Variable power distributor and doherty amplifier

Abstract

A variable power distributor (10) comprises a fixed power distributor (4) which is connected to an input terminal (1) and which outputs a high-frequency signal with power distributed at a ratio of N:1 (N is a real number of 1 or more) from a Port 1 and a Port 2, the Port 1 being connected to a first distribution output terminal (2), and a power amplifier (5) which is connected between the Port 2 and a second distribution output terminal (3), wherein: the maximum gain of the power amplifier (5) with respect to the high-frequency signal is greater than 10 x log (N) [dB]; when the input power to the input terminal (1) is equal to or less than a first switching power, the output power from the first distribution output terminal (2) is greater than or equal to the output power from the second distribution output terminal (3); and when the input power to the input terminal (1) is greater than the first switching power, the output power from the second distribution output terminal (3) is greater than the output power from the first distribution output terminal (2).

Description

Variable power divider and Doherty amplifier

[0001] This disclosure relates to a variable power divider for distributing high-frequency signals and a Doherty amplifier using a variable power divider.

[0002] In recent years, high-power and high-efficiency high-frequency power amplifiers are required for wireless communication base stations and other applications. High electron mobility transistors (HEMTs) using Group III nitride semiconductors such as gallium nitride (GaN) are capable of high-voltage and high-current-density operation, making them suitable for high-power and high-efficiency high-frequency power amplifiers. Furthermore, in fifth-generation mobile communication systems (5G), the difference between average power and peak power (Peak-To-Average Power Ratio: PAPR) is large, so Doherty amplifiers are predominantly used as high-frequency power amplifiers. A Doherty amplifier distributes the input signal using a power divider; one signal is constantly amplified by a carrier amplifier, and the other signal is amplified by a peak amplifier when the input power exceeds a certain level; and the output is a composite of the carrier amplifier output and the peak amplifier output. Generally, when the PAPR is 6 dB, the carrier amplifier and peak amplifier use devices of the same device size (e.g., gate width). On the other hand, when the PAPR is greater than 6 dB, the peak amplifier uses a device with a larger device size than the carrier amplifier. As a result, the input power at which the peak amplifier saturates will be greater than the input power at which the carrier amplifier saturates. If the power distributor is equal distribution, increasing the input power of the input signal until the peak amplifier saturates will cause the carrier amplifier to be overloaded, which may destroy the carrier amplifier. Also, if the power distributor is unequal distribution, distributing more power to the peak amplifier than to the carrier amplifier, the gain of the carrier amplifier path will be smaller when the peak amplifier is OFF (not amplifying), compared to the case of equal distribution, which can lead to efficiency degradation.

[0003] Conventionally, various techniques have been proposed to solve the above problems (see, for example, Patent Documents 1 and 2). In Patent Document 1, a Doherty amplifier is described in which a Wilkinson coupler is used in a power divider, and the resistance value of the resistors constituting the Wilkinson coupler is made variable according to the state of the peak amplifier, thereby making the distribution ratio of the power divider variable. Further, in Patent Document 2, a Doherty amplifier in which a variable attenuator or amplifier is inserted into one output of a power divider is described.

[0004] International Publication No. 2008 / 111172, Japanese Patent Application Laid-Open No. 2006-191590

[0005] However, in the technique of Patent Document 1, when the resistance value of the resistors constituting the Wilkinson coupler is made variable, the impedance of the output terminals of the power divider also changes, which affects the characteristics of the carrier amplifier and the peak amplifier. Further, in Patent Document 2, the relationship between the power divider and the amplifier is not described.

[0006] Therefore, an object of the present disclosure is to solve the above problems and provide a variable power divider and a Doherty amplifier that vary the distribution ratio of the power divider according to the input power input to the power divider.

[0007] In order to achieve the above object, a variable power divider according to one embodiment of the present disclosure is a variable power divider that distributes and outputs a high-frequency signal input to an input terminal from a first distribution output terminal and a second distribution output terminal, and is connected to the input terminal, and a signal in which power is distributed from Port 1 and Port 2 at a ratio of N:1 (N is a real number greater than or equal to 1) is output, and a fixed power divider in which Port 1 is connected to the first distribution output terminal, and a power amplifier connected between Port 2 and the second distribution output terminal, the maximum gain of the power amplifier with respect to the high-frequency signal is greater than 10×log10(N) [dB], when the input power to the input terminal is less than or equal to the first switching power, the output power of the first distribution output terminal may be greater than or equal to the output power of the second distribution output terminal, and when the input power to the input terminal is greater than the first switching power, the output power of the second distribution output terminal is greater than the output power of the first distribution output terminal.

