doherty amplifier

Abstract

The Doherty amplifier comprises: a first filter circuit (6a) that, when an input signal of the first frequency band is input, outputs a first input signal that attenuates the input signal by a first attenuation amount, and when an input signal of the second frequency band different from the first frequency band is input, outputs a second input signal that allows the input signal to pass; and a second filter circuit (6b) that, when an input signal of the first frequency band is input, outputs a third input signal that attenuates the input signal by a second attenuation amount smaller than the first attenuation amount, and when an input signal of the second frequency band is input, outputs a third input signal that attenuates the input signal by an attenuation amount greater than the first attenuation amount. The fourth input signal of attenuation; the first amplifier (8a), whose gate bias voltage is fixed, operates as an auxiliary amplifier when input to the first input signal from the first filter circuit (6a), and operates as a main amplifier when input to the second input signal from the first filter circuit (6a); and the second amplifier (8b), whose gate bias voltage is fixed, operates as a main amplifier when input to the third input signal from the second filter circuit (6b), and operates as an auxiliary amplifier when input to the fourth input signal from the second filter circuit (6b).

Description

Technical Field

[0001] This invention relates to a Doherty amplifier that operates in multiple frequency bands. Background Technology

[0002] In recent years, due to the rapid increase in communication volume, for example, there is a requirement for amplifiers used in 5G mobile communication base stations to be able to efficiently amplify signals with a high PAPR (peak to average power ratio).

[0003] The Doherty amplifier is proposed in Patent Document 1 as an amplifier that efficiently amplifies signals for communication.

[0004] The Doherty amplifier shown in Patent Document 1 is a Doherty amplifier in which the control unit switches the operation stages of the first amplification element and the second amplification element according to whether the operating frequency of the input signal is the first operating frequency or the second operating frequency.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. WO2019 / 09760 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, it is desirable to realize a Doherty amplifier that amplifies input signals at two operating frequencies without controlling the two amplifying elements that constitute the Doherty amplifier.

[0010] The present invention was made in view of the above circumstances, and its object is to obtain a Doherty amplifier that operates in multiple frequency bands without controlling the amplifying elements constituting the Doherty amplifier.

[0011] Methods for solving problems

[0012] The Doherty amplifier of the present invention comprises: a first filter circuit that, when an input signal of a first frequency band is input, outputs a first input signal that attenuates the input signal of the first frequency band by a first attenuation amount, and when an input signal of a second frequency band different from the first frequency band is input, outputs a second input signal that allows the input signal of the second frequency band to pass; and a second filter circuit that, when an input signal of the first frequency band is input, outputs a third input signal that attenuates the input signal of the first frequency band by a second attenuation amount smaller than the first attenuation amount, and when an input signal of the second frequency band is input, outputs a third input signal that attenuates the input signal of the first frequency band by a second attenuation amount smaller than the first attenuation amount, and when an input signal of the second frequency band is input, outputs a third input signal that attenuates the input signal of the second frequency band by a second attenuation amount smaller than the first attenuation amount. The input signal is attenuated by a third attenuation amount greater than the first attenuation amount; a first amplifier, whose gate bias voltage is fixed, operates as an auxiliary amplifier when input to a first input signal from a first filter circuit, and operates as a main amplifier when input to a second input signal from a first filter circuit; and a second amplifier, whose gate bias voltage is fixed, operates as a main amplifier when input to a third input signal from a second filter circuit, and operates as an auxiliary amplifier when input to a fourth input signal from a second filter circuit.

[0013] Invention Effects

[0014] According to the present invention, a first filter circuit and a second filter circuit with different characteristics are provided in the pre-stage of the first amplifier and the second amplifier, so that it is not necessary to control the first amplifier and the second amplifier to operate in multiple frequency bands. Attached Figure Description

[0015] Figure 1 This is a block diagram illustrating the Doherty amplifier of Embodiment 1.

[0016] Figure 2 This is an equivalent circuit diagram showing the first amplifier in the Doherty amplifier of Embodiment 1.

[0017] Figure 3 This is an equivalent circuit diagram showing the second amplifier in the Doherty amplifier of Embodiment 1.

[0018] Figure 4 This is a diagram showing the pass-through loss relative to frequency in the first and second filter circuits of the Doherty amplifier in Embodiment 1.

[0019] Figure 5 This is an equivalent circuit diagram of the first amplifier, the second amplifier, and the output synthesis circuit in the Doherty amplifier of Embodiment 1, which represents the impedance relationship during backoff when an input signal of the first frequency (low frequency region) is input.

[0020] Figure 6This is a graph showing the impedance modification in the Smith chart during backoff when an input signal of the first frequency (low frequency region) is input into the Doherty amplifier of Embodiment 1.

[0021] Figure 7 This is an equivalent circuit diagram showing the impedance relationship of the first amplifier, the second amplifier, and the output synthesis circuit in the Doherty amplifier of Embodiment 1, which is used to represent the back-off impedance relationship when an input signal of the second frequency (high frequency region) is input.

[0022] Figure 8 This is a graph showing the impedance change in the Smith chart during backoff when an input signal of the second frequency (high frequency region) is input into the Doherty amplifier of Embodiment 1.

[0023] Figure 9 This is a diagram that schematically illustrates the functions of the first amplifier and the second amplifier in the Doherty amplifier of Embodiment 1 when input signals of the first frequency band and the second frequency band are input.

[0024] Figure 10 This is a graph showing the drain efficiency of the Doherty amplifier in Embodiment 1 relative to the output power as a simulation result.

[0025] Figure 11 This is a block diagram illustrating the Doherty amplifier in Embodiment 2.

[0026] Figure 12 This is an equivalent circuit diagram showing the first amplifier, the second amplifier, and the output synthesis circuit of the Doherty amplifier in Embodiment 2, which represent the impedance relationship during backoff when an input signal of the third frequency is input.

[0027] Figure 13 This is a graph showing the impedance change in the Smith chart during backoff when an input signal of the third frequency is input to the Doherty amplifier in Embodiment 2. Detailed Implementation

[0028] Implementation Method 1

[0029] according to Figures 1-10 The Doherty amplifier of Embodiment 1 will be described.

[0030] The Doherty amplifier operates in two frequency bands: band 1 and band 2.

[0031] The first and second frequency bands are different frequency regions. The first frequency band is a frequency region lower than the second frequency band. For ease of explanation, the first frequency band is referred to as the low-frequency region, which represents a frequency region lower than the second frequency band, and the second frequency band is referred to as the high-frequency region, which represents a frequency region higher than the first frequency band.

[0032] In the Doherty amplifier, the gate bias voltage applied to each amplifier in the dual parallel amplifier is fixed as the gate bias voltage for operation as a Class B amplifier. Through two filter circuits connected to the front stage of the dual parallel amplifier, the functions of the main amplifier and auxiliary amplifier are switched by the two operating frequency bands with different pass losses according to the operating frequency band.

[0033] A dual parallel amplifier is formed by connecting two amplifiers, a main amplifier and an auxiliary amplifier, in parallel, with equal saturated output power.

[0034] Furthermore, regarding the input signal input to the dual parallel amplifier, when the second frequency in the second frequency band is set to 1.0, the first frequency in the first frequency band satisfies a relationship of 0.5 with respect to the second frequency.

[0035] The Doherty amplifier has a third input matching circuit 3, a distributor 4, a phase correction circuit 5, a first filter circuit 6a, a second filter circuit 6b, a first input matching circuit 7a, a second input matching circuit 7b, a dual parallel amplifier 8 with a first amplifier 8a and a second amplifier 8b, an output combining circuit 9 with a first output circuit 9a and a second output circuit 9b, and an output matching circuit 10 between input terminal 1 and output terminal 2.

[0036] The third input matching circuit 3 is connected between input terminal 1 and the input terminal of distributor 4 to achieve impedance matching between input terminal 1 and distributor 4.

[0037] The third input matching circuit 3 is an impedance matching circuit (IMN) consisting of a matching circuit using lumped constant elements, a matching circuit using distributed constant lines, a matching circuit combining lumped constant and distributed constant elements, or a matching circuit using an LC-type matching circuit.

