JP2016111590A - Doherty amplifier circuit with impedance adjustment circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a doherty amplifier circuit with an impedance adjustment circuit capable of adjusting composition-side impedance without exchanging a transmission line itself or switching a signal route with an RF switch or the like.SOLUTION: The doherty amplifier circuit comprises: a power distributor; a main amplifier and a peak amplifier to which signals distributed by the power distributor are inputted; and an impedance conversion line to which output of the main amplifier and the peak amplifier are inputted. The doherty amplifier circuit also comprises: a first circulator and a first reactance variable element which are connected to the output of the peak amplifier; and a second circulator and a second reactance variable element which are connected to the output of the main amplifier, and the second reactance variable element is adjusted in such a manner that a circuit including the second circulator and the second reactance variable element is open in a view from the output side of the peak amplifier.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a Doherty amplifier circuit, and more particularly to a Doherty amplifier circuit including an impedance adjustment circuit.

  The Doherty amplifier circuit prepares a main amplifier and a peak amplifier, operates only the main amplifier at a low output, and simultaneously operates both the main amplifier and the peak amplifier at a high output. In general, in a Doherty amplifier circuit, an input signal is distributed to a main amplifier and a peak amplifier by a power distributor, and outputs of these two amplifiers are combined (hereinafter referred to as Doherty combining or power combining) and input to an impedance converter. Adjust the output impedance and then output to the load.

  Normally, the impedance of the transmission line after the main amplifier output is different from the impedance of the transmission line after the peak amplifier output. Therefore, for power synthesis, the impedance on the distributor side or the rear stage side (combining side) when viewed from the amplifier It was necessary to make adjustments. When adjusting on the combining side, the impedance of the transmission line between the amplifier and the power combining point was adjusted. Specifically, the adjustment is performed by exchanging the transmission line itself or switching the signal route by an RF (Radio Frequency) switch or the like. The exchange of the transmission line and the switching of the signal route by the RF switch or the like involve complicated work.

  Patent Document 1 discloses a multiband high-efficiency Doherty amplifier circuit. In this configuration, an impedance inverter 120 composed of a circulator 122 and a tuner 121 (capacitor) is connected to the output of the main amplifier 110. The impedance inverter 120 is connected to the controller 123 and modulates the load impedance of the main amplifier 110 by adjusting the capacitance of the capacitor. The impedance inverter 120 performs an impedance inversion to modulate the load impedance.

Special table 2013-527711 gazette

  In Patent Document 1, the output of the peak amplifier 115 is directly connected to the branch point 116 for Doherty synthesis. If the influence of the impedance of the transmission line existing between the peak amplifier 115 and the branch point 116 can be ignored, when the peak amplifier 115 is off, the peak amplifier 115 is cut off from the branch point 116 and cannot be seen.

  However, in reality, the influence of this transmission line cannot be ignored, and a matching circuit is also inserted between the branch point 116 and the peak amplifier 115. Therefore, even if the peak amplifier 115 is turned off, the transmission line and the matching circuit appear to be open stubs. In Patent Document 1, this point is not taken into consideration, and when viewed from the branch point 116, even if the peak amplifier 115 is Off, it does not appear to be OPEN, and it appears that an open stub is connected.

  Therefore, even if the impedance inverter of Patent Document 1 is used, it is necessary to adjust the impedance, and it is necessary to perform adjustment by exchanging the transmission line itself or switching the signal route using an RF switch or the like.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to provide a Doherty amplifier circuit including an impedance adjustment circuit that can adjust the impedance on the synthesis side without exchanging the transmission line itself or switching a signal route by an RF switch or the like. Is to provide.

The present invention is a Doherty amplifier circuit including an electric power distributor, a main amplifier and a peak amplifier to which a signal distributed by the power distributor is input, and an impedance adjustment circuit to which outputs of the main amplifier and the peak amplifier are input. There,
A first circulator and a first reactance variable element connected to the output of the peak amplifier, and a second circulator and a second reactance variable element connected to the output of the main amplifier,
The second reactance variable element is adjusted so that the circuit including the second circulator and the second reactance variable element is open when viewed from the output side of the peak amplifier. It is a Doherty amplifier circuit including an adjustment circuit.

  According to the present invention, it is possible to provide a Doherty amplifier circuit that can adjust the impedance on the synthesis side without replacing the transmission line itself or switching the signal route by an RF switch or the like.

