Combination filter circuit and combination filter device

Abstract

The application relates to a combination filter circuit and a combination filter device. The combination filter circuit comprises a low-pass filter module, an input end of the low-pass filter module being connected with a coupling capacitor, used for receiving a first power carrier signal and filtering components above a first frequency in the first power carrier signal to obtain a second power carrier signal; a high-pass filter module, an input end of the high-pass filter module being connected with an output end of the low-pass filter module, an output end of the high-pass filter module being connected with a carrier cable, used for filtering components below a second frequency in the second power carrier signal to obtain a third power carrier signal, and used for impedance conversion to match the output impedance of the high-pass filter module with the impedance of the carrier cable; the second frequency is greater than the first frequency. The circuit can simultaneously meet the requirements of working loss, working loss, device side impedance and line side impedance.

Description

Technical Field

[0001] This invention relates to the field of power line carrier communication technology, and in particular to a combined filtering circuit and a combined filtering device. Background Technology

[0002] Power line carrier (PLC) is a communication method unique to power systems. PLC communication refers to the technology of transmitting analog or digital signals at high speed using existing power lines via carrier waves. Its biggest advantage is that it does not require rebuilding the network; data transmission can be achieved as long as there are power lines. Combined with filtering equipment, which is part of the high-frequency channel of the line, it can maximize the receiving power of the transceiver.

[0003] Traditional combined filtering circuits have the problem of difficulty in achieving impedance matching with the line side and the equipment side, resulting in the return loss and operating attenuation of signal transmission failing to meet requirements. Summary of the Invention

[0004] Therefore, it is necessary to provide a combined filter circuit that can be easily adjusted to achieve impedance matching with the line side and equipment side, and has excellent return loss and operating attenuation performance.

[0005] On one hand, embodiments of the present invention provide a combined filtering circuit, comprising: a low-pass filter module, the input terminal of which is connected to a coupling capacitor, for receiving a first power line carrier signal and filtering out components above a first frequency in the first power line carrier signal to obtain a second power line carrier signal; a high-pass filter module, the input terminal of which is connected to the output terminal of the low-pass filter module, the output terminal of which is connected to a carrier cable, for filtering out components below a second frequency in the second power line carrier signal to obtain a third power line carrier signal, and also for impedance transformation to match the output impedance of the high-pass filter module with the impedance of the carrier cable; the second frequency is greater than the first frequency.

[0006] Based on the combined filter circuit in this embodiment, compared with the traditional integrated high-pass filter or band-pass filter, this solution uses a low-pass filter module and a high-pass filter module connected in series to obtain a combined filter circuit. Since the low-pass filter module and the high-pass filter module can be designed with parameters independently, and the two modules are connected to the line side and the equipment side respectively, it is relatively convenient to select appropriate parameters according to relevant national or industry standards, so that the combined filter circuit can simultaneously meet the requirements of operating attenuation, operating loss, equipment side impedance and line side impedance.

[0007] In one embodiment, the output terminal of the low-pass filter module includes a first output terminal and a second output terminal, and the input terminal of the high-pass filter module includes a first input terminal and a second output terminal. The first output terminal of the low-pass filter module is connected to the first input terminal of the high-pass filter module, and the second output terminal of the low-pass filter module is connected to the second input terminal of the high-pass filter module and then grounded. The high-pass filter module includes a drain coil, a first capacitor, a first inductor, and an impedance matching transformer. The drain coil is connected between the first input terminal and the second input terminal of the high-pass filter module. One end of the first capacitor is connected to the common terminal of the drain coil and the first input terminal of the high-pass filter module, and the other end of the first capacitor is grounded through the first inductor. The input terminal of the impedance matching transformer is connected to the common terminal of the first capacitor and the first inductor and ground, respectively, and the output terminal of the impedance matching transformer is connected to the carrier cable and ground, respectively.

[0008] In one embodiment, the input terminals of the low-pass filter module include a first input terminal and a second input terminal. The first input terminal of the low-pass filter module is connected to the coupling capacitor, and the second input terminal of the low-pass filter module is grounded. The low-pass filter module includes a first stray capacitor, a second stray capacitor, and a second inductor. The first stray capacitor corresponds to the coupling capacitor and is connected between the first input terminal and the second input terminal of the low-pass filter module. One end of the second inductor is connected to the common terminal of the first stray capacitor and the first input terminal of the low-pass filter module, and the other end of the second inductor is grounded through the second stray capacitor and connected to the common terminal of the drain coil and the first input terminal of the high-pass filter module. The second stray capacitor corresponds to the drain coil.

