Amplifier circuit

Abstract

The amplifier circuit is configured to include: a first amplifier (3) that amplifies a signal to be amplified; an output matching circuit (4) that transmits the signal amplified by the first amplifier (3); and a second amplifier (7) that amplifies the signal transmitted through the output matching circuit (4). The output matching circuit (4) is a lumped constant circuit having a plurality of lumped constant elements. By means of the plurality of lumped constant elements, the impedance seen from the first amplifier (3) toward the second amplifier (7) side when the output power of the second amplifier (7) is lower than the saturation power is made larger than the impedance seen from the first amplifier (3) toward the second amplifier (7) side when the output power of the second amplifier (7) is the saturation power.

Description

Technical Field

[0001] The present invention relates to an amplifier circuit for amplifying a signal. Background Art

[0002] In an amplifier circuit, there is an amplifier circuit having a first amplifier and a second amplifier, and the second amplifier is connected in series on the output side of the first amplifier.

[0003] In Patent Document 1 below, an amplifier circuit using a drive amplifier as the first amplifier and a Doherty amplifier as the second amplifier is disclosed. In this amplifier circuit, an impedance adjustment unit is connected between the drive amplifier and the Doherty amplifier.

[0004] The impedance adjustment unit includes a matching circuit that matches the output load impedance of the drive amplifier with the input impedance of the Doherty amplifier, and a phase adjuster that adjusts the phase of the signal output from the matching circuit to the Doherty amplifier. By adjusting the phase of the signal, the phase adjuster can improve the efficiency of the drive amplifier when the output power of the Doherty amplifier is lower than the saturation power.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014 - 116757 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] In the amplifier circuit disclosed in Patent Document 1, the impedance adjustment unit includes a phase adjuster. The phase adjuster is a distributed constant circuit formed by a transmission line. Since the amplifier circuit disclosed in Patent Document 1 includes a phase adjuster formed by a distributed constant circuit, there is a problem that the circuit size becomes large.

[0010] The present invention has been completed in order to solve the above problems, and an object thereof is to obtain an amplifier circuit that can improve the efficiency of the first amplifier when the output power of the second amplifier is lower than the saturation power without using a distributed constant circuit.

[0011] Means for Solving the Problems

[0012] The amplifier circuit of the present invention includes: a first amplifier that amplifies a signal to be amplified; an output matching circuit that transmits the signal amplified by the first amplifier; and a second amplifier that amplifies the signal transmitted through the output matching circuit. The output matching circuit is a lumped constant circuit having a plurality of lumped constant elements. Through the plurality of lumped constant elements, the impedance seen from the first amplifier toward the second amplifier side when the output power of the second amplifier is lower than the saturation power is made larger than the impedance seen from the first amplifier toward the second amplifier side when the output power of the second amplifier is the saturation power.

[0013] Advantages of the Invention

[0014] According to the present invention, it is possible to improve the efficiency of the first amplifier when the output power of the second amplifier is lower than the saturation power without using a distributed constant circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural diagram showing the amplifier circuit of Embodiment 1.

[0016] Figure 2 It is a structural diagram showing the second amplifier 7 implemented by a Doherty amplifier.

[0017] Figure 3 It is an equivalent circuit diagram showing the equivalent circuit of the first amplifier 3 included in the amplifier circuit of Embodiment 1.

[0018] Figure 4 It is a structural diagram showing an example of the lumped constant elements included in the LPF type matching circuit 5 and the lumped constant elements included in the HPF type matching circuit 6.

[0019] Figure 5 It is a Smith chart showing the input impedance Imp IN of the second amplifier 7.

[0020] Figure 6 It is a Smith chart showing the impedance Imp OUT seen from the current source 22 of the first amplifier 3 toward the second amplifier 7 side.

[0021] Figure 7 It is a Smith chart showing an example of the impedance transformation of the output matching circuit 4.

[0022] Figure 8 It is showing Figure 1 the efficiency of the first amplifier 3 in the amplifier circuit shown.

