RF power amplifier with wide input range

Abstract

The present invention discloses a radio frequency power amplifier operating in a wide input range, relates to a wide input power matching technology, and belongs to the technical field of basic electronic circuits. A wide input range microstrip line matching circuit is used to inject a small amount of third harmonic components into the input signal. Compared with a power amplifier using a traditional microstrip line matching, a power amplifier using a wide input range microstrip line matching has higher efficiency at low input power, broadens the input power range of a high-efficiency power amplifier, and enables the power amplifier that originally worked in a fixed saturation state to have better performance at low input power, and when the input power changes, the performance is stable, and the efficiency is maintained at a high level. At the same time, injecting the third harmonic into the input signal can also improve the efficiency compared to the case of a sine wave input. The radio frequency power amplifier thus realized has a simple structure, high conversion efficiency, and a wide input power range, and can better meet the requirements of the microwave wireless energy transmission system for the transmitter.

Description

Technical Field

[0001] The invention discloses a radio frequency power amplifier operating in a wide input range, relates to a wide input power matching technology, and belongs to the technical field of basic electronic circuits. Background Art

[0002] Microwave Power Transmission (MPT) technology is suitable for medium- and long-distance wireless power transmission. It can not only provide energy to drones, robots, and orbiting satellites, but can also be applied to smart homes, biomedicine, and other fields, offering immeasurable research prospects and important strategic significance. Compared to other wireless power transmission methods, MPT boasts high penetration and is unaffected by the atmospheric environment, clouds, rain, and other factors. Using beamforming and beam steering techniques, it can achieve highly concentrated and directional energy transmission. Closed-loop control technology allows for dynamic adjustment of input power as loads change, ensuring a rational energy supply. These advantages give MPT a significant advantage in the field of medium- and long-distance wireless power transmission.

[0003] Figure 1 The MPT system's closed-loop control structure consists of four components: the transmitter, spatial transmission, receiver, and closed-loop control. The transmitter, responsible for converting DC or AC power into radio frequency (RF) power for feeding the transmit antenna array, is a crucial component of the entire system. To achieve functions such as beamforming and sidelobe suppression, the transmitter antenna typically utilizes an antenna array with adjustable amplitude and phase. Furthermore, MPT system energy management requires the transmitter to be able to provide adjustable power amplitude. Therefore, the transmitter must be able to provide adjustable RF power to each individual antenna element. For microwave transmitters, the power amplifier (PA) is a core component, and its efficiency directly impacts the overall system's transmission efficiency. Conventional PAs used in microwave wireless energy transmission systems experience gain compression when their output power reaches peak power, also known as saturation. This is when the PA reaches its highest operating efficiency. Therefore, conventional PA design methods match the input and output impedances at maximum output power (i.e., the input and output impedances at maximum input power). However, at high frequencies, the parasitic effects of transistors on their output characteristics become increasingly significant. Therefore, as input power varies, the optimal input and output impedances also change due to transistor nonlinearities. Conventional matching, which uses the impedance at saturated output as a reference point, makes it difficult to achieve matching over a wide input power range. This leads to mismatches in the matching network, resulting in a sharp drop in efficiency and, consequently, the overall system efficiency. Therefore, designing a PA that operates over a wide input power range is crucial for the implementation of the entire MPT system. Summary of the Invention

[0004] The object of the present invention is to address the deficiencies of the above-mentioned background technology and provide a radio frequency power amplifier operating in a wide input range. According to the impedance matching space formed by the input impedance and output impedance that meet the design indicators at different input powers, the impedance with the smallest mismatch is selected as the optimal input and output impedance for matching, which can effectively alleviate the mismatch caused by the input power change. Secondly, the injection of the third harmonic of the input signal is also beneficial to improving the efficiency at low input power, solving the technical problem that the power amplifier at the transmitting end of the existing microwave energy transmission system cannot be simultaneously applied to low power and high power input (that is, variable input power cannot be achieved) for efficiency optimization.

