Doherty Amplifier

Abstract

The Doherty amplifier (100) comprises: amplifiers (8, 9) including a main amplifier (8) and an auxiliary amplifier (9); an output circuit (10, 13) for back-off amplification, including a first output circuit (10) provided between the main amplifier (8) and an output combining section (18) of the amplifiers (8, 9) and having a first electrical length (θ1), and a second output circuit (13) provided between the auxiliary amplifier (9) and the output combining section (18) and having a second electrical length (θ2); and a frequency characteristic compensation circuit (15) for broadbanding, which is provided electrically in parallel with the first output circuit (10) and compensates for the frequency characteristic of the impedance in the output circuit (10, 13).

Description

Technical Field

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

[0002] In recent years, the peak-to-average power ratio (PAPR) of modulated signals for communication has increased due to the increase in communication traffic. In order to cope with the increase in PAPR, amplifiers for communication devices are required to improve their efficiency in an operating state (hereinafter referred to as a "fallback operating state") based on an output power lower than the saturated output power.

[0003] In a conventional amplifier, the efficiency in the fallback operation state is lower than the efficiency in the operation state based on the saturated output power (hereinafter referred to as the "saturated operation state"). More specifically, as the output power decreases, the efficiency gradually decreases. In contrast, by using a Doherty amplifier, the efficiency in the fallback operation state can be improved.

[0004] That is, the Doherty amplifier has a main amplifier, a so-called "carrier amplifier". In addition, the Doherty amplifier has an auxiliary amplifier, a so-called "peak amplifier". When the output power requested by the Doherty amplifier (hereinafter referred to as "requested output power") is greater than a prescribed value, the carrier amplifier is set to an on state, and the peak amplifier is set to an on state. On the other hand, when the requested output power is less than the prescribed value, the carrier amplifier is set to an on state, and the peak amplifier is set to an off state.

[0005] Thus, in the fallback operation state based on the output power corresponding to the specified value, the same efficiency as that in the saturated operation state is achieved. More specifically, in the fallback operation state based on the output power about 6 decibels (hereinafter referred to as "dB") lower than the saturated output power, the same efficiency as that in the saturated operation state is achieved. As a result, it is possible to cope with a PAPR of about 6 dB.

[0006] Hereinafter, the difference between the saturated output power and the output power that achieves the same efficiency as that in the saturated operation state in the back-off operation state is referred to as the "back-off amount". That is, the Doherty amplifier can handle the PAPR corresponding to the back-off amount. Therefore, Patent Document 1 discloses a technology for making the back-off amount of the Doherty amplifier larger than 6 dB.

[0007] That is, a phase line (21) is provided between the carrier amplifier (3) and the output synthesis point (13) (see Patent Document 1). Figure 1 In addition, a phase line (23) is provided between the peak amplifier (7) and the output synthesis point (13) (see Patent Document 1). Figure 1 Here, the electrical length (θ1) of the phase line (21) is set to a value based on a predetermined mathematical formula (see equation (1) of patent document 1). In addition, the electrical length (θ2) of the phase line (23) is set to a value based on another predetermined mathematical formula (see equation (2) of patent document 1). Thus, a back-off amount greater than 6 dB is achieved (see equation (3) of patent document 1). Figure 4 wait).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: International Publication No. 2007 / 015462 Summary of the invention

[0011] Problems to be solved by the invention

[0012] As reference Figure 1 to Figure 7 As described later, in the conventional Doherty amplifier, the impedance on the output side relative to the main amplifier varies greatly depending on the frequency, especially when the auxiliary amplifier is set to the off state. Due to the impedance variation, there is a problem that the frequency band in which the operation can be performed (hereinafter referred to as "operating band") is narrow.

[0013] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to simultaneously achieve an increase in the back-off amount and an increase in the operating band (hereinafter referred to as "broadbanding") in a Doherty amplifier.

[0014] Means for solving problems

[0015] The Doherty amplifier of the present invention comprises: an amplifier including a main amplifier and an auxiliary amplifier; an output circuit for amplifying the back-off amount, including a first output circuit arranged between the main amplifier and the output synthesis section of the amplifier and having a first electrical length, and a second output circuit arranged between the auxiliary amplifier and the output synthesis section and having a second electrical length; and a frequency characteristic compensation circuit for broadbanding, which is electrically arranged in parallel with the first output circuit and compensates for the frequency characteristics of the impedance in the output circuit.

[0016] Effects of the Invention

[0017] According to the present invention, since it is configured as described above, it is possible to simultaneously achieve an increase in the backoff amount and a wide bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 1 is a circuit diagram showing main parts of the Doherty amplifier according to the first embodiment.

[0019] Figure 2: is a circuit diagram showing the main parts of a Doherty amplifier for comparison.

[0020] Figure 3 This is an explanatory diagram showing the impedance when the auxiliary amplifier in the Doherty amplifier according to the first embodiment is set to the off state.

[0021] Figure 4 This is an explanatory diagram showing the impedance when the auxiliary amplifier in the comparative Doherty amplifier is set to the off state.

[0022] Figure 5 This is an explanatory diagram showing impedance conversion when the auxiliary amplifier in the Doherty amplifier according to the first embodiment is set to an OFF state.

[0023] Figure 6 This is an explanatory diagram showing impedance conversion when the auxiliary amplifier in the comparative Doherty amplifier is set to the off state.

[0024] Figure 7 It is a characteristic diagram showing the reflection amount with respect to the frequency.

[0025] Figure 8 This is an explanatory diagram showing the impedance when the auxiliary amplifier in the Doherty amplifier according to the first embodiment is set to the on state.

[0026] Fig. 9 1 is a circuit diagram showing main parts of a Doherty amplifier according to a second embodiment.

[0027] Fig.10 1 is a circuit diagram showing main parts of a Doherty amplifier according to a third embodiment.

[0028] Fig.11 1 is a circuit diagram showing main parts of a Doherty amplifier according to a fourth embodiment.

[0029] Fig.12 1 is a circuit diagram showing main parts of a Doherty amplifier according to a fifth embodiment. DETAILED DESCRIPTION

[0030] Hereinafter, in order to explain the present invention in more detail, the mode for carrying out the present invention will be described with reference to the drawings.