It is a figure which shows the Doherty amplifier circuit of the 1st Embodiment of this invention. FIG. 2 is a circuit diagram in which an impedance converter is temporarily changed to a 25Ω termination for the analysis of the Doherty circuit of FIG. 1. 3 is a diagram showing a locus on a Smith chart of load impedance (L2 = 90 °) when the electrical length of the transmission line L1 is changed when viewed from the main amplifier in FIG. 2 at 666 MHz. FIG. It is a figure which shows the Doherty amplifier circuit of other embodiment of this invention. FIG. 6 is a diagram showing a locus on a Smith chart of load impedance (L2 = 90 °, L3 = 180 °) when L1 is changed as viewed from the main amplifier in FIG. 4 at 666 MHz. It is a circuit diagram showing an example in which transmission lines L1 and L2 are replaced with open stubs. FIG. 6 is a circuit diagram showing an example in which transmission lines L1 and L2 are replaced with variable capacitors. FIG. 5 is a circuit diagram showing an example in which transmission lines L1 and L2 are replaced with variable inductors. FIG. 3 is a circuit diagram showing an example in which transmission lines L1 and L2 are replaced with a circuit in which a variable capacitor and a variable inductor are connected in parallel.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.
[Description of configuration]
FIG. 1 is a circuit diagram of a Doherty amplifier circuit 10 according to the first embodiment. A two-distributor 11, a main amplifier 12, a peak amplifier 13, a first circulator 14, and a transmission line L1 for adjusting impedance (here, electrical length). , A second circulator 15, an electric length adjusting transmission line L 2, an impedance conversion line 16 for converting impedance from 25Ω to 50Ω, and an antenna 17.

  In the circuit configuration of FIG. 1, the input signal is distributed to the Doherty amplifier circuit 10 in the same phase by the two distributors 11 and connected to the input to the main amplifier 12 and the input to the peak amplifier 13. These two routes are connected with the same length. Subsequently, the output of the main amplifier 12 is connected to the port 141 of the first circulator 14. The signal input to the port 141 is output to the port 142 of the first circulator, and the output is connected to the branch point 20 (hereinafter also referred to as the synthesis point).

  On the other hand, the output of the peak amplifier 13 is connected to the port 151 of the second circulator 15. The signal input to the port 151 is connected to the synthesis point. The outputs of the main amplifier 12 and the peak amplifier 3 are synthesized at the synthesis point.

  Further, the port 143 of the first circulator is connected to a transmission line L1 for adjusting the Doherty synthesis circuit, and the end of the transmission line L1 is grounded to GND to form a short stub circuit. Similarly, the port 153 of the second circulator is connected to a transmission line L2 for adjusting the Doherty synthesis circuit, and the end of the transmission line L2 is grounded to GND to form a short stub circuit.

The Doherty synthesis circuit here includes two transmission lines that connect between the main and peak amplifiers 12 and 13 and the impedance conversion line 16, and first and second circulators 14 and 15 inserted in the transmission line. The transmission lines L1 and L2, the synthesis point, and the impedance conversion line 16 are indicated.
[Description of operation]
Hereinafter, the operation of the Doherty amplifier circuit of this embodiment will be described by dividing the peak amplifier 13 into an operation OFF state and an ON state.
The peak amplifier 13 is in an operation OFF state due to the low power signal input amplification. At this time, the peak amplifier 13 alone is totally reflected by the OPEN circuit when viewed from the output side, but the Doherty synthesis circuit that is the output load from the main amplifier 12 The circuit including the synthesis point to the OPEN end of the output of the peak amplifier 13 is open and disconnected in the frequency band to be used, in other words, the operation of the Doherty amplifier circuit is not affected. .

  In order to achieve the disconnected state, specifically, the impedance of the transmission line L2 is adjusted by a return path described below. Specifically, the length of the transmission line L2 is adjustable, and the length is selected so as to operate an open stub circuit in which the electrical length is an integer multiple of λ / 2. The return path is the combination point → port 152 of the second circulator 15 → port 153 → transmission line L2 → total reflection at the GND ground point (turnback) → pass the transmission line L2 again → port 153 → port 151 → operation OFF The total reflection at the peak amplifier 15 → the port 151 → the port 152 → the path returning to the synthesis point. As a result, when the output side is viewed from the main amplifier 12, the circuit on the peak amplifier 13 side from the synthesis point 20 is open and disconnected (not affected) in the frequency band to be used.

