JP2006339981A - Doherty amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Doherty amplifier having high efficiency and linearity with simple constitution. <P>SOLUTION: The Doherty amplifier includes: an unequal distribution circuit 6 which distributes an input signal at an unequal ratio; a carrier amplifier 1 which always amplifies one signal distributed by the unequal distribution circuit; and a peak amplifier 2 which amplifies the other signal distributed by the unequal distribution circuit when the input signal exceeds a specified level, and combines the output of the carrier amplifier and the output of the peak amplifier to output the combined output. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a Doherty amplifier capable of realizing high efficiency and low distortion.

  In recent years, mobile communication and wireless LAN (Local Area Network) have made remarkable progress, especially with the explosive spread of mobile phones and the accompanying infrastructure development, which requires lower power consumption not only for mobile terminals but also for base stations. Has been. Thus, there is an increasing demand for improvement in efficiency and linearity of amplifiers used for transmission in base stations.

  However, in a typical amplifier, there is a trade-off between efficiency and linearity, and efficiency is proportional to the input level to the amplifier. Therefore, high efficiency is not obtained until the amplifier output approaches the maximum output power, so it is difficult to achieve amplifier linearity. In view of this, an amplifier with higher efficiency and lower distortion has been developed by combining a technique for amplifying a signal with high efficiency such as a Doherty amplifier and a distortion compensation technique such as low distortion and feedforward.

  As shown in FIG. 5, the conventional standard Doherty amplifier has a carrier amplifier 1 that always operates regardless of the output level (AB operation) and a high output operation (after the carrier amplifier 1 reaches the saturation maximum output). ) Peak amplifier 2 that operates only (class C operation). The input signal is divided into two by the distribution circuit 5, one is input to the carrier amplifier 1 as it is, and the other is input to the peak amplifier 2 via the quarter wavelength transmission line 3.

  The load is connected to the output of the peak amplifier 2, and the output of the carrier amplifier 1 is generally connected to the load via an impedance converter composed of a quarter wavelength transmission line 4. In this Doherty amplifier, when the output level is low, only the carrier amplifier 1 operates and the output of the peak amplifier 2 is cut off.

  In the low level region where only the carrier amplifier 1 operates, the load impedance viewed from the carrier amplifier 1 is higher than the impedance at the peak power (ideally doubled), thereby improving the efficiency of the carrier amplifier 1 in the low level region. To increase. When the output level increases beyond the transition point at which the carrier amplifier 1 saturates, the peak amplifier 2 enters an operating state and supplies current to the load.

  By impedance conversion via the quarter wavelength transmission line 4, the effective impedance at the output of the carrier amplifier 1 is reduced, and the output of the carrier amplifier 1 is maintained at a constant (peak) voltage above the transition point. At the synthesis point of the carrier amplifier 1 and the peak amplifier 2, the signals are at the same level and in phase, and some distortion components are in anti-phase, so that the carrier amplifier 1 and the peak amplifier 2 drive the designed predetermined load impedance. To do. As a result, the output-to-input relationship is substantially linear and has high linearity while having higher efficiency than conventional amplifiers.

  However, in reality, when each amplification operation of the carrier amplifier 1 and the peak amplifier 2 is different from the ideal operation, the relationship between the distortion level and the phase of the signal at the output synthesis point deviates from the ideal state and is output. There was a problem that synthesis was not performed effectively and ideal high efficiency and linearity could not be obtained.

  FIG. 6 shows actual input / output characteristics of each of the carrier amplifier 1 and the peak amplifier 2 in such a conventional Doherty amplifier. Referring to this input / output characteristic, it can be seen that the peak amplifier 2 is not operated at the time of a low input level because it is a bias of class C operation. The Doherty amplifier having the input / output characteristics shown in FIG. 6 has a difference in output level between the carrier amplifier 1 and the peak amplifier 2 during high output operation, and the output of the peak amplifier 2 is smaller than the carrier amplifier 1 by about 3 dB. For this reason, the synthesis levels of the two signals are different, and ideal impedance cannot be driven, so that ideal synthesis is not possible. As a result, high efficiency and linearity cannot be obtained.

In order to solve such a problem and to effectively perform output synthesis, for example, as shown in FIG. 7, a gain compensator 7 is disposed in front of the peak amplifier 2 so that only the signal level is maintained without changing the phase relationship. A Doherty amplifier has been developed in which the synthesis level at the output synthesis point is optimized by adjusting the value (for example, see Patent Document 1).
JP 2002-221646 A

  However, since the conventional Doherty amplifier disclosed in Patent Document 1 described above requires a gain compensator and the like, there is a problem that the structure becomes complicated.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a Doherty amplifier capable of obtaining high efficiency and linearity with a simple configuration.

