Load modulation balanced power amplifier circuit

Abstract

The invention relates to a load modulation balance power amplifier circuit, which belongs to the technical field of wireless communication, and comprises a first bridge and a circulator, one end of a phase impedance adjusting line is connected with a first bridge straight-through port, and the other end of the phase impedance adjusting line is connected with a third port of the circulator; one end of the impedance adjusting line is connected with the first bridge coupling port, and the other end is connected with the circulator first port; one end of the phase adjusting line is electrically connected with the circulator second port, and the other end serves as a circuit output end; the input end of the power divider serves as a circuit input end; the input end of the main power amplifier is electrically connected with the first output port of the power divider; the input end of the auxiliary power amplifier is electrically connected with the second output port of the power divider; one end of the impedance conversion line is electrically connected with the main power amplifier output end, and the other end is electrically connected with the first bridge isolation port; the output end of the auxiliary power amplifier is electrically connected with the input port of the first bridge. A power absorption load does not need to be arranged, the circuit area and cost are saved, higher power back-off efficiency is achieved, and the transistor can be protected.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology. Specifically, this invention relates to a load modulation balanced power amplifier circuit. Background Technology

[0002] In 5G base station system design, power back-off technology is typically employed to maintain system linearity. To ensure continued high efficiency after power back-off, many communication systems use the Doherty architecture for their RF transmitter front-end power amplifiers to improve back-off efficiency. To prevent damage to the power amplifier transistors in the Doherty architecture circuitry from excessive load mismatch, the output is usually connected to a circulator, with a power absorption load added to the third port of the circulator. However, the power absorption load in this solution is typically large and expensive, significantly increasing circuit area and cost. Summary of the Invention

[0003] To address the aforementioned issues and reduce circuit area and cost while maintaining high efficiency during power back-off, this invention discloses a load-modulated balanced power amplifier circuit. This solution eliminates the need for a power absorption load, thereby saving area and reducing costs. It achieves the same performance as a traditional Doherty architecture circuit through two load-modulated balanced power amplifier circuits, while having higher power back-off efficiency and the ability to protect transistors from damage.

[0004] A first aspect of the present invention provides a load-modulated balanced power amplifier circuit, comprising:

[0005] The first bridge is a four-port bridge, including a first bridge isolation port, a first bridge input port, a first bridge through port, and a first bridge coupling port; it is used for load impedance modulation, power combining, and converting reflected signals into impedance modulation.

[0006] The circulator includes a first port, a second port, and a third port. When transmitting a signal, it is used to achieve unidirectional transmission and reverse isolation of the signal, allowing the signal to flow only in a set direction while preventing reverse interference. When receiving a signal, it is used for unidirectional transmission of the signal.

[0007] The phase impedance adjustment line is electrically connected at one end to the first bridge through port and at the other end to the circulator third port.

[0008] An impedance adjustment line is electrically connected at one end to the coupling port of the first bridge and at the other end to the first port of the circulator.

[0009] The phase adjustment line has one end electrically connected to the second port of the circulator, and the other end serves as the circuit output terminal.

[0010] A power divider includes a power divider input terminal, a power divider first output port, and a power divider second output port; it is used to split one input signal into two signals and output them to the main power amplifier and the auxiliary power amplifier respectively; the power divider input terminal serves as the circuit input terminal.

[0011] The main power amplifier has its input terminal electrically connected to the first output port of the power divider.

[0012] The auxiliary power amplifier has its input terminal electrically connected to the second output port of the power divider.

[0013] Impedance transformation line: one end is electrically connected to the output terminal of the main power amplifier, and the other end is electrically connected to the isolation port of the first bridge;

[0014] The output terminal of the auxiliary power amplifier is electrically connected to the input port of the first bridge.

[0015] Furthermore, the circulator rotates counterclockwise;

[0016] The power divider is a Wilkinson power divider, a coupled-line directional coupler, or a Lange coupler;

[0017] The main power amplifier is a Class AB amplifier;

[0018] The auxiliary power amplifier is a Class C amplifier;

[0019] The main power amplifier is an RF power amplifier carrier transistor;

[0020] The auxiliary power amplifier is a peak transistor for an RF power amplifier;

[0021] Impedance transformation lines are used to change impedance values ​​to achieve impedance matching in circuits.

[0022] Phase adjustment line, used to adjust the carrier phase of the circuit;

[0023] Phase impedance adjustment line is used to adjust the phase of circuit signals while also ensuring circuit impedance matching.

[0024] Impedance adjustment lines are used to change the impedance characteristics of a circuit, achieve impedance matching between the source and load, and reduce signal reflection.

[0025] Furthermore, under the combined action of the phase impedance adjustment line, the impedance adjustment line, and the phase adjustment line, the phase difference θ between the circuit reflected signal and the main power amplifier and the auxiliary power amplifier is 0°.

[0026] Furthermore, the first bridge includes a 3dB orthogonal hybrid network bridge;

[0027] The impedance transformation line is a 1 / 4 wavelength impedance transformation line.

[0028] Furthermore, the connection relationships between the main power amplifier, auxiliary power amplifier, impedance transformation line, power divider, and first bridge are replaced as follows:

[0029] The main power amplifier has its input terminal electrically connected to the second output port of the power divider.

[0030] The auxiliary power amplifier has its input terminal electrically connected to the first output port of the power divider.

[0031] Impedance transformation line: one end is electrically connected to the output terminal of the main power amplifier, and the other end is electrically connected to the input port of the first bridge;

[0032] The output terminal of the auxiliary power amplifier is electrically connected to the isolation port of the first bridge.

[0033] Furthermore, the circulator rotates clockwise.

