Dual-band radio frequency energy collection circuit and system based on single transformer

Abstract

The invention discloses a dual-band radio frequency energy collection circuit and system based on a single transformer, and belongs to the technical field of radio frequency energy collection. The circuit comprises an impedance matching unit and a radio frequency rectifier, wherein the impedance matching unit performs impedance matching on two target frequency points of 900MHz and 2.4 GHz; the radio frequency rectifier converts the radio frequency energy signal into a direct current signal; the middle impedance matching unit comprises a capacitor C1, a transformer T1, an inductor L3, an inductor L4 and a capacitor C2; the input end of the capacitor C1 is connected with the radio frequency antenna, and the output end is connected with the primary coil L1 of the transformer T1; one end of a primary coil L1 of the transformer T1 is connected with the capacitor C1, and the other end is grounded; one end of a secondary coil L2 of the transformer T1 is connected with the inductor L4, and the other end is connected with the inductor L3; and one end of the capacitor C2 is connected to a connecting line between the inductor L4 and the input end RFP of the radio frequency rectifier, and the other end of the capacitor C2 is connected to a connecting line between the inductor L3 and the input end RFN of the radio frequency rectifier.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency energy collection, and in particular relates to a dual-band radio frequency energy collection circuit and system based on a single transformer. Background Art

[0002] Wireless Sensor Network (WSN) is an automated system composed of many nodes that can work together without human intervention. Each node in WSN can communicate with other nodes to jointly complete the tasks of monitoring the surrounding environment, data processing and information transmission. This allows people to obtain accurate data at any time even in geographically remote places or places with harsh environmental conditions. Although the future application prospects of wireless sensor networks (WSN) are very attractive, there are still many technical obstacles on its development path. In particular, the energy supply method of nodes has become an important factor restricting its rapid development. Traditionally, WSN nodes rely on batteries for power supply, however, such a solution is difficult to ensure that most nodes can continue to operate stably for more than ten years. In order to extend the working life of nodes, replacing batteries is a possible method, but this becomes impractical in large-scale deployment of WSNs. When faced with thousands or even more nodes, battery replacement will not only bring a huge workload, but also lead to a sharp increase in maintenance costs. More importantly, since many WSN nodes are deployed in remote or harsh areas, battery replacement is almost impossible to achieve. Therefore, to overcome this challenge, researchers and engineers need to explore more innovative and efficient energy supply solutions, among which RF energy harvesting technology is one of the potential technical solutions.

[0003] At present, the impedance matching circuit structure of the mainstream RF energy harvesting circuit in academia is basically based on L-type matching circuit and π-type matching circuit. Among them, the L-type matching circuit has a simple structure and low design difficulty, but its degree of freedom is limited. For the determined source impedance and target impedance, the Q value of the L-type matching circuit is also determined, so the loss of the matching network cannot be optimized through design variables. Compared with the L-type matching circuit, the π-type matching network consists of three reactive element impedances. On the one hand, it can match a larger impedance space. On the other hand, due to the higher degree of design freedom, it can better adjust the Q value of the matching network, thereby optimizing the loss of the matching circuit.

[0004] However, the traditional matching methods, L-type and π-type matching circuits, can only achieve impedance matching at a single frequency point. For outdoor WSN nodes, the energy at a single frequency point is scarce and often insufficient to drive the network nodes to work. Therefore, a multi-frequency impedance matching network is very meaningful for improving the robustness of the RF energy harvesting system. It can ensure that when the energy at a certain frequency point is insufficient, energy at other frequencies can still be collected to realize the power supply of WSN nodes. For this reason, a broadband RF energy harvesting circuit based on a single transformer is proposed. Summary of the invention

[0005] In view of the deficiencies in the prior art, an object of the present invention is to provide a dual-band radio frequency energy harvesting circuit and system based on a single transformer, which solves the problems in the prior art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A dual-band radio frequency energy harvesting circuit based on a single transformer, comprising:

[0008] Impedance matching unit: impedance matching for two target frequency points: 900MHz and 2.4GHz;

