A micro narrowband low-frequency bandpass filter

Abstract

The present invention provides a micro narrow-band low-frequency band-pass filter, which includes a central laminate and a filtering circuit. The central laminate includes a plurality of single-layer dielectric substrates. A metal pattern layer for forming the filtering circuit is provided on the surface of each single-layer dielectric substrate. Input / output terminals are respectively provided on the left and right side surfaces of the central laminate, and the front and rear side surfaces are both grounded electrodes; the metal pattern layer includes a first grounding layer, a first layer of coupling control layer, at least 4 multi-layer resonator units, a second layer of coupling control layer, and a second grounding layer which are arranged in sequence from top to bottom; the front and rear ends of the first and second grounding layers are respectively connected to the grounded electrodes; the front and rear ends of the first and second layers of coupling control layers are respectively connected to a grounded electrode; two adjacent multi-layer resonator units are sequentially coupled and cascaded through the first and second layers of coupling control layers. The present invention can achieve a lower operating frequency and a narrower bandwidth under the conditions that the dielectric material, the thickness of the single-layer dielectric, and the shape remain unchanged.

Description

Technical Field

[0001] The invention relates to a bandpass filter, in particular to a miniature narrow-band low-frequency bandpass filter. Background Art

[0002] Bandpass filters are important passive components in RF systems. A good bandpass filter should have low in-band loss, deep out-of-band suppression, wide stopband suppression range, and should be as small as possible. Traditional bandpass filters mostly use planar structures, occupying a large area and cannot meet the miniaturization requirements of RF front-ends. At the same time, traditional bandpass filters are difficult to integrate.

[0003] In order to achieve greater suppression outside the passband in the actual design of the bandpass filter, it is necessary to introduce transmission zeros at some specific frequencies. Transmission zeros refer to the filter transfer function being equal to zero, that is, from a theoretical point of view, energy cannot pass through the network at this frequency, thus playing a complete isolation role. However, due to the existence of electromagnetic radiation and electromagnetic leakage in actual situations, a small amount of energy will still pass through the network. However, the current bandpass filter usually has fewer transmission zeros, usually no more than 6 transmission zeros (that is, no more than 3 transmission zeros are generated in the stopband above the passband, and no more than 3 transmission zeros are generated in the stopband below the passband). Although it can achieve good performance, the existing structure still cannot meet the requirements when facing more stringent performance requirements. Although the more transmission zeros, the faster the out-of-band attenuation of the filter, the more transmission zeros, the more circuit elements, and therefore the more space is occupied, but now a small volume is required, so there is a contradiction, the contradiction between a large number of circuit elements and limited space.

[0004] In order to meet the requirements of miniaturization and high performance of devices, the traditional method is to use high dielectric constant and low loss dielectric materials to reduce the size of the device while improving device performance. However, in the traditional method, as the dielectric constant increases, the coupling inside the device will increase. After the internal coupling increases to a certain extent, the device performance will be negatively affected; after the dielectric loss is reduced to a certain extent, the conductor loss and radiation loss will become the main factors affecting the device loss. Therefore, starting from the material alone cannot solve the current problem of miniaturization and high performance of devices. It is also necessary to find corresponding solutions from the perspective of circuit design. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a micro narrowband low-frequency bandpass filter, eliminating the design of transmission zeros and instead using a three-dimensional arrangement. At least 4 multilayer resonator structures coupled in series are arranged vertically, enabling lower operating frequencies and narrower bandwidths to be achieved without changing the dielectric material, the thickness of a single layer of dielectric, or the filter's outer shape, facilitating further miniaturization of the micro multilayer ceramic bandpass filter.

[0006] The present invention is implemented as follows: It includes a central stacked body and a filter circuit disposed in the central stacked body. The central stacked body includes a plurality of single-layer dielectric substrates stacked from top to bottom. A metal pattern layer for forming the filter circuit is provided on the surface of each single-layer dielectric substrate. Input / output terminals are respectively provided on the left and right side surfaces of the central stacked body, and the front and back side surfaces of the central stacked body are both ground electrodes.

[0007] The metal pattern layer of the filter circuit includes a first ground layer, a first coupling control layer, at least 4 multilayer resonator units arranged side by side from left to right, a second coupling control layer, and a second ground layer, which are sequentially arranged from top to bottom. The front and back ends of the first ground layer and the second ground layer are respectively connected to the ground electrodes. The front and back ends of the first coupling control layer and the second coupling control layer are respectively connected to one of the ground electrodes. Adjacent two-stage multilayer resonator units are coupled through the first coupling control layer and the second coupling control layer respectively.

