Wideband doherty power amplifier

Abstract

The present invention provides a wideband Doherty power amplifier, comprising a main circuit power amplifier, an auxiliary circuit power amplifier, a quarter wavelength transmission line, a transformer, an output matching network, an input matching network, and a phase shift network. The input matching network and the phase shift network receive an input signal and generate a main circuit power amplifier signal and an auxiliary circuit power amplifier signal having a phase difference of 90°. An output of the auxiliary circuit power amplifier is connected to the quarter wavelength transmission line, and the auxiliary circuit power amplifier signal is received by the auxiliary circuit power amplifier and is connected to a first input end of the transformer by means of the quarter wavelength transmission line. The main power amplifier receives the main circuit power amplifier signal and outputs same to a second input end of the transformer. An output of the transformer is connected to an input end of the output matching network, and an amplified signal is outputted by means of the output matching network.

Description

Broadband Doherty Power Amplifier

[0001] This application claims priority to Chinese Patent Application No. 202410177987.8 filed on February 8, 2024, and the contents of the above-mentioned Chinese patent application disclosure are hereby incorporated by reference in their entirety as part of this application. Technical Field

[0002] The present invention relates to radio frequency front-end integrated circuit design, and more particularly to a transformer-based broadband Doherty power amplifier. Background Art

[0003] With the rapid development of wireless communication technology, modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) and Quadrature Amplitude Modulation (QAM) are widely used in wireless communication systems to achieve higher spectrum utilization and greater data transmission capacity. However, this also introduces the problem of high Peak-to-Average Power Ratio (PAPR), thus posing a significant challenge to the design of RF power amplifiers. High PAPR means that the power amplifier needs to operate in the power back-off region, which reduces the efficiency of the transmitter.

[0004] The Doherty power amplifier is a way to improve the back-off efficiency of a power amplifier. Figure 1 shows the structure of a traditional Doherty power amplifier. Referring to Figure 1, the Doherty power amplifier includes two power amplifiers: a main power amplifier and an auxiliary power amplifier. Typically, the main power amplifier is biased in Class AB, while the auxiliary power amplifier is biased in Class C. The transmission line output by the main power amplifier is a quarter-wavelength line with a characteristic impedance of Ropt (Ropt is the optimal matching point impedance of the main and auxiliary power amplifiers) to achieve impedance transformation. The output matching network matches the impedance from 50 ohms to Ropt / 2, and the phase converter at the input is used to compensate for the phase difference between the main and auxiliary paths. Summary of the Invention

[0005] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, comprising: a main power amplifier and an auxiliary power amplifier, a quarter-wavelength transmission line, a transformer, an output matching network, an input matching network and a phase shift network, wherein the input matching network and the phase shift network receive an input signal and generate a main power amplifier signal and an auxiliary power amplifier signal with a 90° phase difference; the output of the auxiliary power amplifier is connected to the quarter-wavelength transmission line, the auxiliary power amplifier signal is received by the auxiliary power amplifier and connected to a first input end of the transformer via the quarter-wavelength transmission line; the main power amplifier receives the main power amplifier signal and outputs it to a second input end of the transformer; the output of the transformer is connected to the input end of the output matching network, and the amplified signal is output via the output matching network.

[0006] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the main power amplifier is biased as a class AB power amplifier.

[0007] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the auxiliary path power amplifier is biased as a class C power amplifier.

[0008] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, further comprising a main impedance matching network connected between an output terminal of the main power amplifier and a second input terminal of the transformer.

[0009] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the main power amplifier and the auxiliary power amplifier are configured to have an optimal matching point impedance Ropt.

[0010] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the characteristic impedance of the quarter-wavelength transmission line is configured as an optimal matching point impedance Ropt.

[0011] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the input impedance of the output matching network is configured to be twice the optimal matching point impedance Ropt, and the main path and the auxiliary path achieve power synthesis and impedance modulation effects through the transformer.

[0012] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the broadband Doherty power amplifier is configured as a power amplifier for an N77 or N79 frequency band.

[0013] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the broadband Doherty power amplifier is implemented by one of HBT, CMOS, BJT, BiCMOS, and GaN processes.

