Filter circuit and NFC reader for preventing NFC conduction radiation and radiation emission exceeding

Abstract

The application relates to a filter circuit and an NFC card reader for preventing NFC conduction radiation and excessive radiation emission of a vehicle. The circuit comprises an NFC driving module, an EMC filter module, an impedance matching module and an NFC antenna coil connected in sequence, and further comprises a common mode inductor arranged at any position in a signal transmission link between the NFC driving module, the EMC filter module, the impedance matching module and the NFC antenna coil. The circuit can effectively solve the problem of radiation emission and meet the EMC requirements of different scenes.

Description

Technical Field

[0001] This application relates to the field of NFC technology, and in particular to a filter circuit and an NFC reader for preventing excessive conducted radiation and radiated emissions from automotive NFC devices. Background Technology

[0002] In the field of near field communication (NFC), the signal transmission performance of NFC antenna circuits is crucial for achieving efficient and stable EMC in near field communication.

[0003] Traditional NFC antenna circuits use EMC filters to remove high-order harmonics, reducing conducted and radiated emissions. An impedance matching module then modifies the antenna impedance, optimizing the signal spectrum and power transmission efficiency, ultimately generating a 13.56MHz sine wave signal, which is transmitted by the NFC antenna coil for near-field communication. However, traditional NFC antenna circuits have limitations. The EMC filter has limited filtering effectiveness and cannot completely remove high-order harmonics from the square wave signal, resulting in persistent conducted and radiated emissions, thus restricting the application of NFC technology in scenarios with high electromagnetic compatibility requirements.

[0004] Therefore, there is an urgent need to improve the existing NFC antenna circuit to enhance the EMC performance of NFC technology. Utility Model Content

[0005] Therefore, it is necessary to provide a filter circuit and an NFC reader to prevent excessive conducted radiation and radiated emissions from automotive NFC devices.

[0006] In a first aspect, this application provides a filtering circuit to prevent excessive conducted radiation and radiated emissions from automotive NFC, comprising an NFC driver module, an EMC filter module, an impedance matching module, and an NFC antenna coil connected in sequence, and further comprising a common-mode inductor disposed at any position in the signal transmission link between the NFC driver module, the EMC filter module, the impedance matching module, and the NFC antenna coil.

[0007] In one embodiment, a common-mode inductor is disposed between the NFC driver module and the EMC filter module. One end of the common-mode inductor is connected to the TX pin of the NFC driver module, and the other end of the common-mode inductor is connected to the inductor of the EMC filter module.

[0008] In one embodiment, the EMC filtering module includes an inductor unit and a first capacitor unit connected in sequence;

[0009] The common-mode inductor is positioned between the inductor unit and the first capacitor unit, and the first capacitor unit is grounded.

[0010] In one embodiment, the inductor unit includes a first inductor and a second inductor, and the first capacitor unit includes a first capacitor and a second capacitor;

[0011] The first inductor is connected in series between the first output pin of the NFC driver module and the first input terminal of the common-mode inductor; the second inductor is connected in series between the second output pin of the NFC driver module and the second input terminal of the common-mode inductor; the first capacitor is connected in series between the first output terminal of the common-mode inductor and ground; the first output terminal of the common-mode inductor is also connected to the first input terminal of the impedance matching module; the second capacitor is connected in series between the second output terminal of the common-mode inductor and ground; the second output terminal of the common-mode inductor is also connected to the second input terminal of the impedance matching module.

[0012] In one embodiment, a common-mode inductor is disposed between the EMC filter module and the impedance matching module, with one end of the common-mode inductor connected to the capacitor of the EMC filter module and the other end of the common-mode inductor connected to the capacitor of the impedance matching module.

[0013] In one embodiment, the impedance matching module includes a second capacitor unit, a third capacitor unit, and a resistor unit connected in sequence.

[0014] The common-mode inductor is positioned between the second and third capacitor units, and the third capacitor unit is grounded.

