Power amplifier capable of expanding output power rollback range

Abstract

The invention relates to a power amplifier capable of expanding an output power rollback range, and aims to solve the problem that the output rollback range of the power amplifier is relatively small under a high-peak-to-average-ratio modulation signal in the prior art. The power amplifier comprises a power divider, a phase shifter, a main power amplifier (M1), auxiliary power amplifiers (A1 and A2), balanced power amplifiers (B1 and B2), a quarter-wavelength line (ML1), a half-wavelength line (ML2), a combiner, a quarter-wavelength impedance conversion line (TL3), an isolation resistor (Rios), an input coupler, an output coupler and a post-matching network. According to the design, the three-stage Doherty power amplifier is used as a control power amplifier of the load modulation balanced power amplifier, and the output power of the load modulation balanced power amplifier is superposed in the power rollback range, so that the output power rollback range of the original three-stage Doherty power amplifier is remarkably expanded by the innovative structure and the control method.

Description

Technical Field

[0001] The present invention belongs to the technical field of power amplifiers, and in particular relates to a power amplifier capable of extending an output power back-off range. Background Art

[0002] As people's demand for the performance of wireless communication systems continues to grow, the gradual increase in the peak-to-average ratio of modulated signals has become an important means to improve wireless data transmission rates. However, high peak-to-average ratio modulated signals will cause the power amplifier (PA) in the transmitter to be in the power back-off range for a long time. The efficiency curve of traditional Class B or Class AB PAs usually has only one peak. When the output power is backed off by 6dB, the theoretical efficiency is less than 40%, and the efficiency is even lower in actual applications. In order to meet the needs of different application scenarios, there is an urgent need for a power amplifier that can maintain high efficiency in a larger output power back-off range.

[0003] At present, common load modulation power amplifier designs can achieve high efficiency within the power range. For example, the traditional Doherty power amplifier uses two power amplifiers of the same power level, has two efficiency peaks, and can operate at high efficiency in the power back-off range of 6 to 8dB. However, for the 5G NR waveform based on orthogonal frequency division multiplexing technology (OFDM), the peak-to-average ratio is close to 10dB. The peak efficiency of this design in the 6dB back-off range is not enough to improve the back-off efficiency. The recently proposed load modulation balanced power amplifier (LMBA) can generally achieve an output power back-off range of 10dB, while the design using a multi-channel asymmetric Doherty structure can achieve a larger back-off range.

[0004] Although the existing technology has solved the efficiency problem of the power amplifier in the output power back-off range to a certain extent, it still has significant shortcomings. As the peak-to-average ratio of the signal increases, the output power back-off range increases. The power amplifier in the existing technology will have a trough between the two efficiency peaks, which significantly reduces the average efficiency in the range and limits the expansion of the entire output power back-off range. For example, in indoor Wi-Fi communication systems, the peak-to-average ratio of the signal is even close to 12dB, and the existing power amplifier output power back-off range is difficult to meet the application requirements of future wireless communication systems. Summary of the invention

[0005] In order to solve the problem of insufficient output power back-off range in the prior art, the present invention proposes a power amplifier with an expandable output power back-off range, and provides a power amplifier with a larger output power back-off range and high efficiency to meet the needs of future wireless communication systems. Specifically, it can achieve a back-off range of more than 15dB while maintaining a high working efficiency.

[0006] The present invention is a power amplifier capable of extending the output power back-off range, the structure of which includes: a power divider, a phase shifter, a main power amplifier M1, auxiliary power amplifiers A1 and A2, balanced power amplifiers B1 and B2, a quarter-wavelength line ML1, a half-wavelength line ML2, a quarter-wavelength impedance transformation line TL3, an isolation resistor (R ios ), combiner, input coupler, output coupler and post-matching network.

[0007] Furthermore, the power divider can be formed by cascading power dividers or couplers, with the input end connected to the RF signal input, and the four ports of the output end are respectively connected to the input end of the main power amplifier M1, the input end of the auxiliary power amplifier A1 cascaded with the quarter-wavelength line ML1, the input end of the auxiliary power amplifier A2 cascaded with the half-wavelength line ML2, and the input end of the phase shifter. Here, ML1 and ML2 are to ensure that the two auxiliary power amplifiers A1 and A2 have the correct phase offset.

[0008] Furthermore, the input end of the input coupler is connected to the output end of the phase shifter, and the isolation end is connected to the isolation resistor R ios , the coupling terminal is connected to the input terminal of the balanced power amplifier B1, and the through terminal is connected to the input terminal of the balanced power amplifier B2.