[0023] Figure 9 It is a structural diagram showing the second amplifier 7 implemented by an envelope tracking amplifier. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, in order to more specifically describe the present invention, a mode for implementing the present invention will be described with reference to the accompanying drawings.

[0025] Embodiment 1

[0026] Figure 1 is a structural diagram of an amplifier circuit showing Embodiment 1.

[0027] Figure 1 The amplifier circuit shown has an input terminal 1, an input matching circuit 2, a first amplifier 3, an output matching circuit 4, a second amplifier 7, and an output terminal 8.

[0028] An amplification target signal is supplied to the input terminal 1.

[0029] One end of the input matching circuit 2 is connected to the input terminal 1.

[0030] The other end of the input matching circuit 2 is connected to the input side of the first amplifier 3.

[0031] The input matching circuit 2 is realized by lumped constant elements, for example.

[0032] The input matching circuit 2 is a circuit that matches the input impedance of the first amplifier 3 with Figure 1 the impedance on the input side of the amplifier circuit shown.

[0033] The first amplifier 3 is realized by a FET (Field Effect Transistor), an HBT (Heterojunction Bipolar Transistor), or an HEMT (High Electron Mobility Transistor), for example.

[0034] The first amplifier 3 amplifies the amplification target signal transmitted in the input matching circuit 2 and outputs the amplified signal to the output matching circuit 4.

[0035] One end of the output matching circuit 4 is connected to the output side of the first amplifier 3.

[0036] The other end of the output matching circuit 4 is connected to the input side of the second amplifier 7.

[0037] The output matching circuit 4 is a lumped constant circuit having lumped constant elements.

[0038] That is, the output matching circuit 4 includes an LPF (Low Pass Filter) type matching circuit 5 with lumped constant elements and an HPF (High Pass Filter) type matching circuit 6 with lumped constant elements.

[0039] The output matching circuit 4 transmits the signal amplified by the first amplifier 3.

[0040] The output matching circuit 4, through a plurality of lumped constant elements, changes the impedance seen from the first amplifier 3 toward the second amplifier 7 side when the output power of the second amplifier 7 is lower than the saturation power to an impedance larger than the impedance seen from the first amplifier 3 toward the second amplifier 7 side when the output power of the second amplifier 7 is the saturation power.

[0041] Since the output matching circuit 4 is a lumped constant circuit, its circuit size is smaller than that of a circuit formed by a distributed constant circuit.

[0042] One end of the LPF type matching circuit 5 is connected to the output side of the first amplifier 3.

[0043] The other end of the LPF type matching circuit 5 is connected to one end of the HPF type matching circuit 6.

[0044] The LPF type matching circuit 5, for example, has an inductor as a lumped constant element.

[0045] One end of the HPF type matching circuit 6 is connected to the other end of the LPF type matching circuit 5.

[0046] The other end of the HPF type matching circuit 6 is connected to the input side of the second amplifier 7.

[0047] The HPF type matching circuit 6, for example, has an inductor and a capacitor as lumped constant elements.

[0048] The second amplifier 7 is implemented by, for example, Figure 2 the Doherty amplifier shown.

[0049] The second amplifier 7 amplifies the signal transmitted in the output matching circuit 4.

[0050] The second amplifier 7 outputs the amplified signal to the output terminal 8.

[0051] The output terminal 8 is a terminal for outputting the signal amplified by the second amplifier 7 to the outside.

[0052] Figure 2 is a structural diagram showing the second amplifier 7 implemented by the Doherty amplifier.

[0053] Figure 2The Doherty amplifier shown has a splitter 11, a carrier amplifier 12, a peak amplifier 13, a 90-degree line 14, and a combiner 15.

[0054] The splitter 11 divides the signal transmitted in the output matching circuit 4 into two, outputs one signal to the carrier amplifier 12, and outputs the other signal to the peak amplifier 13.

[0055] The carrier amplifier 12 amplifies the signal output from the splitter 11 and outputs the amplified signal to the 90-degree line 14.

[0056] The peak amplifier 13 amplifies the signal output from the splitter 11 when the signal level of the signal is greater than a certain level, and outputs the amplified signal to the combiner 15.

