Load modulation balanced power amplifier based on elliptical low-pass filtering matching network

Abstract

The invention discloses a load modulation balanced power amplifier based on an elliptical low-pass filtering matching network, which is implemented by the following steps of: designing a control signal power amplifier as a main path, and applying the elliptical low-pass filtering matching network in an output matching network; designing a balanced power amplifier as an auxiliary path, applying an elliptical low-pass filtering matching network in an output matching network, biasing the auxiliary path in a class C, and starting to work when a main path is saturated; a power divider is added at an input end, and two straight-through ports are respectively connected with a main path input end and a phase offset line; a power divider is connected behind the phase deviation module, and two straight-through ends are connected to a balanced power amplifier; an output coupler is added to an output end, a control signal is injected into an isolation port of the output coupler, and a balanced power amplifier is connected to a straight-through end of the coupler. Harmonic suppression and fundamental impedance matching are realized through the elliptical low-pass filtering matching network, so that the gain and output efficiency of the power amplifier are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power amplifiers, and particularly to a design of a load modulation balanced power amplifier based on an elliptical low-pass filter matching network. Background Art

[0002] With the rapid development of the fifth-generation mobile communication technology, the requirements for the transmission capacity and data rate of wireless communication systems are constantly increasing. To meet this demand, the system needs to adopt more complex modulation methods, which will significantly increase the peak-to-average power ratio of the signal. This change places higher requirements on radio frequency power amplifiers, which not only need to maintain high efficiency at the peak power point but also must maintain excellent performance within a large output power back-off range. Currently, the industry generally adopts a variety of high-efficiency power amplifier architectures to achieve this goal.

[0003] As a typical representative of load modulation technology, the Doherty power amplifier has been widely used due to its excellent efficiency performance under high output back-off conditions. However, limited by its quarter-wavelength impedance transformation network, the working bandwidth of this architecture has inherent limitations. In contrast, the load modulation balanced amplifier proposed in recent years has received increasing attention due to its potential wideband characteristics and high-efficiency advantages. Notably, by precisely adjusting the amplitude and phase of the control signal of the control amplifier and injecting it into the balanced amplifier through the isolation port of the output coupler, dynamic modulation of the load impedance of the balanced amplifier can be achieved.

[0004] In the design process of the load modulation balanced amplifier, harmonic suppression is a key factor to ensure high efficiency. Although the traditional Chebyshev low-pass filter matching network is widely used in harmonic suppression circuits, its high-order structure often introduces non-negligible insertion loss and has poor sideband roll-off. Summary of the Invention

[0005] Technical Problem: To solve the problem of poor sideband roll-off of the traditional Chebyshev low-pass filter matching network, the present invention provides a load modulation balanced power amplifier based on an elliptical low-pass filter matching network. By improving the Chebyshev low-pass filter matching network into an elliptical low-pass filter matching network, while maintaining good in-band matching characteristics, a steeper stopband roll-off characteristic is provided to achieve better harmonic suppression.

[0006] Technical Solution: To achieve this goal, the load modulation balanced power amplifier based on an elliptical low-pass filter matching network of the present invention adopts the following technical solutions:

[0007] The power amplifier includes a first power distribution module, a phase delay module, a control signal power amplification module, and a balanced power amplifier circuit module. Among them, the control signal power amplification module serves as the main path, and the balanced power amplifier circuit module serves as the auxiliary path. The input end of the first power distribution module is connected to the input signal, and the two output ends are respectively connected to the input ends of the control signal power amplification module and the phase delay module. The output end of the control signal power amplification module is connected to the isolation end of the output coupler of the balanced power amplifier circuit module. The output end of the phase delay module is connected to the balanced power amplifier circuit module, and the output end of the balanced power amplifier circuit module is connected to the load.

[0008] The control signal power amplification module includes a third input matching network, a third transistor, and a third elliptical low-pass filter matching network connected in sequence. The input end of the third input matching network is the input end of the control signal power amplification module, and the output end of the third elliptical low-pass filter matching network is the output end of the control signal power amplification module.

[0009] The balanced power amplifier circuit module serves as the auxiliary path and includes a second power distribution module, a power amplifier circuit module, and an output coupler connected in sequence. The input end of the second power distribution module is the input end of the balanced power amplifier circuit module, and the output end of the output coupler is the output end of the balanced power amplifier circuit module.

