Load modulation variable gain power amplifier based on coupling line

Abstract

The invention belongs to the technical field of wireless communication, relates to a variable gain power amplifier, and particularly provides a load modulation variable gain power amplifier based on a coupling line, which is used for improving the average efficiency of the power amplifier in a deep rollback interval and realizing gain control. According to the invention, the 90-degree coupling line is utilized to realize the impedance modulation effect; compared with a traditional lambda / 4 transmission line structure, the load modulation variable gain power amplifier provided by the invention is wider in bandwidth; compared with the structure of a transformer, the load modulation variable gain power amplifier provided by the invention has the advantages that the loss of the 90-degree coupling line is smaller, the influence on the efficiency is smaller, and the load modulation variable gain power amplifier has obvious advantages in a broadband high-efficiency system. Meanwhile, by means of the distributed characteristics of the coupling lines, the model not only considers magnetic coupling, but also considers electric coupling, the ideal model is closer to reality in the design process, multiple iterations are not needed, and design simplification is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communication, relates to a variable gain power amplifier, and specifically provides a load modulation variable gain power amplifier based on a coupled line. Background Art

[0002] With the rapid development of wireless communication technology, in order to improve the utilization rate of the spectrum and increase the data throughput, various complex modulation methods have been continuously proposed, such as high-order quadrature amplitude modulation (QAMs), orthogonal frequency division multiplexing (OFDM), carrier aggregation, etc.; usually these modulation signals are non-constant envelope signals. Compared with constant envelope signals, non-constant envelope signals have a higher peak-to-average power ratio (PAPR), and generally the more complex the modulation scheme, the higher the PAPR. For example, the typical PAPR of a single-carrier 64QAM signal is about 7.1 dB, while the PAPR of a 64QAM signal with two carriers (a total of 800 MHz) in the FR2 frequency band is about 11.8 dB; at the same time, complex modulation methods have very high requirements for linearity, requiring traditional power amplifiers to operate in a relatively deep back-off range, thus greatly limiting the average efficiency of the system, and this limitation becomes increasingly important in 5G wireless links.

[0003] The traditional way to improve the back-off efficiency is mainly to adopt the Doherty structure. The Doherty structure uses a λ / 4 transmission line to achieve the effect of impedance modulation. As described in the literature “Doherty, W.H. A New High Efficiency Power Amplifier for Modulated Waves [J]. Proc Ire, 1936, 24(9): 1163-1182. DOI: 10.1109 / JRPROC.1936.228468.”, which discloses a load modulation power amplifier based on a λ / 4 transmission line. As Figure 1 shown, by using a transmission line with an electrical length of λ / 4 and utilizing its impedance inversion function, the modulation of the load impedance can be achieved; however, due to the narrowband characteristics of the λ / 4 transmission line, it is difficult to expand the bandwidth of this load modulation power amplifier.

[0004] Based on the Doherty structure, a transformer-based load modulation power amplifier has been proposed, such as in the literature "Pashaeifar M, Vreede L C N and Alavi M S. A millimeter-wave CMOS series-Doherty power amplifier with post-silicon inter-stage passive validation[J]. IEEE Journal of Solid-State Circuits, 2022, 57(10): 2999-3013.", which discloses a transformer-based load modulation power amplifier, as Figure 2 shown. This structure is evolved from the λ / 4 transmission line load modulation power amplifier. The λ / 4 transmission line is equivalent to an LC model, and then this model is theoretically integrated with the matching network, and finally combined into an output network to achieve the modulation of the load impedance. However, in the transformer-based load modulation power amplifier, the transformer is equivalent to a two-section λ / 4 transmission line, which can expand the bandwidth. However, due to the low coupling of the transformer network, its loss is large, which deteriorates the efficiency to a certain extent. And in the actual design process, the transformer model does not consider electrical coupling, while the actual transformer not only has magnetic coupling but also has a certain amount of electrical coupling. Therefore, in the actual design process, continuous iteration is required, which is relatively complex.

