CN209963209U - Balun transformer - Google Patents

Abstract

The utility model provides a balun transformer, which comprises a substrate with a circuit, a signal input port arranged on the substrate, two differential signal output ports, a common-mode inductor and a first shielding wire, wherein two output ends of the common-mode inductor are respectively connected with the two differential signal output ports; the first conductive line of the first shielding line connects the signal input port and the input end of the common mode inductor, the second end of the first conductive line is connected with the input end of the common mode inductor, and the first shielding layer of the first shielding line is grounded. When the transformer is used, an input signal is transmitted to the common-mode inductor from the signal input port through the first conducting wire, the input signal is subjected to electromagnetic coupling matching through the common-mode inductor, an external interference signal is guided into the ground through the first shielding layer, the first conducting wire is prevented from generating induced current, and the signal transmitted on the first conducting wire is prevented from radiating out to cause interference, so that the transformer has better amplitude balance degree and lower insertion loss.

Description

Balun transformer

Technical Field

The utility model belongs to the technical field of communication electronic component, more specifically say, relate to a balun transformer.

Background

Balun (balance-to-balance converter or transmission line balancer) is a key component of balanced circuit layout such as a filter, a microwave balanced mixer, a frequency multiplier, a push-pull amplifier, an antenna feed network and the like. Currently, a common balun transformer mainly achieves balance-unbalance conversion through a high-frequency transformer, and an inductance coil of the high-frequency transformer needs to be connected to a signal input port and/or a signal output port of the balun by using an enameled wire so as to transmit a high-frequency signal through the enameled wire. However, in the process of transmitting a high-frequency signal by the enameled wire, the enameled wire itself may generate an induced current, and the induced current may easily cause unstable line-to-line capacitance to form signal interference, so that the balun transformer has unstable balance-unbalance conversion amplitude, and the balun transformer has a low balance degree of balance-unbalance conversion performance, and cannot meet the requirement of broadband point-to-point communication standard.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a balun transformer aims at solving the balun transformer balanced-unbalanced transformation range that exists and is unstable among the prior art, leads to the lower problem of balun transformer balanced-unbalanced transformation range balanced degree.

In order to achieve the above object, the present invention provides a balun transformer, which includes a substrate, a signal input port and two differential signal output ports disposed on the substrate, and a coupling circuit for enabling the signal input port to communicate with the two differential signal output ports respectively; the coupling circuit comprises a common mode inductor for electromagnetic coupling and a first shielding line for connecting the common mode inductor to the signal input port, the common mode inductor is arranged on the substrate, and two output ends of the common mode inductor are respectively connected with the two differential signal output ports; first shielding line including be used for transmitting the first conducting wire of signal of telecommunication, wrap up in first conducting wire outside first shielding layer with wrap up in the outside first insulating layer of first shielding layer, the one end of first conducting wire with signal input port links to each other, the other end of first conducting wire with two inputs of common mode inductor link to each other, first shielding layer ground connection, first insulating layer is fixed in on the base plate.

Further, the balun transformer further comprises a second shielding wire for connecting the common-mode inductor to the two differential signal output ports respectively, the second shielding wire comprises two second conductive wires connected to the two differential signal output ports respectively, a second shielding layer wrapped outside the two second conductive wires, and a second insulating layer wrapped outside the second shielding layer, the two second conductive wires are connected to the two output ends of the common-mode inductor respectively, the second shielding layer is grounded, and the second insulating layer is fixed on the substrate.

Further, the balun transformer further comprises a resistor for enhancing the balance degree of the balance-unbalance conversion amplitude, the resistor comprises a first resistor for signal isolation, and a second resistor and a third resistor for ground isolation, two ends of the first resistor are respectively connected with the two differential signal output ports, two ends of the second resistor are respectively connected with one of the differential signal output ports and a grounding point, and two ends of the third resistor are respectively connected with the other of the differential signal output ports and the grounding point.

Furthermore, the first resistor, the second resistor and the third resistor are thick film resistors, and the first resistor, the second resistor and the third resistor are respectively packaged on the substrate by adopting epoxy resin layers.

Further, the first resistor, the second resistor and the third resistor have equal resistance.

Furthermore, a first circuit connected with the first resistor and the second resistor, a second circuit connected with the first resistor and the third resistor, and a third circuit connected with the second resistor and the third resistor are arranged on the substrate, and the distance between the first circuit and the second circuit is equal to the distance between pins at two ends of the first resistor; the distance between the first circuit and the third circuit is equal to the distance between the pins at two ends of the second resistor; the distance between the second circuit and the third circuit is equal to the distance between the pins at two ends of the third resistor, and the third circuit is a grounding wire.

