figure 5, it can be seen that the change in the power distribution ratio is greatest when θ2 is set to 50°. The greater the change in the power distribution ratio in response to the change in input power, the better the RF (Radio Frequency) characteristics obtained.

[0027] Figure 6 shows the calculated results of the dependence of the RF characteristics of the second transmission line 862 on the electrical length θ2 in the comparative example. In Figure 6, it can be seen that the linear gain and backoff efficiency are excellent when the electrical length θ2 is set to 50°.

[0028] Next, we will explain the problems in the comparative example. The input impedance of the main amplifier 20, like the input impedance of the auxiliary amplifier 40, depends on the input power. Therefore, when the gate bias condition of the main amplification stage 21 of the first stage of the main amplifier 20 is changed in the Doherty amplifier 800, the dependence of the power distribution ratio of the distribution circuit 60 on the input power as described above cannot be achieved, and the RF characteristics deteriorate significantly.

[0029] Figure 7 shows the dependence of PAE (Power-Added Efficiency) on the gate voltage of the first-stage main amplifier stage 21 in the comparative example. Figure 8 shows the dependence of small-signal gain on the gate voltage of the first-stage main amplifier stage 21 in the comparative example. Figure 9 shows the dependence of saturated output power on the gate voltage of the first-stage main amplifier stage 21 in the comparative example. In Figures 7-9, the horizontal axis is referenced to the pinch-off voltage Vt. Note that the calculations in Figures 3-6 correspond to the result when the gate voltage is 0.46V.

[0030] As shown in Figures 7 and 8, changing the gate voltage from Class AB to Class B significantly degrades efficiency and gain. This is because the input impedance of the main amplifier 20, like that of the auxiliary amplifier 40, is dependent on input power. Figure 10 shows the calculation results of the input impedance ZM1 when the gate voltage of the first stage main amplifier 21 in the comparative example is close to the Class B bias condition. In Figure 10, the calculation results are shown under conditions where the gate voltage of the main amplifier 21 is closer to the Class B bias condition than in Figure 3. In Figure 10 as well, the input power increases in the direction of the arrow. Compared with Figure 3, the dependence of the input impedance ZM1 on input power is greater in Figure 10. It can also be seen that the reactive component is larger for small signals.

[0031] Figure 11 shows the dependence of the power distribution ratio on input power in a comparative example. Figure 11 shows the power distribution ratio when the gate voltage of the main amplifier stage 21 is set to a Class AB bias and when it is set to a bias close to Class B. It can be seen that the change in the power distribution ratio is smaller under bias conditions close to Class B compared to the Class AB case. The input impedance ZM2 at small signals is determined by the electrical length θ1 of the first transmission line 861. However, as mentioned above, the first transmission line 861 is a phase compensation circuit. The electrical length θ1 of the first transmission line 861 is selected so that the pass-through phase of the main amplifier 20 and the auxiliary amplifier 40 from the branching point 64 to the combining point 74 is the same. For this reason, changing the electrical length θ1 increases the combined loss in the combining circuit 70, and the RF characteristics deteriorate.

[0032] Next, the features of the Doherty amplifier 100 of this embodiment will be described. In this embodiment, the method for determining the characteristic impedance and electrical length θ2 of the second transmission line 62 is the same as in the comparative example. That is, the characteristic impedance of the second transmission line 62 is the same as the input impedance ZA1 of the input matching circuit 51 when a large signal is input. Also, the electrical length θ2 of the second transmission line 62 is set so that the input impedance ZA2 is maximized when a small signal is input. In other words, the second transmission line 62 has an electrical length θ2 such that when a small signal is input, the input impedance ZA2 of the second transmission line 62 is higher than the characteristic impedance of the second transmission line 62 and does not have an imaginary component. In the example in Figure 1, the characteristic impedance of the second transmission line 62 is 50Ω and the electrical length θ2 is 50°.