[0009] RF rectifier: converts RF energy signals into DC signals to power subsequent loads;

[0010] The impedance matching unit includes: capacitor C1, transformer T1, inductor L3, inductor L4 and capacitor C2; the input end of capacitor C1 is connected to the RF antenna, and the output end is connected to the primary coil L1 of transformer T1; one end of the primary coil L1 of transformer T1 is connected to capacitor C1, and the other end is grounded; one end of the secondary coil L2 of transformer T1 is connected to inductor L4, and the other end is connected to inductor L3; one end of capacitor C2 is connected to the connecting line between inductor L4 and the input end RF_P of the RF rectifier, and the other end is connected to the connecting line between inductor L3 and the input end RF_N of the RF rectifier.

[0011] Further, the radio frequency rectifier includes: a capacitor C3, a capacitor C4, an N-type field effect transistor M1, an N-type field effect transistor M2, a P-type field effect transistor M3 and a P-type field effect transistor M4;

[0012] One end of capacitor C3 is connected to the positive phase differential input terminal RF_P of the RF rectifier, and the other end is connected to the drain of N-type field effect transistor M1 and P-type field effect transistor M3; the source of N-type field effect transistor M1 is grounded, and the drain is connected to the drain of P-type field effect transistor M3; the source of P-type field effect transistor M3 is connected to the DC voltage output node V out The source of the N-type field effect transistor M2 is grounded, and the drain is connected to the drain of the P-type field effect transistor M4; the source of the P-type field effect transistor M4 is connected to the output voltage node DC voltage output node Vout One end of the capacitor C4 is connected to the negative phase differential input terminal RF_N of the radio frequency rectifier, and the other end is connected to the drains of the N-type field effect transistor M2 and the P-type field effect transistor M4.

[0013] Furthermore, the N-type field effect transistor M1 and the N-type field effect transistor M2 are enhancement-type N-channel MOS field effect transistors.

[0014] A dual-band radio frequency energy harvesting system based on a single transformer comprises the above-mentioned dual-band radio frequency energy harvesting circuit based on a single transformer.

[0015] Furthermore, it also includes a radio frequency antenna, a super capacitor and a power management unit, the radio frequency antenna and the super capacitor are respectively arranged on both sides of the dual-band radio frequency energy collection circuit, and the power management unit is connected to the DC voltage output node V out superior.

[0016] Furthermore, the radio frequency antenna converts the electromagnetic wave into an alternating radio frequency signal, the radio frequency rectifier converts the alternating radio frequency signal into a direct current signal, and then the direct current voltage output by the radio frequency rectifier is regulated and stabilized by the power management unit;

[0017] When there is sufficient RF energy in the environment, the RF rectifier will charge the supercapacitor and store the excess energy. When there is insufficient RF energy in the environment, the supercapacitor will supply power to the electrical load.

[0018] Beneficial effects of the present invention:

[0019] The present invention proposes a broadband RF energy harvesting circuit based on dual transformers, which can simultaneously realize RF energy harvesting of dual frequency bands of 900 MHz and 2.4 GHz, effectively improving the efficiency of the RF energy harvesting system, and the matching network can be integrated on-chip, thereby omitting the need for users to manually configure the off-chip matching network during subsequent chip applications, thereby improving the robustness and ease of use of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 It is a schematic diagram of the overall structure of the energy harvesting circuit of the present invention;

[0022] Figure 2 It is a schematic diagram of the structure of the radio frequency rectifier of the present invention;

[0023] Figure 3It is a matching effect diagram of the present invention; Figure 4 This is a schematic diagram of the principle of realizing broadband impedance matching with a single transformer according to the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. 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.

