A semi-integrated miniaturized LC filter, a manufacturing method and a switch filter bank

Abstract

The application discloses a kind of semi-integrated miniaturized LC filter, preparation method and switch filter group, the LC filter includes ceramic substrate, ceramic substrate is made of top layer, middle layer and bottom layer, wherein multiple capacitors are integrated in ceramic substrate middle layer by LTCC process, pad is provided on the surface of ceramic substrate top layer, multiple inductors are welded on pad;All inductors form the required circuit connection by pad and capacitor, rectangular pad is respectively provided at the left and right ends of ceramic substrate bottom layer, used as the input, output port of LC filter signal, ground pad is provided between the two rectangular pads of ceramic substrate bottom layer, to ensure that LC filter is well grounded.The capacitor is integrated in ceramic substrate in the application, the space occupied by the separated capacitor is saved, and the process is simpler than the process of semi-integrated LC filter and IPD process designed chip LC filter;Small volume separated inductor is used instead of integrated inductor, which can improve the Q value of the filter and reduce the loss.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication technology, specifically to a semi-integrated miniaturized LC filter, its fabrication method, and a switching filter bank, which provides signal separation and interference suppression for radio frequency communication. Background Technology

[0002] An LC filter is a passive device composed of capacitors and inductors arranged according to a specific transfer function. Different transfer functions correspond to different frequency responses and are used in different applications. Because the impedance of capacitors and inductors changes with the signal frequency, different combinations will present very small or very large reactances for specific frequency signals. LC filters utilize this characteristic to allow or block signals of a certain frequency, thus selecting or filtering out signals of a specific frequency. LC filters are widely used in radio frequency communication circuits due to their wide bandwidth coverage, flexible circuit structure, and low cost.

[0003] With the development of radio frequency (RF) communication technology, not only is modularization of RF modules required, but their performance requirements are also becoming increasingly stringent. Traditional LC filters are devices designed according to circuit topology, where discrete inductors and chip capacitors are soldered onto a circuit board and then mounted in a metal cavity. Although traditional LC filters have reduced their size by continuously miniaturizing the discrete inductors and chip capacitors, this is ultimately limited by the minimum component size constraints, hindering further miniaturization. Currently available LC filters are either generally large or have reduced size at the expense of performance, failing to meet the requirements of small size and high performance in applications.

[0004] Integrating inductors and capacitors onto the substrate using LTCC or HTCC processes can successfully reduce the size of LC filters. However, due to the influence of parasitic parameters, the Q value of LC filters is not high, and this advantage disappears when designing LC filters using this method below the P-band. LC filters designed based on silicon-based or gallium arsenide IPD processes have even worse Q values ​​because the capacitors and inductors are planar two-dimensional structures, making them unsuitable for high-performance applications. Furthermore, this method is difficult to apply to circuits with complex topologies and low operating frequencies.

[0005] Semi-lumped or integrated LC filters fabricated using LTCC technology and chip LC filters designed using IPD technology have significantly reduced the size of traditional LC filters. However, compared to traditional LC filters, these filters suffer from lower Q values ​​and poorer suppression, failing to meet the miniaturized and high-performance requirements of certain communication applications. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to provide a semi-integrated miniaturized LC filter and switching filter group with small size, high Q value, low loss, high suppression and low cost.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A semi-integrated miniaturized LC filter includes a ceramic substrate, which is composed of a top layer, a middle layer, and a bottom layer. Multiple capacitors are integrated in the middle layer of the ceramic substrate using an LTCC process. Pads are provided on the surface of the top layer of the ceramic substrate, and multiple inductors are soldered onto these pads. All inductors are connected to the capacitors via the pads to form the required circuit. Rectangular pads are provided at the left and right ends of the bottom layer of the ceramic substrate, serving as the input and output ports for the LC filter signal. A grounding pad is provided between the two rectangular pads on the bottom layer of the ceramic substrate to ensure good grounding of the LC filter.

[0009] Furthermore, the intermediate layer of the ceramic substrate is multi-layered, so that the desired capacitance value can be achieved by increasing or decreasing the number of intermediate layers.