[0034] Furthermore, the power divider uses a second bridge circuit as the power divider;

[0035] The second bridge includes a second bridge isolation port, a second bridge input port, a second bridge through port, and a second bridge coupling port; it is used to split one signal into two signals of different phases; wherein,

[0036] The second bridge isolation port serves as the input terminal of the power divider;

[0037] The second bridge input port is connected to the load ground;

[0038] The second bridge direct-through port is electrically connected to the second output port of the power divider and the input of the auxiliary power amplifier.

[0039] After the second bridge coupling port is connected to the phase shifter, it serves as the first output port of the power divider and is electrically connected to the input terminal of the main power amplifier.

[0040] Furthermore, the power divider uses a second bridge circuit as the power divider;

[0041] The second bridge includes a second bridge isolation port, a second bridge input port, a second bridge through port, and a second bridge coupling port; it is used to split one signal into two signals of different phases; wherein,

[0042] The second bridge isolation port serves as the input terminal of the power divider;

[0043] The second bridge input port is connected to the load ground;

[0044] The second bridge direct-through port is electrically connected to the main power amplifier input terminal as the second output port of the power divider.

[0045] After the second bridge coupling port is connected to the phase shifter, it serves as the first output port of the power divider and is electrically connected to the input terminal of the auxiliary power amplifier.

[0046] A second aspect of the present invention provides a load modulation balanced power amplifier circuit for a TDD system, employing the load modulation balanced power amplifier circuit described in the first aspect of the present invention, and further comprising an RF switch and a low-noise amplifier:

[0047] The radio frequency switch includes a first port, a second port, and a third port; it is used to switch between receiving and transmitting conversion signal channels.

[0048] The connection method of the phase impedance adjustment line is replaced by one end being electrically connected to the first bridge through port and the other end being electrically connected to the second port of the RF switch.

[0049] The low-noise amplifier has its input terminal electrically connected to the third port of the radio frequency switch, and is used to amplify the received signal.

[0050] The third port of the circulator is electrically connected to the first port of the radio frequency switch.

[0051] Furthermore, the input terminal of the power divider is used to connect to the output port or transmit port of the upper-level transceiver; the output terminal of the low-noise amplifier is used to connect to the input port or receive port of the upper-level transceiver; and the output terminal of the circuit is used to connect to the port of the lower-level duplexer.

[0052] The advantages of this invention compared to the prior art are:

[0053] First, the present invention eliminates the power absorption load, thereby saving circuit area, reducing production costs, and improving production efficiency;

[0054] Secondly, this invention offers better overall performance and stronger compatibility: the performance of the two-channel load-modulated balanced power amplifier circuit is the same as the traditional Doherty, but with higher back-off power; the outputs of the main and auxiliary power amplifiers are connected to different bridge ports, allowing adaptation to circulators with different corresponding rotation directions; this invention does not limit the structure of the power divider, allowing it to be either a bridge-type power divider or a Wilkinson power divider; the lengths of the impedance transformation line, phase impedance adjustment line 1, impedance adjustment line 2, and phase adjustment line 3 described in this invention are not limited, and can be as short as 0, adjustable according to the corresponding impedance and phase requirements. Therefore, it offers better overall performance and stronger compatibility.

[0055] Finally, this invention enables the control of the maximum mismatch VSWR by adjusting the phase of the reflected signal, thereby protecting the transistor from damage and enhancing device reliability. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of a power amplifier circuit based on the traditional Doherty architecture.

[0057] Figure 2 This is a schematic diagram of a load modulation balanced amplifier circuit provided in an embodiment of the present invention.

[0058] Figure 3 This is a schematic diagram of a second type of load modulation balanced amplifier circuit provided in an embodiment of the present invention.

[0059] Figure 4 This is a schematic diagram of a third type of load modulation balanced amplifier circuit provided in an embodiment of the present invention.

[0060] Figure 5 This is a schematic diagram of a fourth type of load modulation balanced amplifier circuit provided in an embodiment of the present invention.

[0061] Figure 6 This is a schematic diagram of the bridge circuit when the auxiliary power amplifier is turned off under mismatch conditions.

[0062] Figure 7 This is a schematic diagram of the bridge circuit when the auxiliary power amplifier is turned on under mismatch conditions.

[0063] Figure 8 This is a circuit diagram showing the output power ratio of the main and auxiliary power amplifiers in a 1:1 ratio, provided for an embodiment of the present invention.

[0064] Figure 9 A schematic diagram showing the change in output efficiency as output current when the output power ratio of the main and auxiliary power amplifiers is 1:1.

[0065] Figure 10 A schematic diagram showing the change in output impedance as output current when the output power ratio of the main and auxiliary power amplifiers is 1:1.

[0066] Figure 11 The circuit diagram provided in this embodiment of the invention shows that the output power ratio of the main and auxiliary power amplifiers is 1:2.

[0067] Figure 12 A schematic diagram showing the output efficiency of the main and auxiliary power amplifiers as a function of output current, with the output power ratio of the main amplifier to the auxiliary amplifier being 1:2.

[0068] Figure 13 A schematic diagram showing the change in output impedance as output current when the output power ratio of the main and auxiliary power amplifiers is 1:2.

[0069] Figure 14 This is a schematic diagram of a load modulation balanced amplifier circuit for a TDD system provided in an embodiment of the present invention.

[0070] Reference numerals: 1, circulator first port; 2, circulator second port; 3, circulator third port. Detailed Implementation

[0071] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0072] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0073] Example

[0074] To improve efficiency, current base station communication systems typically employ power amplifier (PA) circuits in the transmitter front-end as follows: Figure 1 The Doherty architecture circuit is shown. To protect the power amplifier (PA) from load mismatch or damage, a circulator and a power absorption load are required at the output of the Doherty architecture circuit. As the output power of the base station's single-pass circuit increases, the corresponding power absorption load also needs to increase, which undoubtedly increases the circuit area and cost. To save on the area and cost of the power amplifier circuit, this invention discloses... Figures 2 to 5 The load-modulated balanced amplifier circuit shown does not require a power absorption load, thus saving area and reducing cost. It achieves the same performance as the traditional Doherty architecture circuit through two load-modulated balanced power amplifier circuits, but with higher power back-off efficiency and transistor protection against damage.