[0009] Furthermore, the input end of the output coupler is connected to the output end of the balanced power amplifier B1, the isolation end is connected to the output end of the balanced power amplifier B2, the coupling end is connected to the input end of the quarter-wavelength impedance transformation line TL3, and the through end is connected to the input end of the rear matching network.

[0010] Furthermore, the input end of the combiner is connected to the output end of the main power amplifier M1, the output end of the auxiliary power amplifier A1, and the output end of the auxiliary power amplifier A2 in sequence, and the output end of the combiner is connected to the output end of the quarter-wavelength impedance transformation line TL3.

[0011] Furthermore, the output of the post-matching network is connected to a system load, which is usually 50 ohms, in order to achieve matching of the output coupler characteristic impedance Z0 to the system impedance 50 ohms.

[0012] Furthermore, the main power amplifier M1, auxiliary power amplifiers A1, A2, and balanced power amplifiers B1 and B2 are all power amplifiers that already include corresponding input and output matching networks.

[0013] Furthermore, the main power amplifier M1 is in class AB bias, the auxiliary power amplifiers A1 and A2 and the balanced power amplifiers B1 and B2 are all in class C bias, and are controlled by different gate voltages and turned on in sequence, and the turn-on order is A1>A2>B1=B2.

[0014] Furthermore, the main power amplifier M1, auxiliary power amplifiers A1, A2, and balanced power amplifiers B1, B2 can be a single transistor, or can be composed of a plurality of transistors connected in parallel or stacked together. The transistor can be realized by a variety of processes, including but not limited to one or any mixture of CMOS, LDMOS, GaN, InP, and GaAs.

[0015] The present invention proposes a power amplifier with an expandable output power back-off range, which has the beneficial effect of using a three-stage Doherty power amplifier as a control power amplifier of a load-modulated balanced power amplifier, further increasing the output power range of the balanced power amplifier on the basis of the output power of the original three-stage Doherty power amplifier, thereby significantly expanding the output power back-off range of the power amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 The invention is a circuit diagram of a power amplifier capable of extending the output power back-off range.

[0018] Figure 2 FIG. 4 is a structural diagram of an equivalent circuit of an embodiment of the present invention.

[0019] Figure 3 Schematic diagram of the variation of drain fundamental current with input voltage according to an embodiment of the present invention

[0020] Figure 4 Schematic diagram of the variation of drain fundamental voltage with input voltage according to an embodiment of the present invention

[0021] Figure 5 This is a comparison diagram of the efficiency of the present invention and the prior art when the output power is backed off by 18 dB. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings and embodiments. For those skilled in the art, all other embodiments obtained based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0023] Figure 1It is a circuit diagram of the present invention, which can be understood as a three-stage Doherty power amplifier used as a control amplifier of LMBA to achieve a large power back-off range. Specifically, the power distributor provides appropriate power distribution for the main power amplifier M1, the auxiliary power amplifiers A1 and A2, and the balanced power amplifiers B1 and B2; the two ends of the quarter-wavelength impedance transformation line TL3 are respectively connected to the coupling end of the output coupler and the output end of the combiner, in order to achieve the impedance transformation between the three-stage Doherty power amplifier load and the output coupler characteristic impedance Z0; the post-matching network is to achieve the matching of the load impedance and the output coupler characteristic impedance. The phase shifter is designed to achieve the correct power synthesis of BA1 and BA2 through the output coupler and the three-stage Doherty power amplifier, thereby achieving the correct load modulation. The design will be specifically described with an embodiment below.

[0024] Figure 2 The equivalent circuit diagram of an embodiment of the present invention is shown in FIG. 1 . The combiner structure includes: the output of the main power amplifier M1 is connected to the input end of the transmission line TL1, the output end of the auxiliary power amplifier A1 is connected to the output end of the transmission line TL1, and then the input end of the transmission line TL2 is connected in series, and the output end of the transmission line TL2 is connected to the output end of the auxiliary power amplifier A2. The output end of the combiner is cascaded to the input end of the impedance transformation line TL3. In order to ensure that power synthesis can be performed at the combining point, the output signals of each sub-amplifier need to have a suitable phase offset, such as Figure 2 shown.

[0025] Assume that the output power P of the power amplifier is known out The back-off points corresponding to the four efficiency peaks, for example, the efficiency peaks are reached at back-off 18dB, 12dB, 6dB and saturated output, respectively, corresponding to different normalized input voltages g i (i=1,2,3). Assume that all sub-amplifiers have the same drain bias voltage V DD and the same knee voltage V K , in ideal condition V K ≈0.