[0033] Similar to the comparative example, the characteristic impedance of the first transmission line 61 is the same as the input impedance ZM1 of the input matching circuit 31 when a large signal is input. Also, the electrical length θ1 of the first transmission line 61 in this embodiment is set to a different value than that in the comparative example. The electrical length θ1 in this embodiment is set so that the input impedance ZM2 is minimized when a small signal is input. In other words, the first transmission line 61 has an electrical length θ1 such that when a small signal is input, the input impedance ZM2 of the first transmission line 61 is lower than the characteristic impedance of the first transmission line 61 and does not have an imaginary component.

[0034] Figure 12 shows the calculation results of the input impedance ZM2 when the electrical length θ1 of the first transmission line 61 is changed in Embodiment 1. In Figure 12, the input impedance ZA2 is shown when the electrical length θ1 is changed in 10° steps. In the calculation in Figure 12, the main amplification stage 21 is set to a bias close to Class B. From Figure 12, it can be seen that the input impedance ZM2 is minimized for small signals, i.e., at the starting point of the arrow, when the electrical length θ1 is 135°. In contrast, the electrical length θ1 of the comparative example was 10°, which was a different value from that of this embodiment.

[0035] By selecting the electrical length θ1 such that the input impedance ZM2 is minimized at small signals, the impedance on the main amplifier 20 side as seen from the branching point 64 is reduced. As a result, a larger amount of power is distributed to the main amplifier 20 at small signals. On the other hand, at large signals, the same power distribution ratio as in the comparative example can be achieved. Therefore, according to this embodiment, a larger change in the power distribution ratio can be achieved.

[0036] Figure 13 shows the dependence of the power distribution ratio on the input power in Embodiment 1. According to the calculation results shown in Figure 13, while the change in the power distribution ratio in the comparative example was about 1.8 dB, it can be seen that a change of 5 dB or more can be achieved in this embodiment. This is equivalent to an improvement of 3.2 dB in small signal gain, and it is possible to obtain the effect of compensating for the gain reduction caused by bringing the gate bias of the main amplification stage 21 closer to Class B.

[0037] The phase compensation circuit 53 provided in the interstage matching circuit is selected so that the pass-through phases of the main amplifier 20 and the auxiliary amplifier 40 are the same from the branching point 64 to the combining point 74. In the example in Figure 1, the pass-through phase of the phase compensation circuit 53 was 125°. By providing the phase compensation circuit 53 in the interstage matching circuit, even if the electrical length θ1 of the first transmission line 61 is changed, the distribution loss in the combining circuit 70 can be minimized by optimizing the pass-through phase of the phase compensation circuit 53 to match the electrical length θ1.

[0038] Figure 14 shows the dependence of PAE on the gate voltage of the first-stage main amplifier stage 21 in Embodiment 1. Figure 15 shows the dependence of small-signal gain on the gate voltage of the first-stage main amplifier stage 21 in Embodiment 1. Figure 16 shows the dependence of saturated output power on the gate voltage of the first-stage main amplifier stage 21 in Embodiment 1. Figure 17 shows the dependence of input reflection on input power in Embodiment 1. In Figures 14-17, the calculation results for this embodiment are shown by solid lines, and the calculation results for the comparative example are shown by dotted lines.

[0039] As shown in Figures 14-16, in this embodiment, even when the bias conditions of the main amplification stage 21 are changed, the change in RF characteristics is small compared to the comparative example, and good characteristics can be maintained. In addition, in this embodiment, good input reflection characteristics can be obtained over a wide range of input power. In this embodiment, as the input power increases, the input impedance ZM2 increases and the input impedance ZA2 decreases. As a result, the change in the input impedance ZIN of the Doherty amplifier 100 becomes small, and good input reflection characteristics can be obtained. In the comparative example, since there is no change in the input impedance ZM2, the input reflection at small signals deteriorates.

