Radio frequency energy rectifying circuit for receiving end of microwave wireless energy transmission system

Abstract

The invention discloses a radio frequency energy rectifying circuit for a receiving end of a microwave wireless energy transmission system, and the circuit comprises an impedance matching network which is used for matching with a microstrip antenna array and is located at the same phase as the microstrip antenna array; the low-pass filter is used for performing low-pass filtering on the alternating current with the frequency of 5.8 GHz output by the microstrip antenna; the rectifier diode is used for converting an alternating current signal filtered by the low-pass filter into a direct current with the frequency of 5.8 GHz; and the straight-through filter is used for carrying out harmonic filtering on the 5.8 GHz direct current transmitted by the rectifier diode to obtain the 5.8 GHz direct current which does not contain harmonic waves. The rectification efficiency of the rectification circuit at the frequency of 5.8 GHz reaches 77.4% and 52.5% respectively, and the output voltage can reach 5.55 V. The designed RF-DC rectifying circuit is subjected to sample manufacturing and testing, the size of the circuit is 3.49 cm * 3.38 cm, the testing result shows that the S11 value of the RF-DC rectifying circuit at the center frequency 5.8 GHz is-26.96 dB, and the RF-DC rectifying circuit has a good matching effect.

Description

Technical Field

[0001] The invention belongs to the field of fully automated products and relates to a radio frequency energy rectification circuit used at a receiving end of a microwave wireless energy transmission system. Background Art

[0002] The research on RF-DC rectifier circuits originated from the research on rectifier antennas. Since the receiving antennas are generally narrowband antennas operating in the microwave frequency bands such as 2.45GHz or 5.8GHz, most RF-DC rectifier circuits are single-band rectifier circuits. In recent years, the research on multi-band rectifier circuits has also been a hot topic. Since Dr. Brown completed the first RF-DC rectifier circuit experiment in the 1960s and obtained a rectification efficiency of nearly 60%, people have begun to conduct a series of research on RF-DC rectifier circuits and rectifier antennas, aiming to improve the efficiency and performance of the entire circuit.

[0003] In 2006, Zbitou et al. proposed an RF-DC rectifier circuit with an operating frequency of 2.45 GHz and applied it to the rectifier antenna. The clutter signal was filtered out by connecting a capacitor at the output end. The experimental device tested it and found that the maximum conversion efficiency of the circuit could reach 65% when the input power was 25 dBm. Park et al. designed a fan-shaped rectifier antenna. The circuit structure can not only effectively suppress high-order harmonics, but also has the characteristics of miniaturization. After testing, its rectification efficiency is as high as 77%. Roberg et al. proposed a class C harmonic suppression diode rectifier circuit based on the principle of class C power amplifier. The influence of high-order harmonics on the circuit was reduced by adding a microstrip structure to the circuit. After testing, the rectification efficiency of the rectifier circuit at a frequency of 2.45 GHz was 72.8%. Yoshida et al. proposed a broadband compact RF-DC rectifier and used a multi-stage matching method to reduce the Q value of the circuit. After testing, the rectification efficiency of the circuit in the frequency band of 0.39 GHz to 2.9 GHz exceeded 50%, and its bandwidth was 152.6%.

[0004] Since the Wi-Fi frequency band is the main operating frequency band of RF sources in the environment and is also part of the industrial, scientific, and medical frequency bands, it is very necessary to design a MWPT system for this frequency band. Summary of the invention

[0005] In order to solve the above problems, the technical solution adopted by the present invention is: a radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system, comprising:

[0006] Impedance matching network: used to match the microstrip antenna array and has the same 50Ω impedance as the microstrip antenna array;

[0007] Low-pass filter: used to low-pass filter the 5.8GHz AC current output by the microstrip antenna:

[0008] Rectifier diode: used to convert the AC signal filtered by the low-pass filter into a 5.8GHz DC power;

[0009] Pass filter: used for filtering the harmonics of the 5.8 GHz direct current transmitted by the rectifier diode to obtain a 5.8 GHz direct current without harmonics.

[0010] Furthermore: the rectifier diode adopts HSMS-28XC series Schottky diode.

[0011] Furthermore: the pass filter includes a second capacitor C2, and the value of the second capacitor C2 is set to 0.1nF.

[0012] Further: the through filter comprises a first transmission line, a second transmission line, a third transmission line and a first capacitor C 1， One end of the first transmission line is connected to the rectifier diode, the other end of the first transmission line is connected to one end of the first capacitor C1, the second transmission line and the third transmission line, and the other end of the first capacitor C1 is connected to the ground.

