KR102478315B1 - Doherty power amplifier and the method of modulating load impedance of the amplifier - Google Patents

Abstract

The present invention relates to a Doherty power amplifier, wherein the Doherty power amplifier according to an embodiment of the present invention receives a first RF signal and distributes it into a plurality of RF signals including a second RF signal and a third RF signal. power divider; a main amplifier for amplifying the second RF signal; an auxiliary amplifier for amplifying the third RF signal; a power combiner combining the RF signal received from the main amplifier and the RF signal received from the auxiliary amplifier, converting the RF signal into one RF signal, and outputting the converted signal; a first transmission line disposed between the main amplifier and the power combiner; And a second transmission line disposed between the auxiliary amplifier and the power combiner, wherein when the power corresponding to the first RF signal is greater than a threshold value, a first impedance of one input terminal of the power combiner connected to the first transmission line and the second impedance of the other input terminal of the power combiner connected to the second transmission line have a complex conjugate relationship with each other, and the power combining method is characterized in that currents or voltages having different phases.

Description

Doherty power amplifier and load impedance modulation method of the device

The present invention relates to a Doherty power amplifying device having improved back-off region efficiency.

A recent wireless communication system uses a modulation scheme having a high peak to average power ratio (PAPR) in order to process a large amount of data.

In order to linearly amplify a modulated signal having such a high PAPR, a power amplifier (PA) mainly operates in a back-off region rather than a maximum output region.

In this case, the efficiency of the power amplification device is rapidly reduced compared to the efficiency when the power amplification device operates in the maximum output region, and the decrease in efficiency of the power amplification device increases power consumption, and in particular, increases battery usage of the mobile device.

According to a recent study, a Doherty power amplifier structure that improves the efficiency of the power amplifier in a back-off region using a load impedance modulation method using two amplifiers has been proposed.

Referring to FIG. 1, a conventional Doherty power amplifier will be described.

The load impedance modulation operation of the Doherty power amplifier is implemented using a Class-AB bias main amplifier (Carrier PA) and a Class-C bias auxiliary amplifier (Peaking PA).

In the high output power region [HP operation] of the Doherty power amplifier shown in FIG. 1, the two amplifiers output the same power, but in the low output power region [LP operation], only the main amplifier (Carrier PA) operates and the auxiliary amplifier (Peaking PA) is turned off.

In this way, the load impedances of the main amplifier and the auxiliary amplifier are modulated according to the magnitude of the output power, so that the efficiency is improved up to an output of 6 dB back-off.

However, in a next-generation wireless communication system requiring high PAPR, in the case of the existing Doherty power amplifier, which improves efficiency only in the 6dB back-off region, the average efficiency improvement effect is reduced. A power amplification device is required.

(KR) Patent Application No. 10-2006-0071179

Through the present invention, it is possible to expand the area in which the efficiency of the Doherty power amplifier is improved.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

A Doherty power amplifier according to an embodiment of the present invention includes a power divider for receiving a first RF signal and distributing it into a plurality of RF signals including a second RF signal and a third RF signal; a main amplifier for amplifying the second RF signal; an auxiliary amplifier for amplifying the third RF signal; a power combiner combining the RF signal received from the main amplifier and the RF signal received from the auxiliary amplifier, converting the RF signal into one RF signal, and outputting the converted signal; a first transmission line disposed between the main amplifier and the power combiner; and a second transmission line disposed between the auxiliary amplifier and the power combiner, wherein when power corresponding to the first RF signal is greater than or equal to a threshold value, a first impedance of one input terminal of the power combiner connected to the first transmission line And the second impedance of the other input terminal of the power combiner connected to the second transmission line is different from each other.

In one embodiment, it is characterized in that the first impedance and the second impedance are complex conjugates to each other in a high output power region.

In one embodiment, the second transmission line includes a plurality of transmission lines connected in series with each other, and the plurality of transmission lines each have different characteristic impedances and electrical lengths.

In one embodiment, it is characterized in that a compensation transmission line for compensating for a phase difference between the main amplifier and the auxiliary amplifier is connected to the input terminal of the main amplifier.

