Transformer balun

Abstract

The invention discloses a transformer balun, relates to the technical field of integrated circuits, and discloses the transformer balun which comprises a primary coil and a secondary coil. One end of the primary coil is grounded to form a single-end port, and a grounding inductor is arranged on a first center tap in the primary coil; and two ends of the secondary coil jointly form a differential port. Namely, the grounding inductor is added to the first center tap in the primary coil of the transformer balun, so that a transmission zero point can be constructed for an even-mode half-side circuit in a broadband range, and the balance degree of the transformer balun is further improved.

Description

Technical Field

[0001] This application relates to the field of integrated circuit technology, and particularly to a transformer balun. Background Art

[0002] The transformer balun is one of the most basic on-chip radio frequency devices in the millimeter-wave and terahertz frequency bands. It can realize the conversion between single-ended signals and differential signals with a compact structure, and at the same time complete the impedance transformation of the front and rear stages.

[0003] Due to the capacitive coupling effect between the primary coil and the secondary coil of the transformer balun, and this effect becomes more serious in the millimeter-wave and terahertz frequency bands as the frequency increases. Therefore, the balance degree of the bandwidth of the transformer balun is low.

[0004] The above content is only used to assist in understanding the technical solution of this application, and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main purpose of this application is to provide a transformer balun, aiming to solve the technical problem of the low balance degree of the bandwidth of the transformer balun.

[0006] To achieve the above purpose, this application proposes a transformer balun, which includes: a primary coil and a secondary coil. The primary coil and the secondary coil are concentrically arranged. One end of the primary coil is grounded, and the other end receives an input signal to form a single-ended port. A grounded inductor is arranged on the first center tap of the primary coil. The two ends of the secondary coil together form a differential port, and the differential port is arranged in the opposite direction to the single-ended port;

[0007] The grounded inductor is used to create a transmission zero for the primary coil.

[0008] In one embodiment, the grounded inductor is an adjustable inductor.

[0009] In one embodiment, a grounded capacitor is arranged on the second center tap of the secondary coil.

[0010] In one embodiment, the grounded capacitor is a planar capacitor, a interdigital capacitor, or a capacitor formed by grounding a metal trace with an open end.

[0011] In one embodiment, the grounded capacitor is set as an adjustable capacitor.

[0012] In one embodiment, the grounded inductor is a capacitor formed by grounding a metal trace with a short circuit at the end.

[0013] In one embodiment, the transformer balun further includes: a first metal layer, a second metal layer, and a third metal layer. The first metal layer is arranged between the second metal layer and the third metal layer;

[0014] The primary coil and the secondary coil are disposed on the first metal layer, the ground inductor is disposed on the second metal layer, the third metal layer is a ground layer, and the ground inductor is connected to the third metal layer.

[0015] In one embodiment, a first connection via is provided between the first metal layer and the second metal layer;

[0016] The ground inductor is connected to the primary coil based on the first connection via.

[0017] In one embodiment, a second connection via is provided between the second metal layer and the third metal layer;

[0018] The ground inductor is connected to the third metal layer based on the second connection via.

[0019] In one embodiment, the ground inductor is disposed away from the single-ended port.

[0020] One or more technical solutions proposed in this application have at least the following technical effects:

[0021] Since the transformer balun is evolved from a symmetric reciprocal four-port network, therefore, it is necessary to form a transformer balun by setting a primary coil grounded at one end and a secondary coil with differential ports. Due to the capacitive coupling effect between the primary coil and the secondary coil of the transformer balun, the capacitive coupling effect will cause the primary coil of the transformer balun not to present a transmission zero point. Adding a ground inductor at the first center tap of the primary coil of the transformer balun can construct a transmission zero point for the primary coil within a wide frequency band, thereby improving the balance of the transformer balun. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a schematic structural diagram of the transformer balun of the present application;

[0025] Figure 2 It is a schematic diagram of a metal layer structure of the transformer balun of the present application;

[0026] Figure 3 This is the final implementation schematic diagram of the transformer balun of the present application;

[0027] Figure 4 This is the balance simulation result of the transformer balun of the present application.