[0015] In one embodiment, the second capacitor unit includes a third capacitor and a fourth capacitor, and the third capacitor unit includes a fifth capacitor and a sixth capacitor.

[0016] The third capacitor is connected in series between the first output terminal of the EMC filter module and the first input terminal of the common mode inductor; the fourth capacitor is connected in series between the second output terminal of the EMC filter module and the second input terminal of the common mode inductor; the fifth capacitor is connected in series between the first output terminal of the common mode inductor and ground; and the sixth capacitor is connected in series between the second output terminal of the common mode inductor and ground.

[0017] In one embodiment, the resistor unit includes a first resistor and a second resistor, the first resistor being connected in series between a first output terminal of the common-mode inductor and a first input terminal of the NFC antenna coil, and the second resistor being connected in series between a second output terminal of the common-mode inductor and a second output terminal of the NFC antenna coil.

[0018] In one embodiment, the NFC antenna coil includes an antenna capacitance, an antenna inductance, and an antenna resistance;

[0019] The antenna capacitor is connected to the impedance matching module at both ends, the antenna inductor is connected in parallel with the antenna capacitor, and the antenna resistor is connected in series between the antenna capacitor and the antenna inductor.

[0020] Secondly, this application also provides an NFC card reader, which includes the filtering circuit in the above embodiments for preventing excessive conducted radiation and radiated emission of automotive NFC.

[0021] The aforementioned filtering circuit and NFC reader for preventing excessive conducted and radiated emissions from automotive NFC have at least the following beneficial effects:

[0022] By setting a common-mode inductor and selecting its location in different positions on the signal transmission link, the common-mode inductor, together with the EMC filter module and the ground capacitance in the impedance matching module, can form a new LC filter network. Alternatively, the common-mode inductor and the ground capacitance in the impedance matching module can be combined to form an LC filter network, effectively solving the radiated emission problem and meeting the EMC requirements of different scenarios. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is one of the schematic diagrams of a filter circuit designed to prevent excessive conducted and radiated emissions from automotive NFC in one embodiment.

[0025] Figure 2 This is a second schematic diagram of a filter circuit designed to prevent excessive conducted and radiated emissions from automotive NFC in one embodiment.

[0026] Figure 3 This is the third schematic diagram of a filter circuit in one embodiment to prevent excessive conducted and radiated emissions from automotive NFC.

[0027] Figure 4 This is a fourth schematic diagram of a filter circuit designed to prevent excessive conducted and radiated emissions from automotive NFC in one embodiment.

[0028] Figure 5 This is the fifth schematic diagram of a filter circuit in one embodiment to prevent excessive conducted radiation and radiated emissions from automotive NFC. Detailed Implementation

[0029] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0031] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0032] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0033] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0034] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0035] In one exemplary embodiment, such as Figure 1 As shown, this application provides a filtering circuit to prevent excessive conducted radiation and radiated emission of automotive NFC, including an NFC driver module 2, an EMC filter module 4, an impedance matching module 6, and an NFC antenna coil 8 connected in sequence. It also includes a common-mode inductor 10, which is disposed at any position in the signal transmission link between the NFC driver module 2, the EMC filter module 4, the impedance matching module 6, and the NFC antenna coil 8.