[0014] According to one aspect of the present invention, a broadband Doherty power amplifier is provided, wherein the main path power amplifier and the auxiliary path power amplifier are configured as power amplifiers with a source-common-gate structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a block diagram showing a conventional Doherty power amplifier;

[0016] FIG2 is a schematic diagram showing the operating principle of a Doherty power amplifier in a low power region;

[0017] FIG3 is a schematic diagram showing the operating principle of a Doherty power amplifier in a high power region;

[0018] FIG4 is a schematic diagram showing an efficiency curve of a Doherty power amplifier;

[0019] FIG5 is a schematic diagram showing a Doherty power amplifier according to an embodiment of the present invention;

[0020] 6 is a schematic diagram showing the working principle of the low power region of the Doherty power amplifier according to an embodiment of the present invention;

[0021] FIG7 is a schematic diagram showing the operating principle of a Doherty power amplifier in a high power region according to an embodiment of the present invention; and

[0022] FIG8 is a schematic diagram showing a Doherty power amplifier according to another embodiment of the present invention. DETAILED DESCRIPTION

[0023] Before proceeding with the detailed description below, it may be helpful to set forth the definitions of certain words and phrases used throughout this patent document. The terms "couple," "connect," and their derivatives refer to any direct or indirect communication between two or more elements, regardless of whether those elements are in physical contact with each other. The terms "transmit," "receive," and "communicate," and their derivatives, encompass both direct and indirect communication. The terms "include," "comprise," and their derivatives, mean including, but not limited to. The term "or" is inclusive, meaning and / or. The phrase "associated with..." and its derivatives mean including, included within, interconnected, containing, contained within, connected or connected with, coupled or coupled with, communicate with, cooperate with, intertwine, juxtapose, approach, bound or bound with, have, have an attribute of, have a relationship with, or have a relationship with, etc. The term "controller" refers to any device, system, or portion thereof that controls at least one operation. Such a controller may be implemented using hardware, or a combination of hardware and software and / or firmware. The functionality associated with any particular controller may be centralized or distributed, whether local or remote. The phrase "at least one of," when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one of the items in the list may be needed. For example, "at least one of A, B, and C" includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A, B, and C.

[0024] Definitions for other specific words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior and future uses of such defined words and phrases.

[0025] In this patent document, the application combination of circuit blocks and the division of sub-circuit blocks are only for illustration. Without departing from the scope of the present disclosure, the application combination of circuit blocks and the division of sub-circuit blocks can have different ways.

[0026] FIG1 through FIG8 discussed below and the various embodiments used to describe the principles of the present disclosure in this patent document are intended only as illustrations and should not be construed in any way to limit the scope of the present disclosure. Those skilled in the art will appreciate that the principles of the present disclosure can be implemented in any suitably arranged system or device.

[0027] FIG. 2 is a schematic diagram illustrating the operating principle of a Doherty power amplifier in a low power region.

[0028] The Doherty power amplifier can operate in a low power region and a high power region. Before the auxiliary power amplifier is turned on, the Doherty power amplifier can be considered to operate in the low power region.

[0029] Figure 2 shows a Doherty power amplifier operating in the low-power region. Because the auxiliary power amplifier is biased in Class C, when the Doherty power amplifier is configured to operate in the low-power region, the signal is completely transmitted by the main power amplifier. Due to the quarter-wavelength line, the main power amplifier's output impedance is 2Ropt. Passing through the quarter-wavelength line, its output impedance is Ropt / 2. Since the auxiliary power amplifier is not operating at this time, the input impedance of the output matching network is Ropt / 2.

[0030] FIG3 is a schematic diagram illustrating the operating principle of a Doherty power amplifier in a high power region.

[0031] When the Doherty power amplifier is configured to operate in the high-power region, both the main and auxiliary power amplifiers are enabled. Taking into account the load-pull effect, the output impedance of both amplifiers is Ropt. Passing through the quarter-wavelength line, the output impedance of the quarter-wavelength line is Ropt, and therefore, the input impedance of the output matching network is Ropt / 2.

[0032] The Doherty power amplifier can achieve 6dB back-off when transitioning from the high-power saturation region to the low-power saturation region. Since only the main power amplifier works in the low-power region and the output impedance is as high as 2Ropt, the back-off efficiency can be improved.

[0033] FIG. 4 is a diagram illustrating an efficiency curve of a Doherty power amplifier.

[0034] 4 , the efficiency of the Doherty power amplifier is improved relative to that of a conventional class AB power amplifier (general class AB power amplifier) ​​at a 6 dB back-off point.