[0038] The input terminal of distributor 4 is connected to the output terminal of the third input matching circuit 3, one output terminal is connected to the input terminal of the phase correction circuit 5, and the other output terminal is connected to the second filter circuit 6b. The input signal input from input terminal 1 is distributed to one output terminal and the other output terminal.

[0039] The distributor 4 is a Wilkinson distributor or a hybrid circuit, which is composed of circuits using lumped constant elements, circuits using distributed constant lines, circuits combining lumped constant and distributed constants, or circuits using LC-type matching circuits.

[0040] Phase correction circuit 5 is connected between one output terminal of distributor 4 and the input terminal of first filter circuit 6a to make the electrical length of the path from one output terminal of distributor 4 to the output synthesis point 9A, which becomes the output terminal of output synthesis circuit 9, i.e., the electrical length of the path on the side of first amplifier 8a, equal to the electrical length of the path from the other output terminal of distributor 4 to the output synthesis point 9A of output synthesis circuit 9, i.e., the electrical length of the path on the side of second amplifier 8b.

[0041] The phase correction circuit 5 consists of a circuit using lumped constant elements, a circuit using distributed constant lines, a circuit combining lumped constants and distributed constants, or a circuit using LC-type matching circuits.

[0042] The input terminal of the first filter circuit 6a is connected to the output terminal of the phase correction circuit 5. The input signal output from one output terminal of the distributor 4 is input to the first filter circuit 6a via the phase correction circuit 5.

[0043] When the first filter circuit 6a receives an input signal of the first frequency band, it outputs a first input signal that attenuates the input signal of the first frequency band by a first attenuation amount of XdB. When it receives an input signal of the second frequency band, it outputs a second input signal that allows the input signal of the second frequency band to pass through.

[0044] In the first filter circuit 6a, when the input signal is in the first frequency band, the first input signal is attenuated by XdB, thus outputting a signal with a small amplitude. When the input signal is in the second frequency band, the second input signal is not attenuated, thus outputting a signal with a large amplitude.

[0045] The amplitude of the input signal mentioned here refers to the amplitude of the signal's envelope. The amplitude of the input signal described below also refers to the amplitude of the signal's envelope.

[0046] like Figure 4 As shown by solid line A, the first filter circuit 6a is a high-pass filter circuit with the first frequency band set to an attenuation of XdB and the second frequency band set to an attenuation of 0dB (pass).

[0047] The first filter circuit 6a is a high-pass filter circuit with reactive reflection loss, which is a filter circuit using lumped constant elements, a filter circuit using distributed constant lines, a filter circuit combining lumped constant and distributed constant elements, and a filter circuit using LC-type matching circuits.

[0048] When a reactive high-pass filter circuit is used in the first filter circuit 6a, miniaturization is achieved as the first filter circuit 6a.

[0049] Alternatively, the first filter circuit 6a can replace the reactive high-pass filter circuit with a resistive high-pass filter circuit such as an attenuator.

[0050] When a resistive high-pass filter circuit is used in the first filter circuit 6a, the reflected power is lost in the first filter circuit 6a, thus achieving stable operation of the first amplifier 8a.

[0051] The input terminal of the second filter circuit 6b is connected to the other output terminal of the distributor 4, and is input to the input signal output from the other output terminal of the distributor 4.

[0052] When the second filter circuit 6b is input with an input signal of the first frequency band, it outputs a third input signal that allows the input signal of the first frequency band to pass through. When the second filter circuit 6b is input with an input signal of the second frequency band, it outputs a fourth input signal that attenuates the input signal of the second frequency band by a first attenuation amount of XdB.

[0053] In the second filter circuit 6b, when the input signal is in the first frequency band, the third input signal is not attenuated, so the output signal has a large amplitude. When the input signal is in the second frequency band, the fourth input signal is attenuated by XdB, so the output signal has a small amplitude.

[0054] like Figure 4 As shown by solid line B, the second filter circuit 6b is a low-pass filter circuit with the first frequency band set to an attenuation of 0dB (pass) and the second frequency band set to an attenuation of XdB.

[0055] The second filter circuit 6b is a low-pass filter circuit with reactive reflection loss, which is a filter circuit using lumped constant elements, a filter circuit using distributed constant lines, a filter circuit combining lumped constant and distributed constant elements, or a filter circuit using an LC-type matching circuit.

[0056] When using a reactive high-pass filter circuit in the second filter circuit 6b, miniaturization is achieved as the second filter circuit 6b.

[0057] Alternatively, the second filter circuit 6b can replace the reactive low-pass filter circuit with a resistive low-pass filter circuit such as an attenuator.

[0058] When a resistive high-pass filter circuit is used in the second filter circuit 6b, the reflected power is lost in the second filter circuit 6b, thus achieving stable operation of the second amplifier 8b.

[0059] In the second filter circuit 6b, when the input signal is in the first frequency band, the third input signal is set to an unattenuated signal (attenuation 0dB: pass). However, the third input signal can also be set to a signal attenuated by a second attenuation that is smaller than the first attenuation XdB.

[0060] Furthermore, in the second filter circuit 6b, when the input signal is in the second frequency band, the fourth input signal is set to a signal attenuated by the first attenuation amount XdB. However, the fourth input signal can also be set to a signal attenuated by the third attenuation amount, which is greater than or equal to the first attenuation amount XdB.

[0061] In summary, the characteristics of the first filter circuit 6a and the second filter circuit 6b can be set as follows: when the input signal is in the first frequency band, the amplitude of the first input signal output from the first filter circuit 6a is smaller than the amplitude of the third input signal output from the second filter circuit 6b; when the input signal is in the second frequency band, the amplitude of the second input signal output from the first filter circuit 6a is larger than the amplitude of the fourth input signal output from the second filter circuit 6b.

[0062] Regarding the attenuation XdB in the first filter circuit 6a relative to the first frequency band and the attenuation XdB in the second filter circuit 6b relative to the second frequency band, as an example, it is set to 6dB when it is desirable to improve the efficiency of the first amplifier 8a and the second amplifier 8b, and set to 3dB when it is desirable to achieve both efficiency and linearity of the first amplifier 8a and the second amplifier 8b.

[0063] The first input matching circuit 7a is connected between the output of the first filter circuit 6a and the input 8a1 of the first amplifier 8a, and is an impedance matching circuit (IMN) for input matching of the first amplifier 8a.

[0064] The first input matching circuit 7a is an impedance matching circuit (IMN) consisting of a matching circuit using lumped constant elements, a matching circuit using distributed constant lines, a matching circuit combining lumped constant and distributed constant elements, or a matching circuit using an LC-type matching circuit.

[0065] Alternatively, the first input matching circuit 7a can also be connected between the output of the phase correction circuit 5 and the input of the first filter circuit 6a.

[0066] The second input matching circuit 7b is connected between the output of the second filter circuit 6b and the input 8b1 of the second amplifier 8b, and is an impedance matching circuit (IMN) for input matching of the second amplifier 8b.

[0067] The second input matching circuit 7b is an impedance matching circuit (IMN) consisting of a matching circuit using lumped constant elements, a matching circuit using distributed constant lines, a matching circuit combining lumped constant and distributed constant elements, or a matching circuit using an LC-type matching circuit.

[0068] Alternatively, the second input matching circuit 7b can also be connected between another output of the distributor 4 and the input of the second filter circuit 6b.

[0069] The dual parallel amplifier 8 is composed of a first amplifier 8a and a second amplifier 8b. The first amplifier 8a and the second amplifier 8b are respectively biased to the threshold voltage that allows them to operate as B-level amplifiers, which is the threshold voltage of the transistors constituting the first amplifier 8a and the second amplifier 8b.

[0070] In addition, the threshold voltage in this invention includes the value of the threshold voltage itself and a value with a ± design margin for the threshold voltage value.

[0071] The input terminal 8a1 of the first amplifier 8a is connected to the gate bias terminal 11a, where the gate bias voltage is fixed. When the first input signal output from the first filter circuit 6a via the first input matching circuit 7a is input to the input terminal 8a1, the amplitude of the first input signal is smaller than the amplitude of the third input signal. Therefore, compared with the second amplifier 8b, it starts up later and operates as an auxiliary amplifier. When the second input signal output from the first filter circuit 6a is input to the input terminal 8a1, the amplitude of the second input signal is larger than the amplitude of the fourth input signal. Therefore, compared with the second amplifier 8b, it starts up earlier and operates as a main amplifier.