[0010] The power amplifier circuit module has two paths. The first path includes a first input matching network, a first transistor, and a first elliptical low-pass filter matching network connected in sequence. The second path includes a second input matching network, a second transistor, and a second elliptical low-pass filter matching network connected in sequence. The input ends of the first input matching network and the second input matching network are respectively connected to the power distribution module, and the output ends of the first elliptical low-pass filter matching network and the second elliptical low-pass filter matching network are respectively connected to the output coupler.

[0011] The input signal is evenly divided into a first path signal and a second path signal by the first power distribution module. The first path signal is amplified by the control signal power amplification module, and the output signal is connected to the isolation port of the output coupler. After the second path signal passes through the phase delay module and the second power distribution module, it is further divided into two path signals. One path signal sequentially passes through the first input matching network, the first transistor, and the first elliptical low-pass filter matching network of the power amplifier circuit module to one through port of the output coupler. The other path signal sequentially passes through the second input matching network, the second transistor, and the second elliptical low-pass filter matching network of the power amplifier circuit module to the other through port of the output coupler. By setting the phase delay, the main path signal and the auxiliary path signal will be combined into a total output signal at the output port of the output coupler and output to the load.

[0012] The third elliptical low-pass filter matching network, the first elliptical low-pass filter matching network, and the second elliptical low-pass filter matching network are third-order low-pass filter matching networks, which are designed in the form of series inductance - parallel capacitance and finally presented in the form of microstrip line equivalent inductance and capacitance.

[0013] While achieving in-band impedance matching, the third elliptical low-pass filter matching network, the first elliptical low-pass filter matching network, and the second elliptical low-pass filter matching network provide a better sideband steepness than the Chebyshev low-pass filter matching network, and achieve harmonic suppression to improve the efficiency of the overall architecture.

[0014] The control signal power amplification module is a carrier power amplifier, and the balanced power amplifier circuit module is a peak power amplifier to expand the output power back-off range.

[0015] The first power distribution module, the second power distribution module, and the output coupler all adopt quadrature couplers.

[0016] The implementation method of the load modulation balanced power amplifier based on the elliptical low-pass filter matching network of the present invention includes the following steps:

[0017] S1: Add a quadrature coupler at the input port and use it as a power divider to divide the input signal into two signals with equal amplitude and orthogonal phases. Using a single-input structure can avoid relatively difficult dynamic phase control and the design of a dual-input load modulation balanced power amplifier.

[0018] S2: Select the DC bias of the control signal power amplification module and the balanced power amplifier to determine the static operating point. Bias the control signal power amplification module as class B and the balanced power amplifier as class C, so that the balanced power amplifier turns on when the control signal power amplification module is saturated.

[0019] S3: Design the corresponding input matching network according to the source impedance obtained by source pulling in the electromagnetic simulation software based on the selected RF transistor model.

[0020] S4: Determine the impedance transformation ratio of the output matching network according to the load pulling result of the third transistor, design the corresponding Chebyshev low-pass filter matching network, and then convert the capacitance of the first shunt stub into a series structure of inductance and capacitance to realize the conversion from the Chebyshev low-pass filter matching network to the elliptical low-pass filter matching network.

[0021] S5: Determine the impedance transformation ratio of the output matching network according to the load pulling results of the first transistor and the second transistor. The design method is the same as that of the output matching network of the control signal power amplification module, and design the corresponding elliptical low-pass filter matching network.

[0022] S6: Convert the capacitance and inductance values of the designed three elliptical low-pass filter matching networks into microstrip line structures;

[0023] S7: In the design of the balanced power amplifier circuit module, use the same quadrature coupler as the power divider and output coupler respectively, where the control signal is input to the isolation port of the quadrature coupler, and the three signals are synthesized at the load end;

[0024] S8: Adjust the length of the transmission line in the phase delay module to achieve broadband phase shift between the control power amplifier and the balanced path power amplifier. Through appropriate phase control, maximize the efficiency within the target frequency band.

[0025] Advantageous effects: Compared with the prior art, the present invention uses an elliptical low-pass filter matching network as the output matching network of the power amplifier, achieving a good harmonic suppression effect, and having a good impedance transformation effect within the band. Within the designed frequency band, while achieving a high saturated output power, it still maintains a high efficiency within a large back-off output power range. Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the load modulation balanced power amplifier and its implementation method based on the elliptical low-pass filter matching network in the specific embodiment of the present invention;

[0027] In the figure: the first power distribution module 1, the phase delay module 2, the control signal power amplification module 3, the third input matching network 31, the third transistor 32, the third elliptical low-pass filter matching network 33; the balanced power amplifier circuit module 4, the second power distribution module 41, the power amplifier circuit module 42, the first input matching network 421, the first transistor 422, the first elliptical low-pass filter matching network 423, the second input matching network 424, the second transistor 425, the second elliptical low-pass filter matching network 426, the output coupler 43.