  In order to achieve the separated state, L2 is adjusted so that the electrical length of the above-mentioned path is an integral multiple of λ / 2 when the wavelength of the high-frequency signal to be used is λ. When adjusted in this way, the RF signal that has entered the transmission line L2 is totally reflected by GND, and as a result, reciprocates through the transmission line L2. If the electrical length of the transmission line L2 is an integral multiple (k times) of λ / 2, the electrical length becomes k × (λ / 2) × 2 = kλ, and the transmission line L2 totally reflects the input RF signal. As a result, the short stub operates as an open stub at the operating frequency. With this adjustment, when the output from the main amplifier is viewed, the circuit on the peak amplifier side is open and disconnected from the synthesis point.

In this adjustment, the load impedance viewed from the main amplifier 12 is changed, but on the Smith chart, it means that the distance from the center (50Ω) of the Smith chart is changed. (This means that the size of the circle, which is the locus on the Smith chart, is adjusted by adjusting the electrical length of the transmission line L1, which will be described later.)
On the other hand, by adjusting the electrical length of the transmission line L1 on the output side of the main amplifier 12, the impedance of the load viewed from the main amplifier output can be adjusted. Specifically, by changing the length of the transmission line L1, the position of the load impedance is circulated on a circle centered on the middle (50Ω) of the Smith chart. In other words, the locus of the impedance of the load is a circle centered on the middle (50Ω) of the chart, and becomes a locus that circulates on this circle by changing the electrical length of the transmission line L1.

  In order to make a simple study, the Doherty amplifier circuit in FIG. 1 was analyzed with a circuit (FIG. 2) in which 25Ω → 50Ω impedance conversion was eliminated and 25Ω terminated. The impedance conversion from 25Ω to 50Ω was defined to be broadband. FIG. 3 is a Smith chart of the analysis result. Here, FIG. 3 shows a locus on the Smith chart of the load impedance as seen from the main amplifier side when the electrical length of the transmission line L1 is changed with the transmission line L2 fixed at an electrical length of 90 ° at a frequency of 666 MHz. It is. The electrical length of the transmission line L1 is set at 100Ω on the Smith chart. This is the point of the real part 2 and the imaginary part 0 on the circumference on the Smith chart. The electrical length of the transmission line L1 is adjusted so as to come to that point. The reason for setting this point is that, in general, when only the main amplifier is operating, it operates efficiently when the load impedance is 100Ω or in the vicinity thereof.

Note that the physical lengths of the transmission lines L1 and L2 after the electrical length adjustment may be different.
A state where both the peak amplifier and the main amplifier are operated by the high power signal input amplification At this time, the output power of the main amplifier 12 and the output power of the peak amplifier 13 are combined at the combining point. The signal output from the main amplifier 12 is input to the port 141 of the first circulator 14, and the output is output to the port 142. On the other hand, the signal output from the peak amplifier 13 is input to the port 151 of the second circulator 15 and output to the port 152. The two outputs are then power combined. The electrical length is not changed when a high power signal is input compared to when a small signal is input. The phase at the synthesis point of the route on the main amplifier 12 side and the route on the peak amplifier 13 side remains in phase, and power is synthesized in that state. The description of the λ / 4 line is omitted.

  When the frequency band to be used is changed, the electrical lengths of the transmission lines L1 and L2 may be adjusted according to the center frequency of the band.

  In the Doherty amplifier circuit of this embodiment, the electrical length is adjusted so as to be optimal in the frequency band to be used first, and the electrical length is not adjusted unless the frequency band is changed. The electrical length is adjusted when the frequency band to be used is changed.

In this embodiment, input signals are input to the main amplifier 12 and the peak amplifier 13 with the same phase. However, signals may be input to the two amplifiers with different phases. The phase adjustment may be performed on the synthesis side.
[Description of effects]
As described above, according to the Doherty amplifier circuit of this embodiment, the impedance on the synthesis side can be adjusted without exchanging the transmission line itself or switching the signal route with an RF switch or the like. Further, there is no need to adjust the phase on the distribution side. Further, by having this impedance adjustment circuit, it is easy to change the frequency of the Doherty amplifier circuit.
(Example)
FIG. 4 is a diagram showing a Doherty amplifier circuit that is a more specific embodiment of the first embodiment. In this embodiment, the composite point of the outputs of the first and second circulators is constituted by the hybrid coupler (HYB) 46. Specifically, the hybrid coupler 46 is a 90 ° hybrid coupler. The Doherty combining point in this embodiment is the combined output of the hybrid 46 coupler. Further, the two distributors 41 are constituted by hybrid type power distributors 41.

  The main amplifier 42, the peak amplifier 43, the first circulator 44, the second circulator 45, the transmission lines L1, L2, the transmission line L3 for impedance conversion, and the antenna 47 are the same as those in the first embodiment. The ports 441, 442, and 443 of the first circulator 44 are the same as the ports 141, 142, and 143 of the circulator 14 of the first embodiment, respectively. Furthermore, the ports 451, 452, and 453 of the second circulator 45 are the same as the ports 151, 152, and 153 of the circulator 15 of the first embodiment, respectively.