[0009] In one embodiment, the capacitance of the second stray capacitor is 300pF.

[0010] In one embodiment, the combined filter circuit further includes a second capacitor disposed between the output of the impedance matching transformer and the carrier cable.

[0011] In one embodiment, the combined filter circuit further includes an isolating switch and a surge arrester; both the isolating switch and the surge arrester are disposed between the first input terminal of the low-pass filter and the second input terminal of the low-pass filter.

[0012] In one embodiment, the impedance ratio of the drain coil is 1.41:1.

[0013] On the other hand, embodiments of the present invention also provide a combined filtering device, comprising: a housing; and a combined filtering circuit as described in any of the above embodiments, disposed inside the housing.

[0014] Based on the combined filtering device in this embodiment, compared with the traditional integrated high-pass or band-pass filter, the combined filtering circuit in this solution uses a low-pass filter module and a high-pass filter module connected in series to obtain a combined filtering circuit. Since the low-pass filter module and the high-pass filter module can be designed with parameters independently, and the two modules are connected to the line side and the equipment side respectively, it is relatively convenient to select appropriate parameters according to relevant national or industry standards, so that the combined filtering circuit can simultaneously meet the requirements of operating attenuation, operating loss, equipment side impedance and line side impedance.

[0015] In one embodiment, the number of the combined filter circuits is two, and the combined filter device further includes a differential network for connecting the two combined filter circuits to a carrier cable so that the two combined filter circuits are coupled in phase.

[0016] In one embodiment, the housing is made of stainless steel. Attached Figure Description

[0017] 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.

[0018] Figure 1 This is a block diagram of the combined filter circuit in one embodiment;

[0019] Figure 2 This is a schematic diagram of the combined filter circuit in one embodiment;

[0020] Figure 3 This is a schematic diagram of the combined filter circuit in another embodiment;

[0021] Figure 4 This is a schematic diagram of the combined filter circuit in yet another embodiment;

[0022] Figure 5 This is a schematic diagram of the combined filter circuit in another embodiment;

[0023] Figure 6 This is a graph showing experimental data on return attenuation and operating attenuation for different line impedances in one embodiment.

[0024] Figure 7 The figure shows experimental data of return attenuation and operating attenuation for different coupling capacitors in one embodiment.

[0025] Figure 8 This is a schematic diagram of the combined filtering device in one embodiment. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Regarding the problem mentioned in the background technology of traditional combined filter circuits, which makes it difficult to achieve impedance matching with both the line side and the equipment side, resulting in unacceptable return loss and operating attenuation in signal transmission, the inventors discovered through research that the reason for this problem is that the International Electrotechnical Commission (IEC) standard stipulates that the nominal impedance range on the line side is 200Ω to 400Ω for phase-to-ground coupling and 400Ω to 700Ω for phase-to-phase coupling. However, the nominal impedance on the line side of the current combined filter device JL-400-B8ZD is 300Ω or 400Ω (phase-to-ground) and 600Ω or 800Ω (phase-to-phase), while the nominal impedance on the line side of the combined filter device MCD80 is 240Ω or 320Ω (phase-to-ground). The line impedance of the above devices is not a range, but only two points, and the transition between 300Ω and 400Ω is achieved by jumpers and changing tuning capacitors. Therefore, the return loss of the high-frequency channel of the power line carrier is only 6-8dB, which is far from the return loss b≥12dB specified by the power grid. Thus, the high-frequency channel cannot effectively transmit the carrier signal.