[0028] Figure 2 It is an ideal schematic diagram of the reference plane of the output coupler of the load modulation balanced power amplifier, Figure 2 where (a) represents before the balanced power amplifier is turned on, Figure 2 and (b) represents after the balanced power amplifier is turned on;

[0029] Figure 3 It is the low-pass filter matching network designed with lumped elements and its performance comparison; Figure 3 where (a) is the Chebyshev low-pass filter matching network, Figure 3 and (b) is the elliptical low-pass filter matching network, Figure 3 and (c) is the comparison of the transfer functions of the two networks.

[0030] Figure 4 Schematic diagram of the load modulation balanced power amplifier designed for the present invention.

[0031] Figure 5 In the specific embodiment of the present invention, simulation curves of drain efficiency and gain varying with output power achieved within the operating frequency band of 1.4 - 1.8 GHz.

[0032] Figure 6 In the specific embodiment of the present invention, curves of drain efficiency and gain varying with output power of the measured load modulation balanced power amplifier at frequencies of 1.4 - 1.8 GHz. Specific Embodiment

[0033] The technical solution of the present invention will be further introduced below in combination with specific embodiments and the accompanying drawings.

[0034] As Figure 1 shown, the power amplifier includes a first power distribution module 1, a phase delay module 2, a control signal power amplification module 3, and a balanced power amplifier circuit module 4. Among them, the control signal power amplification module 3 serves as the main path and includes a third input matching network 31, a third transistor 32, and a third elliptical low - pass filter matching network 33. The balanced power amplifier circuit module 4 serves as the auxiliary path and includes a second power distribution module 41, a first input matching network 421, a first transistor 422, a first elliptical low - pass filter matching network 423, a second input matching network 424, a second transistor 425, a second elliptical low - pass filter matching network 426, and an output coupler 43. The input signal is divided into a first - path signal and a second - path signal by the first power distribution module 1. The first - path signal is amplified by the control signal power amplification module 3, and the output signal is connected to the isolation port of the output coupler 43. The second - path signal passes through the phase delay module 2 and the second power distribution module 41 and then is divided into two signals. One signal sequentially passes through the first input matching network 421, the first transistor 422, and the first elliptical low - pass filter matching network 423 of the power amplifier circuit module 42 to the through port of the output coupler 43. The other signal sequentially passes through the second input matching network 424, the second transistor 425, and the second elliptical low - pass filter matching network 426 of the power amplifier circuit module 42 to the other through port of the output coupler 43. By setting a reasonable phase delay, the main - path signal and the auxiliary - path signal are combined into a total output signal at the output port of the output coupler 43 and output to the load.

[0035] Further, as Figure 2 shown, a theoretical analysis is carried out on the output combining network of the load modulation balanced power amplifier. This architecture can be divided into two operating states, namely the low - power operating region and the high - power operating region. In the low - power operating region, asFigure 2 (a), the balanced amplifier is in the off state, and the system performance is completely determined by the control amplifier at this time; when entering the high-power region, such as Figure 2 (b), the balanced amplifier is activated and the control amplifier enters the saturation state. The signal injection of the control amplifier will perform load modulation on the balanced amplifier, and the increase in the system output power mainly comes from the contribution of the balanced amplifier.

[0036] Figure 3 For the Chebyshev low-pass filter matching network (a), the elliptic low-pass filter matching network (b), and the comparison of the transfer functions of the two networks (c). First, the optimal load impedance of the transistor in the control signal power amplification module at the center frequency of 1.6G is Z L = 12.5 + j13Ω. To match it to the characteristic impedance of the coupler, the impedance transformation ratio is obtained as 4. Then, according to the matching bandwidth and the matching order, a Chebyshev low-pass filter matching network that can realize the impedance transformation from the complex impedance 12.5 + j13Ω to 50Ω is obtained, such as Figure 3 (a). Then, the capacitor of the first parallel stub is replaced with a series connection of an inductor and a capacitor. The values of the replaced capacitor and inductor are calculated by the following formula:

[0037]

[0038] where f H is the high-frequency cut-off frequency, and f p is the frequency where the attenuation pole is located. The improved elliptic low-pass filter matching network, as shown in Figure 3 (b), can not only achieve good impedance matching in the band, but also achieve better suppression at the harmonic frequencies than the Chebyshev low-pass filter matching network, as shown in Figure 3 (c). Near the harmonic, the improved elliptic low-pass filter matching network has a better steepness. For the output matching network of the balanced control amplifier, the design method also follows the above method.