The balun transformer further comprises a feedback inductor, a third shielding line and a fourth shielding line, wherein the feedback inductor, the third shielding line and the fourth shielding line are used for forming a signal feedback bypass, the third shielding line comprises a third conductive line, a third shielding layer and a third insulating layer, the third shielding layer is wrapped outside the third conductive line, the third insulating layer is wrapped outside the third shielding layer, the third conductive line is connected with the input end of the feedback inductor, the third shielding layer is respectively connected with one differential signal output port and a grounding point through the first line, and the third insulating layer is fixed on the substrate; the fourth shielding line comprises a fourth conductive line, a fourth shielding layer and a fourth insulating layer, the fourth shielding layer wraps the outside of the fourth conductive line, the fourth insulating layer wraps the outside of the fourth shielding layer, the fourth conductive line is connected with the output end of the feedback inductor, the fourth shielding layer is grounded, and the fourth insulating layer is fixed on the substrate.

Further, the substrate is a ceramic plate, and the first conducting wire is connected with the ceramic plate in an electronic spot welding mode.

Further, the common mode inductor comprises a manganese-zinc ferrite core and two coils wound on the manganese-zinc ferrite core.

Further, each of the coils is a flat coil.

The utility model provides a balun transformer's beneficial effect lies in: compared with the prior art, the utility model provides a balun transformer adopts first shielded wire to replace the enameled wire that common mode inductor input end connection signal input port used, through the signal transmission line of first shielded wire as common mode inductor input end, effectively avoids the inside first conductor wire of first shielded wire to produce induced-current and form the interference to transmission signal to improve balun transformer balance-unbalance conversion's steadiness ability, made balun transformer have very superior in-band range, phase balance degree. Meanwhile, the first shielding wire is used as a signal transmission line of the input end of the common mode inductor, so that external electromagnetic interference and radio frequency interference can be effectively prevented from entering the first shielding wire to increase the loss of transmission signals, and the signals transmitted on the first conductive wire can be effectively prevented from radiating to cause interference, thereby effectively reducing the loss of the transmission signals and enabling the transformer to have lower insertion loss.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the embodiments or the prior art descriptions will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive labor.

Fig. 1 is a schematic structural diagram of a balun transformer provided in an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a common mode inductor according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a signal input port and a differential signal output port provided on a substrate according to an embodiment of the present invention.

Wherein, the first main mark of each figure in the figure:

1-a substrate; 11-signal input port; 12-differential signal output ports; 13-a first line; 14 second lines; 15-a third line;

2-a common mode inductor; a 21-manganese-zinc ferrite core; 22-a coil;

3-a first shield wire; 31-a first electrically conductive line; 32-a first shielding layer; 33-a first insulating layer;

4-a second shielded wire; 41-a second electrically conductive line; 42-a second shielding layer; 43-a second insulating layer;

5-a resistor; 51-a first resistance; 52-second resistance; 53-third resistance;

6-a feedback inductor; 7-a third shielded wire; 71-a third shielding layer; 72-a third insulating layer;

8-a fourth shielded wire; 81-a fourth shielding layer; 82-fourth insulating layer.

Detailed Description

In order to make the technical problem, technical solution and advantageous effects to be solved by the present invention more clearly understood, the following description is given in conjunction with the accompanying drawings and embodiments to illustrate the present invention in further detail. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

It will be understood that when an element is referred to as being "connected" or "disposed" to another element, it can be directly on the other element or be indirectly connected to the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically limited otherwise. The meaning of "a number" is one or more unless specifically limited otherwise.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.