[0075] Example 1

[0076] In a first aspect, the present invention provides a load-modulated balanced power amplifier circuit, such as... Figure 2 As shown, it specifically includes:

[0077] The first bridge is a four-port bridge, including a first bridge isolation port, a first bridge input port, a first bridge through port, and a first bridge coupling port; it is used for load impedance modulation, power combining, and converting reflected signals into impedance modulation.

[0078] The circulator includes a first port 1, a second port 2, and a third port 3. When transmitting a signal, it is used to achieve unidirectional transmission and reverse isolation of the signal, allowing the signal to flow only in the set direction while preventing reverse interference. When receiving a signal, it is used to transmit the signal unidirectionally.

[0079] The phase impedance adjustment line is electrically connected at one end to the first bridge through port and at the other end to the circulator third port.

[0080] An impedance adjustment line is electrically connected at one end to the coupling port of the first bridge and at the other end to the first port of the circulator.

[0081] The phase adjustment line has one end electrically connected to the second port of the circulator, and the other end serves as the circuit output terminal.

[0082] A power divider includes a power divider input terminal, a power divider first output port, and a power divider second output port; it is used to split one input signal into two signals and output them to the main power amplifier and the auxiliary power amplifier respectively; the power divider input terminal serves as the circuit input terminal.

[0083] The main power amplifier has its input terminal electrically connected to the first output port of the power divider.

[0084] The auxiliary power amplifier has its input terminal electrically connected to the second output port of the power divider.

[0085] Impedance transformation line: one end is electrically connected to the output terminal of the main power amplifier, and the other end is electrically connected to the isolation port of the first bridge;

[0086] The output terminal of the auxiliary power amplifier is electrically connected to the input port of the first bridge.

[0087] Furthermore, the circulator rotates counterclockwise.

[0088] In communication circuits, the rotation direction of a circulator refers to the fixed sequence of signal transmission directions. It determines that signals can only flow in a specific direction and cannot be transmitted in the opposite direction. For example, if a signal enters from port 1 and exits from port 2, or enters from port 2 and exits from port 3, this direction is "counterclockwise rotation," and the opposite is "clockwise rotation."

[0089] Optionally, the power divider is a Wilkinson power divider, a coupled-line directional coupler, a Lange coupler, or other radio frequency devices with similar functions.

[0090] The main power amplifier and auxiliary power amplifier are used to amplify the input signal. The main power amplifier operates in Class AB and is a Class AB amplifier. The auxiliary power amplifier operates in Class C and is a Class C amplifier. The main power amplifier provides the high gain and high efficiency required for small signals, and the power and efficiency required for large signals. The auxiliary power amplifier provides the power and efficiency required for large signals.

[0091] Furthermore, the main power amplifier is a carrier transistor of an RF power amplifier, and the auxiliary power amplifier is a peak transistor of an RF power amplifier.

[0092] The first bridge is used to take the signals input from the first bridge input terminal and the first bridge isolation terminal, and after load modulation and balancing, output them to the phase impedance adjustment line and the impedance adjustment line through the first bridge direct terminal and the first bridge coupling terminal, respectively.

[0093] Each port of the first bridge has the following functions:

[0094] The first bridge isolation port provides the impedance modulated by the load;

[0095] The first bridge input port provides the impedance modulated by the load;

[0096] The first bridge direct-through port passes through a phase impedance adjustment line and a circulator, converting the reflected signal into impedance modulation;

[0097] The first bridge coupling port transmits signals to the external load via impedance adjustment lines, circulators, and phase adjustment lines.

[0098] Optionally, the first bridge can be a 3dB orthogonal (90°) hybrid network bridge or other types of four-port bridges.

[0099] An impedance matching line is a conductor used to change the impedance value to achieve impedance matching. An example is a quarter-wavelength impedance matching line.

[0100] A phase adjustment line is a wire used to adjust the phase of a carrier wave.

[0101] A phase impedance adjustment line is a wire used to adjust the phase of a signal while also ensuring impedance matching.

[0102] Impedance adjustment wires are conductors that reduce signal reflection by changing the impedance characteristics of the line (such as resistance, capacitance, and inductance) to achieve impedance matching between the source and load ends.

[0103] This invention does not limit the length of the impedance transformation line, phase impedance adjustment line, impedance adjustment line, and phase adjustment line; the shortest length can be 0. Their lengths are set according to the following principles:

[0104] Under the combined action of the phase impedance adjustment line, the impedance adjustment line and the phase adjustment line, the phase difference θ between the reflected signal and the main and auxiliary power amplifiers is 0°.

[0105] The optimal efficiency impedance and saturation power impedance of the main power amplifier are matched to the port impedance modulated by the first bridge load through a matching network.

[0106] The optimal saturation power impedance of the auxiliary power amplifier is matched to the port impedance modulated by the first bridge load through a matching network.

[0107] Example 2

[0108] A second aspect of the invention provides another load-modulated balanced power amplifier circuit, such as... Figure 3 As shown, the difference from Example 1 is:

[0109] The main power amplifier has its input terminal electrically connected to the second output port of the power divider.

[0110] The auxiliary power amplifier has its input terminal electrically connected to the first output port of the power divider.

[0111] Impedance transformation line: one end is electrically connected to the output terminal of the main power amplifier, and the other end is electrically connected to the input port of the first bridge;

[0112] The output terminal of the auxiliary power amplifier is electrically connected to the isolation port of the first bridge.

[0113] The remaining circuit structure is the same as in Example 1.