[0010] Furthermore, through circuit design, the circuit connection of the LC filter forms a circuit topology in which all inductors are arranged symmetrically according to their inductance values ​​and all capacitors are arranged symmetrically according to their capacitance values; the multiple capacitors integrated in the middle layer of the ceramic substrate are symmetrically arranged on the top middle layer in the form of electrodes according to their capacitance values ​​and connected to the pads on the top layer, so as to reduce the three-dimensional modeling and simulation cycle.

[0011] Furthermore, a reinforcing ceramic layer is provided on the upper surface of the top layer and the lower surface of the bottom layer of the ceramic substrate. The outer surface of the reinforcing ceramic layer has electrodes that are connected one-to-one with the corresponding electrodes on the upper surface of the top layer and the lower surface of the bottom layer to increase the mechanical strength of the ceramic substrate. The pads are provided on the upper surface of the reinforcing ceramic layer above the top layer, and two rectangular pads are provided at the left and right ends of the lower surface of the reinforcing ceramic layer below the bottom layer. The grounding pad is provided on the lower surface of the reinforcing ceramic layer between the two rectangular pads.

[0012] Furthermore, a metal frame is wrapped around the ceramic substrate. The metal frame is a rectangular structure with openings at the top and bottom. One opening of the metal frame is flush with the bottom layer of the ceramic substrate. The metal frame is reflow soldered to the ceramic substrate. A cover plate is welded parallel to the other opening of the metal frame to improve the shielding performance of the filter.

[0013] This invention also provides a method for fabricating a semi-integrated miniaturized LC filter, comprising the following steps:

[0014] S1. Design a circuit topology based on the filter performance indicators, in which all inductors are arranged symmetrically according to their inductance values ​​and all capacitors are arranged symmetrically according to their capacitance values.

[0015] S2. All capacitors are integrated into the ceramic substrate using the LTCC process. All capacitors are symmetrically arranged on the ceramic substrate in the form of electrodes according to their capacitance values.

[0016] S3. Wrap a metal frame around the ceramic substrate and reflow solder it to the ceramic substrate. Symmetrically solder all the inductors onto the corresponding pads on the ceramic substrate. Finally, weld the cover plate with parallel seams.

[0017] The present invention also provides a switch filter bank, comprising multiple parallel LC filters, all of which are the aforementioned semi-integrated miniaturized LC filters. The input ports of the parallel filters are connected to an input matching network via a switch, and the input matching network is used to connect to the input radio frequency signal. The output ports of the parallel filters are connected to an output matching network via a switch, and the output matching network is used to output the radio frequency signal. The switch is used to control the channel through which the radio frequency signal passes, thereby enabling communication between signals of different frequencies.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention integrates all capacitors into a ceramic substrate, eliminating the space occupied by separate capacitors. It is also simpler to manufacture than integrated or semi-lumped LC filters made by LTCC process and chip LC filters designed by IPD process.

[0020] 2. This invention uses stacked plate technology to integrate multiple capacitors in a ceramic substrate and small-volume discrete inductors to replace integrated inductors, which can improve the Q value of the filter and reduce losses. Compared with traditional LC filters, IPD filters and LTCC integrated filters, especially in the frequency band below P-band, the LC filter of this invention is not only small in size, but also retains high performance indicators.

[0021] 3. Reinforcing ceramic layers are set on the upper surface of the top layer and the lower surface of the bottom layer of the ceramic substrate, which reduces the influence of parasitic parameters on the grounding of integrated capacitor electrodes and also increases the mechanical strength of the ceramic substrate.

[0022] 4. The present invention symmetrically sets the inductors in the circuit topology according to their inductance values, which not only reduces the number of inductors and lowers the cost, but also retains high performance indicators, while reducing the amount of debugging and improving production efficiency; symmetrically setting the capacitor values ​​in the circuit topology reduces the number of capacitors and shortens the three-dimensional modeling and simulation cycle. Attached Figure Description

[0023] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0024] Figure 1 This is a top view of the semi-integrated miniaturized LC filter of the present invention;

[0025] Figure 2 for Figure 1 A bottom view;

[0026] Figure 3 This is a schematic diagram of the ceramic substrate for integrating the capacitor array in this invention;

[0027] Figure 4 This is a schematic diagram of the solder pads in this invention;

[0028] Figure 5 This is a schematic diagram of the circuit topology of the semi-integrated miniaturized LC filter of the present invention;

[0029] Figure 6 This is a schematic diagram of the overall structure of the semi-integrated miniaturized LC filter of the present invention;

[0030] Figure 7 This is a schematic diagram of the LC switch filter bank of the present invention.

