A three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter

Abstract

The application provides a three-dimensional integrated low-temperature co-fired ferrite differential band-pass filter, which is applied to the fields of radio frequency front-end modules, satellite communication and radar systems and the like, adopts a differential filter form of a symmetrical circuit form, processes capacitors and inductors by using a low-temperature co-fired ferrite (LTCF) process, designs the inductors by using a multilayer spiral inductor structure, and designs the capacitors by using a multilayer laminated capacitor structure. The application embeds inductor characteristics into a dielectric matrix, does not need to externally connect separate inductors, reduces a parasitic effect, and improves circuit stability. Ferrite material has natural absorption and inhibition effects on common mode signals, and in combination with differential circuit design, the filter has excellent common mode noise suppression capability, and can effectively improve the electromagnetic compatibility performance of a system.

Description

A three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter Technical Field

[0001] This invention relates to the technical fields of radio frequency front-end modules, satellite communication and radar systems, and in particular to a three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter. Background Technology

[0002] In recent years, integrated filters based on low-temperature co-fired ceramic (LTCC) technology have attracted widespread attention in microwave and millimeter-wave circuits and systems. This technology enables the direct embedding of passive components such as inductors and capacitors within multilayer ceramic substrates, significantly improving circuit integration through a three-dimensional integrated structure. This provides an effective technical path for achieving filter miniaturization and high reliability. Especially in fields such as RF front-end modules, satellite communications, and radar systems, LTCC filters have become a hot topic in current research and engineering applications due to their excellent high-frequency characteristics, good temperature stability, and outstanding mechanical strength.

[0003] However, LTCC technology faces significant challenges in designing bandpass filters for the specific frequency band of 31–56 MHz. Due to the relatively low frequency, achieving good bandpass characteristics often requires large inductance and capacitance values. Limited by the linewidth, interlayer alignment accuracy, and dielectric constant of the dielectric material inherent in the LTCC process, manufacturing high-value inductors with high quality factors within a limited volume is particularly difficult. Even if structural optimization (such as using helical inductors or multilayer winding designs) can improve the inductance value to some extent, it remains difficult to maintain both low DC resistance and a high self-resonant frequency while meeting the required inductance, resulting in filter performance falling short of expectations—such as excessive insertion loss, difficulty in bandwidth expansion, or insufficient out-of-band rejection.

[0004] Furthermore, even if the electrical performance is barely up to standard, the bulky structure required to achieve higher inductance will significantly increase the device size, which defeats the original intention of miniaturizing integrated filters and limits their use in space-sensitive applications such as portable devices, drone communications, or high-density integrated modules.

[0005] On the other hand, at the circuit architecture level, with the increasing demands for anti-interference capabilities and signal transmission rates in communication systems, differential circuit structures are gradually becoming the preferred solution for high-performance filters due to their excellent common-mode noise suppression capabilities and higher signal integrity. Traditionally, differential filtering is achieved by adding an external balun structure to a single-ended filter to complete the single-ended to differential signal conversion. However, this method not only introduces additional insertion loss and phase imbalance but also requires strict consideration of impedance matching and electromagnetic compatibility between the balun and the filter, significantly increasing design complexity and system uncertainty. Furthermore, balun components are often large, further expanding the overall circuit space and making it difficult to meet the high integration requirements of modern electronic systems.

[0006] Therefore, under current technological conditions, there is an urgent need for a new solution that can achieve low-frequency, high-performance, and small-size differential bandpass filters without relying on external balun structures, in order to overcome the multiple limitations faced by existing LTCC processes and traditional architectures in low-frequency differential filtering applications. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter. The low-temperature co-fired ferrite (LTCF) facilitates the miniaturization of integrated inductors, resulting in a significant reduction in filter size. The differential filter employing a symmetrical circuit configuration simplifies the design and avoids introducing additional insertion loss and phase imbalance.