[0114] In Examples 1 and 2, the outputs of the main and auxiliary power amplifiers are connected to the ports of the first bridge differently, corresponding to circulators with different rotation directions, as shown in the figure. Figure 2 and Figure 3 The commutator rotates in the direction of rotation. In this embodiment, the circulator rotates clockwise.

[0115] Example 3

[0116] A third aspect of the invention provides another load-modulated balanced power amplifier circuit, such as... Figure 4 As shown, unlike Embodiment 1, the power divider uses a second bridge circuit as the power divider:

[0117] The second bridge includes a second bridge isolation port, a second bridge input port, a second bridge through port, and a second bridge coupling port; it is used to split one signal into two signals of different phases; wherein...

[0118] The second bridge isolation port serves as the input terminal of the power divider;

[0119] The second bridge input port is connected to the load ground;

[0120] The second bridge direct-through port is electrically connected to the second output port of the power divider and the input of the auxiliary power amplifier.

[0121] After the second bridge coupling port is connected to the phase shifter, it serves as the first output port of the power divider and is electrically connected to the input terminal of the main power amplifier.

[0122] The remaining circuit structure is the same as in Example 1.

[0123] The power divider described in this invention functions to split one signal into two signals. The structure of the power divider is not limited; for example… Figure 2 Wilkinson power dividers can be used. Figure 4 A bridge power divider is used.

[0124] The first bridge and the second bridge can be of the same model or different models. In this invention, their functions are different. The main function of the second bridge is to split one signal into two signals with different phases, while the main functions of the first bridge include load impedance modulation, power combining, and converting reflected signals into impedance modulation.

[0125] Example 4

[0126] A fourth aspect of the invention provides another load-modulated balanced power amplifier circuit, such as... Figure 5 As shown, unlike Embodiment 2, the power divider uses a second bridge circuit as the power divider:

[0127] The second bridge includes a second bridge isolation port, a second bridge input port, a second bridge through port, and a second bridge coupling port; it is used to split one signal into two signals of different phases; wherein...

[0128] The second bridge isolation port serves as the input terminal of the power divider;

[0129] The second bridge input port is connected to the load ground;

[0130] The second bridge direct-through port is electrically connected to the main power amplifier input terminal as the second output port of the power divider.

[0131] After the second bridge coupling port is connected to the phase shifter, it serves as the first output port of the power divider and is electrically connected to the input terminal of the auxiliary power amplifier.

[0132] The remaining circuit structure is the same as in Example 2.

[0133] Example 5

[0134] This invention can be applied not only to FDD (Frequency Division Duplexing) base station systems, but also to TDD (Time Division Duplexing) base station systems.

[0135] A fifth aspect of the invention provides a load-modulated balanced power amplifier circuit for a TDD system, such as... Figure 14 As shown, unlike Embodiment 1, it also includes an RF switch and a low-noise amplifier:

[0136] An RF switch, including an RF switch first port, an RF switch second port, and an RF switch third port, is used to switch between receive and transmit signal conversion channels.

[0137] The phase impedance adjustment line is electrically connected at one end to the first bridge through port and at the other end to the second port of the radio frequency switch.

[0138] The low-noise amplifier has its input terminal electrically connected to the third port of the radio frequency switch, and is used to amplify the received signal.

[0139] The third port of the circulator is electrically connected to the first port of the radio frequency switch.

[0140] The remaining circuit structure is the same as in Example 1.

[0141] like Figure 14 As shown on the left, “RX Input”, the power divider input is used to connect to the output (transmit) port of the upstream transceiver.

[0142] like Figure 14 As shown in the "TX Output" on the left, the output of the low-noise amplifier is used to connect to the input (receive) port of the upstream transceiver.

[0143] As shown in the "TX / RX port" on the right side of the figure, the circuit output is used to connect to the port of the next-stage duplexer.

[0144] The same technical effect can be achieved by using Examples 2 to 4, which will not be described in detail here.

[0145] The circuit working principle of Examples 1 to 5:

[0146] When the load-modulated balanced power amplifier circuit is working, the power divider splits the input power into two signals, which are respectively input to the main power amplifier (carrier power amplifier transistor) and the auxiliary power amplifier (peak power amplifier transistor). After being amplified by the main power amplifier and the auxiliary power amplifier, the two signals enter the first bridge at the same time. After being actively load-modulated and balanced in the first bridge, the signals are output from the coupling port of the first bridge, and then output to the external load after passing through the impedance adjustment line, the circulator and the phase adjustment line.

[0147] The operation of a load-modulated balanced power amplifier circuit is divided into a first operating state and a second operating state, depending on whether the circuit output matches the external load. The operating mechanisms of the main power amplifier and the auxiliary power amplifier are different in different operating states.

[0148] The first operating state is the operating state when the circuit output matches the external load.

[0149] When the circuit output matches the external load, the main power amplifier operates in Class AB and the auxiliary power amplifier operates in Class C. This invention is equivalent to a Doherty architecture power amplifier circuit with active load modulation. When the input power is low, the auxiliary power amplifier is not yet turned on; only the main power amplifier is working. The output impedance of the auxiliary power amplifier is open-circuit ∞, and the output impedance of the main power amplifier is high impedance Z1 = 2*Z0^2*Z4 / (Z3*Z4+Z0^2) (where Z0 is the characteristic impedance of the first bridge, Z3 is the load impedance of the direct-through port of the first bridge, and Z4 is the load impedance of the coupled port of the first bridge). However, when the input power increases to a certain value, the auxiliary power amplifier is turned on. At this time, the output impedance of the auxiliary power amplifier gradually decreases from infinity. Simultaneously, the signal enters the load, actively modulating the load of the main power amplifier, and the output impedance of the main power amplifier also begins to gradually decrease from high impedance. When the auxiliary power amplifier is fully turned on, the output impedances of both the main and auxiliary power amplifiers are simultaneously at their optimal saturation power output impedances; at this time, the output impedances of the main power amplifier and the auxiliary power amplifier are Z1 and Z2, respectively.