In one embodiment, tan (θ _PM °) for the phase (θ _PM °) corresponding to the compensation transmission line is proportional to tan (θ °) for the phase (θ °) corresponding to the first transmission line. characterized by

A method for modulating the load impedance of a Doherty power amplifier according to another embodiment of the present invention includes receiving a first RF signal by a power divider and distributing it into a plurality of RF signals including a second RF signal and a third RF signal. step; amplifying the second RF signal by a main amplifier; Modulating, by a first transmission line, an impedance of one input terminal of the power coupler to an optimum load impedance required for an output terminal of a main amplifier; amplifying the third RF signal by an auxiliary amplifier; Modulating, by the second transmission line, the impedance of the other input terminal of the power coupler to an optimum load impedance required for the output terminal of the auxiliary amplifier; and combining the output RF signal of the first transmission line and the output RF signal of the second transmission line. Modulating the impedance of one input terminal and the impedance of the other input terminal of the power combiner according to a coupling ratio between an output RF signal of a first transmission line and an output RF signal of a second transmission line in the power combiner. .

In one embodiment, the method of modulating the load impedance of the Doherty power amplifier may further include compensating for a phase difference between a main amplifier and an auxiliary amplifier by receiving the second RF signal through a compensation transmission line.

According to the Doherty power amplifier according to an embodiment of the present invention, it has an extended back-off region by using an outphasing power combiner.

According to the Doherty power amplifier according to an embodiment of the present invention, power efficiency can be improved in a wireless communication system or a wireless energy power transmission system, and the efficiency of the entire system can be improved.

According to the Doherty power amplification device of the present invention, it can be applied to the design of a CMOS power amplification device integrated circuit that is mainly used, and since the efficiency of the power amplification device for mobile devices can be improved, the power consumption of the device can be reduced and the battery usage time can be increased. can

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

1 is a circuit diagram of a conventional Doherty power amplifier.
Figure 2 is a circuit diagram showing two ways of combining the output power of the main amplifier and the auxiliary amplifier of the power combiner.
3(a) is a conceptual diagram illustrating a current coupling method of an outphasing Doherty power amplifier according to an embodiment of the present invention.
3(b) is a conceptual diagram illustrating a voltage coupling method of an outphasing Doherty power amplifier according to an embodiment of the present invention.
4 is a conceptual diagram of an impedance transformer using two transmission lines connected in series.
5(a) is a conceptual diagram illustrating a current coupling method of an outphasing Doherty power amplifier according to an embodiment of the present invention.
5(b) is a conceptual diagram illustrating a voltage coupling method of an outphasing Doherty power amplifier according to an embodiment of the present invention.
6(a) shows the load impedance of the outphasing Doherty power amplifying device in a low output power region (LP operation).
6(b) shows the load impedance of the outphasing Doherty power amplifier in a high output power region (HP operation).
Figure 7 (a) shows the load impedance of the outphasing Doherty power amplifier in the low output power region (LP operation).
7(b) shows the load impedance of the outphasing Doherty power amplifying device in a high output power region (HP operation).
8(a) is a graph showing the load impedance of an outphasing Doherty power amplifier.
8(b) is a Smith chart showing the load impedance of the output stage of the auxiliary amplifier of the outphasing Doherty power amplifier.
9 is a graph showing Power Added Efficiency (PAE) according to power of an output signal of an outphasing Doherty power amplifier according to an embodiment of the present invention.

Since the present invention can have various changes and various embodiments, specific embodiments will be described in detail with reference to the drawings. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals have been used for like elements throughout the description of each figure.

Terms such as first, second, A, and B may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. The term and/or includes a combination of a plurality of related items or any one of a plurality of related items.

It should be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. something to do. On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

Throughout the specification and claims, when a part includes a certain component, it means that it may further include other components, not excluding other components unless otherwise stated.

Figure 2 is a circuit diagram showing two ways of combining the output power of the main amplifier and the auxiliary amplifier of the power combiner.

FIG. 2(a) is a circuit diagram showing a current coupling type power combiner, and FIG. 2(b) is a circuit diagram showing a voltage coupling type power combiner.

2 shows that when the input power (S1) of one input terminal of the current coupling type power combiner and the input power (S2) of the other input terminal are combined, the output power (Stotal) of the power combiner is the same.

In addition, the input power (S1) of one input terminal of the current coupling type power combiner and the input power (S2) of the other input terminal have the same magnitude. If this is expressed as an equation, it is as shown in Equation 1 below.

[Equation 1]

That is, when the impedance of the load at the output end of the current-coupled power combiner is R _L , the following condition is satisfied for the impedance of the two input ends of the current-coupled power combiner.

In addition, the following condition is established for the impedance of the input terminal of the power combiner of the voltage coupling method.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a conceptual diagram of an outphasing Doherty power amplifier according to an embodiment of the present invention.