[0025] Example 1

[0026] like Figure 1 As shown, a dual-band RF energy harvesting circuit based on a single transformer includes an impedance matching unit and a RF rectifier; the impedance matching unit is used to complete the impedance matching of two target frequency points of 900 MHz and 2.4 GHz, and the RF rectifier is used to complete the conversion of RF energy signals into DC signals to power the subsequent loads;

[0027] The impedance matching unit includes: capacitor C1, transformer T1, inductor L3, inductor L4 and capacitor C2; the input end of capacitor C1 is connected to the RF antenna, and the output end is connected to the primary coil L1 of transformer T1; one end of the primary coil L1 of transformer T1 is connected to capacitor C1, and the other end is grounded; one end of the secondary coil L2 of transformer T1 is connected to inductor L4, and the other end is connected to inductor L3; one end of capacitor C2 is connected to the connection line between inductor L4 and the input end RF_P of the RF rectifier, and the other end is connected to the connection line between inductor L3 and the input end RF_N of the RF rectifier.

[0028] Among them, the impedance matching unit uses transformer T1 as a partition, and the matching circuit can be divided into a high-frequency matching part and a low-frequency matching part. The primary coil L1 and capacitor C1 complete the matching of the low-frequency band, and the secondary inductor L2 and inductor L3, inductor L4, and capacitor C2 complete the matching of the high-frequency point. The two parts are coupled together through the magnetic field coupling effect of the transformer to complete the dual-band matching. It should be added that after the two are cascaded together, the impedance matching effects of the two will affect each other, so further fine-tuning is still required when actually designing component parameters.

[0029] Capacitor C1 and primary coil L1 of transformer T1 form resonance point ω1, secondary coil L2, inductor L3, inductor L4 and capacitor C2 of transformer T1 form resonance point ω2, the front and rear stages are coupled through the mutual inductance of transformer T1, and the positions of the two poles can be adjusted by the coupling coefficient k.

[0030] In this embodiment, the Q value of the transformer and the capacitor has a crucial influence on the loss of the matching network, so high Q value devices should be selected as much as possible. In addition, the coupling coefficient k of the transformer determines the distribution of the matching frequency band. The larger the k value, the farther the matching frequencies are distributed, and vice versa. The parameters of the capacitor determine the in-band flatness of the matching frequency band and need to be selected carefully.

[0031] The following is a brief introduction to explain the principle of single transformer to achieve broadband impedance matching. Figure 4 As shown in the figure, starting from a single transformer, an impedance adjustment network composed of transformers, its effective components can be divided into the primary coil L1 of transformer T1, the secondary coil L2 of transformer T1, capacitor C1, capacitor C2, and inevitable parasitic resistances R1 and R2. Among them, the port current and voltage characteristics of the transformer can be equivalently described by the Z parameter matrix:

[0032]

[0033] In the above formula, R1 represents the parasitic resistance of the primary coil of the transformer, R2 represents the parasitic resistance of the secondary coil of the transformer, ω represents the angular frequency, and j represents the imaginary unit.

[0034] therefore, Figure 4 The Z parameter of the two-port network composed of the transformer shown in combination with capacitors C1 and C2 can be described as:

[0035]

[0036] Where, det Z m Represents Z m The determinant of the matrix, Z m11 Represents the matrix Z m The value of the first row and first column, Z m12 Denotes the matrix Z m The value of the first row and second column, Z m22 Represents the matrix Z m The value of the second row and second column. When the impedance matching network and the antenna impedance complete conjugate matching, the impedance value of the impedance matching network viewed from the antenna end and the antenna Rant are conjugate complex numbers of each other. Therefore, for a standard 50 ohm antenna, in the Z parameter of the above formula, Z 11 The imaginary part of Imag(Z 11 )=0;

[0037] Substituting all the component symbols and solving the equation described above, we can get

[0038]

[0039] ξ=(ω1 / ω2) 2

[0040] Where ξ is the square of the self-resonant frequency ratio of the transformer primary and secondary networks, ω L,H The angular frequency solution for impedance matching with the antenna Rant;

[0041] It can be seen that the double-tuned impedance matching network composed of a single transformer has four poles (considering the positive and negative, there are actually only two natural frequency poles), which can achieve dual-band impedance matching.