[0040] From the above, the Doherty amplifier 100 according to this embodiment can significantly change the power distribution ratio in response to changes in input power, thereby obtaining good RF characteristics. Furthermore, stable RF characteristics can be obtained even with changes in the bias conditions of the main amplifier 20. In addition, complex circuits are not required, thus suppressing circuit complexity.

[0041] In this embodiment, when a small signal is input, the first line 61 is configured to have an electrical length θ1 such that the input impedance ZM2 has no imaginary component, that is, the absolute value of the real component is maximized. Similarly, when a small signal is input, the second line 62 is configured to have an electrical length θ2 such that the input impedance ZA2 has no imaginary component, that is, the absolute value of the real component is maximized. In practice, even if the input impedances ZM2 and ZA2 have some imaginary components, the effects of this embodiment can be obtained. Specifically, it is sufficient that the absolute value of the imaginary component is less than 10% of the absolute value of the real component. That is, the first line 61 may have an electrical length θ1 such that, when a small signal is input, the input impedance ZM2 of the first line 61 is lower than the characteristic impedance of the first line 61 and the imaginary component is less than 10% of the real component. Also, the second line 62 may have an electrical length θ2 such that, when a small signal is input, the input impedance ZA2 of the second line 62 is higher than the characteristic impedance of the second line 62 and the imaginary component is less than 10% of the real component.

[0042] In this embodiment, an asymmetric Doherty amplifier is described as an example. However, not limited to this, the same effects can be expected even for a symmetric Doherty amplifier in which the gate widths of the final-stage transistors are the same for the main amplifier and the auxiliary amplifier.

[0043] Also, the ratio of the input impedance ZM1 of the input matching circuit 31 to the input impedance ZA1 of the input matching circuit 51 when a large signal is input only needs to be equal to the reciprocal of the ratio of the gate width of the final-stage main amplification stage 22 to the gate width of the final-stage auxiliary amplification stage 42. For example, in the case of a symmetric Doherty amplifier, even if ZM1 = ZA1 = 50Ω or ZM1 = ZA1 = 25Ω for a large signal, the value of the input impedance of the input matching circuit can be arbitrary. When the gate width of the auxiliary amplifier 40 is 1.5 times the gate width of the main amplifier 20, for example, ZM1 = 30Ω and ZA1 = 20Ω may be used.

[0044] Also, even if the phase compensation circuit 53 is provided not in the auxiliary amplifier 40 but in the inter-stage matching circuit 32 of the main amplifier 20, the same effects as those of this embodiment can be obtained.

[0045] Also, in this embodiment, an example of a two-stage amplifier has been shown, but the main amplifier 20 and the auxiliary amplifier 40 may be amplifiers with three or more stages.

[0046] The above-described modifications can be appropriately applied to the Doherty amplifier according to the following embodiment. Note that since the Doherty amplifier according to the following embodiment has many common points with Embodiment 1, the description will focus on the differences from Embodiment 1.

[0047] Embodiment 2. In this embodiment, the first line 61 and the second line 62 are not microstrip lines but lumped constant circuits, which is different from Embodiment 1. Other configurations are the same as those in Embodiment 1.

[0048] FIGS. 18A - 18D are diagrams showing examples of the lumped constant circuits according to Embodiment 2. The lumped constant circuits constituting the first line 61 and the second line 62 may be π-type LPF (Low Pass Filter) as shown in FIG. 18A, or may be π-type HPF (High Pass Filter) as shown in FIG. 18B. The lumped constant circuit may be a T-type LPF as shown in FIG. 18C, or may be a T-type HPF as shown in FIG. 18D. The capacitance value and inductance value of the lumped constant circuit are designed to have an impedance equivalent to that of the first line 61 and the second line 62 in Embodiment 1 at the design center frequency.

[0049] The lumped constant circuits constituting the first line 61 and the second line 62 are formed of, for example, surface mount type capacitors and inductors. The lumped constant circuit may be formed of MIM (Metal - Insulator - Metal) capacitors integrated in MMIC and spiral inductors.