[0031] Implementation Method 1

[0032] Figure 1 1 is a circuit diagram showing the main parts of the Doherty amplifier according to the first embodiment. Figure 1 , the Doherty amplifier of embodiment 1 is described.

[0033] Unless otherwise specified, the value of the electrical length is assumed to be a value at a predetermined frequency (hereinafter referred to as "reference frequency") f_ref. The reference frequency f_ref is set to the same value as the center frequency f_center in a used frequency band (hereinafter referred to as "used frequency band"), for example.

[0034] In the drawings, reference numeral 1 denotes an input terminal. The input terminal 1 is electrically connected to a signal source (not shown). The input terminal 1 receives a signal input to the Doherty amplifier 100. An input matching circuit 2 ("IMN" in the drawings) is provided between the input terminal 1 and the distributor 3. The input matching circuit 2 is a circuit for achieving impedance matching between the input terminal 1 and the distributor 3. The input matching circuit 2 is composed of, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on a lumped constant and a distributed constant, an LC type matching circuit, or a circuit using one or more λ / 4 lines.

[0035] The distributor 3 distributes the output signal of the input matching circuit 2 to two paths P1 and P2. The distributor 3 outputs the distributed signal. One path (hereinafter, sometimes referred to as "first path") P1 of the two paths P1 and P2 is a path including the main amplifier 8. The other path (hereinafter, sometimes referred to as "second path") P2 of the two paths P1 and P2 is a path including the auxiliary amplifier 9.

[0036] The distributor 3 is constituted by, for example, a Wilkinson divider or a hybrid circuit. Each circuit in the hybrid circuit is constituted by, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC matching circuit, or a circuit using one or more λ / 4 lines.

[0037] An input matching circuit (hereinafter referred to as "first input matching circuit") 4 is provided between the distributor 3 and the main amplifier 8. The first input matching circuit 4 is a circuit for obtaining input matching to the main amplifier 8. The first input matching circuit 4 is composed of, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on a lumped constant and a distributed constant, an LC type matching circuit, or a circuit using one or more λ / 4 lines.

[0038] A phase correction circuit 5 is provided between the distributor 3 and the auxiliary amplifier 9. The phase correction circuit 5 is a circuit that makes the electrical length of the second path P2 equal to the electrical length of the first path P1. The phase correction circuit 5 is composed of, for example, a transmission line 6. The transmission line 6 has an electrical length equal to the difference in electrical length between the paths P1 and P2.

[0039] An input matching circuit (hereinafter referred to as "second input matching circuit") 7 is provided between the distributor 3 and the auxiliary amplifier 9. More specifically, the second input matching circuit 7 is provided between the phase correction circuit 5 and the auxiliary amplifier 9. The second input matching circuit 7 is a circuit for obtaining input matching to the auxiliary amplifier 9. The second input matching circuit 7 is composed of, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on a lumped constant and a distributed constant, an LC type matching circuit, or a circuit using one or more λ / 4 lines.

[0040] The main amplifier 8 amplifies the output signal of the first input matching circuit 4. The main amplifier 8 outputs the amplified signal. The main amplifier 8 is composed of a transistor. Specifically, for example, the main amplifier 8 is composed of a FET (Field Effect Transistor), an HBT (Heterojunction Bipolar Transistor) or a HEMT (High Electron Mobility Transistor). The gate bias of the main amplifier 8 is set to a value corresponding to the so-called "A class", a value corresponding to the so-called "B class", or a value between the A class and the B class.

[0041] The auxiliary amplifier 9 amplifies the output signal of the second input matching circuit 7. The auxiliary amplifier 9 outputs the amplified signal. The auxiliary amplifier 9 is composed of a transistor. Specifically, for example, the auxiliary amplifier 9 is composed of a FET, a HBT, or a HEMT. The gate bias of the auxiliary amplifier 9 is set to a value corresponding to the so-called "Class C".

[0042] Hereinafter, the main amplifier 8 and the auxiliary amplifier 9 are sometimes simply collectively referred to as "amplifiers". In the amplifiers 8 and 9, the electrical characteristics of the output relative to the bias amount (for example, output resistance and output amplitude) are the same. Therefore, assuming that the bias amounts of the amplifiers 8 and 9 are set to the same value, the electrical characteristics of the output of the main amplifier 8 are the same as the electrical characteristics of the output of the auxiliary amplifier 9. In addition, in this case, the saturated output power of the main amplifier 8 is the same as the saturated output power of the auxiliary amplifier 9.

[0043] In the drawings, reference numeral 18 indicates a portion (hereinafter referred to as an "output combining portion") for combining the outputs of the amplifiers 8 and 9. A first output circuit 10 is provided between the main amplifier 8 and the output combining portion 18. The first output circuit 10 is composed of, for example, two transmission lines 11 and 12. One of the two transmission lines 11 and 12 (hereinafter referred to as the "first transmission line") 11 has an electrical length of 90 degrees or approximately 90 degrees. The other of the two transmission lines 11 and 12 (hereinafter referred to as the "second transmission line") 12 has an electrical length less than 90 degrees.

[0044] In addition, a second output circuit 13 is provided between the auxiliary amplifier 9 and the output combining section 18. The second output circuit 13 is composed of, for example, a transmission line (hereinafter referred to as a "third transmission line") 14. The third transmission line 14 has an electrical length of less than 90 degrees. Hereinafter, the first output circuit 10 and the second output circuit 13 are sometimes simply collectively referred to as an "output circuit".

[0045] Here, the electrical length θ1 of the first output circuit 10 (hereinafter referred to as "first electrical length"), i.e., the total electrical length of the first transmission line 11 and the second transmission line 12, is set to a value based on the following equation (1). In addition, the characteristic impedance of the first output circuit 10 is set to the same value as the optimal load impedance Ropt1 of the main amplifier 8 in the saturated operation state.

[0046]

[0047] In addition, the electrical length θ2 of the second output circuit 13 (hereinafter referred to as "second electrical length"), that is, the electrical length of the third transmission line 14, is set to a value based on the following formula (2). In addition, the characteristic impedance of the second output circuit 13 is set to the same value as the optimal load impedance Ropt2 of the auxiliary amplifier 9 in the saturated operation state. Here, Ropt2 is set to the same value as Ropt1. For example, Ropt1 = Ropt, and Ropt2 = Ropt.