[0005] The present invention adopts the following technical solutions to achieve the above-mentioned purpose:

[0006] The present invention uses a third-harmonic-injected input excitation signal to synthesize the fundamental and third harmonics to form a steeper saddle wave, accelerating the transition from cutoff to conduction, reducing power loss in the constant current region, and thus improving efficiency. Simultaneously, a wide-input matching circuit at the input provides both a lossless path for the fundamental and third harmonics, as well as wide-input matching. Matching is achieved using a 1 / 12th wavelength short-circuited microstrip line connected in parallel with branches, allowing the fundamental and third harmonics to be transmitted to the transistor gate without phase or amplitude deviation. Specifically proposed is an RF power amplifier operating over a wide input range, comprising an input-side wide-input matching module, an amplifier circuit, a DC power supply and bias module, and an output-side wide-input matching module. The input end of the input wide input matching module is connected to the saddle wave microwave input signal, and outputs the fundamental wave and third harmonic without phase and amplitude deviation; the DC power supply and bias module provides energy for the amplifier circuit, and the input end of the amplifier circuit receives the fundamental wave and third harmonic without phase and amplitude deviation, and under the action of the bias signal output by the DC power supply and bias module, blocks or passes the fundamental wave and third harmonic without phase and amplitude deviation; the output wide input matching module receives the fundamental wave and third harmonic without phase and amplitude deviation output by the amplifier circuit, suppresses the harmonics of the received signal, and then outputs the fundamental wave signal adapted to the microwave input signal to the transmitting antenna.

[0007] This invention proposes a matching technology based on a wide input power range. Using a function that measures the degree of mismatch, the optimal input and output impedances are found in the impedance matching space at different input powers. Based on harmonic control of the microstrip line, the length of the microstrip line is fixed, while the width is adjustable, and the width is controlled within a certain range. Within this range, although the output impedance varies, the mismatch is minimal, and the efficiency drop is within a controllable range. The resulting RF power amplifier maintains good performance over a wide input power range, better meeting the transmitter requirements of microwave wireless energy transmission systems.

[0008] The present invention proposes a function for measuring the degree of mismatch. The objective function is to minimize the mean square error between the optimal input / output impedance at each input power point and the optimal input / output impedance matching a wide input range. By using an optimization algorithm in computer-aided software, the minimized value within the input power range can be found, and the optimal impedance actually used for matching network design is obtained. Then, the specific parameters of each microstrip line segment in the matching network are synthesized using the Kuroda rule.

[0009] The present invention adopts the above technical solution and has the following beneficial effects:

[0010] (1) Cost advantage: Compared with the use of multi-way matching circuits for segmented matching and transistor circuits that require multiple different saturation powers, this application uses a power amplifier with a wide input range matching to solve the problem of efficiency degradation at different input powers, eliminating multiple RF devices, reducing the size of the structure, and reducing the circuit complexity, thereby greatly reducing cost expenditure.

[0011] (2) Performance Advantages: Compared with traditional microwave RF power amplifiers that only achieve high efficiency near the saturation power point, the present invention can achieve a high efficiency level from low input power to saturation input power range. It proposes the idea of ​​wide input matching, which ensures the performance of the power amplifier when the power changes, thereby achieving efficiency improvement over a wide range. The function that measures the mismatch can solve the optimal impedance point before matching, greatly reducing the work of subsequent tuning. The third harmonic injection method further improves efficiency. Compared with traditional power amplifiers, the efficiency is greatly improved at low input power, and the efficiency is almost the same at saturation input power, achieving excellent performance over a wide input power range.

[0012] (3) Modularity and easy integration: The solution provided by the present invention is conducive to modular implementation. The hardware circuits and chips used for implementation are relatively mature in the field of communications, and subsequent chip design is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a closed-loop control structure of the microwave wireless energy transmission system.

[0014] FIG2(a) and FIG2(b) are the overall block diagram and specific circuit diagram of the high-efficiency RF power amplifier operating in a wide input range proposed in this application.

[0015] Figure 3 This is a comparison chart of the fundamental wave with different amounts of third harmonic added.

[0016] Figure 4 This is a schematic diagram of input matching and gate bias.

[0017] Figure 5It is a schematic diagram comparing the efficiency achieved by the method proposed in the invention with the original efficiency.