Referring to fig. 1 to fig. 3, a balun transformer according to an embodiment of the present invention will be described. The utility model provides a balun transformer, including base plate 1, set up signal input port 11 and two difference signal output port 12 on base plate 1, and be used for realizing that signal input port 11 communicates with two difference signal output port 12 respectively; the coupling circuit comprises a common mode inductor 2 used for electromagnetic coupling and a first shielding wire 3 used for connecting the common mode inductor 2 to a signal input port 11, wherein the common mode inductor 2 is arranged on a substrate 1, and two output ends of the common mode inductor 2 are respectively connected with two differential signal output ports 12; the first shielding line 3 includes a first conductive line 31 for transmitting an electrical signal, a first shielding layer 32 wrapped outside the first conductive line 31, and a first insulating layer 33 wrapped outside the first shielding layer 32, one end of the first conductive line 31 is connected to the signal input port 11, the other end of the first conductive line 31 is connected to two input ends of the common mode inductor 2, the first shielding layer 32 is grounded, and the first insulating layer 33 is fixed on the substrate 1. When the transformer is used, an input signal is transmitted from the signal input port 11 to the input end of the common mode inductor 2 through the first conductive line 31, the input signal is electromagnetically coupled and matched through the common mode inductor 2, and external interference signals such as external electromagnetic interference and radio frequency interference are introduced into the ground through the first shielding layer 32, so that induced current generated by the first conductive line 31 can be avoided, meanwhile, the signal transmitted on the first conductive line 31 can be effectively prevented from being radiated out to cause interference, and the transformer has better amplitude balance degree and lower insertion loss.

The utility model provides a balun transformer, compared with the prior art, adopt first shielded wire 3 to replace 2 enameled wires that connect signal input port 11 and use of common mode inductor, through the signal transmission line of first shielded wire 3 as 2 inputs of common mode inductor, effectively avoid 3 inside first conductive wires 31 of first shielded wire to produce induced-current and disturb transmission signal formation, thereby improved balun transformer balance-unbalance conversion's steadiness ability, make the balun transformer have very superior in-band range, phase balance degree. Meanwhile, the first shielding line 3 is used as a signal transmission line at the input end of the common mode inductor 2, so that external electromagnetic interference and radio frequency interference can be effectively prevented from entering the first shielding line 3 to increase the loss of transmission signals, and the signals transmitted on the first conductive line 31 can be effectively prevented from radiating out to cause interference, thereby effectively reducing the loss of the transmission signals and enabling the transformer to have lower insertion loss.

Furthermore, the utility model provides a balun transformer under the condition of not addding electric capacity, can guarantee that this excellent filtering characteristic has balun unbalance to balanced signal's converting capacity again, has better electric property, good impedance matching effect, lower insertion loss, better high-pass band selectivity and higher output signal range balanced characteristic, simple structure is compact, small.

Preferably, please refer to fig. 2 together, as the specific implementation of the balun transformer provided in the embodiment of the present invention, the common mode inductor 2 includes a manganese-zinc ferrite core and two coils 22 wound around the manganese-zinc ferrite core 21, the inductor is manufactured by using the low-loss manganese-zinc ferrite core 21, so that the balun transformer achieves the purpose of being suitable for low-frequency band use, and has a broadband characteristic (0.5 MHz-6 GHz) from low-frequency to high-frequency ultra-bandwidth application, thereby realizing that the balun transformer can work in a wider bandwidth and has application requirements of low insertion loss and excellent amplitude balance, expanding the variety of the balun transformer, saving the assembly space, and simultaneously satisfying the test requirements of GJB1661 and GJB360B, and achieving the military requirements. Other components and working principles of the transformer and the inductor are implemented by using the prior art known to those skilled in the art, and are not described in detail herein.

Preferably, referring to fig. 2, as a specific implementation of the balun transformer provided by the embodiment of the present invention, the coil 22 is a flat coil. The combination of the flat coil and the maximum area of the manganese-zinc ferrite core 21 has the advantages of large magnetic induction intensity and stable performance, and the specific saturated magnetic density and the large cross section of the manganese-zinc ferrite core 21 can be applied to reduce the magnetic conductivity of the manganese-zinc ferrite core 21, thereby reducing the influence of bias current, achieving the maximum utilization of the magnetic induction intensity, having lower loss ratio, particularly better environmental adaptability and stable performance, and preventing the normal operation of an electromagnetic interference device.

Further, please refer to fig. 1 together, as a specific implementation manner of the balun transformer provided in the embodiment of the present invention, the balun transformer further includes a second shielding wire 4 for connecting the common mode inductor 2 to the two differential signal output ports 12 respectively, the second shielding wire 4 includes two second conductive wires 41 connected to the two differential signal output ports 12 respectively, a second shielding layer 42 wrapped outside the two second conductive wires 41, and a second insulating layer 43 wrapped outside the second shielding layer 42, and the two second conductive wires 41 are connected to two output ends of the common mode inductor 2 respectively, the second shielding layer 42 is grounded, and the second insulating layer 43 is fixed on the substrate 1.