[0150] Z1=Z0*((Z3*Z4-Z0^2)*(-j*I2 / I1)+2*Z0*Z4) / (Z3*Z4+Z0^2),

[0151] Z2=Z0*((Z0^2-Z3*Z4)*(j*I1 / I2)+2*Z0*Z3) / (Z3*Z4+Z0^2);

[0152] Where I1 is the main power amplifier output current, I2 is the auxiliary power amplifier output current, Z0 is the characteristic impedance of the first bridge, Z3 is the load impedance of the direct-through port of the first bridge, Z4 is the load impedance of the coupled port of the first bridge, and j is an imaginary number. In this configuration, the output impedances of the main and auxiliary power amplifier transistors modulate each other, thereby achieving high efficiency in both power return and saturation states.

[0153] The second operating state is the operating state when the circuit output is mismatched with the external load:

[0154] When the circuit output is mismatched with the external load, the main power amplifier operates in Class AB, and the auxiliary power amplifier operates in Class C. The schematic diagram at this time is as follows: Figure 6 and Figure 7 As shown.

[0155] The reflected signal generated by the unmatched load is input to the direct-through port of the first bridge through the third port of the circulator. At this time, the output of the main power amplifier, the output of the auxiliary power amplifier, and the reflected power of the external load form a load-modulated balanced amplifier circuit in the first bridge. When the input power is small, the auxiliary power amplifier is not turned on, and the input port of the first bridge is relatively open. At this time, only the input power P1 of the main power amplifier and the reflected power P3 are load-balanced modulated in the first bridge. The impedance of the main power amplifier is Z1 = 2^(0.5)*Z0*j*I3) / I1 (where Z0 is the characteristic impedance of the first bridge, I3 is the signal reflected from the direct-through port of the first bridge, and j is an imaginary number). When the input power increases to a certain value, the auxiliary power amplifier is turned on. At this time, the input power P1 of the main power amplifier, the input power P2 of the auxiliary power amplifier, and the reflected power P3 are load-balanced modulated in the first bridge simultaneously. By adjusting the phase of the feedback signal, the output impedance of the main and auxiliary power amplifiers does not change too drastically, protecting the power amplifier from damage by the reflected signal, thus playing a protective role. At this point, the output impedances of the main and auxiliary power amplifiers as a function of current are Z1 and Z2, respectively:

[0156] Z1=-Z0*j*(I2+2^(0.5)*I3) / I1,

[0157] Z2=Z0*(-Z4*j*I1+2*Z0*I2+2^(0.5)*Z0*I3) / (Z4*I2);

[0158] Where I1 is the main power amplifier output current, I2 is the auxiliary power amplifier output current, I3 is the signal fed back from the direct-through port of the first bridge, Z0 is the characteristic impedance of the first bridge, Z4 is the load impedance of the coupling port of the first bridge, and j is an imaginary number. By adjusting the phase impedance adjustment line, impedance adjustment line, and phase adjustment line, the output impedance modulation of the main and auxiliary power amplifiers can be achieved, and the load mismatch VSWR will not be too large and damage the power transistors, thereby protecting the main and auxiliary power amplifiers.

[0159] Circuit working principle when the output power of the main and auxiliary power amplifiers is 1:1:

[0160] When the output power ratio of the main and auxiliary power amplifiers is 1:1, the circuit structure is based on... Figure 8 Taking the example shown, let the output impedance of the main and auxiliary power amplifiers at maximum output saturation power be Ropt, and the impedance transformation line be set as a 1 / 4 wavelength impedance transformation line. The first bridge uses a 3dB orthogonal (90°) hybrid network bridge. The input power is split into two signals by the power divider, which are input to the main power amplifier and the auxiliary power amplifier respectively. After being amplified by the power amplifiers, they enter the first bridge. The two signals undergo active load modulation and power combining in the bridge, and then are sent to the circulator, and finally output to the external load. Its two operating states are as follows.

[0161] First working status:

[0162] When the circuit output is matched to the load Zload = Ropt, the main power amplifier operates in Class AB, and the auxiliary power amplifier operates in Class C. At low input power, the auxiliary power amplifier is not yet activated; only the main power amplifier is active. The impedance at the first bridge input port is open-circuit ∞, and the output impedance of the main power amplifier is 2*Ropt (Ropt is the optimal impedance for output power matching), operating in high-efficiency mode. However, as the input power increases to a certain value, the auxiliary power amplifier is activated. At this point, the output impedance of the auxiliary power amplifier gradually decreases from infinity, and active modulation begins. Simultaneously, the output impedance of the main power amplifier also begins to decrease from 2*Ropt. When the auxiliary power amplifier is fully activated, its output power equals that of the main power amplifier. At this point, the output impedance of both the auxiliary and main power amplifiers is Ropt.

[0163] Assuming the saturation power current of both the main and auxiliary power amplifiers is Ib, the load impedances Z1 and Z2 of the main and auxiliary power amplifiers can be calculated based on the impedance parameter matrix of the four-port orthogonal (90°) hybrid network bridge, as follows:

[0164] When the auxiliary power amplifier is not turned on: Z1=2*Ropt, Z2=∞;

[0165] When the auxiliary power amplifier is turned on:

[0166] Z1 = (1 + β) * Ropt / 2 (where 0 ≤ β ≤ 1),

[0167] Z2=(1+β)*Ropt / (2*β) (where 0≤β≤1);

[0168] When both the main and auxiliary power amplifiers reach their saturation power β=1, Z1=Ropt, Z2=Ropt.