[0008] Further, each of the multilayer resonator units includes n metal layers, where n is an odd number and n≥5. One end of each metal layer is an open end and the other end is a short end, and the open ends and short ends of any two adjacent metal layers are arranged alternately. Any short end is connected to one of the ground electrodes.

[0009] One of the metal layers of the outermost multilayer resonator units on the left and right is an input / output connection layer, and the open ends of the input / output connection layer are also respectively connected to one of the input / output terminals.

[0010] Further, n is an odd number; the input / output connection layer is a middle-layer metal layer.

[0011] Further, the single-layer dielectric substrate where the first coupling control layer and the second coupling control layer are located is more than or not more than the single-layer dielectric substrate where the multilayer resonator is located.

[0012] Further, when the states of two adjacent multi-layer resonator units remain unchanged, the first coupling control layer and the second coupling control layer control the coupling amount between two adjacent multi-layer resonator units by changing the distances from the two adjacent multi-layer resonator units; the farther the first coupling control layer and the second coupling control layer are from the multi-layer resonator units, the greater the coupling amount. On the contrary, the closer the first coupling control layer and the second coupling control layer are to the multi-layer resonator units, the stronger the shielding effect and the smaller the coupling amount.

[0013] Further, the metal pattern layer of the filter circuit further includes a cross-coupling layer, which is disposed between the second coupling control layer and the second ground layer and is used for cross-coupling between two non-adjacent multi-layer resonator units. The cross-coupling layer is used to adjust the out-of-band attenuation speed and out-of-band attenuation amplitude of the filter.

[0014] The present invention has the following advantages:

[0015] 1. The filter of the present invention is changed to a three-dimensional setting. Its filter circuit is provided with at least 4 multi-layer resonator units coupled in series in sequence in the vertical direction. Each multi-layer resonator structure is composed of no less than 5 metal layers, which can effectively reduce the resonance frequency of the resonator, and further reduce the operating frequency of the filter under the conditions of limited size and limited dielectric constant.

[0016] 2. The uppermost layer and the lowermost layer of the filter circuit are both ground layers (the first ground layer and the second ground layer), which can be used to provide the reference ground required by the filter, and at the same time can shield the electromagnetic wave propagation inside and outside the filter, reduce electromagnetic radiation and electromagnetic leakage, and make the band-pass filter have low in-band loss.

[0017] 3. The upper and lower layers of the multi-layer resonator unit respectively have a coupling control layer (the first coupling control layer and the second coupling control layer), which can control the coupling strength between the resonators, and further adjust the filter bandwidth; a cross-coupling layer can be used to adjust the attenuation speed and attenuation amplitude of the filter.

[0018] 4. The whole filter structure is not provided with vias, and the coupling is only realized through printed patterns, which can more conveniently manufacture a specified structure and reduce the difficulty of process implementation.

[0019] It can be seen that the present invention can achieve lower operating frequency and narrower bandwidth without changing the dielectric material, the thickness of the single-layer dielectric, and the shape of the filter, which is convenient for further miniaturization of the miniature multilayer ceramic bandpass filter. It can realize a narrowband bandpass filter with a relative bandwidth of only 5.5% within a size of 2.5mm×2.0mm, while the sizes of filters based on multilayer ceramic structures on the market are mostly 4.5mm×3.2mm and 3.2mm×2.5mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0021] Figure 1 It is a schematic diagram of the external structure of the central stacked body of the miniature narrow-band low-frequency bandpass filter according to an embodiment of the present invention.

[0022] Figure 2 It is a schematic diagram of the internal structure of the central stack of the present invention.

[0023] Figure 3 It is a front view structural schematic diagram of the central stack of the present invention.

[0024] Figure 4 It is a schematic structural diagram of the first grounding layer and the second grounding layer of the filter circuit of the present invention.

[0025] Figure 5 It is a schematic structural diagram of the first metal layer of four multi-layer resonator units arranged side by side in the filter circuit of the present invention.

[0026] Figure 6 It is a schematic structural diagram of the second metal layer of four multi-layer resonator units arranged side by side in the filter circuit of the present invention.

[0027] Figure 7 It is a schematic structural diagram of the third metal layer of four multi-layer resonator units arranged side by side in the filter circuit of the present invention.

[0028] Figure 8 It is a schematic structural diagram of the fourth metal layer of four multi-layer resonator units arranged side by side in the filter circuit of the present invention.

[0029] Figure 9 It is a schematic structural diagram of the fifth metal layer of four multi-layer resonator units arranged side by side in the filter circuit of the present invention.

