Sequential power amplifier and its control method

Abstract

The present disclosure provides a sequential power amplifier that achieves phase distortion compensation using sequential operation. [Solution] The sequential power amplifier according to this disclosure comprises a main amplifier that performs signal amplification at a constant load regardless of the input level, and an auxiliary amplifier that performs signal amplification at high power output when the input level is above a predetermined level, and whose phase distortion characteristics are different from those of the main amplifier. The phase distortion characteristics of the main amplifier are inverse to those of the auxiliary amplifier.

Description

Technical Field

[0005] , ,

[0001] The present disclosure relates to a sequential power amplifier and a control method thereof.

Background Art

[0002] In recent years, high-performance amplifiers that combine technologies for efficiently amplifying signals, such as Doherty amplifiers, with distortion compensation technologies have been proposed. For example, Patent Document 1 discloses a Doherty amplifier in which a carrier amplifier and a peak amplifier having different AM-PM characteristics (amplitude-phase characteristics) are connected in parallel. The carrier amplifier is composed of LD-MOSFET, and the peak amplifier is composed of GaAsFET.

[0003] In the AM-PM characteristics of LD-MOSFET, the phase delay increases as the input power or output power increases, and in the AM-PM characteristics of GaAsFET, the phase advance increases as the input power or output power increases. That is, these two types of amplification elements have inverse characteristics in terms of AM-PM characteristics. In the Doherty amplifier of Patent Document 1, by using these two types of amplification elements as a carrier amplifier and a peak amplifier, respectively, the phase change of the AM-PM characteristics of the synthesized amplified signal is canceled out to reduce phase distortion. <​​​​​​​​​​​​​​​​​​​​​Sequential power amplifiers are known for their "sequential operation," where the auxiliary amplifier starts operating after the main amplifier has started. In sequential operation, only the main amplifier operates until the output power reaches its peak level, at which point both the main and auxiliary amplifiers begin operating. Unlike Doherty amplifiers, in sequential power amplifiers, the main amplifier operates under a constant load. Therefore, the main amplifier enters an overdrive state after reaching its peak level.

[0006] Patent Document 1 does not mention compensation for phase distortion (AM-PM characteristics) using sequential operation in such a sequential power amplifier.

[0007] The purpose of this disclosure is, in view of the above-mentioned problems, to provide a sequential power amplifier and a control method thereof that realizes phase distortion compensation using sequential operation. [Means for solving the problem]

[0008] The sequential power amplifier according to this disclosure comprises a main amplifier that performs signal amplification at a constant load regardless of the input level, and an auxiliary amplifier that performs signal amplification at high power output when the input level is above a predetermined level, and whose phase distortion characteristics differ from those of the main amplifier.

[0009] The control method for a sequential power amplifier according to this disclosure involves a main amplifier that amplifies the signal at a constant load regardless of the input level, and an auxiliary amplifier, whose phase distortion characteristics differ from those of the main amplifier, that amplifies the signal when the input level exceeds a predetermined level. [Effects of the Invention]

[0010] According to this disclosure, phase distortion compensation can be achieved using sequential operation. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example configuration of a sequential power amplifier related to this disclosure. [Figure 2] This figure shows an example of the efficiency characteristics of a sequential power amplifier with respect to output power. [Figure 3] This is a flowchart illustrating the operation of a sequential power amplifier. [Figure 4] This diagram shows the AM-PM characteristics of a sequential power amplifier. [Figure 5] This figure shows an example of the amplitude distortion and phase distortion characteristics with respect to output power of a comparative example sequential power amplifier using compound transistors. [Figure 6] This figure shows an example of the amplitude distortion and phase distortion characteristics with respect to output power of a comparative example sequential power amplifier using silicon-based transistors. [Figure 7] This diagram illustrates the amplitude distortion of a sequential power amplifier using compound transistors. [Figure 8] This diagram illustrates the phase distortion of a sequential power amplifier using compound transistors. [Modes for carrying out the invention]

[0012] Embodiments of this disclosure will be described in detail below with reference to the drawings. In each drawing, the same or corresponding elements are denoted by the same reference numerals, and redundant explanations will be omitted where necessary for clarity.

[0013] This disclosure relates to a phase distortion improvement technology for sequential power amplifiers, which are high-frequency amplifiers used in base stations and the like for wireless communication systems.

