Doherty-like power amplifier with improved rollback efficiency

Abstract

The invention discloses a Doherty-like power amplifier with improved rollback efficiency, which relates to an amplifier and comprises an input power distribution network for isolating a DR stage of a driving amplification unit from an adaptive bias circuit; the output end of the DR stage of the driving amplification unit is connected with the input end of the PA stage of the power output unit; the self-adaptive biasing circuit is used for detecting the envelope change of the input signal of the power amplifier in real time according to the radio frequency signal transmitted by the input power distribution network and outputting a voltage signal; the power output unit PA level is provided with an input end used for receiving a voltage signal, and the voltage signal is used for controlling bias tail tube current of the power output unit PA level; and the input end of the output matching balun network is connected with the PA-level output end of the power output unit. Compared with a traditional AB-type power amplifier, better rollback efficiency is achieved, only one path of power output unit PA level is needed, the load modulation effect does not need to be considered, and broadband application can be achieved.

Description

Technical Field

[0001] The present invention relates to an amplifier, and more particularly to a Doherty-like power amplifier with improved back-off efficiency. Background Art

[0002] As the most power-consuming module in a transmitting system, the power-added efficiency (PAE) of a power amplifier (PA) is crucial, representing its ability to convert DC power into AC power. If an amplifier is not efficient enough, it is not conducive to the energy consumption of the entire system. Due to the non-linear factors of the amplifier, in high-order communications (such as 16QAM, 64QAM, etc.), the power amplifier in a general transmitter system usually operates at the back-off point of 6 - 8 dBm in the saturation region. When operating at the back-off point, the efficiency of a traditional class-AB power amplifier will decrease significantly, affecting the energy efficiency of the entire system. To improve the efficiency at the back-off point, researchers have proposed many power amplifiers with special structures, including the Doherty power amplifier. The traditional Doherty power amplifier structure is composed of two-way power amplifiers combined for output, and the two-way PAs work at different inputs through active load modulation. One is biased in class-AB and the other is biased in class-C. At low inputs, the main power amplifier is turned on while the auxiliary power amplifier is turned off. When the input increases, the auxiliary power amplifier is turned on, enabling the entire circuit to maintain a high efficiency, so that the circuit can also have a high operating efficiency at the back-off point.

[0003] However, the traditional Doherty power amplifier has the following problems when in use: 1. It requires two-way PAs, and also includes structures such as bias adjustment and passive devices, which will cause an increase in chip area.

[0004] 2. In the millimeter-wave frequency band, strong parasitic effects will affect the circuit function, resulting in limited output power and efficiency of the Doherty power amplifier operating in this frequency band, and the back-off efficiency curve is not obvious.

[0005] 3. The traditional Doherty PA relies on a quarter-wavelength line and an impedance transformation network (such as Zopt→2Zopt transformation), making it difficult to achieve broadband matching, so the bandwidth is limited. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a Doherty-like power amplifier with improved back-off efficiency in view of the deficiencies of the prior art. By controlling the current magnitude of the bias tube of the power output unit PA stage through an envelope-tracking-based adaptive bias circuit, the output current of the power output unit PA stage is made larger to achieve a larger output power, and the efficiency continues to increase, thereby achieving a better back-off efficiency compared with the traditional class-AB power amplifier. And the present invention only requires one-way power output unit PA stage, without considering the load modulation effect, and can achieve broadband applications.

[0007] A Doherty-like power amplifier with improved back-off efficiency according to the present invention includes: An input power distribution network that outputs two RF signals. One of the RF signals is input into the DR stage of the drive amplification unit, and the other RF signal is input into the adaptive bias circuit to isolate the DR stage of the drive amplification unit and the adaptive bias circuit; The DR stage of the drive amplification unit, whose output end is connected to the input end of the PA stage of the power output unit; The adaptive bias circuit is used to detect the change of the envelope of the input signal of the power amplifier in real time according to the RF signal delivered by the input power distribution network and output a voltage signal; The PA stage of the power output unit has an input end for receiving the voltage signal, and the voltage signal is used to control the bias tail pipe current of the PA stage of the power output unit to adjust the output power and conversion efficiency of the PA stage of the power output unit; The output matching balun network, whose input end is connected to the output end of the PA stage of the power output unit.

