Matching circuit for NFC antenna

Abstract

The present application provides a matching circuit for an NFC antenna, including a first filtering circuit and a first coupling circuit. The first end of the first inductor in the first filtering circuit is connected to the first signal transmitting end of the NFC chip, and the second end of the first inductor is connected to the first end of the first capacitor. The second end of the first capacitor in the first filtering circuit is connected to the first end of the first coupling circuit, the second end of the first coupling circuit is connected to the first end of the antenna network, and the third end of the first coupling circuit is connected to the ground terminal and the second end of the antenna network. The first inductor and the first capacitor constitute a first filtering circuit with a bandpass circuit characteristic, and the high-frequency signal and the low-frequency signal can be effectively isolated from being emitted outward through the first inductor and the first capacitor, respectively, and the high-frequency and low-frequency interferences can be filtered out. In addition, the first capacitor and the first coupling circuit can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the transmitting end of the NFC chip to the antenna network.

Description

Technical Field

[0001] The present application relates to the field of antenna technology, and in particular to a matching circuit for an NFC antenna. Background Art

[0002] Figure 1 Figure 1 is a typical Near Field Communication (NFC) differential antenna network diagram, which mainly includes EMC (Electro Magnetic Compatibility) filter circuit, coupling circuit and antenna network. Figure 1 As shown in the figure, the inductor L0 and the capacitor C0 in the EMC filter circuit form a low-pass filter, which can filter out high-frequency interference and prevent EMI (Electromagnetic Interference) caused by high-frequency harmonics. The coupling circuit can transfer the energy after passing through the EMC filter circuit to the antenna network by matching impedance. The coupling circuit and the EMC filter circuit together constitute the matching circuit of the antenna network, and their joint action makes the antenna network work. It can be seen that the matching circuit is particularly important for the antenna network. Summary of the invention

[0003] The present application provides a matching circuit for an NFC antenna, which is used to provide a new matching network for the NFC antenna, and simultaneously achieve the effects of high-frequency and low-frequency filtering and impedance matching.

[0004] In a first aspect, the present application provides a matching circuit for an NFC antenna, comprising: a first filtering circuit and a first coupling circuit;

[0005] The first filtering circuit includes a first inductor and a first capacitor, a first end of the first inductor is connected to a first signal transmitting end of the NFC chip, and a second end of the first inductor is connected to a first end of the first capacitor;

[0006] The second end of the first capacitor is connected to the first end of the first coupling circuit, the second end of the first coupling circuit is connected to the first end of the antenna network, and the third end of the first coupling circuit is connected to the ground end and the second end of the antenna network.

[0007] In one possible design, the first coupling circuit includes: a second capacitor and a third capacitor;

[0008] The first end of the second capacitor is the first end of the first coupling circuit, the second end of the second capacitor is the third end of the first coupling circuit, the first end of the second capacitor is connected to the first end of the third capacitor, and the second end of the third capacitor is the second end of the first coupling circuit.

[0009] In a possible design, the device further includes: a first series circuit; the first series circuit includes a first series resistor and a first series capacitor;

[0010] A first end of the first series resistor is connected to a first signal receiving end of the NFC chip, and a second end of the first series resistor is connected to a first end of the first series capacitor;

[0011] The second end of the first series capacitor is connected to the second end of the first inductor; or, the second end of the first series capacitor is connected to the first end of the second capacitor; or, the second end of the first series capacitor is connected to the second end of the third capacitor.

[0012] In a possible design, the first coupling circuit further includes: a first matching resistor;

[0013] The first end of the first matching resistor is connected to the second end of the third capacitor, and the second end of the first matching resistor is connected to the first end of the antenna network.

[0014] In one possible design, the first coupling circuit further includes: a first isolation inductor;

[0015] The first end of the first isolation inductor is connected to the second end of the third capacitor, and the second end of the first isolation inductor is connected to the first end of the first matching resistor; or

[0016] The first end of the first isolation inductor is connected to the second end of the first matching resistor, and the second end of the first isolation inductor is connected to the first end of the antenna network.

[0017] In one possible design, the NFC chip further includes a third signal transmitting terminal;

[0018] The third signal transmitting end is connected to the first end of the first inductor.