[0035] However, the traditional Doherty power amplifier architecture, in which a quarter-wavelength line is introduced into the main power amplifier path to achieve impedance transformation, also introduces matching network bandwidth issues. As shown in Figure 2, in the low-power region, the impedance transformation ratio of the quarter-wavelength line in the main power amplifier path is as high as 4 (from 2Ropt to Ropt / 2), thus achieving high back-off efficiency only within a narrow bandwidth. Furthermore, in the Doherty power amplifier architectures shown in Figures 2 and 3, the output matching network needs to achieve an impedance transformation from 50 ohms to Ropt / 2, which also limits the operating bandwidth of the entire architecture.

[0036] In view of the bandwidth problem of the traditional Doherty power amplifier, the present invention proposes a novel transformer-based Doherty power amplifier to achieve high back-off efficiency within a wide bandwidth.

[0037] FIG5 is a schematic diagram illustrating a Doherty power amplifier according to an embodiment of the present invention.

[0038] The Doherty power amplifier according to the embodiment of the present invention includes a main power amplifier, an auxiliary power amplifier, a quarter-wavelength transmission line, a transformer, an output matching network, an input matching network and a phase shift network.

[0039] Referring to Figure 5, a signal is input from the input terminal and provided to the input matching network and phase shift network. The input matching network and phase shift network generate two signals (a main power amplifier signal and an auxiliary power amplifier signal) with a 90° phase difference, and these signals are provided to the main power amplifier and the auxiliary power amplifier, respectively. The output of the auxiliary power amplifier is connected to a quarter-wavelength transmission line and then connected to the first input terminal of the transformer via the quarter-wavelength transmission line. The output of the main power amplifier is connected to the second input terminal of the transformer. The output of the transformer is connected to the input terminal of the output matching network, and the amplified signal is output through the output matching network.

[0040] Compared with the traditional Doherty power amplifier, the Doherty power amplifier according to the embodiment of the present invention adjusts the output matching network to reduce the impedance transformation ratio of the output matching network. It not only introduces a transformer but also places a quarter-wavelength transmission line in the auxiliary path.

[0041] FIG6 is a schematic diagram illustrating the operating principle of a Doherty power amplifier in a low power region according to an embodiment of the present invention.

[0042] FIG6 shows a Doherty power amplifier according to an embodiment of the present invention. Because the auxiliary power amplifier is biased in Class C, when the Doherty power amplifier is configured to operate in the low-power region, the signal is entirely transmitted by the main power amplifier. Due to the interaction of the quarter-wavelength line and the transformer, the output impedance at the main power amplifier is 2Ropt. Furthermore, because the auxiliary power amplifier is not configured to operate, the output of the quarter-wavelength line connected to the auxiliary power amplifier is short-circuited, resulting in a load impedance of 0. Since the output of the quarter-wavelength transmission line is connected to the first input of the transformer, the output of the main power amplifier is connected to the second input of the transformer, and the output of the transformer is connected to the input of the output matching network, the output matching network is adjusted so that the impedance seen by the transformer port connected to the output matching network is 2Ropt.

[0043] FIG. 7 is a schematic diagram illustrating the operating principle of a Doherty power amplifier in a high power region according to an embodiment of the present invention.

[0044] When the Doherty power amplifier is configured for high power operation, both the main and auxiliary power amplifiers are enabled. Taking load pull into account, the output impedance of both amplifiers is Ropt. Passing through the quarter-wavelength transmission line, the output impedance of the quarter-wavelength transmission line is Ropt. Because the output of the quarter-wavelength transmission line is connected to the first input of the transformer, the output of the main power amplifier is connected to the second input of the transformer, and the output of the transformer is connected to the input of the output matching network, the output matching network is adjusted so that the impedance seen by the transformer port connected to the output matching network is 2Ropt.

[0045] The back-end matching network of a traditional Doherty amplifier needs to realize impedance transformation from 50 ohms to Ropt / 2. However, the Doherty power amplifier according to an embodiment of the present invention reduces the impedance transformation ratio of the back-end matching network (from 50 ohms to 2Ropt) while realizing the function of the Doherty power amplifier. At the same time, the quarter-wavelength line is placed in the auxiliary path to avoid the problem of large impedance transformation in the low-power area affecting the structural bandwidth, thereby achieving the goal of improving the back-off efficiency in a broadband range.

[0046] FIG8 is a schematic diagram showing a Doherty power amplifier according to another embodiment of the present invention.

[0047] The Doherty power amplifier according to the embodiment of the present invention includes a main power amplifier and an auxiliary power amplifier, a quarter-wavelength transmission line, a transformer, an output matching network, an input matching network and a phase shift network, and a main impedance matching network.