[0057] The 90-degree line 14 is a line for making the electrical length of the output side line of the carrier amplifier 12 90 degrees.

[0058] The combiner 15 combines the signal transmitted in the 90-degree line 14 and the signal amplified by the peak amplifier 13, and outputs the combined signal of the two signals.

[0059] Figure 3 It is an equivalent circuit diagram showing the equivalent circuit of the first amplifier 3 included in the amplifier circuit of Embodiment 1.

[0060] As Figure 3 shown, the equivalent circuit of the first amplifier 3 is represented by a current source 22, an inductor 23, and a capacitor 24.

[0061] The greater the signal level of the signal to be amplified transmitted in the input matching circuit 2, the greater the current output by the current source 22.

[0062] The inductor 23 is part of the parasitic components from the current source 22 to one end of the LPF type matching circuit 5.

[0063] The capacitor 24 is part of the parasitic components from the current source 22 to one end of the LPF type matching circuit 5.

[0064] The parasitic components included in the first amplifier 3, that is, the parasitic components from the current source 22 to one end of the LPF type matching circuit 5, are represented by the inductor 23 and the capacitor 24.

[0065] Figure 4 It is a structural diagram showing an example of the lumped constant elements included in the LPF type matching circuit 5 and the lumped constant elements included in the HPF type matching circuit 6.

[0066] The LPF type matching circuit 5 includes a first inductor 31 as a lumped constant element.

[0067] One end of the first inductor 31 is connected to the output side of the first amplifier 3.

[0068] The other end of the first inductor 31 is respectively connected to one end of the second inductor 32 and one end of the capacitor 33 included in the HPF type matching circuit 6.

[0069] The HPF type matching circuit 6 includes the second inductor 32, the capacitor 33, and the DC blocking capacitor 34 as lumped constant elements.

[0070] One end of the second inductor 32 is respectively connected to the other end of the first inductor 31 and one end of the capacitor 33.

[0071] The other end of the second inductor 32 is connected to one end of the DC cut-off capacitor 34.

[0072] One end of the capacitor 33 is respectively connected to the other end of the first inductor 31 and one end of the second inductor 32.

[0073] The other end of the capacitor 33 is connected to the input side of the second amplifier.

[0074] One end of the DC blocking capacitor 34 is connected to the other end of the second inductor 32.

[0075] The other end of the DC blocking capacitor 34 is grounded.

[0076] Figure 7 The shown HPF type matching circuit 6 has the DC blocking capacitor 34. However, this is just an example, and the HPF type matching circuit 6 may also not have the DC blocking capacitor 34 and ground the other end of the second inductor 32.

[0077] Next, the operation of Figure 1 the shown amplifier circuit will be described.

[0078] The second amplifier 7 is implemented by Figure 2 the shown Doherty amplifier. Therefore, the input impedance Imp IN of the second amplifier 7, as Figure 5 shown, changes from the back-off state to the saturation state.

[0079] Here, the saturation state means the state where the output power of the second amplifier 7 is the saturation power.

[0080] The back-off state means the state where the output power of the second amplifier 7 is lower than the saturation power, and also means the state where the peak amplifier 13 can perform signal amplification operation.

[0081] Figure 5 is the Smith chart showing the input impedance Imp IN of the second amplifier 7.

[0082] In Figure 5 the Smith chart shown, the input impedance Imp of the second amplifier 7 at saturation is represented at the center of the Smith chart IN，S .

[0083] The input impedance of the second amplifier 7 during back-off is as Figure 5 shown as Imp IN，B , and the input reflection phase of the second amplifier 7 during back-off is as Figure 5 shown as The input reflection phase of the second amplifier 7 during back-off has an absolute value greater than zero.

[0084] Figure 6 is a Smith chart representing the impedance Imp OUT seen from the current source 22 of the first amplifier 3 towards the second amplifier 7 side.

[0085] The impedance Imp OUT changes from back-off to saturation of the second amplifier 7 as Figure 6 shown.