[0008] Furthermore, in order to achieve the above objective, a Doherty amplifier using a variable power distributor according to one embodiment of the present disclosure comprises a variable power distributor, a carrier amplifier connected to a first distribution output terminal, a peak amplifier connected to a second distribution output terminal, and output terminals connected to the carrier amplifier and the peak amplifier, wherein the input power to the input terminal at which the peak amplifier switches from OFF operation to ON operation is smaller than the first switching power.

[0009] The variable power distributor according to this disclosure allows for variable distribution ratio of signals output from the first and second distribution output terminals of the variable power distributor, while also allowing for variable phase difference of the pass-through phase of signals output from the first and second distribution output terminals. Furthermore, by using the variable power distributor according to this disclosure in a Doherty amplifier, the efficiency of the Doherty amplifier can be improved.

[0010] Figure 1 is a diagram illustrating a variable power distributor according to Embodiment 1. Figure 2 is a diagram illustrating an example of the configuration of a fixed power distributor according to Embodiment 1. Figure 3 is a diagram illustrating an example of the configuration of a power amplifier according to Embodiment 1. Figure 4 is a diagram illustrating an example of the relationship between input power and gain to a power amplifier according to Embodiment 1. Figure 5 is a diagram illustrating an example of the relationship between input power to a variable power distributor according to Embodiment 1 and output power from the first and second distribution output terminals. Figure 6 is a diagram illustrating another example of the relationship between input power to a variable power distributor according to Embodiment 1 and output power from the first and second distribution output terminals. Figure 7 is a diagram illustrating an example of a fixed power distributor according to Embodiment 1 configured with a branch line coupler. Figure 8 is a diagram illustrating a variable power distributor according to Embodiment 2. Figure 9 is a diagram illustrating an example of the relationship between input power to a variable power distributor according to Embodiment 2 and output power from the first and second distribution output terminals. Figure 10 shows an example of the relative phase difference of the pass-through phase of the signals output from the first and second distribution output terminals with respect to the input power to the variable power distributor according to Embodiment 2. Figure 11 shows an example of a Doherty amplifier using the variable power distributor of the present disclosure according to Embodiment 3. Figure 12 shows another example of a Doherty amplifier using the variable power distributor of the present disclosure according to Embodiment 3. Figure 13 shows yet another example of a Doherty amplifier using the variable power distributor of the present disclosure according to Embodiment 3.

[0011] The following describes a variable power divider and a Doherty amplifier using a variable power divider according to an embodiment, with reference to the drawings. The embodiments described below are all specific examples of this disclosure. The numerical values, shapes, materials, components, arrangement positions of components, and connection configurations shown in the following embodiments are examples and are not intended to limit this disclosure. Furthermore, the figures are not necessarily strictly illustrative. In each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations may be omitted or simplified. In this specification, "connection" means an electrical connection, including not only cases where two circuit elements are directly connected, but also cases where two circuit elements are indirectly connected with another circuit element inserted between them. Also, in this specification, "log" refers to the common logarithm, and the base 10 is omitted.

[0012] (Embodiment 1) A variable power distributor according to Embodiment 1 will be described with reference to Figure 1. Figure 1 is a diagram illustrating a variable power distributor 10 according to Embodiment 1.

[0013] The variable power distributor 10 includes an input terminal 1 to which a high-frequency signal is input, a first distribution output terminal 2 and a second distribution output terminal 3 to which the distributed signal is output, a fixed power distributor 4, and a power amplifier 5. The variable power distributor 10 also includes a V1 terminal 6 and a V2 terminal 7. The V1 terminal 6 is an example of a first voltage input terminal. The V2 terminal 7 is an example of a second voltage input terminal. The fixed power distributor 4 includes Port 1 and Port 2. Port 1 is an example of a first port. Port 2 is an example of a second port. The fixed power distributor 4 is connected to the input terminal 1 and outputs a signal with power distributed from Port 1 and Port 2 in a ratio of N:1 (where N is a real number of 1 or more). Port 1 is connected to the first distribution output terminal 2. On the other hand, Port 2 is connected to the power amplifier 5. The power amplifier 5 is connected to terminals V1 6 and V2 7, and a first voltage 8 and a second voltage 9 supplied from outside the variable power distributor 10 are applied to them, respectively. The output of the power amplifier 5 is connected to the second distribution output terminal 3. In other words, the power amplifier 5 is connected between Port 2 and the second distribution output terminal 3. Each circuit element will be described in detail below.