[0169] As shown in the above formula, the working principle of this circuit is the same as that of the traditional Doherty circuit. When the input power is relatively low, it can improve the efficiency of the main power amplifier. When Ropt = 50 ohms, the efficiency curves of the main, auxiliary, and combined power amplifiers as a function of the normalized output current of the main power amplifier are as follows: Figure 9 As shown in the figure, the output impedance of the main and auxiliary power amplifiers varies with the normalized output current of the main power amplifier. Figure 10 As shown.

[0170] Second working state:

[0171] When the circuit output is mismatched with the external load, the main power amplifier operates in Class AB and the auxiliary power amplifier operates in Class C. The reflected signal generated by the mismatched load enters the first bridge through port through the third port of the circulator. At this time, the output of the main power amplifier, the output of the auxiliary power amplifier and the load reflected power form a load-modulated balanced amplifier circuit in the bridge.

[0172] Let the signal reflected due to mismatch be \(I_c\cdot e^{j\theta}\) (where \(I_c\) is the amplitude of the reflected signal, and the amplitude range of \(I_c\) is \(0 < I_c\leq I_b + I_b\), \(j\) is the imaginary unit, and \(\theta\) is the phase). Then, after load modulation balance, the output impedances of the main and auxiliary power amplifiers are \(Z_1'\) and \(Z_2'\) respectively, and the input impedance of the through port of the bridge is \(Z_3'\). The corresponding values can be obtained as follows:

[0173] When the auxiliary power amplifier is not turned on:

[0174] \(Z_1'=\frac{R_{opt}\cdot I_b}{\sqrt{2}\cdot I_c\cdot e^{j\theta}}\),

[0175] \(Z_2'=\infty\),

[0176] \(Z_3'=R_{opt}\cdot(1 - \frac{\sqrt{2}\cdot I_b}{I_c\cdot e^{j\theta}})\);

[0177] When the auxiliary power amplifier is turned on:

[0178] \(Z_1'=\frac{R_{opt}\cdot I_b}{\beta\cdot I_b+\sqrt{2}\cdot I_c\cdot e^{j\theta}}\) (where \(0\leq\beta\leq1\)),

[0179] \(Z_2'=R_{opt}\cdot(\frac{2\beta(3 + \beta)}{1 + 3\beta}-1+\frac{(3 + \beta)\sqrt{2}\cdot I_c\cdot e^{j\theta}}{(1 + 3\beta)\cdot I_b} / \beta)\) (where \(0\leq\beta\leq1\)),

[0180] \(Z_3'=R_{opt}\cdot\frac{3(\beta^2 - 1)\sqrt{2}\cdot I_b}{I_c\cdot e^{j\theta}}+3+\beta}{1 + 3\beta}\) (where \(0\leq\beta\leq1\));

[0181] When both the main and auxiliary power amplifiers reach the saturation power (\(\beta = 1\)):

[0182] \(Z_1'=\frac{R_{opt}\cdot I_b}{I_b+\sqrt{2}\cdot I_c\cdot e^{j\theta}}\), ​​​​​​​​​​​​​Z1´=Ropt*Ib / (2^(0.5)*Ic),

[0188] Z2´=∞,

[0189] Z3´=Ropt*(1-2^(0.5)*Ib / Ic);

[0190] When the auxiliary power amplifier is turned on and both the main and auxiliary power amplifiers reach their saturation power β=1:

[0191] Z1´=Ropt*Ib / (Ib+2^(0.5)*Ic),

[0192] Z2´=Ropt*(1+2^(0.5)*Ic / Ib),

[0193] Z3´=Ropt.

[0194] As can be seen from the above formula, when the main and auxiliary power amplifiers are at maximum saturation power output, if a short circuit or open circuit occurs at the second port of the circulator, the entire output signal is reflected to the first bridge through port (i.e., Ic=2*Ib). After the load modulation balance of the bridge, when the output signals reach the output ports of the main and auxiliary power amplifiers, the output impedances Z1´ and Z2´ become Ropt*(1+2^(1.5)) and Ropt*(1+2^(1.5)), that is, the maximum load mismatch VSWR is 3.83. By controlling the maximum load mismatch VSWR, the power transistors are protected from damage.

[0195] Circuit working principle when the output power ratio of the main and auxiliary power amplifiers is 1:2:

[0196] When the output power ratio of the main and auxiliary power amplifiers is 1:2, the circuit structure is based on... Figure 11 Taking the example shown, let the output impedances of the main and auxiliary power amplifiers at maximum output saturation power be 3*Ropt / 2 and 3*Ropt / 4 respectively. The impedance transformation line is set as a 1 / 4 wavelength impedance transformation line, and the first bridge uses a 3dB orthogonal (90°) hybrid network bridge. The input power is split into two signals by the power divider, which are input to the main and auxiliary power amplifiers respectively. After amplification, they enter the bridge. The two signals undergo active load modulation and power combining in the bridge before being sent to the circulator and finally output to the load. Its two operating states are as follows.

[0197] First working status:

[0198] When the circuit output is matched to the load Zload = Ropt, the main power amplifier operates in Class AB, and the auxiliary power amplifier operates in Class C. At low input power, the auxiliary power amplifier is not yet activated; only the main power amplifier is active. The impedance at the first bridge input port is open-circuit ∞, and the output impedance of the main power amplifier is 3 * Ropt (Ropt is the optimal impedance for output power matching), operating in high-efficiency mode. However, when the input power increases to a certain value, the auxiliary power amplifier is activated. At this time, the output impedance of the auxiliary power amplifier gradually decreases from infinity, and active modulation begins. Simultaneously, the output impedance of the main power amplifier also begins to gradually decrease from 3 * Ropt. When the auxiliary power amplifier is fully activated, its output power equals that of the main power amplifier. At this point, the output impedance of the auxiliary power amplifier is 3 * Ropt / 4, and the output impedance of the main power amplifier is also 3 * Ropt / 2.