[0014] FIG. 1 is a diagram showing a configuration example of a sequential power amplifier according to the present disclosure. As shown in FIG. 1, the sequential power amplifier 10 includes a main amplifier 11, an auxiliary amplifier 12, a power distributor 13, and a power combiner 14. In FIG. 1, only the main components are shown for simplicity of explanation. The sequential power amplifier 10 may include a matching circuit or the like that matches the impedance between the input terminal IN and the power distributor 13 or the power combiner 14 and the output terminal OUT.

[0015] The sequential power amplifier 10 performs a "sequential operation" in which the auxiliary amplifier 12 operates after the main amplifier 11 operates. As the input / output power increases, the sequential operation switches from a state where only the main amplifier 11 operates and the auxiliary amplifier 12 stops to a state where both the main amplifier 11 and the auxiliary amplifier 12 operate.

[0016] In the sequential power amplifier 10, the main amplifier 11 operates up to the peak level at a constant load. After reaching the peak level, the main amplifier 11 enters an overdrive state. In the overdrive state, one or more transistors in the main amplifier 11 saturate.

[0017] The power distributor 13 distributes the input RF signal (hereinafter referred to as the input signal) to the main amplifier 11 and the auxiliary amplifier 12. The power distributor 13 is composed of a 1 / 4 wavelength transmission line, a 90° hybrid circuit, or the like for making the phase relationship of the output signals of the main amplifier 11 and the auxiliary amplifier 12 in-phase at the signal combining point of the power combiner 14.

[0018] The main amplifier 11 performs a signal amplification operation at a constant load regardless of the input level. An amplifier set to a bias condition such as class A, class AB, or class B is used for the main amplifier 11 so that it operates linearly.

[0019] The auxiliary amplifier 12 performs an amplification operation only when the input level is at or above a predetermined level. For the auxiliary amplifier 12, a Class-C biased amplifier is used so that it operates only at high output power.

[0020] Figure 2 is a diagram showing an example of the efficiency characteristic with respect to the output power of the sequential power amplifier. In Figure 2, the horizontal axis represents the output power, and the vertical axis represents the efficiency. As shown in Figure 2, the sequential power amplifier 10 can achieve high-efficiency operation in a region above the back-off level where the auxiliary amplifier 12 starts operating, for example, by operating the main amplifier 11 in Class-AB and the auxiliary amplifier 12 in Class-C. Here, the back-off represents the difference between the average output power and the saturation power. The back-off region indicates a region where the average output power is smaller compared to the saturation power.

[0021] The power combiner 14 combines the outputs of the main amplifier 11 and the auxiliary amplifier 12 and outputs them as an output RF signal (hereinafter referred to as the output signal). Specifically, when the auxiliary amplifier 12 performs an amplification operation, the power combiner 14 outputs an output signal obtained by adding the output from the auxiliary amplifier 12 to the output from the main amplifier 11 to the output terminal OUT.

[0022] Here, the operation of the sequential power amplifier 10 will be described with reference to Figure 3. Figure 3 is a flowchart for explaining the operation of the sequential power amplifier 10. As shown in Figure 3, an input signal is applied to the input terminal IN (S1). The input signal input from the input terminal IN is distributed by the power divider 13 and input to the main amplifier 11 and the auxiliary amplifier 12.

[0023] The main amplifier 11 performs an amplification operation on the distributed signal until the input signal reaches the peak level at a constant load (S2). Then, only the power of the main amplifier 11 is output from the output terminal OUT (S3). After that, after the input level rises and reaches the peak level, the main amplifier 11 reaches the saturation power (S4). Thus, in a region where the input level is lower than the back-off level, the auxiliary amplifier 12 does not operate, and only the main amplifier 11 operates.

[0024] When the signal level is above the backoff level, the auxiliary amplifier 12 amplifies the distributed signal (S5). The power combiner 14 combines the outputs of the main amplifier 11 and the auxiliary amplifier 12 (S6). That is, when the signal level is above the backoff level, the output from the auxiliary amplifier 12 is added to the output of the main amplifier 11.

[0025] On the other hand, in a Doherty amplifier, the carrier amplifier maintains high-efficiency amplification operation through load modulation while the input power is between the backoff level and the peak level. Above the backoff level, the outputs of the carrier amplifier and the peak amplifier are combined. This operation of a Doherty amplifier differs from the operation of the sequential power amplifier 10 of this disclosure.