[0008] The technical solution adopted in this invention is as follows:

[0009] A three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter is provided. In the circuit corresponding to the differential bandpass filter, all capacitors adopt a multilayer shingled capacitor structure, all inductors adopt a multilayer spiral inductor structure, and all capacitors and inductors are prepared by low-temperature co-fired ferrite LTCF process.

[0010] Among them, the internal layer connection relationship of the multilayer shingled capacitor structure adopted by each capacitor is as follows: the odd-numbered layers from top to bottom all extend to one side and are provided with a first via, and the odd-numbered layers are connected through the first via; the even-numbered layers from top to bottom all extend to the other side and are provided with a second via, and the even-numbered layers are connected through the second via.

[0011] The internal layer connection relationship of the multilayer spiral inductor structure adopted by each inductor is as follows: each layer is rotated counterclockwise from top to bottom. A via is set at the tail of the upper layer rotating counterclockwise between two adjacent layers, and a via is set at the head of the lower layer rotating counterclockwise, which is collinear with the central axis of the tail via of the upper layer. The two adjacent layers are connected by the via that is collinear with the central axis.

[0012] Furthermore, a via is provided at the end of the last layer from top to bottom in the multi-layer spiral inductor structure used in the inductor.

[0013] Furthermore, the connection between the capacitor and the inductor is achieved by connecting the via at the tail of the last layer from top to bottom in the multilayer spiral inductor structure used by the inductor with the first or second via in the multilayer shingled capacitor structure used by the capacitor.

[0014] Furthermore, the two inductors are connected by a via at the end of the last layer from top to bottom in the multilayer spiral inductor structure of one inductor and a via at the end of the last layer from top to bottom in the multilayer spiral inductor structure of the other inductor.

[0015] Furthermore, for the connection of two capacitors, the odd or even number of layers in the multilayer shingled capacitor structure used by one capacitor are extended from the top to the middle layer in the multilayer shingled capacitor structure used by the other capacitor, and a new via is provided in the extended part, which is connected to the first or second via in the multilayer shingled capacitor structure used by the other capacitor.

[0016] Furthermore, the circuit of the low-temperature co-fired ferrite differential bandpass filter is a differential circuit with vertical and horizontal symmetry.

[0017] Furthermore, the circuit includes: a first capacitor C1, a twelfth capacitor C12 symmetrical to the first capacitor C1, a sixth capacitor C6, a seventh capacitor C7 symmetrical to the sixth capacitor C6, a fifth capacitor C5, an eighth capacitor C8 symmetrical to the fifth capacitor C5, a first resonant unit, a second resonant unit symmetrical to the first resonant unit, a third resonant unit and a fourth resonant unit, and a first port TermG1, a second port TermG2, a third port TermG3 and a fourth port TermG4.

[0018] Furthermore, the first resonant unit includes a third capacitor C3 and a second inductor L2 connected in parallel; the second resonant unit includes an eleventh capacitor C11 and a fifth inductor L5 connected in parallel.

[0019] The third resonant unit includes a first inductor L1, a sixth inductor L6, and a second capacitor C2. The first terminal of the first inductor L1 is grounded, the second terminal of the first inductor L1 is connected to the first terminal of the second capacitor C2, the second terminal of the second capacitor C2 is connected to the first terminal of the sixth inductor L6, and the second terminal of the sixth inductor L6 is grounded.

[0020] The fourth resonant unit includes a third inductor L3, a fourth inductor L4, and a fourth capacitor C4. The first terminal of the third inductor L3 is grounded, the second terminal of the third inductor L3 is connected to the first terminal of the fourth capacitor C4, the second terminal of the fourth capacitor C4 is connected to the first terminal of the fourth inductor L4, and the second terminal of the fourth inductor L4 is grounded.