[0014] A high-frequency signal with input power Pin [dBm] is input from input terminal 1. The high-frequency signal is distributed by the fixed power distributor 4, and a signal of 10 × log(N / (N+1)) + Pin [dBm] is output from Port 1, and a signal of 10 × log(1 / (N+1)) + Pin [dBm] is output from Port 2. Note that power loss occurring in the fixed power distributor 4 is ignored. The signal from Port 1 is output from the first distribution output terminal 2. In other words, a signal of 10 × log(N / (N+1)) + Pin [dBm] is output from the first distribution output terminal 2. On the other hand, the signal from Port 2 is input to the power amplifier 5.

[0015] Figure 2 shows an example of the configuration of a fixed power distributor 4 according to Embodiment 1. The fixed power distributor 4 can be configured, for example, with a Wilkinson coupler. In Figure 2, the fixed power distributor 4 is shown as a Wilkinson coupler 14. The Wilkinson coupler 14 comprises a first transmission line 11, a second transmission line 12, and a resistor 13. The characteristic impedance of the first transmission line 11 is Z1, one end is connected to input terminal 1, and the other end is connected to Port 1. The characteristic impedance of the second transmission line 12 is Z2, one end is connected to input terminal 1, and the other end is connected to Port 2. The resistor 13 is connected between Port 1 and Port 2. For example, when the distribution ratio N = 1, the values ​​of Z1, Z2, the resistance R of resistor 13, the output impedance Zp1 of Port 1, and the output impedance Zp2 of Port 2 should be Z1 = 70.7Ω, Z2 = 70.7Ω, R = 100Ω, Zp1 = 50Ω, and Zp2 = 50Ω. Also, when the distribution ratio N = 3, the values ​​should be Z1 = 33.3Ω, Z2 = 100Ω, R = 66.7Ω, Zp1 = 16.7Ω, and Zp2 = 50Ω. Furthermore, when the distribution ratio N = 20, the values ​​should be Z1 = 11.5Ω, Z2 = 229.1Ω, R = 52.5Ω, Zp1 = 2.5Ω, and Zp2 = 50Ω. For a distribution ratio N, Zp2 is 50Ω, but Zp1 becomes less than 50Ω when N is greater than 1. Therefore, an impedance conversion circuit may be provided between Port 1 and the first distribution output terminal 2.

[0016] Figure 3 shows an example of the configuration of a power amplifier 5 according to Embodiment 1. The power amplifier 5 comprises a field-effect transistor 15, an input matching circuit 16 connected between Port 2 of the fixed power distributor 4 and the gate of the field-effect transistor 15, an output matching circuit 17 connected between the drain of the field-effect transistor 15 and the second distribution output terminal 3, an inductor 18 connected between the gate of the field-effect transistor 15 and terminal V1 6, and an inductor 19 connected between the drain of the field-effect transistor 15 and terminal V2 7. The source of the field-effect transistor 15 is grounded. A first voltage 8 is supplied to terminal V1 6 from an external source and applied to the gate of the field-effect transistor 15 as a gate voltage. A second voltage 9 is supplied to terminal V2 7 from an external source and applied to the drain of the field-effect transistor 15 as a drain voltage. The maximum gain of the power amplifier 5 for high-frequency signals is greater than 10 × log(N) [dB]. For example, the device size (e.g., gate width), the first voltage 8, and the second voltage 9 of the field-effect transistor 15 are set so that the maximum gain of the power amplifier 5 is greater than 10 × log(N) [dB] for high-frequency signals. Note that the input matching circuit 16 and the output matching circuit 17 are not necessarily required. Also, the inductor 18 only needs to be able to suppress leakage of high-frequency signals to the V1 terminal 6 side, and may be configured as a resistor.

[0017] Figure 4 shows an example of the relationship between input power and gain to the power amplifier 5 according to Embodiment 1. The field-effect transistor 15 is a high electron-mobility transistor using gallium nitride, and its gate width is 0.4 mm. The frequency of the high-frequency signal is 4.1 GHz, the first voltage 8 is a negative voltage, and the second voltage 9 is 28 V. In Figure 4, the horizontal axis represents the input power to the power amplifier 5, and the vertical axis represents the gain of the power amplifier 5. Condition 1 is when a voltage 0.5 V lower than the pinch-off voltage of the field-effect transistor 15 is applied to the V1 terminal 6 as the first voltage 8, i.e., the gate voltage, and Condition 2 is when a voltage 0.6 V lower than the pinch-off voltage is applied to the V1 terminal 6. In both conditions, as the input power increases, the gain increases, the gain is maximized at a certain input power, and the gain decreases as the input power increases further. Under condition 1, the maximum gain is 15.1 dB when the input power is 15.9 dBm, and under condition 2, the maximum gain is 14.2 dB when the input power is 16.8 dBm. The relationship between the input power to the power amplifier 5 and the gain can be changed by the gate voltage.