[0036] Near Field Communication (NFC), operating at a frequency of 13.56MHz, allows NFC-enabled card readers, mobile phones, NFC cards, and watches to exchange data when they are close to each other. By integrating inductive card readers, inductive cards, and point-to-point communication functions onto a single chip, it enables applications such as mobile payments, electronic ticketing, access control, mobile identity verification, and anti-counterfeiting using mobile phones, NFC cards, and watches. It is also used in automotive NFC access control, automotive NFC start-up anti-theft systems, and automotive WPC wireless chargers with NFC. The NFC driver module 2, which can refer to the NFC chip, outputs a square wave through two different output pins, TX1 and TX2, forming a 13.56MHz signal. After passing through the subsequent EMC filter module 4 and impedance matching module 6, it forms a sine wave. The EMC filter module 4 reduces high-order harmonic components in the square wave signal to lower radiation. The impedance matching module 6 changes the antenna impedance, optimizing signal spectrum characteristics and power transmission efficiency. The NFC antenna coil 8 transmits the sine wave signal for near-field communication. Generally, the above-described structure can eliminate most of the radiation and achieve the basic functions of near-field communication. However, due to the presence of high-order harmonic radiation in the square wave signal and the limited filtering effect of the EMC filter module 4, the aforementioned radiation problems remain significant. For example, the Fourier series expansion of the square wave signal contains a large number of high-order harmonic components, mainly concentrated in the high-frequency range (such as 81.4MHz, 94.9MHz, etc.). These harmonics propagate through wires or space, leading to conducted radiation and radiated emission problems. Furthermore, the cutoff frequency and suppression capability of the LC filter network in the EMC filter module 4 are limited, making it impossible to completely attenuate high-order harmonics, resulting in the continued prominence of conducted radiation current method (CEC) and radiated emission (RE) problems in practical applications.

[0037] By setting the common-mode inductor 10 and selecting different positions of the common-mode inductor 10 in the signal transmission link, the common-mode inductor 10, together with the ground capacitor in the EMC filter module 4 and the impedance matching module 6, can form a new LC filter network. Alternatively, the common-mode inductor 10 and the ground capacitor in the impedance matching module 6 can be combined to form a new LC filter network, effectively solving the radiated emission problem and meeting the EMC requirements of different scenarios.

[0038] Example 1

[0039] In one exemplary embodiment, such as Figure 2 As shown, the common mode inductor 10 is disposed between the NFC driver module 2 and the EMC filter module 4. One end of the common mode inductor 10 is connected to the TX pin of the NFC driver module 2, and the other end of the common mode inductor 10 is connected to the inductor of the EMC filter module 6.

[0040] For example, due to the large amount of high-order harmonic radiation generated by square wave signals, it is difficult to effectively filter out the radiation by relying solely on EMC filter module 4 and impedance matching module 6. By placing common-mode inductor 10 between NFC driver module 2 and EMC filter module 4, when the output power of NFC driver module 2 is high, common-mode inductor 10 is placed in front, allowing it to combine with the ground capacitance in EMC filter module 4 and impedance matching module 6 as much as possible, forming a new LC filter network on the communication transmission link. This enhances the interference filtering capability of the entire filter circuit for preventing excessive conducted and radiated emissions in automotive NFC, effectively reducing high-order harmonic interference generated by square wave signals at high output power, reducing conducted and radiated interference problems, and ensuring that interference limit requirements are met even under high power output conditions, thus guaranteeing good near-field communication performance. At the same time, it also improves the applicability and stability of the filter circuit for preventing excessive conducted and radiated emissions in automotive NFC under high-power scenarios.

[0041] Example 2

[0042] In one exemplary embodiment, such as Figure 3 As shown, the EMC filter module 4 includes an inductor unit 42 and a first capacitor unit 44 connected in sequence; wherein, a common mode inductor 10 is disposed between the inductor unit 42 and the first capacitor unit 44, and the first capacitor unit 44 is grounded.

[0043] For example, due to the large amount of high-order harmonic radiation generated by the square wave signal, it is difficult to effectively filter out the radiation by relying solely on the EMC filter module 4 and the impedance matching module 6. For the EMC filter module 4, which consists of an inductor unit 42 connected in sequence and a grounded first capacitor unit 44, a common-mode inductor 10 is placed between the inductor unit 42 and the first capacitor unit 44. When the NFC driver module 2 outputs a high-power square wave signal, the signal first passes through the inductor unit 42 and then reaches the common-mode inductor 10. The common-mode inductor 10 combines with the grounded capacitor in the first capacitor unit 44 to form a new LC filter network on the communication transmission link. This can also enhance the radiation filtering capability of the entire filter circuit that prevents excessive conducted radiation and radiated emission in automotive NFC, effectively reducing high-order harmonic radiation and mitigating conducted radiation and radiated emission problems. It provides another feasible placement for the common-mode inductor 10, improves the flexibility and applicability of the circuit design, and ensures the EMC performance of NFC technology.