[0026] <Comparative Example> Now, let's discuss the sequential power amplifier used as a comparative example. In sequential power amplifiers, the same type of semiconductor device is typically used for the main amplifier and auxiliary amplifier, which are usually arranged in parallel. However, in sequential power amplifiers using the same type of semiconductor device, the amplifier is set to a low bias point in Class C, which leads to a problem where the AM-AM characteristics (Amplitude Modulation - Amplitude Modulation: input power - output power characteristics, also known as "amplitude distortion characteristics") and AM-PM characteristics (Amplitude Modulation - Phase Modulation: output power - output phase characteristics, also known as "phase distortion characteristics") deteriorate, and the linearity of the input and output signals is no longer maintained.

[0027] Figure 5 shows an example of the amplitude distortion and phase distortion characteristics with respect to output power of a comparative example sequential power amplifier using compound transistors. In this comparative example, compound transistors are used for both the main amplifier and the auxiliary amplifier. Compound transistors used as high-frequency amplification elements include gallium arsenide FETs (GaAs Field Effect Transistors: GaAsFETs) and gallium nitride FETs (GaN Field Effect Transistors: GaNFETs).

[0028] Figure 6 shows an example of the amplitude distortion and phase distortion characteristics with respect to output power of a comparative example sequential power amplifier using silicon-based transistors. In this comparative example, silicon-based transistors are used for both the main amplifier and the auxiliary amplifier. One example of a silicon-based transistor used as a high-frequency amplification element is the laterally diffused metal-oxide-semiconductor field effect transistor (LD-MOSFET).

[0029] In Figures 5 and 6, the horizontal axis represents output power, and the vertical axis represents amplitude ratio and phase difference. The amplitude ratio represents the amplitude ratio (gain) of the input signal and the output signal, and the phase difference represents the phase lag or lead of the output signal relative to the input signal. As shown in Figures 5 and 6, when the output power of the main amplifier saturates and the auxiliary amplifier operates, a discontinuity in gain and phase occurs, for example, at the switching point between an amplifier biased to Class AB and an amplifier biased to Class C. This discontinuity may include cases where the amount of change in gain or phase relative to the output power exceeds a predetermined amount. For example, as shown in Figures 5 and 6, even if the gain and phase change continuously at the amplifier switching point, a sharp change is also included in the definition of "discontinuity."

[0030] Here, we will explain the amplitude distortion and phase distortion of a sequential power amplifier in more detail, using an example where both the main amplifier and auxiliary amplifier are composed of compound transistors. Figures 7 and 8 illustrate the characteristics of the sequential power amplifier using the compound transistors shown in Figure 5.

[0031] Figure 7 illustrates the amplitude distortion of a sequential power amplifier using compound transistors. In Figure 7, the horizontal axis represents output power, and the vertical axis represents the amplitude ratio.

[0032] As described above, in a sequential power amplifier, the auxiliary amplifier starts operating after the main amplifier has started. As shown in Figure 7, during the period when only the main amplifier is operating, the gain of the sequential power amplifier after sequential operation does not change at low output levels, according to the AM-AM characteristics of the main amplifier, and decreases above a certain output level. When the input level increases further and the auxiliary amplifier starts operating after the main amplifier has started, the gain of the sequential power amplifier after sequential operation changes according to the AM-AM characteristics of the auxiliary amplifier. At the output power when the auxiliary amplifier is operating, the amplitude of the auxiliary amplifier is lower than the amplitude of the main amplifier, but as the output power increases further, the amplitude of the auxiliary amplifier becomes higher than the amplitude of the main amplifier. After that, the amplitude of the auxiliary amplifier gradually decreases. Therefore, a discontinuity in gain occurs when switching between the main amplifier and the auxiliary amplifier.

[0033] Comparing the example using silicon-based transistors in Figure 6 with the example using compound-based transistors in Figure 7, the amplitude distortion in both examples exhibits a gain reduction in the gain suppression direction due to the characteristics of sequential power amplifiers. In other words, regardless of the material of the amplifying elements used in the main amplifier and auxiliary amplifier, the gain is suppressed at the saturation level, so there is no significant difference in the amplitude distortion during synthesis.