[0028] The implementation, functional features and advantages of the purpose of the present application will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0031] In addition, if there are descriptions such as "first", "second", etc. involved in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first", "second" may explicitly or implicitly include at least one of the features. In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution where A and B are satisfied simultaneously. In addition, the technical solutions between the embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0032] The embodiments of the present application provide a transformer balun, referring to Figure 1 , Figure 1 This is the structural schematic diagram of the transformer balun of the present application.

[0033] In this embodiment, the transformer balun includes a primary coil and a secondary coil. The primary coil and the secondary coil are concentrically arranged. One end of the primary coil is grounded, and the other end receives an input signal to form a single-ended port. A grounding inductor is provided at the first center tap of the primary coil. The two ends of the secondary coil together form a differential port, and the differential port is arranged in the opposite direction to the single-ended port.

[0034] The grounding inductor is used to create a transmission zero point for the primary coil.

[0035] It should be noted that the primary coil is the input coil in the transformer balun and is used to receive single-ended signals. The secondary coil is the output coil in the transformer balun and is used to output differential signals. The single-ended port is a port form where one end of the signal is grounded and the other end is the signal input terminal. The center tap is the tap in the middle of the coil and is used to lead out the middle point of the coil, which can be used to connect other circuit elements (such as inductors or capacitors) to achieve specific circuit functions. Among them, the first center tap is the center tap of the primary coil. The differential port outputs signals from two opposite ports, and the signal amplitudes of the two ports are equal but the phases are opposite. The transmission zero point is the point where the output signal is zero.

[0036] In this embodiment, since the differential signal has good anti-interference ability and high signal integrity, and the single-ended signal is easily affected by electromagnetic interference during transmission, the primary coil and the secondary coil are provided in the transformer balun so that the secondary coil can convert the signal into a differential signal to improve the anti-interference ability.

[0037] It should be noted that the grounding inductor is an inductor element with one end grounded and the other end connected to the first center tap. The grounding inductor is arranged away from the single-ended port.

[0038] Among them, the grounding inductor is an adjustable inductor.

[0039] It should be noted that setting the grounding inductor as an adjustable inductor can adjust the value of the grounding inductor connected to the first center tap according to different requirements, and then flexibly create a transmission zero point for the primary coil, eliminate the capacitive coupling effect generated between the primary coil and the secondary coil within the corresponding bandwidth range, thereby improving the balance of the transformer balun within the corresponding bandwidth range.

[0040] In this embodiment, an adjustable grounding inductor is provided at the center tap of the primary coil. By adjusting the inductance of the grounding inductor, the impedance of the primary coil is optimized, so that the impedance of the primary coil is balanced with the impedance of the secondary coil, and signal reflection and loss can also be reduced.

[0041] In a specific implementation, the single-ended output of an antenna or other signal source is connected to the non-grounded end of the primary coil of a transformer balun, and both ends of the secondary coil are connected to the differential input of the subsequent circuit. The signal induces an alternating magnetic field in the primary coil, and then the alternating magnetic field induces a differential signal in the secondary coil through magnetic coupling between the primary coil and the secondary coil. By adjusting the grounding inductor to create a transmission zero of the even-mode half circuit for the primary coil, the input impedance of the primary coil is adjusted to match the output impedance of the signal source, and then the differential signal is input into the subsequent circuit.

[0042] This embodiment provides a transformer balun. Since the transformer balun is evolved from a symmetric reciprocal four-port network, it is necessary to form a transformer balun by setting a primary coil grounded at one end and a secondary coil with differential ports. Due to the capacitive coupling effect between the primary coil and the secondary coil of the transformer balun, the capacitive coupling effect will cause the primary coil of the transformer balun not to present a transmission zero. Adding a grounding inductor at the first center tap of the primary coil of the transformer balun can construct a transmission zero for the primary coil within a wide frequency band, thereby improving the balance of the transformer balun.