[0019] In a second aspect, the present application provides a matching circuit for an NFC antenna, including: a first filtering circuit, a first coupling circuit, a second filtering circuit, and a second coupling circuit;

[0020] The first filtering circuit includes a first inductor and a first capacitor, a first end of the first inductor is connected to a first signal transmitting end of the NFC chip, and a second end of the first inductor is connected to a first end of one end of the first capacitor;

[0021] The second end of the first capacitor is connected to the first end of the first coupling circuit, the second end of the first coupling circuit is connected to the first end of the antenna network, and the third end of the first coupling circuit is connected to the ground end;

[0022] The second filtering circuit includes a second inductor and a fourth capacitor, a first end of the second inductor is connected to the second signal transmitting end of the NFC chip, and a second end of the second inductor is connected to the first end of the fourth capacitor;

[0023] The second end of the fourth capacitor is connected to the first end of the second coupling circuit, the second end of the second coupling circuit is connected to the second end of the antenna network, and the third end of the second coupling circuit is connected to the ground end.

[0024] In one possible design, the first coupling circuit includes: a second capacitor and a third capacitor;

[0025] The first end of the second capacitor is the first end of the first coupling circuit, the second end of the second capacitor is the third end of the first coupling circuit, the first end of the second capacitor is connected to the first end of the third capacitor, and the second end of the third capacitor is the second end of the first coupling circuit.

[0026] In one possible design, the second coupling circuit includes: a fifth capacitor and a sixth capacitor;

[0027] The first end of the fifth capacitor is the first end of the second coupling circuit, the second end of the fifth capacitor is the third end of the second coupling circuit, the first end of the fifth capacitor is connected to the first end of the sixth capacitor, and the second end of the sixth capacitor is the second end of the second coupling circuit.

[0028] In a possible design, the device further includes: a first series circuit; the first series circuit includes a first series resistor and a first series capacitor;

[0029] A first end of the first series resistor is connected to a first signal receiving end of the NFC chip, and a second end of the first series resistor is connected to a first end of the first series capacitor;

[0030] The second end of the first series capacitor is connected to the second end of the first inductor; or, the second end of the first series capacitor is connected to the first end of the second capacitor; or, the second end of the first series capacitor is connected to the second end of the third capacitor.

[0031] In a possible design, the invention further includes: a second series circuit; the second series circuit includes a second series resistor and a second series capacitor;

[0032] A first end of the second series resistor is connected to a second signal receiving end of the NFC chip, and a second end of the second series resistor is connected to a first end of the second series capacitor;

[0033] The second end of the second series capacitor is connected to the second end of the second inductor; or, the second end of the second series capacitor is connected to the first end of the fifth capacitor; or, the second end of the second series capacitor is connected to the second end of the sixth capacitor.

[0034] In a possible design, the first coupling circuit further includes: a first matching resistor;

[0035] The first end of the first matching resistor is connected to the second end of the third capacitor, and the second end of the first matching resistor is connected to the first end of the antenna network.

[0036] In one possible design, the second coupling circuit further includes a second matching resistor;

[0037] The first end of the second matching resistor is connected to the second end of the sixth capacitor, and the second end of the second matching resistor is connected to the second end of the antenna network.

[0038] The present application provides a matching circuit for an NFC antenna, the matching circuit comprising a first filtering circuit and a first coupling circuit. The first filtering circuit comprises a first inductor and a first capacitor, the first end of the first inductor being connected to the first signal transmitting end of the NFC chip, and the second end of the first inductor being connected to the first end of the first capacitor. The second end of the first capacitor is connected to the first end of the first coupling circuit, the second end of the first coupling circuit is connected to the first end of the antenna network, and the third end of the first coupling circuit is connected to the ground terminal and the second end of the antenna network. The first inductor and the first capacitor constitute a first filtering circuit with a bandpass circuit characteristic, wherein the first inductor can effectively isolate the high-frequency signal from being emitted outward to filter out high-frequency interference, and the first capacitor can isolate the low-frequency signal from being emitted outward to filter out low-frequency interference, and can achieve filtering effects on both low-frequency interference and high-frequency interference. In addition, the first capacitor and the first coupling circuit can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the transmitting end of the NFC chip to the antenna network. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0040] Figure 1 A circuit diagram of an NFC antenna network in the prior art;

[0041] Figure 2A schematic diagram of a matching circuit of an NFC antenna provided in an embodiment of the present application;

[0042] Figure 3 A schematic diagram of a matching circuit of another NFC antenna provided in an embodiment of the present application;

[0043] Figure 4 A schematic diagram of a matching circuit of another NFC antenna provided in an embodiment of the present application;

[0044] Figure 5 A schematic diagram of a matching circuit for another NFC antenna provided in an embodiment of the present application. DETAILED DESCRIPTION

[0045] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of methods and devices consistent with some aspects of the present application as detailed in the appended claims.