[0030] Figure 10 It is a schematic diagram of the structure of the first coupling control layer and the second coupling control layer of the filter circuit of the present invention.

[0031] Figure 11 It is a schematic diagram of the structure of the cross-coupling layer of the filter circuit of the present invention. Detailed implementation mode

[0032] The object of the present invention is to provide a micro narrow-band low-frequency band-pass filter, which can achieve a lower operating frequency and a narrower bandwidth under the conditions of unchanged dielectric material, unchanged single-layer dielectric thickness, and unchanged filter shape, facilitating the further miniaturization of the micro multi-layer ceramic band-pass filter.

[0033] The overall inventive concept of the present invention is as follows: changing the existing planar structure with a large occupied area to a three-dimensional structure. Its filtering circuit abandons the existing zero-point structure and instead uses a plurality of multi-layer resonator units arranged side by side and cascaded in sequence, which can greatly reduce the occupied area. And each multi-layer resonator unit is composed of no less than 5 metal layers, which can effectively reduce the resonance frequency of the resonator, and thus reduce the operating frequency of the filter under the conditions of limited size and limited dielectric constant; the entire top and bottom layers of the filtering circuit are ground layers, with a large coverage area and many grounding points, which can wrap the filtering circuit very tightly, thereby shielding the electromagnetic wave propagation inside and outside the filter, reducing electromagnetic radiation and electromagnetic leakage, and making the band-pass filter have low in-band loss; by respectively arranging a coupling control layer on the upper and lower layers of the multi-layer resonator unit to control the coupling strength between the resonators, and then adjusting the filter bandwidth to achieve narrow-band; and then adjusting the attenuation speed and attenuation amplitude of the filter through a layer of cross-coupling layer; and there are no through holes in the overall filter structure, and only coupling is achieved through printed patterns, which can more conveniently manufacture a specified structure and reduce the process implementation difficulty. Thus, it can achieve a lower operating frequency and a narrower bandwidth under the conditions of unchanged dielectric material, unchanged single-layer dielectric thickness, and unchanged filter shape, facilitating the further miniaturization of the micro multi-layer ceramic band-pass filter. Specific embodiment

[0035] As Figures 1 to 11 shown, this embodiment provides a micro narrow-band low-frequency band-pass filter, including a central laminate and a filtering circuit arranged in the central laminate.

[0036] Mainly as Figure 1 and Figure 2 shown, the central laminate 100 includes a plurality of single-layer dielectric substrates 101 stacked from top to bottom. A metal pattern layer for forming the filtering circuit 200 is provided on the surface of each single-layer dielectric substrate 101. Input / output terminals 102 are respectively provided on the left and right side surfaces of the central laminate 100, and the front and back side surfaces of the central laminate 100 are both grounding electrodes 103.

[0037] Mainly as Figure 3 shown, the filtering circuit 200 is composed of a metal pattern layer, and the metal pattern layer can be directly printed or coated on the surface of the single-layer dielectric substrate 101 to form the filtering circuit 200.

[0038] The metal pattern layer includes a first ground layer 1, a first layer of coupling control layer 2, at least 4 multi-layer resonator units 3 arranged side by side from left to right, a second layer of coupling control layer 4, and a second ground layer 5, which are arranged successively from top to bottom; both the front and rear ends of the first ground layer 1 and the second ground layer 5 are respectively connected to the ground electrode 103; both the front and rear ends of the first layer of coupling control layer 2 and the second layer of coupling control layer 4 are respectively connected to one of the ground electrodes 103; two adjacent multi-layer resonator units 3 are successively coupled in cascade through the first layer of coupling control layer 2 and the second layer of coupling control layer 4.

[0039] As Figure 1 and Figure 4 shown, the topmost layer and the bottommost layer of the filter circuit 200 are entirely ground layers (i.e., the first ground layer 1 and the second ground layer 5), with a large coverage area and many grounding points, which can tightly wrap the filter circuit, thereby shielding the electromagnetic wave propagation inside and outside the filter, reducing electromagnetic radiation and electromagnetic leakage, and enabling the bandpass filter to have a low in-band loss.

[0040] As Figure 10 shown, the metal patterns of the first layer of coupling control layer 2 and the second layer of coupling control layer 4 are both symmetrically distributed (the axis of symmetry is the center line in the filter input and output direction, equivalent to Figure 10 the horizontal center line in it, making the pattern symmetric up and down), and are simultaneously connected to two ground electrodes 103. This symmetric pattern design facilitates layout, and at the same time, because both sides are short-circuited, it is equivalent to adding an isolation structure between the multi-layer resonator units, thereby reducing the coupling between two adjacent multi-layer resonator units, achieving the goal of reducing the coupling amount within a limited space, and further realizing the performance of the narrowband filter.