[0042] like Figure 2 As shown, the radio frequency rectifier includes: a capacitor C3, a capacitor C4, an N-type field effect transistor M1, an N-type field effect transistor M2, a P-type field effect transistor M3 and a P-type field effect transistor M4;

[0043] One end of capacitor C3 is connected to the input terminal RF_P of the RF rectifier, and the other end is connected to the drain of N-type field effect transistor M1 and P-type field effect transistor M3; the source of N-type field effect transistor M1 is grounded, and the drain is connected to the drain of P-type field effect transistor M3; the source of P-type field effect transistor M3 is connected to the DC voltage output node V out The source of the N-type field effect transistor M2 is grounded, and the drain is connected to the drain of the P-type field effect transistor M4; the source of the P-type field effect transistor M4 is connected to the DC voltage output node V out One end of the capacitor C4 is connected to the input end RF_N of the radio frequency rectifier, and the other end is connected to the drains of the N-type field effect transistor M2 and the P-type field effect transistor M4.

[0044] In this embodiment, the N-type field effect transistor M1 and the N-type field effect transistor M2 are enhancement-type N-channel MOS field effect transistors;

[0045] The following is combined with Figure 2 Explain the working process of the RF rectifier:

[0046] Assuming the circuit has entered steady state, V x and V y are the voltages of nodes X and Y respectively. When the voltage V RF,P Greater than the voltage V at the input terminal RF_N RF,N When V RF,N The voltage V at node Y is affected by y Falling, N-type field effect tube M1 is turned off, P-type field effect tube M3 is turned on, V RF,P Through the P-type field effect transistor M3, the voltage output node V out Charging; due to V RF,P The voltage V at node X x Rising, P-type field effect tube M4 is turned off, N-type field effect tube M2 is turned on, and the ground node charges node Y through N-type field effect tube M2; similarly, when V RF,P <VRF,N , its working process is dual and can be analyzed similarly.

[0047] The size of the RF rectifier has a great influence on the output impedance of the RF rectifier. Increasing the width-to-length ratio of the field effect tube in the RF rectifier can reduce the output impedance of the rectifier, thereby reducing the impedance matching difficulty of relieving a large impedance conversion ratio. However, an excessively large size will also cause the reverse leakage current of the RF rectifier to increase at a larger RF input power, thereby deteriorating the conversion efficiency of the rectifier. In addition, due to this level effect of the field effect tube, a larger size will also cause the threshold voltage V th Increase, so a compromise must be considered.

[0048] Example 2

[0049] In this embodiment, a simulation experiment is performed on the dual-band RF energy harvesting circuit in Embodiment 1;

[0050] The experimental process includes:

[0051] In the integrated circuit simulation software Cadence Virtuoso, build a schematic diagram, use the port component in the analog library to simulate the antenna impedance, and set its impedance to 50 ohms. Figure 1 Build a test circuit based on the circuit topology, set the simulation analysis type to hb, select large signal S parameter LSSP analysis, and set the port power sweep range to -30dBm to 30dBm. Simulate 900MHz frequency and 2.4GHz frequency respectively, and observe the S11(dB) parameter.

[0052] The simulation results are as follows Figure 3 As shown, Figure 3 It can be seen that:

[0053] The yellow line shows the LSSP matching at 900MHz. It can be seen that when the antenna input power is in the power range of -13dBm to -4dBm, S11 is lower than -10dB, indicating that the impedance matching effect is good within this power range.

[0054] The yellow line shows the LSSP matching at 2.4 GHz. It can be seen that when the antenna input power is in the power range of -16 dBm to -2.5 dBm, S11 is lower than -10 dB, indicating that the impedance matching effect is good within this power range.

[0055] Based on the above analysis, it can be seen that the proposed impedance matching unit has a dual-band impedance matching effect and has a good power matching dynamic range.

[0056] Example 3

[0057] In this embodiment, a dual-band RF energy harvesting system based on a single transformer is proposed, including the RF energy harvesting circuit in Embodiment 1, and also including: a RF antenna, a super capacitor, and a power management unit; the RF antenna and the super capacitor are respectively arranged on both sides of the dual-band RF energy harvesting circuit, and the power management unit is connected to the DC voltage output node V out superior.