[0039] After that, the input matching network of each amplifier is designed, and a multi-stub matching network is used to achieve broadband impedance matching. The schematic diagram of the load-modulated balanced power amplifier implemented by simulation is as shown in Figure 4 .

[0040] Figure 5 is the electromagnetic simulation result of the load-modulated balanced power amplifier based on the elliptic low-pass filter matching network. This design uses a commercial 10w RF gallium nitride transistor. The gate bias voltage of the transistor in the control signal power amplification module is set to -2.9V, and the drain voltage is 14V to achieve early saturation; the gate bias voltage of the balanced power amplifier is set to -5.2V, and the drain voltage is 28V. Figure 4The curves of the drain efficiency and gain obtained from electromagnetic simulation versus the output power are shown. The simulation results indicate that, within the frequency band of 1.4 - 1.8 GHz, this design can achieve excellent performance with a saturated output power of 44.8 - 46.4 dBm, a saturated drain efficiency of 70.1% - 86.7%, and a saturated gain greater than 13.2 dB. Meanwhile, at the 6 dB, 8 dB, and 10 dB back-off points, the drain efficiencies can reach 62.2% - 73.8%, 65.2% - 72.2%, and 63.1% - 71.3% respectively, and within the entire 10 dB back-off range, the drain efficiency is greater than 60%. It can be seen from the simulation results that the harmonic suppression achieved by the load modulation balanced power amplifier based on the elliptical low-pass filter matching network can effectively improve the efficiency performance of the overall power amplifier architecture.

[0041] Figure 6 The experimental measurement results of the load modulation balanced power amplifier based on the elliptical low-pass filter matching network are shown. It can be seen from the figure that within the frequency band of 1.4 - 1.8 GHz, this design can achieve excellent performance with a saturated output power of 44.3 - 44.8 dBm, a saturated drain efficiency of 70.4% - 77.9%, and a saturated gain greater than 12.8 dB. Meanwhile, at the 6 dB, 8 dB, and 10 dB back-off points, the drain efficiencies can reach 62.9% - 77.7%, 66.6% - 73.4%, and 59.0% - 65.8% respectively, and within the entire 10 dB back-off range, the drain efficiency is greater than 59%. Due to the lack of accuracy in transistor modeling, there are some deviations between the simulation and measured data. However, the test results still prove that this invention plays a very obvious role in improving the efficiency of the overall power amplifier architecture, and the harmonic suppression achieved by the elliptical low-pass filter matching network can effectively improve the efficiency of the power amplifier.

Claims

1. A load modulation balanced power amplifier based on an elliptical low-pass filter matching network, characterized in that: The power amplifier includes a first power distribution module (1), a phase delay module (2), a control signal power amplification module (3), and a balanced power amplifier circuit module (4); wherein, the control signal power amplification module (3) serves as the main path, and the balanced power amplifier circuit module (4) serves as the auxiliary path. The input end of the first power distribution module (1) is connected to an input signal, and the two output ends are respectively connected to the input ends of the control signal power amplification module (3) and the phase delay module (2). The output end of the control signal power amplification module (3) is connected to the isolation end of the output coupler of the balanced power amplifier circuit module (4), the output end of the phase delay module (2) is connected to the balanced power amplifier circuit module (4), and the output end of the balanced power amplifier circuit module (4) is connected to a load.

2. The load modulation balanced power amplifier based on the elliptical low-pass filter matching network according to claim 1, wherein: The control signal power amplification module (3) includes a third input matching network (31), a third transistor (32), and a third elliptical low-pass filter matching network (33) connected in sequence; the input end of the third input matching network (31) is the input end of the control signal power amplification module (3), and the output end of the third elliptical low-pass filter matching network (33) is the output end of the control signal power amplification module (3).

3. The load modulation balanced power amplifier based on an elliptical low-pass filter matching network according to claim 1, wherein: The balanced power amplifier circuit module (4) serves as the auxiliary path and includes a second power distribution module (41), a power amplifier circuit module (42), and an output coupler (43) connected in sequence; the input end of the second power distribution module (41) is the input end of the balanced power amplifier circuit module (4), and the output end of the output coupler (43) is the output end of the balanced power amplifier circuit module (4).