[0046] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0047] like Figure 1 As shown in the figure, the inductor L0 and the capacitor C0 in the EMC filter circuit form a low-pass filter, which can filter out high-frequency interference and prevent EMI interference caused by high-frequency harmonics. The coupling circuit can transfer the energy after passing through the EMC filter circuit to the antenna network by matching impedance. The coupling circuit and the EMC filter circuit together constitute the matching circuit of the antenna network, and their joint action makes the antenna network work. It can be seen that the matching circuit is particularly important for the antenna network.

[0048] In view of the above problems, the present application provides a matching circuit for an NFC antenna. The inventive concept of the matching circuit for the NFC antenna provided in the present application is that the matching circuit includes a first filtering circuit and a first coupling circuit. Among them, the first filtering circuit includes a first inductor and a first capacitor, the first inductor and the first capacitor are connected in series, and the first capacitor is connected to the first coupling circuit and is not grounded. Compared with the prior art that the inductor and the capacitor in the EMC filtering circuit can only filter out high-frequency interference in parallel, the first inductor in the first filtering circuit can effectively isolate the high-frequency signal from being emitted outward to achieve the high-frequency interference filtering effect, and the first capacitor can isolate the low-frequency signal from being emitted outward to achieve the low-frequency interference filtering effect, so that the first filtering circuit in the matching circuit of the NFC antenna can achieve the filtering effect on both low-frequency interference and high-frequency interference. In addition, the first capacitor and the first coupling circuit can form a capacitor T-type impedance matching effect, which can better transfer energy from the transmitting end of the NFC chip to the antenna network, and then the configuration of the specifications of each device in the first coupling circuit can be used to ensure the realization of maximum power transmission.

[0049] The technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0050] Figure 2 A schematic diagram of a matching circuit of an NFC antenna provided in an embodiment of the present application. Figure 2 As shown, the matching circuit 100 of the NFC antenna provided in the embodiment of the present application includes: a first filtering circuit 101 and a first coupling circuit 102.

[0051] The first filter circuit 101 includes a first inductor L1 and a first capacitor Cs0. The first end of the first inductor L1 is connected to the first signal transmitting end of the NFC chip 200, and the second end of the first inductor L1 is connected to the first end of the first capacitor Cs0. Figure 2 TXN in.

[0052] The second end of the first capacitor Cs0 is connected to the first end of the first coupling circuit 102 , the second end of the first coupling circuit 102 is connected to the first end of the antenna network 300 , and the third end of the first coupling circuit 102 is connected to the ground GND and the second end of the antenna network 300 .

[0053] Optionally, the matching circuit 100 further includes: a first series circuit, wherein the first series circuit includes a first series resistor R1 and a first series capacitor C1.

[0054] The first end of the first series resistor R1 is connected to the first signal receiving end of the NFC chip 200, the second end of the first series resistor R1 is connected to the first end of the first series capacitor C1, and the second end of the first series capacitor C1 is connected to the second end of the first inductor L1. The first signal receiving end of the NFC chip 200 can be, for example Figure 2 RX in. Or in some embodiments, the second end of the first series capacitor C1 is connected to the first end of the first coupling circuit 102; or the second end of the first series capacitor C1 is connected to the second end of the first coupling circuit. For example, the second end of the first series capacitor C1 can be connected to Figure 2 At A, B, and P, it should be noted that Figure 2 Only the second end of the first series capacitor C1 is shown to be connected to A, and the corresponding figures of B and P are not shown.

[0055] Depend on Figure 2 It can be seen that the first inductor L1 and the first capacitor Cs0 are connected in series, and the two constitute a first filter circuit 101 with a bandpass circuit characteristic. The first inductor L1 can effectively isolate high-frequency signals from being emitted to filter out high-frequency interference, and the first capacitor Cs0 can isolate low-frequency signals from being emitted to filter out low-frequency interference, so that the first filter circuit 101 can achieve a filtering effect on both low-frequency interference and high-frequency interference.

[0056] In addition, the connection between the first capacitor Cs0 and the first coupling circuit 102 can form a capacitive T-type impedance matching effect, so that energy can be better transferred from the first signal transmitting end of the NFC chip 200 to the antenna network 300 .

[0057] In some embodiments, the NFC chip 200 may further include a third signal transmitting terminal, for example Figure 2 The third signal transmitting terminal TXP is connected to the first end of the first inductor L1 to form a two-way drive to enhance the emission strength of the NFC chip 200 .

[0058] In a possible design, the first coupling circuit 102 includes: a second capacitor Cs1 and a third capacitor Cs2.