[0072] That is, when the input signal input to input terminal 1 is in the first frequency band, the first amplifier 8a operates as an auxiliary amplifier, and when the input signal input to input terminal 1 is in the second frequency band, the first amplifier 8a operates as a main amplifier.

[0073] In the first amplifier 8a, the saturated output power when operating as the main amplifier is equal to the saturated output power when operating as the auxiliary amplifier.

[0074] The first amplifier 8a uses transistors such as field-effect transistors (FETs), heterojunction bipolar transistors (HBTs), and high electron mobility transistors (HEMTs).

[0075] In addition, the first amplifier 8a may also include the circuit structure elements required for an amplifier, such as a stabilization circuit connected to the input side of the transistor and a bias circuit connected to the output side.

[0076] The gate electrode of the transistor that serves as the first amplifier 8a becomes the input terminal 8a1, the drain electrode becomes the output terminal 8a2, and it is connected to the power supply potential Vcc via a load resistor, while the source electrode is connected to the ground node.

[0077] The input terminal 8a1 is connected to the gate bias terminal 11a, and the gate bias terminal 11a is connected to the power supply potential Vcc via a resistor (bias resistor).

[0078] A threshold voltage of the transistor is applied to the gate bias terminal 11a so that the transistor, which is the first amplifier 8a, operates as a Class B amplifier.

[0079] Figure 2 The equivalent circuit of the first amplifier 8a is shown. That is, the first amplifier 8a can be regarded as consisting of a current source Ia based on the current flowing between the drain and source of the transistor and the parasitic capacitance between the drain and ground of the transistor, i.e., the output capacitance Ca.

[0080] The output capacitance Ca of the first amplifier 8a is compensated by an inductor or the like, or is taken in as part of the first output circuit 9a. From the viewpoint of electrical length, the current source Ia is directly connected to the first output circuit 9a.

[0081] The input terminal 8b1 of the second amplifier 8b is connected to the gate bias terminal 11b, where the gate bias voltage is fixed. When the third input signal, output from the second filter circuit 6b via the second input matching circuit 7b, is input to the input terminal 8b1, the amplitude of the third input signal is larger than the amplitude of the first input signal. Therefore, compared with the first amplifier 8a, it starts up earlier and operates as the main amplifier. When the fourth input signal, output from the second filter circuit 6b, is input to the input terminal 8b1, the amplitude of the fourth input signal is smaller than the amplitude of the second input signal. Therefore, compared with the first amplifier 8a, it starts up later and operates as an auxiliary amplifier.

[0082] That is, when the input signal input to input terminal 1 is in the first frequency band, the second amplifier 8b operates as the main amplifier, and when the input signal input to input terminal 1 is in the second frequency band, the second amplifier 8b operates as the auxiliary amplifier.

[0083] In the second amplifier 8b, the saturated output power when operating as the main amplifier is equal to the saturated output power when operating as the auxiliary amplifier.

[0084] The second amplifier 8b uses transistors such as FET, HBT, and HEMT.

[0085] In addition, the second amplifier 8b may also include the circuit structure elements required for an amplifier, such as a stabilization circuit connected to the input side of the transistor and a bias circuit connected to the output side.

[0086] The gate electrode of the transistor that serves as the second amplifier 8b becomes the input terminal 8b1, the drain electrode becomes the output terminal 8b2, and it is connected to the power supply potential Vcc via a load resistor, while the source electrode is connected to the ground node.

[0087] Input terminal 8b1 is connected to gate bias terminal 11b, which is connected to power supply potential Vcc via a resistor (bias resistor).

[0088] A threshold voltage of the transistor is applied to the gate bias terminal 11b so that the transistor, which is the first amplifier 8a, operates as a Class B amplifier.

[0089] The gate bias terminal 11b can also be the same as the gate bias terminal 11a.

[0090] Figure 3 The equivalent circuit of the second amplifier 8b is shown. That is, the second amplifier 8b can be considered as consisting of a current source Ib based on the current flowing between the drain and source of the transistor and the parasitic capacitance between the drain and ground of the transistor, i.e., the output capacitance Cb.

[0091] The output capacitance Cb of the second amplifier 8b is compensated by an inductor or the like, or is taken as part of the second output circuit 9b. From the viewpoint of electrical length, the current source Ib is directly connected to the second output circuit 9b.

[0092] In summary, the first amplifier 8a and the second amplifier 8b have the same function and structure. However, the amplitudes of the input signals input to the first amplifier 8a and the second amplifier 8b through the first filter circuit 6a and the second filter circuit 6b are different. Therefore, the first amplifier 8a and the second amplifier 8b start at different times.

[0093] Due to the difference in the start-up timing of the first amplifier 8a and the second amplifier 8b, the output load impedances of the first amplifier 8a and the second amplifier 8b are different.

[0094] When the input signal is in the first frequency band, the second amplifier 8b starts earlier than the first amplifier 8a. The second amplifier 8b functions as the main amplifier, while the first amplifier 8a functions as the auxiliary amplifier.

[0095] The output load impedance of the first amplifier 8a is much higher than that of the second amplifier 8b, for example, more than 10 times. From the perspective of the load modulation of the Doherty amplifier, the first amplifier 8a is in the off state, and the output terminal 8a2 of the first amplifier 8a is considered to be open.

[0096] At this time, through the first output circuit 9a and the second output circuit 9b, there is an output circuit with an electrical length of nearly 90 degrees on the output side of the second amplifier 8b. The output of the second amplifier 8b becomes a load condition that achieves high efficiency even at low output. Therefore, the second amplifier 8b operates efficiently even at low output.

[0097] Furthermore, when the input signal is in the second frequency band, the first amplifier 8a starts up earlier than the second amplifier 8b. The output load impedance of the second amplifier 8b is much higher than that of the first amplifier 8a, for example, more than 10 times. From the perspective of the load modulation of the Doherty amplifier, the second amplifier 8b is in the off state, and the output terminal 8b2 of the second amplifier 8b is considered to be open.

[0098] As a result, the first amplifier 8a functions as the main amplifier, and the second amplifier 8b functions as the auxiliary amplifier.

[0099] At this time, through the first output circuit 9a and the second output circuit 9b, there is an output circuit with an electrical length of nearly 90 degrees on the output side of the first amplifier 8a. The output of the first amplifier 8a becomes a load condition that achieves high efficiency even at low output. Therefore, the first amplifier 8a operates efficiently even at low output.

[0100] The output synthesis circuit 9 consists of a first output circuit 9a and a second output circuit 9b. During the back-off operation, it amplifies the output load (output reflection coefficient) of the main amplifier when either the first amplifier 8a or the second amplifier 8b functions as the main amplifier, depending on the frequency.

[0101] The first output circuit 9a modulates the output load relative to the first amplifier 8a.

[0102] The input terminal of the first output circuit 9a is connected to the output terminal of the first amplifier 8a, and the output terminal is connected to the output synthesis point 9A.

[0103] The first output circuit 9a is a transmission line with the following characteristics: its electrical length is shorter than 90 degrees relative to the first frequency band, and its electrical length is 90 degrees relative to the second frequency band. Its characteristic impedance is equal to the optimal load impedance of the first amplifier 8a at saturation output.

[0104] Furthermore, the first output circuit 9a is not limited to the transmission line, as long as the above conditions are met.

[0105] In the first output circuit 9a, the value shorter than 90 degrees relative to the first frequency band is, for example, a range of less than 90 degrees to 45 degrees.

[0106] Furthermore, the value of 90 degrees for electrical length relative to the second frequency band includes the value of 90 degrees itself and the value of 90 degrees with ± design margin for the load modulation that allows the first amplifier 8a to operate most efficiently relative to the second frequency band.

[0107] The second output circuit 9b modulates the output load relative to the second amplifier 8b.

[0108] The input terminal of the second output circuit 9b is connected to the output terminal of the second amplifier 8b, and the output terminal is connected to the output synthesis point 9A.