[0032] For the reasons mentioned above, please refer to Figure 1 This invention provides a combined filtering circuit 100, which includes a low-pass filter module 110 and a high-pass filter module 130. The input terminal of the low-pass filter module 110 is connected to a coupling capacitor, used to receive a first power line carrier signal and filter out components above a first frequency in the first power line carrier signal to obtain a second power line carrier signal. The input terminal of the high-pass filter module 130 is connected to the output terminal of the low-pass filter module 110, and the output terminal of the high-pass filter module 130 is connected to a carrier cable, used to filter out components below a second frequency in the second power line carrier signal to obtain a third power line carrier signal, and also used for impedance transformation to match the output impedance of the high-pass filter module 130 with the impedance of the carrier cable. The second frequency is greater than the first frequency. It is understood that a conventional combined filter circuit 100 is a single high-pass filter or band-pass filter. However, in this application, a combined filter circuit 100 is constructed by connecting a low-pass filter module 110 and a high-pass filter module 130 in series. Since the parameters of the low-pass filter module 110 and the high-pass filter module 130 can be designed separately, the low-pass filter module 110 can be connected to the line side. The parameters of the low-pass filter module 110 can be designed separately to ensure that the return loss of the combined filter circuit 100 meets the requirements when the line side impedance is 400Ω to 700Ω (phase-to-phase). The parameters of the high-pass filter module 130 can be designed to match the impedance of the combined filter circuit 100 with the carrier cable. For example, the output impedance of the combined filter circuit 100 can be designed to be 75Ω so that the operating attenuation of the combined filter circuit 100 is below 2dB.

[0033] Based on the combined filter circuit 100 in this embodiment, compared with the traditional integrated high-pass filter or band-pass filter, this solution uses a low-pass filter module 110 and a high-pass filter module 130 connected in series to obtain the combined filter circuit 100. Since the low-pass filter module 110 and the high-pass filter module 130 can be designed with parameters independently, and the two modules are connected to the line side and the equipment side respectively, it is relatively convenient to select appropriate parameters according to relevant national or industry standards, so that the combined filter circuit 100 can simultaneously meet the requirements of operating attenuation, operating loss, equipment side impedance and line side impedance.

[0034] In one embodiment, see Figure 2 The low-pass filter module 110 has a first output terminal and a second output terminal. The high-pass filter module 130 has a first input terminal and a second output terminal. The first output terminal of the low-pass filter module 110 is connected to the first input terminal of the high-pass filter module 130, and the second output terminal of the low-pass filter module 110 is connected to the second input terminal of the high-pass filter module 130 and then grounded. The high-pass filter module includes a drain coil 131, a first capacitor 133, a first inductor 135, and an impedance matching transformer 137. The drain coil 131 is connected between the first input terminal and the second input terminal of the high-pass filter module 130. The drain coil 131 can maximize the protection of the primary ground without interruption and can withstand any transient overvoltage on the power line. One end of the first capacitor 133 is connected to the common terminal of the drain coil 131 and the first input terminal of the high-pass filter module 130, and the other end of the first capacitor 133 is grounded through the first inductor. The first capacitor 133 and the first inductor can be used for reactive power compensation to improve signal transmission efficiency. The input terminals of the impedance matching transformer 137 are connected to the common terminal of the first capacitor 133 and the first inductor, and to ground, respectively. The output terminals of the impedance matching transformer 137 are connected to the carrier cable and ground, respectively. Transformers are commonly used for impedance transformation; the impedance matching transformer 137 is used to perform impedance transformation to match the impedance of the carrier cable. The impedance matching transformer 137 can also isolate overvoltages; an impedance matching transformer 137 capable of withstanding a one-minute 5kV AC overvoltage can be selected.

[0035] In one embodiment, such as Figure 3As shown, the input terminals of the low-pass filter module 110 include a first input terminal and a second input terminal. The first input terminal of the low-pass filter module 110 is connected to a coupling capacitor, and the second input terminal is grounded. The low-pass filter module 110 includes a first stray capacitor 151, a second stray capacitor 153, and a second inductor 155. The first stray capacitor 151 corresponds to the coupling capacitor, and is the stray capacitance generated by the coupling capacitor when it is placed between the lines. The first stray capacitor 151 is connected between the first input terminal and the second input terminal of the low-pass filter module 110. One end of the second inductor 155 is connected to the common terminal of the first stray capacitor 151 and the first input terminal of the low-pass filter module 110, and the other end of the second inductor 155 is grounded through the second stray capacitor 153 and connected to the common terminal of the first input terminal of the drain coil 131 and the high-pass filter module 130. The second stray capacitor 153 corresponds to the drain coil 131, and is the stray capacitor generated by the drain coil 131 when it is installed between lines. The capacitance values ​​of the first stray capacitor 151 and the second stray capacitor 153 may be related to the manufacturing process and wiring method of the equipment. These two stray capacitors will always exist when using the combined filter circuit 100. In a conventional combined filter circuit 100, these two stray capacitors will seriously affect the transmission performance. However, in this embodiment, these two natural stray capacitors and the second inductor 155 are used together to form a π-type low-pass filter, ensuring that the return loss is above 20dB, thus improving the return loss of the combined filter circuit 100.