[0199] Assuming the saturation power current of both the main and auxiliary power amplifiers is Ib, the load impedances Z1 and Z2 of the main and auxiliary power amplifiers can be calculated based on the impedance parameter matrix of the four-port orthogonal (90°) hybrid network bridge, as follows:

[0200] When the auxiliary power amplifier is not turned on: Z1=9*Ropt / 2, Z2=∞;

[0201] When the auxiliary power amplifier is turned on:

[0202] Z1 = (1 + β) * Ropt / 2 (where 0 ≤ β ≤ 2),

[0203] Z2=(1+β)*Ropt / (2*β) (where 0≤β≤2);

[0204] When both the main and auxiliary power amplifiers reach their saturation power β=2, Z1=3*Ropt / 2, Z2=3*Ropt / 4.

[0205] As shown in the above formula, the circuit operates on the same principle as a traditional asymmetric Doherty circuit, which improves the efficiency of the main power amplifier when the input power is relatively small. When Ropt = 50 ohms, the efficiency curves of the main and auxiliary power amplifiers and the combined circuit as a function of the normalized output current of the main power amplifier are as follows: Figure 12 As shown in the figure, the output impedance of the main and auxiliary power amplifiers varies with the normalized output current of the main power amplifier. Figure 13 As shown.

[0206] Second working state:

[0207] When the circuit output is mismatched with the external load, the main power amplifier operates in Class AB and the auxiliary power amplifier operates in Class C. The reflected signal generated by the mismatched load is input to the first bridge through port through the third port of the circulator. At this time, the output of the main power amplifier, the output of the auxiliary power amplifier and the load reflected power form a load modulation balanced amplifier circuit in the bridge.

[0208] Let the signal reflected due to mismatch be \(I_c\cdot e^{j\theta}\) (where \(I_c\) is the amplitude of the reflected signal, and the amplitude range of \(I_c\) is \(0 < I_c\leq I_b + I_b\), \(j\) is the imaginary unit, and \(\theta\) is the phase). Then, the output impedances of the main and auxiliary power amplifiers after load modulation balance are \(Z1'\) and \(Z2'\) respectively, and the input impedance of the through port of the first bridge is \(Z3'\). The corresponding formulas are as follows.

[0209] When the auxiliary power amplifier is not turned on:

[0210] \(Z1'=\frac{9\cdot R_{opt}\cdot I_b}{2^{2.5}\cdot I_c\cdot e^{j\theta}}\),

[0211] \(Z2'=\infty\),

[0212] \(Z3'=R_{opt}\cdot(1 - \frac{\sqrt{2}\cdot I_b}{I_c\cdot e^{j\theta}})\);

[0213] When the auxiliary power amplifier is turned on:

[0214] \(Z1'=\frac{9\cdot R_{opt}\cdot I_b}{4\cdot\beta\cdot I_b + 2^{n2.5}\cdot I_c\cdot e^{j\theta}}\) (where \(0\leq\beta\leq2\)),

[0215] \(Z2'=R_{opt}\cdot(\frac{2\cdot\beta\cdot(3 + \beta)}{1 + 3\cdot\beta}-1+\frac{(3 + \beta)\cdot\sqrt{2}\cdot I_c\cdot e^{j\theta}}{(1 + 3\cdot\beta)\cdot I_b} / \beta)\) (where \(0\leq\beta\leq2\)),

[0216] \(Z3'=R_{opt}\cdot\frac{3\cdot(\beta^2 - 1)\cdot\sqrt{2}\cdot I_b}{I_c\cdot e^{j\theta}}+3 + \beta}{1 + 3\cdot\beta}\) (where \(0\leq\beta\leq1\));

[0217] When both the main and auxiliary power amplifiers reach the saturation power (\(\beta = 2\)),

[0218] \(Z1'=\frac{9\cdot R_{opt}\cdot I_b}{8\cdot I_b + 2^{2.5}\cdot I_c\cdot e^{j\theta}}\),

[0219] \(Z2'=R_{opt}\cdot\frac{13 + 5\cdot\sqrt{2}\cdot I_c\cdot e^{j\theta} / I_b}{14}\),

[0220] \(Z3'=R_{opt}\cdot\frac{9\cdot\sqrt{2}\cdot I_b}{I_c\cdot e^{j\theta}}+5}{7}\).

[0221] By adjusting the lengths of the phase impedance adjustment line, impedance adjustment line, and phase adjustment line, the phase difference between the reflected signal and the main and auxiliary power amplifiers is made \(0^{\circ}\), that is, \(\theta = 0^{\circ}\). At this time, the corresponding \(Z1'\) and \(Z2'\) become:

[0222] When the auxiliary power amplifier is not turned on:

[0223] Z1´=9*Ropt*Ib / (2^(2.5)*Ic),

[0224] Z2´=∞,

[0225] Z3´=Ropt*(1-2^(0.5)*Ib / Ic);

[0226] When the auxiliary power amplifier is turned on and both the main and auxiliary power amplifiers reach their saturation power β=2:

[0227] Z1´=9*Ropt*Ib / (8*Ib+2^(2.5)*Ic),

[0228] Z2´=Ropt*(13+5*2^(0.5)*Ic / Ib) / 14,

[0229] Z3´=Ropt*(9*2^(0.5)* Ib / Ic+5) / 7.

[0230] As can be seen from the above formula, when the main and auxiliary power amplifiers are at maximum saturation power output, if a short circuit or open circuit occurs at the second port of the circulator, the entire output signal is reflected to the first bridge through port (i.e., Ic=3*Ib). After the load modulation balance of the bridge, when the output ports of the main and auxiliary power amplifiers are reached, the output impedances Z1´ and Z2´ become 9*Ropt / (8+2^(2.5)*3) and Ropt*(13+5*2^(0.5)*3) / 14, respectively. That is, their maximum load mismatch VSWRs are 4.16 and 3.26, respectively. By controlling the maximum load mismatch VSWR, the power transistors are protected from damage.