[0109] The second output circuit 9b is a transmission line with the following characteristics: its electrical length is longer than 90 degrees relative to the first frequency band and 180 degrees relative to the second frequency band. Its characteristic impedance is equal to the optimal load impedance of the second amplifier 8b at saturation output.

[0110] Furthermore, the second output circuit 9b is not limited to the transmission line, as long as the above conditions are met.

[0111] In the second output circuit 9b, the value of the electrical length longer than 90 degrees relative to the first frequency band is, for example, a range from 90 degrees to (90+16) degrees.

[0112] Furthermore, the value of 180 degrees for electrical length relative to the second frequency band includes the value of 180 degrees itself and a value with ± design margin for the 180 degrees value for the second amplifier 8b being disconnected relative to the second frequency band and the open load of the output terminal 8b2 being passed and the output terminal of the second output circuit 9b being open.

[0113] In summary, the output synthesis circuit 9 has the following characteristics: during the back-off operation, the output load (output reflection coefficient) of the main amplifier is increased when the first amplifier 8a or the second amplifier 8b functions as the main amplifier, depending on the frequency.

[0114] That is, the first output circuit 9a and the second output circuit 9b can be defined as having the following characteristics: when the frequency band of the input signal is the second frequency band, the first amplifier 8a functions as the main amplifier, and therefore the output load (output reflection coefficient) of the first amplifier 8a is increased according to the frequency of the input signal; when the frequency band of the input signal is the first frequency band, the second amplifier 8b functions as the main amplifier, and therefore the output load (output reflection coefficient) of the second amplifier 8b is increased according to the frequency of the input signal.

[0115] Through the first output circuit 9a - output synthesis point 9A - second output circuit 9b, the output terminal 8a2 of the first amplifier 8a and the output terminal 8b2 of the second amplifier 8b are not isolated.

[0116] When an input signal of the second frequency band is input to input terminal 1, and the first amplifier 8a receives the second input signal of the second frequency band and functions as a main amplifier, and the second amplifier 8b receives the fourth input signal of the second frequency band and functions as an auxiliary amplifier, a 90-degree transmission line based on the first output circuit 9a is connected to the output terminal 8a2 of the first amplifier 8a, and a 180-degree transmission line based on the second output circuit 9b is connected to the output terminal 8b2 of the second amplifier 8b, the load modulation, i.e., the apparent load impedance, changes in the first amplifier 8a, which functions as a main amplifier.

[0117] As a result, in the Doherty amplifier, with a second-band input signal input to input terminal 1, efficient operation is achieved at the backoff point where the output power is lower than the saturation output.

[0118] Furthermore, when an input signal of the first frequency band is input to input terminal 1, and the first amplifier 8a receives the first input signal of the first frequency band and functions as an auxiliary amplifier, and the second amplifier 8b receives the third input signal of the first frequency band and functions as a main amplifier, when a transmission line longer than 90 degrees based on the second output circuit 9b is connected to the output terminal 8b2 of the second amplifier 8b, and a transmission line shorter than 90 degrees based on the first output circuit 9a is connected to the output terminal 8a2 of the first amplifier 8a, the load modulation, i.e., the apparent load impedance, changes in the second amplifier 8b, which functions as a main amplifier.

[0119] As a result, in the Doherty amplifier, even with an input signal of the first frequency band input to input terminal 1, efficient operation is achieved at the backoff point where the output power is lower than the saturation output.

[0120] The output matching circuit 10 is connected between the output combining point 9A and the output terminal 2 of the output combining circuit 9 to achieve impedance matching between the impedance of the output combining point 9A and the impedance of the load connected to the output terminal 2.

[0121] The output matching circuit 10 utilizes circuits that use lumped constant elements, circuits that use distributed constant lines, circuits that combine lumped constant and distributed constant elements, LC-type matching circuits, etc.

[0122] Next, the operation of the Doherty amplifier in Embodiment 1 will be explained.

[0123] Initially, we will describe the case where an input signal of the first frequency (specifically 1.6 GHz) of the first frequency band is input to input terminal 1.

[0124] The input signal of the first frequency in the first frequency band is input to the distributor 4 via the third input matching circuit 3. The distributor 4 distributes the input signal to one output terminal and another output terminal and outputs it.

[0125] The input signal output from one of the output terminals of the distributor 4 is phase-corrected by the phase correction circuit 5 and then input to the first filter circuit 6a. The first filter circuit 6a filters the input signal and outputs the first input signal.

[0126] In the filtering based on the first filter circuit 6a, the input signal is a signal of the first frequency band. Therefore, the input signal is set as the first input signal attenuated by the first attenuation amount XdB.

[0127] The first input signal is input to the input terminal 8a1 of the first amplifier 8a via the first input matching circuit 7a.

[0128] The input signal output from the other output terminal of distributor 4 is input to the second filter circuit 6b.

[0129] Since the input signal is a signal of the first frequency band, the second filter circuit 6b outputs a third input signal that does not attenuate the input signal but allows it to pass.

[0130] The third input signal is input to the input terminal 8b1 of the second amplifier 8b via the second input matching circuit 7b.

[0131] When comparing the amplitude of the first input signal input to the input terminal 8a1 of the first amplifier 8a and the amplitude of the third input signal input to the input terminal 8b1 of the second amplifier 8b, the first input signal is attenuated by XdB by the first filter circuit 6a. Therefore, the amplitude of the third input signal is larger than the amplitude of the first input signal.

[0132] Therefore, when the first amplifier 8a scans the amplitude (input power) of the first input signal from low input to saturation, and when the second amplifier 8b scans the amplitude (input power) of the third input signal from low input to saturation, the second amplifier 8b starts first, and the first amplifier 8a starts later.

[0133] Therefore, the second amplifier 8b operates as the main amplifier, and the first amplifier 8a operates as the auxiliary amplifier.

[0134] The Doherty amplifier in Implementation 1 operates as a Doherty amplifier as follows: when an input signal of the first frequency of the first frequency band is input to the input terminal 1, the second amplifier 8b operates as the main amplifier and the first amplifier 8a operates as the auxiliary amplifier, and the input signal of the first frequency input to the input terminal 1 is amplified and output from the output terminal 2.

[0135] Here, using Figure 5 and Figure 6 We examine the output load (output reflection coefficient) of the second amplifier 8b, which operates as the main amplifier when a 1.6 GHz input signal is input to input terminal 1, during the back-off operation.

[0136] Now, let R be the optimal load for the saturated output of both amplifier 8a and amplifier 8b. opt Let the characteristic impedance of the first output circuit 9a and the second output circuit 9b be R. opt .

[0137] The first amplifier 8a operates as an auxiliary amplifier. Therefore, during the retraction operation, the first amplifier 8a becomes disconnected and stops, and the output terminal 8a2 of the first amplifier 8a becomes an open circuit terminal.

[0138] The output load Γ1 at the output synthesis point 9A is 0.5 × R. opt .

[0139] By amplifying the output reflection coefficient Γ2 corresponding to the reactance of the first output circuit 9a and by load modulation based on the second output circuit 9b, the output load Γ3 in the second amplifier 8b is reduced from the output load Γ1 (=0.5×R) opt Increase to 2×R opt above.

[0140] That is, such as Figure 6 As the impedance modification of Γ1 to Γ3 in the Smith chart, i.e., the load modulation, is represented as a representative trajectory in the first frequency band, the output load Γ3 in the second amplifier 8b increases to 2×R through the expansion of the output load Γ1 from the output load Γ1 to the output reflection coefficient Γ2 corresponding to the reactance of the first output circuit 9a, as shown by curve S1, and the load modulation based on the second output circuit 9b, as shown by curve M1. opt above.

[0141] Furthermore, at saturated output, the output loads of both amplifier 8a and amplifier 8b are matched to R. opt .

[0142] As a result, the Doherty amplifier in Implementation 1 operates as a Doherty amplifier in the following way: when a 1.6 GHz input signal is input to input terminal 1, due to the load modulation effect of output synthesis circuit 9, the output load (output reflection coefficient) of the second amplifier 8b relative to the optimal load R at saturated output. opt It is increased to more than twice the size, achieving efficient load even during backoff operations where the output power is lower than the saturation output.