[0036] In one embodiment, see Figure 4 The filter circuit 100 also includes a second capacitor 139, which is located between the output of the impedance matching transformer 137 and the carrier cable. The second capacitor 139 is used to prevent the power frequency voltage from entering the impedance matching transformer 137 and causing magnetic saturation, thereby avoiding intermodulation distortion.

[0037] In one embodiment, see Figure 5 The filter circuit 100 also includes an isolating switch 170 and a surge arrester 190; both the isolating switch 170 and the surge arrester 190 are disposed between the first input terminal and the second input terminal of the low-pass filter.

[0038] In one specific embodiment, the second stray capacitance 153 is 300pF. After the parameters of the coupling capacitor and the high-pass filter module 130 are determined according to relevant standards, the second stray capacitance 153 should be controlled at 300pF during the manufacturing and setting of the drain coil 131. Combined with the impedance ratio of the drain coil 131 being 1.41:1 and the second capacitor 139 being 50000pF / 2kV (related to the carrier cable), the following can be obtained: Figure 6The operating attenuation of the combined filter circuit 100 and the return loss under different line-side impedances (400Ω, 600Ω, and 800Ω) are considered. Figure 7 The study also included return losses with coupling capacitors of different capacitance values ​​(3900pF, 5000pF, and 10000pF). It is evident that the attenuation is below 2dB at high frequencies, while the return loss is above 12dB, meeting international and national standards.

[0039] This invention also provides a combined filtering device, which includes a housing and a combined filtering circuit 100. Please refer to [link / reference]. Figure 1 The combined filtering circuit 100 includes a low-pass filter module 110 and a high-pass filter module 130. The input terminal of the low-pass filter module 110 is connected to a coupling capacitor to receive a first power line carrier signal and filter out components above a first frequency in the first power line carrier signal to obtain a second power line carrier signal. The input terminal of the high-pass filter module 130 is connected to the output terminal of the low-pass filter module 110, and the output terminal of the high-pass filter module 130 is connected to a carrier cable. It is used to filter out components below a second frequency in the second power line carrier signal to obtain a third power line carrier signal, and also for impedance transformation to match the output impedance of the high-pass filter module 130 with the impedance of the carrier cable. The second frequency is greater than the first frequency. It is understood that a conventional combined filter circuit 100 is a single high-pass filter or band-pass filter. However, in this application, a combined filter circuit 100 is constructed by connecting a low-pass filter module 110 and a high-pass filter module 130 in series. Since the parameters of the low-pass filter module 110 and the high-pass filter module 130 can be designed separately, the low-pass filter module 110 can be connected to the line side. The parameters of the low-pass filter module 110 can be designed separately to ensure that the return loss of the combined filter circuit 100 meets the requirements when the line side impedance is 400Ω to 700Ω (phase-to-phase). The parameters of the high-pass filter module 130 can be designed to match the impedance of the combined filter circuit 100 with the carrier cable. For example, the output impedance of the combined filter circuit 100 can be designed to be 75Ω so that the operating attenuation of the combined filter circuit 100 is below 2dB.

[0040] Based on the combined filtering device in this embodiment, the combined filtering circuit 100 set inside the housing of the combined filtering device is different from the traditional integrated high-pass filter or band-pass filter. This solution uses a low-pass filter module 110 and a high-pass filter module 130 connected in series to obtain the combined filtering circuit 100. Since the low-pass filter module 110 and the high-pass filter module 130 can be designed with parameters independently, and the two modules are connected to the line side and the equipment side respectively, it is relatively convenient to select appropriate parameters according to relevant national or industry standards, so that the combined filtering circuit 100 can simultaneously meet the requirements of working attenuation, working loss, equipment side impedance and line side impedance.