[0086] In Figure 6 the Smith chart shown, the impedance Imp OUT，S at saturation is represented at the center of the Smith chart. When the impedance Imp OUT seen from the current source 22 towards the second amplifier 7 side is the impedance Imp OUT，S at saturation, the output power of the first amplifier 3 is the maximum power. That is, the output power of the first amplifier 3 is the saturation power.

[0087] From back-off to saturation, the input impedance Imp IN of the second amplifier 7 changes. Therefore, from back-off to saturation, the impedance Imp OUT seen from the current source 22 towards the second amplifier 7 side also changes. The impedance during back-off is Imp OUT，B .

[0088] By changing the lumped constant elements of the output matching circuit 4, the input impedance Imp IN，S of the second amplifier 7 at saturation can be changed.

[0089] In Figure 1 the amplifier circuit shown, the lumped constant elements of the output matching circuit 4 are designed in such a way that the input impedance Imp IN，S of the second amplifier 7 at saturation is transformed by the output matching circuit 4 into the impedance Imp OUT，S at which the output power of the first amplifier 3 is the maximum power.

[0090] In the case where the output matching circuit 4 described above has lumped constant elements, the impedance Imp as seen from the current source 22 toward the second amplifier 7 side OUT matches the impedance Imp at which the output power of the first amplifier 3 is maximum power OUT，S .

[0091] By changing the lumped constant elements of the output matching circuit 4, the input impedance Imp of the second amplifier 7 during back-off can be changed IN，B .

[0092] In Figure 1 the amplifier circuit shown, the impedance Imp as seen from the current source 22 toward the second amplifier 7 side during back-off OUT，B is made by the output matching circuit 4 to be larger than the impedance Imp as seen from the current source 22 toward the second amplifier 7 side at saturation OUT，S . The lumped constant elements of the output matching circuit 4 are designed in such a way

[0093] Specifically, the lumped constant elements of the output matching circuit 4 are designed so that the transmission phase of the parasitic component from the current source 22 to one end of the output matching circuit 4 the transmission phase of the LPF type matching circuit 5 the transmission phase of the HPF type matching circuit 6 and the input reflection phase of the second amplifier 7 have an absolute value of the sum within the threshold Th. As the threshold Th, for example, a value of 0 or more and 45 or less is assumed

[0094] For example, in the case where 0 is used as the threshold Th and the lumped constant elements of the output matching circuit 4 are designed so that the absolute value of the sum is 0 degrees, the input reflection phase of the second amplifier 7 becomes 0 degrees, and the efficiency of the first amplifier 3 when the second amplifier 7 performs a back-off operation is the highest efficiency

[0095] Figure 7 is a Smith chart showing an example of impedance transformation of the output matching circuit 4

[0096] In Figure 7 , assuming that the input impedance Imp of the second amplifier 7 at saturation IN，S is 50 Ω and the impedance Imp at which the output power of the first amplifier 3 is maximum power OUT，S is 75 Ω

[0097] L1 is the inductance of the first inductor 31, L2 is the inductance of the second inductor 32, and L3 is the inductance of the inductor 23 which is part of the parasitic component

[0098] C1 is the capacitance of capacitor 33, and C2 is the capacitance of capacitor 24 which is part of the parasitic components.

[0099] In Figure 7 the Smith chart shown, the input impedance Imp of the second amplifier 7 at saturation is represented at the center of the Smith chart IN，S .

[0100] In addition, in Figure 7 the Smith chart shown, the impedance transformation at saturation is represented by a dotted line, and the impedance transformation at back-off is represented by a solid line.

[0101] When the second amplifier 7 is saturated, the input impedance Imp of the second amplifier 7 IN，S is transformed by C1, L2, L1 + L3, and C2 into the impedance Imp at which the output power of the first amplifier 3 is the maximum power OUT，S i.e., 75 Ω (refer to Figure 7 the dotted line).

