JP6467956B2 - Doherty amplifier circuit with load impedance adjustment circuit - Google Patents

Description

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

  The Doherty amplifier circuit has a main amplifier and a peak amplifier, and operates only the main amplifier when the output is low, and simultaneously operates both the main amplifier and the peak amplifier when the output is high. In general, a Doherty amplifier circuit distributes an input signal to a main amplifier and a peak amplifier with a power distributor, and synthesizes the outputs of these two amplifiers (hereinafter sometimes referred to as Doherty synthesis or power synthesis). The input impedance is adjusted and output impedance is then output to a load such as an antenna.

  In general, when the peak amplifier is OFF and only the main amplifier is operating, it operates with high efficiency when the impedance of the load is at or near 100Ω.

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  The load impedance seen from the output of the main amplifier when only the main amplifier is operating when the peak amplifier is OFF can adjust the impedance on the circumference passing through 25Ω and 100Ω centered on 50Ω at the center on the Smith chart The range is generally adjusted to operate with high efficiency when the load impedance is 100Ω in the operating frequency band.

  However, the optimum operating point of the load impedance of a main amplifier (FET: Field Effect transistor) that actually operates is not necessarily 100Ω. The optimum operating point depends on the amplifier (FET) to be used and the output power to be used, and it is considered that there is an optimum operating point somewhere within the range of 50Ω to 200Ω. Therefore, it is desirable that the load impedance value can be arbitrarily adjusted in the Doherty amplifier circuit.

  An object of the present invention is to solve the above-described problems and provide a Doherty amplifier circuit capable of adjusting a load impedance viewed from the output of a main amplifier to an arbitrary value.

The present invention is a Doherty amplifier circuit including a power distributor, a main amplifier and a peak amplifier to which a signal distributed by the power distributor is input, and a combiner that combines outputs of the main amplifier and the peak amplifier. ,
The output of the peak amplifier is connected to a first circulator, the output from the first circulator is connected to the input port of the synthesizer, the remaining terminal of the first circulator, and the isolation port of the synthesizer Connect the first impedance variable section to the connection point,
Further, a second impedance variable unit is connected between the output of the main amplifier and the combiner, and the load impedance viewed from the output of the main amplifier is adjusted to an arbitrary value by adjusting the second impedance variable unit. A Doherty amplifier circuit comprising a load impedance adjustment circuit to be set.

  According to the present invention, it is possible to provide a Doherty amplifier circuit that can adjust the load impedance viewed from the output of the main amplifier to an arbitrary value.

It is a circuit diagram showing a Doherty amplifier circuit of a 1st embodiment of the present invention. 1 is a locus on a Smith chart of load impedance (L23 = fixed at 80 °) when L1 is changed as viewed from the main amplifier in FIG. 1 at 666 MHz. 1 is a locus on a Smith chart of load impedance (L23 = fixed at 85 °) when L1 is changed as viewed from the main amplifier in FIG. 1 at 666 MHz. FIG. 2 is a circuit diagram showing a Doherty amplifier circuit according to a second embodiment of the present invention, in which the main amplifier and the peak amplifier are connected to the Doherty synthesis circuit and the signal input to the two distributors is reversed in the circuit of FIG. is there. It is a circuit diagram which shows the Doherty amplifier circuit of the 3rd Embodiment of this invention. (a), (b) is obtained by replacing the transmission line L11 whose phase has been adjusted on the distributor side with a circulator 80 in the circuit of FIG. It is a figure which shows the Doherty amplifier circuit of the 4th Embodiment of this invention. (a), (b) changes the place which terminated 50 ohms in the empty terminal of the circulator 80 by the side of a distributor of Drawing 5 into the short stub which has transmission line L11. It is a figure which shows the Doherty amplifier circuit of the 5th Embodiment of this invention. (a), (b) is a circuit diagram which shows the Doherty amplifier circuit which provided the circulator and short stub circuit which were connected to the peak amplifier output also in the main amplifier output side. It is a circuit diagram which shows the open stub which replaces the short stub of the circuit of FIG. It is a circuit diagram which shows the variable capacitor which replaces the short stub of the circuit of FIG. It is a circuit diagram which shows the variable inductor which replaces the short stub of the circuit of FIG. It is a circuit diagram which shows the reactance circuit which replaces the short stub of the circuit of FIG.