[0026] Definition i is the normalized input voltage corresponding to the back-off point:

[0027]

[0028] The drain fundamental current of each sub-amplifier is as follows: Figure 3 As shown, the drain fundamental voltage is Figure 4 As shown. Combined Figure 3 and Figure 4 The basic working principle of the present invention is described as follows: the main power amplifier is always in working state, and as the input power increases, when the total output power reaches P bo3 =P outAfter -18dB, the drain fundamental voltage of the main power amplifier M1 reaches its maximum value, ushering in the first efficiency peak, and the auxiliary power amplifier A1 starts to work; as the input power increases, when the total output power reaches P bo2 =P out After -12dB, the drain fundamental current of the main power amplifier M1 reaches its maximum value and remains unchanged in the subsequent process. The drain fundamental voltage of the auxiliary power amplifier A1 reaches its maximum value, ushering in the second efficiency peak. At the same time, the auxiliary power amplifier A2 starts to work. As the input power increases, when the total output power reaches P bo2 =P out -6dB, the drain fundamental currents of auxiliary power amplifier A1 and auxiliary power amplifier A2 both reach their maximum values ​​and remain unchanged in the subsequent process. The drain fundamental voltage of auxiliary power amplifier A2 reaches its maximum value, ushering in the third efficiency peak. At the same time, balanced power amplifiers B1 and B2 start working. Finally, as the input power increases, the final balanced power amplifier also reaches saturation, and the total output power reaches its maximum value. Finally, the present invention achieves 4 fallback efficiency peaks, and the design of the combiner network is relatively simple. The efficiency curve of the present invention is compared with the prior art. Figure 5 As shown, it can be seen that the present invention effectively expands the output power back-off range of the power amplifier.

[0029] Those skilled in the art should understand that the main power amplifier M1, auxiliary power amplifiers A1, A2, and balanced power amplifiers B1, B2 in this embodiment can be a single transistor, or can be composed of a plurality of transistors connected in parallel or stacked together. The transistor can be implemented by a variety of processes, including but not limited to one or any mixture of CMOS, LDMOS, GaN, InP, and GaAs.

[0030] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A power amplifier capable of extending the output power back-off range, characterized in that: The power amplifier comprises: a power divider, a phase shifter, a main power amplifier (M1), auxiliary power amplifiers (A1, A2), a balanced power amplifier (B1, B2), a quarter-wavelength line (ML1), a half-wavelength line (ML2), a combiner, a quarter-wavelength impedance transformation line (TL3), an isolation resistor (R ios ), input coupler, output coupler, post-matching network; The input end of the power divider is connected to the radio frequency signal input, and the four ports of the output end are respectively connected to the input end of the main power amplifier (M1), the input end of the quarter-wavelength line (ML1) cascaded auxiliary power amplifier (A1), the input end of the half-wavelength line (ML2) cascaded auxiliary power amplifier (A2), and the input end of the phase shifter; The input end of the input coupler is connected to the other end of the phase shifter, and the isolation end is connected to the isolation resistor (R ios ), the coupling terminal is connected to the input terminal of the balanced power amplifier (B1), and the through terminal is connected to the input terminal of the balanced power amplifier (B2); The input end of the output coupler is connected to the output end of the balanced power amplifier (B1), the isolation end is connected to the output end of the balanced power amplifier (B2), the coupling end is connected to one end of a quarter-wavelength impedance transformation line (TL3), and the through end is connected to the input end of the rear matching network.

2. The power amplifier according to claim 1, characterized in that: The input end of the combiner is connected to the output end of the main power amplifier M1, the output end of the auxiliary power amplifier A1, and the output end of the auxiliary power amplifier A2 in sequence, and the output end of the combiner is connected to the output end of the quarter-wavelength impedance transformation line TL3.

3. The power amplifier according to claim 1, characterized in that: One end of the post-matching network is connected to the through end of the output coupler, and the other end is connected to the system load, which is usually 50 ohms.

4. The power amplifier according to claim 1, characterized in that: The main power amplifier (M1), auxiliary power amplifiers (A1, A2), and balanced power amplifiers (B1, B2) are all power amplifiers that already include corresponding input and output matching networks.

5. The power amplifier according to claim 1, characterized in that: The main power amplifier (M1) is in class AB bias, the auxiliary power amplifiers (A1 and A2) and the balanced power amplifiers (B1 and B2) are all in class C bias, and are controlled by different gate voltages and turned on in sequence, and the turn-on order is A1>A2>B1=B2.

6. According to the power amplifier of claim 1, the main power amplifier M1, auxiliary power amplifiers A1, A2, and balanced power amplifiers B1, B2 can be a single transistor, or can be composed of a plurality of transistors connected in parallel or stacked together. The transistor can be realized by a variety of processes, including but not limited to one or any mixture of CMOS, LDMOS, GaN, InP, and GaAs.

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