[0031] In the diagram: 1. Ceramic substrate; 2. Pad; 3. Inductor; 4. Rectangular pad; 5. Ground pad; 6. Metal frame; 7. Cover plate. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings.

[0033] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown in the figure, a semi-integrated miniaturized LC filter in this specific embodiment includes a ceramic substrate 1, which is composed of a top layer, a middle layer and a bottom layer. Multiple capacitors are integrated in the middle layer of the ceramic substrate using LTCC technology. Pads are provided on the surface of the top layer of the ceramic substrate, and multiple inductors are soldered on the pads. All inductors are connected to the capacitors through the pads to form the required circuit. Rectangular pads are provided at the left and right ends of the bottom layer of the ceramic substrate, which are used as the input port and output port of the LC filter signal. A grounding pad is provided between the two rectangular pads on the bottom layer of the ceramic substrate to ensure that the LC filter is well grounded.

[0034] In this solution, the capacitor is integrated into the ceramic substrate using the LTCC process. This not only eliminates the space occupied by separate capacitors and achieves high Q value and capacitance consistency through stacked plate technology, but also avoids damage to the capacitor body during the assembly process. Compared with semi-lumped LC filters fabricated using the LTCC process and chip LC filters designed using the IPD process, the process is simpler. The ceramic substrate uses a ceramic material with a dielectric constant of 6.8±0.3@11GHz, a dielectric loss of 0.05@11GHz, and a coefficient of thermal expansion of 5.3ppm / ℃.

[0035] In this embodiment, the intermediate layer of the ceramic substrate is multi-layered. This allows the required capacitance value to be achieved simply by increasing or decreasing the number of intermediate layers or the size of the intermediate layer electrodes in the three-dimensional structure, based on the capacitance value of filters at different frequencies. This fully demonstrates its flexibility and modular design.

[0036] See Figure 5 To reduce the 3D modeling and simulation cycle, this embodiment designs the circuits of inductors and capacitors so that the circuit connection of the filter forms a circuit topology in which all inductors are arranged symmetrically according to their inductance values ​​and all capacitors are arranged symmetrically according to their capacitance values. Multiple capacitors integrated in the middle layer of the ceramic substrate are symmetrically arranged on the top middle layer in the form of electrodes according to their capacitance values ​​and connected to the pads on the top layer, thereby reducing the 3D modeling and simulation cycle. Figure 5 In this circuit, C represents a capacitor and L represents an inductor. To achieve high rectangularity, two transmission zeros are introduced at the low and high ends of the filter. All capacitors are arranged symmetrically according to their capacitance values, i.e., with C8 as the axis of symmetry, C1 and C15, C2 and C14, C3 and C13, etc., are arranged symmetrically with equal inductance values, ultimately reducing the number of capacitance values ​​to eight. To minimize the number and specifications of inductors in the circuit topology and to improve production efficiency, all inductors are arranged symmetrically with equal inductance values, ultimately reducing the number of inductance values ​​to three, namely L1, L2, and L3.

[0037] This allows for the integration of multiple capacitors into a ceramic substrate using stacked planar technology and the replacement of integrated inductors with small-volume discrete inductors, thereby improving the Q value of the filter and reducing losses. Compared with traditional LC filters, IPD filters, and LTCC integrated filters, especially in the frequency band below P-band, the LC filter of this invention is not only small in size but also retains high performance.

[0038] To further improve the Q value of integrated capacitors, this invention places the grounding electrode of capacitors C1, C2, C4, C5, C7, C9, C11, C12, C14 and C15 (i.e. capacitors on non-main circuits) close to the grounding pad and the signal electrode away from the grounding pad when modeling.