[0048]

[0049] γ in the above equations (1) and (2) is a value corresponding to the back-off amount (hereinafter referred to as "requested back-off amount") OBO requested by the Doherty amplifier 100. More specifically, γ is a value based on the following equation (3).

[0050] OBO[dB]=10log 10 (γ) (3)

[0051] That is, the total electrical length of the second transmission line 12 and the third transmission line 14 is set to 90 degrees or approximately 90 degrees. Therefore, the total electrical length of the first transmission line 11, the second transmission line 12, and the third transmission line 14 is set to 180 degrees or approximately 180 degrees. In other words, the total electrical length of the first output circuit 10 and the second output circuit 13 is set to 180 degrees or approximately 180 degrees.

[0052] In addition, the parasitic components of the main amplifier 8 are compensated by an inductor (not shown). Alternatively, the parasitic components of the main amplifier 8 are taken into the first output circuit 10 in terms of the circuit. Therefore, from the perspective of electrical length, the first output circuit 10 is directly connected to the output portion of the main amplifier 8. In addition, the parasitic components of the auxiliary amplifier 9 are compensated by another inductor (not shown). Alternatively, the parasitic components of the auxiliary amplifier 9 are taken into the second output circuit 13 in terms of the circuit. Therefore, from the perspective of electrical length, the second output circuit 13 is directly connected to the output portion of the auxiliary amplifier 9.

[0053] Hereinafter, the characteristic indicating the impedance with respect to the frequency is referred to as "frequency characteristic". The Doherty amplifier 100 includes a frequency characteristic compensation circuit 15. The frequency characteristic compensation circuit 15 is a circuit for compensating the frequency characteristics in the output circuits 10 and 13 when the auxiliary amplifier 9 is set to the off state. For the compensation of the frequency characteristics by the frequency characteristic compensation circuit 15, refer to Figure 1 to Figure 7 I will talk about this later.

[0054] The frequency characteristic compensation circuit 15 is electrically connected in parallel with the first output circuit 10. The frequency characteristic compensation circuit 15 is composed of, for example, an open stub 16 having an electrical length of 180 degrees or substantially 180 degrees. In the drawings, reference numeral 17 indicates a portion (hereinafter referred to as a "connection portion") where the first transmission line 11, the second transmission line 12, and the open stub 16 are connected.

[0055] In the portion P3 of the paths P1 and P2 on the output side of the amplifiers 8 and 9 (hereinafter referred to as a "partial path"), so-called "isolation" is not performed. Figure 1 As shown, the partial path P3 is a portion of the paths P1 and P2 that includes the first output circuit 10 , the second output circuit 13 , and the output combining section 18 .

[0056] An output matching circuit 19 ("OMN" in the figure) is provided between the output combining section 18 and the output terminal 20. The output matching circuit 19 is a circuit for achieving impedance matching between the output combining section 18 and the output terminal 20. The output matching circuit 19 is composed of, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC type matching circuit, or a circuit using one or more λ / 4 lines. The output terminal 20 is electrically connected to a load 21.

[0057] The main parts of the Doherty amplifier 100 are composed of an input terminal 1, an input matching circuit 2, a distributor 3, a first input matching circuit 4, a phase correction circuit 5, a second input matching circuit 7, a main amplifier 8, an auxiliary amplifier 9, a first output circuit 10, a second output circuit 13, a frequency characteristic compensation circuit 15, an output matching circuit 19 and an output terminal 20.

[0058] Next, refer to Figure 1 to Figure 7 The operation of the Doherty amplifier 100 will be described with a focus on impedance conversion when the auxiliary amplifier 9 is set to an off state. At the same time, the effect of the Doherty amplifier 100 will be described. In addition, it is assumed that Ropt1=Rop, and Ropt2=Ropt.

[0059] Figure 2 FIG. 1 shows a Doherty amplifier 100′ for comparison with the Doherty amplifier 100. Figure 2 As shown, the Doherty amplifier 100' does not include the frequency characteristic compensation circuit 15. That is, the Doherty amplifier 100' corresponds to the conventional Doherty amplifier described in Patent Document 1 and the like.

[0060] Figure 3 1 shows the impedance of the Doherty amplifier 100 when the auxiliary amplifier 9 is set to the disconnected state. In the figure, Γ1 represents the impedance of the output terminal 20 side observed from the output combining section 18. In addition, Γ2 represents the impedance of the output terminal 20 side observed from the output section of the second transmission line 12. In addition, Γ3 represents the impedance of the output terminal 20 side observed from the connecting section 17. In addition, Γ4 represents the impedance of the output terminal 20 side observed from the output section of the first transmission line 11. In addition, Γ5 represents the impedance of the output terminal 20 side observed from the output section of the main amplifier 8.

[0061] Figure 4 The impedance of the Doherty amplifier 100' is shown when the auxiliary amplifier 9 is set to the disconnected state. In the figure, Γ1' represents the impedance of the output terminal 20 side observed from the output combining section 18. In addition, Γ2' represents the impedance of the output terminal 20 side observed from the output section of the second transmission line 12. In addition, Γ4' represents the impedance of the output terminal 20 side observed from the output section of the first transmission line 11. In addition, Γ5' represents the impedance of the output terminal 20 side observed from the output section of the main amplifier 8.

[0062] Figure 5 Γ2, Γ4, and Γ5 are depicted in the Smith chart. In the figure, arrow A1 shows the impedance conversion from Γ2 to Γ4. In addition, arrow A2 shows the impedance conversion from Γ4 to Γ5. Figure 5 As shown, Γ2, Γ4, and Γ5 change according to the frequency.

[0063] Figure 6 Γ2', Γ4' and Γ5' are depicted in the Smith chart. In the figure, arrow A1' shows the impedance conversion from Γ2' to Γ4'. In addition, arrow A2' shows the impedance conversion from Γ4' to Γ5'. Figure 6 As shown, Γ2', Γ4', and Γ5' vary according to the frequency.

[0064] Hereinafter, a frequency domain f_high higher than the center frequency f_center in the use frequency band, that is, a frequency domain f_high higher than the reference frequency f_ref, is referred to as a “high frequency domain”. Also, a frequency domain f_low lower than the center frequency f_center in the use frequency band, that is, a frequency domain f_low lower than the reference frequency f_ref, is referred to as a “low frequency domain”.