  In order to solve the above problems, a Doherty amplifier according to the present invention includes an unequal distribution circuit that distributes an input signal at an unequal ratio, and a carrier amplifier that always amplifies one of the signals distributed by the unequal distribution circuit. A peak amplifier that amplifies the other signal distributed by the unequal distribution circuit when the input signal exceeds a predetermined level, and combines and outputs the output of the carrier amplifier and the output of the peak amplifier To do.

  According to the Doherty amplifier according to the present invention, different levels of signals are supplied to the carrier amplifier and the peak amplifier by the unequal distribution circuit, so that the carrier amplifier output and the peak amplifier output are effectively combined at the same level. can do. Therefore, high efficiency and linearity can be obtained with a simple configuration.

  Hereinafter, a Doherty amplifier according to an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the same components as those of the conventional Doherty amplifier described in the background art section are denoted by the same reference numerals as those used in the background art section.

  FIG. 1 is a circuit diagram showing a configuration of a Doherty amplifier according to Embodiment 1 of the present invention. This Doherty amplifier is configured by replacing the distribution circuit 5 of the conventional Doherty amplifier shown in FIG. That is, the Doherty amplifier includes an input terminal IN, a carrier amplifier 1, a peak amplifier 2, a quarter wavelength transmission line 3, a quarter wavelength transmission line 4, a non-uniform distribution circuit 6, and an output terminal OUT.

  The non-uniform distribution circuit 6 is composed of, for example, a non-compensation type Wilkinson coupler, and divides the input signal input from the input terminal IN into two unevenly, outputs one from the port A, and outputs the other from the port B. Output. Specifically, the unequal distribution circuit 6 distributes so that the output of the port B is smaller than the output of the port A by about 3 dB. The signal output from the boat A is sent to the peak amplifier 2 via the quarter wavelength transmission line 3, and the signal output from the port B is sent to the carrier amplifier 1.

  The carrier amplifier 1 always operates (class AB operation) regardless of the output level, amplifies the signal sent from the port B of the unequal distribution circuit 6 and sends it to the quarter wavelength transmission line 4. The quarter wavelength transmission line 4 converts the impedance of the signal output from the carrier amplifier 1 and outputs the converted signal. The quarter wavelength transmission line 3 is composed of a 50Ω transmission line, and sends a signal sent from the port A of the unequal distribution circuit 6 to the peak amplifier 2.

  The peak amplifier 2 operates only at the time of high output operation, that is, after the carrier amplifier 1 reaches the saturation maximum output (class C operation), and passes from the port A of the unequal distribution circuit 6 via the quarter wavelength transmission line 3. Amplify the signal sent and output. The output of the quarter wavelength transmission line 4 and the output of the peak amplifier 2 are combined and output from the output terminal OUT.

  Next, the details of the unequal distribution circuit 6 will be described. The non-uniform distribution circuit 6 includes a first quarter wavelength transmission line 21, a second quarter wavelength transmission line 22, a third quarter wavelength transmission line 23, and a fourth quarter wavelength transmission line 24. And a resistor R1.

  One end of the first quarter wavelength transmission line 21 is connected to the input terminal IN, and the other end is connected to one end of the third quarter wavelength transmission line 23. The other end of the third quarter wavelength transmission line 23 is connected to the port A. One end of the second quarter wavelength transmission line 22 is connected to the input terminal IN, and the other end is connected to one end of the fourth quarter wavelength transmission line 24. The other end of the fourth quarter wavelength transmission line 24 is connected to the port B. The resistor R1 includes a connection point between the first quarter-wave transmission line 21 and the third quarter-wave transmission line 23, a second quarter-wave transmission line 22, and the fourth quarter-wave transmission. A connection point with the line 24 is connected.

Each characteristic impedance necessary for the first quarter wavelength transmission line 21 to the fourth quarter wavelength transmission line 24 in the non-uniform distribution circuit 6 is obtained as follows. Here, the characteristic impedance of the first quarter wavelength transmission line 21 is Z ₂ , the characteristic impedance of the second quarter wavelength transmission line 22 is Z ₃ , and the characteristic impedance of the third quarter wavelength transmission line 23. Is Z ₄ , and the characteristic impedance of the fourth quarter-wave transmission line 24 is Z ₅ .