[0231] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A load-modulated balanced power amplifier circuit, characterized in that, include: The first bridge is a four-port bridge, including a first bridge isolation port, a first bridge input port, a first bridge through port, and a first bridge coupling port; it is used for load impedance modulation, power combining, and converting reflected signals into impedance modulation. The circulator includes a first port, a second port, and a third port. When transmitting a signal, it is used to achieve unidirectional transmission and reverse isolation of the signal, allowing the signal to flow only in a set direction while preventing reverse interference. When receiving a signal, it is used for unidirectional transmission of the signal. The phase impedance adjustment line is electrically connected at one end to the first bridge through port and at the other end to the circulator third port. An impedance adjustment line is electrically connected at one end to the coupling port of the first bridge and at the other end to the first port of the circulator. The phase adjustment line has one end electrically connected to the second port of the circulator, and the other end serves as the circuit output terminal. A power divider, including a power divider input terminal, a power divider output first port, and a power divider output second port; It is used to split one input signal into two signals and output them to the main power amplifier and the auxiliary power amplifier respectively; the input terminal of the power divider is used as the circuit input terminal; The main power amplifier has its input terminal electrically connected to the first output port of the power divider. The auxiliary power amplifier has its input terminal electrically connected to the second output port of the power divider. Impedance transformation line: one end is electrically connected to the output terminal of the main power amplifier, and the other end is electrically connected to the isolation port of the first bridge; The output terminal of the auxiliary power amplifier is electrically connected to the input port of the first bridge.

2. The load-modulated balanced power amplifier circuit according to claim 1, characterized in that: The circulator rotates counterclockwise. The power divider is a Wilkinson power divider, a coupled-line directional coupler, or a Lange coupler; The main power amplifier is a Class AB amplifier; The auxiliary power amplifier is a Class C amplifier; The main power amplifier is a radio frequency power amplifier carrier tube; The auxiliary power amplifier is the peak transistor of the RF power amplifier; Impedance transformation lines are used to change impedance values ​​to achieve impedance matching in circuits. Phase adjustment line, used to adjust the carrier phase of the circuit; Phase impedance adjustment line is used to adjust the phase of circuit signals while also ensuring circuit impedance matching. Impedance adjustment lines are used to change the impedance characteristics of a circuit, achieve impedance matching between the source and load, and reduce signal reflection.

3. The load-modulated balanced power amplifier circuit according to claim 1, characterized in that: Under the combined action of the phase impedance adjustment line, impedance adjustment line, and phase adjustment line, the phase difference θ between the circuit reflected signal and the main power amplifier and auxiliary power amplifier is 0°.

4. The load-modulated balanced power amplifier circuit according to claim 1, characterized in that: The first bridge includes a 3dB orthogonal hybrid network bridge; The impedance transformation line is a 1 / 4 wavelength impedance transformation line.

5. The load-modulated balanced power amplifier circuit according to claim 1, characterized in that, The connection relationships between the main power amplifier, auxiliary power amplifier, impedance transformation line, power divider, and first bridge are replaced as follows: The main power amplifier has its input terminal electrically connected to the second output port of the power divider. The auxiliary power amplifier has its input terminal electrically connected to the first output port of the power divider. Impedance transformation line: one end is electrically connected to the output terminal of the main power amplifier, and the other end is electrically connected to the input port of the first bridge; The output terminal of the auxiliary power amplifier is electrically connected to the isolation port of the first bridge.

6. The load-modulated balanced power amplifier circuit according to claim 5, characterized in that: The circulator rotates clockwise.

7. A load-modulated balanced power amplifier circuit according to any one of claims 1 to 4, characterized in that, The power divider uses a second bridge circuit as the power divider; The second bridge includes a second bridge isolation port, a second bridge input port, a second bridge through port, and a second bridge coupling port; it is used to split one signal into two signals of different phases; wherein, The second bridge isolation port serves as the input terminal of the power divider; The second bridge input port is connected to the load ground; The second bridge direct-through port is electrically connected to the second output port of the power divider and the input of the auxiliary power amplifier. After the second bridge coupling port is connected to the phase shifter, it serves as the first output port of the power divider and is electrically connected to the input terminal of the main power amplifier.

8. A load-modulated balanced power amplifier circuit according to any one of claims 5 to 6, characterized in that, The power divider uses a second bridge circuit as the power divider; The second bridge includes a second bridge isolation port, a second bridge input port, a second bridge through port, and a second bridge coupling port; it is used to split one signal into two signals of different phases; wherein, The second bridge isolation port serves as the input terminal of the power divider; The second bridge input port is connected to the load ground; The second bridge direct-through port is electrically connected to the main power amplifier input terminal as the second output port of the power divider. After the second bridge coupling port is connected to the phase shifter, it serves as the first output port of the power divider and is electrically connected to the input terminal of the auxiliary power amplifier.

9. A load-modulated balanced power amplifier circuit for a TDD system, characterized in that, The load-modulated balanced power amplifier circuit according to any one of claims 1 to 8 further includes an RF switch and a low-noise amplifier. The radio frequency switch includes a first port, a second port, and a third port; it is used to switch between receiving and transmitting conversion signal channels. The connection method of the phase impedance adjustment line is replaced by one end being electrically connected to the first bridge through port and the other end being electrically connected to the second port of the RF switch. The low-noise amplifier has its input terminal electrically connected to the third port of the radio frequency switch, and is used to amplify the received signal. The third port of the circulator is electrically connected to the first port of the radio frequency switch.

10. The load-modulated balanced power amplifier circuit for a TDD system according to claim 9, characterized in that: The input terminal of the power divider is used to connect to the output port or transmit port of the upstream transceiver. The output of the low-noise amplifier is used to connect to the input or receiving port of the upstream transceiver. The output terminal of the circuit is used to connect to the port of the next-level duplexer.

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