FIG. 5 shows the analysis result of the load impedance of the main amplifier output when the peak amplifier 42 is OFF and only the main amplifier 43 is operating. Here, FIG. 5 shows a load impedance (L2 = 90 °, when viewed from the main amplifier side) when the electrical length of the transmission line L1 is changed with the transmission line L2 fixed at an electrical length of 90 ° at a frequency of 666 MHz. L3 = 180 °) on the Smith chart. The circuit of the present embodiment is similar to the Doherty amplifier circuit of FIG. 2 in that the load impedance of the main amplifier 42 is the impedance on the circumference passing through two points of 25Ω and 100Ω centering on the middle (50Ω) on the Smith chart. Can be adjusted. In this case as well, the electrical length of the transmission line L1 may be set at a location of 100Ω on the Smith chart.
(Other embodiments)
In the first embodiment, transmission lines L1 and L2 having variable electrical lengths are used as impedance adjustment elements. However, the present invention is not limited to this, and the reactance variable circuit shown in FIGS. 6 to 9 can also be used.

  In FIG. 6, the transmission lines L1 and L2 are short stubs replaced with open stubs 60. 7 is similarly replaced with a variable capacitance capacitor 70, and FIG. 8 is replaced with an inductor 80 with variable inductance. FIG. 9 is a reactance variable circuit combining them, and is a circuit in which a variable capacitance capacitor 70 and an inductor 80 with variable inductance are connected in parallel.

  Also in the reactance variable circuit of FIGS. 6 to 9, when the operating frequency is λ, the electrical length is an integral multiple of λ / 2. When adjusted in this way, the phase of the signal reflected from the synthesis point and entering from the ports 153 and 453 of the second circulators 15 and 45 is adjusted so as to be totally reflected by the reactance variable circuit shown in FIGS.

  The Doherty amplifier circuit of the present invention can be used for, for example, a television transmitter, a power amplifier, and the like.

10 Doherty amplifier circuit 11, 41 2 Divider 12, 42 Main amplifier 13, 43 Peak amplifier 14, 44 First circulator 15, 45 Second circulator 16 Impedance conversion line 17, 47 Antenna 20 Branch point 46 Hybrid coupler 60 Open Stub 70 Capacitance variable capacitor 80 Inductance variable inductor 141, 142, 143, 151, 152, 153 Port

Claims (7)

A power distributor, a main amplifier and a peak amplifier to which a signal distributed by the power distributor is input, and a Doherty amplifier circuit including an impedance adjustment circuit to which outputs of the main amplifier and the peak amplifier are input,
A first circulator and a first reactance variable element connected to the output of the peak amplifier, and a second circulator and a second reactance variable element connected to the output of the main amplifier,
Impedance adjustment, wherein the second reactance variable element is adjusted so that the circuit including the second circulator and the second reactance variable element is open as viewed from the output side of the peak amplifier Doherty amplifier circuit with circuit.   The impedance of the first reactance variable element is adjusted so that the load impedance of the circuit including the first circulator and the first reactance variable element as viewed from the output side of the peak amplifier is approximately 100Ω. A Doherty amplifier circuit comprising the impedance adjustment circuit according to claim 1.   An impedance of a path connecting the output point of the main amplifier and the peak amplifier, the second circulator, the second reactance variable element, the output point of the peak amplifier, and the second circulator is λ / 2 ( The Doherty amplifier circuit comprising the impedance adjustment circuit according to claim 1 or 2, wherein the reactance variable element is adjusted so that λ corresponds to an integer multiple of a use frequency).   4. The circuit according to claim 1, wherein the circuit including the second circulator and the second reactance variable element viewed from the output side of the peak amplifier is open in a frequency band to be used. 5. The Doherty amplifier circuit provided with the impedance adjustment circuit of description.   5. The impedance adjustment circuit according to claim 1, wherein a transmission line having a variable electrical length, a variable capacitor, a variable inductor, or a parallel connection circuit of a variable capacitor and a variable inductor is used as the reactance variable element. Doherty amplification circuit provided.     6. A Doherty amplifier circuit comprising the impedance adjustment circuit according to claim 1, wherein a hybrid coupler is used as the impedance conversion circuit.   The Doherty amplifier circuit provided with the impedance adjustment circuit of any one of Claim 1 to 6 which adjusts the said reactance variable element with the frequency band to be used.

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