[0143] Furthermore, the input signal is not limited to 1.6GHz. Relative to the frequency of the first frequency band, the output load Γ3 in the second amplifier 8b is reduced from the output load Γ1 (=0.5×R). opt Increase to 2×R opt above.

[0144] Next, we will describe the case where an input signal of the second frequency (specifically 4.2 GHz) of the second frequency band is input to input terminal 1.

[0145] The input signal of the second frequency in the second band is input to the distributor 4 via the third input matching circuit 3. The distributor 4 distributes the input signal to one output terminal and another output terminal and outputs it.

[0146] The input signal output from one of the output terminals of the distributor 4 is phase-corrected by the phase correction circuit 5 and then input to the first filter circuit 6a.

[0147] Since the input signal is a signal in the second frequency band, the first filter circuit 6a outputs a second input signal that allows the input signal to pass without attenuating it.

[0148] The second input signal is input to the input terminal 8a1 of the first amplifier 8a via the first input matching circuit 7a.

[0149] The input signal output from the other output terminal of distributor 4 is input to the second filter circuit 6b. The second filter circuit 6b filters the input signal and outputs the fourth input signal.

[0150] In the filtering based on the second filter circuit 6b, the input signal is a signal of the second frequency band. Therefore, the input signal is set as the fourth input signal attenuated by the first attenuation amount XdB.

[0151] When comparing the amplitude of the second input signal input to the input terminal 8a1 of the first amplifier 8a and the amplitude of the fourth input signal input to the input terminal 8b1 of the second amplifier 8b, the fourth input signal is attenuated by XdB by the second filter circuit 6b. Therefore, the amplitude of the second input signal is larger than the amplitude of the fourth input signal.

[0152] Therefore, when the first amplifier 8a scans the amplitude (input power) of the first input signal from low input to saturation, and when the second amplifier 8b scans the amplitude (input power) of the third input signal from low input to saturation, the first amplifier 8a starts first, and the second amplifier 8b starts later.

[0153] Therefore, the first amplifier 8a operates as the main amplifier, and the second amplifier 8b operates as the auxiliary amplifier.

[0154] The Doherty amplifier in Implementation 1 operates as a Doherty amplifier as follows: when an input signal of the second frequency of the second frequency band is input to the input terminal 1, the first amplifier 8a operates as the main amplifier and the second amplifier 8b operates as the auxiliary amplifier, and the input signal of the second frequency input to the input terminal 1 is amplified and output from the output terminal 2.

[0155] Here, using Figure 7 and Figure 8 We will examine the output load (output reflection coefficient) of the second amplifier 8b, which operates as the main amplifier when a 4.2 GHz input signal is input to input terminal 1, during the back-off operation.

[0156] The optimal load for saturated output of amplifiers 8a and 8b, and the characteristic impedance of output circuits 9a and 9b, are set to the same R as when a 1.6 GHz input signal is applied to input terminal 1. opt .

[0157] The second amplifier 8b operates as an auxiliary amplifier. Therefore, during the retraction operation, the second amplifier 8b becomes disconnected and stops, and the output terminal 8b2 of the second amplifier 8b becomes an open circuit terminal.

[0158] The output load Γ4 at the output synthesis point 9A is 0.5 × R. opt .

[0159] By amplifying the output reflection coefficient Γ5 corresponding to the reactance of the second output circuit 9b and modulating the load based on the first output circuit 9a, the output load Γ6 in the first amplifier 8a is reduced from the output load Γ4 (=0.5×R) opt Increase to 2×R opt above.

[0160] That is, such as Figure 8As the impedance modification of Γ4 to Γ6 in the Smith chart, i.e., the load modulation, is represented as a representative trajectory in the second frequency band, the output load Γ6 in the first amplifier 8a increases to 2×R, as shown by curve S2, from the output load Γ4 to the output reflection coefficient Γ5 corresponding to the reactance of the second output circuit 9b, and by curve M2, based on the load modulation of the first output circuit 9a. opt above.

[0161] Furthermore, at saturated output, the output loads of both amplifier 8a and amplifier 8b are matched to R. opt .

[0162] As a result, the Doherty amplifier of Embodiment 1 operates as a Doherty amplifier in the following way: when a 4.2 GHz input signal is input to input terminal 1, due to the effect of load modulation by output synthesis circuit 9, the output load (output reflection coefficient) of the first amplifier 8a relative to the optimal load R at saturated output. opt It is increased to more than twice the size, achieving efficient load even during backoff operations where the output power is lower than the saturation output.

[0163] Furthermore, the input signal is not limited to 4.2GHz. Relative to the frequency of the first frequency band, the output load Γ3 in the second amplifier 8b is reduced from the output load Γ1 (=0.5×R). opt Increase to 2×R opt above.

[0164] Based on the above description, in the Doherty amplifier of Embodiment 1, as follows: Figure 9 As shown in the figure, when the input signals of the first frequency band and the second frequency band are input, the functions of the first amplifier 8a and the second amplifier 8b are roughly illustrated. When the gate bias voltages of the first amplifier 8a and the second amplifier 8b are fixed to the gate bias voltages that operate as B-class amplifiers, the operation of the first amplifier 8a and the second amplifier 8b is switched to main amplifier and auxiliary amplifier according to the magnitude of the amplitude of the input signals input to the first amplifier 8a and the second amplifier 8b.

[0165] As a result, the Doherty amplifier in Implementation 1 can operate in multiple frequency bands of the input signal in the first frequency band and the second frequency band without controlling the gate bias voltage in the first amplifier 8a and the second amplifier 8b.

[0166] Furthermore, the Doherty amplifier in Implementation 1 operates as a Doherty amplifier that achieves efficient load even during backoff operation when the output power is lower than the saturation output, thanks to the load modulation effect of the output synthesis circuit 9.

[0167] Furthermore, in the Doherty amplifier of embodiment 1, such as Figure 10 As shown, when an input signal of 1.6 GHz as the first frequency band is input to input terminal 1 and when an input signal of 4.2 GHz as the second frequency band is input to input terminal 1, the drain efficiency relative to the output power is obtained with no less than that.

[0168] Implementation Method 2

[0169] according to Figures 11-13 The Doherty amplifier of Embodiment 2 will be described.

[0170] The Doherty amplifier of Embodiment 1 is a Doherty amplifier that amplifies the input signal relative to the first and second frequency bands. In contrast, the Doherty amplifier of Embodiment 2 is a Doherty amplifier that amplifies the input signal relative to the third frequency band, which is different from the first and second frequency bands.

[0171] The third frequency band is a frequency range that is higher than the second frequency band.

[0172] Furthermore, regarding the input signal input to the dual parallel amplifier constituting the Doherty amplifier, when the second frequency in the second frequency band is set to 1.0, the first frequency in the first frequency band satisfies a relationship of 0.5 with respect to the second frequency, and the third frequency in the third frequency band satisfies a relationship of 1.5 with respect to the second frequency.

[0173] The Doherty amplifier in Embodiment 2 differs from the Doherty amplifier in Embodiment 1 in that the first filter circuit 61a and the second filter circuit 61b, as well as the output synthesis circuit 91 composed of the first output circuit 91a and the second output circuit 91b, are different, but the other structural components are the same.

[0174] In addition, in each figure, the same labels indicate the same or equivalent parts.

[0175] When the first filter circuit 61a receives an input signal of the first frequency band, it outputs a first input signal that attenuates the input signal of the first frequency band by a first attenuation amount of XdB. When it receives an input signal of the second frequency band, it outputs a second input signal that allows the input signal of the second frequency band to pass through. When it receives an input signal of the third frequency band, it outputs a fifth input signal that attenuates the input signal of the third frequency band by a fourth attenuation amount.

[0176] The fourth attenuation is the same as the first attenuation by X dB. That is, when the first filter circuit 61a receives an input signal of the third frequency band, it outputs a fifth input signal that attenuates the input signal of the third frequency band by X dB.