3(a) is a conceptual diagram illustrating a current coupling method of an outphasing Doherty power amplifier according to an embodiment of the present invention, and FIG. 3(b) is a Doherty power amplifier according to an embodiment of the present invention. It is a conceptual diagram explaining the voltage coupling method of

The Doherty power amplifier according to an embodiment of the present invention includes a power divider 110, a main amplifier 120, an auxiliary amplifier 130, a power combiner 140, a first transmission line 150, a second transmission line ( 160) and a compensation transmission line 170. The second transmission line 160 may include a third transmission line 162 and a fourth transmission line 164 connected in series.

The power divider 110 serves as a power divider for receiving the first RF signal and distributing the first RF signal into a second RF signal and a third RF signal. The power combiner 140 combines the outputs of the respective amplifiers 120 and 130 and converts them into a single RF signal, and serves as a power combiner.

The two amplifiers 120 and 130 are combined by a power divider 110 and a power combiner 140 to operate as a Doherty power amplifier. The main amplifier 120 operates in Class-AB and amplifies the second RF signal, and the auxiliary amplifier 130 operates in Class-C and amplifies the third RF signal.

A first transmission line 150 for generating load modulation is disposed at the output terminal of the main amplifier 120, a second transmission line 160 is disposed at the output terminal of the auxiliary amplifier 130, and an input terminal of the main amplifier 120. A compensation transmission line 170 for compensating for a phase difference between the main amplifier 120 and the auxiliary amplifier 130 is disposed. The compensation transmission line 170 adjusts the phase of the input voltage to provide a phase difference required for outphasing coupling.

The second transmission line 160 includes a third transmission line 162 and a fourth transmission line 164 connected in series in a configuration for impedance modulation. The third transmission line 162 and the fourth transmission line 164 have different electrical lengths. Also, the third transmission line 162 and the fourth transmission line 164 have different characteristic impedances.

Referring to (a) of FIG. 3 , in the case of using the current coupling method, the first transmission line 150 is a transmission line having a characteristic impedance Z ₀ and an electrical length of θ°, and the third transmission line 162 has a characteristic impedance It is an electrical length θ _offset ° transmission line with Z _opt , and the fourth transmission line 164 connected in series with the third transmission line 162 is an electrical length 180 ° - θ ° transmission line with characteristic impedance Z ₀ . The compensation transmission line 170 is a transmission line having an electrical length of θ _PM °. Here, the electrical length is the length obtained by dividing the actual length by the wavelength λ, and is expressed as a multiple of the wavelength of a periodic electric signal propagating through the transmission line, and the wavelength is expressed as an angle. For example, a transmission line having an electrical length of 90° means that the transmission line is 1/4λ of the wavelength of an electric signal propagated.

Referring to (b) of FIG. 3, in the case of using the voltage coupling method, the first transmission line 150 is a transmission line having a characteristic impedance Z ₀ and an electrical length of 90°+θ°, and the third transmission line 162 is a transmission line having an electrical length θ _offset ° and having a characteristic impedance Z _opt , and a fourth transmission line 164 connected in series with the third transmission line 162 is a transmission line having a characteristic impedance Z ₀ and an electrical length of 90 ° - θ ° , and the compensation transmission line 170 is a transmission line having an electrical length of 180 ° + θ _PM °.

Here, θ° may be differently determined according to the required degree of power backoff.

As a result, the current or voltage is combined with the required phase difference in the power combiner, and the required load impedance modulation is accurately implemented. The power combiner assumes a lossless combiner.

4 is a conceptual diagram of an impedance transformer using two transmission lines connected in series.

Two transmission lines connected in series are a transmission line with electrical length of 90° each having characteristic impedance Z ₀ *k ^0.5 and a transmission line with electrical length of 90° with characteristic _impedance Z ₀ . Convert the impedance to k*Z _L at the input with k. The impedance transformer as shown in FIG. 4 can also be configured as a transmission line equivalent circuit using lumped elements and distributed elements.

5 is a conceptual diagram of an outphasing Doherty power amplifier including an impedance transformer according to another embodiment of the present invention.

5(a) is a conceptual diagram illustrating a current coupling method of an outphasing Doherty power amplification device according to an embodiment of the present invention, and FIG. 5(b) is an outphasing Doherty power according to an embodiment of the present invention. It is a conceptual diagram explaining the voltage coupling method of the amplification device.

Since the embodiment of FIG. 5 has an impedance transformer added to the embodiment of FIG. 3, detailed descriptions of common components are omitted.

When R _opt is a high or low value that is difficult to implement directly in practice, the Doherty power amplification device structure can be used by adding an impedance transformer circuit to expand or reduce the impedance at a constant rate.