[0018] Explanation of the numbers in the figure: TL1~TL11 are the first to eleventh microstrip lines, C f1 is the DC blocking capacitor at the input, C f2 is the output DC blocking capacitor, C1 and C2 are the first and second capacitors, C ds is the drain-source capacitance, Q is the transistor, R L For load. DETAILED DESCRIPTION

[0019] The present invention proposes a high-efficiency radio frequency power amplifier operating over a wide input range. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings.

[0020] In response to the current situation that the power amplifier at the transmitting end of the existing microwave energy transmission system cannot be simultaneously applied to low-power and high-power input situations and cannot optimize the power amplifier efficiency under variable input power conditions, this application proposes a wide-input matching power amplifier circuit as shown in Figure 2(a). The circuit mainly includes a wide-input matching module at the input end, an amplification circuit, a DC power supply and bias module, and a wide-input matching module at the output end, and uses a function to measure the mismatch to select the optimal impedance point for matching.

[0021] The input end of the input-end wide input matching module is connected to the microwave input signal. The present invention synthesizes the fundamental wave and the third harmonic component with the same phase into a saddle wave microwave input signal; the gate of the amplifier circuit is connected to the output end of the input-end wide input matching module, and the saddle wave microwave input signal is gain amplified under the excitation of the DC power supply and the bias signal output by the bias module; the input end of the output-end wide input matching module is connected to the output end of the amplifier circuit for fundamental wave matching. When the saddle wave microwave input signal changes, the output impedance is obtained according to the load pull, and an impedance matching space adapted to different input powers is generated. The output impedance with the smallest mismatch degree is selected for fundamental wave matching, and the microwave signal after fundamental wave matching is output to the transmitting antenna.

[0022] As shown in Figure 2(b), the fundamental signal generated by the current source is input to the input DC blocking capacitor C f1 The input end wide input matching module includes: a first microstrip line TL1, a second microstrip line TL2, and a third microstrip line TL3. One end of the first microstrip line TL1, the second microstrip line TL2, and the third microstrip line TL3 are connected. The other end of the first microstrip line TL1 is connected to the input end DC blocking capacitor C f1The other end of the third microstrip line TL3 is connected to the other electrode of the first microstrip line TL1, the other end of the third microstrip line TL3 is grounded, the electrical lengths of the first microstrip line TL1 and the second microstrip line TL2 are integer multiples of one-sixth of the fundamental wave wavelength, and the electrical length of the third microstrip line TL3 is one-twelfth of the fundamental wave wavelength; the DC power supply and bias module includes: a fourth microstrip line TL4, a first capacitor C1, an eleventh microstrip line TL11, and a second capacitor C2, one end of the fourth microstrip line TL4 and one electrode of the first capacitor C1 are connected to the DC power supply V gs The other end of the fourth microstrip line TL4 is connected to the other end of the second microstrip line TL2, the other electrode of the first capacitor C1 is grounded, and one end of the eleventh microstrip line TL11 and one electrode of the second capacitor C2 are connected to the DC power supply V d , the other electrode of the second capacitor C2 is grounded; the amplifier circuit includes: a transistor Q, the drain of the transistor Q is connected to the other end of the eleventh microstrip line TL11; the output end wide input matching module includes: a drain-source capacitor C ds , the fifth microstrip line TL5, the sixth microstrip line TL6, the seventh microstrip line TL7, the eighth microstrip line TL8, the ninth microstrip line TL9, the tenth microstrip line TL10, the output end DC blocking capacitor C f2 , where the drain-source capacitance C ds The fifth microstrip line TL5, the sixth microstrip line TL6, the seventh microstrip line TL7, and the eighth microstrip line TL8 form a harmonic suppression circuit, which is used to suppress the harmonic components in the output signal of the amplifier circuit and then output a fundamental signal containing a small amount of harmonics. The drain-source capacitor C ds One end of the fifth microstrip line TL5 is connected to the drain of the transistor Q, and the drain-source capacitor C ds The other pole of the sixth microstrip line TL6 is grounded, one end of the sixth microstrip line TL6 is connected to the other end of the fifth microstrip line TL5, the seventh microstrip line TL7 and the eighth microstrip line TL8 are open microstrip lines connected to the common point of the fifth microstrip line TL5 and the sixth microstrip line TL6, one end of the ninth microstrip line TL9, one end of the tenth microstrip line TL10, and the output end DC blocking capacitor C f2 One end of each of the six microstrip lines TL6 is connected to the other end of the output DC blocking capacitor C f2 The other pole is connected to the load R L .