[0039] To reduce the parasitic parameter impact of grounding the integrated capacitor electrodes and increase the mechanical strength of the ceramic substrate, this embodiment also provides reinforcing ceramic layers on the upper surface of the top layer and the lower surface of the bottom layer of the ceramic substrate. Electrodes corresponding to the top surface electrodes and bottom surface electrodes are located on the outer surface of the reinforcing ceramic layers to increase the mechanical strength of the ceramic substrate and improve the Q value of the capacitor in the integrated intermediate layer. Pads are placed on the upper surface of the reinforcing ceramic layer above the top layer, and two rectangular pads are placed at the left and right ends of the lower surface of the reinforcing ceramic layer below the bottom layer. A grounding pad is placed on the lower surface of the reinforcing ceramic layer between the two rectangular pads.

[0040] The final thickness of the ceramic substrate is controlled at 1 mm. The thickness of the ceramic substrate can also be controlled by increasing or decreasing the thickness of the reinforcing ceramic layer.

[0041] See Figure 6 In specific implementation, the present invention also includes a metal frame 6 surrounding the ceramic substrate. The metal frame is a rectangular structure with openings at the top and bottom. One opening end face of the metal frame is flush with the bottom layer of the ceramic substrate. The metal frame is reflow soldered to the ceramic substrate. A cover plate 7 is welded parallel to the other opening end face of the metal frame to improve the shielding performance of the filter.

[0042] The key point of this semi-integrated miniaturized LC filter is that it maintains a small size while possessing advantages such as high Q value, high rectangularity coefficient, and high suppression. The advantage of this invention is that it utilizes LTCC technology to stack separate capacitors within a ceramic substrate. This not only reduces the volume occupied by the separate capacitors, but the integrated method also ensures high Q value and capacitance consistency, and avoids damage to the capacitor ceramic body during the assembly process. Simultaneously, the separate inductors are retained, and their Q value remains unaffected. Compared to traditional LC filters, IPD filters, and LTCC lumped filters, the filter's size is not only reduced, but high performance indicators are also maintained. The advantages are particularly evident when designing LC filters in frequency bands below the L-band.

[0043] This invention also provides a method for fabricating a semi-integrated miniaturized LC filter, comprising the following steps:

[0044] S1. Based on the filter performance index (filter frequency), design a circuit topology in which all inductors are arranged symmetrically according to their inductance values ​​and all capacitors are arranged symmetrically according to their capacitance values.

[0045] S2. All capacitors are integrated into the ceramic substrate using the LTCC process. All capacitors are symmetrically arranged on the ceramic substrate in the form of electrodes according to their capacitance values.

[0046] S3. Wrap a metal frame around the ceramic substrate and reflow solder it to the ceramic substrate. Symmetrically solder all the inductors onto the corresponding pads on the ceramic substrate, and then adjust and apply adhesive. Finally, weld the cover plate with parallel seams.

[0047] In specific implementation, in step S2, the ceramic substrate consists of a top layer, a middle layer, and a bottom layer. All capacitors are integrated in the middle layer of the ceramic substrate using LTCC technology. Pads are provided on the surface of the top layer of the ceramic substrate. All inductors form the required circuit connection through the pads and capacitors. Rectangular pads are provided at the left and right ends of the bottom layer of the ceramic substrate, which are used as the input and output ports of the LC filter signal. A grounding pad is provided between the two rectangular pads on the bottom layer of the ceramic substrate to ensure that the LC filter is well grounded.

[0048] The intermediate layer is multi-layered, designed for filters in different frequency bands. Depending on the capacitance value, the required capacitance value can be achieved by simply adding or removing the number of integrated intermediate layers in the three-dimensional structure, fully demonstrating its flexibility.

[0049] This invention, based on the specifications of LC filters, designs a circuit topology in which all inductors are symmetrically arranged according to their inductance values, and all capacitors are symmetrically arranged according to their capacitance values. All inductors are integrated into a ceramic substrate using LTCC technology, and all capacitors are symmetrically arranged on the ceramic substrate as electrodes according to their capacitance values. The metal frame is then reflow soldered onto the ceramic substrate, and the inductors are manually soldered onto their corresponding pads. After debugging, adhesive is applied and cured, and finally, the cover plate is welded with parallel seams. In this way, for filters of different frequency bands, the required capacitance values ​​can be achieved simply by increasing or decreasing the number of layers and electrode area in the integrated ceramic substrate within the three-dimensional structure, fully demonstrating its flexibility and modular design.