[0102] When the second amplifier 7 is at back-off, the input impedance Imp of the second amplifier 7 IN，B is transformed by C1, L2, L1 + L3, and C2 into an impedance Imp larger than the impedance Imp at which the output power of the first amplifier 3 is the maximum power OUT，S Imp (refer to OUT，B (the solid line in Figure 7 ). As Figure 7 shown, the impedance Imp OUT，B is on the real axis of the Smith chart.

[0103] When the second amplifier 7 is at back-off, the input impedance Imp of the second amplifier 7 IN，B becomes an impedance Imp larger than the impedance Imp at which the output power of the first amplifier 3 is the maximum power OUT，S Imp. In addition, the input impedance Imp of the second amplifier 7 OUT，B becomes onto the real axis of the Smith chart. Therefore, high-efficiency operation of the first amplifier 3 at back-off can be achieved. IN，B

[0104] Therefore, in Figure 1 the amplifier circuit shown, if the inductors L1, L2, and capacitor C1 are designed according to the inductance L3 and capacitor C in the way of applying Figure 7 the Smith chart shown, it is possible to maintain the maximum output power of the first amplifier 3 at saturation while achieving high-efficiency operation of the first amplifier 3 at back-off.

[0105] Figure 8 is an explanatory diagram showing Figure 1 the efficiency of the first amplifier 3 in the amplifier circuit shown.

[0106] In Figure 8 the horizontal axis represents the output power [dBm] of the first amplifier 3, and the vertical axis represents the efficiency [%] of the first amplifier 3.

[0107] In Figure 8 the efficiency characteristic of the first amplifier 3 in the amplifier circuit shown by the solid line Figure 1 is shown. Figure 8 It represents the efficiency characteristic of the first amplifier 3 when the lumped constant elements of the output matching circuit 4 are designed such that the threshold Th is 0 and the absolute value of the sum is 0 degrees.

[0108] The dashed line represents the efficiency characteristic of the first amplifier 3 (hereinafter referred to as the "first assumed efficiency characteristic") when the impedance Imp OUT seen from the current source 22 looking toward the second amplifier 7 side is fixed to the input impedance Imp IN，B of the second amplifier 7 at back-off. Here, back-off refers to the state in which the signal level of the signal output from the distributor 11 is the lowest signal level in the state where the peak amplifier 13 can perform the signal amplification operation.

[0109] The dotted line represents the efficiency characteristic of the first amplifier 3 (hereinafter referred to as the "second assumed efficiency characteristic") when the impedance Imp OUT seen from the current source 22 looking toward the second amplifier 7 side is fixed to the input impedance Imp IN，S of the second amplifier 7 at saturation.

[0110] The impedance Imp OUT，B seen from the current source 22 looking toward the second amplifier 7 side at back-off is OUT，S larger than the impedance Imp at saturation. Therefore, the output power of the first amplifier 3 at back-off is lower than the output power of the first amplifier 3 at saturation, and the efficiency of the first amplifier 3 at back-off is higher than the efficiency of the first amplifier 3 at saturation.

[0111] The impedance Imp OUT seen from the current source 22 looking toward the second amplifier 7 side changes from back-off to saturation. Therefore, at back-off, the efficiency characteristic of the first amplifier 3 overlaps with the first assumed efficiency characteristic shown by the dashed line, and at saturation, the efficiency characteristic of the first amplifier 3 overlaps with the second assumed efficiency characteristic shown by the dotted line.

[0112] Therefore, the efficiency of the first amplifier 3 at back-off is higher than the efficiency shown by the second assumed efficiency characteristic.

[0113] The output power of the first amplifier 3 at saturation is greater than the output power shown by the first assumed efficiency characteristic.

[0114] Figure 8Represents the efficiency characteristic of the first amplifier 3 when using 0 as the threshold Th and designing the lumped constant elements of the output matching circuit 4 in such a way that the absolute value of the sum is 0 degrees.

[0115] When using 45 as the threshold Th and designing the lumped constant elements of the output matching circuit 4 in such a way that the absolute value of the sum is 45 degrees, the efficiency characteristic of the first amplifier 3 is lower than that when designing the lumped constant elements of the output matching circuit 4 in such a way that the absolute value of the sum is 0 degrees.

