JP6795284B2 - Doherty amplifier circuit with impedance adjustment circuit - Google Patents

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 low output, and operates both the main amplifier and peak amplifier at the same time at high output. Generally, in a Doherty amplifier circuit, an input signal is distributed to a main amplifier and a peak amplifier by a power distributor, and the outputs of these two amplifiers are combined (hereinafter referred to as Doherty synthesis or power synthesis) 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 output of the main amplifier and the impedance of the transmission line after the output of the peak amplifier are different. Therefore, in order to combine power, the impedance is on the distributor side or the rear stage side (synthesis side) of the front stage when viewed from the amplifier. Needed to be adjusted. When adjusting on the synthesis side, the impedance of the transmission line between the amplifier and the power synthesis point was adjusted. Specifically, the adjustment was made by exchanging the transmission line itself or switching the signal route with an RF (Radio Frequency) switch or the like. Replacing the transmission line and switching the signal route with an RF switch or the like involves complicated work.

Patent Document 1 discloses a multi-band high-efficiency Doherty amplifier circuit. This is an impedance inverter 120 composed of a circulator 122 and a tuner 121 (capacitor) connected to the output of the main amplifier 110. The impedance inverter 120 is connected to the controller 123 and adjusts the capacitance of the capacitor to modulate the load impedance of the main amplifier 110. The impedance inverter 120 performs impedance inversion to modulate the load impedance.

Special Table 2013-527711

In Patent Document 1, the output of the peak amplifier 115 is directly connected to the branch point 116 of 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 look like open stubs. This point is not taken into consideration in Patent Document 1, and when viewed from the branch point 116, even if the peak amplifier 115 is Off, it does not look like OPEN, and it looks like 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 adjust the impedance by exchanging the transmission line itself or switching the signal route by an RF switch or the like.

An object of the present invention is a Doherty amplifier circuit provided with an impedance adjustment circuit that solves the above-mentioned problems and can adjust the impedance on the synthesis side without exchanging the transmission line itself or switching the signal route by an RF switch or the like. Is to provide.

The present invention is a Doherty amplifier circuit including a power distributor, a main amplifier and a peak amplifier to which signals distributed by the power distributor are input, and an impedance adjustment circuit to which the outputs of the main amplifier and the peak amplifier are input. There,
It includes 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, which is characterized by adjusting the second reactance variable element so that the circuit including the second circulator and the second reactance variable element as seen from the output side of the peak amplifier is open. It is a Doherty amplifier circuit equipped with an adjustment circuit.

According to the present invention, it is possible to provide a Doherty amplifier circuit capable of adjusting the impedance on the synthesis side without exchanging 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 1st Embodiment of this invention. It is a circuit diagram which tentatively changed the impedance conversion part to the 25Ω termination for the analysis of the Doherty circuit of FIG. It is a figure which shows the locus on the Smith chart of the load impedance (L2 = 90 °) when the electric length of the transmission line L1 is changed when viewed from the main amplifier in FIG. 2 at 666MHz. It is a figure which shows the Doherty amplifier circuit of another embodiment of this invention. It is a figure which shows the locus on the Smith chart of the load impedance (L2 = 90 °, L3 = 180 °) when L1 is changed when viewed from the main amplifier in FIG. 4 at 666 MHz. It is a circuit diagram which shows the example which replaced the transmission lines L1 and L2 with an open stub. It is a circuit diagram which shows the example which replaced the transmission lines L1 and L2 with a variable capacitor. It is a circuit diagram which shows the example which replaced the transmission lines L1 and L2 with a variable inductor. It is a circuit diagram which shows the example which replaced the transmission lines L1 and L2 with the circuit which connected the variable capacitor and the variable inductor in parallel.

(First Embodiment)
The first embodiment of the present invention will be described with reference to FIGS. 1 to 3.
[Description of configuration]
FIG. 1 is a circuit diagram of the Doherty amplifier circuit 10 of the first embodiment, which includes a 2 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, a transmission line L2 for adjusting the electrical length, an impedance conversion line 16 for converting impedance from 25Ω to 50Ω, and an antenna 17 are provided.

In the circuit configuration of FIG. 1, the input signal is distributed in the same phase by the two distributors 11 to the Doherty amplifier circuit 10, and is connected to the input to the main amplifier 12 and the input to the peak amplifier 13, respectively. These two routes are connected at 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 a 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 port 151 is connected to the synthesis point. The outputs of the main amplifier 12 and the peak amplifier 3 are combined at the synthesis point.