[0050] In Embodiment 1, the electrical length of the first and second lines 61 and 62, which are microstrip lines, is determined by the input impedance of the input matching circuits 31 and 51. In this case, the electrical length may increase, potentially leading to a larger circuit size. On the other hand, in this embodiment, since lumped-parameter circuits are used as the first and second lines 61 and 62, the circuit size is determined independently of the impedance of the input matching circuits 31 and 51. Therefore, the Doherty amplifier 100 can be miniaturized.

[0051] The technical features described in each embodiment may be used in combination as appropriate.

[0052] 11 Input terminal, 12 Output terminal, 20 Main amplifier, 21, 22 Main amplification stage, 31 Input matching circuit, 32 Interstage matching circuit, 33 Output matching circuit, 40 Auxiliary amplifier, 41, 42 Auxiliary amplification stage, 51 Input matching circuit, 52 Interstage matching circuit, 53 Phase compensation circuit, 54 Interstage matching circuit, 55 Output matching circuit, 60 Distribution circuit, 61 First line, 62 Second line, 64 Branch point, 65, 66, 67, 68 Node, 70 Combining circuit, 71 λ / 4 line, 72 Impedance transformation circuit, 74 Combining point, 100, 800 Doherty amplifier, 861 First line, 862 Second line

Claims

1. The amplifier comprises: a main amplifier; an auxiliary amplifier; a distribution circuit configured to distribute the signal from the input terminal to the main amplifier and the auxiliary amplifier at a branching point; a combining circuit configured to combine the signal from the main amplifier and the signal from the auxiliary amplifier and output it from the output terminal; and a phase compensation circuit whose electrical length is set such that the electrical length of the path from the input terminal through the main amplifier to the output terminal is the same as the electrical length of the path from the input terminal through the auxiliary amplifier to the output terminal. The main amplifier comprises: a first input matching circuit connected to the distribution circuit; and a plurality of main amplification stages connected in series to the output side of the first input matching circuit. The auxiliary amplifier comprises: a second input matching circuit connected to the distribution circuit; and a plurality of auxiliary amplification stages connected in series to the output side of the second input matching circuit. The distribution circuit comprises: a first line connected between the branching point and the first input matching circuit; and a second line connected between the branching point and the second input matching circuit. A Doherty amplifier characterized in that the characteristic impedance of the first transmission line is the same as the input impedance of the first input matching circuit when a large signal with power that saturates the main amplifier and the auxiliary amplifier is input, the first transmission line has an electrical length such that when a small signal with lower power than the large signal is input, the input impedance of the first transmission line is lower than the characteristic impedance of the first transmission line and the imaginary component is less than 10% of the real component, the characteristic impedance of the second transmission line is the same as the input impedance of the second input matching circuit when a large signal is input, the second transmission line has an electrical length such that when a small signal is input, the input impedance of the second transmission line is higher than the characteristic impedance of the second transmission line and the imaginary component is less than 10% of the real component, and the phase compensation circuit is provided in the interstage matching circuit of the plurality of main amplification stages or the interstage matching circuit of the plurality of auxiliary amplification stages.

2. The Doherty amplifier according to claim 1, characterized in that the first transmission line has an electrical length such that the input impedance of the first transmission line does not have an imaginary component when the small signal is input, and the second transmission line has an electrical length such that the input impedance of the second transmission line does not have an imaginary component when the small signal is input.

3. The Doherty amplifier according to claim 1 or 2, characterized in that the first line and the second line are each microstrip lines.

4. The Doherty amplifier according to claim 1 or 2, characterized in that the first transmission line and the second transmission line are each lumped-parameter circuits.

5. The Doherty amplifier according to any one of claims 1 to 4, characterized in that the ratio of the input impedance of the first input matching circuit to the input impedance of the second input matching circuit when a large signal is input is equal to the reciprocal of the ratio of the gate width of the final stage among the plurality of main amplification stages to the gate width of the final stage among the plurality of auxiliary amplification stages.

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