[0041] Among them, as Figures 5 to 9 shown, each multi-layer resonator unit 3 includes n metal layers, n is an odd number, and n≥5, for example, it can be 5 layers, 7 layers, 9 layers, etc. Increasing the number of metal layers of the resonator unit 3 can equivalently increase the capacitance and inductance of the resonator, thereby reducing the operating frequency of the resonator. One end of each metal layer is an open end K, and the other end is a short end D, and the open ends K and short ends D of any two adjacent metal layers are arranged alternately, and any short end D is connected to one of the ground electrodes. The so-called alternate arrangement, as Figure 5 shown, the rear end of the first metal layer 31 (the topmost layer) is a short end D, which is connected to the rear ground electrode 103 of the central laminate 100, and the front end is an open end K; again, as Figure 6 shown, the front end of the second metal layer 32 is a short end D, which is connected to the front ground electrode of the central laminate 100, and the rear end is an open end K; again, as Figure 7As shown, the third metal layer 33 is the same as the first metal layer, with the short - circuit end D at the rear, connected to the rear - end ground electrode of the central laminate 100, and the open - circuit end K at the front; again, Figure 8 as shown, the settings of the open - circuit end K and the short - circuit end D of the fourth metal layer 34 are the same as those of the second metal layer 32. Again, Figure 9 as shown, the fifth metal layer 35 is arranged in the same direction as the first metal layer 31 and the third metal layer 33, and so on. Moreover, this rule also applies to the case where the number of metal layers of the multi - layer resonator unit 3 exceeds 5 layers. Staggered grounding can significantly reduce the operating frequency, while grounding on the same side has a very insignificant effect on reducing the operating frequency.

[0042] Moreover, the open - circuit ends 31 of the third metal layer of the multi - layer resonator units 3 on the outermost left and right sides are respectively connected to one of the input / output ends 102.

[0043] The single - layer dielectric substrate 101 where the first coupling control layer 2 and the second coupling control layer 4 are located is more than or not more than the single - layer dielectric substrate 101 where the multi - layer resonator unit 3 is located. Here, more than or not more than means that the layer where it is located is more than the layer where the resonator is located. For example, if the multi - layer resonator is located on the fourth to eighth single - layer dielectric substrates 101, and the first coupling control layer 2 is on the third single - layer dielectric substrate 101, that is, the first coupling control layer 2 and the second coupling control layer 4 are completely outside the single - layer dielectric substrate 101 where the multi - layer resonator unit is located, this state is more than (as Figure 2 and Figure 3 shown); if the first coupling control layer 2 and the second coupling control layer 4 are respectively on the fourth or fifth single - layer dielectric substrate 101, thus directly blocking between two multi - layer resonator units 3, this state is not more than (not shown).

[0044] When the adjacent two layers of the multi-layer resonator units 3 remain in the same state (including position, shape, dielectric material, etc.), the first coupling control layer 2 and the second coupling control layer 4 control the coupling amount between the adjacent two layers of multi-layer resonator units 3 by changing the distances (vertical and horizontal distances) from the adjacent two layers of multi-layer resonator units 3. That is: the farther the first coupling control layer 2 and the second coupling control layer 4 are from the multi-layer resonator unit 3, the greater the coupling amount; conversely, the closer the first coupling control layer 2 and the second coupling control layer 4 are to the multi-layer resonator unit, the stronger this shielding effect is, and the smaller the coupling amount. For easy understanding, for example: a multi-layer resonator unit 3 is like a light source, and this light source can illuminate the adjacent multi-layer resonator unit 3, and this illumination process is called coupling. If an opaque object is placed between two multi-layer resonator units 3, then the larger the area blocked by this opaque object, the less light the adjacent multi-layer resonator unit 3 receives, and the weaker the coupling. The first coupling control layer 2 and the second coupling control layer 4 both grounded are equivalent to such an opaque object, which can block part of the energy from being transmitted from one-level multi-layer resonator unit 3 to the next-level multi-layer resonator unit 3. The more parts are blocked, the smaller the coupling amount. However, for blocking, it is not necessarily that direct contact is required to be called blocking. The farther the first coupling control layer 2 and the second coupling control layer 4 are from the multi-layer resonator unit 3, the smaller this shielding effect is, and the stronger the coupling; conversely, the stronger this shielding effect is, the weaker the coupling.