[0018] Figure 5 shows an example of the relationship between the input power to the variable power distributor 10 according to Embodiment 1 and the output power from the first distribution output terminal 2 and the second distribution output terminal 3. In Figure 5, the horizontal axis represents the input power to the variable power distributor 10, and the vertical axis represents the output power from the first distribution output terminal 2 and the second distribution output terminal 3. The distribution ratio N is N = 20, and the power amplifier 5 is the case of condition 1 in Figure 4. The input power to the variable power distributor 10 at which the output power from the first distribution output terminal 2 and the output power from the second distribution output terminal 3 are equal is defined as the first switching power. In the case of Figure 5, the first switching power is 25.4 dBm. When the input power to input terminal 1 is less than or equal to the first switching power, the output power from the first distribution output terminal 2 is greater than or equal to the output power from the second distribution output terminal 3. On the other hand, when the input power to input terminal 1 is greater than the first switching power, the output power from the second distribution output terminal 3 is greater than the output power from the first distribution output terminal 2. In other words, the relative magnitudes of the output power of the first distribution output terminal 2 and the output power of the second distribution output terminal 3 can be swapped using the first switching power as the boundary.

[0019] Figure 6 shows another example of the relationship between the input power to the variable power distributor 10 according to Embodiment 1 and the output power from the first distribution output terminal 2 and the second distribution output terminal 3. In Figure 6, the horizontal axis represents the input power to the variable power distributor 10, and the vertical axis represents the output power from the first distribution output terminal 2 and the second distribution output terminal 3. The distribution ratio N is N = 20, and the power amplifier 5 is under condition 2 in Figure 4. In the case of Figure 6, the first switching power is 27.2 dBm, which is greater than the first switching power in Figure 5. As shown in Figures 5 and 6, the first switching power can be adjusted by the first voltage 8 applied to the V1 terminal 6 of the power amplifier 5.

[0020] According to the variable power distributor 10 of Embodiment 1, the power ratio of the output power from the first distribution output terminal 2 and the second distribution output terminal 3 to the input power of the variable power distributor 10 can be varied. Furthermore, the relative magnitudes of the output power from the first distribution output terminal 2 and the output power from the second distribution output terminal 3 can be swapped using a first switching power as the boundary. The first switching power can be adjusted by a first voltage 8 applied to the power amplifier 5 via the V1 terminal 6.

[0021] In this embodiment 1, the first switching power is adjusted by the first voltage 8 as the gate voltage, but the first switching power may also be adjusted by the second voltage 9 as the drain voltage. Changing the drain voltage of the field-effect transistor 15 changes the gain and saturation power of the power amplifier 5, so the same effect as changing the first voltage 8 can be obtained.

[0022] In this embodiment 1, the fixed power distributor 4 and the power amplifier 5 may be formed on the same semiconductor chip. In this case, GaN, GaAs, or Si substrates may be used as the semiconductor substrate. By forming the fixed power distributor 4 and the power amplifier 5 on the same semiconductor chip, the variable power distributor 10 can be miniaturized.

[0023] In this embodiment 1, the power amplifier 5 is connected to terminals V1 6 and V2 7, but it may be connected to only one of terminals V1 6 and V2 7. For example, the variable power distributor 10 does not need to have both terminals V1 6 and V2 7, but may have only one of them.

[0024] In this embodiment 1, the fixed power distributor 4 is described in the case where it is configured with a Wilkinson coupler 14, but it is not limited to this and may be configured with a branch line coupler. Figure 7 is a diagram showing an example in which the fixed power distributor 4 according to embodiment 1 is configured with a branch line coupler 24. The branch line coupler 24 includes a third transmission line 20, a fourth transmission line 21, a fifth transmission line 22, and a sixth transmission line 23. The connection point between the fourth transmission line 21 and the fifth transmission line 22 is terminated with 50Ω. The characteristic impedance of the third transmission line 20 and the fifth transmission line 22 is Z1, and the characteristic impedance of the fourth transmission line 21 and the sixth transmission line 23 is Z2. For example, when the distribution ratio N = 1, Z1 and Z2 can be set to Z1 = 35.4Ω and Z2 = 50Ω. Furthermore, when the distribution ratio N = 3, Z1 = 43.3 Ω and Z2 = 86.6 Ω should be used. Also, when the distribution ratio N = 20, Z1 = 48.8 Ω and Z2 = 223.6 Ω should be used.