[0059] The first end of the second capacitor Cs1 is the first end of the first coupling circuit 102 , the second end of the second capacitor Cs1 is the third end of the first coupling circuit 102 , the first end of the second capacitor Cs1 is connected to the first end of the third capacitor Cs2 , and the second end of the third capacitor Cs2 is the second end of the first coupling circuit 102 .

[0060] It can be seen that a capacitor T-type matching can be formed between the first capacitor Cs0 and the second capacitor Cs1 and the third capacitor Cs2 in the first coupling circuit 102, so that the energy can be better transferred from the first signal transmitting end of the NFC chip 200 to the antenna network 300 by utilizing the advantages of the capacitor T-type matching.

[0061] In a possible design, the first coupling circuit 102 may further include: a first matching resistor Rq.

[0062] The first end of the first matching resistor Rq is connected to the second end of the third capacitor Cs2, and the second end of the first matching resistor Rq is connected to the first end of the antenna network 300. The purpose of setting the first matching resistor Rq is to adjust the resistance value of the first coupling circuit 102.

[0063] Depend on Figure 2 It can be seen that the NFC chip 200 has a loop, and the components in the matching circuit 100 can be arranged at the first end of the antenna network 300. Therefore, Figure 2 The matching circuit 100 of the NFC antenna shown may be applicable to a single-ended NFC antenna.

[0064] In some embodiments, the single-ended NFC antenna may be a cellular antenna or a GPS antenna. In order to isolate the influence of the NFC chip on the cellular antenna or the GPS antenna, the first coupling circuit 102 may further include a first isolation inductor Ls.

[0065] like Figure 3 As shown, the first end of the first isolation inductor Ls is connected to the second end of the third capacitor Cs2, and the second end of the first isolation inductor Ls is connected to the first end of the first matching resistor Rq.

[0066] Alternatively, a first isolation inductor Ls is connected in series between the first matching resistor Rq and the antenna network 300. Specifically, a first end of the first isolation inductor Ls is connected to a second end of the first matching resistor Rq, and a second end of the first isolation inductor Ls is connected to a first end of the antenna network 300. The connection relationship of this embodiment is not shown in the drawings.

[0067] Optionally, the antenna network 300 includes a seventh capacitor Ca, a first resistor Ra, and a third inductor La. The first end of the seventh capacitor Ca is the first end of the antenna network 300 and is connected to the first end of the first resistor Ra, the second end of the first resistor Ra is connected to the first end of the third inductor La, and the second end of the third inductor La is connected to the second end of the seventh capacitor Ca and is the second end of the antenna network 300.

[0068] In the matching circuit of the NFC antenna provided in the embodiment of the present application, the first inductor and the first capacitor constitute a first filter circuit with bandpass circuit characteristics, wherein the first inductor can effectively isolate the high-frequency signal from being emitted outward to filter out high-frequency interference, and the first capacitor can isolate the low-frequency signal from being emitted outward to filter out low-frequency interference, and can achieve filtering effects on both low-frequency interference and high-frequency interference. In addition, the first capacitor and the first coupling circuit can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the transmitting end of the NFC chip to the antenna network.

[0069] Figure 4 A matching circuit diagram of another NFC antenna provided in an embodiment of the present application is shown in FIG. Figure 4 As shown, the embodiment of the present application provides a corresponding matching circuit for a differential NFC antenna, wherein the differential NFC antenna has two loops, namely two signal transmitting ends and two signal receiving ends, relative to a single-ended NFC antenna, to form corresponding loops.

[0070] like Figure 4 As shown, the matching circuit 100 of the NFC antenna provided in the embodiment of the present application includes: a first filtering circuit 101, a first coupling circuit 102, a second filtering circuit 104 and a second coupling circuit 105.

[0071] The first filter circuit 101 includes a first inductor L1 and a first capacitor Cs0. The first end of the first inductor L1 is connected to the first signal transmitting end of the NFC chip 200, and the second end of the first inductor L1 is connected to the first end of the first capacitor Cs0. Figure 4 TXN in.

[0072] A second end of the first capacitor Cs0 is connected to a first end of the first coupling circuit 102 , a second end of the first coupling circuit 102 is connected to a first end of the antenna network 300 , and a third end of the first coupling circuit 102 is connected to the ground end GND.

[0073] The second filter circuit 104 includes a second inductor L2 and a fourth capacitor Cs0', wherein the first end of the second inductor L2 is connected to the second signal transmitting end of the NFC chip 200, and the second end of the second inductor L2 is connected to the first end of the fourth capacitor Cs0'. Figure 4 TXP in.