[0041] In one embodiment, see Figure 2 The low-pass filter module 110 has a first output terminal and a second output terminal. The high-pass filter module 130 has a first input terminal and a second output terminal. The first output terminal of the low-pass filter module 110 is connected to the first input terminal of the high-pass filter module 130, and the second output terminal of the low-pass filter module 110 is connected to the second input terminal of the high-pass filter module 130 and then grounded. The high-pass filter module includes a drain coil 131, a first capacitor 133, a first inductor 135, and an impedance matching transformer 137. The drain coil 131 is connected between the first input terminal and the second input terminal of the high-pass filter module 130. The drain coil 131 can maximize the protection of the primary ground without interruption and can withstand any transient overvoltage on the power line. One end of the first capacitor 133 is connected to the common terminal of the drain coil 131 and the first input terminal of the high-pass filter module 130, and the other end of the first capacitor 133 is grounded through the first inductor. The first capacitor 133 and the first inductor can be used for reactive power compensation to improve signal transmission efficiency. The input terminals of the impedance matching transformer 137 are connected to the common terminal of the first capacitor 133 and the first inductor, and to ground, respectively. The output terminals of the impedance matching transformer 137 are connected to the carrier cable and ground, respectively. Transformers are commonly used for impedance transformation; the impedance matching transformer 137 is used to perform impedance transformation to match the impedance of the carrier cable. The impedance matching transformer 137 can also isolate overvoltages; an impedance matching transformer 137 capable of withstanding a one-minute 5kV AC overvoltage can be selected.

[0042] In one embodiment, such as Figure 3As shown, the input terminals of the low-pass filter module 110 include a first input terminal and a second input terminal. The first input terminal of the low-pass filter module 110 is connected to a coupling capacitor, and the second input terminal is grounded. The low-pass filter module 110 includes a first stray capacitor 151, a second stray capacitor 153, and a second inductor 155. The first stray capacitor 151 corresponds to the coupling capacitor, and is the stray capacitance generated by the coupling capacitor when it is placed between the lines. The first stray capacitor 151 is connected between the first input terminal and the second input terminal of the low-pass filter module 110. One end of the second inductor 155 is connected to the common terminal of the first stray capacitor 151 and the first input terminal of the low-pass filter module 110, and the other end of the second inductor 155 is grounded through the second stray capacitor 153 and connected to the common terminal of the first input terminal of the drain coil 131 and the high-pass filter module 130. The second stray capacitor 153 corresponds to the drain coil 131, and is the stray capacitor generated by the drain coil 131 when it is installed between lines. The capacitance values ​​of the first stray capacitor 151 and the second stray capacitor 153 may be related to the manufacturing process and wiring method of the equipment. These two stray capacitors will always exist when using the combined filter circuit 100. In a conventional combined filter circuit 100, these two stray capacitors will seriously affect the transmission performance. However, in this embodiment, these two natural stray capacitors and the second inductor 155 are used together to form a π-type low-pass filter, ensuring that the return loss is above 20dB, thus improving the return loss of the combined filter circuit 100.

[0043] In one embodiment, see Figure 4 The filter circuit 100 also includes a second capacitor 139, which is located between the output of the impedance matching transformer 137 and the carrier cable. The second capacitor 139 is used to prevent the power frequency voltage from entering the impedance matching transformer 137 and causing magnetic saturation, thereby avoiding intermodulation distortion.

[0044] In one embodiment, see Figure 5 The filter circuit 100 also includes an isolating switch 170 and a surge arrester 190; both the isolating switch 170 and the surge arrester 190 are disposed between the first input terminal and the second input terminal of the low-pass filter.

[0045] In one embodiment, see Figure 8 The combined filter circuit 100 consists of two circuits. The combined filter device also includes a differential network 210, which connects the two combined filter circuits 100 to the carrier cable to enable phase-to-phase coupling. The differential network 210 is commonly used to connect phase-to-ground coupled combined filter circuits 100 into phase-to-phase coupling. Figure 8This is just one example. The differential network 210 includes a differential transformer 211 and a third capacitor 213. The two ends of the primary side of the differential transformer 211 are connected to the first output terminals of the high-pass filter modules 130 of the two combined filter circuits 100, respectively. The middle tap of the primary side of the differential transformer 211 is connected in series with the second output terminals of the high-pass filter modules 130 of the two combined filter circuits 100 and then grounded. The secondary side of the differential transformer 211 is connected to the carrier cable and grounded through the third capacitor 213, respectively. When the combined filter equipment operates in phase-to-phase coupling mode, if one of the combined filter circuits 100 fails, the unfaulty combined filter circuit 100 can operate in phase-to-ground coupling mode, and signal transmission can still be performed.