[0013] Furthermore: the length of the first transmission line is λ / 4, the length of the second transmission line is λ / 4, the length of the second transmission line is λ / 8, and the value of the first capacitor C1 is set to 0.1 nF.

[0014] Furthermore: the impedance matching network adopts a microstrip single-branch impedance matching network.

[0015] The present invention provides a radio frequency energy rectifier circuit for the receiving end of a microwave wireless energy transmission system. By analyzing the rectifier circuit topology and the characteristics of the rectifier diode to select a suitable type of rectifier diode, in order to obtain a higher rectification efficiency, a detailed analysis is performed on the selection of capacitance and load values, and the key parts of the RF-DC rectifier circuit are optimized and designed by ADS simulation software. Next, the designed RF-DC rectifier circuit is converted into a layout form and sample processing and testing are carried out, and a MWPT system test environment is built. By adjusting the distance between the microwave transmitting end and the receiving end of the system, the DC voltage output obtained at the output end of the RF-DC rectifier circuit is measured. After testing, the designed MWPT rectifier system can convert radio frequency energy into DC energy for load use, and the output voltage level can reach the volt level.

[0016] Through simulation analysis of its schematic and layout, it is found that when the input power is 16dBm and 18dBm, the rectification efficiency of the rectifier circuit at 5.8GHz frequency reaches 77.4% and 52.5% respectively, and the output voltage can reach 5.55V. The designed RF-DC rectifier circuit is sampled and tested, and its circuit size is 3.49cm×3.38cm. The test results show that its S11 value at the center frequency of 5.8GHz is -26.96dB, which has a good matching effect.

[0017] This application has the following advantages:

[0018] The rectification efficiency is high, the structure is compact and compact, and the practicability is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0020] Figure 1 It is the structure diagram of RF-DC rectifier circuit system;

[0021] Figure 2 This is the schematic diagram of the voltage doubler rectifier circuit;

[0022] Figure 3 The following are the simulation results of different diode models. (a) is S 11 Simulation results,(b) efficiency simulation results;

[0023] Figure 4 This is a simulation diagram of a voltage doubler rectifier circuit;

[0024] Figure 5 The following are the simulation results of rectification efficiency, (a) is under different capacitance values, (b) is under different loads;

[0025] Figure 6 This is the structure diagram of the λ / 4 traditional output filter;

[0026] Figure 7 (a) is a diagram of a λ / 4 parallel cross filter, and (b) is a simulation result of a λ / 4 parallel cross filter;

[0027] Figure 8 It is a microstrip single-branch impedance matching network diagram, (a) is the series connection case, (b) is the parallel connection case;

[0028] Fig. 9 is the reflection coefficient S11 Simulation result diagram;

[0029] Fig.10 It is a complete RF-DC rectifier circuit diagram;

[0030] Fig.11 The following are the simulation results of the RF-DC rectifier circuit, where (a) is the efficiency simulation result, (b) is the output voltage simulation result, (c) is the output impedance simulation result, and (d) is the reflection coefficient S 11 Simulation result diagram;

[0031] Fig.12 is the schematic-layout simulation result, (a) is the efficiency simulation result, and (b) is the reflection coefficient S 11 Simulation result diagram;

[0032] Fig.13 This is a sample diagram of a rectifier circuit;

[0033] Fig.14 is the reflection coefficient S of the rectifier circuit 11 Simulation result diagram. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] A RF energy rectifier circuit used at the receiving end of a microwave wireless energy transmission system mainly works at the back end of a microstrip antenna array and is mainly responsible for converting the RF energy captured by the microstrip antenna array into DC energy for use by back-end devices, such as Figure 1 The figure shows the structure diagram of the RF-DC rectifier circuit system. It can be found that the RF-DC rectifier circuit is mainly composed of four parts, among which:

[0037] Impedance matching network: used to match the microstrip antenna array and has the same 50Ω impedance as the microstrip antenna array;

[0038] Low-pass filter: used to low-pass filter the 5.8GHz AC current output by the microstrip antenna:

[0039] Rectifier diode: used to convert the AC signal filtered by the low-pass filter into a 5.8GHz DC power;

[0040] Pass filter: used for filtering the harmonics of the 5.8 GHz direct current transmitted by the rectifier diode to obtain a 5.8 GHz direct current without harmonics.

[0041] In order to prevent the high-order harmonic components in the rectification process from being reflected back to the microstrip antenna array, an impedance matching network and a low-pass filter need to be added between the microstrip antenna array and the rectifier diode. The impedance matching network achieves an ideal matching mode between the microstrip antenna array and the rectifier diode through impedance transformation to ensure maximum power transmission. Considering the actual situation, the diode cannot rectify all the transmitted RF signals, and high-order harmonics will inevitably be generated. Therefore, the role of the pass-through filter is to send the unnecessary harmonic components back to the diode, thereby improving the transmission efficiency of the circuit.