[0008] At high input signal power, the current magnitude of the bias transistor of the PA stage of the power output unit is controlled by the envelope tracking-based adaptive bias circuit, so that the output current of the PA stage of the power output unit is larger to achieve a larger output power, and the efficiency continues to increase, thereby achieving a better back-off efficiency compared with traditional class AB power amplifiers. And the present invention only needs one PA stage of the power output unit and does not need to consider the load modulation effect, and can achieve broadband applications. The present invention has achieved good output power and back-off effect through a 140 GHz broadband PA based on TSMC 65 nm process.

[0009] Preferably, the adaptive bias circuit includes a detector and a buffer stage; the input end of the detector inputs an RF signal, and the output end of the detector is connected to the input end of a buffer stage, and the voltage signal is output from the input end of the buffer stage.

[0010] Preferably, the detector includes a self-mixing differential pair composed of a first transistor M1 and a second transistor M2 and a load network; the gates of the first transistor M1 and the second transistor M2 are respectively used as an input terminal to input the INP signal and the INN signal of the RF signal; the sources of the first transistor M1 and the second transistor M2 are connected and connected to the common terminal; the drains of the first transistor M1 and the second transistor M2 are connected and connected to the load network, and the connection end of the load network and the drains of the first transistor M1 and the second transistor M2 is used as the output end of the detector and is connected to the buffer stage.

[0011] Preferably, the load network is a resistor or a PMOS transistor.

[0012] Preferably, the output terminal of the detector is grounded through a first capacitor C1.

[0013] Preferably, the buffer stage includes a fourth transistor M4, a first resistor R1, and a filter network; the gate of the fourth transistor M4 is connected to the output terminal of the detector, the source of the fourth transistor M4 is grounded, the drain of the fourth transistor M4 is connected to one end of the first resistor R1 and the input terminal of the filter network at the same time, the other end of the first resistor R1 is connected to the power supply terminal, and the output terminal of the filter network outputs an output voltage.

[0014] Preferably, the power output unit PA stage includes an amplifier structure with cross-neutralization capacitors and a power supply tail pipe composed of a fifth transistor M5 and a sixth transistor M6; a voltage signal is input to the gate of the fifth transistor M5, a fixed bias signal is input to the gate of the sixth transistor M6, the sources of the fifth transistor M5 and the sixth transistor M6 are both grounded, and the drains of the fifth transistor M5 and the sixth transistor M6 are commonly connected to the amplifier structure with cross-neutralization capacitors.

[0015] Preferably, the amplifier structure with cross-neutralization capacitors is a common-source amplifier structure with cross-neutralization capacitors or a cascode amplifier structure with cross-neutralization capacitors.

[0016] Preferably, the drive amplification unit DR stage includes a common-source amplifier structure with cross-neutralization capacitors.

[0017] Preferably, the drive amplification unit DR stage includes an amplifier structure with cross-neutralization capacitors and a power supply tail pipe.

[0018] Advantageous Effects The advantages of the present invention are as follows: 1. A bias voltage is set for the compensation tube inside the Doherty-like power amplifier of the present invention, enabling the PA stage of the power output unit to maintain a high efficiency at low input power. As the input power increases, the output power increases accordingly until the power corresponding to the set output current. However, at this time, the PA stage of the power output unit does not enter the saturation region, and the efficiency of the PA stage of the power output unit continues to increase with the increase of the input signal. At high input signal power, the current magnitude of the bias tube of the PA stage of the power output unit is controlled by an envelope tracking-based adaptive bias circuit, so that the PA stage of the power output unit outputs a larger current to achieve a larger output power, and the efficiency thus continues to increase, thereby achieving a better back-off efficiency compared to traditional class-AB power amplifiers. And the present invention only requires one PA stage of the power output unit, without considering the load modulation effect, and can achieve broadband applications. The present invention has achieved good output power and back-off effects through a 140 GHz broadband PA based on TSMC 65 nm process.

[0019] 2. High back-off efficiency: Traditional Doherty-like requires multiple power combining schemes, and it is difficult to balance broadband matching and low insertion loss, which will bring large losses and reduce efficiency and back-off efficiency. This will be more obvious at millimeter-wave high frequencies due to strong parasitic effects. The present invention only requires one structure, with smaller losses and area compared to traditional two-way structures, is more suitable for high-frequency design, can avoid the losses caused by power combining, and the efficiency can reach the level of a single-way power amplifier.