[0023] The following describes the implementation of the input-end wide input matching module, the optimal impedance point selection, and the output-end wide input matching module.

[0024] 1. Input wide input matching module

[0025] like Figure 3 The following is a comparison of the fundamental wave with different third harmonic contents added. The transistor gate input signal amplitude is:

[0026] V in =V gs +VRF {sin(ωt+θ)+asin(3ωt+θ)},

[0027] In the above formula, a is the ratio of the third harmonic content to the fundamental content, from Figure 3 It can be seen that if a>0.5, the saddle wave valley is too low, which is not conducive to the stable operation of the system. When a<0.3, the slope of the saddle wave is not much different from that of the sine wave, and the efficiency improvement is small. After measurement, a=0.35 meets the requirements. Since the impedance of the microwave signal source does not match the impedance of the transistor input, input matching is performed when designing a power amplifier in a traditional way. Since the traditional matching is for the fundamental wave, for the matching circuit that injects the third harmonic, it is necessary to consider the impact of the matching on the third harmonic. Therefore, a 1 / 12 wavelength short-circuited microstrip line is used in parallel with the branch, and a 1 / 6 wavelength integer multiple microstrip line is used in series for matching. According to the input impedance of the transistor, the width of each microstrip line is adjusted, such as Figure 4 As shown in the figure, the length of TL3 is one twelfth of the fundamental wave wavelength. The electrical length of this microstrip line to the third harmonic is 90°, which can be regarded as an impedance converter. The third harmonic is in an open circuit state when viewed from point B to point A, so it has little effect on the third harmonic. The lengths of TL1 and TL2 are integer multiples of one-sixth of the fundamental wave wavelength, which can meet the requirement of no phase and amplitude deviation between the fundamental wave and the third harmonic. The gate bias uses a quarter-wavelength series short-circuit microstrip line TL4 to block the fundamental wave and the third harmonic.

[0028] 2. Optimal impedance point selection

[0029] Traditional matching is designed based on the target impedance at saturated output power. This results in the fundamental impedance value being difficult to reach the target value when the input power decreases, especially at low power. The mismatch is large, the matching effect is very poor, and the efficiency deteriorates seriously. Therefore, in order to achieve wide input range operation, a new matching method is needed to alleviate this deterioration. First, the appropriate target impedance must be selected. In order to measure the performance of the power amplifier working over a wide input range, the MLE (matching loss efficiency) function is introduced. Assuming that the matching network is lossless and reciprocal, the MLE can be expressed as:

[0030]

[0031] G in , G out is the reflection coefficient at the input and output ends. Networks with different degrees of matching correspond to different MLE values. Since input matching and output matching are performed separately, MLE can also be simplified to:

[0032]

[0033] Г is the reflection coefficient of the matching network. The reflection coefficient can reflect the matching situation. When the reflection coefficient is minimum, the matching is best and the corresponding MLE is minimum. In order to make the MLE as small as possible within the input power range, the objective function is introduced:

[0034]

[0035] Where N is the number of selected input power points, MLE i is the optimal matching loss efficiency function value of the i-th input power point, MLE i0 is the matching loss efficiency function value of the wide input range matching at the i-th input power point. The optimal input impedance Z can also be obtained more intuitively in the form of impedance. ipt0 :

[0036]

[0037] The optimal output impedance Z can also be obtained more intuitively in the form of impedance opt0 :

[0038]

[0039] Where Z ipti 、Z opti are the optimal input impedance and output impedance at the i-th input power point respectively. The goal is to minimize the mean square error between the optimal input impedance at each input power point and the optimal input impedance matching the wide input range, and the optimal input impedance Z matching the wide input range can be obtained. ipt0 , with the goal of minimizing the mean square error between the optimal output impedance at each input power point and the optimal output impedance matching a wide input range, the optimal output impedance Z matching a wide input range can be obtained. opt0 By using an optimization algorithm in MATLAB to minimize the above equation within the target operating range, we can obtain the optimal input impedance and optimal output impedance points that meet the minimum objective function, and then perform matching to obtain a wide input range matching circuit. Based on the impedance matching space formed by the input impedance and output impedance that meet the design indicators at different input powers, the parameters of the first to third microstrip lines and the fifth to tenth microstrip lines are designed. For example, the traditional Smith chart matching method is used for design, where the width of each microstrip line meets the width constraint corresponding to the impedance matching space.

