A single-transformer-based dual-band radio frequency energy harvesting circuit and system

Abstract

The application discloses a kind of dual-band radio frequency energy harvesting circuit and system based on single transformer, belong to radio frequency energy harvesting technical field;Circuit includes impedance matching unit and radio frequency rectifier, impedance matching unit carries out impedance matching to 900MHz and 2.4GHz two target frequency points;Radio frequency rectifier converts radio frequency energy signal into direct current signal;Middle impedance matching unit includes: capacitor C1, transformer T1, inductance L3, inductance L4 and capacitor C2;The input end of capacitor C1 is connected to radio frequency antenna, and the output end is connected to the primary coil L1 of transformer T1;The primary coil L1 of transformer T1 is connected to capacitor C1 at one end, and is grounded at the other end;The secondary coil L2 of transformer T1 is connected to inductance L4 at one end, and is connected to inductance L3 at the other end;Capacitor C2 is connected to the connecting line between inductance L4 and radio frequency rectifier input end RF_P at one end, and is connected to the connecting line between inductance L3 and radio frequency rectifier input end RF_N at the other end.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency energy harvesting technology, specifically relating to a dual-band radio frequency energy harvesting circuit and system based on a single transformer. Background Technology

[0002] Wireless Sensor Networks (WSNs) are automated systems composed of numerous nodes that can work collaboratively without human intervention. Each node in a WSN can communicate with other nodes to jointly perform tasks such as monitoring the surrounding environment, processing data, and transmitting information. This allows for the acquisition of accurate data at any time, even in geographically remote or harsh environments. While the future applications of WSNs are very promising, several technical obstacles remain in their development. Of particular note is the power supply method for nodes, which has become a significant factor restricting their rapid development. Traditionally, WSN nodes rely on battery power; however, this approach cannot guarantee that most nodes can operate stably for more than a decade. Battery replacement is a possible method to extend node lifespan, but this becomes impractical in large-scale WSN deployments. When dealing with thousands or even more nodes, battery replacement not only incurs a huge workload but also leads to a sharp increase in maintenance costs. More importantly, because many WSN nodes are deployed in remote or harsh environments, battery replacement is virtually impossible. Therefore, to overcome this challenge, researchers and engineers need to explore more innovative and efficient energy supply solutions, among which radio frequency energy harvesting technology is a promising option.

[0003] Currently, the impedance matching circuit structures in mainstream RF energy harvesting circuits in academia are mainly L-type and π-type matching circuits. L-type matching circuits are simple in structure and easy to design, but their degrees of freedom are limited. For a given source impedance and target impedance, the Q value of an L-type matching circuit is also determined, therefore the loss of the matching network cannot be optimized through design variables. In contrast to L-type matching circuits, π-type matching networks use three reactive impedance elements. On the one hand, they can match a larger impedance range; on the other hand, due to their greater design freedom, the Q value of the matching network can be better adjusted, thereby optimizing the loss of the matching circuit.

[0004] However, traditional matching methods, such as L-type and π-type matching circuits, can only achieve impedance matching at a single frequency. For outdoor WSN nodes, energy at a single frequency is scarce and often insufficient to power the network nodes. Therefore, multi-frequency impedance matching networks are significant for improving the robustness of RF energy harvesting systems, ensuring that energy can still be harvested from other frequencies to power the WSN nodes even when energy at one frequency is insufficient. To address this, a broadband RF energy harvesting circuit based on a single transformer is proposed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a dual-band radio frequency energy harvesting circuit and system based on a single transformer, thereby solving the problems in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions:

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

[0008] Impedance matching unit: performs impedance matching for the two target frequencies of 900MHz and 2.4GHz;

[0009] Radio frequency rectifier: Converts radio frequency energy signals into DC signals to power downstream loads;

[0010] The impedance matching unit includes: capacitor C1, transformer T1, inductor L3, inductor L4, and capacitor C2; the input terminal of capacitor C1 is connected to the RF antenna, and the output terminal 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 terminal RF_P of the RF rectifier, and the other end is connected to the connection line between inductor L3 and the input terminal RF_N of the RF rectifier.

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

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

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

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

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

[0016] Furthermore, the radio frequency antenna converts electromagnetic waves into alternating radio frequency signals, the radio frequency rectifier converts the alternating radio frequency signals into DC signals, and the power management unit then regulates and stabilizes the DC voltage output by the radio frequency rectifier.

[0017] When there is sufficient radio frequency energy in the environment, the radio frequency rectifier charges the supercapacitor to store the excess energy. When there is insufficient radio frequency energy in the environment, the supercapacitor supplies power to the electrical load.