In addition, since there may be a difference between the optimal load impedances of the main amplifier and the auxiliary amplifier under different actual bias conditions of the same maximum output, an impedance transformer circuit is added to the first transmission line 150 and the second transmission line 160 so that the first transmission line 150 and the second transmission line 160 are The impedance R _opt seen at the input terminal of the transmission line 150 is converted into the optimum impedance R _{opt_c} required for the output terminal of the main amplifier 120, and the impedance R _opt seen at the input terminal of the fourth transmission line 164 is converted to the output terminal of the auxiliary amplifier 130. It can be converted to the required optimum impedance R _{opt_pf} . Thus, the main amplifier 120 and the auxiliary amplifier 130 operate under optimal operating conditions through the first transmission line 150 and the second transmission line 160 . The output of the first transmission line 150 and the output of the second transmission line 160 thus output are combined by the first power combiner 140 .

6 shows a method of modulating the load impedance of the current coupling method of the outphasing Doherty power amplifier of FIG. 3 according to an embodiment of the present invention, and FIG. 6 (a) shows a method in a low output power region (LP operation) The load impedance of the outphasing Doherty power amplification device is shown, and FIG. 6(b) shows the load impedance of the outphasing Doherty power amplification device in a high output power region (HP operation).

Referring to (a) of FIG. 6, in a low output power region, that is, when the power corresponding to the first RF signal is less than the threshold value, since the auxiliary amplifier 130 is turned off, the auxiliary amplifier 130 There is no output current component, and the output stage impedance becomes infinite.

The third transmission line 162 has an electrical length of θ _offset °, and the fourth transmission line has an electrical length of 180°-θ°. The third transmission line 162 and the fourth transmission line 164 connected in series are connected in parallel with the load R _L of the output terminal of the power combiner. If the conditions of Equation 2 and Equation 3 are satisfied, an impedance of (G _L +jB) ^-1 is provided from the input terminal of the power combiner connected to the first transmission line through the first transmission line 150. At the output of the main amplifier 120, it is converted to a load impedance of kR _opt .

[Equation 2]

[Equation 3]

where k is the load impedance modulation ratio.

Referring to (b) of FIG. 6, in a high output power region, the power corresponding to the first RF signal is greater than the threshold, and the first impedance seen from one input end of the power combiner and the second impedance seen from the other input end of the power coupler are different. are different, and the first impedance and the second impedance are complex conjugate numbers. For example, the main amplifier 120 and the auxiliary amplifier 130 output the same power and combine currents with different phases, so that (G _L/2 +jB _L ) ^-1 and (G The complex conjugated load impedance of _L/2- jB _L ) ^-1 is shown.

[Equation 4]

If the condition of Equation 4 is satisfied, (G _L/2 +jB _L ) ^-1 load impedance is modulated to the load impedance R _opt at the output terminal of the main amplifier 120 through the first transmission line 150, ( The load impedance of G _L/2- jB _L ) ^-1 is converted to 180°- θ ° through the fourth transmission line 164 and modulated into the load impedance of R _opt at the output terminal of the auxiliary amplifier 130. The relationship between the backoff power and the load impedance modulation ratio and structures such as Equations 2, 3, and 4 are summarized as follows. Here, α is the ratio between the transmission line characteristic impedance and the optimum load impedance R _opt .

Also for compensating the phase difference between the main and auxiliary amplifiers.

When the condition is established, accurate load impedance modulation occurs. That is, tan (θ _PM °) for the phase (θ _PM °) corresponding to the compensation transmission line 170 and tan (θ °) for the phase (θ °) corresponding to the first transmission line 150 is proportional to

인 경우 높은 전력 영역에서 및 낮은 전력 영역에서의 임피던스 변조 동작 대역폭은 평행하게 되며, 아웃페이징 도허티 전력 증폭 장치 구조의 전체 임피던스 변조 동작 대역폭을 최대화할 수 있다.It is possible to adjust the impedance modulation operation bandwidth in a high power area and the impedance modulation operation bandwidth in a low power area according to the ratio α between the characteristic impedance of the transmission line and _Rop . only

In this case, impedance modulation operation bandwidths in the high power area and in the low power area are parallel, and the total impedance modulation operation bandwidth of the outphasing Doherty power amplifier structure can be maximized.

7 illustrates a method of modulating a load impedance of an outphasing Doherty power amplifier of a voltage coupling method according to an embodiment of the present invention.