(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 showing a Doherty amplifier circuit 10 according to a first embodiment of the present invention. The signal input to the input port 201 is divided by the two distributors 20 in half at 0 ° phase and −90 ° phase. The dual distributor 20 is a 90 ° 3 dB hybrid coupler. No signal is input to the isolation port 202. One of the distributed signals is output to the −90 ° phase port 204 and input to the main amplifier 30 through the transmission line L11. On the other hand, the other of the distributed signals is output to the 0 ° phase port 203 and input to the peak amplifier 40 through the transmission line L12.

  The output of the main amplifier 30 is connected to one end of the transmission line L1. The other end of the transmission line L1 is connected to the 0 ° phase input port 501 of the combiner 50. The synthesizer 50 is a 90 ° 3 dB hybrid coupler. However, the synthesizer 50 is reversely connected to the bi-distributor 20.

  The output terminal of the peak amplifier 40 is connected to the port 601 of the circulator 60. The signal input to the port 601 is output to the port 602 adjacent to the circulator 60 and then input to the −90 ° phase input port 502 of the synthesizer 50. Further, the remaining port 603 of the circulator 60 is connected to the isolation port 503 of the synthesizer 50. A connection point 604 between the port 603 and the isolation port 503 is connected to one end of a transmission line L23 for adjusting the impedance of the Doherty synthesis circuit. The other end of the transmission line L23 is grounded (GND).

  Here, the Doherty synthesis circuit is a transmission line (including L1) from the main amplifier 30 to the 0 ° phase input port 501 of the synthesizer 50, the synthesizer 50, the isolation port 503 of the synthesizer 50, the transmission line L23, and the circulator 60. The signal path connecting the first port 603, the signal line (including the peak amplifier 40 and the circulator 60) between the peak amplifier 40 (operation OFF) to the −90 ° phase input port of the synthesizer 50, the transmission line L23, the transmission This is a general term for signal paths between the line L23 and GND. Although elements that do not directly contribute to power synthesis, such as a peak amplifier, are included, they are referred to herein as Doherty synthesis circuits for convenience.

  In the combiner 50, the output of the main amplifier 30 and the output of the peak amplifier 40 are combined and output to the output port 504, which is the combining point. The output is output to the antenna 70 which is the load of the entire Doherty amplifier circuit 10.

  When both the main amplifier and peak amplifier operate, the phase of both outputs is matched at the Doherty synthesis point. For this purpose, the phase difference between the impedance of the transmission line L1 on the output side of the main amplifier 30 and the signal passing through the circulator 60 on the output side of the peak amplifier 40 is adjusted by the impedances of the transmission lines L11 and L12 on the power distributor side. doing. For example, it is adjusted by the electrical length of L11 and L22. When the passing phase of circulator 60 and the passing phase of L1 are the same, L11 and L22 also have the same electrical length. When both the main amplifier and the peak amplifier operate, the power is synthesized because the phases are aligned at the output point.

In this state, even if the impedance of L23 is changed, it is not necessary to adjust the electrical length of the transmission lines of L11, L12, and L1. However, actually, there are not many cases where the passing phase in the circulator 60 and the passing phase in the transmission line L1 are the same. Therefore, the phase difference between the main amplifier side and the peak amplifier side is adjusted by L11 and L12 so that electric power can be combined.
(Description of operation)
Hereinafter, the operation of the Doherty amplifier circuit according to the present embodiment will be described. The description will be given separately for the peak amplifier 40 in an operation OFF state and an ON state.
[Low power signal input amplification and peak amplifier operation is off]
In the present embodiment, when the peak amplifier is not operating by the low power signal input amplification, the peak amplifier 40 alone is totally reflected by an open circuit as viewed from the output side. For this purpose, as viewed from the main amplifier 30, the state including the synthesis point (output port 504) to the open end of the output of the peak amplifier 40 is made open and disconnected in the frequency band to be used. In other words, the operation of the Doherty amplifier circuit 10 is not affected. In order to achieve the disconnected state, the impedance of the transmission line L23 is adjusted. The “separated state” will be described with a Smith chart (impedance chart). The circumference of the Smith chart intersects the real axis at two locations (right and left when viewed from the center of the circumference on the real axis), but the disconnected state means that the load impedance value is the value of the right intersection (for example, It is in a state of being around 100Ω. Changing the impedance of L23 can change the size (radius) of the circumference. In this state, the load impedance is adjusted to a desired value by adjusting the impedance (reactance) of L1. Speaking of the Smith chart, it is to set the desired position on the circumference centered on the center (50Ω) of the load impedance chart.