[0040] 3. Output wide input matching module

[0041] From the above analysis, we can see that in theory, matching the optimal impedance point solved by the optimization algorithm can achieve good working performance in a wider input power range. However, in the actual production of the power amplifier, the influence of the board parameters and the actual microstrip line must be considered, and all aspects should be taken into consideration as much as possible when designing the matching circuit.

[0042] By performing load pulling on the transistor, the optimal fundamental impedance at different input powers can be obtained. It can be found that the impedance change is caused by the nonlinear output capacitance (i.e., the parasitic capacitance of the transistor). Since the input power change affects the nonlinear capacitance of the transistor, and the nonlinear capacitance affects the fundamental impedance and generates second harmonics and other higher harmonics, it is necessary to consider the effect of the nonlinear capacitance of the transistor on the fundamental impedance when designing the output end wide input matching circuit. The present invention integrates the nonlinear capacitance of the transistor into the matching circuit, which can more effectively alleviate the impact of the input power change on the fundamental impedance. Specifically, the drain-source capacitance C is integrated into the matching circuit. ds The capacitance value is designed to take into account the capacitance of the transistor's own parasitic capacitance, and a suitable fundamental matching circuit is constructed by using nonlinear capacitance and an external matching circuit (fifth to tenth microstrip lines) to match the optimal output impedance Z over a wide input range. opt0 By matching the fundamental wave matching circuit to the load end, the input power range of the power amplifier can be widened. When designing the width of the microstrip line, the width should be controlled as much as possible within the width range corresponding to the impedance space to avoid large jumps in the width of the microstrip line. In summary, when the input power changes, the fundamental wave impedance value that can maintain the same efficiency is sought. These values ​​form an impedance matching space. As long as the impedance formed by the combination of the nonlinear capacitor and the external matching circuit falls within this impedance space, good performance can be maintained over the entire input power range. Thus, the wide input matching concept proposed by the present invention can achieve the following. Figure 5 The efficiency improvement shown in FIG. 1 shows that when the input power changes, the efficiency does not change much, that is, the RF power amplifier designed in the present invention realizes the adaptation of efficiency to input power.

[0043] The above embodiments are merely illustrative of the technical concepts of the present invention and are not intended to limit the scope of protection of the present invention. For example, by adopting the E, F, or J class topologies as the basic topologies of a power amplifier, designing a wide input matching circuit at the input end and a wide input matching circuit at the output end according to the inventive concept of the present invention, and determining the optimal input impedance point and the optimal output impedance point for matching the wide input range, the efficiency of the power amplifier can be improved. Any modifications made to the technical solution based on the technical concepts proposed by the present invention fall within the scope of protection of the present invention.

Claims

1. A radio frequency power amplifier operating in a wide input range, characterized in that: include: The input end of the wide input matching module is connected to the microwave input signal injected with the third harmonic, and outputs the fundamental wave and the third harmonic without phase and amplitude deviation. The amplifier circuit has its input end connected to the output end of the input wide input matching module, and performs gain amplification processing on the fundamental wave and the third harmonic without phase and amplitude deviation. A DC power supply and bias module, used to provide energy to the amplifier circuit and output a bias signal for controlling the amplifier circuit to block or pass the output signal, and, The output end wide input matching module has its input end connected to the output end of the amplifier circuit, suppresses the harmonics of the output signal of the amplifier circuit, and then outputs the fundamental wave signal adapted to the microwave input signal to the transmitting antenna; Obtain an impedance matching space that adapts to changes in microwave input signals: use a matching loss function to measure the working performance of the RF power amplifier in a wide input range, convert the matching loss function into an impedance form, and take minimizing the mean square error between the optimal input impedance at each input power point and the optimal input impedance matching the wide input range as the goal to obtain the optimal input impedance matching the wide input range; take minimizing the mean square error between the optimal output impedance at each input power point and the optimal output impedance matching the wide input range as the goal to obtain the optimal output impedance matching the wide input range; the optimal input impedance matching the wide input range and the optimal output impedance matching the wide input range form an impedance matching space that adapts to changes in microwave input signals.