[0065] When the requested output power with respect to the Doherty amplifier 100 is greater than or equal to a predetermined value, the main amplifier 8 is set to the on state, and the auxiliary amplifier 9 is set to the on state. On the other hand, when the requested output power with respect to the Doherty amplifier 100 is less than the predetermined value, the main amplifier 8 is set to the on state, and the auxiliary amplifier 9 is set to the off state. This is also true for the Doherty amplifier 100'.

[0066] When the auxiliary amplifier 9 is set to the off state, the impedance of the auxiliary amplifier 9 side viewed from the output portion of the auxiliary amplifier 9 becomes infinite ("Open" in the figure). Therefore, when the auxiliary amplifier 9 is set to the off state, the second output circuit 13 functions as an open stub. Here, since the electrical length of the second output circuit 13 is less than 90 degrees, when the auxiliary amplifier 9 is set to the off state, the second output circuit 13 functions as a capacitive load.

[0067] Γ1 in the Doherty amplifier 100 has the same impedance as 0.5×Ropt. In addition, Γ1′ in the Doherty amplifier 100′ also has the same impedance as 0.5×Ropt. This is because the output matching circuit 19 is provided.

[0068] In contrast, Γ2 in the Doherty amplifier 100 is a capacitive impedance (see Figure 5 ). In addition, Γ2' in the Doherty amplifier 100' is also a capacitive impedance (refer to Figure 6 ). This is because the second output circuit 13 functions as a capacitive load.

[0069] In the Doherty amplifier 100, since the second transmission line 12 is provided, Γ2 is converted into Γ3. Furthermore, since the frequency characteristic compensation circuit 15 is provided, Γ3 is converted into Γ4. That is, since the second transmission line 12 and the frequency characteristic compensation circuit 15 are provided, Γ2 is converted into Γ4 (refer to Figure 5 ).

[0070] Γ3 is an impedance smaller than 0.5×Ropt at the center frequency f_center and is an inductive impedance in the high frequency domain f_high and a capacitive impedance in the low frequency domain f_low. In contrast, Γ4 is a capacitive impedance in the high frequency domain f_high and an inductive impedance in the low frequency domain f_low (see Figure 5 ). This is due to the frequency characteristics in the frequency characteristics compensation circuit 15. The frequency characteristics in the frequency characteristics compensation circuit 15 will be described later.

[0071] On the other hand, in the Doherty amplifier 100', since the second transmission line 12 is provided, Γ2' is converted into Γ4' (see Figure 6 Γ4' is an inductive impedance in the high frequency domain f_high and a capacitive impedance in the low frequency domain f_low (refer to Figure 6 ).

[0072] That is, the second transmission line 12 in the Doherty amplifier 100 plays a function of making Γ4 closer to the real axis Re than Γ2 by making Γ3 closer to the real axis Re than Γ2. In other words, the second transmission line 12 in the Doherty amplifier 100 plays a function of returning the impedance (Γ1→Γ2) away from the real axis Re to the vicinity of the real axis Re through the second output circuit 13 (Γ2→Γ3).

[0073] Furthermore, the second transmission line 12 in the Doherty amplifier 100' plays a role in bringing Γ4' closer to the real axis Re than Γ2'. In other words, the second transmission line 12 in the Doherty amplifier 100' plays a role in returning the impedance (Γ1'→Γ2') away from the real axis Re to the vicinity of the real axis Re (Γ2'→Γ4') through the second output circuit 13.

[0074] In the Doherty amplifier 100, since the first transmission line 11 is provided, Γ4 is converted into Γ5 (see Figure 5 ). In addition, in the Doherty amplifier 100', since the first transmission line 11 is provided, Γ4' is converted into Γ5' (refer to Figure 6 ).

[0075] Γ5 is an impedance greater than 2×Ropt (refer to Figure 5 ). Therefore, by using the Doherty amplifier 100, a back-off greater than 6 dB can be achieved. In addition, Γ5' is an impedance greater than 2×Ropt (refer to Figure 6 ). Therefore, by using the Doherty amplifier 100 ′, a back-off amount greater than 6 dB can be achieved.

[0076] Here, if Figure 5 and Figure 6 As shown, the variation of Γ5′ with respect to frequency is larger than the variation of Γ5 with respect to frequency. Therefore, the operating frequency band of the Doherty amplifier 100′ is narrower than the operating frequency band of the Doherty amplifier 100.

[0077] In other words, the variation of Γ5 with respect to frequency is smaller than the variation of Γ5' with respect to frequency. Therefore, the operating frequency band of the Doherty amplifier 100 is wider than the operating frequency band of the Doherty amplifier 100'. This is because the frequency characteristic compensation circuit 15 is provided to compensate the frequency characteristics in the output circuits 10 and 13.

[0078] That is, regarding the frequency characteristics in the first transmission line 11, the impedance is inductive in the high frequency domain f_high, and the impedance is capacitive in the low frequency domain f_low. In addition, regarding the frequency characteristics in the circuit (hereinafter referred to as "synthesized circuit") composed of the second transmission line 12 and the third transmission line 14, the impedance is inductive in the high frequency domain f_high, and the impedance is capacitive in the low frequency domain f_low.

[0079] Therefore, in the high frequency domain f_high, when the output terminal 20 side is viewed from the output portion of the main amplifier 8, the inductive impedance of the first transmission line 11 and the inductive impedance of the synthesizing circuit are in a mutually reinforcing relationship. On the other hand, in the low frequency domain f_low, when the output terminal 20 side is viewed from the output portion of the main amplifier 8, the capacitive impedance of the first transmission line 11 and the capacitive impedance of the synthesizing circuit are in a mutually reinforcing relationship. Therefore, Γ5' in the Doherty amplifier 100' varies greatly depending on the frequency.

[0080] In contrast, regarding the frequency characteristics in the frequency characteristics compensation circuit 15 , the impedance is capacitive in the high frequency range f_high, is infinite in the center frequency f_center, and is inductive in the low frequency range f_low.