[0050] See Figure 7 This invention also provides a switch filter bank, comprising multiple parallel LC filters, all of which are the aforementioned semi-integrated miniaturized LC filters. The input ports of the parallel filters are connected to an input matching network via switches, and the input matching network is used to connect to the input radio frequency (RF) signal. The output ports of the parallel LC filters are connected to an output matching network via switches, and the output matching network is used to output the RF signal. The switches control the channel through which the RF signal passes, enabling communication between signals of different frequencies. This switch filter bank is mainly used in multi-channel communication devices, such as phased-array radar receivers.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made. All obvious changes derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A semi-integrated miniaturized LC filter, characterized in that, The system includes a ceramic substrate, which consists of a top layer, a middle layer, and a bottom layer. Multiple capacitors are integrated in the middle layer of the ceramic substrate using LTCC technology. Pads are provided on the surface of the top layer of the ceramic substrate, and multiple inductors are soldered onto these pads. All inductors are connected to the capacitors via the pads to form the required circuitry. Rectangular pads are provided at both ends of the bottom layer of the ceramic substrate, serving as the input and output ports for the LC filter signal. A grounding pad is provided between the two rectangular pads on the bottom layer of the ceramic substrate to ensure good grounding of the LC filter. Through circuit design, the circuit connection of the LC filter forms a circuit topology in which all inductors are arranged symmetrically according to their inductance values ​​and all capacitors are arranged symmetrically according to their capacitance values. Multiple capacitors integrated in the middle layer of the ceramic substrate are symmetrically arranged on the top middle layer in the form of electrodes according to their capacitance values ​​and connected to the pads on the top layer to reduce the three-dimensional modeling and simulation cycle. A reinforcing ceramic layer is provided on the top surface of the top layer and the bottom surface of the bottom layer of the ceramic substrate. The outer surface of the reinforcing ceramic layer has electrodes that are connected one-to-one with the corresponding electrodes on the top surface of the top layer and the bottom surface of the bottom layer to increase the mechanical strength of the ceramic substrate. The pads are provided on the top surface of the reinforcing ceramic layer above the top layer, and two rectangular pads are provided on the left and right ends of the bottom surface of the reinforcing ceramic layer below the bottom layer. The grounding pad is provided on the bottom surface of the reinforcing ceramic layer between the two rectangular pads. A metal frame surrounds the ceramic substrate. The metal frame is a rectangular structure with openings at the top and bottom. One opening of the metal frame is flush with the bottom layer of the ceramic substrate. The metal frame and the ceramic substrate are reflow soldered together. A cover plate is welded parallel to the other opening of the metal frame to improve the shielding performance of the filter.

2. The semi-integrated miniaturized LC filter according to claim 1, characterized in that, The ceramic substrate has multiple intermediate layers, and the desired capacitance value can be achieved by increasing or decreasing the number of intermediate layers.

3. The method for fabricating a semi-integrated miniaturized LC filter according to claim 1, characterized in that, Includes the following steps: S1. Design a circuit topology based on the filter performance indicators, in which all inductors are arranged symmetrically according to their inductance values ​​and all capacitors are arranged symmetrically according to their capacitance values. S2. All capacitors are integrated into the ceramic substrate using the LTCC process. All capacitors are symmetrically arranged on the ceramic substrate in the form of electrodes according to their capacitance values. S3. Wrap a metal frame around the ceramic substrate and reflow solder it to the ceramic substrate. Symmetrically solder all the inductors onto the corresponding pads on the ceramic substrate. Finally, weld the cover plate with parallel seams.

4. A switching filter bank, characterized in that, It includes multiple parallel LC filters, all of which are semi-integrated miniaturized LC filters as described in claim 1. The input ports of the parallel filters are connected to an input matching network via a switch, and the input matching network is used to connect to the input radio frequency signal. The output ports of the parallel filters are connected to an output matching network via a switch, and the output matching network is used to output the radio frequency signal. The switch is used to control the channel through which the radio frequency signal passes, so as to realize communication between signals of different frequencies.

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