  Next, a method for adjusting L23 will be described. When a low power signal is input, the peak amplifier 40 does not operate, only the main amplifier 30 operates, and the combiner 50 is in an unbalanced combined state. Therefore, the isolation port 503 is not in an isolated (insulated) state with respect to the input side, and the unbalanced portion is output. The route of the output signal is divided into three routes.

  The three routes are those that are reflected at the connection point 604 between the isolation port 503 and the transmission line L23 and returned to the isolation port 503, those that go from the connection point 604 to the circulator 60 side, and those that pass from the connection point 604 through L23 to GND. There are 3 routes of what is reflected at. A signal returning to the isolation port 503 of the synthesizer 50 is divided into two by the synthesizer 50 and returns to the main amplifier 30, and a standing wave is standing. You can adjust how the standing wave stands by changing L23. By adjusting the standing wave, the load impedance viewed from the main amplifier 30 can be arbitrarily adjusted.

  Specifically, the load impedance when the Doherty synthesis circuit including the peak amplifier 40 whose operation is OFF is viewed from the output terminal of the main amplifier 30 is an integral multiple of λ / 2 (λ is a used frequency). The transmission line L23 having a length (electric length) for operating the open stub circuit having the length of is selected. In other words, the electrical length of L23 is adjusted so that the electrical length of the synthesis circuit looks like an open stub circuit having an integral multiple of λ / 2 when viewed from the synthesis point (output port 504).

  Since there is signal reflection, it is difficult to specify which part of the electrical length should actually be λ / 2. Therefore, as an actual adjustment method, adjust the electrical length of L23 while measuring the Smith chart so that the position of the load impedance on the Smith chart is at the intersection (near 100Ω) on the right side of the real axis on the circle. adjust. As a result, when the peak amplifier is OFF, the peak amplifier side appears to be open when viewed from the synthesis point. Then, adjust the load impedance to the desired value by adjusting the impedance (reactance) of L1.

  Note that if the frequency band used by the Doherty amplifier circuit 10 is changed, λ naturally changes, so the electrical length of the transmission line L23 is adjusted. Since L1 and L23 need only be adjusted, it is possible to easily cope with changes in the frequency band.

  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.

  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 an open stub appears to be connected.

  FIG. 2 shows the load impedance as seen from the main amplifier side when the electrical length of the transmission line L1 is changed with the electrical length of the transmission line L23 fixed at 80 ° at the frequency of 666 MHz in the circuit of FIG. It is a locus on the Smith chart. FIG. 3 shows Smith of load impedance as seen from the main amplifier side when the electrical length of the transmission line L1 is changed in the state of FIG. 1 with the electrical length of the transmission line L23 being fixed at 85 ° at a frequency of 666 MHz. It is a trajectory on the chart.