[0045] The metal pattern layer of the filter circuit 200 further includes a cross-coupling layer 6, and the cross-coupling layer 6 is located between the second coupling control layer 2 and the second grounding layer 5. As Figure 11 shown, the cross-coupling layer 6 is similar to a Z-shaped pattern, and is used to realize cross-coupling between two non-adjacent layers of multi-layer resonator units 3 to adjust the out-of-band attenuation speed and out-of-band attenuation amplitude of the filter.

[0046] The above embodiments of the present invention have the following advantages:

[0047] The filter of the present invention is redesigned with a three-dimensional structure. Its filtering circuit is provided with at least 4 multi-layer resonator units that are sequentially coupled and cascaded in the vertical direction. Each multi-layer resonator structure is composed of no less than 5 metal layers, which can effectively reduce the resonance frequency of the resonator, and then reduce the operating frequency of the filter under the conditions of limited size and limited dielectric constant. The uppermost layer and the lowermost layer of the filtering circuit are both ground layers (the first ground layer and the second ground layer), which can be used to provide the reference ground required by the filter, and at the same time can shield the electromagnetic wave propagation inside and outside the filter, reduce electromagnetic radiation and electromagnetic leakage, and enable the band-pass filter to have low in-band loss. The upper and lower layers of the multi-layer resonator unit are respectively provided with a coupling control layer (the first coupling control layer and the second coupling control layer), which can control the coupling strength between the resonators, and then adjust the filter bandwidth. A layer of cross-coupling layer can be used to adjust the attenuation speed and attenuation amplitude of the filter. The overall filter structure is not provided with vias, and the coupling is only realized through printed patterns, which can more conveniently manufacture a specified structure and reduce the difficulty of process implementation.

[0048] It can be seen that the present invention can achieve a lower operating frequency and a narrower bandwidth without changing the dielectric material, the thickness of a single dielectric layer, and the shape of the filter, which is convenient for the further miniaturization of the micro multi-layer ceramic band-pass filter.

[0049] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments we described are illustrative rather than used to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered by the scope protected by the claims of the present invention.

Claims

1. A micro narrowband low-frequency bandpass filter, characterized in that: It includes a central laminate and a filtering circuit disposed in the central laminate. The central laminate includes a plurality of single-layer dielectric substrates stacked from top to bottom. A metal pattern layer for forming the filtering circuit is provided on the surface of each single-layer dielectric substrate. Input / output terminals are respectively provided on the left and right side surfaces of the central laminate, and the front and rear side surfaces of the central laminate are both ground electrodes; The metal pattern layer of the filtering circuit includes a first ground layer, a first coupling control layer, at least 4 multi-layer resonator units arranged side by side from left to right, a second coupling control layer, and a second ground layer, which are arranged in sequence from top to bottom; both the front and rear ends of the first ground layer and the second ground layer are respectively connected to one of the ground electrodes; Both the front and rear ends of the first coupling control layer and the second coupling control layer are respectively connected to one of the ground electrodes; two adjacent multi-layer resonator units are coupled through the first coupling control layer and the second coupling control layer respectively; Each multi-layer resonator unit includes n metal layers, and n≥5. One end of each metal layer is an open end, and the other end is a short end. The open ends and short ends of any two adjacent metal layers are arranged alternately, and any short end is connected to one of the ground electrodes; One of the metal layers of the multi-layer resonator units on the outermost left and right sides is an input / output connection layer, and the open ends of the input / output connection layer are also respectively connected to one of the input / output terminals; When the states of two adjacent multi-layer resonator units remain unchanged, the first coupling control layer and the second coupling control layer control the coupling amount between two adjacent multi-layer resonator units by changing the distance from the two adjacent multi-layer resonator units, so as to adjust the filter bandwidth and achieve narrowband; The farther the first coupling control layer and the second coupling control layer are from the multi-layer resonator units, the greater the coupling amount. On the contrary, the closer the first coupling control layer and the second coupling control layer are to the multi-layer resonator units, the stronger this shielding effect is, and the smaller the coupling amount is.

2. The miniature narrowband low-frequency band-pass filter according to claim 1, wherein: The n is an odd number; The input / output connection layer is an intermediate layer metal layer.

3. The miniature narrowband low-frequency band-pass filter according to claim 1, wherein: The single-layer dielectric substrate where the first coupling control layer and the second coupling control layer are located exceeds or does not exceed the single-layer dielectric substrate where the multi-layer resonator units are located.

4. A miniature narrowband low-frequency bandpass filter according to claim 1, characterized in that: The metal pattern layer of the filtering circuit further includes a cross-coupling layer, which is arranged between the second coupling control layer and the second ground layer for cross-coupling between two non-adjacent multi-layer resonator units.

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