[0081] Therefore, in the high frequency range f_high, when the output terminal 20 side is viewed from the output section of the main amplifier 8, the capacitive impedance of the frequency characteristic compensation circuit 15 functions to cancel the inductive impedance of the output circuits 10 and 13. On the other hand, in the low frequency range f_low, when the output terminal 20 side is viewed from the output section of the main amplifier 8, the inductive impedance of the frequency characteristic compensation circuit 15 functions to cancel the capacitive impedance of the output circuits 10 and 13. Therefore, the change of Γ5 with respect to the frequency is smaller than the change of Γ5' with respect to the frequency.

[0082] Thus, the Doherty amplifier 100 can increase the back-off amount similarly to the Doherty amplifier 100' by providing the output circuits 10 and 13. In addition, the Doherty amplifier 100 can increase the operating frequency band compared to the Doherty amplifier 100' by providing the frequency characteristic compensation circuit 15.

[0083] Figure 7 1 is a characteristic diagram showing the reflection amount of the output power of the main amplifier 8 with respect to the frequency. In the figure, the characteristic line I represents the reflection amount when the auxiliary amplifier 9 in the Doherty amplifier 100 is set to the disconnected state. On the other hand, the characteristic line II represents the reflection amount when the auxiliary amplifier 9 in the Doherty amplifier 100' is set to the disconnected state.

[0084] like Figure 7 As shown, by using the Doherty amplifier 100, the amount of reflection can be reduced in a wider frequency range than when using the Doherty amplifier 100'. Therefore, by using the Doherty amplifier 100, the operating frequency band can be expanded compared to when using the Doherty amplifier 100'.

[0085] Next, refer to Figure 8 The impedance of the Doherty amplifier 100 when the auxiliary amplifier 9 is set to the on state will be described. More specifically, the impedance in the saturation operation state will be described.

[0086] In the figure, Γ5 represents the impedance of the output terminal 20 side viewed from the output section of the main amplifier 8. Also, Γ6 represents the impedance of the output terminal 20 side viewed from the output section of the auxiliary amplifier 9.

[0087] When the auxiliary amplifier 9 is set to the on state, Γ5 is the same impedance as Ropt. Here, as described above, Ropt1=Ropt. Therefore, Γ5 is in a state of matching with the optimal load impedance Ropt1 of the main amplifier 8.

[0088] In this case, Γ6 is the same impedance as Ropt. Here, as described above, Ropt2=Ropt. Therefore, Γ6 is in a state of matching with the optimal load impedance Ropt2 of the auxiliary amplifier 9.

[0089] Next, a modification of the Doherty amplifier 100 will be described.

[0090] The phase correction circuit 5 is not limited to the transmission line 6. For example, the phase correction circuit 5 is composed of a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC type matching circuit, or a circuit using one or more λ / 4 lines.

[0091] The first output circuit 10 is not limited to the first transmission line 11 and the second transmission line 12. For example, the first output circuit 10 may be composed of one transmission line (not shown) having an electrical length of 90 degrees or more.

[0092] The second output circuit 13 is not limited to the third transmission line 14. For example, the second output circuit 13 may be composed of a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC matching circuit, or a circuit using one or more λ / 4 lines.

[0093] The frequency characteristic compensation circuit 15 is not limited to the open short stub 16. For example, the frequency characteristic compensation circuit 15 may be composed of a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC type matching circuit, or a transmission line having an electrical length of 90 degrees or approximately 90 degrees. That is, the frequency characteristic compensation circuit 15 may also be composed of a short stub.

[0094] As described above, the Doherty amplifier 100 includes: amplifiers 8 and 9, which include a main amplifier 8 and an auxiliary amplifier 9; output circuits 10 and 13 for back-off amplification, which include a first output circuit 10 provided between the main amplifier 8 and the output combining section 18 of the amplifiers 8 and 9 and having a first electrical length θ1, and a second output circuit 13 provided between the auxiliary amplifier 9 and the output combining section 18 and having a second electrical length θ2; and a frequency characteristic compensation circuit 15 for broadbanding, which is provided electrically in parallel with the first output circuit 10 and compensates for the frequency characteristic of the impedance in the output circuits 10 and 13. Thus, it is possible to simultaneously achieve an increase in the back-off amount and broadbanding.

[0095] Furthermore, when the auxiliary amplifier 9 is set to the off state, the second output circuit 13 functions as an open stub, whereby the second output circuit 13 functions as a capacitive load. This makes it possible to increase the back-off amount.

[0096] Furthermore, in the high frequency range f_high relative to the reference frequency f_ref, the capacitive impedance of the frequency characteristic compensation circuit 15 cancels the inductive impedance of the output circuits 10 and 13, and in the low frequency range f_low relative to the reference frequency f_ref, the inductive impedance of the frequency characteristic compensation circuit 15 cancels the capacitive impedance of the output circuits 10 and 13. Thus, a wide bandwidth can be achieved.

[0097] In addition, the first electrical length θ1 is set to be based on the mathematical expression using the value γ corresponding to the requested back-off amount OBO. The second electrical length θ2 is set to be based on the mathematical formula using the value γ corresponding to the requested back-off amount OBO. That is, the first electrical length θ1 is set to a value based on the above equation (1), and the second electrical length θ2 is set to a value based on the above equation (2). Thus, it is possible to increase the amount of retreat.

[0098] In addition, the first output circuit 10 is composed of the first transmission line 11 and the second transmission line 12, and the second output circuit 13 is composed of the third transmission line 14. The second transmission line 12 and the third transmission line 14 constitute a composite circuit, and the electrical length of the first transmission line 11 is set to 90 degrees, and the electrical length of the composite circuit is set to 90 degrees, thereby setting the electrical length of the output circuits 10 and 13 to 180 degrees. As a result, the back-off amount can be expanded. In addition, the frequency characteristic compensation circuit 15 can be electrically provided in parallel with the first output circuit 10.

[0099] Furthermore, the frequency characteristic compensation circuit 15 is composed of an open stub having an electrical length of 180 degrees. Thus, the frequency characteristic compensation circuit 15 can be realized.

[0100] In addition, the term "90 degrees" in the claims of the present application naturally includes a full 90 degrees and also includes approximately 90 degrees. In addition, the term "180 degrees" in the claims of the present application naturally includes a full 180 degrees and also includes approximately 180 degrees.