[0018] The beneficial effects of this invention are:

[0019] This invention proposes a broadband radio frequency energy harvesting circuit based on dual transformers that can simultaneously harvest radio frequency energy in both 900MHz and 2.4GHz bands, effectively improving the efficiency of the radio frequency energy harvesting system. Furthermore, the matching network can be integrated on-chip, thus eliminating 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. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

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

[0023] Figure 3This is a diagram illustrating the matching effect of the present invention;

[0024] Figure 4 This is a schematic diagram illustrating the principle of broadband impedance matching achieved by a single transformer in this invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1

[0027] like Figure 1 As shown, a dual-band radio frequency energy harvesting circuit based on a single transformer includes an impedance matching unit and a radio frequency rectifier. The impedance matching unit is used to complete the impedance matching of two target frequencies, 900MHz and 2.4GHz, and the radio frequency rectifier is used to complete the conversion of radio frequency energy signals to DC signals to power the downstream load.

[0028] The impedance matching unit includes: capacitor C1, transformer T1, inductor L3, inductor L4, and capacitor C2; the input terminal of capacitor C1 is connected to the RF antenna, and the output terminal 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 terminal RF_P of the RF rectifier, and the other end is connected to the connection line between inductor L3 and the input terminal RF_N of the RF rectifier.

[0029] The impedance matching unit uses transformer T1 as a divider, separating the matching circuit into a high-frequency matching section and a low-frequency matching section. The primary coil L1 and capacitor C1 complete the low-frequency band matching, while the secondary inductor L2, inductors L3 and L4, and capacitor C2 complete the high-frequency band matching. The two sections are coupled together through the magnetic field coupling effect of the transformer, jointly achieving dual-band matching. It should be noted that because the impedance matching effects of the two sections are mutually affected after cascading, further fine-tuning of the component parameters is still necessary during actual design.

[0030] Capacitor C1 and the primary coil L1 of transformer T1 form a resonant point ω1. The secondary coil L2, inductor L3, inductor L4 of transformer T1 and capacitor C2 form a resonant point ω2. The two 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.

[0031] In this embodiment, the Q values ​​of the transformer and capacitor have a crucial impact on the losses of the matching network; therefore, high-Q devices should be selected whenever possible. Furthermore, the coupling coefficient k of the transformer determines the distribution of the matching frequency band; a larger k value results in wider distributions between matching frequencies, and vice versa. The parameters of the capacitor determine the in-band flatness of the matching frequency band and require careful selection.

[0032] The following is a brief explanation of the principle of achieving broadband impedance matching with a single transformer. For example... Figure 4 As shown, starting from a single transformer, an impedance regulation network composed of transformers can be effectively divided into the primary coil L1 of transformer T1, the secondary coil L2 of transformer T1, capacitors C1 and C2, and unavoidable parasitic resistances R1 and R2. The port current-voltage characteristics of the transformer can be equivalently described by the Z-parameter matrix.

[0033]

[0034] 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.

[0035] therefore, Figure 4 The Z-parameters of the two-port network formed by the transformer and capacitors C1 and C2 shown can be described as follows:

[0036]

[0037] In the formula, det Z m Z represents m The determinant value of a matrix, Z m11 Representation matrix Z m The value of the first row and first column, Z m12 Representation matrix Z m The value of the first row and second column, Z m22 Representation matrix Z m The value in the second row and second column. When the impedance matching network and the antenna impedance are conjugate matched, the impedance value of the impedance matching network seen from the antenna end and the antenna Rant are conjugate complex numbers. Therefore, for a standard 50-ohm antenna, in the Z parameter of the above formula, Z... 11 The imaginary part of Z should be 0 to satisfy the matching condition, that is: Imag(Z 11 ) = 0;

[0038] Substituting all the component symbols and solving the equation described above, we can obtain...

[0039]

[0040] In the formula, ξ is the square of the ratio of the self-resonant frequencies of the transformer's primary and secondary networks, and ω L,H To find the angular frequency solution that provides impedance matching with the antenna Rant;

[0041] As can be seen, the dual-tuned impedance matching network composed of a single transformer has 4 poles (considering 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 RF rectifier includes: capacitor C3, capacitor C4, N-type field-effect transistor M1, N-type field-effect transistor M2, P-type field-effect transistor M3, and 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 drains 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 its 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 N-type field-effect transistor M2 is grounded, and its drain is connected to the drain of P-type field-effect transistor M4; the source of P-type field-effect transistor M4 is connected to the DC voltage output node V. out One end of capacitor C4 is connected to the input terminal RF_N of the RF rectifier, and the other end is connected to the drain of N-type field-effect transistor M2 and P-type field-effect transistor M4.