(a) of FIG. 7 shows the load impedance of the outphasing Doherty power amplification device in the low output power region (LP operation), and FIG. 7 (b) shows the outphasing Doherty power amplification device in the high output power region (HP operation). represents the load impedance of Impedance conversion is similar to the description of FIG. 6, so a detailed description thereof will be omitted.

8 shows the load impedance of an outphasing Doherty power amplifier according to an embodiment of the present invention. 8(a) is a graph showing the load impedance of the outphasing Doherty power amplification device, and FIG. 8(b) is a Smith chart showing the load impedance of the auxiliary amplifier output stage of the outphasing Doherty power amplification device.

As shown in FIG. 8, as the output power increases, the main amplifier is modulated from the load impedance of kR _opt to the load impedance of R _opt , and the auxiliary amplifier is modulated from the infinite load impedance to the load impedance of kR _opt . there is.

9 is a graph showing Power Added Efficiency (PAE) according to power of an output signal of an outphasing Doherty power amplifier according to an embodiment of the present invention.

As shown in the simulation results shown in FIG. 9, the outphasing Doherty power amplifier according to an embodiment of the present invention has a backoff region of about 6 dB when the load impedance modulation ratio k is 2, and the modulation ratio k is 3 It can be seen that the back-off area is about 7 dB when the modulation ratio k is 4 and the back-off area is about 9 dB when the modulation ratio k is 4. That is, it can be seen that as the modulation ratio k increases, the backoff region with improved efficiency expands.

It can be seen that the load impedance modulation ratio can be easily changed by the outphasing Doherty power amplification device according to an embodiment of the present invention, whereby the back-off region with improved efficiency is expanded by increasing the load impedance modulation ratio. there is.

The above description is merely an example of the technical idea of the present invention, and various modifications and variations can be made to those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed according to the claims below, and all technical ideas within the equivalent range should be construed as being included in the scope of the present invention.

110: power divider
120: main amplifier
130: auxiliary amplifier
140: power combiner
150: first transmission line
160: network
162: third transmission line
164: 4th transmission line
170: second transmission line

Claims (7)

A power divider for receiving the first RF signal and distributing it into a plurality of RF signals including a second RF signal and a third RF signal;
a main amplifier for amplifying the second RF signal;
an auxiliary amplifier for amplifying the third RF signal;
a power combiner combining the RF signal received from the main amplifier and the RF signal received from the auxiliary amplifier, converting the RF signal into one RF signal, and outputting the converted signal;
a first transmission line disposed between the main amplifier and the power combiner; and
A second transmission line disposed between the auxiliary amplifier and the power combiner;
When the power corresponding to the first RF signal is greater than or equal to the threshold, the first input impedance measured at one input end of the power combiner connected to the first transmission line and the second input impedance measured at the other input end of the power combiner connected to the second transmission line A Doherty power amplifier, characterized in that the second input impedance is a complex conjugate with each other.
delete According to claim 1,
The second transmission line includes a plurality of transmission lines connected in series with each other, and the electrical length and characteristic impedance corresponding to each of the plurality of transmission lines are different from each other.
According to claim 1,
Doherty power amplifier, characterized in that a compensation transmission line for compensating for the phase difference between the main amplifier and the auxiliary amplifier is connected to the input terminal of the main amplifier.
According to claim 4,
Doherty, characterized in that tan (θ _PM °) for the phase (θ _PM °) corresponding to the compensation transmission line is proportional to tan (θ °) for the phase (θ °) corresponding to the first transmission line power amplification device.
A method for modulating a load impedance of a Doherty power amplifier using the Doherty power amplifier according to any one of claims 1 and 3 to 5,
receiving, by a power divider, the first RF signal and distributing it into a plurality of RF signals including a second RF signal and a third RF signal;
amplifying the second RF signal by a main amplifier;
modulating the impedance of the output terminal of the main amplifier with a first transmission line;
amplifying the third RF signal by an auxiliary amplifier;
modulating the impedance of the output terminal of the auxiliary amplifier with a second transmission line;
coupling the output RF signal of the first transmission line and the output RF signal of the second transmission line; and
Modulating the impedance of one input terminal and the impedance of the other input terminal of the power coupler according to the coupling ratio of the output RF signal of the first transmission line and the output RF signal of the second transmission line in the power combiner.
A method for modulating the load impedance of a Doherty power amplifier comprising a.
According to claim 6,
Compensating for a phase difference between a main amplifier and an auxiliary amplifier by receiving the second RF signal by a compensation transmission line
A method for modulating the load impedance of the Doherty power amplification device, characterized in that it further comprises.

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