[0021] Furthermore, the first port TermG1 is connected to the first terminal of the first capacitor C1 and the first terminal of the sixth capacitor C6, respectively. The second terminal of the first capacitor C1 is connected to the first terminal of the third capacitor C3 and the first terminal of the second capacitor C2, respectively. The second terminal of the sixth capacitor C6 is connected to the second port TermG2, which is also connected to the first terminal of the fifth capacitor C5. The second terminal of the fifth capacitor C5 is connected to the second terminal of the third capacitor C3 and the first terminal of the fourth capacitor C4, respectively. The third port TermG3 is connected to the first terminal of the twelfth capacitor C12 and the first terminal of the seventh capacitor C7, respectively. The second terminal of the twelfth capacitor C12 is connected to the second terminal of the second capacitor C2 and the first terminal of the eleventh capacitor C11, respectively. The second terminal of the seventh capacitor C7 is connected to the fourth port TermG4, which is also connected to the first terminal of the eighth capacitor C8, which is connected to the second terminal of the fourth capacitor C4 and the second terminal of the eleventh capacitor C11, respectively.

[0022] Furthermore, by loading differential-mode signals (i.e., signals with equal amplitude but opposite phase) into TermG1 and TermG3, the circuit will be split into two identical circuits along the vertically symmetrical axis of symmetry, according to the principles of electric and magnetic walls.

[0023] The beneficial technical effects of this invention are as follows:

[0024] This invention utilizes low-temperature co-fired ferrite (LTCF) as the substrate material, which possesses both high relative permeability and high relative permittivity, laying the material foundation for the miniaturization of inductors and capacitors. Furthermore, its natural magnetism suppresses common-mode noise, further enhancing the common-mode rejection capability and electromagnetic compatibility of differential circuits. In terms of circuit architecture, this invention directly employs a symmetrical differential topology, achieving true differential filtering without the need for an external balun, effectively avoiding performance degradation and increased size introduced by baluns. The proposed three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter is a differential filter that combines ultra-miniaturization, high-frequency bandwidth, high common-mode rejection, and high reliability. It effectively solves the problem that traditional filters struggle to achieve miniaturization, high performance, and integration in the sub-100MHz frequency band. It not only achieves a balance between filter performance and miniaturization in the low-frequency band but also significantly improves the reliability, consistency, and production applicability of the device through LTCF material and integrated processing. This provides an advanced solution for filtering and EMC protection in modern communication equipment, radar systems, and high-speed data interfaces, demonstrating significant technological advancement and broad application prospects. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 is a circuit topology diagram of a differential bandpass filter in symmetrical circuit form provided in an embodiment of the present invention;

[0027] Figure 2 is a main diagram of the 156nH inductor provided in an embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of each layer corresponding to the 156nH inductor provided in the embodiment of the present invention, wherein (a) is the first layer from top to bottom, (b) is the second layer from top to bottom, (c) is the third layer from top to bottom, (d) is the fourth layer from top to bottom, (e) is the fifth layer from top to bottom, and (f) is the sixth layer from top to bottom.

[0029] Figure 4 is a main diagram of the 10pF capacitor provided in an embodiment of the present invention;

[0030] Figure 5 is a side view of the 10pF capacitor provided in an embodiment of the present invention;

[0031] Figure 6 is a main diagram of the 50pF capacitor provided in an embodiment of the present invention;

[0032] Figure 7 is a side view of the 50pF capacitor provided in an embodiment of the present invention;

[0033] Figure 8 is a main diagram of the three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter provided in an embodiment of the present invention;

[0034] Figure 9 is a top view of the three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter provided in an embodiment of the present invention;

[0035] Figure 10 is a side view of the three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter provided in an embodiment of the present invention, wherein (a) is a side view, (b) is a layer diagram of the 10pf capacitor C3 on the right side in (a), (c) is a layer diagram of the 250pf capacitor C5 on the right side in (a), (d) is a layer diagram of the 10pf capacitor C6 on the right side in (a), and (e) is a layer diagram of the 136nH inductor on the right side in (a).