In this embodiment, the second shielding wire 4 is used to replace the enameled wire used by the common mode inductor 2 to connect the signal output end, and the second shielding wire 4 is used as a signal transmission line at the output end of the common mode inductor 2, so that the interference of the transmission signal caused by the induced current generated by the second conductive wire 41 inside the second shielding wire 4 is effectively avoided, and thus the stability of the balun transformer in the balance-unbalance conversion is improved, and the balun transformer has very excellent in-band amplitude and phase balance. Meanwhile, the second shielding wire 4 is used as a signal transmission line at the output end of the common mode inductor 2, so that the loss of transmission signals can be effectively reduced, and the insertion loss of the transformer is low.

Further, please refer to fig. 1 together, as a specific implementation manner of the balun transformer provided in the embodiment of the present invention, the balun transformer further includes a resistor 5 for enhancing the balance degree of the balance-unbalance conversion amplitude, the resistor 5 includes a first resistor 51 for signal isolation and a second resistor 52 and a third resistor 53 for ground isolation, two differential signal output ports 12 are respectively connected to two ends of the first resistor 51, two ends of the second resistor 52 are respectively connected to one differential signal output port 12 and the ground point, and two ends of the third resistor 53 are respectively connected to the other differential signal output port 12 and the ground point.

In this embodiment, a resistor 5 is provided between the common mode inductor 2 and the signal output terminal to enhance the amplitude balance of balun transformer balun. Specifically, the resistor 5 includes a first resistor 51, a second resistor 52 and a third resistor 53 connected in series with each other, and the first resistor 51, the second resistor 52 and the third resistor 53 are integrated on the substrate 1 in a triangular arrangement, the first resistor 51 isolates the signal, and the second resistor 52 and the third resistor 53 isolate the ground, so that the amplitude of the signal output by the signal output end is more stable, the in-band optimum amplitude and the phase balance degree of the balun transformer are enhanced, and the insertion loss of the balun transformer is lower.

Furthermore, the first resistor 51, the second resistor 52 and the third resistor 53 are thick-film resistors, and the first resistor 51, the second resistor 52 and the third resistor 53 are respectively packaged on the substrate 1 by using epoxy resin layers, so that the first resistor 51, the second resistor 52 and the third resistor 53 are integrally formed on the substrate 1, the volume of the balun transformer is reduced, and the balun transformer is convenient to integrate with other circuit elements.

Preferably, the resistances of the first resistor 51, the second resistor 52 and the third resistor 53 are equal in size, so as to further stabilize the amplitude of the balun transformer balun transformation and enhance the amplitude balance degree of the balun transformer balun transformation.

Preferably, the first resistor 51, the second resistor 52 and the third resistor 53 are all 150 Ω.

Preferably, the substrate 1 is a ceramic substrate, and the first conductive line 31 of the first shielding line 3 is connected to the ceramic substrate by electronic spot welding to reduce the capacitance between the first shielding line 3 and the ceramic substrate, so as to optimize the amplitude of balun transformer balun transformation and enhance the amplitude balance degree of balun transformer balun transformation.

Preferably, the second conductive line 41 is connected with the ceramic substrate by electronic spot welding, and the first insulating layer 33 and the second insulating layer 43 are encapsulated on the ceramic substrate by using epoxy resin layers, so as to reduce the capacitance among the second conductive line 41, the first insulating layer 33, the second insulating layer 43 and the ceramic substrate, thereby optimizing the amplitude of balun transformer balun and enhancing the amplitude balance degree of balun transformer balun.

Further, please refer to fig. 1 together, as a specific implementation of the balun transformer provided in the embodiment of the present invention, a first line 13 connected to the first resistor 51 and the second resistor 52, a second line 14 connected to the first resistor 51 and the third resistor 53, and a third line 15 connected to the second resistor 52 and the third resistor 53 are disposed on the substrate 1, and a distance between the first line 13 and the second line 14 is equal to a distance between pins at two ends of the first resistor 51; the distance between the first line 13 and the third line 15 is equal to the distance between the pins at the two ends of the second resistor 52; the distance between the second line 14 and the third line 15 is equal to the distance between the pins at both ends of the third resistor 53, and the third line 15 is a ground line.

The first line 13, the second line 14 and the third line 15 are printed on the substrate 1 in a printing mode, and the first line 13, the second line 14 and the third line 15 are provided with pads for welding connection, so that wiring and welding connection of electronic elements are facilitated, and the volume of the balun transformer is reduced.