[0043] Further, the grounding inductor is an inductor formed by a metal trace with a terminal short circuit.

[0044] It should be noted that a terminal short circuit means that the first center tap of the primary coil is directly connected to the ground through a conductor, forming a path with zero resistance. A metal trace is a conductive path for transmitting current in a printed circuit board (PCB) or an integrated circuit (IC). Among them, the metal trace is usually made of copper or other conductive materials, having low resistance and good electrical conductivity.

[0045] In this embodiment, by using a metal trace with a terminal short circuit to implement the grounding inductor, the inductor can be integrated into the metal layer of the circuit board or chip, without additional inductor components, thereby reducing the complexity of the transformer balun and improving the integration and reliability of the circuit at the same time.

[0046] In this embodiment, the grounding inductor is implemented by a metal trace with a terminal short circuit, which can effectively suppress high-frequency interference, and the length, width, and shape of the metal trace can be controlled by precise manufacturing processes, so as to achieve an accurate inductance value. This not only improves the anti-interference ability of the circuit, but also improves the flexibility and accuracy of circuit design, and can better meet specific electrical performance requirements.

[0047] Optionally, a grounding capacitor is provided at the second center tap of the secondary coil.

[0048] It should be noted that the second center tap is the tap in the middle of the secondary coil, which is used to extract signals or connect other circuit elements at the middle position of the secondary coil. The ground capacitance is a capacitive element with one end connected to the ground, which is used for filtering, decoupling, or adjusting the phase and amplitude of signals. In high-frequency circuits, the ground capacitance can effectively suppress high-frequency interference and improve the anti-interference ability of the circuit.

[0049] In this embodiment, a ground capacitance is selectively arranged on the second center tap of the secondary coil, that is, at the middle position of the secondary coil, the ground capacitance can be selectively connected according to the design requirements. This design method provides additional flexibility to optimize the signal transmission characteristics and impedance matching.

[0050] In the specific implementation, by adjusting the value of the ground inductance in the primary coil, the balance of the transformer balun in the broadband range is improved. If the balance cannot always meet the requirements, a ground capacitance C can be added to the second center tap of the secondary coil, and at the same time, the values of L and C are adjusted to achieve the balance target.

[0051] Among them, the ground capacitance is an adjustable capacitance.

[0052] In this embodiment, the adjustable ground capacitance can be used to adjust the impedance characteristics of the secondary coil to match the input impedance in the primary coil, so that the transformer balun achieves impedance balance within the bandwidth range.

[0053] Furthermore, the ground capacitance is a planar capacitor, an interdigital capacitor, or a capacitor formed by a metal trace with an open end.

[0054] It should be noted that a planar capacitor is a capacitive structure composed of two parallel metal plates with an insulating medium in between. An interdigital capacitor is composed of multiple interleaved metal finger-shaped electrodes. Among them, the capacitance value of the interdigital capacitor can be controlled by adjusting the number, width, and spacing of the finger-shaped electrodes. A metal trace with an open end is a metal trace structure with one end connected to the circuit and the other end open, and its capacitance value depends on the length, width, and dielectric constant of the trace.

[0055] In this embodiment, the ground capacitance can be implemented by a planar capacitor, an interdigital capacitor, or a metal trace with an open end, providing multiple implementation methods. According to different application scenarios and performance requirements, the most suitable capacitive structure can be selected, improving the flexibility and adaptability of the design.

[0056] It should be noted that by setting a ground capacitance in the transformer balun and defaulting the capacitance value of the ground capacitance to zero, when a ground capacitance is needed, the hardware connection of the ground capacitance is avoided. Therefore, the capacitance value of the ground capacitance can be directly adjusted according to the requirements, improving the convenience of the balance compensation adjustment of the transformer balun.