[0177] In the first filter circuit 61a, when the input signal is in the first frequency band, the first input signal is attenuated by XdB, thereby outputting a signal with a small amplitude. When the input signal is in the second frequency band, the second input signal is not attenuated, thus outputting a signal with a large amplitude. When the input signal is in the third frequency band, the third input signal is attenuated by XdB, thereby outputting a signal with a small amplitude.

[0178] The first filter circuit 61a is a bandpass filter circuit that attenuates the input signal when the input signal is in the first and third frequency bands and allows the input signal to pass when the input signal is in the second frequency band.

[0179] The first filter circuit 61a is a reactive bandpass filter circuit composed of reactive reflection losses, such as a filter circuit using lumped constant elements, a filter circuit using distributed constant lines, a filter circuit combining lumped constants and distributed constants, and a filter circuit using LC-type matching circuits.

[0180] When a reactive high-pass filter circuit is used in the first filter circuit 61a, miniaturization is achieved as the first filter circuit 61a.

[0181] Alternatively, the first filter circuit 61a can replace the reactive bandpass filter circuit with a resistive bandpass filter circuit such as an attenuator.

[0182] When a resistive high-pass filter circuit is used in the first filter circuit 61a, the reflected power is lost in the first filter circuit 61a, thus achieving stable operation of the first amplifier 8a.

[0183] Furthermore, the first filter circuit 61a can also replace the bandpass filter circuit and use filter banks whose input signal paths differ according to the first to third frequency bands.

[0184] When the input signal of the first frequency band is input, the second filter circuit 61b outputs a third input signal that allows the input signal of the first frequency band to pass. When the input signal of the second frequency band is input, it outputs a fourth input signal that attenuates the input signal of the second frequency band by a first attenuation amount of XdB. When the input signal of the third frequency band is input, it outputs a sixth input signal that attenuates the input signal of the third frequency band by a fifth attenuation amount that is smaller than the fourth attenuation amount.

[0185] The fifth attenuation is 0dB. That is, when the second filter circuit 61b is input with a third frequency band input signal, it outputs a sixth input signal that allows the third frequency band input signal to pass.

[0186] In the second filter circuit 61b, when the input signal is in the first frequency band, the third input signal is not attenuated, so the output signal has a large amplitude. When the input signal is in the second frequency band, the fourth input signal is attenuated by XdB, so the output signal has a small amplitude. When the input signal is in the third frequency band, the sixth input signal is not attenuated, so the output signal has a large amplitude.

[0187] The second filter circuit 61b is a band-stop filter circuit that allows the input signal to pass through when the input signal is in the first and third frequency bands and attenuates the input signal when the input signal is in the second frequency band.

[0188] The second filter circuit 61b is a reactive band-stop filter circuit composed of reactive reflection losses, such as a filter circuit using lumped constant elements, a filter circuit using distributed constant lines, a filter circuit combining lumped constants and distributed constants, and a filter circuit using LC-type matching circuits.

[0189] When a reactive high-pass filter circuit is used in the second filter circuit 61b, miniaturization is achieved as the second filter circuit 61b.

[0190] Alternatively, the second filter circuit 61b can replace the reactive band-stop filter circuit with a resistive band-stop filter circuit such as an attenuator.

[0191] When a resistive high-pass filter circuit is used in the second filter circuit 61b, the reflected power is lost in the second filter circuit 61b, thus achieving stable operation of the second amplifier 8b.

[0192] Furthermore, the second filter circuit 61b can also replace the band-stop filter circuit and use filter banks whose input signal paths differ according to the first to third frequency bands.

[0193] In summary, the characteristics of the first filter circuit 61a and the second filter circuit 61b can be set as follows: when the input signal is in the first frequency band, the amplitude of the first input signal output from the first filter circuit 61a is smaller than the amplitude of the third input signal output from the second filter circuit 61b; when the input signal is in the second frequency band, the amplitude of the second input signal output from the first filter circuit 61a is larger than the amplitude of the fourth input signal output from the second filter circuit 61b; and when the input signal is in the third frequency band, the amplitude of the fifth input signal output from the first filter circuit 61a is smaller than the amplitude of the sixth input signal output from the second filter circuit 61b.

[0194] Regarding the attenuation XdB relative to the third frequency band in the first filter circuit 61a, as an example, it is set to 6dB if it is desired to improve the efficiency of the second amplifier 8b, and set to 3dB if it is desired to achieve both efficiency and linearity of the second amplifier 8b.

[0195] The first amplifier 8a and the second amplifier 8b are respectively biased to the threshold voltage that allows them to operate as Class B amplifiers, which is the threshold voltage of the transistors constituting the first amplifier 8a and the second amplifier 8b.

[0196] The input terminal 8a1 of the first amplifier 8a is connected to the gate bias terminal 11a, where the gate bias voltage is fixed. When the first input signal output from the first filter circuit 61a via the first input matching circuit 7a is input to the input terminal 8a1, the amplitude of the first input signal is smaller than the amplitude of the third input signal. Therefore, compared with the second amplifier 8b, it starts up later and operates as an auxiliary amplifier. When the second input signal output from the first filter circuit 61a is input to the input terminal 8a1, the amplitude of the second input signal is larger than the amplitude of the fourth input signal. Therefore, compared with the second amplifier 8b, it starts up earlier and operates as a main amplifier. When the fifth input signal output from the first filter circuit 61a is input to the input terminal 8a1, the amplitude of the fifth input signal is smaller than the amplitude of the sixth input signal. Therefore, compared with the second amplifier 8b, it starts up later and operates as an auxiliary amplifier.

[0197] That is, when the input signal input to input terminal 1 is in the first frequency band, the first amplifier 8a operates as an auxiliary amplifier; when the input signal input to input terminal 1 is in the second frequency band, the first amplifier 8a operates as a main amplifier; and when the input signal input to input terminal 1 is in the third frequency band, the first amplifier 8a operates as an auxiliary amplifier.

[0198] In the first amplifier 8a, the saturated output power when operating as the main amplifier is equal to the saturated output power when operating as the auxiliary amplifier.

[0199] The input terminal 8b1 of the second amplifier 8b is connected to the gate bias terminal 11b, where the gate bias voltage is fixed. When the third input signal, output from the second filter circuit 61b via the second input matching circuit 7b, is input to the input terminal 8b1, the amplitude of the third input signal is larger than the amplitude of the first input signal. Therefore, compared to the first amplifier 8a, it starts up earlier and operates as the main amplifier. When the fourth input signal, output from the second filter circuit 61b, is input to the input terminal 8b1, the amplitude of the fourth input signal is smaller than the amplitude of the second input signal. Therefore, compared to the second amplifier 8b, it starts up later and operates as an auxiliary amplifier. When the sixth input signal, output from the second filter circuit 61b, is input to the input terminal 8b1, the amplitude of the sixth input signal is larger than the amplitude of the fifth input signal. Therefore, compared to the first amplifier 8a, it starts up earlier and operates as the main amplifier.

[0200] That is, when the input signal input to input terminal 1 is in the first frequency band, the second amplifier 8b operates as the main amplifier; when the input signal input to input terminal 1 is in the second frequency band, the second amplifier 8b operates as the auxiliary amplifier; and when the input signal input to input terminal 1 is in the third frequency band, the second amplifier 8b operates as the main amplifier.

[0201] In the second amplifier 8b, the saturated output power when operating as the main amplifier is equal to the saturated output power when operating as the auxiliary amplifier.

[0202] In summary, similar to the case described in the Doherty amplifier of Embodiment 1, the first amplifier 8a and the second amplifier 8b have the same function and structure. However, the amplitudes of the input signals input to the first amplifier 8a and the second amplifier 8b through the first filter circuit 61a and the second filter circuit 61b are different. Therefore, the timing of the start-up of the first amplifier 8a and the second amplifier 8b is different.

[0203] Due to the difference in the start-up timing of the first amplifier 8a and the second amplifier 8b, the output load impedances of the first amplifier 8a and the second amplifier 8b are different.

[0204] When the input signals are in the first and second frequency bands, the first amplifier 8a and the second amplifier 8b operate in the same manner as the Doherty amplifier in Embodiment 1.

[0205] When the input signal is in the third frequency band, the second amplifier 8b starts up earlier than the first amplifier 8a. The second amplifier 8b functions as the main amplifier, while the first amplifier 8a functions as the auxiliary amplifier.