[0034] Figure 8 illustrates the phase distortion of a sequential power amplifier using compound transistors. In Figure 8, the horizontal axis represents output power, and the vertical axis represents the phase difference. As shown in Figure 8, during the period when only the main amplifier is operating, the phase after sequential operation of the sequential power amplifier does not change at low output levels, according to the AM-PM characteristics of the main amplifier, and advances above a certain output level. When the input level increases and the auxiliary amplifier operates after the main amplifier, the phase after sequential operation of the sequential power amplifier advances further according to the AM-PM characteristics of the auxiliary amplifier. At the output power when the auxiliary amplifier is operating, the phase advance of the auxiliary amplifier is greater than the phase advance of the main amplifier, but as the output power increases further, the phase advance of the auxiliary amplifier becomes smaller than the phase advance of the main amplifier. After that, the phase advance of the auxiliary amplifier gradually increases. Therefore, a phase discontinuity occurs when switching between the main amplifier and the auxiliary amplifier.

[0035] In contrast, as shown in Figure 6, in a sequential power amplifier using silicon transistors, during the period when only the main amplifier is operating, the phase after sequential operation of the sequential power amplifier does not change at low output levels, depending on the AM-PM characteristics of the main amplifier, but lags above a certain output level. When the output level increases further and the auxiliary amplifier operates after the main amplifier, the phase after sequential operation of the sequential power amplifier lags even further, depending on the AM-PM characteristics of the auxiliary amplifier.

[0036] Referring to the example using a silicon-based transistor in Figure 6 and the example using a compound-based transistor in Figure 8, it can be seen that the phase can fluctuate in either the positive or negative direction from the linear phase region, depending on the semiconductor properties of the amplifying element. In other words, the AM-PM characteristics of a silicon-based transistor are the opposite of those of a compound-based transistor.

[0037] Thus, because the phase distortion of a sequential power amplifier arises from the combination of two amplifying elements, the main amplifier and the auxiliary amplifier, the phase lag or lead does not simply increase with increasing output power, but rather the phase change becomes complex. As shown in Figures 5 and 6, the curve showing the phase distortion characteristics becomes discontinuous, which presents a problem in distortion compensation methods, such as those using polynomial approximation for inverse compensation, as the approximation becomes insufficient. As a result, the adjacent channel leakage ratio (ACLR) deteriorates, and the error vector magnitude (EVM), which is the error in phase and amplitude, also deteriorates.

[0038] <Embodiment> In this embodiment, while taking advantage of the characteristics of sequential operation, the amplification elements used in the main amplifier 11 and the auxiliary amplifier 12 are each characterized by opposite AM-PM characteristics. Of the amplification elements whose phase distortion characteristics increase with respect to the phase in the linear region and those whose phase distortion characteristics decrease, one is used in the main amplifier 11 and the other in the auxiliary amplifier 12. That is, one of the main amplifier 11 and the auxiliary amplifier 12 will experience a larger phase lag as the input power or output power increases, while the other will experience a larger phase lead as the input power or output power increases.

[0039] Figure 4 shows the AM-PM characteristics of a sequential power amplifier 10 that uses a compound transistor as the main amplifier 11 and a silicon transistor as the auxiliary amplifier 12. For example, a GaAsFET can be used as the main amplifier 11 and an LD-MOSFET as the auxiliary amplifier 12. In Figure 4, the horizontal axis represents output power and the vertical axis represents phase difference.

[0040] As shown in Figure 4, the AM-PM characteristics of the main amplifier 11, which uses compound transistors, and the auxiliary amplifier 12, which uses silicon transistors, cancel each other out. In other words, the phase fluctuation curve associated with the increase in output power can be made as discontinuous as possible. This makes it possible to realize a sequential power amplifier 10 in which known distortion compensation is easily effective.

[0041] Furthermore, since the main amplifier 11 has operating characteristics that do not perform load modulation, it can maintain a harmonic matching state across the power dynamic range. For this reason, it is also possible to use a Class F amplifier element that performs Class F operation or inverse Class F operation as the main amplifier 11. In Class F operation, even-order harmonics are short-circuited and odd-order harmonics are open-circuited, while in inverse Class F operation, odd-order harmonics are short-circuited and even-order harmonics are open-circuited.

[0042] This makes it possible to improve efficiency from the backoff level to the peak level compared to a Doherty amplifier using, for example, a Class B biased amplifier. However, in a Doherty amplifier, because the load fluctuates from the backoff level to the peak level, it is more difficult to use a Class F amplifier with harmonic matching compared to a sequential amplifier.

[0043] As described above, in this embodiment, the linearity of phase distortion can be improved by operating the main amplifier 11 under a constant load, and then, during sequential operation in which the auxiliary amplifier 12 operates after the main amplifier 11 reaches a saturation level, compensating for the AM-PM characteristics of the main amplifier 11 with the AM-PM characteristics of the auxiliary amplifier 12.