[0074] A second end of the fourth capacitor Cs0 ′ is connected to a first end of the second coupling circuit 105 , a second end of the second coupling circuit 105 is connected to a second end of the antenna network 300 , and a third end of the second coupling circuit 105 is connected to the ground GND.

[0075] Optionally, the antenna network 300 includes a seventh capacitor Ca, a first resistor Ra, and a third inductor La. The first end of one end of the seventh capacitor Ca is the first end of the antenna network 300 and is connected to the first end of one end of the first resistor Ra, the second end of the other end of the first resistor Ra is connected to the first end of one end of the third inductor La, and the second end of the other end of the third inductor La is connected to the second end of the other end of the seventh capacitor Ca and is the second end of the antenna network 300.

[0076] Depend on Figure 4 It can be seen that the second filter circuit 104 and the first filter circuit 101 are symmetrically centered on the horizontal line where the ground terminal GND is located, and the second coupling circuit 105 and the first coupling circuit 102 are symmetrically centered on the horizontal line where the ground terminal GND is located. The first inductor L1 and the first capacitor Cs0 are connected in series, and the two constitute the first filter circuit 101 with a bandpass circuit characteristic. The first inductor L1 can effectively isolate the high-frequency signal from being emitted outward to filter out high-frequency interference, and the first capacitor Cs0 can isolate the low-frequency signal from being emitted outward to filter out low-frequency interference, so that the first filter circuit 101 can achieve a filtering effect on both low-frequency interference and high-frequency interference. The second inductor L2 and the fourth capacitor Cs0' are connected in series, and the two constitute a second filter circuit with a bandpass circuit characteristic. The second inductor L2 can effectively isolate the high-frequency signal from being emitted outward to filter out high-frequency interference, and the fourth capacitor Cs0' can isolate the low-frequency signal from being emitted outward to filter out low-frequency interference, so that the second filter circuit 104 can achieve a filtering effect on both low-frequency interference and high-frequency interference.

[0077] In addition, the connection between the first capacitor Cs0 and the first coupling circuit 102 can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the first signal transmitting end of the NFC chip 200 to the antenna network 300. The connection between the fourth capacitor Cs0' and the second coupling circuit 105 can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the second signal transmitting end of the NFC chip 200 to the antenna network 300. Optionally, the matching circuit 100 further includes: a first series circuit, the first series circuit including a first series resistor R1 and a first series capacitor C1.

[0078] The first end of the first series resistor R1 is connected to the first signal receiving end of the NFC chip 200, the second end of the first series resistor R1 is connected to the first end of the first series capacitor C1, and the second end of the first series capacitor C1 is connected to the second end of the first inductor L1. The first signal receiving end of the NFC chip 200 can be, for example Figure 2RX in. Or in some embodiments, the second end of the first series capacitor C1 is connected to the first end of the first coupling circuit 102; or the second end of the first series capacitor C1 is connected to the second end of the first coupling circuit. For example, the second end of the first series capacitor C1 can be connected to Figure 4 At A, B, and P, it should be noted that Figure 4 Only the second end of the first series capacitor C1 is shown to be connected to A, and the corresponding figures of B and P are not shown.

[0079] In a possible design, the first coupling circuit 102 includes: a second capacitor Cs1 and a third capacitor Cs2.

[0080] The first end of the second capacitor Cs1 is the first end of the first coupling circuit 102 , the second end of the second capacitor Cs1 is the third end of the first coupling circuit 102 , the first end of the second capacitor Cs1 is connected to the first end of the third capacitor Cs2 , and the second end of the third capacitor Cs2 is the second end of the first coupling circuit 102 .

[0081] It can be seen that a capacitor T-type matching can be formed between the first capacitor Cs0 and the second capacitor Cs1 and the third capacitor Cs2 in the first coupling circuit 102, so that the energy can be better transferred from the first signal transmitting end of the NFC chip 200 to the antenna network 300 by utilizing the advantages of the capacitor T-type matching.

[0082] In a possible design, the second coupling circuit 105 may include: a fifth capacitor Cs1 ′ and a sixth capacitor Cs2 ′.

[0083] The first end of the fifth capacitor Cs1' is the first end of the second coupling circuit 105, the second end of the fifth capacitor Cs1' is the third end of the second coupling circuit 105, the first end of the fifth capacitor Cs1' is connected to the first end of the sixth capacitor Cs2', and the second end of the sixth capacitor Cs2' is the second end of the second coupling circuit 105.