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

[0045] The following is in conjunction with the appendix Figure 2 Explanation of the working process of an RF rectifier:

[0046] Assuming the circuit has reached a steady state, V x and V y Let V be the voltage at node X and node Y, respectively, when the voltage V at input terminal RF_P... RF,P The voltage V at the input terminal RF_N is greater than the voltage V. RF,N At that time, due to V RF,N The effect of the voltage V at node Y y When the voltage drops, N-type MOSFET M1 turns off, P-type MOSFET M3 turns on, and V... RF,P The voltage output node V is controlled via the P-type MOSFET M3. out Charging; due to V RF,P The effect of the voltage V at node X x When V rises, P-type MOSFET M4 turns off, N-type MOSFET M2 turns on, and the ground node charges node Y through N-type MOSFET M2; similarly, when V... RF,P <V RF,NIts working process is dual and can be analyzed similarly.

[0047] The size of an RF rectifier significantly affects its output impedance. Increasing the aspect ratio of the field-effect transistor (FET) in the RF rectifier can reduce the output impedance, thereby simplifying impedance matching for high impedance transition ratios. However, excessively large sizes can also lead to increased reverse leakage current at higher RF input power, thus degrading the rectifier's conversion efficiency. Furthermore, due to the field-effect transistor's inherent properties, larger sizes can also lead to a higher threshold voltage Vth. th The increase is necessary, so a compromise must be considered.

[0048] Example 2

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

[0050] The experimental procedure includes:

[0051] In the integrated circuit simulation software Cadence Virtuoso, a schematic diagram was built, and the antenna impedance was simulated using the port component in the analog library, with its impedance set to 50 ohms. Figure 1 The circuit topology was used to build a test circuit. The simulation analysis type was set to hb, and large signal S-parameter LSSP analysis was selected. The port power scan range was -30dBm to 30dBm. The 900MHz and 2.4GHz frequencies were simulated respectively, and the S11(dB) parameter was observed.

[0052] Simulation results are as follows Figure 3 As shown, Figure 3 It can be seen from this:

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

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

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

[0056] Example 3

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

[0058] In a radio frequency (RF) energy harvesting system, the RF antenna converts electromagnetic waves in space into alternating RF signals. The RF rectifier converts these alternating RF signals into direct current (DC) signals. The power management unit (PMU) then conditions the DC output voltage of the RF rectifier to a stable and usable voltage. Typically, a supercapacitor is also included in the system for energy storage. When there is sufficient RF energy in the environment, the PMU charges the supercapacitor, storing excess energy. When RF energy is insufficient, the supercapacitor supplies power to the electrical load, ensuring a stable power supply. During this process, the impedance matching unit acts as an impedance converter. This is because the input impedance of the RF rectifier and the RF antenna differs significantly. Without impedance matching, most of the power sent from the antenna to the RF rectifier would be reflected back and fail to reach the RF rectifier, affecting the system's functionality.

[0059] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0060] The foregoing has shown and described 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. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A dual-band radio frequency energy harvesting circuit based on a single transformer, characterized in that, include: Impedance matching unit: performs impedance matching for the two target frequencies of 900MHz and 2.4GHz; Radio frequency rectifier: Converts radio frequency energy signals into DC signals to power downstream loads; The impedance matching unit includes: capacitor C1, transformer T1, inductor L3, inductor L4, and capacitor C2; the input terminal of capacitor C1 is connected to the RF antenna, and the output terminal 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 terminal RF_P of the RF rectifier, and the other end is connected to the connection line between inductor L3 and the input terminal RF_N of the RF rectifier.

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

3. The dual-band radio frequency energy harvesting circuit based on a single transformer according to claim 2, characterized in that, The N-type field-effect transistors M1 and M2 are enhancement-mode N-channel MOSFETs.

4. A dual-band radio frequency energy harvesting system based on a single transformer, characterized in that, Includes a dual-band radio frequency energy harvesting circuit based on a single transformer as described in any one of claims 1-3.

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

6. A dual-band radio frequency energy harvesting system based on a single transformer according to claim 5, characterized in that, The radio frequency antenna converts electromagnetic waves into alternating radio frequency signals, the radio frequency rectifier converts the alternating radio frequency signals into DC signals, and the power management unit then regulates and stabilizes the DC voltage output by the radio frequency rectifier. When there is sufficient radio frequency energy in the environment, the radio frequency rectifier charges the supercapacitor to store the excess energy. When there is insufficient radio frequency energy in the environment, the supercapacitor supplies power to the electrical load.

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