The point of the real part 2.0 and the imaginary part 0 becomes the load impedance 100Ω on the circumference of the Smith chart of FIGS. Similarly, in order to make the load impedance 90Ω, it is set to be the point of the real part 1.8 and the imaginary part 0 in FIGS. To make it 150 Ω, the point is set so that the real part is 3.0 and the imaginary part is 0.
[High-power signal input amplification with both peak amplifier and main amplifier operating]
When both the peak amplifier and the main amplifier are operating, the Doherty amplifier circuit 10 is a circuit that combines the output power of the main amplifier 30 and the output power of the peak amplifier 40. Here, the signal after each amplifier output is adjusted by the transmission line on the distributor side so that the phase of the route on the main amplifier 30 side and the route on the peak amplifier 40 side at the synthesis point is in phase. The power is synthesized by the device 50.
(Explanation of effect)
According to the present embodiment, by adjusting the electrical length of the transmission line L23, when the operation of the peak amplifier 40 is OFF, the peak amplifier side appears to be open when viewed from the synthesis point. Then, the load impedance of the main amplifier can be adjusted to a desired value by adjusting the impedance of the transmission line L1. Furthermore, it becomes easy to cope with the case where the frequency band used for the Doherty amplifier circuit is changed.
(Second Embodiment)
FIG. 4 is a diagram showing a Doherty amplifier circuit 100 according to the second embodiment of the present invention. This circuit is obtained by reversing the connection of the main amplifier 30 and the peak amplifier 40 in the circuit of FIG. 1 to the connection to the two distributors 20 and the combiner 50. The input signal is input to the input port 201 of the bi-distributor 20, and no signal is input to the isolation port 202. The 0 ° phase port of the two distributors 20 is connected to the transmission line L11, and the transmission line L11 is connected to the main amplifier 30. The output of the main amplifier 30 is connected to the transmission line L1, and the output of L1 is connected to the −90 ° phase input port 502 of the synthesizer 50.

On the other hand, the −90 ° phase port 204 of the two distributor 20 is connected to the transmission line L12, and the transmission line L12 is connected to the peak amplifier 40. The output of the peak amplifier 40 is connected to the port 601 of the circulator 60 and output to the adjacent port 602. The port 602 is connected to the 0 ° phase input port 501 of the synthesizer 50. The remaining port 603 of the circulator is connected to the isolation port 503 of the synthesizer 50, and the connection point 604 is connected to one end of the transmission line L23. The other end of the transmission line L23 is grounded to GND. Thus, the Doherty amplifier circuit 100 in which the connection relationship with FIG. 1 is reversed has the same effect as FIG.
(Third embodiment)
FIG. 5 is a diagram showing a Doherty amplifier circuit according to a third embodiment of the present invention. FIG. 5A is a circuit in which the transmission line L11 whose phase has been adjusted on the distributor side in the circuit of FIG. This circulator 80 has the same phase characteristics as the circulator 60 connected to the peak amplifier output side, and terminates the empty terminal by 50Ω. Further, the transmission line L12 has the same phase characteristics as the transmission line L1. That is, the same phase characteristic is given to the task between the transmission lines in the front and rear stages sandwiching the amplification stage and the circulators. The reason is to shorten the track length. The main amplifier side line and the peak amplifier side line only need to be in phase, so the front stage and the back stage of the amplification stage, that is, the circulator and L12 of the front stage of the main amplifier, and the circulator of L1 and the post stage of the peak amplifier The phase characteristics may be matched to each. In that case, however, the line length becomes longer than the above-described task.

FIG. 5B is similar to the circuit of FIG. 4 with respect to FIG. 1 except that the connection of the main amplifier and the peak amplifier to the two distributors and the combiner is reversed from that in FIG. This circuit can achieve the same effect.
(Fourth embodiment)
FIG. 6 is a diagram showing a Doherty amplifier circuit according to a fourth embodiment of the present invention. FIG. 6 (a) is obtained by replacing the portion terminated with 50Ω at the empty terminal of the distribution side circulator of FIG. 5 (a) with a short stub having a transmission line L11. In general, the input port impedance of FETs for high power applications is totally reflected, so that the power reflected at the input of the main amplifier and peak amplifier can be combined into the isolation resistance side of the distributor and absorbed. The short stub length L11 is adjusted.