[0044] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0045] Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps shown in any of the drawings may be changed as appropriate.

[0046] Some or all of the above embodiments may also be described as follows, but are not limited to the following: (Note 1) A main amplifier that performs signal amplification at a constant load regardless of the input level, An auxiliary amplifier that performs signal amplification when the input level is above a predetermined level and has phase distortion characteristics different from those of the main amplifier, Equipped with, Sequential power amplifier. (Note 2) The phase distortion characteristics of the main amplifier are inverse to those of the auxiliary amplifier. The sequential power amplifier described in Appendix 1. (Note 3) Of the amplification elements using compound transistors and amplification elements using silicon transistors, one is used in the main amplifier and the other is used in the auxiliary amplifier. The sequential power amplifier described in Appendix 1. (Note 4) The aforementioned silicon-based transistor is an LD-MOSFET. The aforementioned compound transistor is a GaNFET or a GaAsFET. The sequential power amplifier described in Appendix 3. (Note 5) The aforementioned main amplifier is a Class F amplification element. The sequential power amplifier described in Appendix 1. (Note 6) A power distributor that splits an input signal received at an input terminal into two signals, outputs one of the two signals to the main amplifier, and outputs the other signal to the auxiliary amplifier, When the auxiliary amplifier performs amplification, a power combiner outputs an output signal to the output terminal that is the sum of the output from the main amplifier and the output from the auxiliary amplifier, Equipped with, The sequential power amplifier described in Appendix 1. (Note 7) The main amplifier performs signal amplification at a constant load regardless of the input level. An auxiliary amplifier whose phase distortion characteristics differ from those of the main amplifier, which performs signal amplification when the input level exceeds a predetermined level (high power output). Control methods for sequential power amplifiers. (Note 8) The input signal received at the input terminal is split into two signals, one of which is output to the main amplifier, and the other signal is output to the auxiliary amplifier. When the auxiliary amplifier performs amplification, it outputs an output signal to the output terminal that is the sum of the output from the main amplifier and the output from the auxiliary amplifier. The control method for the sequential power amplifier described in Appendix 7.

[0047] Some or all of the elements (e.g., configuration and function) described in Appendices 2 to 6 that are dependent on Appendice 1 may also be dependent on Appendice 7 in the same manner as in Appendices 2 to 6. Some or all of the elements described in any appendice may be applicable to various hardware, software, recording means, systems, and methods for recording software. [Explanation of Symbols]

[0048] 10 Sequential Power Amplifier 11 Main amplifier 12 Auxiliary Amplifier 13 Power divider 14 Power combiner IN input terminal OUT output terminal

Claims

1. A main amplifier that performs signal amplification at a constant load regardless of the input level, An auxiliary amplifier that performs signal amplification when the input level is above a predetermined level and has phase distortion characteristics different from those of the main amplifier, Equipped with, Sequential power amplifier.

2. The phase distortion characteristics of the main amplifier are inverse to those of the auxiliary amplifier. The sequential power amplifier according to claim 1.

3. Of the amplification elements using compound transistors and amplification elements using silicon transistors, one is used in the main amplifier and the other is used in the auxiliary amplifier. The sequential power amplifier according to claim 1.

4. The aforementioned silicon-based transistor is an LD-MOSFET. The aforementioned compound transistor is a GaNFET or a GaAsFET. The sequential power amplifier according to claim 3.

5. The main amplifier is a Class F amplifier. The sequential power amplifier according to claim 1.

6. A power distributor that splits an input signal received at an input terminal into two signals, outputs one of the two signals to the main amplifier, and outputs the other signal to the auxiliary amplifier, When the auxiliary amplifier performs amplification, a power combiner outputs an output signal to the output terminal that is the sum of the output from the main amplifier and the output from the auxiliary amplifier, Equipped with, The sequential power amplifier according to claim 1.

7. The main amplifier performs signal amplification at a constant load regardless of the input level. An auxiliary amplifier whose phase distortion characteristics differ from those of the main amplifier, which performs signal amplification when the input level exceeds a predetermined level (high power output). Control methods for sequential power amplifiers.

8. The input signal received at the input terminal is split into two signals, one of which is output to the main amplifier, and the other signal is output to the auxiliary amplifier. When the auxiliary amplifier performs amplification, it outputs an output signal to the output terminal that is the sum of the output from the main amplifier and the output from the auxiliary amplifier. A method for controlling a sequential power amplifier according to claim 7.

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