[0020] 3. Suitable for high-frequency design and high-order modulation communication systems: The present invention has a single-way structure with a smaller area and is suitable for the environment with strong parasitics at millimeter-wave high frequencies. The adaptive bias circuit used in the present invention can meet the high-speed communication requirements of high-order modulation signals, which determines that the present invention has good communication capabilities.

[0021] 4. Good broadband design performance: The structure based on slot-line coupled balun at the output end belongs to a distributed matching structure. Compared with the traditional transformer-based lumped matching structure, it has better broadband characteristics and is more suitable for broadband design. And the present invention is a Doherty-like power amplifier based on current source control. Compared with the traditional Doherty power amplifier, it can achieve no load modulation effect and is suitable for broadband design. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the modular structure of the Doherty-like power amplifier of the present invention; Figure 2a It is a schematic diagram of the structure of the asymmetric Wilkinson power divider circuit of the present invention; Figure 2b It is a schematic diagram of the structure of the triple-coupled transformer circuit of the present invention; Figure 3 Schematic diagram of the three-coupled transformer structure of the present invention; Figure 4 Schematic diagram of the output matching balun network structure of the present invention; Figure 5a Schematic diagram of the first embodiment of the DR-stage circuit structure of the drive amplification unit of the present invention; Figure 5b Schematic diagram of the second embodiment of the DR-stage circuit structure of the drive amplification unit of the present invention; Figure 6a Schematic diagram of the first embodiment of the PA-stage circuit structure of the power output unit of the present invention; Figure 6b Schematic diagram of the second embodiment of the PA-stage circuit structure of the power output unit of the present invention; Figure 7 Graph showing the influence of the bias voltage magnitude of the compensation power supply tail tube on the back-off point power of the present invention; Figure 8 Back-off curve graph when the bias voltage of the compensation power supply tail tube changes in the present invention; Figure 9 Graph showing the influence of the bias tube on the saturation power and the back-off amount of the present invention; Figure 10 Schematic diagram of the circuit structure of the adaptive bias circuit of the present invention; Figure 11a Schematic diagram of the first embodiment of the detector circuit structure of the present invention; Figure 11b Schematic diagram of the second embodiment of the detector circuit structure of the present invention; Figure 12a Schematic diagram of the first embodiment of the detector load network circuit structure of the present invention; Figure 12b Schematic diagram of the second embodiment of the detector load network circuit structure of the present invention; Figure 13 Graph showing the variation of the output voltage of the adaptive bias circuit with the input power in the present invention; Figure 14 Communication performance waveform graph of the adaptive bias circuit of the present invention; Figure 15 Small-signal simulation diagram of the Doherty-like power amplifier of the present invention; Figure 16 Large-signal simulation diagram of the Doherty-like power amplifier of the present invention; Figure 17 Large-signal simulation diagrams of the Doherty-like power amplifier of the present invention at different frequencies. Detailed implementation manners

[0023] The present invention will be further described below in conjunction with embodiments, but it does not constitute any limitation to the present invention. Any person's limited number of modifications within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0024] As Figure 1 shown, a Doherty-like power amplifier with improved back-off efficiency of the present invention includes an input power distribution network 100, an output matching balun network 400, an adaptive bias circuit 500, a drive amplification unit DR stage 200, and a power output unit PA stage 300.

[0025] Among them, the input power distribution network 100 is an asymmetric power distribution network, which outputs two radio frequency signals. One of the radio frequency signals is input into the drive amplification unit DR stage 200, and the other radio frequency signal is input into the adaptive bias circuit 500, aiming to match the input of the drive amplification unit DR stage 200 and maintain the isolation between the adaptive bias circuit and the drive amplification unit DR stage 200, so that the input power can enter the radio frequency link as much as possible. Common structures of the asymmetric power distribution network include asymmetric Wilkinson power dividers, three-coupled transformers, etc., and their circuit structures are respectively as Figure 2a and Figure 2b shown. Among them, it is difficult for the asymmetric Wilkinson power divider to output differentially, so a three-coupled transformer is commonly used as the asymmetric power divider. Its three-dimensional structure is as Figure 3 shown. The two transformers connected to the output end of the three-coupled transformer are the high-layer metal and the low-layer metal of the input end respectively, so that the mutual coupling at both output ends can be smaller and the isolation can be larger, while ensuring that the radio frequency input matching has a smaller insertion loss.

[0026] The output matching balun network 400 is used for power matching of the output stage, and common structures include transformers and slot-line baluns. At high frequencies, the slot-line balun has lower losses and better broadband characteristics compared to the transformer network, and its structure is as Figure 4 shown. Since it is a prior art, no more detailed description will be given here.