[0057] In a specific implementation, in a millimeter-wave communication system, the single-ended output of a millimeter-wave signal source is connected to the non-grounded end of a primary coil, and both ends of a secondary coil are respectively connected to the differential input ends of a subsequent circuit. A metal trace with a terminal short circuit is set on the first center tap of the primary coil as a grounding inductor, and according to the signal frequency and transmission requirements, a planar capacitor, a interdigital capacitor or a metal trace with an open terminal is selected to be set on the second center tap of the secondary coil as a grounding capacitor.

[0058] The corresponding working principle is as follows: A single-ended signal is induced to the secondary coil through the primary coil to form a differential signal. By using the grounding inductor to adjust the impedance characteristics of the primary coil, the impedance of the primary coil is matched with the impedance of the secondary coil. If the balance degree of the transformer balun within the target bandwidth cannot meet the requirements only by adjusting the inductance value of the grounding inductor, then the impedance characteristics of the secondary coil are adjusted by using the grounding capacitor to achieve the balance degree target of the transformer balun within the target bandwidth and optimize the signal transmission efficiency.

[0059] In this embodiment, it can be known from the even-odd mode analysis that for a three-port balun evolved from a symmetric reciprocal four-port network, its balance condition is that there is a transmission zero in the even-mode half circuit of the original symmetric reciprocal four-port network. The transformer balun is also evolved from a transformer, which is a symmetric reciprocal four-port network. Due to the capacitive coupling effect between transformer coils, for an uncompensated transformer balun, it is difficult for the even-mode half circuit of the corresponding transformer to present a transmission zero, and the balun balance degree is poor. By the proposed method, inductors and capacitors are added at the center taps of the primary coil and the secondary coil, and a transmission zero can be constructed for the even-mode half circuit within a wide bandwidth, thereby improving the balance degree of the transformer balun.

[0060] Based on the first embodiment of the present application, in the second embodiment of the present application, the same or similar content as that in the above-mentioned first embodiment can be referred to the above introduction and will not be repeated hereinafter. On this basis, please refer to Figure 2 , Figure 2 is a schematic diagram of the metal layer structure of the transformer balun of the present application. The transformer balun further includes: a first metal layer, a second metal layer and a third metal layer, and the first metal layer is disposed between the second metal layer and the third metal layer;

[0061] The primary coil and the secondary coil are disposed on the first metal layer, the grounding inductor is disposed on the second metal layer, the third metal layer is a grounding layer, and the grounding inductor is connected to the third metal layer.

[0062] It should be noted that the first metal layer (corresponding to Figure 2 QA inFigure 2 QB) in the figure is located on the top layer of the multi-layer metal structure. The third metal layer (corresponding to Figure 2 C3) in the figure is located in the middle layer of the multi-metal structure. The ground layer provides a stable reference potential for the circuit, improving the stability and reliability of the signal.

[0063] In this embodiment, the multi-layer metal structure allows different circuit functions to be distributed on different metal layers, realizing function partitioning and optimization, improving the circuit integration and design flexibility, reducing the mutual interference between components, and enhancing the signal stability and transmission efficiency.

[0064] In this embodiment, the primary coil and the secondary coil are arranged on the first metal layer, and the ground inductor is arranged on the second metal layer, which can achieve efficient signal induction and conversion, optimize the impedance matching of the circuit, not only improve the high-frequency performance, but also enhance the signal transmission efficiency, reduce signal loss, and optimize the phase and amplitude characteristics of the signal.

[0065] Furthermore, a first connection through-hole is provided between the first metal layer and the second metal layer;

[0066] The ground inductor is connected to the primary coil based on the first connection through-hole.

[0067] It should be noted that the first connection through-hole is a vertical conductive channel for connecting the first metal layer and the second metal layer. The through-hole is usually filled with a conductive material (such as copper) to achieve electrical connection between different metal layers.