[0036] Figure 11 is a schematic diagram of the connection method between two capacitors provided in the embodiment of the present invention, wherein (a) is a connection method of two capacitors arranged vertically on the same vertical plane, and (b) is a connection method of two capacitors arranged horizontally on the same horizontal plane.

[0037] Figure 12 is a schematic diagram of the connection method between two inductors provided in an embodiment of the present invention;

[0038] Figure 13 is a schematic diagram of the connection method between the inductor and the capacitor provided in an embodiment of the present invention;

[0039] Figure 14 is a schematic diagram of the simulation results of the three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter provided in the embodiment of the present invention.

[0040] Explanation of reference numerals in the attached diagram: 1-via between the first and second metal layers, 2-via between the second and third metal layers, 3-via between the third and fourth metal layers, 4-via between the fourth and fifth metal layers, 5-via between the fifth and sixth metal layers, 6-interlayer via, 7-capacitor C2, 8-inductor L3, 9-inductor L4, 10-capacitor C12, 11-capacitor C7, 12-capacitor C8, 13-capacitor C11, 14-inductor L5. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] This embodiment uses the circuit shown in Figure 1 as an example to illustrate the technical solution of the present invention. The circuit in Figure 1 is a Chebyshev bandpass filter composed of differential circuits, which has vertical and horizontal symmetry. The circuit includes a first capacitor C1, a twelfth capacitor C12 symmetrical to the first capacitor C1, a sixth capacitor C6, a seventh capacitor C7 symmetrical to the sixth capacitor C6, a fifth capacitor C5, an eighth capacitor C8 symmetrical to the fifth capacitor C5, a first resonant unit, a second resonant unit symmetrical to the first resonant unit, a third resonant unit, and a fourth resonant unit.

[0043] The first resonant unit includes a third capacitor C3 and a second inductor L2 connected in parallel; the second resonant unit includes an eleventh capacitor C11 and a fifth inductor L5 connected in parallel.

[0044] The third resonant unit includes a first inductor L1, a sixth inductor L6, and a second capacitor C2. The first terminal of the first inductor L1 is grounded, the second terminal of the first inductor L1 is connected to the first terminal of the second capacitor C2, the second terminal of the second capacitor C2 is connected to the first terminal of the sixth inductor L6, and the second terminal of the sixth inductor L6 is grounded.

[0045] The fourth resonant unit includes a third inductor L3, a fourth inductor L4, and a fourth capacitor C4. The first terminal of the third inductor L3 is grounded, the second terminal of the third inductor L3 is connected to the first terminal of the fourth capacitor C4, the second terminal of the fourth capacitor C4 is connected to the first terminal of the fourth inductor L4, and the second terminal of the fourth inductor L4 is grounded.

[0046] The first port TermG1 is connected to the first terminal of the first capacitor C1 and the first terminal of the sixth capacitor C6. The second terminal of the first capacitor C1 is connected to the first terminal of the third capacitor C3 and the first terminal of the second capacitor C2. The second terminal of the sixth capacitor C6 is connected to the second port TermG2. The second port TermG2 is also connected to the first terminal of the fifth capacitor C5. The second terminal of the fifth capacitor C5 is connected to the second terminal of the third capacitor C3 and the first terminal of the fourth capacitor C4. The third port TermG3 is connected to the first terminal of the twelfth capacitor C12 and the first terminal of the seventh capacitor C7. The second terminal of the twelfth capacitor C12 is connected to the second terminal of the second capacitor C2 and the first terminal of the eleventh capacitor C11. The second terminal of the seventh capacitor C7 is connected to the fourth port TermG4. The fourth port TermG4 is also connected to the first terminal of the eighth capacitor C8. The second terminal of the eighth capacitor C8 is connected to the second terminal of the fourth capacitor C4 and the second terminal of the eleventh capacitor C11.