2. The RF power amplifier operating in a wide input range according to claim 1, characterized in that: The ratio of the third harmonic content to the fundamental signal content in the microwave input signal is 0.3-0.

5.

3. The RF power amplifier operating in a wide input range according to claim 1, characterized in that: The input-end wide input matching module includes: a first microstrip line, a second microstrip line, and a third microstrip line, wherein one end of the first microstrip line, the second microstrip line, and the third microstrip line are connected, the other end of the first microstrip line is connected to a microwave input signal injected with a third harmonic, the other end of the third microstrip line is grounded, the electrical lengths of the first microstrip line and the second microstrip line are integer multiples of one-sixth of the fundamental wave wavelength, and the electrical length of the third microstrip line is one-twelfth of the fundamental wave wavelength.

4. The RF power amplifier operating in a wide input range according to claim 1, characterized in that: The amplifying circuit is a transistor, the gate of the transistor is connected to the output end of the input wide input matching module, and the source of the transistor is grounded.

5. The RF power amplifier operating in a wide input range according to claim 1, characterized in that: The DC power supply and bias module includes: a fourth microstrip line, a first capacitor, an eleventh microstrip line, and a second capacitor, wherein one end of the fourth microstrip line and one electrode of the first capacitor are commonly connected to a DC power supply that generates a bias signal, the other end of the fourth microstrip line is connected to the input end of the amplifier circuit, the other electrode of the first capacitor is grounded, one end of the eleventh microstrip line and one electrode of the second capacitor are commonly connected to the DC power supply, and the other electrode of the second capacitor is grounded.

6. The RF power amplifier operating in a wide input range according to claim 5, characterized in that: The electrical length of the fourth microstrip line is one quarter of the fundamental wave wavelength.

7. The RF power amplifier operating in a wide input range according to claim 3, characterized in that: The output-end wide input matching module includes: a drain-source capacitor, a fifth microstrip line, a sixth microstrip line, a seventh microstrip line, an eighth microstrip line, a ninth microstrip line, a tenth microstrip line, and an output-end DC blocking capacitor, wherein one electrode of the drain-source capacitor and one end of the fifth microstrip line are both connected to the output end of the amplifier circuit, the other electrode of the drain-source capacitor is grounded, one end of the sixth microstrip line is connected to the other end of the fifth microstrip line, one end of the seventh microstrip line, and one end of the eighth microstrip line, the other end of the seventh microstrip line and the other end of the eighth microstrip line are both open, one end of the ninth microstrip line, one end of the tenth microstrip line, and one electrode of the output-end DC blocking capacitor are all connected to the other end of the sixth microstrip line, the other electrode of the output-end DC blocking capacitor is connected to the load, and the capacitance value of the drain-source capacitor takes into account the nonlinear capacitance value of the amplifier circuit.

8. The RF power amplifier operating in a wide input range according to claim 7, characterized in that: The widths of the first microstrip line, the second microstrip line, the third microstrip line, the fifth microstrip line, the sixth microstrip line, the seventh microstrip line, the eighth microstrip line, the ninth microstrip line and the tenth microstrip line are determined according to an impedance matching space adapted to changes in microwave input signals.

9. The RF power amplifier operating in a wide input range according to claim 1, characterized in that: The expression for minimizing the mean square error between the optimal input impedance at each input power point and the optimal input impedance matching a wide input range is: The expression for minimizing the mean square error between the optimal output impedance at each input power point and the optimal output impedance matching a wide input range is: Where N is the number of selected input power points, Z ipti , Z opti are the optimal input impedance and output impedance at the i-th input power point, Z ipt0 To match the optimal input impedance over a wide input range, Z opt0 To match the optimal output impedance over a wide input range.

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