[0042] Since the diode is the core component of the RF-DC rectifier circuit and the application frequency band of this article is relatively high, the Schottky diode is selected to complete the rectification process. The Schottky diode has the advantages of high operating frequency, low power consumption, and large current, and has always been the first choice for small and medium power rectifier devices. At the same time, the key parameters that affect the characteristics of the Schottky diode include its internal junction capacitance, parasitic resistance, junction resistance group, and reverse breakdown voltage. Since the junction capacitance and junction resistance will change with the operating frequency and input power, the diode exhibits nonlinear characteristics. At the same time, the diode's input voltage V and internal junction voltage Vd are also important parameters that affect its performance.

[0043] The rectification efficiency of the diode is affected by two key parameters: the series resistance RS and the junction capacitance Cj. The smaller the values ​​of the two, the higher the rectification efficiency. Therefore, choosing the right type of diode is crucial to the design of the RF-DC rectifier circuit. This application uses the HSMS-28XC series diode with higher capacity and smaller volume. Since it is composed of two diodes connected inside, it is very suitable for use in the voltage doubler rectifier circuit. Table 1 shows the comparison of the parameters of three different types of diodes.

[0044] Table 1 Comparison of parameters of different types of diodes

[0045]

[0046] From Table 1, we can find that HSMS-285C has the highest reverse breakdown voltage and is suitable for low-power applications, HSMS-282C has the highest reverse breakdown voltage and is suitable for high-power applications, and HSMS-286C is between the two and is suitable for medium-power applications. By comparing other parameters, we find that HSMS-282C and HSMS-286C have better performance than HSMS-285C.

[0047] In order to intuitively compare the rectification efficiency of the three diodes under the same conditions, this application uses the ADS simulation software to build the following Figure 2 As shown in the voltage doubler rectifier circuit diagram, the initial values ​​of the two capacitors in the circuit are set to 100pF and the load resistance is set to 1000Ω.

[0048] like Figure 3 The following are the simulation results of different diode models. Figure 3 From the S11 simulation results shown in (a), it can be found that the HSMS-286C diode obtains the lowest S11 value when the input power is 19dBm, indicating that it has excellent matching performance. Figure 3 The rectification efficiency results shown in (b) show that the initial operating powers of the three diodes are -10dBm, -23dBm and 4dBm, respectively, and as the input power increases, the rectification efficiency begins to rise significantly. In particular, HSMS-286C achieves the highest rectification efficiency of 51.62% at an input power of 13dBm, so after comprehensive consideration, this application chooses to use diode HSMS-286C to design the RF-DC rectification circuit.

[0049] After determining the diode model, the linear components in the circuit, especially the capacitor and resistor, should be considered, especially the influence of the input impedance in the rectifier circuit. Since the parameter selection of these linear components directly affects the input impedance of the circuit and the impedance matching process, it affects the overall efficiency of the system. In order to obtain higher rectification efficiency, the undetermined coefficient method is used to determine the capacitance and resistance values ​​in the circuit.

[0050] By establishing the following in the simulation software Figure 4 As shown in the simulation diagram of the voltage doubler rectifier circuit, the capacitor and load resistor values ​​are initially set to 1nF and 1kΩ, and the following can be obtained: Figure 5 The rectification efficiency simulation results are shown.

[0051] from Figure 5From the corresponding rectification efficiency curves under different capacitance values ​​shown in (a), it can be found that, except for the 1pF capacitor, other capacitance values ​​have little effect on the rectification efficiency of the circuit. Considering that the second capacitor C2 of the direct-pass filter in the circuit is used to supply power to the afterload, its charging and discharging time is very important. Therefore, the present application sets the value of the second capacitor C2 to 0.1nF, and also sets the value of the first low-pass filter capacitor C1 to 0.1nF to optimize the performance of the circuit.

[0052] Next, adjust the resistance of the load resistor. Set the initial value of the load resistor in the circuit to 500Ω and increase it to 2000Ω in steps of 500Ω. You can get the following: Figure 5 (b) shows the comparison curve of rectification efficiency under different loads. The simulation results show that as the load resistance increases, the rectification efficiency gradually decreases. Since the impedance value of most sensor nodes is above 1 kΩ, but a higher load value will affect the rectification efficiency of the circuit, the load resistance value is set to 1 kΩ in this application to balance the rectification efficiency and circuit performance.