[0047] When differential-mode signals (i.e., signals with equal amplitude but opposite phase) are applied to TermG1 and TermG3, the circuit will be split into two identical circuits along the vertical axis of symmetry, according to the principles of electric and magnetic walls. Specifically, the connection between L1 and L6 is broken, and L1 and L6 are grounded respectively. C2 is split into two 100pF capacitors connected in series and broken in the middle, with the break points grounded respectively. The same applies to L3, L4, and C4 in the fourth resonant unit.

[0048] After the circuit is split into two identical circuits, the upper part of the circuit consists of TermG1, C1, L1, C2-1 (the upper part after splitting C2), C3, L2, L3, C4-1 (the upper part after splitting C4), C5, C6, and TermG2. Among them, C3, L2, L1, C2-1, L3, and C4-1 constitute resonant units, which are important components of the bandpass filtering function. C1, C5, and the previous resonant units are all transformed from the prototype low-pass filter, except that the former is transformed into a capacitor and the latter into a resonator. Their values ​​are determined by the prototype low-pass filter. The function of C6 is to provide an additional transmission zero, so that the stopband attenuation is faster.

[0049] TermG1, TermG2, TermG3, and TermG4 represent ports, which are externally loaded signals and external impedances. Each port can be considered as a resistor with a resistance value of Z connected in series with a voltage source and then grounded.

[0050] The circuit in Figure 1 actually contains only capacitors and inductors. As shown in Figure 1, there are three capacitor values: 10pF, 250pF, and 50pF, and two inductor values: 136nH and 156nH.

[0051] Both capacitors and inductors are manufactured using LTCF technology. The dielectric material has a relative permittivity of 19 and a relative permeability of 5, and the metal material is silver. The composition of the five different capacitor and inductor values ​​will now be described.

[0052] Figure 2 is a schematic diagram of the structure of a 156nH inductor. The inductor is a six-layer spiral inductor that winds counterclockwise from top to bottom. The first layer from top to bottom is shown in Figure 3(a), the second layer is shown in Figure 3(b), the third layer is shown in Figure 3(c), the fourth layer is shown in Figure 3(d), the fifth layer is shown in Figure 3(e), and the sixth layer is shown in Figure 3(f).

[0053] In Figure 3, label 1 shows the vias between the first and second metal layers of the 156nH inductor; label 2 shows the vias between the second and third metal layers; label 3 shows the vias between the third and fourth metal layers; label 4 shows the vias between the fourth and fifth metal layers; and label 5 shows the vias between the fifth and sixth metal layers. For the 136nH inductor, its structure is exactly the same as in Figure 2, the only difference being its smaller size. Those skilled in the art will know that the size of an inductor is determined by its inductance value; the larger the inductance value, the larger the inductor size.

[0054] Figures 4 and 5 are schematic diagrams of the structure of a 10pF capacitor. This capacitor is a six-layer shingled capacitor, with each metal film layer having a thickness of 4µm. The first, third, and fifth layers extend to one end, and interlayer vias 6 are provided in the extended portions. The first, third, and fifth layers are connected through the interlayer vias 6. The second, fourth, and sixth layers extend to the other end, and interlayer vias 6 are provided in the extended portions. The second, fourth, and sixth layers are connected through the interlayer vias 6.

[0055] Figures 6 and 7 show the structural diagrams of a 50pF capacitor, which is an eight-layer shingled capacitor. Its structure is similar to that of a 10pF capacitor, differing only in size and the number of layers. The 250pF capacitor is also an eight-layer shingled capacitor, with the same structure as the 50pF capacitor, differing only in size.