[0084] It can be seen that a capacitor T-type matching can be formed between the fourth capacitor Cs0 ′ and the fifth capacitor Cs1 ′ and the sixth capacitor Cs2 ′ in the second coupling circuit 105 , so that the energy can be better transferred from the second signal transmitting end of the NFC chip 200 to the antenna network 300 by utilizing the advantage of the capacitor T-type matching.

[0085] Optionally, the matching circuit 100 further includes: a second series circuit.

[0086] The second series circuit may include a second series resistor R2 and a second series capacitor C2.

[0087] The first end of the second series resistor R2 is connected to the second signal receiving end of the NFC chip 200, the second end of the second series resistor R2 is connected to the first end of the second series capacitor C2, and the second end of the second series capacitor C2 is connected to the second end of the second inductor L2. The second signal receiving end of the NFC chip 200 can be, for example Figure 4 RXP in.

[0088] Alternatively, in some embodiments, the second end of the second series capacitor C2 is connected to the first end of the second coupling circuit 105; or alternatively, the second end of the second series capacitor C2 is connected to the second end of the second coupling circuit 105. For example, the second end of the second series capacitor C2 may be connected to Figure 4 At A', B', and P', it should be noted that Figure 4 Only the second end of the second series capacitor C2 is shown to be connected to A', and the corresponding figures at B' and P' are not shown.

[0089] In a possible design, the first coupling circuit 102 may further include: a first matching resistor Rq.

[0090] The first end of the first matching resistor Rq is connected to the second end of the third capacitor Cs2, and the second end of the first matching resistor Rq is connected to the first end of the antenna network 300. The purpose of setting the first matching resistor Rq is to adjust the resistance value of the first coupling circuit 102.

[0091] Optionally, the second coupling circuit 105 may further include a second matching resistor Rq′.

[0092] The first end of the second matching resistor Rq' is connected to the second end of the sixth capacitor Cs2', and the second end of the second matching resistor Rq' is connected to the second end of the antenna network 300. The resistance value of the second matching resistor Rq' is equal to that of the first matching resistor Rq, and the specific value can be set according to the actual working conditions. In addition, the purpose of setting the second matching resistor Rq' is to adjust the resistance value of the second coupling circuit 105.

[0093] It should be noted that Figure 4 The figure shows a matching circuit of a differential NFC antenna, wherein the NFC antenna has two loops, a loop formed between the first signal transmitting end and the first signal receiving end of the NFC chip 200, and a loop formed between the second signal transmitting end TXP and the second signal receiving end RXP of the NFC chip 200. The first signal transmitting end and the first signal receiving end of the NFC chip 200 are respectively as shown in FIG. Figure 4 TXN and RXN in the table represent the Figure 4 For the differential NFC antenna shown, the phase difference between the first signal transmitting end TXN and the second signal transmitting end TXP is 180° to achieve a differential effect.

[0094] Based on the symmetry of the first filter circuit 101 and the second filter circuit 104, the first coupling circuit 102 and the second coupling circuit 105 are symmetric, the inductance values ​​of the first inductor L1 and the second inductor L2 are the same, the capacitance values ​​of the first capacitor Cs0 and the fourth capacitor Cs0' are the same, the capacitance values ​​of the second capacitor Cs1 and the fifth capacitor Cs1' are equal, and the capacitance values ​​of the third capacitor Cs2 and the sixth capacitor Cs2' are equal.

[0095] The first series capacitor and the second series circuit are symmetrical, so the second series resistor R2 and the first series resistor R1 have the same resistance value. The second series capacitor C2 and the first series capacitor C1 have the same capacitance value, and the specific capacitance value can be set according to actual working conditions.

[0096] The matching circuit of the NFC antenna provided in the embodiment of the present application, the first inductor and the first capacitor constitute a first filter circuit with a bandpass circuit characteristic, wherein the first inductor can effectively isolate the high-frequency signal from being emitted outward to filter out high-frequency interference, and the first capacitor can isolate the low-frequency signal from being emitted outward to filter out low-frequency interference, and can achieve filtering effects on both low-frequency interference and high-frequency interference. In addition, the first capacitor and the first coupling circuit can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the first transmitting end of the NFC chip to the antenna network. The second inductor and the fourth capacitor constitute a second filter circuit with a bandpass circuit characteristic, wherein the second inductor can effectively isolate the high-frequency signal from being emitted outward to filter out high-frequency interference, and the fourth capacitor can isolate the low-frequency signal from being emitted outward to filter out low-frequency interference, and can achieve filtering effects on both low-frequency interference and high-frequency interference. In addition, the fourth capacitor and the second coupling circuit can form a capacitor T-type impedance matching effect, so that energy can be better transferred from the second transmitting end of the NFC chip to the antenna network.