[0116] However, the efficiency characteristic of the first amplifier 3 at back-off when designing the lumped constant elements of the output matching circuit 4 in such a way that the absolute value of the sum is 45 degrees lies between the first assumed efficiency characteristic shown by the dashed line and the second assumed efficiency characteristic shown by the dotted line. Therefore, even when designing the lumped constant elements of the output matching circuit 4 in such a way that the absolute value of the sum is 45 degrees, the efficiency of the first amplifier 3 at back-off is higher than the efficiency shown by the second assumed efficiency characteristic.

[0117] In addition, when using 90 as the threshold Th and designing the lumped constant elements of the output matching circuit 4 in such a way that the absolute value of the sum is 90 degrees, the efficiency characteristic of the first amplifier 3 overlaps with the second assumed efficiency characteristic shown by the dotted line. Therefore, high-efficiency operation at back-off cannot be achieved.

[0118] In the above-described first embodiment, the amplifier circuit is configured to include: a first amplifier 3 that amplifies a signal to be amplified; an output matching circuit 4 that transmits the signal amplified by the first amplifier 3; and a second amplifier 7 that amplifies the signal transmitted in the output matching circuit 4. The output matching circuit 4 is a lumped constant circuit having a plurality of lumped constant elements. Through the plurality of lumped constant elements, the impedance seen from the first amplifier 3 toward the second amplifier 7 side when the output power of the second amplifier 7 is lower than the saturation power is made larger than the impedance seen from the first amplifier 3 toward the second amplifier 7 side when the output power of the second amplifier 7 is the saturation power. Therefore, the amplifier circuit can improve the efficiency of the first amplifier 3 when the output power of the second amplifier 7 is lower than the saturation power without using a distributed constant circuit.

[0119] In Figure 1 the shown amplifier circuit, the output matching circuit 4 has a first inductor 31, a second inductor 32, and a capacitor 33 as the plurality of lumped constant elements. Moreover, through the first inductor 31, the second inductor 32, and the capacitor 33, the impedance Imp OUT，B at back-off is made OUT，S larger than the impedance Imp at saturation.

[0120] However, as long as the impedance Imp during back-off can be made OUT，B to be larger than the impedance Imp at saturation OUT，S it is sufficient, and it is not limited to the output matching circuit 4 having the first inductor 31, the second inductor 32, and the capacitor 33 as a plurality of lumped constant elements.

[0121] That is, the output matching circuit 4 only needs to have lumped constant elements that make the transmission phase of the output matching circuit 4 Therefore, the output matching circuit 4 can also have any combination of lumped constant elements such as a series inductor, a parallel inductor, a series capacitor, a parallel capacitor, a series resistor, or a parallel resistor, thereby achieving the transmission phase

[0122] Embodiment 2

[0123] In Figure 1 the amplifier circuit shown, the second amplifier 7 is implemented by a Doherty amplifier.

[0124] In Embodiment 2, an amplifier circuit in which the second amplifier 7 is implemented by an envelope tracking amplifier will be described.

[0125] The structure of the amplifier circuit of Embodiment 2 is the same as the structure of the amplifier circuit of Embodiment 1. The structural diagram showing the amplifier circuit of Embodiment 2 is Figure 1 .

[0126] Similar to the Doherty amplifier, the envelope tracking amplifier is an amplifier whose input impedance Imp IN changes. The input impedance Imp at saturation of the envelope tracking amplifier IN，S is different from the input impedance Imp during back-off of the envelope tracking amplifier IN，B .

[0127] Figure 9 is a structural diagram showing the second amplifier 7 implemented by an envelope tracking amplifier.

[0128] The envelope tracking amplifier as the second amplifier 7 has a high-frequency amplifier 41 and a power supply modulator 42.

[0129] The high-frequency amplifier 41 amplifies the signal transmitted in the output matching circuit 4.

[0130] The high-frequency amplifier 41 outputs the amplified signal to the output terminal 8.

[0131] The power supply modulator 42 supplies a power supply voltage corresponding to the amplitude of the signal transmitted in the output matching circuit 4 to the high-frequency amplifier 41.