[0005] In view of the above-mentioned many problems, the present invention proposes a coupled-line-based load modulation variable gain power amplifier, aiming to improve the average efficiency of the power amplifier in the deep back-off region and achieve gain control. Summary of the Invention

[0006] The purpose of the present invention is to provide a coupled-line-based load modulation variable gain power amplifier to improve the average efficiency of the power amplifier in the deep back-off region and achieve gain control. The present invention uses a coupled line to replace the λ / 4 transmission line, and uses its own broadband characteristics to effectively expand the bandwidth. And, the coupling degree of the coupled line is high, the loss is low, and the impact on the efficiency is small. At the same time, using the distributed characteristics of the coupled line, its model not only considers magnetic coupling, but also considers electrical coupling. In the design process, its ideal model is closer to the actual situation and does not require multiple iterations, which is beneficial to simplify the design.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A load modulation variable gain power amplifier based on a coupled line, comprising: an input network, a main path power amplifier, a secondary path power amplifier, and an output network; characterized in that the main path power amplifier and the secondary path power amplifier have the same structure, and respectively include: a driver stage amplifier and a power stage amplifier; both the input network and the output network adopt 90° coupled lines, the coupled end of the input network is connected to the driver stage of the main path power amplifier, and the through end of the input network is connected to the driver stage of the secondary path power amplifier; the coupled end of the output network is connected to the power stage of the secondary path power amplifier, and the through end of the output network is connected to the power stage of the main path power amplifier.

[0009] Further, the input end of the output network serves as the output end of the load modulation variable gain power amplifier and is connected to a load, and the isolation end of the output network is open-circuited; the input end of the input network serves as the input end of the load modulation variable gain power amplifier and is connected to an input impedance, and the isolation end of the input network is connected to an isolation resistor.

[0010] Further, the driver stage amplifier adopts a cascode structure, and the power stage amplifier adopts a common source structure.

[0011] Further, the gain control of the load modulation variable gain power amplifier is controlled by a control voltage Vc1; a control terminal is led out from the source of the common gate structure of the driver stage amplifier, a control transistor is provided, the source of the control transistor is connected to the control terminal, the gate of the control transistor is connected to the control voltage Vc1, and the drain of the control transistor is connected to the supply voltage.

[0012] Further, the main path power amplifier is biased in the Class-AB mode, and the secondary path power amplifier is biased in the Class-C mode.

[0013] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0014] The present invention provides a load modulation variable gain power amplifier based on a coupled line, which improves the traditional Doherty structure, uses a 90° coupled line to replace the traditional λ / 4 transmission line to achieve the effect of impedance modulation; compared with the traditional λ / 4 transmission line structure, the load modulation variable gain power amplifier provided by the present invention has a wider bandwidth; compared with the transformer structure, the 90° coupled line in the load modulation variable gain power amplifier provided by the present invention has less loss and less impact on efficiency, and has obvious advantages in broadband high-efficiency systems. At the same time, using the distributed characteristics of the coupled line, its model not only considers magnetic coupling but also considers electric coupling, and its ideal model is closer to the actual situation during the design process, without the need for multiple iterations, which is beneficial to simplifying the design. Description of the Drawings

[0015] Figure 1It is a schematic diagram of the principle of a load modulation power amplifier based on a λ / 4 transmission line in the prior art.

[0016] Figure 2 It is a schematic diagram of the principle of a load modulation power amplifier based on a transformer in the prior art.

[0017] Figure 3 It is a schematic diagram of the principle of the coupled line structure in the present invention.

[0018] Figure 4 It is a schematic diagram of the principle of a load modulation variable gain power amplifier based on a coupled line in the present invention.

[0019] Figure 5 It is a graph showing the curve relationships of the output current, output voltage, impedance, and input voltage of the main path power amplifier and the auxiliary path power amplifier in the present invention.

[0020] Figure 6 It is a gain curve graph of a load modulation variable gain power amplifier based on a coupled line in the present invention.

[0021] Figure 7 It is a PAE curve graph of a load modulation variable gain power amplifier based on a coupled line in the present invention. Detailed implementation manners

[0022] To make the objectives, technical solutions, and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] The present invention provides a load modulation variable gain power amplifier based on a coupled line, which is improved on the basis of the traditional Doherty structure. It uses a 90° coupled line to replace the traditional λ / 4 transmission line to achieve the effect of impedance modulation. Compared with the traditional λ / 4 transmission line structure, it has a wider bandwidth. Compared with the transformer structure, the 90° coupled line has less loss and has less impact on efficiency, showing obvious advantages in a broadband and high-efficiency system.