[0025] In this embodiment 1, the power amplifier 5 was described as being composed of a field-effect transistor 15, but it is not limited to this and may be composed of a bipolar transistor. In the case of a bipolar transistor, the first voltage 8 is the base voltage and the second voltage 9 is the collector voltage.

[0026] In this embodiment 1, the frequency of the high-frequency signal was described as 4.1 GHz, but it is not limited to this, and may be a frequency other than 4.1 GHz, or it may be a high-frequency signal with a bandwidth (for example, 100 MHz).

[0027] As described above, the variable power distributor 10 according to this embodiment is a variable power distributor 10 that distributes a high-frequency signal input to an input terminal 1 from a first distribution output terminal 2 and a second distribution output terminal 3, and comprises a fixed power distributor 4 connected to the input terminal 1 that outputs a signal with power distributed from Port 1 and Port 2 in a ratio of N:1 (where N is a real number of 1 or more), with Port 1 connected to the first distribution output terminal 2, and a power amplifier 5 connected between Port 2 and the second distribution output terminal 3, wherein the maximum gain of the power amplifier 5 for high-frequency signals is greater than 10 × log(N) [dB], and when the input power to the input terminal 1 is less than or equal to the first switching power, the output power from the first distribution output terminal 2 is greater than or equal to the output power from the second distribution output terminal 3, and when the input power to the input terminal 1 is greater than the first switching power, the output power from the second distribution output terminal 3 is greater than the output power from the first distribution output terminal 2.

[0028] This enables a variable power distributor 10 that can change the distribution ratio of power output from the first distribution output terminal 2 and the second distribution output terminal 3 with respect to the input power to the input terminal 1, and can also swap the relative magnitudes of the output power from the first distribution output terminal 2 and the output power from the second distribution output terminal 3 using the first switching power.

[0029] (Embodiment 2) Next, a variable power distributor according to Embodiment 2 will be described with reference to Figure 8. Figure 8 is a diagram illustrating the variable power distributor 30 according to Embodiment 2. The variable power distributor 30 according to Embodiment 2 has the same configuration as the variable power distributor 10 according to Embodiment 1 shown in Figure 1, so the explanation of the circuit configuration will be omitted.

[0030] Figure 9 shows an example of the relationship between the input power to the variable power distributor 30 according to Embodiment 2 and the output power from the first distribution output terminal 2 and the second distribution output terminal 3. In Figure 9, the horizontal axis represents the input power to the variable power distributor 30, and the vertical axis represents the output power from the first distribution output terminal 2 and the second distribution output terminal 3. The field-effect transistor 15 constituting the power amplifier 5 is a high electron-mobility transistor using gallium nitride, and its gate width is 0.4 mm. The frequency of the high-frequency signal is 10 GHz, the first voltage 8 is 1.5 V lower than the pinch-off voltage of the field-effect transistor 15, the second voltage 9 is 28 V, and the distribution ratio N is N = 3. The input power to the variable power distributor 30 at which the output power from the first distribution output terminal 2 and the output power from the second distribution output terminal 3 are equal is defined as the first switching power.

[0031] In the case of Figure 9, the first switching power is 25 dBm. At power levels lower than the first switching power, the output power of the first distribution output terminal 2 is greater than the output power of the second distribution output terminal 3. On the other hand, at power levels greater than the first switching power, the output power of the second distribution output terminal 3 is greater than the output power of the first distribution output terminal 2. In other words, the relative magnitudes of the output powers of the first distribution output terminal 2 and the second distribution output terminal 3 can be reversed, with the first switching power as the dividing line.

[0032] Figure 10 shows an example of the relative phase difference between the pass-through phase of the signals output from the first distribution output terminal 2 and the second distribution output terminal 3 with respect to the input power to the variable power distributor 30 according to Embodiment 2. In Figure 10, the horizontal axis represents the input power to the variable power distributor 30, and the vertical axis represents the relative phase difference between the pass-through phase of the signal output from the first distribution output terminal 2 and the pass-through phase of the signal output from the second distribution output terminal 3. The phase difference is set to 0 when the input power to the variable power distributor 30 is the second switching power. In the case of Figure 10, the second switching power is 17.6 dBm, and when the input power to input terminal 1 is the second switching power, the phase difference changes in a step-like manner (from -39 degrees to 39 degrees). This is because the power amplifier 5 is a Class C amplifier, and when the input power to the variable power distributor 30 is the second switching power, the power amplifier 5 switches from OFF operation to ON operation. In conventional power distributors, the phase difference does not change with input power. For example, in the case of a Wilkinson coupler, the phase difference is constant at 0 degrees, while in the case of a branch line coupler, the phase difference is constant at 90 degrees.