[0027] As Figure 5a shown, Figure 5a shows an implementation manner of the drive amplification unit DR stage 200, which is a common-source amplifier structure with cross-neutralization capacitors, providing a larger output for the subsequent-stage amplifier. Figure 5b is another implementation manner of the drive amplification unit DR stage 200, which consists of a common-source amplifier structure with cross-neutralization capacitors and a power supply tail tube. Among them, the power supply tail tube includes a compensation tube and a bias tube. Since the common-source amplifier structure with cross-neutralization capacitors has been applied in the DR stage of the traditional Doherty-like power amplifier and the present invention does not improve it, no detailed description will be given here.

[0028] As Figure 6a and Figure 6b shown, the power output unit PA stage 300 includes an amplifier structure with cross-neutralization capacitors and a power supply tail pipe composed of a fifth transistor M5 and a sixth transistor M6. The gate of the fifth transistor M5 inputs the voltage signal output by the adaptive bias circuit 500, and this voltage signal is an adaptive bias signal. The gate of the sixth transistor M6 inputs a fixed bias signal. The sources of the fifth transistor M5 and the sixth transistor M6 are both grounded, and the drains of the fifth transistor M5 and the sixth transistor M6 are commonly connected to the amplifier structure with cross-neutralization capacitors.

[0029] Among them, Figure 6a FIG. shows an implementation manner of the power output unit PA stage 300. In this implementation manner, the power output unit PA stage 300 is composed of a common-source amplifier structure with cross-neutralization capacitors and a power supply tail pipe. It should be noted that in a Doherty-like power amplifier, the drive amplification unit DR stage 200 and the power output unit PA stage 300 can be composed of multiple stages to provide greater gain; and according to Figure 5b and Figure 6a 's circuit structure, it can be seen that the drive amplification unit DR stage 200 can adopt the same circuit structure as the power output unit PA stage 300, thereby improving the control ability of the circuit back-off efficiency.

[0030] Figure 6b As another implementation manner of the power output unit PA stage 300, in this implementation manner, the power output unit PA stage 300 adopts a combination of a cascode amplifier structure with cross-neutralization capacitors and a power supply tail pipe, thereby improving the saturated output power and efficiency.

[0031] In the power output unit PA stage 300, the power supply tail pipe is further divided into a compensation tube and a bias tube. Specifically, the fifth transistor M5 serves as the bias tube, and the sixth transistor M6 serves as the compensation tube. The compensation tube is given a fixed bias to provide an initial amplification state for the circuit. Therefore, the size of the compensation tube and the magnitude of its bias voltage determine the back-off point power and efficiency of the circuit. As Figure 7 shown is the curve of the circuit output power change when the bias voltage of the compensation tube changes, Figure 8To compensate for the circuit back-off curve under the change of the bias of the tube. It can be seen that when the bias tube is determined, the saturated output power of the circuit is fixed, and the back-off point power and efficiency are affected by the bias of the compensation tube. Another power supply tail tube is the bias tube, and the bias voltage of this tube is given by the adaptive bias circuit 500. When a relatively small RF signal is input, the adaptive bias circuit 500 outputs a relatively small voltage, about 0.2V. At this time, the bias tube hardly provides current, and the output current of the power output unit PA stage 300 is determined by the compensation tube, and this is the initial state of the circuit. When the input RF signal reaches a certain level, the adaptive bias circuit 500 outputs a high voltage to the bias tube. At this time, the output current of the circuit is jointly determined by the bias tube and the compensation tube, and the circuit outputs a greater power.

[0032] The gate width and bias voltage of the transistor control the current output ability of the transistor. In high-order communication, it is usually required that the power amplifier operates at a power back-off of 3 - 6 dBm. This means that the bias tube needs to provide 1 - 2 times the current of the compensation tube. Therefore, the size of the bias tube is set to be about 1 - 2 times the size of the compensation tube. Figure 9 That is, it shows the change of the circuit back-off curve when the gate width of the bias tube of the power output unit PA stage 300 changes from 20um to 160um. It can be seen that when the gate width of the bias tube becomes larger, the saturated power and the maximum PAE will increase when the back-off amount remains almost unchanged. Therefore, to ensure a sufficient back-off amount, the bias tube of the power output unit PA stage 300 needs to be as large as possible, and can be set to 1 - 4 times the size of the compensation tube according to requirements.