[0097] The following is an illustrative explanation of the selection of the capacitance values ​​of the second capacitor Cs1 and the third capacitor Cs2 in the above embodiment.

[0098] The necessary condition for achieving maximum power transfer is that the load impedance and source impedance are conjugate matched. Assume that R match for Figure 4 The target impedance to be matched is viewed from left to right from the first signal transmitting terminal TXN to the second signal transmitting terminal TXP. Figure 4 The matching circuit 100 shown in FIG. 1 can be divided into two parts from the first capacitor Cs0, so that the matching circuit 100 shown in FIG. 1 can be formed as follows: Figure 5 The circuit shown in the figure can be used to simulate a source impedance of R match ,because Figure 4 It is a symmetrical design centered on the horizontal line where the ground terminal is located, so the source impedance R match Can be separated into two R r1 Resistor, whose resistance is R match / 2. From Figure 5 The impedance of the disconnection shown looking to the left is assumed to be Z tr To achieve maximum power transfer, Figure 5 Looking to the right at the disconnection point shown, if the impedance of this part is Z tr The conjugate impedance Z tr * can achieve maximum power transmission. Based on this, the values ​​of the second capacitor Cs1 and the third capacitor Cs2 can be calculated by the following deduction.

[0099] Reference Figure 5 As shown and for the sake of simplifying the calculation, the seventh capacitor Ca in the antenna network 300 is neglected, and the above-mentioned assumed impedance Z tr and conjugate impedance Z tr *Satisfy the following formula (Ⅰ):

[0100]

[0101] Here, ω represents the angular frequency.

[0102] After reorganizing formula (I), we can obtain formulas (1) and (2) as shown below:

[0103]

[0104] Further according to formula (2), we can get the following formulas (3) and (4):

[0105]

[0106]

[0107] Substituting formula (3) and (4) into formula (1), we can obtain the following formula (5):

[0108]

[0109] Further arranging the above formulas, we can obtain the corresponding formulas (6) and (7) for calculating the second capacitor Cs1 and the third capacitor Cs2 respectively:

[0110]

[0111] With a known source impedance R match , the first inductor L1, the first matching resistor Rq and the first resistor Ra, in order to maximize the transmission of real power, the value of the second capacitor Cs1, that is, the capacitance value of the second capacitor, can be calculated by the above formula (6). Correspondingly, since the second capacitor Cs1 and the fifth capacitor Cs1' are the same, the value of the fifth capacitor Cs1' can also be obtained.

[0112] When the second capacitor Cs1, the third inductor La, the first matching resistor Rq and the first resistor Ra are known, the value of the third capacitor Cs2 can be calculated by the above formula (7). Accordingly, since the third capacitor Cs2 and the sixth capacitor Cs2' are the same, the value of the sixth capacitor Cs2' can also be obtained. At this point, based on the goal of maximum power transmission, the capacitance value selection of each device in the first coupling circuit 102 and the second coupling circuit in the matching circuit 100 is completed, and the capacitor T-type matching is completed, so that the energy of the NFC chip 200 is transmitted from the first signal transmitting terminal TXN and the second signal transmitting terminal TXP to the antenna network 300 with maximum power.

[0113] It should be noted that the above selection of values ​​of each component in the first coupling circuit and the second coupling circuit is only for schematic illustration and is not a limitation on the method of selecting the values ​​of the components.

[0114] In addition, the resistance of the first series resistor R1 and the second series resistor R2 is match The difference is at least an order of magnitude.

[0115] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the claims.

[0116] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A matching circuit for an NFC antenna, characterized in that: include: a first filtering circuit and a first coupling circuit; The first filtering circuit includes a first inductor and a first capacitor, wherein a first end of the first inductor is connected to a first signal transmitting end of the NFC chip, and a second end of the first inductor is connected to a first end of the first capacitor; the first inductor and the first capacitor are connected in series; The second end of the first capacitor is connected to the first end of the first coupling circuit, the second end of the first coupling circuit is connected to the first end of the antenna network, and the third end of the first coupling circuit is connected to the ground end and the second end of the antenna network; The first coupling circuit includes: a second capacitor and a third capacitor; The first end of the second capacitor is the first end of the first coupling circuit, the second end of the second capacitor is the third end of the first coupling circuit, the first end of the second capacitor is connected to the first end of the third capacitor, and the second end of the third capacitor is the second end of the first coupling circuit.