[0101] Implementation Method 2

[0102] Fig. 9 2 is a circuit diagram showing the main parts of the Doherty amplifier according to the second embodiment. Fig. 9 , the Doherty amplifier of embodiment 2 is described. Fig. 9 In, with Figure 1 The same components and the like are denoted by the same reference numerals and the description thereof will be omitted.

[0103] like Fig. 9 As shown, the Doherty amplifier 100a includes a main amplifier 8a and an auxiliary amplifier 9a. The main parts of the Doherty amplifier 100a are composed of an input terminal 1, an input matching circuit 2, a distributor 3, a first input matching circuit 4, a phase correction circuit 5, a second input matching circuit 7, a main amplifier 8a, an auxiliary amplifier 9a, a first output circuit 10, a second output circuit 13, a frequency characteristic compensation circuit 15, an output matching circuit 19 and an output terminal 20.

[0104] In the amplifiers 8 and 9 of the Doherty amplifier 100, the electrical characteristics of the outputs with respect to the bias amount (e.g., output resistance and output amplitude) are the same. Therefore, assuming that the bias amounts of the amplifiers 8 and 9 are set to the same value, the electrical characteristics of the output of the main amplifier 8 are the same as the electrical characteristics of the output of the auxiliary amplifier 9. In this case, the saturated output power of the main amplifier 8 is the same as the saturated output power of the auxiliary amplifier 9.

[0105] In contrast, in the amplifiers 8a and 9a of the Doherty amplifier 100a, the electrical characteristics of the outputs with respect to the bias amount are different from each other. Therefore, assuming that the bias amounts of the amplifiers 8a and 9a are set to the same value, the electrical characteristics of the output of the main amplifier 8a are different from the electrical characteristics of the output of the auxiliary amplifier 9a. In addition, in this case, the saturated output power of the main amplifier 8a is different from the saturated output power of the auxiliary amplifier 9a.

[0106] In addition, in the Doherty amplifier 100, the optimal load impedance Ropt1 of the main amplifier 8 in the saturated operation state is the same as the optimal load impedance Ropt2 of the auxiliary amplifier 9 in the saturated operation state. For example, Ropt1=Ropt, and Ropt2=Ropt. In contrast, in the Doherty amplifier 100a, the optimal load impedance Ropt1 of the main amplifier 8a in the saturated operation state is different from the optimal load impedance Ropt2 of the auxiliary amplifier 9a in the saturated operation state. For example, with respect to Ropt1=Ropt, Ropt2=Ropt'.

[0107] In the Doherty amplifier 100a, the characteristic impedance of the first output circuit 10 is set to the same value as the optimal load impedance Ropt1 of the main amplifier 8a in the saturated operation state. That is, the characteristic impedance is set to the same value as Ropt. In addition, in the Doherty amplifier 100a, the characteristic impedance of the second output circuit 13 is set to the same value as the optimal load impedance Ropt2 of the auxiliary amplifier 9a in the saturated operation state. That is, the characteristic impedance is set to the same value as Ropt'.

[0108] In the Doherty amplifier 100 a , the output matching circuit 19 achieves impedance matching between the output combining unit 18 and the output terminal 20 so that the impedance R on the output terminal 20 side becomes a value represented by the following equation (4).

[0109] R=(Ropt×Ropt') / (Ropt+Ropt') (4)

[0110] As described above, in the Doherty amplifier 100a, the saturated output power of the main amplifier 8a is different from the saturated output power of the auxiliary amplifier 9a. Even in this case, the same operation as that of the Doherty amplifier 100 can simultaneously achieve an increase in the back-off amount and a wide bandwidth.

[0111] Implementation 3

[0112] Fig.10 2 is a circuit diagram showing the main parts of the Doherty amplifier according to Embodiment 3. Fig.10 , the Doherty amplifier of embodiment 3 is described. Fig.10 In, with Figure 1 The same components and the like are denoted by the same reference numerals and the description thereof will be omitted.

[0113] like Fig.10 As shown in FIG. 1 , an output matching circuit (hereinafter referred to as “first output matching circuit”) 31 is provided between the main amplifier 8 and the first output circuit 10. The first output matching circuit 31 is composed of, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC type matching circuit, or a circuit using one or more λ / 4 lines. When viewed from the output portion of the main amplifier 8, the electrical length of the first output matching circuit 31 is set to a value that is an integer multiple of 180 degrees or a value that is an integer multiple of approximately 180 degrees.

[0114] In addition, an output matching circuit (hereinafter referred to as "second output matching circuit") 32 is provided between the auxiliary amplifier 9 and the second output circuit 13. The second output matching circuit 32 is composed of, for example, a lumped constant circuit, a distributed constant circuit, a composite circuit based on lumped constants and distributed constants, an LC type matching circuit, or a circuit using one or more λ / 4 lines. When viewed from the output portion of the auxiliary amplifier 9, the electrical length of the second output matching circuit 32 is set to a value that is an integer multiple of 180 degrees or a value that is an integer multiple of approximately 180 degrees.

[0115] The main parts of the Doherty amplifier 100b are composed of an input terminal 1, an input matching circuit 2, a distributor 3, a first input matching circuit 4, a phase correction circuit 5, a second input matching circuit 7, a main amplifier 8, an auxiliary amplifier 9, a first output circuit 10, a second output circuit 13, a frequency characteristic compensation circuit 15, an output matching circuit 19, an output terminal 20, a first output matching circuit 31 and a second output matching circuit 32.

[0116] Since the first output matching circuit 31 is provided, the optimal load impedance Ropt1 of the main amplifier 8 in the saturated operation state is converted into the optimal load impedance Ropt1' of the amplifier (hereinafter referred to as "the first amplifier") 33 composed of the main amplifier 8 and the first output matching circuit 31. That is, the optimal load impedance Ropt1' is a value different from the optimal load impedance Ropt1. For example, with respect to Ropt1=Ropt, Ropt1'=Ropt".

[0117] Since the second output matching circuit 32 is provided, the optimal load impedance Ropt2 of the auxiliary amplifier 9 in the saturated operation state is converted into the optimal load impedance Ropt2' of the amplifier (hereinafter referred to as "the second amplifier") 34 composed of the auxiliary amplifier 9 and the second output matching circuit 32. That is, the optimal load impedance Ropt2' is a value different from the optimal load impedance Ropt2. For example, with respect to Ropt2=Ropt, Ropt2'=Ropt".