[0033] According to the variable power distributor 30 of Embodiment 2, the power ratio of the output power from the first distribution output terminal 2 and the second distribution output terminal 3 to the input power of the variable power distributor 30 can be varied. Furthermore, the relative magnitudes of the output power from the first distribution output terminal 2 and the output power from the second distribution output terminal 3 can be swapped at the first switching power. In addition, the phase difference of the pass-through phase of the signals output from the first distribution output terminal 2 and the second distribution output terminal 3 can be changed in a step-like manner when the input power is at the second switching power.

[0034] The second switching power can be adjusted by the first voltage 8 applied to the power amplifier 5. The lower the first voltage 8 is than the pinch-off voltage of the field-effect transistor 15, the greater the second switching power.

[0035] In this embodiment 2, the frequency of the high-frequency signal was described as 10 GHz, but it is not limited to this, and may be a frequency other than 10 GHz, or it may be a high-frequency signal with a bandwidth (for example, 100 MHz).

[0036] As described above, the variable power distributor 30 according to this embodiment has the same components as the variable power distributor 10 according to Embodiment 1, the power amplifier 5 is a Class C amplifier, and when the input power to the input terminal 1 is the second switching power, the phase difference of the pass-through phase of the signals output from the first distribution output terminal 2 and the second distribution output terminal 3 changes in a step-like manner.

[0037] This realizes a variable power distributor 30 in which the phase difference of the signal pass-through phases output from the first distribution output terminal 2 and the second distribution output terminal 3 changes in a step-like manner.

[0038] (Embodiment 3) Next, a Doherty amplifier using the variable power distributor of the present disclosure according to Embodiment 3 will be described with reference to Figure 11. Figure 11 is a diagram showing an example of a Doherty amplifier using the variable power distributor 10 of the present disclosure.

[0039] The Doherty amplifier 100 comprises a variable power distributor 10, a carrier amplifier 31 connected to the first distribution output terminal 2, a peak amplifier 32 connected to the second distribution output terminal 3, and an output terminal 33 connected to the carrier amplifier 31 and the peak amplifier 32. The power amplifier 5 constituting the variable power distributor 10 is connected to terminals V1 6 and V2 7, and a first voltage 8 and a second voltage 9 supplied from outside the variable power distributor 10 are applied to them, respectively. The saturation power of the peak amplifier 32 is greater than the saturation power of the carrier amplifier 31. The Doherty amplifier 100 will be described in detail below. A detailed explanation of the variable power distributor 10 will be omitted.

[0040] The Doherty amplifier 100 receives a high-frequency signal from input terminal 1, distributes the power by a variable power distributor 10, and outputs signals from the first distribution output terminal 2 and the second distribution output terminal 3, respectively. The signal from the first distribution output terminal 2 is input to the carrier amplifier 31. The carrier amplifier 31 is, for example, a Class AB amplifier, and the signal input to the carrier amplifier 31 is always amplified. The signal from the second distribution output terminal 3 is input to the peak amplifier 32. The peak amplifier 32 is, for example, a Class C amplifier, and the signal input to the peak amplifier 32 is amplified when the input power exceeds a certain level. When the peak amplifier 32 is amplified, it is considered to be in ON operation, and in all other cases, it is considered to be in OFF operation.

[0041] The distribution ratio N of the fixed power distributor 4 is N=20, and the field-effect transistor 15 of the power amplifier 5 is a high electron-mobility transistor using gallium nitride with a gate width of 0.4 mm. The first voltage 8 is 0.5 V lower than the pinch-off voltage of the field-effect transistor 15, and the second voltage 9 is 28 V. The frequency of the high-frequency signal is 4.1 GHz. Figure 5 shows the relationship between the input power to the variable power distributor 10 and the output power from the first distribution output terminal 2 and the second distribution output terminal 3. From Figure 5, for example, when the input power to the variable power distributor 10 is 20 dBm, the output power of the first distribution output terminal 2 is 19.8 dBm, and the output power of the second distribution output terminal 3 is 4.1 dBm, so that almost all of the input power to the variable power distributor 10 is output from the first distribution output terminal 2. The signal from the first distribution output terminal 2 is amplified by the carrier amplifier 31 and output from the output terminal 33. On the other hand, the signal from the second distribution output terminal 3 is input to the peak amplifier 32, but since the peak amplifier 32 is in OFF operation, it is not amplified. Conventional Doherty amplifiers use an equal-distribution Wilkinson coupler as a power distributor. In the case of an equal-distribution Wilkinson coupler, the input power of the Wilkinson coupler is equally distributed, and a power 3 dB lower than the input power is output from the distribution output terminal. Conventional Doherty amplifiers have a gain approximately 3 dB lower than the Doherty amplifier 100 of this embodiment 3. Furthermore, when the input power to the variable power distributor 10 increases, the peak amplifier 32 turns ON, and the outputs of the carrier amplifier 31 and the peak amplifier 32 are combined and output from the output terminal 33. The input power to the variable power distributor 10 at which the peak amplifier 32 turns ON from OFF operation is set lower than the first switching power.