[0206] The output load impedance of the first amplifier 8a is much higher than that of the second amplifier 8b, for example, more than 10 times. From the perspective of the load modulation of the Doherty amplifier, the first amplifier 8a is in the off state, and the output of the first amplifier 8a is considered to be open.

[0207] At this time, through the first output circuit 91a and the second output circuit 91b, there is an output circuit with an electrical length of nearly 90 degrees on the output side of the second amplifier 8b. The output of the second amplifier 8b becomes a load condition that achieves high efficiency even at low output. Therefore, the second amplifier 8b operates efficiently even at low output.

[0208] The first output circuit 91a is a transmission line with the following characteristics: its electrical length is shorter than 90 degrees relative to the first frequency band, its electrical length is 90 degrees relative to the second frequency band, and its electrical length is greater than 90 degrees relative to the third frequency band. Its characteristic impedance is equal to the optimal load impedance of the first amplifier 8a at saturation output.

[0209] Furthermore, the first output circuit 91a is not limited to the transmission line, as long as the above conditions are met.

[0210] In the first output circuit 91a, the value of the electrical length shorter than 90 degrees relative to the first frequency band is, for example, a range of less than 90 degrees to 45 degrees.

[0211] The value of 90 degrees for electrical length relative to the second frequency band includes the value of 90 degrees itself and the value of 90 degrees with ± design margin for the load modulation that allows the first amplifier 8a to operate most efficiently relative to the second frequency band.

[0212] Compared to the third frequency band, the electrical length is 90 degrees or more, for example, up to 135 degrees.

[0213] The second output circuit 91b is a transmission line with the following characteristics: its electrical length is longer than 90 degrees relative to the first frequency band, 180 degrees relative to the second frequency band, and shorter than 270 degrees relative to the third frequency band. Its characteristic impedance is equal to the optimal load impedance of the second amplifier 8b at saturation output.

[0214] Furthermore, the second output circuit 91b is not limited to the transmission line, as long as the above conditions are met.

[0215] In the second output circuit 91b, the value of the electrical length longer than 90 degrees relative to the first frequency band is, for example, a range from 90 degrees to (90+16) degrees.

[0216] For the second frequency band, the value of 180 degrees for electrical length includes the value of 180 degrees itself and a value with ± design margin for the 180 degrees for the second amplifier 8b being disconnected relative to the second frequency band and the open load of the output terminal 8b2 being passed and the output terminal of the second output circuit 91b being open.

[0217] Compared to the third frequency band, the value of the electrical length shorter than 270 degrees is, for example, the range from less than 270 degrees to (270-16) degrees.

[0218] In summary, the output synthesis circuit 91, composed of the first output circuit 91a and the second output circuit 91b, has the following characteristics: during the back-off operation, it amplifies the output load (output reflection coefficient) of the main amplifier when either the first amplifier 8a or the second amplifier 8b functions as the main amplifier, depending on the frequency.

[0219] That is, the first output circuit 91a and the second output circuit 91b can be configured with the following characteristics: when the frequency band of the input signal is the second frequency band, the first amplifier 8a functions as the main amplifier, and therefore the output load (output reflection coefficient) of the first amplifier 8a is increased according to the frequency of the input signal. When the frequency band of the input signal is the first frequency band and the third frequency band, the second amplifier 8b functions as the main amplifier, and therefore the output load (output reflection coefficient) of the second amplifier 8b is increased according to the frequency of the input signal.

[0220] Through the first output circuit 91a - output synthesis point 91A - second output circuit 91b, the output terminal 8a2 of the first amplifier 8a and the output terminal 8b2 of the second amplifier 8b are not isolated.

[0221] Next, the operation of the Doherty amplifier in Embodiment 2 will be explained.

[0222] The operation of the Doherty amplifier in Embodiment 1 is the same as that of the input terminal 1 when an input signal of the first frequency of the first frequency band (specifically 1.6 GHz) is input to the input terminal 1, and when an input signal of the second frequency of the second frequency band (specifically 4.2 GHz) is input to the input terminal 1.

[0223] Therefore, we will explain the case where an input signal of the third frequency (specifically 6.3 GHz) of the third frequency band is input to input terminal 1.

[0224] The input signal of the third frequency in the third frequency band is input to the distributor 4 via the third input matching circuit 3. The distributor 4 distributes the input signal to one output terminal and another output terminal and outputs it.

[0225] The input signal output from one of the output terminals of the distributor 4 is phase-corrected by the phase correction circuit 5 and then input to the first filter circuit 61a. The first filter circuit 61a filters the input signal and outputs the fifth input signal.

[0226] In the filtering based on the first filter circuit 61a, the input signal is a signal of the third frequency band. Therefore, the input signal is set as the fifth input signal attenuated by XdB.

[0227] The fifth input signal is input to the input terminal 8a1 of the first amplifier 8a via the first input matching circuit 7a.

[0228] The input signal output from the other output terminal of distributor 4 is input to the second filter circuit 61b.

[0229] Since the input signal is a signal in the third frequency band, the second filter circuit 61b outputs a sixth input signal that allows the input signal to pass without attenuating it.

[0230] The sixth input signal is input to the input terminal 8b1 of the second amplifier 8b via the second input matching circuit 7b.

[0231] When comparing the amplitude of the fifth input signal input to the input terminal 8a1 of the first amplifier 8a and the amplitude of the sixth input signal input to the input terminal 8b1 of the second amplifier 8b, the fifth input signal is attenuated by XdB by the first filter circuit 61a. Therefore, the amplitude of the sixth input signal is larger than the amplitude of the fifth input signal.

[0232] Therefore, when the first amplifier 8a scans the amplitude (input power) of the fifth input signal from low input to saturation, and when the second amplifier 8b scans the amplitude (input power) of the sixth input signal from low input to saturation, the second amplifier 8b starts first, and the first amplifier 8a starts later.

[0233] Therefore, the second amplifier 8b operates as the main amplifier, and the first amplifier 8a operates as the auxiliary amplifier.

[0234] The Doherty amplifier in embodiment 2 operates as a Doherty amplifier as follows: when an input signal of the third frequency of the third frequency band is input to the input terminal 1, the second amplifier 8b operates as the main amplifier and the first amplifier 8a operates as the auxiliary amplifier, and the input signal of the third frequency input to the input terminal 1 is amplified and output from the output terminal 2.

[0235] Here, using Figure 12 and Figure 13We will examine the output load (output reflection coefficient) of the second amplifier 8b, which operates as the main amplifier when the third input signal is input to input terminal 1 and the back-off action is performed.

[0236] The optimal load for saturated output of the first amplifier 8a and the second amplifier 8b, and the characteristic impedance of the first output circuit 91a and the second output circuit 91b, are set to the same R as when input signals of the first frequency and the second frequency are input to input terminal 1. opt .

[0237] The first amplifier 8a operates as an auxiliary amplifier. Therefore, during the retraction operation, the first amplifier 8a becomes disconnected and stops, and the output terminal 8a2 of the first amplifier 8a becomes an open circuit terminal.

[0238] The output load Γ7 at the output synthesis point 91A is 0.5 × R. opt .

[0239] By amplifying the output reflection coefficient Γ8 corresponding to the reactance of the first output circuit 91a and by load modulation based on the second output circuit 91b, the output load Γ9 in the second amplifier 8b is reduced from the output load Γ7 (=0.5×R) opt Increase to 2×R opt above.

[0240] That is, such as Figure 13 As the impedance modification of Γ7 to Γ9 in the Smith chart represents the load modulation situation as a representative trajectory in the third frequency band, the output load Γ9 in the second amplifier 8b increases to 2×R, as shown by curve S3, from the output load Γ7 to the output reflection coefficient Γ8 corresponding to the reactance of the first output circuit 91a, and by curve M3, based on the load modulation of the second output circuit 91b. opt above.

[0241] Furthermore, at saturated output, the output loads of both amplifier 8a and amplifier 8b are matched to R. opt .