[0044] In one exemplary embodiment, such as Figure 3As shown, the inductor unit 42 includes a first inductor L1 and a second inductor L2, and the first capacitor unit 44 includes a first capacitor C1 and a second capacitor C2. The first inductor L1 is connected in series between the first output pin TX1 of the NFC driver module 2 and the first input terminal of the common-mode inductor 10. The second inductor L2 is connected in series between the second output pin TX2 of the NFC driver module 2 and the second input terminal of the common-mode inductor 10. The first capacitor C1 is connected in series between the first output terminal of the common-mode inductor 10 and the ground terminal. The first output terminal of the common-mode inductor 10 is also connected to the first input terminal of the impedance matching module 6. The second capacitor C2 is connected in series between the second output terminal of the common-mode inductor 10 and the ground terminal. The second output terminal of the common-mode inductor 10 is also connected to the second input terminal of the impedance matching module 6.

[0045] For example, the first inductor L1 of the inductor unit 42 is connected in series between the first output pin TX1 of the NFC driver module 2 and the first input terminal of the common-mode inductor 10, and the second inductor L2 is connected in series between the second output pin TX2 of the NFC driver module 2 and the second input terminal of the common-mode inductor 10. The first capacitor C1 of the first capacitor unit 44 is connected in series between the first output terminal of the common-mode inductor 10 and the ground terminal, and the second capacitor C2 is connected in series between the second output terminal of the common-mode inductor 10 and the ground terminal. The output terminal of the common-mode inductor 10 is connected to the input terminal of the impedance matching module 6. This connection method allows the high-power signal to pass through the first and second inductors L2 before reaching the common-mode inductor 10 after being output from the NFC driver module 2. At this time, the common-mode inductor 10, together with the first capacitor C1 and the second capacitor C2, forms an effective LC filter network on the communication transmission link. Furthermore, it can be combined with the ground capacitor in the subsequent impedance matching module 6 to further form a stronger LC filter network. The LC filter network effectively reduces high-order harmonic radiation, enhances the radiation filtering capability of the entire filter circuit that prevents excessive conducted and radiated emissions from automotive NFC, and meets EMC requirements.

[0046] In this embodiment, a specific circuit design scheme is provided for the common-mode inductor 10 when it is placed in the EMC filter module 4.

[0047] Example 3

[0048] In one exemplary embodiment, such as Figure 4 As shown, the common-mode inductor 10 is disposed between the EMC filter module 4 and the impedance matching module 6. One end of the common-mode inductor 10 is connected to the capacitor of the EMC filter module 4, and the other end of the common-mode inductor 10 is connected to the capacitor of the impedance matching module 6.

[0049] For example, square wave signals generate significant high-order harmonic radiation. By placing the common-mode inductor 10 between the EMC filter module 4 and the impedance matching module 6, the common-mode inductor 10, together with the ground capacitance in the EMC filter module 4 and the impedance matching module 6, forms a new LC filter network, providing a more reasonable circuit design scheme.

[0050] Example 4

[0051] In one exemplary embodiment, such as Figure 5 As shown, the impedance matching module 6 includes a second capacitor unit 62, a third capacitor unit 64 and a resistor unit 66 connected in sequence; wherein, the common mode inductor 10 is disposed between the second capacitor unit 62 and the third capacitor unit 64, and the third capacitor unit 64 is grounded.

[0052] For example, the impedance matching module 6 consists of a second capacitor unit 62, a third capacitor unit 64, and a resistor unit 66 connected in sequence, with the third capacitor unit 64 grounded. A common-mode inductor 10 is positioned between the second capacitor unit 62 and the third capacitor unit 64. The signal first passes through the second capacitor unit 62 and then reaches the common-mode inductor 10. Because the common-mode inductor 10 is in this position, it only combines with the third capacitor unit 64 to form a new LC filter network, thus meeting EMC requirements.