In this embodiment, the first resistor 51 and the second resistor 52 are connected by welding through the first line 13, the first resistor 51 and the third resistor 53 are connected by welding through the second line 14, and the second resistor 52 and the third resistor 53 are connected by welding through the third line 15, so that the use of connecting lines among the first resistor 51, the second resistor 52 and the third resistor 53 is reduced, the interference of capacitance among the connecting lines is effectively avoided, the amplitude balance degree of balance-unbalance conversion of the balun transformer is enhanced, the trouble of wiring is reduced, and the volume of the balun transformer is reduced.

Further, as the specific implementation manner of the transformer type balun provided by the embodiment of the present invention, the first line 13, the second line 14 and the third line 15 are printed on the ceramic substrate by the circuit printing method, respectively, so as to reduce the volume of the transformer type balun. The first epoxy resin layer is arranged on the ceramic substrate and used for packaging the first circuit 13, the second circuit 14 and the third circuit 15 on the ceramic substrate, the first epoxy resin layer is used for packaging the first circuit 13, the second circuit 14 and the third circuit 15 on the ceramic substrate, so that the stability of the first circuit 13, the second circuit 14 and the third circuit 15 attached on the ceramic substrate is enhanced, the first circuit 13, the second circuit 14 and the third circuit 15 are prevented from being easily bent, short-circuited or even broken when being vibrated or impacted, and the vibration resistance and the impact resistance of the transformer type balun are effectively improved.

Further, as a specific implementation manner of the transformer balun provided by the embodiment of the present invention, the pins of the input and/or output terminals of the common mode inductor 2 are supported on the first epoxy resin layer, the second epoxy resin layer is disposed on the first epoxy resin layer and encapsulates and fixes the pins of the input and/or output terminals of the common mode inductor 2 on the first epoxy resin layer, and the common mode inductor 2 is supported and fixed on the second epoxy resin layer, the pins of the input and/or output terminals of the common mode inductor 2 are encapsulated and fixed on the first epoxy resin layer through the second epoxy resin layer, so as to enhance the stability of the pins of the input and/or output terminals of the common mode inductor 2, prevent the pins of the input and/or output terminals of the common mode inductor 2 from easily bending short circuit or even breaking when being subjected to vibration or impact, therefore, the vibration resistance and impact resistance of the transformer type balun are effectively improved.

Further, as the embodiment of the utility model provides a transformer balun's concrete implementation mode is equipped with the third epoxy layer with common mode inductor 2 encapsulation and be fixed in on the second epoxy layer to prevent that common mode inductor 2 from taking place easily when receiving vibration or impact and rocking or vibrate and cause the damage, set up the steadiness on ceramic substrate with reinforcing common mode inductor 2, thereby effectively improve transformer balun anti-vibration, the ability of shocking resistance.

Further, please refer to fig. 1 together, as a specific implementation manner of the balun transformer provided in the embodiment of the present invention, the balun transformer further includes a feedback inductor 6, a third shielding line 7 and a fourth shielding line 8 for forming a signal feedback bypass, the third shielding line 7 includes a third conductive line, a third shielding layer 71 wrapped outside the third conductive line and a third insulating layer 72 wrapped outside the third shielding layer 71, the third conductive line is connected to an input end of the feedback inductor 6, the third shielding layer 71 is respectively connected to a differential signal output port 12 and a ground point through a first line 13, and the third insulating layer 72 is fixed on the substrate 1; the fourth shielding line 8 includes a fourth conductive line, a fourth shielding layer 81 wrapped outside the fourth conductive line, and a fourth insulating layer 82 wrapped outside the fourth shielding layer 81, the fourth conductive line is connected to the output end of the feedback inductor 6, the fourth shielding layer 81 is grounded, and the fourth insulating layer 82 is fixed on the substrate 1.

In this embodiment, an input signal is transmitted from the signal input port 11 to the common mode inductor 2, and the input signal is distributed to the two differential signal output ports 12 after being subjected to the balance-unbalance conversion by the common mode inductor 2, so that the line-to-line capacitance of the feedback inductor 6 can play a role of a bypass at the ground end, and signal feedback is formed, and interference formed by the line-to-line capacitance of the feedback inductor 6 is avoided, thereby further optimizing the amplitude of the balance-unbalance conversion of the balun transformer and enhancing the amplitude balance degree of the balance-unbalance conversion of the balun transformer.