[0056] Figures 8, 9, and 10 are the main view, top view, and side view of the bandpass filter, respectively. The overall dimensions of the bandpass filter are 10mm × 10mm × 1mm. In this embodiment, the bandpass filter is designed with a total of eighteen layers. In Figure 10(a), the middle part is the minimum number of layers, from top to bottom: a 50pF capacitor on the upper layer and a 156nH inductor on the lower layer, for a total of fifteen layers, because a ground plane layer is required. The left and right parts of Figure 10(a) are symmetrical. Taking the right part of Figure 10(a) as an example, from top to bottom, it consists of a 10pF capacitor C3, a 250pF capacitor C5, a 10pF capacitor C6, and a 136nH inductor L2, as shown in Figure 10(b).

[0057] As shown in Figure 10(a), the 50pF capacitor in the upper layer of the middle part extends from the fifth layer from top to bottom and connects to the 250pF capacitor C5 on the right side from the first layer from top to bottom; correspondingly, as shown in Figure 10(a), the 250pF capacitor C8 on the left side extends from the first layer from top to bottom to the middle part and connects to the upper 50pF capacitor from the second, fourth, sixth, and eighth layers from top to bottom through interlayer vias 6. Figure 10(b) shows the layer arrangement of the 10pF capacitor C3, Figure 10(c) shows the layer arrangement of the 250pF capacitor C5, Figure 10(d) shows the layer arrangement of the lower 10pF capacitor C6, and Figure 10(e) shows the layer arrangement of the 136nH inductor L2.

[0058] Figure 11 illustrates the connection methods between two capacitors. As shown in Figure 11(a), two capacitors arranged vertically on the same vertical plane can be connected by aligning the vias on their respective sides. As shown in Figure 11(b), two capacitors arranged horizontally on the same horizontal plane can be connected by extending one of the odd or even layers of one capacitor into the structure of the other capacitor, with a new via provided in the extended portion. This new via is aligned with the odd or even layer via on the corresponding side of the other capacitor.

[0059] Figure 12 shows the connection method between two inductors. As shown in Figure 12, the two inductors are connected by a via at the end of the last layer from top to bottom in the multilayer spiral inductor structure of one inductor and a via at the end of the last layer from top to bottom in the multilayer spiral inductor structure of the other inductor.

[0060] Figure 13 shows the connection method between the inductor and the capacitor. Based on the design of this embodiment, the inductors are all located at the bottom, and the capacitors C6 and C7, which are also located at the bottom, are not connected to the inductors. Therefore, the capacitor at the top and the inductor at the bottom in Figure 13 are connected through the via provided at the tail of the last layer from top to bottom in the multilayer spiral inductor structure used by the inductor and the first or second via in the multilayer shingled capacitor structure used by the capacitor, thereby realizing the connection between the capacitor and the inductor.

[0061] Those skilled in the art should note that in practical applications, the specific number of layers for each capacitor and inductor is not limited to the even number of layers given in this embodiment, but can also be an odd number of layers, and can be designed according to the specific capacitor and inductor values ​​and the required dimensions.

[0062] In this embodiment, in order to reduce interference between signals, a certain degree of redundancy is left, and the model is not shrunk to its minimum.

[0063] The layout of the components is basically based on Figure 1. From the perspective of the components, it is divided into two layers. The components numbered 8, 9, 11, and 14 in Figure 9, and the components symmetrical to them, are located in the second layer, and the rest are located in the first layer.

[0064] Compared with existing filters based on low-temperature co-fired ceramics (LTCC) or other materials, the differential filter based on low-temperature co-fired ferrite (LTCF) technology provided by this invention fully utilizes the magnetic properties of ferrite materials, achieving the following significant technical effects and innovative advantages:

[0065] This invention achieves monolithic integration of miniaturization and high-performance magnetoelectric functions: the core of the invention lies in the use of low-temperature co-fired ferrite (LTCF) technology. This material system simultaneously possesses high relative permeability (…). =5) and high relative permittivity ( =19) characteristics. High permeability allows for a significant reduction in the size of magnetic components while maintaining the same inductance; high dielectric constant also benefits the miniaturization of capacitor components. Through precise multilayer design (single layer thickness 50) Ultimately, the overall size of the filter was successfully controlled within an extremely small volume of 10mm×10mm×1mm, achieving a high degree of integration of magneto-electric functions, which is unmatched by traditional LTCC or PCB solutions.