[0042] Since the saturation power of the peak amplifier 32 is greater than the saturation power of the carrier amplifier 31, the input power to the peak amplifier 32 at which it saturates is greater than the input power to the carrier amplifier 31 at which it saturates. In conventional Doherty amplifiers that use an equal-distribution Wilkinson coupler as a power distributor, the same power is output from the distribution output terminals of the power distributor, and if the input power is increased until the peak amplifier 32 saturates, the carrier amplifier 31 may be overloaded and destroyed. In the Doherty amplifier 100 of this embodiment 3, when the input power to the variable power distributor 10 becomes greater than the first switching power, the output power from the second distribution output terminal 3 becomes greater than the output power from the first distribution output terminal 2. Even if the input power to the variable power distributor 10 is increased and the peak amplifier 32 is saturated, it is possible to prevent the carrier amplifier 31 from being destroyed by overloading.

[0043] In this embodiment 3 of the Doherty amplifier 100, the case in which the carrier amplifier 31 and the peak amplifier 32 are configured as single-stage amplifiers has been described, but the invention is not limited to this, and the carrier amplifier 31 and the peak amplifier 32 may be configured as multi-stage amplifiers connected in series. Figure 12 shows another example of a Doherty amplifier using the variable power distributor 10 of this disclosure. The Doherty amplifier 200 comprises a variable power distributor 10, a carrier amplifier 34 connected in two stages in series to the first distribution output terminal 2, a peak amplifier 35 connected in two stages in series to the second distribution output terminal 3, and an output terminal 33 connected to the carrier amplifier 34 and the peak amplifier 35. The power amplifier 5 constituting the variable power distributor 10 is connected to terminal V1 6 and terminal V2 7, and a first voltage 8 and a second voltage 9 supplied from outside the variable power distributor 10 are applied to them, respectively. By connecting the carrier amplifier 34 and the peak amplifier 35 in series in a multi-stage amplifier configuration, it is possible to further reduce the device size of the power amplifier 5 that constitutes the variable power distributor 10.

[0044] Also, in the Doherty amplifier 100 of the third embodiment, although the case where the carrier amplifier 31 and the peak amplifier 32 are configured by the same single-stage amplifier has been described, the present invention is not limited to this, and the carrier amplifier 31 and the peak amplifier 32 may be configured by amplifiers having different numbers of stages. FIG. 13 is a diagram showing yet another example of a Doherty amplifier using the variable power divider 10 of the present disclosure. The Doherty amplifier 300 includes a variable power divider 10, a carrier amplifier 36 connected to the first distribution output terminal 2 and connected in series in two stages, a peak amplifier 37 connected to the second distribution output terminal 3 and configured by a single-stage amplifier, and an output terminal 33 connected to the carrier amplifier 36 and the peak amplifier 37. The power amplifier 5 constituting the variable power divider 10 is connected to the V1 terminal 6 and the V2 terminal 7, and the first voltage 8 and the second voltage 9 supplied from the outside of the variable power divider 10 are respectively applied. In the Doherty amplifier 300, the power amplifier 5 constituting the variable power divider 10 is used as the pre-stage amplifier of the peak amplifier 37. By using the power amplifier 5 constituting the variable power divider 10 as the pre-stage amplifier of the peak amplifier 37, the number of stages constituting the peak amplifier 37 can be made smaller than the number of stages constituting the carrier amplifier 36.

[0045] In the Doherty amplifier {100} of the third embodiment, when the power amplifier {5} of the variable power divider {10} and the peak amplifier {32} are on the same semiconductor substrate, the power amplifier {5} and the peak amplifier {32} may be formed in the same semiconductor chip. In this case, a GaN, GaAs, or Si substrate may be used as the semiconductor substrate. By forming the power amplifier {5} of the variable power divider {10} and the peak amplifier {32} in the same semiconductor chip, the Doherty amplifier {100} can be miniaturized.

[0046] Similarly, in the Doherty amplifier {200} of the third embodiment, the power amplifier {5} and the peak amplifier {35} may be formed in the same semiconductor chip. Also, in the Doherty amplifier {300} of the third embodiment, the power amplifier {5} and the peak amplifier {37} may be formed in the same semiconductor chip.