The above description is only exemplary of the present invention and should not be taken as limiting the scope of the present invention, as any modifications, equivalents, improvements and the like made within the spirit and principles of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. A balun transformer comprises a substrate, a signal input port and two differential signal output ports which are arranged on the substrate, and a coupling circuit used for enabling the signal input port to be communicated with the two differential signal output ports respectively; the method is characterized in that: the coupling circuit comprises a common mode inductor for electromagnetic coupling and a first shielding line for connecting the common mode inductor to the signal input port, the common mode inductor is arranged on the substrate, and two output ends of the common mode inductor are respectively connected with the two differential signal output ports; first shielding line including be used for transmitting the first conducting wire of signal of telecommunication, wrap up in first conducting wire outside first shielding layer with wrap up in the outside first insulating layer of first shielding layer, the one end of first conducting wire with signal input port links to each other, the other end of first conducting wire with two inputs of common mode inductor link to each other, first shielding layer ground connection, first insulating layer is fixed in on the base plate.

2. A balun transformer as claimed in claim 1, wherein: the balun transformer further comprises a second shielding wire used for connecting the common mode inductor to the two differential signal output ports respectively, the second shielding wire comprises two second conductive wires connected with the two differential signal output ports respectively, a second shielding layer wrapping the two second conductive wires and a second insulating layer wrapping the second shielding layer, the two second conductive wires are connected with the two output ends of the common mode inductor respectively, the second shielding layer is grounded, and the second insulating layer is fixed on the substrate.

3. A balun transformer as claimed in claim 2, wherein: the balun transformer further comprises a resistor used for enhancing the balance degree of the balance-unbalance conversion amplitude, the resistor comprises a first resistor used for signal isolation, and a second resistor and a third resistor used for grounding isolation, two ends of the first resistor are respectively connected with the two differential signal output ports, two ends of the second resistor are respectively connected with one of the differential signal output ports and a grounding point, and two ends of the third resistor are respectively connected with the other of the differential signal output ports and the grounding point.

4. A balun transformer as claimed in claim 3, wherein: the first resistor, the second resistor and the third resistor are thick film resistors, and the first resistor, the second resistor and the third resistor are respectively packaged on the substrate by adopting epoxy resin layers.

5. A balun transformer as claimed in claim 3, wherein: the first resistor, the second resistor and the third resistor have equal resistance.

6. A balun transformer as claimed in claim 3, wherein: a first circuit connected with the first resistor and the second resistor, a second circuit connected with the first resistor and the third resistor, and a third circuit connected with the second resistor and the third resistor are arranged on the substrate, and the distance between the first circuit and the second circuit is equal to the distance between pins at two ends of the first resistor; the distance between the first circuit and the third circuit is equal to the distance between the pins at two ends of the second resistor; the distance between the second circuit and the third circuit is equal to the distance between the pins at two ends of the third resistor, and the third circuit is a grounding wire.

7. A balun transformer as claimed in claim 6, wherein: the balun transformer further comprises a feedback inductor, a third shielding line and a fourth shielding line, wherein the feedback inductor, the third shielding line and the fourth shielding line are used for forming a signal feedback bypass, the third shielding line comprises a third conductive line, a third shielding layer and a third insulating layer, the third shielding layer is wrapped outside the third conductive line, the third insulating layer is wrapped outside the third shielding layer, the third conductive line is connected with the input end of the feedback inductor, the third shielding layer is respectively connected with one differential signal output port and a grounding point through the first line, and the third insulating layer is fixed on the substrate; the fourth shielding line comprises a fourth conductive line, a fourth shielding layer and a fourth insulating layer, the fourth shielding layer wraps the outside of the fourth conductive line, the fourth insulating layer wraps the outside of the fourth shielding layer, the fourth conductive line is connected with the output end of the feedback inductor, the fourth shielding layer is grounded, and the fourth insulating layer is fixed on the substrate.

8. A balun transformer according to any one of claims 1 to 7, characterized in that: the substrate is a ceramic plate, and the first conducting wire is connected with the ceramic plate in an electronic spot welding mode.

9. A balun transformer according to any one of claims 1 to 7, characterized in that: the common mode inductor comprises a manganese-zinc ferrite core and two coils wound on the manganese-zinc ferrite core.

10. A balun transformer as claimed in claim 9, wherein: each of the coils is a flat coil.

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