[0132] The power supply voltage supplied from the power supply modulator 42 to the high-frequency amplifier 41 varies according to the amplitude change of the signal transmitted in the output matching circuit 4.

[0133] Since the power supply voltage supplied from the power supply modulator 42 changes, the input impedance Imp of the high-frequency amplifier 41 IN changes.

[0134] In the above-described second embodiment, the amplifier circuit is configured such that the second amplifier 7 is implemented by an envelope tracking amplifier. Similar to the amplifier circuit of the first embodiment, the amplifier circuit of the second embodiment can improve the efficiency of the first amplifier 3 when the output power of the second amplifier 7 is lower than the saturation power without using a distributed constant circuit.

[0135] Furthermore, the present invention enables free combination of the respective embodiments, or modification of any constituent elements of the respective embodiments, or omission of any constituent elements in the respective embodiments.

[0136] Industrial Applicability

[0137] The present invention is applicable to an amplifier circuit for amplifying a signal.

[0138] Reference Numeral Explanation

[0139] 11: input terminal; 2: input matching circuit; 3: first amplifier; 4: output matching circuit; 5: LPF type matching circuit; 6: HPF type matching circuit; 7: second amplifier; 8: output terminal; 11: distributor; 12: carrier amplifier; 13: peak amplifier; 14: 90-degree line; 15: synthesizer; 21: transistor; 22: current source; 23: inductor; 24: capacitor; 31: first inductor; 32: second inductor; 33: capacitor; 34: DC blocking capacitor; 41: high-frequency amplifier; 42: power supply modulator.

Claims

1. An amplifier circuit, characterized in that, The amplifier circuit has: a first amplifier that amplifies a signal to be amplified; an output matching circuit that transmits the signal amplified by the first amplifier; and a second amplifier that amplifies the signal transmitted in the output matching circuit, one end of the output matching circuit is directly connected to the output side of the first amplifier, the other end of the output matching circuit is directly connected to the input side of the second amplifier, the output matching circuit is composed of a lumped constant circuit having a plurality of lumped constant elements and does not include a distributed constant circuit, and through the plurality of lumped constant elements, the impedance seen from the first amplifier to the second amplifier side when the output power of the second amplifier is lower than the saturation power becomes larger than the impedance seen from the first amplifier to the second amplifier side when the output power of the second amplifier is the saturation power; wherein the output matching circuit changes the impedance seen from the first amplifier to the second amplifier side when the output power of the second amplifier is lower than the saturation power through the plurality of lumped constant elements in such a manner that the absolute value of the sum of the transmission phase of the parasitic components included in the first amplifier, the transmission phase of the output matching circuit, and the input reflection phase of the second amplifier is within a threshold value, and the threshold value is greater than or equal to 0 degrees and less than or equal to 45 degrees.

2. The amplifier circuit according to claim 1, wherein as the plurality of lumped constant elements, the output matching circuit has: a first inductor, one end of which is connected to the output side of the first amplifier; a second inductor, one end of which is connected to the other end of the first inductor, and the other end of which is grounded; and a capacitor, one end of which is connected to the other end of the first inductor and one end of the second inductor respectively, and the other end of which is connected to the input side of the second amplifier.

3. The amplifier circuit according to claim 1, wherein the threshold value is 45 degrees, the output matching circuit changes the impedance seen from the first amplifier to the second amplifier side when the output power of the second amplifier is lower than the saturation power through the plurality of lumped constant elements in such a manner that the absolute value of the sum is within 45 degrees.

4. The amplifier circuit according to claim 1, wherein the threshold value is 0 degrees, the output matching circuit changes the impedance seen from the first amplifier to the second amplifier side when the output power of the second amplifier is lower than the saturation power through the plurality of lumped constant elements in such a manner that the absolute value of the sum is 0 degrees.

5. The amplifier circuit according to claim 1, wherein the second amplifier is a Doherty amplifier.

6. The amplifier circuit according to claim 1, wherein the second amplifier is an envelope tracking amplifier.

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