4. The load modulation balanced power amplifier based on an elliptical low-pass filter matching network according to claim 3, wherein: The power amplifier circuit module (42) has two paths. The first path includes a first input matching network (421), a first transistor (422), and a first elliptical low-pass filter matching network (423) connected in sequence, and the second path includes a second input matching network (424), a second transistor (425), and a second elliptical low-pass filter matching network (426) connected in sequence; the input ends of the first input matching network (421) and the second input matching network (424) are respectively connected to the power distribution module (41), and the output ends of the first elliptical low-pass filter matching network (423) and the second elliptical low-pass filter matching network (426) are respectively connected to the output coupler (43).

5. The load modulation balanced power amplifier based on an elliptical low-pass filter matching network according to claim 3, wherein: The input signal is evenly divided into a first path signal and a second path signal by the first power distribution module (1); the first path signal is amplified by the control signal power amplification module (3), and the output signal is connected to the isolation port of the output coupler (43); the second path signal passes through the phase delay module (2) and the second power distribution module (41), and then is divided into two path signals. One path signal sequentially passes through the first input matching network (421), the first transistor (422), and the first elliptical low-pass filter matching network (423) of the power amplifier circuit module (42) to a through port of the output coupler (43); the other path signal sequentially passes through the second input matching network (424), the second transistor (425), and the second elliptical low-pass filter matching network (426) of the power amplifier circuit module (42) to another through port of the output coupler (43); by setting the phase delay, the main path signal and the auxiliary path signal are combined into a total output signal at the output port of the output coupler (43) and output to the load.

6. The load modulation balanced power amplifier based on the elliptical low-pass filter matching network according to claim 5, wherein: The third elliptical low-pass filter matching network (33), the first elliptical low-pass filter matching network (423), and the second elliptical low-pass filter matching network (426) are third-order low-pass filter matching networks, which are designed in the form of series inductance - parallel capacitance and finally presented in the form of microstrip line equivalent inductance and capacitance.

7. The load modulation balanced power amplifier based on the elliptical low-pass filter matching network according to claim 6, characterized in that: While achieving in-band impedance matching, the third elliptical low-pass filter matching network (33), the first elliptical low-pass filter matching network (423), and the second elliptical low-pass filter matching network (426) provide a better sideband steepness than the Chebyshev low-pass filter matching network, and achieve harmonic suppression to improve the efficiency of the overall architecture.

8. The load modulation balanced power amplifier based on the elliptical low-pass filter matching network according to claim 1, characterized in that: The control signal power amplification module (3) is a carrier power amplifier, and the balanced power amplifier circuit module (4) is a peak power amplifier to expand the output power back-off range.

9. The load modulation balanced power amplifier based on an elliptical low-pass filter matching network according to claim 1, wherein: The first power distribution module (1), the second power distribution module (41), and the output coupler (43) all adopt quadrature couplers.

10. The implementation method of the load modulation balanced power amplifier based on the elliptical low-pass filter matching network according to claim 1 includes the following steps: S1: Add a quadrature coupler at the input port and use it as a power distributor to divide the input signal into equal-amplitude and phase-orthogonal signals. Using a single-input structure can avoid relatively difficult dynamic phase control and the design of a dual-input load modulation balanced power amplifier; S2: Select the DC bias of the control signal power amplification module and the balanced power amplifier to determine the static operating point. Bias the control signal power amplification module as class B and the balanced power amplifier as class C, so that the balanced power amplifier is turned on when the control signal power amplification module is saturated; S3: Design the corresponding input matching network according to the source impedance obtained by source pulling in the electromagnetic simulation software based on the selected radio frequency transistor model; S4: Determine the impedance transformation ratio of the output matching network according to the load-pull result of the third transistor, design the corresponding Chebyshev low-pass filter matching network, and then convert the capacitor of the first shunt stub into an inductor-capacitor series structure to achieve the conversion from the Chebyshev low-pass filter matching network to the elliptical low-pass filter matching network; S5: Determine the impedance transformation ratio of the output matching network according to the load-pull results of the first transistor and the second transistor, which is the same as the design method of the output matching network of the control signal power amplification module, and design the corresponding elliptical low-pass filter matching network; S6: Convert the capacitance and inductance values of the designed three elliptical low-pass filter matching networks into microstrip line structures; S7: Use the same quadrature coupler as the power divider and the output coupler respectively in the design of the balanced power amplifier circuit module, where the control signal is input to the isolation port of the quadrature coupler, and the three signals are combined at the load end; S8: Adjust the length of the transmission line in the phase delay module to achieve broadband phase shift between the control power amplifier and the balanced path power amplifier, and maximize the efficiency within the target frequency band through appropriate phase control.

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