[0048] Referring to Figure 8, a signal is input from the input terminal and provided to the input matching network and phase shift network. The input matching network and phase shift network generate two signals (the main power amplifier signal and the auxiliary power amplifier signal) with a 90° phase difference, and these signals are provided to the main power amplifier and the auxiliary power amplifier respectively. The output of the auxiliary power amplifier is connected to a quarter-wavelength transmission line and then connected to the first input terminal of the transformer via the quarter-wavelength transmission line. The output of the main power amplifier is connected to the second input terminal of the transformer through the main impedance matching network. The output of the transformer is connected to the input terminal of the output matching network, and the amplified signal is output through the output matching network.

[0049] Compared with the traditional Doherty power amplifier, the Doherty power amplifier according to an embodiment of the present invention adds a main impedance matching network after the main power amplifier, which can adjust the output impedance of the main power amplifier in the low power area, so that the main power amplifier enters the saturation area in advance, thereby achieving a greater (greater than 6dB) back-off power efficiency improvement.

[0050] According to an embodiment of the present invention, the main impedance matching network may be configured as a T-type impedance matching network or a π-type impedance matching network.

[0051] According to the embodiment of the present invention, any transistor made by HBT, CMOS, BJT, BiCMOS, or GaN processes may be used to implement the main power amplifier and the auxiliary power amplifier according to the embodiment of the present invention.

[0052] The Doherty power amplifier according to an embodiment of the present invention can be applied to 3G / 4G / 5G communication systems. For example, the Doherty power amplifier can be configured as a power amplifier for the N77 or N79 frequency band.

[0053] According to an embodiment of the present invention, the main power amplifier and the auxiliary power amplifier can be configured as an amplifier structure applied to a 3G / 4G / 5G communication system. For example, the main power amplifier and the auxiliary power amplifier can be configured as power amplifiers with a common source and common gate structure to increase circuit isolation and circuit gain.

[0054] Although the present disclosure has been described with exemplary embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

[0055] Any description in the present invention should not be construed as implying that any particular element, step, or function is essential to be included in the scope of the claims. The scope of the patented subject matter is defined solely by the claims.

Claims

1. A broadband Doherty power amplifier, comprising a main power amplifier and an auxiliary power amplifier, a quarter-wavelength transmission line, a transformer, an output matching network, an input matching network, and a phase shift network, wherein: The input matching network and the phase shift network receive the input signal and generate a main power amplifier signal and an auxiliary power amplifier signal with a 90° phase difference; The output of the auxiliary power amplifier is connected to a quarter-wavelength transmission line, and the auxiliary power amplifier signal is received by the auxiliary power amplifier and connected to the first input end of the transformer through the quarter-wavelength transmission line; The main power amplifier receives the main power amplifier signal and outputs it to the second input terminal of the transformer; The output of the transformer is connected to the input of the output matching network, and the amplified signal is output through the output matching network.

2. The broadband Doherty power amplifier according to claim 1, wherein: The main power amplifier is biased as a class AB power amplifier.

3. The broadband Doherty power amplifier according to claim 1, wherein: The auxiliary path power amplifier is biased as a class C power amplifier. 4 . The broadband Doherty power amplifier according to claim 1 , further comprising a main impedance matching network, wherein the main impedance matching network is connected between the output terminal of the main power amplifier and the second input terminal of the transformer.

5. The broadband Doherty power amplifier according to claim 1, wherein: The main power amplifier and the auxiliary power amplifier are configured to have an optimal matching point impedance Ropt.

6. The broadband Doherty power amplifier according to claim 5, wherein: The characteristic impedance of the quarter-wavelength transmission line is configured as the best matching point impedance Ropt.

7. The broadband Doherty power amplifier according to claim 5, wherein: The input impedance of the output matching network is configured to be twice the optimal matching point impedance Ropt.

8. The broadband Doherty power amplifier according to claim 1, wherein: The broadband Doherty power amplifier is configured as a power amplifier for the N77 or N79 frequency band.

9. The broadband Doherty power amplifier according to claim 1, wherein: The broadband Doherty power amplifier is implemented by one of HBT, CMOS, BJT, BiCMOS and GaN processes.

10. The broadband Doherty power amplifier according to claim 1, wherein: The main power amplifier and the auxiliary power amplifier are configured as power amplifiers with a source-common-gate structure.

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