[0033] The schematic diagram of the adaptive bias circuit 500 is as Figure 10 shown, and it is composed of a detector and a buffer stage. The structure of the detector is as Figure 11a and Figure 11b shown. It can be seen that in the two implementation manners of the detector, it is composed of a self-mixing differential pair and a load network. Among them, the self-mixing differential pair is composed of a first transistor M1 and a second transistor M2, and these two transistors can be PMOS or NMOS transistors. Specifically, the gates of the first transistor M1 and the second transistor M2 are respectively used as an input terminal to input the INP signal and the INN signal of the RF signal. The sources of the first transistor M1 and the second transistor M2 are connected and connected to the common terminal. Among them, as Figure 11a shown, in this implementation manner, the common terminal is the ground terminal, and the load network is connected to the power supply terminal. As Figure 11bAs shown, in this embodiment, the common terminal is the power supply terminal, and the load network is grounded. The drains of the first transistor M1 and the second transistor M2 are connected and connected to the load network, and the connection end of the load network and the drains of the first transistor M1 and the second transistor M2 serves as the output terminal of the detector and is connected to the buffer stage. The output terminal of the detector is grounded through the first capacitor C1. That is, the bias of the self-mixing differential pair is provided by the input power distribution network 100 of the previous stage. This bias voltage is controlled to be slightly less than the threshold voltage, so that the adaptive bias circuit 500 works normally after reaching a certain input power and maintains a low input before this input.

[0034] As Figure 12a and Figure 12b shown, the load network of the present invention can be replaced with a resistor or a PMOS transistor. Specifically, based on the embodiment where the common terminal is the power supply terminal, as Figure 12a shown is the circuit diagram where the load network is a PMOS transistor; and Figure 12b is the circuit diagram where the load network is a resistor. When in use, the equivalent resistance can be changed by changing the resistor size or the PMOS transistor bias voltage, thereby controlling the bandwidth of the envelope detector to meet higher communication requirements.

[0035] The buffer stage includes a fourth transistor M4, a first resistor R1, and a filter network. The gate of the fourth transistor M4 is connected to the output terminal of the detector. The source of the fourth transistor M4 is grounded. The drain of the fourth transistor M4 is simultaneously connected to one end of the first resistor R1 and the input terminal of the filter network. The other end of the first resistor R1 is connected to the power supply terminal. The output terminal of the filter network outputs the output voltage. Based on the buffer stage with the above circuit structure, it can increase the envelope amplitude of the detection output and provide a certain reverse isolation, and the filter network in the buffer stage is used to prevent the radio frequency signal of the tail tube from leaking into the adaptive bias circuit.

[0036] Figure 13 Shows the output voltage of the adaptive bias circuit 500 under different input powers. It can be seen that the output voltage of the adaptive bias circuit 500 remains at a low value when the input power is less than a certain value, and after the input power is greater than a certain threshold, the output voltage rapidly increases to close to the power supply voltage of 1.2V. In addition, the bias voltage of the differential pair of the detector can adjust the turn-on power and turn-on speed of the detector. When the bias voltage of the differential pair of the detector shown in the figure changes from 0.33 to 0.38V, the adaptive bias circuit 500 has a smaller turn-on power and a slower turn-on speed. In addition, the load network of the detector will also affect the turn-on power of the adaptive bias circuit 500. At the same time, the load network will affect the amplification and filtering capabilities of the detector, thereby affecting its communication rate.

[0037] Based on the above power amplifier circuit structure, the Doherty-like power amplifier circuit with high back-off efficiency based on envelope tracking technology proposed by the present invention can achieve high-order communication. The communication performance of the circuit depends on the communication rate of the adaptive bias, that is, the tracking speed of the adaptive bias circuit 500 for the modulation signal envelope determines the signal rate that the circuit can process. Figure 14 The figure shows the output curve of the adaptive bias circuit 500 under the condition of a modulation signal with a given rate. It can be seen that when the 16QAM modulation signal is input at a bit rate of 10Gps, the output of the adaptive bias circuit 500 can still track the envelope well. Therefore, the circuit has good communication capabilities.

[0038] As Figure 15 shown, the Doherty-like power amplifier of the present invention finally realizes a bandwidth design of 132 - 152 GHz, with a maximum gain of 25.6 dB, and the range where the input-output matching is less than -10 dB is greater than 20 GHz. The large-signal simulation data of its variation with the input power at 140 GHz is as Figure 16 shown. Figure 17 It shows that within the entire observed bandwidth, an output power greater than 10 dBm is achieved, with a maximum of 14.1 dBm, and the best energy efficiency is greater than 12.3%.