[0066] Excellent high-frequency broadband filtering performance: As shown in the simulation results in Figure 14, where the horizontal axis represents frequency and the vertical axis represents return loss and insertion loss in dB, this differential filter achieves good bandpass characteristics in the frequency range of 31MHz to 56MHz, with a 3dB absolute bandwidth exceeding 25MHz. Its differential transmission coefficient (S21DD) curve is smooth, and the insertion loss in the passband is small, indicating high signal transmission efficiency. The differential reflection coefficient (S11DD) has an extremely low depth in the passband, proving that the port impedance is well matched, effectively suppressing signal reflection and ensuring signal integrity.

[0067] The unique advantages of high permeability materials: Traditional LTCC filters mainly rely on dielectric properties, while this invention utilizes LTCF materials. The high permeability of 5 (=5) has led to the following breakthroughs:

[0068] Built-in magnetic components: Successfully "embed" the inductance characteristics into the dielectric substrate, eliminating the need for external discrete inductors, reducing parasitic effects, and improving circuit stability;

[0069] Enhanced common-mode rejection: Ferrite materials have a natural absorption and suppression effect on common-mode signals. Combined with differential circuit design, this filter inherently possesses excellent common-mode noise rejection capability, which can effectively improve the electromagnetic compatibility (EMC) performance of the system.

[0070] Achieving higher inductance: With the same volume and number of turns, a much higher inductance can be obtained than that of non-magnetic media, making it possible to design compact low-frequency broadband filters.

[0071] Excellent process consistency and reliability: The LTCF process combines unique ferrite slurry casting, precision through-hole forming, lamination and co-firing technologies. All functional layers are integrated and formed in a single high-temperature co-firing process, forming a dense and robust monolithic structure. This avoids performance dispersion and reliability issues caused by multiple assemblies, ensuring product performance consistency and long-term reliability, making it very suitable for modern, large-scale mass production.