  From the ratio between the signal levels of port A and port B, the division ratio k is obtained according to the following equation (1).

k ² = Pb / Pa (1)
Here, k> 0, Pa is the signal magnitude [W] of port A, and Pb is the signal magnitude [W] of port B.

  Next, the resistance value R of the resistor R1 is obtained according to the following equation (2).

R = Z ₀ × (1 + k ² ) / k (2)
Here, Z ₀ is the impedance of the system.

Next, the characteristic impedance Z ₂ of the first quarter-wave transmission line 21, the characteristic impedance Z ₃ of the second quarter-wave transmission line 22, the characteristic impedance Z ₄ of the third quarter-wave transmission line 23 and the characteristic impedance Z ₅ of the fourth quarter-wave transmission line 24 is determined according to the following equation (3) to (6).

Z ₂ = Z ₀ × {k (1 + k) ² } ^1/2 (3)
Z ₃ = Z ₀ × {(1 + k ² ) / k ³ } ^1/2 (4)
Z ₄ = Z ₀ × k ^1/2 (5)
Z ₅ = Z ₀ / k ^1/2 (6)
Considering the case where the output of port B is distributed so that the output of port B is smaller by about 3 dB than the output of port A, the signal size of port A is Pa: the signal size of port B is Pb = 2: 1. Become. Therefore, the division ratio k is calculated from the equation (1) as k ² = 1/2.
So
k = (1/2) ^1/2 = 0.0701
become. Next, the resistance value R is calculated from the equation (2) as follows: R = Z ₀ × (1 + k ² ) /k=106.07Ω
become.

The characteristic impedance Z ₂ is calculated from the equation (3): Z ₂ = Z ₀ × {k (1 + k) ² } ^1/2 = 51.494Ω
And the characteristic impedance Z ₃ is Z ₃ = Z ₀ × {(1 + k ² ) / k ³ } ^1/2 = 102.982Ω from the equation (4).
And the characteristic impedance Z ₄ is obtained from the equation (5) as follows: Z ₄ = Z ₀ × k ^1/2 = 42.044Ω
And the characteristic impedance Z ₅ is obtained from the equation (6) as follows: Z ₅ = Z ₀ / k ^1/2 = 59.46Ω
become.

  Each of the first to fourth quarter wavelength transmission lines 21 to 24 is composed of a pattern formed on the substrate, and each characteristic impedance is a pattern length, a pattern width, a pattern thickness, and a ratio of the substrate. It is determined by the dielectric constant, the thickness of the substrate, the frequency of the signal to pass through, and the like.

  FIG. 2 shows input / output characteristics of each of the carrier amplifier 1 and the peak amplifier 2 in the Doherty amplifier according to the first embodiment of the present invention. The non-uniform distribution circuit 6 performs non-uniform distribution so that the output of the port B is smaller than the output of the port A by about 3 dB, thereby changing the signal level input to the carrier amplifier 1 and the peak amplifier 2 as shown in the figure. be able to. As a result, a signal 3 dB larger than the carrier amplifier 1 is input to the peak amplifier 2.

  For this reason, as shown in FIG. 2, the output level at the time of high output operation of the carrier amplifier and the peak amplifier can be made the same. Therefore, an ideal impedance is driven, and high efficiency and linearity can be obtained without adding a gain compensator or the like.

  In the Doherty amplifier according to the first embodiment, a non-compensation type Wilkinson coupler is used as the unequal distribution circuit 6, but a compensation type Wilkinson coupler may be used. FIG. 3 is a circuit diagram showing a configuration of an unequal distribution circuit 6a formed of a compensation type Wilkinson coupler.

The non-uniform distribution circuit 6a is provided between the input terminal IN of the non-uniform distribution circuit 6 shown in FIG. 1 and the first quarter wavelength transmission line 21 and the second quarter wavelength transmission line 22. A quarter wavelength transmission line 25 having a characteristic impedance Z ₁ is added.

  In this case, the characteristic impedance of each transmission line is obtained according to the following formulas (7) to (11).