[0046] In one embodiment, the housing is made of stainless steel. Conventionally, the housing of combined filtering equipment is made of aluminum alloy, ensuring good insulation performance even in outdoor environments such as sunlight, rain, fog, hail, and snow. In one embodiment, a waterproof groove is provided on the housing to further prevent rainwater from entering the housing and affecting the insulation performance.

[0047] In one embodiment, the support porcelain insulator of the grounding switch combined with the filter circuit 100 is made of epoxy resin to ensure that it will not crack.

[0048] In one embodiment, the connection terminals for connecting to the coupling filter and carrier cable are located on the side of the housing.

[0049] In the description of this specification, references to terms such as "some embodiments," "other embodiments," and "ideal embodiments" 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, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0050] 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.

[0051] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A combination filter circuit, characterized by, include: A low-pass filter module, wherein the input terminal of the low-pass filter module is connected to a coupling capacitor, is used to receive a first power line carrier signal and filter out components above a first frequency in the first power line carrier signal to obtain a second power line carrier signal; A high-pass filter module is provided, with its input connected to the output of a low-pass filter module and its output connected to a carrier cable. The high-pass filter module filters out components below a second frequency in the second power line carrier signal to obtain a third power line carrier signal. It also performs impedance transformation to match the output impedance of the high-pass filter module with the impedance of the carrier cable. The second frequency is greater than the first frequency. The low-pass filter module and the high-pass filter module are designed with parameters separately. The output terminal of the low-pass filter module includes a first output terminal and a second output terminal, and the input terminal of the high-pass filter module includes a first input terminal and a second input terminal. The first output terminal of the low-pass filter module is connected to the first input terminal of the high-pass filter module, and the second output terminal of the low-pass filter module is connected to the second input terminal of the high-pass filter module and then grounded. The high-pass filter module includes a drain coil, a first capacitor, a first inductor, and an impedance matching transformer; The drain coil is connected between the first input terminal and the second input terminal of the high-pass filter module; One end of the first capacitor is connected to the common terminal of the drain coil and the first input terminal of the high-pass filter module, and the other end of the first capacitor is grounded through the first inductor; The input terminal of the impedance matching transformer is connected to the common terminal of the first capacitor and the first inductor and the ground terminal, respectively; the output terminal of the impedance matching transformer is connected to the carrier cable and the ground, respectively. The low-pass filter module includes a first input terminal and a second input terminal. The first input terminal of the low-pass filter module is connected to the coupling capacitor, and the second input terminal of the low-pass filter module is grounded. The low-pass filter module includes a first stray capacitor, a second stray capacitor, and a second inductor. The first stray capacitor corresponds to the coupling capacitor, and the first stray capacitor is connected between the first input terminal of the low-pass filter module and the second input terminal of the low-pass filter module. One end of the second inductor is connected to the common terminal of the first stray capacitor and the first input terminal of the low-pass filter module, and the other end of the second inductor is grounded through the second stray capacitor and connected to the common terminal of the drain coil and the first input terminal of the high-pass filter module; wherein, the second stray capacitor corresponds to the drain coil.

2. The combination filter circuit of claim 1, wherein, The capacitance of the second stray capacitor is 300pF.

3. The combination filter circuit of claim 1, wherein, The combined filter circuit also includes a second capacitor, which is disposed between the output terminal of the impedance matching transformer and the carrier cable.

4. The combination filter circuit of claim 1, wherein, The combined filtering circuit also includes an isolating switch and a surge arrester; both the isolating switch and the surge arrester are disposed between the first input terminal and the second input terminal of the low-pass filter.

5. The combination filter circuit of claim 1, wherein, The impedance ratio of the drain coil is 1.41:

1.

6. A combination filter device, characterized by include: case; The combination filter circuit according to any one of claims 1-5, is disposed inside the housing.

7. The combination filter device of claim 6, wherein, The number of the combination filter circuits is two, and the combination filter device further comprises a differential network for connecting the two combination filter circuits with a carrier cable to couple the two combination filter circuits in phase-phase.

8. The combination filter device of claim 6, wherein, The housing is made of stainless steel.

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