[0039] The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can still be made, and these will not affect the implementation effect of the present invention and the practicality of the patent.

Claims

1. A Doherty-like power amplifier with improved back-off efficiency, characterized in that: include: An input power distribution network (100) outputs two radio frequency signals, wherein one of the radio frequency signals is input into the driving amplifier unit DR stage (200), and the other of the radio frequency signals is input into the adaptive bias circuit (500), so that the driving amplifier unit DR stage (200) and the adaptive bias circuit (500) are isolated; A driving amplifier unit DR stage (200), an output end of which is connected to an input end of a power output unit PA stage (300); An adaptive bias circuit (500) is used to detect changes in the envelope of a power amplifier input signal in real time according to the radio frequency signal transmitted by the input power distribution network (100), and output a voltage signal; A power output unit PA stage (300), provided with an input end for receiving the voltage signal, wherein the voltage signal is used to control the bias tail pipe current of the power output unit PA stage (300) so as to adjust the output power and conversion efficiency of the power output unit PA stage (300); The output matching balun network (400) has an input end connected to the output end of the power output unit PA stage (300).

2. A Doherty-like power amplifier with improved back-off efficiency according to claim 1, characterized in that: The adaptive bias circuit (500) comprises a detector and a buffer stage; the input end of the detector inputs a radio frequency signal, the output end of the detector is connected to the input end of the buffer stage, and the input end of the buffer stage outputs the voltage signal.

3. A Doherty-like power amplifier with improved back-off efficiency according to claim 2, characterized in that: The detector includes a self-mixing differential pair consisting of a first transistor M1 and a second transistor M2, and a load network; the gates of the first transistor M1 and the second transistor M2 are respectively used as input terminals to input an INP signal and an INN signal of a radio frequency signal; the sources of the first transistor M1 and the second transistor M2 are connected and connected to a common terminal; the drains of the first transistor M1 and the second transistor M2 are connected and connected to a load network, and the load network and the drain connection terminal of the first transistor M1 and the second transistor M2 are connected to a buffer stage as the output terminal of the detector.

4. The Doherty-like power amplifier with improved back-off efficiency according to claim 3, characterized in that: The load network is a resistor or a PMOS transistor.

5. The Doherty-like power amplifier with improved back-off efficiency according to claim 3, characterized in that: The output end of the detector is grounded via a first capacitor C1.

6. A Doherty-like power amplifier with improved back-off efficiency according to any one of claims 2 to 5, characterized in that: The buffer stage includes a fourth transistor M4, a first resistor R1 and a filter network; the gate of the fourth transistor M4 is connected to the output end of the detector, the source of the fourth transistor M4 is grounded, the drain of the fourth transistor M4 is simultaneously connected to one end of the first resistor R1 and the input end of the filter network, the other end of the first resistor R1 is connected to the power supply end, and the output end of the filter network outputs an output voltage.

7. The Doherty-like power amplifier with improved back-off efficiency according to claim 1, characterized in that: The power output unit PA stage (300) comprises an amplifier structure with a cross-neutralizing capacitor and a power tail tube composed of a fifth transistor M5 and a sixth transistor M6; a gate of the fifth transistor M5 inputs a voltage signal, a gate of the sixth transistor M6 inputs a fixed bias signal, sources of the fifth transistor M5 and the sixth transistor M6 are both grounded, and drains of the fifth transistor M5 and the sixth transistor M6 are commonly connected to the amplifier structure with a cross-neutralizing capacitor.

8. The Doherty-like power amplifier with improved back-off efficiency according to claim 7, characterized in that: The amplifier structure with cross-neutralizing capacitors is a common-source amplifier structure with cross-neutralizing capacitors or a common-source and common-gate amplifier structure with cross-neutralizing capacitors.

9. The Doherty-like power amplifier with improved back-off efficiency according to claim 7, characterized in that: The driver amplifier unit DR stage (200) comprises a common source amplifier structure with cross-neutralizing capacitors.

10. The Doherty-like power amplifier with improved back-off efficiency according to claim 7, characterized in that: The driver amplifier unit DR stage (200) comprises an amplifier structure with a cross-neutralizing capacitor and a power tail pipe.

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