Further, the port 143 of the first circulator is connected to the 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 the 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 referred to here is two transmission lines connecting between the main and peak amplifiers 12 and 13 and the impedance conversion line 16, and the first and second circulators 14 and 15 inserted in the transmission line. Refers to transmission lines L1 and L2, synthesis points, and impedance conversion lines 16.
[Description of operation]
Hereinafter, the operation of the Doherty amplifier circuit of the present embodiment will be described separately for the state in which the peak amplifier 13 is OFF and the state in which the operation is ON.
-Peak amplifier 13 is off due to low power signal input amplification At this time, the peak amplifier 13 alone is fully reflected in the OPEN circuit when viewed from the output side, but the Doherty synthesis circuit, which is the output load from the main amplifier 12. When you look at it, make sure that the circuit from the synthesis point to the OPEN end of the output of the peak amplifier 13 is open and disconnected in the frequency band you want to use, in other words, it does not affect the operation of the Doherty amplifier circuit. ..

Specifically, in order to make the separated state, the impedance of the transmission line L2 is adjusted by the 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 integral multiple of λ / 2. The return path is the synthesis point → port 152 of the second circulator 15 → port 153 → transmission line L2 → total internal reflection at the GND grounding point (return) → pass through the transmission line L2 again → port 153 → port 151 → operation OFF It is a path returning to total reflection at the peak amplifier 15 → port 151 → port 152 → 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 in an open and disconnected (unaffected) state in the frequency band to be used.

In order to make the separated state, when the wavelength of the high frequency signal to be used is λ, L2 is adjusted so that the electric length of the above-mentioned path is an integral multiple of λ / 2. When adjusted in this way, the RF signal that has entered the transmission line L2 is totally reflected by GND, and as a result, it reciprocates on the transmission line L2. If the electric length of the transmission line L2 is an integral multiple (k times) of λ / 2, the electric 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 frequency used. When adjusted in this way, when the output is viewed from the main amplifier, the circuit on the peak amplifier side is open and disconnected from the synthesis point.

In this adjustment, the load impedance seen 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 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 seen from the output of the main amplifier can be adjusted. Specifically, by changing the length of the transmission line L1, the position of the load impedance is rotated on the circumference centered on the center (50Ω) of the Smith chart. In other words, the impedance trajectory of the load is the circumference centered on the center (50Ω) of the chart, and by changing the electrical length of the transmission line L1, it becomes a trajectory that orbits on this circumference.

For a simple examination, the analysis was performed using a circuit (Fig. 2) in which the impedance conversion from 25Ω to 50Ω was eliminated from the Doherty amplifier circuit in FIG. 1 and the termination was 25Ω. Impedance conversion from 25Ω to 50Ω was defined as wideband. FIG. 3 is a Smith chart of the analysis results. Here, FIG. 3 shows the locus on the Smith chart of the load impedance seen from the main amplifier side when the electric length of the transmission line L1 is changed while the transmission line L2 is fixed at a frequency of 666 MHz and the electric length is 90 °. 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. Adjust the electrical length of the transmission line L1 so that it comes to that point. The reason for setting this point is that, in general, when only the main amplifier is operating, it operates with high efficiency when the load impedance is 100Ω or its vicinity.

The physical lengths of the transmission lines L1 and L2 after adjusting the electrical length may be different.
-A state in which both the peak amplifier and the main amplifier operate in 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 synthesis point. The signal after the output of 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 after the output of 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 large power signal is input compared to when a small signal is input. The phases of the root on the main amplifier 12 side and the route on the peak amplifier 13 side at the synthesis point remain in phase, and power is combined in that state. The description of the λ / 4 line will be omitted.

When the frequency band 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 the present embodiment, the electric length is adjusted so as to be optimum in the frequency band used first, and the electric length is not adjusted unless the frequency band is changed. The electrical length is adjusted when the frequency band used is changed.

Further, in the present embodiment, the input signals are input to the main amplifier 12 and the peak amplifier 13 in the same phase. However, signals may be input to the two amplifiers in different phases. The phase adjustment may be performed on the synthesis side.
[Explanation of effect]
As described above, according to the Doherty amplifier circuit of the present embodiment, the impedance on the synthesis side can be adjusted without exchanging the transmission line itself or switching the signal route by an RF switch or the like. Moreover, it is not necessary to adjust the phase on the distribution side. Further, by having this impedance adjustment circuit, it becomes easy to change the frequency of the Doherty amplifier circuit.
(Example)
FIG. 4 is a diagram showing a Doherty amplifier circuit that embodies the first embodiment. In this embodiment, the combined points of the outputs of the first and second circulators are configured by the hybrid coupler (HYB) 46. Specifically, the hybrid coupler 46 is a 90 ° hybrid coupler. The Doherty synthesis point in this embodiment is the synthesis output of the hybrid 46 coupler. Further, the 2 distributor 41 is composed of a hybrid power distributor 41.