Fig. 6 (b) shows the connection of the main amplifier and peak amplifier of Fig. 6 (a) to the two distributors and the combiner, but has the same effect as the circuit of Fig. 6 (a). .
(Fifth embodiment)
FIG. 7 is a diagram showing a Doherty amplifier circuit according to a fifth embodiment of the present invention. In FIG. 7A, the circulator and the short stub circuit connected to the peak amplifier output are similarly provided on the main amplifier output side. In this circuit, since the passing phase between the two circulators is the same, phase adjustment on the distributor side is not necessary. Furthermore, even if the lengths of L1 and L23 connected to the two circulators are changed, the passing phase of the circulator does not change, so that the power can be combined regardless of the length. The transmission line L1 shown in FIG. 7A also has a function of adjusting the load impedance as viewed from the main amplifier side, in addition to the phase adjustment function.

FIG. 7 (b) is the one in which the connection of the main amplifier and the peak amplifier of FIG. 7 (a) to the Doherty synthesis circuit is reversed, but has the same effect as the circuit of FIG. 7 (a).
(Other embodiments)
8-11 is a figure which shows other embodiment of this invention. FIG. 8 shows a circuit in which an open stub is connected instead of connecting a short stub to the circulator. Similarly, FIG. 9 shows a circuit in which a variable capacitor is connected instead of the short stub, and FIG. 10 shows a circuit in which a variable inductor is connected. FIG. 11 shows a circuit in which a reactance variable circuit (FIG. 11) in which a variable capacitor and a variable inductor are connected in parallel is connected.

  The short stub of the Doherty amplifier circuit shown in FIGS. 1 to 7 can be replaced with these circuits. When the transmission line L1 at the rear stage of the amplifier shown in FIGS. 7A and 7B is replaced, the load impedance can be adjusted in the same manner as L1.

  The present invention can be used for a television transmitter, a power amplifier, a high-frequency circuit, and the like.

10, 100 Doherty amplifier circuit 20 Bi-distributor 201 Input port 202 Isolation port 203 0 ° phase port 204 -90 ° phase port
L11, L12, L1, L23 Transmission line 50 Synthesizer 501 0 ° phase input port 502 -90 ° phase input port 503 Isolation port 504 Output port 60, 80 Circulator 601, 602, 603 Port 604 Connection point 70 Antenna

Claims (7)

A power distributor, a main amplifier and a peak amplifier to which a signal distributed by the power distributor is input, a Doherty amplifier circuit including a synthesizer that combines outputs of the main amplifier and the peak amplifier,
The output of the peak amplifier is connected to a first circulator, the output from the first circulator is connected to the input port of the synthesizer, the remaining terminal of the first circulator, and the isolation port of the synthesizer Connect the first impedance variable section to the connection point, connect the second impedance variable section between the output of the main amplifier and the combiner, and adjust the second impedance variable section A Doherty amplifier circuit comprising a load impedance adjustment circuit that sets an arbitrary value for the load impedance viewed from the output of the main amplifier.   2. The first impedance variable unit according to claim 1, wherein, when the peak amplifier is off, the first impedance variable unit is adjusted so that a circuit from an combining point of the combiner to an output terminal of the peak amplifier is open. , Doherty amplifier circuit with load impedance adjustment circuit. Said power divider and according to claim 1 or 2 using a hybrid coupler as the combiner, Doherty amplifier circuit having a load impedance adjusting circuit. The Doherty amplifier circuit having a load impedance adjustment circuit according to claim 3 , wherein the hybrid coupler is a 3 dB 90 ° hybrid coupler. A second circulator provided between the main amplifier and the power divider, as claimed in any one of the second 4 from claim 1 circulator short stub provided, equipped with a load impedance adjusting circuit Doherty amplifier circuit. The Doherty provided with the load impedance adjustment circuit according to any one of claims 1 to 4 , wherein a third circulator is provided between the main amplifier and the synthesizer, and a short stub is provided in the third circulator. Amplification circuit. As the first or second impedance varying unit, the open stub to the fourth circulator, a variable capacitor, a variable inductor, or from claim 1 using a circuit parallel connection circuit is connected to the variable capacitor and the variable inductor 6 A Doherty amplifier circuit comprising the load impedance adjustment circuit according to any one of the above items.

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