[0053] In the rectifier circuit, the diode will inevitably generate fundamental wave, higher harmonics and DC components. In order to ensure that only the DC component is transmitted to the back-end equipment, a pass filter is required to block the fundamental wave and higher harmonic components in the stop band. However, in practical applications, the third and higher harmonic components are usually small, and it is expensive to completely filter out all higher harmonics. Therefore, when designing an output pass filter, the main goal is to filter out the third and lower harmonic components.

[0054] like Figure 6 The figure shows the structure of the λ / 4 traditional output filter, which usually consists of a transmission line with a length of λ / 4 and a capacitor with an appropriate capacitance. When the capacitance value is large, the λ / 4 transmission line can be regarded as a short-circuit state, thereby ensuring that only the DC component can pass through. At this time, the input impedance of the even harmonic component is approximately 0, which is equivalent to a short-circuit state. Its harmonic components will be repeatedly rectified without generating other losses; while the input impedance of the fundamental frequency and odd harmonic components is infinite, which is equivalent to an open circuit state, and will also be reflected back to the diode for repeated rectification.

[0055] The advantage of this filter structure is that it is easy to build and can effectively suppress the transmission of high-order harmonics. However, the disadvantage is that the introduction of linear elements will produce parasitic parameters, which is more obvious in high-frequency applications, which will reduce the efficiency of the circuit and increase unnecessary energy loss. Next, this application introduces several common microstrip branch-type output pass filters, which have the advantage of effectively avoiding the adverse effects of parasitic parameters.

[0056] like Figure 7(a) shows a λ / 4 parallel cross filter, which is implemented by connecting a section of open microstrip line with a length of λ / 4 in series with a section of open microstrip line with a length of λ / 8, and then connecting a section of microstrip line with a length of λ / 4 in parallel. The above structure is simulated by the simulation software ADS, and the following can be obtained: Figure 7 (b) shows the simulation results. The S21 parameters of the structure at 5.8 GHz and 11.6 GHz are both lower than -10 dB, indicating that the filter structure can effectively reflect the fundamental frequency and the second harmonic frequency. In addition, the reflection coefficient S11 values ​​of the two are -0.304 dB and -0.515 dB, respectively, both showing good reflection effects. Although the λ / 4 traditional straight-through filter introduces linear elements, it only contains a microstrip line structure, so this application adopts this structure as the filter structure.

[0057] like Figure 8 The figure shows a microstrip single-branch impedance matching network. The special thing is that the circuit contains an open or short-circuited microstrip line structure, so there are generally two basic structures: series and parallel. Figure 8 (a) is a series structure, and (b) is a parallel structure. Therefore, when the dielectric constant of the medium is known, the impedance matching process of the load and the input end can be effectively completed by adjusting the length and impedance of the microstrip line in the circuit.

[0058] The through filter comprises a first transmission line, a second transmission line, a third transmission line and a first capacitor C 1， One end of the first transmission line is connected to the rectifier diode, the other end of the first transmission line is connected to one end of the first capacitor C1, the second transmission line and the third transmission line, and the other end of the first capacitor C1 is connected to the ground.

[0059] The length of the first transmission line is λ / 4, the length of the second transmission line is λ / 4, the length of the second transmission line is λ / 8, and the value of the first capacitor C1 is set to 0.1 nF.

[0060] Since the RF-DC rectifier circuit designed in this application operates at a single frequency point, in order to reduce the circuit size and adjust the matching effect, this application chooses to use a microstrip single-branch matching circuit to implement the matching process.

[0061] Next, the simulation software ADS is used to establish the RF-DC rectifier circuit diagram without adding the impedance matching network. The dielectric board uses FR4 material with a thickness of 1.6mm, and the capacitance and load in the circuit are set to 0.1nF and 1kΩ respectively, and the input power Pin range is set to -40dBm~40dBm. By simulating the circuit. According to the design principle of the microstrip single-branch impedance matching network, the simulation software ADS is used to build its schematic diagram, the output impedance of the impedance matching network is set to (53.378-3.88j)Ω, its input impedance is set to 50Ω, and the microstrip line part in the network is parameterized. By optimizing the value of S11, the following can be obtained: Fig. 9 The S11 simulation results are shown.

[0062] Fig. 9 The results show that at an operating frequency of 5.8 GHz, the S11 value reaches -49.98 dB, indicating that good conjugate matching is successfully achieved through this microstrip single-branch impedance matching circuit. Next, the optimized impedance matching circuit is integrated between the input end and the diode of the RF-DC rectifier circuit to form Fig.10 The complete RF-DC rectifier circuit diagram is shown in FIG. 1 , and the RF-DC rectifier circuit simulation result is obtained by simulating it as shown in FIG. 10 .