[0047] As described above, the Doherty amplifier 100 according to the present embodiment includes the variable power divider 10 according to Embodiment 1, the carrier amplifier 31 connected to the first distribution output terminal 2, the peak amplifier 32 connected to the second distribution output terminal 3, and an output terminal 33 connected to the carrier amplifier 31 and the peak amplifier 32. The input power to the input terminal 1 at which the peak amplifier 32 switches from the OFF operation to the ON operation is smaller than the first switching power.

[0048] According to the Doherty amplifier 100 according to Embodiment 3, the gain of the Doherty amplifier 100 when the peak amplifier 32 is in the OFF operation can be increased. Further, even if the input power to the variable power divider 10 is increased to saturate the peak amplifier 32, it is possible to prevent the carrier amplifier 31 from being damaged due to over-input.

[0049] The variable power divider according to the present disclosure can vary the phase difference of the passing phases of the signals output from the first distribution output terminal and the second distribution output terminal while varying the distribution ratio of the signals output from the first distribution output terminal and the second distribution output terminal, and can be used as a power divider of a high-frequency power amplifier of a base station for wireless communication. Further, by using the variable power divider according to the present disclosure in a Doherty amplifier, the efficiency of the Doherty amplifier can be improved.

[0050] 1 Input terminal 2 First distribution output terminal 3 Second distribution output terminal 4 Fixed power divider 5 Power amplifier 6 V1 terminal 7 V2 terminal 8 First voltage 9 Second voltage 10, 30 Variable power divider 11 First transmission line 12 Second transmission line 13 Resistance 14 Wilkinson coupler 15 Field effect transistor 16 Input matching circuit 17 Output matching circuit 18, 19 Inductor 20 Third transmission line 21 Fourth transmission line 22 Fifth transmission line 23 Sixth transmission line 24 Branch line coupler 31, 34, 36 Carrier amplifier 32, 35, 37 Peak amplifier 33 Output terminal 100, 200, 300 Doherty amplifier

Claims

1. A variable power distributor that distributes a high-frequency signal input to an input terminal from a first distribution output terminal and a second distribution output terminal, comprising: a fixed power distributor connected to the input terminal and outputting a signal with power distributed from a first port and a second port in a ratio of N:1 (where N is a real number of 1 or more), and the first port being connected to the first distribution output terminal; and a power amplifier connected between the second port and the second distribution output terminal, wherein the maximum gain of the power amplifier for the high-frequency signal is greater than 10 × log(N) [dB], and when the input power to the input terminal is less than or equal to the first switching power, the output power from the first distribution output terminal is greater than or equal to the output power from the second distribution output terminal, and when the input power to the input terminal is greater than the first switching power, the output power from the second distribution output terminal is greater than the output power from the first distribution output terminal.

2. The variable power distributor according to claim 1, characterized in that the power amplifier is connected to a first voltage input terminal, and the first switching power is adjusted by a first voltage which is the gate voltage or base voltage of the power amplifier applied to the first voltage input terminal.

3. The variable power distributor according to claim 1, characterized in that the power amplifier is connected to a second voltage input terminal, and the first switching power is adjusted by a second voltage which is the drain voltage or collector voltage of the power amplifier applied to the second voltage input terminal.

4. The variable power distributor according to claim 1, characterized in that the fixed power distributor and the power amplifier are formed within the same semiconductor chip.

5. The variable power distributor according to claim 1, wherein the power amplifier is a Class C amplifier, and when the input power to the input terminal is the second switching power, the phase difference between the pass phase of the signal output from the first distribution output terminal and the pass phase of the signal output from the second distribution output terminal changes in a step-like manner.

6. A Doherty amplifier comprising: a variable power distributor according to claim 1; a carrier amplifier connected to the first distribution output terminal; a peak amplifier connected to the second distribution output terminal; and an output terminal connected to the carrier amplifier and the peak amplifier, wherein the input power to the input terminal at which the peak amplifier switches from OFF operation to ON operation is smaller than the first switching power.

7. The Doherty amplifier according to claim 6, characterized in that the carrier amplifier is a single-stage amplifier or a multi-stage amplifier connected in series.

8. The Doherty amplifier according to claim 6, characterized in that the peak amplifier is a single-stage amplifier or a multi-stage amplifier connected in series.

9. The Doherty amplifier according to claim 8, characterized in that the number of stages of the peak amplifier is less than the number of stages of the carrier amplifier.

10. The Doherty amplifier according to claim 6, characterized in that the power amplifier and the peak amplifier are formed on the same semiconductor chip.

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