[0024] In terms of the working principle:

[0025] The coupled line structure is as Figure 3 shown, where Port 1 is the input end, Port 2 is the coupling end, Port 3 is the isolation end, Port 4 is the through end, I1 to I4 respectively represent the currents of Ports 1 to 4, and V1 to V4 respectively represent the voltages of Ports 1 to 4; by using the odd-even mode analysis method to analyze the port voltages and currents, the voltage-current relationships between its ports can be obtained, that is, the Z-parameter matrix is:

[0026]

[0027] Among them, Z oeis the even-mode characteristic impedance of the coupled line, Z oo is the odd-mode characteristic impedance of the coupled line, θ is the electrical length of the coupled line, and j is the imaginary unit; letting θ = 90°, we can obtain:

[0028]

[0029] Assume that the load Z o is connected to port 1, then V1 = -I1Z o , substituting it into the above matrix, we have:

[0030]

[0031] Substituting the above equation into the matrix again, we have:

[0032]

[0033] Assume that the current at port 2 is I a represents the amplitude of I2, port 3 is open-circuited, the current I3 = 0, and the current I4 = I m , I m represents the amplitude of I4, substituting it into the above equation, we can obtain:

[0034]

[0035] Let we have:

[0036]

[0037] Substituting it into the above equation, we can obtain:

[0038]

[0039] From the above equation, it can be seen that if the phase difference and magnitude between the input to ports 2 and 4 are reasonably controlled, an impedance modulation effect can be achieved between ports 2 and 4.

[0040] Based on the above theoretical research, the present invention proposes a load modulation variable gain power amplifier based on a coupled line, and its schematic diagram is as shown in Figure 4As shown, the output network uses a 90° coupled line to achieve the effect of impedance modulation. The input network also requires a 90-degree coupled line to make the phases of the two currents (the main path and the auxiliary path) differ by 90°. The branch connected to port 4 of the input network is defined as the main path, and the branch connected to port 2 of the input network is defined as the auxiliary path; port 1 of the output network is the output terminal and is connected to the load, port 2 of the output network is connected to the power amplifier of the auxiliary path, port 3 of the output network is open-circuited, and port 4 of the output network is connected to the power amplifier of the main path; port 1 of the input network is the input terminal and is connected to the input impedance, port 2 of the input network is connected to the power amplifier of the main path, port 3 of the input network is connected to the isolation resistor, usually 50Ω, and port 4 of the input network is connected to the power amplifier of the auxiliary path.

[0041] Specifically, the coupled-line-based load modulation variable gain power amplifier includes: an input network, a main path power amplifier, an auxiliary path power amplifier, and an output network; among them, the main path power amplifier and the auxiliary path power amplifier have the same structure and respectively include: a driver stage amplifier and a power stage amplifier; the driver stage amplifier adopts a cascode structure, and the power stage amplifier adopts a common-source structure; port 2 of the input network is connected to the driver stage (the input end of the driver stage amplifier) of the main path power amplifier, and port 4 of the input network is connected to the driver stage (the input end of the driver stage amplifier) of the auxiliary path power amplifier; port 2 of the output network is connected to the power stage (the output end of the power stage amplifier) of the power amplifier of the auxiliary path, and port 4 of the output network is connected to the power stage (the output end of the power stage amplifier) of the power amplifier of the main path.

[0042] Furthermore, the gain control of the above-mentioned coupled-line-based load modulation variable gain power amplifier is controlled by the control voltage Vc1; a control terminal is led out from the source of the common-gate structure of the driver stage amplifier (cascode structure), the control terminal is connected to the source of the control transistor, the gate of the control transistor is connected to the control voltage Vc1, and the drain of the control transistor is connected to the supply voltage; the control voltage Vc1 is used as the gain control signal to perform gain tuning on the main path and the auxiliary path respectively.

[0043] Assuming under the current control scheme, the gain change of the driver stage of the coupled-line-based load modulation variable gain power amplifier in the present invention can be expressed as:

[0044]

[0045] Among them, G1 and G2 respectively represent the gains of the driver stage in state 1 and state 2, gm1 and gm2 respectively represent the transconductances of the driver stage in state 1 and state 2, and ID1 and ID2 respectively represent the static currents of the driver stage in state 1 and state 2.