2. The matching circuit of the NFC antenna according to claim 1, characterized in that: Also includes: A first series circuit; the first series circuit comprises a first series resistor and a first series capacitor; A first end of the first series resistor is connected to a first signal receiving end of the NFC chip, and a second end of the first series resistor is connected to a first end of the first series capacitor; The second end of the first series capacitor is connected to the second end of the first inductor; or, the second end of the first series capacitor is connected to the first end of the second capacitor; or, the second end of the first series capacitor is connected to the second end of the third capacitor.

3. The matching circuit of the NFC antenna according to claim 2, characterized in that: The first coupling circuit further includes: a first matching resistor; The first end of the first matching resistor is connected to the second end of the third capacitor, and the second end of the first matching resistor is connected to the first end of the antenna network.

4. The matching circuit of the NFC antenna according to claim 3, characterized in that: The first coupling circuit further includes: a first isolation inductor; The first end of the first isolation inductor is connected to the second end of the third capacitor, and the second end of the first isolation inductor is connected to the first end of the first matching resistor; or The first end of the first isolation inductor is connected to the second end of the first matching resistor, and the second end of the first isolation inductor is connected to the first end of the antenna network.

5. The matching circuit of the NFC antenna according to any one of claims 1 to 4, characterized in that: The NFC chip also includes a third signal transmitting terminal; The third signal transmitting end is connected to the first end of the first inductor.

6. A matching circuit for an NFC antenna, characterized in that: include: A first filtering circuit, a first coupling circuit, a second filtering circuit, and a second coupling circuit; The first filtering circuit includes a first inductor and a first capacitor, wherein a first end of the first inductor is connected to a first signal transmitting end of the NFC chip, and a second end of the first inductor is connected to a first end of one end of the first capacitor; the first inductor and the first capacitor are connected in series; The second end of the first capacitor is connected to the first end of the first coupling circuit, the second end of the first coupling circuit is connected to the first end of the antenna network, and the third end of the first coupling circuit is connected to the ground end; The second filtering circuit includes a second inductor and a fourth capacitor, wherein a first end of the second inductor is connected to a second signal transmitting end of the NFC chip, and a second end of the second inductor is connected to a first end of the fourth capacitor; the second inductor and the fourth capacitor are connected in series; The second end of the fourth capacitor is connected to the first end of the second coupling circuit, the second end of the second coupling circuit is connected to the second end of the antenna network, and the third end of the second coupling circuit is connected to the ground end; The first coupling circuit includes: a second capacitor and a third capacitor; The first end of the second capacitor is the first end of the first coupling circuit, the second end of the second capacitor is the third end of the first coupling circuit, the first end of the second capacitor is connected to the first end of the third capacitor, and the second end of the third capacitor is the second end of the first coupling circuit; The second coupling circuit includes: a fifth capacitor and a sixth capacitor; The first end of the fifth capacitor is the first end of the second coupling circuit, the second end of the fifth capacitor is the third end of the second coupling circuit, the first end of the fifth capacitor is connected to the first end of the sixth capacitor, and the second end of the sixth capacitor is the second end of the second coupling circuit.

7. The matching circuit of the NFC antenna according to claim 6, characterized in that: Also includes: A first series circuit; the first series circuit comprises a first series resistor and a first series capacitor; A first end of the first series resistor is connected to a first signal receiving end of the NFC chip, and a second end of the first series resistor is connected to a first end of the first series capacitor; The second end of the first series capacitor is connected to the second end of the first inductor; or, the second end of the first series capacitor is connected to the first end of the second capacitor; or, the second end of the first series capacitor is connected to the second end of the third capacitor.

8. The matching circuit of the NFC antenna according to claim 7, characterized in that: Also includes: A second series circuit; the second series circuit comprises a second series resistor and a second series capacitor; A first end of the second series resistor is connected to a second signal receiving end of the NFC chip, and a second end of the second series resistor is connected to a first end of the second series capacitor; The second end of the second series capacitor is connected to the second end of the second inductor; or, the second end of the second series capacitor is connected to the first end of the fifth capacitor; or, the second end of the second series capacitor is connected to the second end of the sixth capacitor.

9. The matching circuit of the NFC antenna according to claim 8, characterized in that: The first coupling circuit further includes: a first matching resistor; The first end of the first matching resistor is connected to the second end of the third capacitor, and the second end of the first matching resistor is connected to the first end of the antenna network.

10. The matching circuit of the NFC antenna according to claim 9, characterized in that: The second coupling circuit also includes a second matching resistor; The first end of the second matching resistor is connected to the second end of the sixth capacitor, and the second end of the second matching resistor is connected to the second end of the antenna network.

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