[0072] The differential bandpass filter designed in this invention has a center frequency of 43.5MHz and a bandwidth of 25MHz. In terms of material selection, low-temperature co-fired ferrite (LTCF) is used. Compared with LTCC, LTCF maintains a high dielectric constant while also having a high permeability, which facilitates the miniaturization of integrated inductors and significantly reduces the size of the filter. In terms of circuit, this invention adopts a differential filter form with a symmetrical circuit. This method is not only simple to design, but also does not introduce additional insertion loss and phase imbalance.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter, characterized in that, In the circuit corresponding to the differential bandpass filter, all capacitors adopt a multilayer shingled capacitor structure, and all inductors adopt a multilayer spiral inductor structure. All capacitors and inductors are fabricated using a low-temperature co-fired ferrite (LTCF) process. Specifically, the internal layer connection relationship of the multilayer shingled capacitor structure is as follows: from top to bottom, odd-numbered layers extend to one side and are connected via a first via; from top to bottom, even-numbered layers extend to the other side and are connected via a second via. Similarly, the internal layer connection relationship of the multilayer spiral inductor structure is as follows: from top to bottom, the layers rotate counter-clockwise. A via is provided at the tail of the upper layer that winds counterclockwise around two adjacent layers, and a via is provided at the head of the lower layer that winds counterclockwise around the upper layer, collinear with the central axis of the via at the tail of the upper layer. The two adjacent layers are connected by vias with collinear central axes. The differential bandpass filter circuit specifically includes: a first capacitor C1, a twelfth capacitor C12 symmetrical to the first capacitor C1, a sixth capacitor C6, a seventh capacitor C7 symmetrical to the sixth capacitor C6, a fifth capacitor C5, an eighth capacitor C8 symmetrical to the fifth capacitor C5, a first resonant unit, a second resonant unit, a third resonant unit, and a fourth resonant unit symmetrical to the first resonant unit, as well as a first port TermG1 and a second port TermG1. The resonant unit comprises rmG2, the third port TermG3, and the fourth port TermG4; the first resonant unit includes a third capacitor C3 and a second inductor L2 connected in parallel; the second resonant unit includes an eleventh capacitor C11 and a fifth inductor L5 connected in parallel; the third resonant unit includes a first inductor L1, a sixth inductor L6, and a second capacitor C2, wherein the first terminal of the first inductor L1 is grounded, the second terminal of the first inductor L1 is connected to the first terminal of the second capacitor C2, the second terminal of the second capacitor C2 is connected to the first terminal of the sixth inductor L6, and the second terminal of the sixth inductor L6 is grounded; the fourth resonant unit includes a third inductor L3, a fourth inductor L4, and a fourth capacitor C4, wherein the third inductor... The first terminal of inductor L3 is grounded. The second terminal of the third inductor L3 is connected to the first terminal of the fourth capacitor C4. The second terminal of the fourth capacitor C4 is connected to the first terminal of the fourth inductor L4. The second terminal of the fourth inductor L4 is grounded. The first port TermG1 is connected to the first terminal of the first capacitor C1 and the first terminal of the sixth capacitor C6. The second terminal of the first capacitor C1 is connected to the first terminal of the third capacitor C3 and the first terminal of the second capacitor C2. The second terminal of the sixth capacitor C6 is connected to the second port TermG2. The second port TermG2 is also connected to the first terminal of the fifth capacitor C5. The second terminal of the fifth capacitor C5 is connected to the second terminal of the third capacitor C3 and the first terminal of the fourth capacitor C4.The third port, TermG3, is connected to the first terminal of the twelfth capacitor C12 and the first terminal of the seventh capacitor C7. The second terminal of the twelfth capacitor C12 is connected to the second terminal of the second capacitor C2 and the first terminal of the eleventh capacitor C11. The second terminal of the seventh capacitor C7 is connected to the fourth port, TermG4. The fourth port, TermG4, is also connected to the first terminal of the eighth capacitor C8. The second terminal of the eighth capacitor C8 is connected to the second terminal of the fourth capacitor C4 and the second terminal of the eleventh capacitor C11.

2. The three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter according to claim 1, characterized in that, In the multi-layer spiral inductor structure used in the inductor, a via is set at the tail of the last layer from top to bottom.

3. The three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter according to claim 2, characterized in that, The connection between the capacitor and the inductor is achieved by connecting the via at the tail of the last layer from top to bottom in the multilayer spiral inductor structure used by the inductor with the first or second via in the multilayer shingled capacitor structure used by the capacitor.

4. The three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter according to claim 3, characterized in that, The two inductors are connected by a via at the end of the last layer from top to bottom in the multilayer spiral inductor structure of one inductor and a via at the end of the last layer from top to bottom in the multilayer spiral inductor structure of another inductor.

5. The three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter according to claim 4, characterized in that, For connecting two capacitors, the odd or even number of layers in the multilayer shingled capacitor structure of one capacitor are extended from the top to the middle layer in the multilayer shingled capacitor structure of the other capacitor, and a new via is provided in the extended part. The new via is connected to the first or second via in the multilayer shingled capacitor structure of the other capacitor.

6. The three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter according to claim 5, characterized in that, The circuit of the low-temperature co-fired ferrite differential bandpass filter is a differential circuit with vertical and horizontal symmetry.

7. The three-dimensional integrated low-temperature co-fired ferrite differential bandpass filter according to claim 6, characterized in that, When differential-mode signals, i.e. signals with equal amplitude but opposite phase, are loaded into TermG1 and TermG3, the differential bandpass filter circuit will be split into two identical circuits along the vertical axis of symmetry, according to the principles of electric and magnetic walls.

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