[0046] Furthermore, the load modulation process of the above-mentioned coupled-line-based load modulation variable gain power amplifier is specifically as follows:

[0047] To achieve the desired impedance modulation effect, the main path power amplifier is biased in Class-AB mode and the auxiliary path power amplifier is biased in Class-C mode; assuming that the optimal load impedance of the main path power amplifier and the auxiliary path power amplifier is Z o ; at low power input, the main path remains on and the auxiliary path remains off, i.e., I a = 0, and the impedance seen by the main path and the auxiliary path at this time can be obtained as:

[0048]

[0049] The impedance seen by the main path at this time is twice the optimal load impedance. Therefore, the output fundamental voltage of the main path power amplifier will increase by two times;

[0050] As the input power increases, the efficiency reaches the first peak point. At this time, the main path power amplifier reaches saturation, the output fundamental voltage of the main path power amplifier reaches the maximum, and at the same time the auxiliary path power amplifier turns on. At this time, the impedance seen by the main path power amplifier and the auxiliary path power amplifier is:

[0051]

[0052] As the input power further increases, as the auxiliary path current increases, the impedance seen by the main path decreases, but the output fundamental voltage of the main path power amplifier remains unchanged; finally, the main path and the auxiliary path currents are equal. At this time, the impedance seen by both the main path power amplifier and the auxiliary path power amplifier is the optimal load impedance Z o , and both reach saturation, and the efficiency reaches the second peak point.

[0053] As Figure 5 shown are the curve relationships of the output current, output voltage, impedance of the main path power amplifier and the auxiliary path power amplifier with the input voltage. Figure 5 In (a) is the current, Figure 5 in (b) is the voltage, Figure 5 in (c) is the impedance. Under ideal operating conditions, the current and voltage of the main path are I1 and V1, and the current and voltage of the auxiliary path are I2 and V2. The impedance seen by the main path is Figure 5 the red curve in (c), and the impedance seen by the auxiliary path is Figure 5 the green curve in (c). It can be seen from the figure that in the ideal load modulation process, the current gain of the auxiliary path needs to reach twice the current gain of the main path after it turns on, and the voltage of the main path will reach saturation when the auxiliary path turns on and remain in the saturation state until the auxiliary path also reaches saturation. The impedance seen by the main path in this process changes from 2Z o to Z o , and the impedance seen by the auxiliary path changes from infinity to Z o .

[0054] Figure 6 and Figure 7 are respectively the gain curve and the PAE curve of the load modulation variable gain power amplifier based on the coupled line in the present invention. It can be seen from the PAE curve that the efficiency of the power amplifier is significantly improved within the 6 dB back-off range.

[0055] As described above, the above are only the specific embodiments of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or alternative features with similar purposes; all the features disclosed, or all the steps in any method or process, except for the mutually exclusive features and / or steps, can be combined in any manner.

Claims

1. A load-modulated variable-gain power amplifier based on coupled lines, comprising: Input network, main power amplifier, auxiliary power amplifier and output network; characterized in that the main power amplifier and the auxiliary power amplifier adopt the same structure, respectively including: a driver stage amplifier and a power stage amplifier; the input network and the output network both adopt 90° coupling lines, the coupling end of the input network is connected to the driver stage of the main power amplifier, and the through end of the input network is connected to the driver stage of the auxiliary power amplifier; the coupling end of the output network is connected to the power stage of the auxiliary power amplifier, and the through end of the output network is connected to the power stage of the main power amplifier.

2. The load-modulated variable gain power amplifier based on coupled lines according to claim 1, characterized in that: The input end of the output network is used as the output end of the load-modulated variable gain power amplifier and connected to the load, and the isolation end of the output network is open; the input end of the input network is used as the input end of the load-modulated variable gain power amplifier and connected to the input impedance, and the isolation end of the input network is connected to the isolation resistor.

3. The load-modulated variable gain power amplifier based on coupled lines according to claim 1, characterized in that: The driver stage amplifier adopts a cascode structure, and the power stage amplifier adopts a common source structure.

4. The load-modulated variable gain power amplifier based on coupled lines according to claim 1, characterized in that: The gain control of the load modulated variable gain power amplifier is controlled by a control voltage Vc1; a control transistor is arranged at a source lead control end of a common gate structure of a driving stage amplifier, the source of the control transistor is connected to the control end, the gate of the control transistor is connected to the control voltage Vc1, and the drain of the control transistor is connected to a power supply voltage.

5. The load-modulated variable gain power amplifier based on coupled lines according to claim 1, characterized in that: The main power amplifier is biased in Class-AB mode, and the auxiliary power amplifier is biased in Class-C mode.

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