The main amplifier 42, the peak amplifier 43, the first circulator 44, the second circulator 45, the transmission lines L1 and L2, the transmission line L3 for impedance conversion, and the antenna 47 are the same as those in the first embodiment. Further, 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. Further, 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 output of the main amplifier in a state where the peak amplifier 42 is turned off and only the main amplifier 43 is operating. Here, FIG. 5 shows the load impedance (L2 = 90 °, seen from the main amplifier side) when the electric length of the transmission line L1 is changed while the transmission line L2 is fixed at a frequency of 666 MHz and the electric length is 90 °. L3 = 180 °) is the trajectory on the Smith chart. Similar to the Doherty amplifier circuit of FIG. 2, the circuit of this embodiment has the load impedance of the main amplifier 42 on the circumference centered on the center (50Ω) on the Smith chart and passing through two points of 25Ω and 100Ω. Can be adjusted to. In this case as well, the electrical length of the transmission line L1 may be set to 100Ω on the Smith chart.
(Other embodiments)
In the first embodiment, transmission lines L1 and L2 having variable electrical lengths are used as the impedance adjusting element. However, the present invention is not limited to this, and the reactance variable circuits shown in FIGS. 6 to 9 can also be used.

As shown in FIG. 6, the transmission lines L1 and L2 are replaced with open stubs 60 instead of short stubs. FIG. 7 shows the capacitor 70 with a variable capacitance, and FIG. 8 shows an inductor 80 with a variable inductance. FIG. 9 is a reactance variable circuit that combines them, in which a capacitance variable capacitor 70 and an inductance variable inductor 80 are connected in parallel.

Also in the case of the reactance variable circuit of FIGS. 6 to 9, when the operating frequency is λ, the electric length is an integral multiple of λ / 2. When adjusted in this way, the signals reflected at the synthesis point and coming in from the ports 153 and 453 of the second circulators 15 and 45 are phase-adjusted so as to be totally reflected by the reactance variable circuits of FIGS. 6 to 9.

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

10 Doherty amplifier circuit 11,41 2 Distributor 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 Variable Capacitor 80 Inductor with Variable Inductance 141, 142, 143, 151, 152, 153 Ports

Claims (6)

A Doherty amplifier circuit including a power distributor, a main amplifier and a peak amplifier to which signals distributed by the power distributor are input, and an impedance adjustment circuit to which the outputs of the main amplifier and the peak amplifier are input. A first circulator and a first reactorance variable element connected to the output of the main amplifier and a second circulator and a second reactorance variable element connected to the output of the peak amplifier are provided, and the peak amplifier is turned off. In the state, the second reactorance variable element is adjusted so that the circuit including the second circulator and the second reactorance variable element as viewed from the output side of the main amplifier is open. Moreover , the portion from the combined point of the outputs of the main amplifier and the peak amplifier to the second circulator , and the entire part from the second circulator to the tip of the second reactors variable element via the second reactors variable element. reflected in part that returns folding into the second circulator, totally reflected by a portion folded back to the second circulator at the output of the peak amplifier from the second circulator, from the second circulator to said combining point the electrical length of the path comprising the back portion, (the lambda used frequency) lambda / 2 Doherty amplifier with an impedance adjusting circuit and adjusts said second variable reactance element so as to correspond to an integral multiple of circuit. The impedance of the first reactance variable element is adjusted so that the load impedance of the circuit including the second circulator and the second reactance variable element as seen from the output side of the main amplifier becomes approximately 100Ω. The doherty amplifier circuit provided with the impedance adjusting circuit according to claim 1. The impedance adjustment circuit according to claim 1 or 2, wherein the circuit including the second circulator and the second reactance variable element viewed from the output side of the main amplifier is open in the frequency band used. Doherty amplifier circuit with. Claims 1 to 3 in which a transmission line having a variable electric length, a variable capacitor, a variable inductor, or a parallel connection circuit of a variable capacitor and a variable inductor is used as the first reactance variable element and the second reactance variable element. A Doherty amplification circuit including the impedance adjustment circuit according to any one item. The Doherty amplifier circuit including the impedance adjustment circuit according to any one of claims 1 to 4, wherein the combined point of the outputs of the main amplifier and the peak amplifier is configured by a hybrid coupler. The doherty amplifier circuit including the impedance adjustment circuit according to any one of claims 1 to 5, which adjusts the first reactance variable element and the second reactance variable element according to the frequency band used.

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