[0053] In this embodiment, the common-mode inductor 10 is placed between the second capacitor unit 62 and the third capacitor unit 64, achieving a similar effect to placing the common-mode inductor 10 between the EMC filter module 4 and the impedance matching module 6. This provides another option for the placement of the common-mode inductor 10, increasing the flexibility of the circuit design.

[0054] In one exemplary embodiment, such as Figure 5 As shown, the second capacitor unit 62 includes a third capacitor C3 and a fourth capacitor C4, and the third capacitor unit 64 includes a fifth capacitor C5 and a sixth capacitor C6; wherein, the third capacitor C3 is connected in series between the first output terminal of the EMC filter module 4 and the first input terminal of the common mode inductor 10, the fourth capacitor C4 is connected in series between the second output terminal of the EMC filter module 4 and the second input terminal of the common mode inductor 10, the fifth capacitor C5 is connected in series between the first output terminal of the common mode inductor 10 and the ground terminal, and the sixth capacitor C6 is connected in series between the second output terminal of the common mode inductor 10 and the ground terminal.

[0055] In one exemplary embodiment, such as Figure 5 As shown, the resistor unit includes a first resistor and a second resistor. The first resistor R1 is connected in series between the first output terminal of the common mode inductor 10 and the first input terminal of the NFC antenna coil 8, and the second resistor R2 is connected in series between the second output terminal of the common mode inductor 10 and the second output terminal of the NFC antenna coil 8.

[0056] For example, after the signal is output from the EMC filter module 4, the third capacitor C3 is connected in series between the first output terminal of the EMC filter module 4 and the first input terminal of the common-mode inductor 10, and the fourth capacitor C4 is connected in series between the second output terminal of the EMC filter module 4 and the second input terminal of the common-mode inductor 10, so that the signal can be transmitted to the common-mode inductor 10 relatively smoothly. Figure 5 The common-mode inductor 10 is positioned to form an LC filter network with the fifth capacitor C5 and the sixth capacitor C6, which can meet EMC requirements and provides another option for the placement of the common-mode inductor 10, increasing the flexibility of circuit design.

[0057] The first resistor R1 is connected in series between the first output terminal of the common-mode inductor 10 and the first input terminal of the NFC antenna coil 8, and the second resistor R2 is connected in series between the second output terminal of the common-mode inductor 10 and the second input terminal of the NFC antenna coil 8. The first resistor R1 and the second resistor R2 are used to adjust the antenna Q value.

[0058] In this embodiment, when the common-mode inductor 10 is placed in the impedance matching module 6, a specific circuit design scheme is provided, which can not only meet the radiation filtering requirements, but also increase the flexibility of circuit design.

[0059] In one exemplary embodiment, such as Figure 2-5 As shown, the NFC antenna coil includes an antenna capacitor C. ANT Antenna inductance L ANT and antenna resistance R ANT Among them, the antenna capacitance C ANT Both ends are connected to the impedance matching module, and the antenna inductance L ANT With antenna capacitance C ANT Parallel connection, antenna resistance R ANT Series connected to antenna capacitor C ANT and antenna inductance L ANT between.

[0060] In this embodiment, the NFC antenna coil achieves efficient signal transmission and stable operation through the antenna capacitor CANT, antenna inductor LANT, and antenna resistor RANT. The antenna capacitor CANT is connected to the impedance matching module, which helps optimize the input and output matching of the signal and reduce signal reflection loss. The antenna inductor LANT is connected in parallel with the antenna capacitor CANT, which can adjust the resonant frequency of the antenna, enabling the antenna to operate at a specific frequency and enhancing signal reception and transmission capabilities. The antenna resistor RANT is connected in series between the two, which can effectively suppress high-frequency interference and improve signal quality. This allows the NFC antenna coil to transmit data more stably and quickly during communication, significantly improving the performance of the NFC device.