[0058] In the RF energy collection system, the RF antenna is responsible for converting electromagnetic waves in space into alternating RF signals, and the function of the RF rectifier is to convert alternating RF signals into DC signals. The DC voltage output by the RF rectifier is then regulated to a stable and usable DC voltage by the power management unit. Usually, there is also a supercapacitor in the system responsible for energy storage. When the RF energy in the environment is sufficient, the power management unit will charge the supercapacitor and store the excess energy. When the RF energy in the environment is insufficient, the supercapacitor will supply power to the power load to stabilize the power supply. In this process, the impedance matching unit plays the role of impedance conversion. This is because the input impedance of the RF rectifier and the impedance of the RF antenna are quite different. If impedance matching is not performed, most of the power sent to the RF rectifier by the antenna will be reflected back and cannot enter the RF rectifier, affecting the function of the system.

[0059] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0060] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A dual-band RF energy harvesting circuit based on a single transformer, characterized in that: include: Impedance matching unit: impedance matching for two target frequency points: 900MHz and 2.4GHz; RF rectifier: converts RF energy signals into DC signals to power subsequent loads; The impedance matching unit includes: capacitor C1, transformer T1, inductor L3, inductor L4 and capacitor C2; the input end of capacitor C1 is connected to the RF antenna, and the output end is connected to the primary coil L1 of transformer T1; one end of the primary coil L1 of transformer T1 is connected to capacitor C1, and the other end is grounded; one end of the secondary coil L2 of transformer T1 is connected to inductor L4, and the other end is connected to inductor L3; one end of capacitor C2 is connected to the connecting line between inductor L4 and the input end RF_P of the RF rectifier, and the other end is connected to the connecting line between inductor L3 and the input end RF_N of the RF rectifier.

2. The dual-band RF energy harvesting circuit based on a single transformer according to claim 1, characterized in that: The radio frequency rectifier includes: a capacitor C3, a capacitor C4, an N-type field effect transistor M1, an N-type field effect transistor M2, a P-type field effect transistor M3 and a P-type field effect transistor M4; One end of capacitor C3 is connected to the positive phase differential input terminal RF_P of the RF rectifier, and the other end is connected to the drain of N-type field effect transistor M1 and P-type field effect transistor M3; the source of N-type field effect transistor M1 is grounded, and the drain is connected to the drain of P-type field effect transistor M3; the source of P-type field effect transistor M3 is connected to the DC voltage output node V out The source of the N-type field effect transistor M2 is grounded, and the drain is connected to the drain of the P-type field effect transistor M4; the source of the P-type field effect transistor M4 is connected to the output voltage node DC voltage output node V out One end of the capacitor C4 is connected to the negative phase differential input terminal RF_N of the radio frequency rectifier, and the other end is connected to the drains of the N-type field effect transistor M2 and the P-type field effect transistor M4.

3. The dual-band RF energy harvesting circuit based on a single transformer according to claim 2, characterized in that: The N-type field effect transistor M1 and the N-type field effect transistor M2 are enhancement type N-channel MOS field effect transistors.

4. A dual-band RF energy harvesting system based on a single transformer, characterized in that: A dual-band radio frequency energy harvesting circuit based on a single transformer comprising the steps of any one of claims 1 to 3.

5. The dual-band RF energy harvesting system based on a single transformer according to claim 4, characterized in that: The dual-band radio frequency energy collection circuit also includes a radio frequency antenna, a super capacitor, and a power management unit. The radio frequency antenna and the super capacitor are respectively arranged on both sides of the dual-band radio frequency energy collection circuit. The power management unit is connected to the DC voltage output node V out superior.

6. The dual-band RF energy harvesting system based on a single transformer according to claim 5, characterized in that: The radio frequency antenna converts the electromagnetic wave into an alternating radio frequency signal, the radio frequency rectifier converts the alternating radio frequency signal into a direct current signal, and then the direct current voltage output by the radio frequency rectifier is regulated and stabilized by the power management unit; When there is sufficient RF energy in the environment, the RF rectifier will charge the supercapacitor and store the excess energy. When there is insufficient RF energy in the environment, the supercapacitor will supply power to the electrical load.

Images