[0118] Therefore, the Doherty amplifier 100b can be regarded as being provided with a first amplifier 33 having an optimal load impedance Ropt1' relative to the Doherty amplifier 100, replacing the main amplifier 8 having the optimal load impedance Ropt1. In addition, the Doherty amplifier 100b can be regarded as being provided with a second amplifier 34 having an optimal load impedance Ropt2' relative to the Doherty amplifier 100, replacing the auxiliary amplifier 9 having the optimal load impedance Ropt2.

[0119] Therefore, the operation of the Doherty amplifier 100b can be regarded as the same as the operation of the Doherty amplifier 100. By using the Doherty amplifier 100b, as in the case of using the Doherty amplifier 100, it is possible to simultaneously achieve an increase in the back-off amount and a wide bandwidth.

[0120] In addition, the Doherty amplifier 100 b may also include amplifiers 8 a , 9 a instead of the amplifiers 8 , 9 .

[0121] Furthermore, the Doherty amplifier 100 b may include only one of the first output matching circuit 31 and the second output matching circuit 32 .

[0122] As described above, the Doherty amplifier 100b includes: the first output matching circuit 31, which is provided between the main amplifier 8 and the first output circuit 10 and has an electrical length that is an integral multiple of 180 degrees; and the second output matching circuit 32, which is provided between the auxiliary amplifier 9 and the second output circuit 13 and has an electrical length that is an integral multiple of 180 degrees. Even in such a case, by the same operation as that of the Doherty amplifier 100, it is possible to simultaneously achieve an increase in the back-off amount and a wide bandwidth.

[0123] As described above, the term "180 degrees" described in the claims of the present application naturally includes a perfect 180 degrees and also includes approximately 180 degrees.

[0124] Implementation 4

[0125] Fig.11 2 is a circuit diagram showing the main parts of the Doherty amplifier according to Embodiment 4. Fig.11 , the Doherty amplifier of embodiment 4 is described. Fig.11 In, with Figure 1 The same components and the like are denoted by the same reference numerals and the description thereof will be omitted.

[0126] like Fig.11 As shown, a circuit (hereinafter referred to as "first circuit") 41 is provided between the first output circuit 10 and the output combining unit 18. The electrical length of the first circuit 41 is set to a value that is an integer multiple of 180 degrees or a value that is an integer multiple of approximately 180 degrees. The first circuit 41 is composed of, for example, a transmission line 42.

[0127] In addition, a circuit (hereinafter referred to as "second circuit") 43 is provided between the second output circuit 13 and the output combining unit 18. The electrical length of the second circuit 43 is set to a value corresponding to an integral multiple of 180 degrees or a value corresponding to an integral multiple of approximately 180 degrees. The second circuit 43 is composed of, for example, a transmission line 44.

[0128] The main parts of the Doherty amplifier 100c are composed of an input terminal 1, an input matching circuit 2, a distributor 3, a first input matching circuit 4, a phase correction circuit 5, a second input matching circuit 7, a main amplifier 8, an auxiliary amplifier 9, a first output circuit 10, a second output circuit 13, a frequency characteristic compensation circuit 15, an output matching circuit 19, an output terminal 20, a first circuit 41 and a second circuit 43.

[0129] The operation of the Doherty amplifier 100c is the same as that of the Doherty amplifier 100. By using the Doherty amplifier 100c, as in the case of using the Doherty amplifier 100, it is possible to simultaneously achieve an increase in the back-off amount and a wide bandwidth.

[0130] In addition, the Doherty amplifier 100 c may also include amplifiers 8 a and 9 a instead of the amplifiers 8 and 9 .

[0131] Furthermore, the Doherty amplifier 100 c may include at least one of the first output matching circuit 31 and the second output matching circuit 32 .

[0132] Furthermore, the Doherty amplifier 100 c may include only one of the first circuit 41 and the second circuit 43 .

[0133] As described above, the Doherty amplifier 100c includes: the first circuit 41, which is provided between the first output circuit 10 and the output combining section 18 and has an electrical length that is an integral multiple of 180 degrees; and the second circuit 43, which is provided between the second output circuit 13 and the output combining section 18 and has an electrical length that is an integral multiple of 180 degrees. Even in such a case, by the same operation as that of the Doherty amplifier 100, it is possible to simultaneously achieve an increase in the back-off amount and a wide bandwidth.

[0134] As described above, the term "180 degrees" described in the claims of the present application naturally includes a perfect 180 degrees and also includes approximately 180 degrees.

[0135] Implementation method 5

[0136] Fig.12 1 is a circuit diagram showing the main parts of the Doherty amplifier according to Embodiment 5. Fig.12 , the Doherty amplifier of embodiment 5 is described. Fig.12 In, with Figure 1 The same components and the like are denoted by the same reference numerals and the description thereof will be omitted.

[0137] like Fig.12 As shown, the Doherty amplifier 100d has an input terminal (hereinafter sometimes referred to as "first input terminal") 51 for the main amplifier 8. That is, the first input matching circuit 4 is provided between the first input terminal 51 and the main amplifier 8. The first input terminal 51 receives a signal input to the first path P1.

[0138] The Doherty amplifier 100d also has an input terminal (hereinafter sometimes referred to as "second input terminal") 52 for the auxiliary amplifier 9. That is, the second input matching circuit 7 is provided between the second input terminal 52 and the auxiliary amplifier 9. The second input terminal 52 receives a signal input to the second path P2.

[0139] The first input terminal 51 and the second input terminal 52 are electrically connected to a signal source 53. The signal source 53 is constituted by, for example, an inverter, a DAC (Digital-to-Analog Converter) or a DDS (Direct Digital Synthesizer).

[0140] The main parts of the Doherty amplifier 100d are composed of the first input matching circuit 4, the second input matching circuit 7, the main amplifier 8, the auxiliary amplifier 9, the first output circuit 10, the second output circuit 13, the frequency characteristic compensation circuit 15, the output matching circuit 19, the output terminal 20, the first input terminal 51 and the second input terminal 52.

[0141] In the Doherty amplifier 100d, the gate bias voltages of the main amplifier 8 and the auxiliary amplifier 9 are set to values ​​close to the threshold voltage for the gate bias voltage. Thus, the main amplifier 8 is switched on / off according to the presence or absence of a signal input to the first input terminal 51. In addition, the auxiliary amplifier 9 is switched on / off according to the presence or absence of a signal input to the second input terminal 52.