[0068] In this embodiment, the first connection through-hole provides a direct electrical connection between the first metal layer and the second metal layer, ensuring the signal transmission efficiency between the ground inductor and the primary coil, reducing the connection loss, thereby precisely adjusting the impedance characteristics of the primary coil, improving the accuracy of impedance matching, and reducing signal reflection and transmission loss, and enhancing the signal transmission efficiency.

[0069] In a specific implementation, in a millimeter-wave communication system, the single-ended output of the millimeter-wave signal source is connected to the non-ground end of the primary coil, and the two ends of the secondary coil are respectively connected to the differential input ends of the subsequent circuit. Through the first connection through-hole, the ground inductor on the second metal layer is connected to the primary coil on the first metal layer.

[0070] The corresponding working principle is as follows: The single - ended signal is induced to the secondary coil through the primary coil to form a differential signal. By adjusting the inductance value of the grounding inductor and further adjusting the impedance characteristics of the primary coil through the first connection via, the impedance of the primary coil is matched with that of the secondary coil. If the balance within the target bandwidth of the transformer balun cannot meet the requirements only by adjusting the inductance value of the grounding inductor, then the impedance characteristics of the secondary coil are adjusted using the grounding capacitor to achieve the balance target of the transformer balun within the target bandwidth and optimize the signal transmission efficiency.

[0071] Further, a second connection via is provided between the second metal layer and the third metal layer;

[0072] The grounding inductor is connected to the third metal layer based on the second connection via.

[0073] It should be noted that the second connection via is a vertical conductive path for connecting the second metal layer and the third metal layer. The connection via is usually filled with a conductive material (such as copper) to achieve electrical connection between different metal layers.

[0074] In this embodiment, through the second connection via, the grounding inductor can achieve a stable electrical connection with the grounding layer, providing a stable reference potential, reducing the grounding impedance, and improving the signal stability and anti - interference ability.

[0075] In this implementation, the design of the second connection via can reduce the parasitic effect on the signal transmission path, improve the transmission quality of high - frequency signals, and improve the high - frequency performance of the circuit.

[0076] In a specific implementation, in a millimeter - wave communication system, the single - ended output of the millimeter - wave signal source is connected to the non - grounded end of the primary coil, and both ends of the secondary coil are respectively connected to the differential input ends of the subsequent circuit. Through the second connection via, the grounding inductor on the second metal layer is connected to the third metal layer (grounding layer).

[0077] In this embodiment, through the multi - layer metal design, the primary coil and the secondary coil are arranged on the first metal layer, the grounding inductor is arranged on the second metal layer, and the third metal layer serves as the grounding layer. Through the hierarchical design, not only the circuit integration and design flexibility are improved, but also the signal transmission efficiency and high - frequency performance are optimized. At the same time, a stable signal reference is provided, and the anti - interference ability of the circuit is improved.

[0078] Exemplarily, to help understand the implementation structure of the transformer balun obtained by combining this embodiment with the above - mentioned embodiment, please refer to Figure 3 , Figure 3 is the final implementation schematic diagram of the transformer balun of this application. Specifically:

[0079] Connect several metal gold layers provided by the chip process in a specific manner to form an on-chip transformer structure with 1 primary coil and 1 secondary coil, and further ground one end of the primary coil to form a transformer balun structure with 1 single-ended port and 1 differential port. As Figure 1 shown, specific components are added at the center taps of the two coils of the transformer balun to complete the balance compensation of the transformer balun within a wideband.

[0080] For the wideband balance compensation transformer balun described in 1, an inductor L is added to the center tap of the primary coil (the coil corresponding to the single-ended port) to ground to improve the balance of the transformer balun; an optional bypass capacitor C to ground can be added to the center tap of the secondary coil (the coil corresponding to the differential port) to further adjust the balance of the transformer balun. When implemented on-chip, the above-grounded inductor L can be realized by a metal trace grounded at the terminal, and the above bypass capacitor C can be realized by a metal trace with an open terminal or a planar / finger structure.