[0061] In one exemplary embodiment, this application also provides an NFC reader that includes a filtering circuit as described in the above embodiments to prevent excessive conducted radiation and radiated emissions from automotive NFC devices.

[0062] In the description of this specification, references to terms such as "some embodiments," "other embodiments," 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 this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0063] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A filtering circuit for preventing excessive conducted and radiated emissions from automotive NFC, comprising an NFC driver module, an EMC filtering module, an impedance matching module, and an NFC antenna coil connected in sequence, characterized in that, It also includes a common-mode inductor, which is disposed at any position in the signal transmission link between the NFC driver module, the EMC filter module, the impedance matching module and the NFC antenna coil.

2. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 1, characterized in that, The common-mode inductor is disposed between the NFC driver module and the EMC filter module. One end of the common-mode inductor is connected to the TX pin of the NFC driver module, and the other end of the common-mode inductor is connected to the inductor of the EMC filter module.

3. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 1, characterized in that, The EMC filtering module includes an inductor unit and a first capacitor unit connected in sequence. The common-mode inductor is disposed between the inductor unit and the first capacitor unit, and the first capacitor unit is grounded.

4. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 3, characterized in that, The inductor unit includes a first inductor and a second inductor, and the first capacitor unit includes a first capacitor and a second capacitor; In this configuration, the first inductor is connected in series between the first output pin of the NFC driver module and the first input terminal of the common-mode inductor; the second inductor is connected in series between the second output pin of the NFC driver module and the second input terminal of the common-mode inductor; the first capacitor is connected in series between the first output terminal of the common-mode inductor and ground; the first output terminal of the common-mode inductor is also connected to the first input terminal of the impedance matching module; the second capacitor is connected in series between the second output terminal of the common-mode inductor and ground; and the second output terminal of the common-mode inductor is also connected to the second input terminal of the impedance matching module.

5. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 1, characterized in that, The common-mode inductor is disposed between the EMC filter module and the impedance matching module. One end of the common-mode inductor is connected to the capacitor of the EMC filter module, and the other end of the common-mode inductor is connected to the capacitor of the impedance matching module.

6. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 1, characterized in that, The impedance matching module includes a second capacitor unit, a third capacitor unit, and a resistor unit connected in sequence. The common-mode inductor is disposed between the second capacitor unit and the third capacitor unit, and the third capacitor unit is grounded.

7. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 6, characterized in that, The second capacitor unit includes a third capacitor and a fourth capacitor, and the third capacitor unit includes a fifth capacitor and a sixth capacitor; The third capacitor is connected in series between the first output terminal of the EMC filter module and the first input terminal of the common-mode inductor; the fourth capacitor is connected in series between the second output terminal of the EMC filter module and the second input terminal of the common-mode inductor; the fifth capacitor is connected in series between the first output terminal of the common-mode inductor and ground; and the sixth capacitor is connected in series between the second output terminal of the common-mode inductor and ground.

8. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to claim 6, characterized in that, The resistor unit includes a first resistor and a second resistor. The first resistor is connected in series between the first output terminal of the common-mode inductor and the first input terminal of the NFC antenna coil, and the second resistor is connected in series between the second output terminal of the common-mode inductor and the second output terminal of the NFC antenna coil.

9. The filter circuit for preventing excessive conducted radiation and radiated emission of automotive NFC according to any one of claims 1-8, characterized in that, The NFC antenna coil includes antenna capacitance, antenna inductance, and antenna resistance; The antenna capacitor is connected to the impedance matching module at both ends, the antenna inductor is connected in parallel with the antenna capacitor, and the antenna resistor is connected in series between the antenna capacitor and the antenna inductor.

10. An NFC card reader, characterized in that, The NFC reader includes a filtering circuit as described in any one of claims 1-8 to prevent excessive conducted radiation and radiated emission of automotive NFC.

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