Z ₁ = Z ₀ × {k / (1 + k ² )} ^1/4 (7)
Z ₂ = Z ₀ × {k ^3/4 (1 + k ² ) ^1/4 } ^1/2 (8)
Z ₃ = Z ₀ × (1 + k ² ) ^1/4 / k ^5/4 (9)
Z ₄ = Z ₀ × k ^1/2 (10)
Z ₅ = Z ₀ / k ^1/2 (11)
The Doherty amplifier using the non-uniform distribution circuit 6a composed of the compensation type Wilkinson coupler also has the same operation and effect as the Doherty amplifier using the non-uniform distribution circuit 6 composed of the non-compensation type Wilkinson coupler.

  Furthermore, as the unequal distribution circuit 6, a coupler that is used in the microwave band, such as a branch line coupler, can be used. FIG. 4 is a circuit diagram showing a configuration of an unequal distribution circuit 6b formed of a branch line coupler.

  The non-uniform distribution circuit 6b includes a first quarter wavelength transmission line 31, a second quarter wavelength transmission line 32, a third quarter wavelength transmission line 33, and a fourth quarter wavelength transmission line. It is composed of three. One end of the first quarter wavelength transmission line 31 is connected to the input terminal IN, and the other end is connected to the isolation port IP. One end of the second quarter wavelength transmission line 32 is connected to the port B, and the other end is connected to the port A. One end of the third quarter wavelength transmission line 31 is connected to the input terminal IN, and the other end is connected to the port B. One end of the fourth quarter-wave transmission line 34 is connected to the isolation port IP, and the other end is connected to the port A.

The characteristic impedance Z _{1 of} the first quarter wavelength transmission line 31 and the second quarter wavelength transmission line 32, and the third quarter wavelength transmission line 33 and the fourth quarter wavelength transmission line 34 The characteristic impedance Z ₂ is obtained by the following equations (12) and (13).

Z ₁ = Z ₀ (12)
^{_{Z 2 = Z 0/2 1/2}} ... (13)
Here, Z ₀ is the impedance of the system.

In the non-uniform distribution circuit 6b, the input signals can be distributed unevenly by appropriately determining the characteristic impedances Z ₁ and Z ₂ . Similar to the unequal distribution circuit 6 described above, distribution in which the output of the port B is smaller than the output of the port A by about 3 dB is characteristic impedance Z ₁ = 35.40 [Ω] and characteristic impedance Z ₂ = 28 .89 [Ω].

  The Doherty amplifier using the unequal distribution circuit 6b made of this branch line coupler also has the same operation and effect as the Doherty amplifier using the unequal distribution circuit 6 made of the non-compensation type Wilkinson coupler.

1 is a circuit diagram showing a configuration of a Doherty amplifier according to Embodiment 1 of the present invention. FIG. It is a figure which shows the input-output characteristic of each single-piece | unit of the carrier amplifier and the peak amplifier in the Doherty amplifier which concerns on Example 1 of this invention. It is a circuit diagram which shows the structure of the unequal distribution circuit used for the other structure of the Doherty amplifier which concerns on Example 1 of this invention. It is a circuit diagram which shows the structure of the unequal distribution circuit used for the further another structure of the Doherty amplifier which concerns on Example 1 of this invention. It is a circuit diagram which shows the structure of the conventional standard Doherty amplifier. It is a figure which shows the input / output characteristic of each single-piece | unit of the carrier amplifier and peak amplifier in the conventional standard Doherty amplifier. It is a circuit diagram which shows the structure of the other conventional Doherty amplifier.

  The present invention can be applied to an amplifier used in a mobile phone or the like.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carrier amplifier, 2 ... Peak amplifier, 3 ... 1/4 wavelength transmission line, 4 ... 1/4 wavelength transmission line (impedance converter), 6 ... Unequal distribution circuit (non-compensation type Wilkinson coupler), 6a ... Unequal distribution circuit (compensation type Wilkinson coupler), 6b... Unequal distribution circuit (branch line coupler).

Claims (3)

An unequal distribution circuit that distributes the input signal at an unequal ratio;
A carrier amplifier that always amplifies one of the signals distributed by the non-uniform distribution circuit;
A peak amplifier that amplifies the other signal distributed by the non-uniform distribution circuit when an input signal is equal to or higher than a predetermined level;
A Doherty amplifier characterized by combining and outputting the output of the carrier amplifier and the output of the peak amplifier.   2. The Doherty amplifier according to claim 1, wherein the non-uniform distribution circuit comprises an uncompensated Wilkinson coupler, a compensated Wilkinson coupler, or a branch line coupler. 3. The Doherty amplifier according to claim 1, wherein the one signal output from the unequal distribution circuit and the other signal have a difference of 3 dB.

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