[0242] As a result, the Doherty amplifier in Implementation 1 operates as a Doherty amplifier in the following way: when the third input signal is input to input terminal 1, due to the effect of load modulation by the output synthesis circuit 9, the output load (output reflection coefficient) of the second amplifier 8b relative to the optimal load R at saturated output. opt It is increased to more than twice the size, achieving efficient load even during backoff operations where the output power is lower than the saturation output.

[0243] As can be seen from the above, in the Doherty amplifier of Embodiment 2, when the gate bias voltages of the first amplifier 8a and the second amplifier 8b are fixed at the gate bias voltages that operate as B-stage amplifiers, the operation of the first amplifier 8a and the second amplifier 8b is switched to main amplifier and auxiliary amplifier depending on the magnitude of the amplitude of the input signal input to the first amplifier 8a and the second amplifier 8b.

[0244] As a result, the Doherty amplifier in Embodiment 2 can operate in multiple frequency bands of the input signals in the first frequency band, the second frequency band, and the third frequency band without controlling the gate bias voltages in the first amplifier 8a and the second amplifier 8b.

[0245] The Doherty amplifier in Embodiment 2 has the same effect as the Doherty amplifier in Embodiment 1. Moreover, it operates as a Doherty amplifier in such a way that, relative to the input signal of the third frequency band, it also achieves efficient load during backoff operation when the output power is lower than the saturation output, thanks to the load modulation effect of the output synthesis circuit 9.

[0246] Furthermore, the Doherty amplifier in Embodiment 1 is designed to amplify signals in the first and second frequency bands as input signals, while the Doherty amplifier in Embodiment 2 is designed to amplify signals in the first to third frequency bands as input signals. However, it can also be designed to amplify signals in the fourth and fifth frequency bands or even signals in multiple higher frequency bands.

[0247] As input signals, when dealing with signals of four or more frequency bands, the pass and attenuation frequency bands of the first filter circuit 6a and the second filter circuit 6b are reversed, and the pass and attenuation frequency bands are reversed alternately for each frequency band. This makes the output synthesis circuit 9 composed of the first output circuit 9a and the second output circuit 9b have the following characteristics: during backoff operation, the output load (output reflection coefficient) of the main amplifier is increased according to the frequency when the first amplifier 8a or the second amplifier 8b functions as the main amplifier.

[0248] Based on the higher-order frequency, when the first amplifier 8a or the second amplifier 8b functions as the main amplifier, the output circuit of the main amplifier is set to a relationship of 90 degrees + 180 degrees × n (where n is a natural number).

[0249] Furthermore, the first filter circuit 6a and the second filter circuit 6b are composed of filter banks.

[0250] Furthermore, it is possible to freely combine the various embodiments, modify any structural elements of each embodiment, or omit any structural elements in each embodiment.

[0251] Industrial availability

[0252] The Doherty amplifier of the present invention is suitable for amplifiers that efficiently amplify communication signals, such as amplifiers for mobile communication base stations.

[0253] Label Explanation

[0254] 1: Input terminal; 2: Output terminal; 3: Third input matching circuit; 4: Distributor; 5: Phase correction circuit; 6a, 61a: First filter circuit; 6b, 61b: Second filter circuit; 7a: First input matching circuit; 7b: Second input matching circuit; 8: Dual parallel amplifier; 8a: First amplifier; 8b: Second amplifier; 9: Output combining circuit; 9a, 91a: First output circuit; 9b, 91b: Second output circuit; 10: Output matching circuit; 11a, 11b: Gate bias terminals.

Claims

1. A Doherty amplifier, the Doherty amplifier having: The first filter circuit, when input with a first frequency band, outputs a first input signal that attenuates the input signal of the first frequency band by a first attenuation amount, and when input with a second frequency band different from the first frequency band, outputs a second input signal that allows the input signal of the second frequency band to pass through. The second filter circuit, when input to the first frequency band, outputs a third input signal that attenuates the input signal of the first frequency band by a second attenuation amount smaller than the first attenuation amount; and when input to the second frequency band, outputs a fourth input signal that attenuates the input signal of the second frequency band by a third attenuation amount greater than the first attenuation amount. A first amplifier, whose gate bias voltage is fixed, operates as an auxiliary amplifier when a first input signal from the first filter circuit is input, and operates as a main amplifier when a second input signal from the first filter circuit is input; and The second amplifier, whose gate bias voltage is fixed, operates as a main amplifier when a third input signal from the second filter circuit is input, and operates as an auxiliary amplifier when a fourth input signal from the second filter circuit is input.

2. The Doherty amplifier according to claim 1, wherein, The gate bias voltage applied to the first amplifier is the threshold voltage of the first amplifier. The gate bias voltage applied to the second amplifier is the threshold voltage of the second amplifier.

3. The Doherty amplifier according to claim 1 or 2, wherein, The second attenuation is 0 dB, and the third attenuation is the same as the first attenuation.

4. The Doherty amplifier according to any one of claims 1 to 3, wherein, The second frequency band is higher than the first frequency band. The first filter circuit is a high-pass filter circuit. The second filter circuit is a low-pass filter circuit.

5. The Doherty amplifier according to claim 4, wherein, The high-pass filter is composed of a reactive filter circuit.

6. The Doherty amplifier according to claim 4, wherein, The high-pass filter is composed of a resistive filter circuit.

7. The Doherty amplifier according to any one of claims 1 to 6, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. Its electrical length is shorter than 90 degrees relative to the first frequency band. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is longer than 90 degrees relative to the first frequency band.

8. The Doherty amplifier according to any one of claims 1 to 6, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. Its electrical length relative to the second frequency band is 90 degrees. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is 180 degrees relative to the second frequency band.

9. The Doherty amplifier according to any one of claims 1 to 6, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. Its electrical length is shorter than 90 degrees relative to the first frequency band and is 90 degrees relative to the second frequency band. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is longer than 90 degrees relative to the first frequency band and is 180 degrees relative to the second frequency band.

10. The Doherty amplifier according to any one of claims 1 to 3, wherein, When the first filter circuit receives an input signal of a third frequency band, which is different from the first and second frequency bands, it outputs a fifth input signal that attenuates the input signal of the third frequency band by a fourth attenuation amount. When the second filter circuit receives the input signal of the third frequency band, it outputs a sixth input signal with a fifth attenuation amount that attenuates the input signal of the third frequency band by a amount smaller than the fourth attenuation amount. The first amplifier operates as an auxiliary amplifier when it receives the fifth input signal from the first filter circuit. The second amplifier operates as the main amplifier when the sixth input signal from the second filter circuit is input.

11. The Doherty amplifier according to claim 10, wherein, The fourth attenuation is the same as the first attenuation, and the fifth attenuation is 0.

12. The Doherty amplifier according to claim 10 or 11, wherein, The second frequency band is higher than the first frequency band, and the third frequency band is higher than the second frequency band. The first filter circuit is a bandpass filter circuit. The second filter circuit is a band-stop filter circuit.

13. The Doherty amplifier according to claim 12, wherein, The bandpass filter is composed of a reactive filter.

14. The Doherty amplifier according to claim 12, wherein, The bandpass filter is composed of a resistive filter.

15. The Doherty amplifier according to any one of claims 10 to 14, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. Its electrical length is shorter than 90 degrees relative to the first frequency band. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is longer than 90 degrees relative to the first frequency band.

16. The Doherty amplifier according to any one of claims 10 to 14, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. Its electrical length relative to the second frequency band is 90 degrees. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is 180 degrees relative to the second frequency band.

17. The Doherty amplifier according to any one of claims 10 to 14, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. The electrical length relative to the third frequency band is more than 90 degrees. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is shorter than 270 degrees relative to the third frequency band.

18. The Doherty amplifier according to any one of claims 10 to 14, wherein, The Doherty amplifier has: The first output circuit has its input terminal connected to the output terminal of the first amplifier and its output terminal connected to the output combining point. Its electrical length is shorter than 90 degrees relative to the first frequency band, 90 degrees relative to the second frequency band, and more than 90 degrees relative to the third frequency band. as well as The second output circuit has its input terminal connected to the output terminal of the second amplifier and its output terminal connected to the output synthesis point. Its electrical length is longer than 90 degrees relative to the first frequency band, 180 degrees relative to the second frequency band, and shorter than 270 degrees relative to the third frequency band.

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