[0081] Based on the 22nm FDSOI CMOS process, a 150GHz wideband balance compensation transformer balun as Figure 2 shown can be realized. The center tap of the primary coil (as shown in 3) is realized by connecting the terminal to a metal trace on the ground loop. The center tap of the secondary coil does not choose to add a capacitor. The primary coil of the transformer balun is jointly realized by the top thick metal QB layer and the QA layer (the corresponding via layer is used at the connection), the secondary coil is realized by the top thick metal QA, the ground loop is realized by the lower thin metal C3 layer, and the grounded inductor connected to the center tap of the primary coil is realized by QB, C3, and the metals and vias between them.

[0082] It should be noted that the above-grounded inductor L can be realized by a metal trace with a short circuit at the terminal, and the grounded capacitor C can be realized by a planar capacitor, a finger capacitor, or a metal trace with an open terminal.

[0083] In the actual design process, for a specific original transformer balun structure, the balance of the balun within a wideband can be improved by adjusting the value of L. If the balance always fails to meet the requirements, a capacitor C can be added and the values of L and C can be adjusted simultaneously to achieve the balance target.

[0084] Refer to Figure 4 . The simulation results show that compared with the original transformer balun without center tap compensation, the common mode rejection ratio of the compensated transformer balun is increased by more than 20dB in the operating frequency band of 120 - 162GHz, and the common mode rejection ratio exceeds 30dB in a relatively wide frequency band, thus verifying the feasibility of the proposed technical solution.

[0085] It should be noted that the above examples are only for understanding the present application and do not constitute a limitation on the transformer balun of the present application. Based on this technical concept, more simple transformations in various forms are within the protection scope of the present application.

[0086] The above are only partial embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structural transformation made by using the content of the specification and drawings of the present application under the technical concept of the present application, or any direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A transformer balun, characterized in that, The transformer balun includes: a primary coil and a secondary coil, the primary coil and the secondary coil are concentrically arranged, one end of the primary coil is grounded, and the other end receives an input signal to form a single-ended port. A grounding inductor is provided at a first center tap of the primary coil. Two ends of the secondary coil together form a differential port, and the differential port is arranged in the opposite direction to the single-ended port; The grounding inductor is used to create a transmission zero point for the primary coil.

2. The transformer balun according to claim 1, wherein The grounding inductor is an adjustable inductor.

3. The transformer balun according to claim 1, characterized in that, A grounding capacitor is provided at a second center tap of the secondary coil.

4. The transformer balun according to claim 3, characterized in that, The grounding capacitor is a planar capacitor, an interdigital capacitor, or a capacitor formed by grounding a metal trace with an open end.

5. The transformer balun according to claim 3, characterized in that, The grounding capacitor is set as an adjustable capacitor.

6. The transformer balun according to claim 1, wherein The grounding inductor is a capacitor formed by grounding a metal trace with a shorted end.

7. The transformer balun according to claim 1, characterized in that, The transformer balun further includes: a first metal layer, a second metal layer, and a third metal layer, the first metal layer is disposed between the second metal layer and the third metal layer; The primary coil and the secondary coil are disposed on the first metal layer, the grounding inductor is disposed on the second metal layer, the third metal layer is a grounding layer, and the grounding inductor is connected to the third metal layer.

8. The transformer balun according to claim 7, wherein A first connection via is provided between the first metal layer and the second metal layer; The grounding inductor is connected to the primary coil based on the first connection via.

9. The transformer balun according to claim 7, characterized in that, A second connection via is provided between the second metal layer and the third metal layer; The grounding inductor is connected to the third metal layer based on the second connection via.

10. The transformer balun according to claim 1, characterized in that, The grounding inductor is arranged away from the single-ended port.

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