[0063] according to Fig.11 (a) It can be found that when the input power is set to 16dBm, the rectification efficiency of the circuit is increased to 77.3%; Fig.11 (b) It can be found that under the same input power, the output voltage reaches 5.55V; Fig.11 It can be found in (c) that after the impedance matching network is introduced into the RF-DC rectifier circuit, the real part of the input impedance at the operating frequency of 5.8 GHz is closer to 50 Ω and the imaginary part is closer to 0 Ω compared with the case without adding the impedance matching network. In addition, Fig.11 It can be found in (d) that its S11 parameter reaches the minimum value of -49.97dB at an input power of 16dBm, far exceeding the expected effect, indicating that the introduction of the impedance matching network significantly optimizes the circuit performance.

[0064] In order to get closer to the actual measurement results, this application converts the designed RF-DC rectifier circuit into a layout form and performs a schematic-layout joint simulation. The simulation results are shown in Fig.12 As shown. Fig.12 As can be seen in (a), the schematic diagram and the joint simulation have the highest rectification efficiency at 16dBm and 18dBm input powers, which are 77.4% and 52.5% respectively. This is because the actual rectification efficiency is reduced due to factors such as through holes and linear elements in the circuit. Fig.12It can be found in (b) that the S11 value at a frequency of 5.8 GHz is -26.27 dB, which has a good matching effect.

[0065] like Fig.13 The figure shows the fabricated RF-DC rectifier circuit sample, which has an overall size of 34.92mm×33.78mm and is characterized by simple structure and miniaturization. This application mainly tests the S11 value and output voltage of the RF-DC rectifier circuit. By welding an SMA connector at the input end of the circuit and feeding it with an Agilent N5242A vector network analyzer, the following values ​​can be obtained: Fig.14 The reflection coefficient S shown 11 Test results. From the measurement results, it can be found that the S11 value of the rectifier circuit at an operating frequency of 5.8 GHz is similar to the simulation result, proving the feasibility of the design.

[0066] In order to better test the performance of the RF-DC rectifier circuit, the designed RF-DC rectifier circuit is fed with a RF signal generator model DSG3136B, and its output voltage value is measured. As shown in Table 2, when the input power is 20dBm and the load resistance changes from 500Ω to 12kΩ, the output voltage value of the circuit is

[0067] Table 2 Output voltage values ​​corresponding to different load resistance values

[0068] Load value(Ω) Output voltage value (V) 50 0.4 500 1.7 1k 2.11 3k 3.04 4k 3.19 10k 3.48 12k 3.56

[0069] It can be found from the table that when the load resistance changes from 500Ω to 12kΩ, the output voltage is constantly increasing. And when the load is 12kΩ, the output voltage can reach 3.56V, indicating that the designed RF-DC rectifier circuit is suitable for the conversion of RF-DC signals. Since the input signal passes through a multi-level circuit and manual welding will cause a certain deviation and attenuation in the measured data, there is a certain difference between the measurement results and the simulation, especially for 5.8GHz high-frequency signals, which will produce worse results under the same error.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system, characterized in that: include: Impedance matching network: used to match the microstrip antenna array and has the same 50Ω impedance as the microstrip antenna array; Low-pass filter: used to low-pass filter the 5.8GHz AC current output by the microstrip antenna: Rectifier diode: used to convert the AC signal filtered by the low-pass filter into a 5.8GHz DC power; Through filter: used for filtering the harmonics of the 5.8 GHz direct current transmitted by the rectifier diode to obtain a direct current without harmonics.

2. The radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system according to claim 1, characterized in that: The rectifier diode adopts HSMS-28XC series Schottky diode.

3. The radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system according to claim 1, characterized in that: The pass filter includes a second capacitor C2, and the value of the second capacitor C2 is set to 0.1 nF.

4. The radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system according to claim 1, characterized in that: The pass filter includes a first transmission line, a second transmission line, a third transmission line and a first capacitor C1, wherein one end of the first transmission line is connected to the rectifier diode, the other end of the first transmission line is connected to one end of the first capacitor C1, the second transmission line and the third transmission line, and the other end of the first capacitor C1 is connected to the ground.

5. The radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system according to claim 1, characterized in that: The length of the first transmission line is λ / 4, the length of the second transmission line is λ / 4, the length of the second transmission line is λ / 8, and the value of the first capacitor C1 is set to 0.1 nF.

6. The radio frequency energy rectification circuit for a receiving end of a microwave wireless energy transmission system according to claim 1, characterized in that: The impedance matching network adopts a microstrip single-branch impedance matching network.

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