[0142] Therefore, when the requested output power is equal to or greater than the specified value, the signal source 53 inputs a signal to each of the first input terminal 51 and the second input terminal 52. As a result, the main amplifier 8 is set to the on state, and the auxiliary amplifier 9 is set to the on state. On the other hand, when the requested output power is less than the specified value, the signal source 53 inputs a signal only to the first input terminal 51. As a result, the main amplifier 8 is set to the on state, and the auxiliary amplifier 9 is set to the off state.

[0143] That is, the Doherty amplifier 100d can achieve both the expansion of the back-off amount and the widening of the bandwidth by the same operation as the Doherty amplifier 100. In addition, each amplifier 8, 9 uses a dedicated input terminal 51, 52, thereby being able to appropriately control the on / off of each amplifier 8, 9. As a result, the efficiency of the Doherty amplifier 100d can be further improved. In addition, the gain of the Doherty amplifier 100d can be further improved.

[0144] In addition, the Doherty amplifier 100 d may include a phase correction circuit 5 . In this case, the phase correction circuit 5 may be provided between the second input terminal 52 and the second input matching circuit 7 .

[0145] Furthermore, the Doherty amplifier 100 d may also include amplifiers 8 a , 9 a instead of the amplifiers 8 , 9 .

[0146] Furthermore, the Doherty amplifier 100 d may include at least one of the first output matching circuit 31 and the second output matching circuit 32 .

[0147] Furthermore, the Doherty amplifier 100 d may include at least one of the first circuit 41 and the second circuit 43 .

[0148] As described above, the Doherty amplifier 100d includes the first input terminal 51 for the main amplifier 8 and the second input terminal 52 for the auxiliary amplifier 9, and the first input terminal 51 and the second input terminal 52 are electrically connected to the signal source 53, respectively. Thus, the on / off of each amplifier 8, 9 can be appropriately controlled. As a result, the efficiency of the Doherty amplifier 100d can be further improved. In addition, the gain of the Doherty amplifier 100d can be further improved.

[0149] Furthermore, the present application can realize free combination of the embodiments, modification of arbitrary components of the embodiments, or omission of arbitrary components of the embodiments within the scope of the invention.

[0150] Industrial Applicability

[0151] The Doherty amplifier of the present invention can be used in, for example, a communication device.

[0152] Description of symbols

[0153] 1: Input terminal; 2: Input matching circuit; 3: Distributor; 4: First input matching circuit; 5: Phase correction circuit; 6: Transmission line; 7: Second input matching circuit; 8, 8a: Main amplifier; 9, 9a: Auxiliary amplifier; 10: First output circuit; 11: First transmission line; 12: Second transmission line; 13: Second output circuit; 14: Third transmission line; 15: Frequency characteristic compensation circuit; 16: Open stub; 17: Connector; 18: Output synthesis section; 19: output matching circuit; 20: output terminal; 21: load; 31: first output matching circuit; 32: second output matching circuit; 33: first amplifier; 34: second amplifier; 41: first circuit; 42: transmission line; 43: second circuit; 44: transmission line; 51: first input terminal; 52: second input terminal; 53: signal source; 100, 100a, 100b, 100c, 100d: Doherty amplifiers.

Claims

1. A Doherty amplifier, comprising: an amplifier, comprising a main amplifier and an auxiliary amplifier; an output circuit for back-off amount amplification, comprising a first output circuit provided between the main amplifier and the output combining section of the amplifier and having a first electrical length, and a second output circuit provided between the auxiliary amplifier and the output combining section and having a second electrical length; a frequency characteristic compensation circuit for broadbanding, which is electrically connected in parallel with the first output circuit and compensates for the frequency characteristic of the impedance in the output circuit; a first output matching circuit provided between the main amplifier and the first output circuit and having an electrical length corresponding to an integral multiple of 180 degrees; as well as a second output matching circuit provided between the auxiliary amplifier and the second output circuit and having an electrical length corresponding to an integral multiple of 180 degrees, The first output circuit is composed of a first transmission line and a second transmission line. The second output circuit is composed of a third transmission line. The second transmission line and the third transmission line constitute a synthesis circuit, The electrical length of the first transmission line is set to 90 degrees, and the electrical length of the combining circuit is set to 90 degrees, whereby the electrical length of the output circuit is set to 180 degrees.

2. The Doherty amplifier according to claim 1, characterized in that: When the auxiliary amplifier is set to the off state, the second output circuit functions as an open stub, whereby the second output circuit functions as a capacitive load.

3. The Doherty amplifier according to claim 1, characterized in that: In a high frequency domain relative to a reference frequency, the capacitive impedance of the frequency characteristic compensation circuit cancels out the inductive impedance of the output circuit, and in a low frequency domain relative to the reference frequency, the inductive impedance of the frequency characteristic compensation circuit cancels out the capacitive impedance of the output circuit.

4. The Doherty amplifier according to claim 1, characterized in that: The first electrical length θ1 is set to a value based on the mathematical formula θ1=arctan(-√((γ(γ-1)) / (γ-4))) using a value γ corresponding to the requested back-off amount. The second electrical length θ2 is set to a value based on a mathematical formula θ2=arctan(√((γ-4)(γ-1)) / γ)) using a value γ corresponding to the requested back-off amount.

5. The Doherty amplifier according to claim 1, characterized in that: The frequency characteristic compensation circuit is composed of an open stub having an electrical length of 180 degrees.

6. The Doherty amplifier according to claim 1, characterized in that: The saturated output power of the main amplifier is different from the saturated output power of the auxiliary amplifier.

7. The Doherty amplifier according to claim 1, characterized in that: The Doherty amplifier has: a first circuit provided between the first output circuit and the output combining section and having an electrical length corresponding to an integral multiple of 180 degrees; as well as The second circuit is provided between the second output circuit and the output combining section and has an electrical length corresponding to an integral multiple of 180 degrees.

8. The Doherty amplifier according to claim 1, characterized in that: The Doherty amplifier has a first input terminal for the main amplifier and a second input terminal for the auxiliary amplifier. The first input terminal and the second input terminal are electrically connected to a signal source, respectively.

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