Band-pass filter and electronic device

Abstract

The invention provides a band-pass filter and electronic equipment. The band-pass filter comprises a signal input end and a signal output end, a first resonant cavity, a second resonant cavity and a third resonant cavity are formed in a circuit between the signal input end and the signal output end; the first resonant cavity comprises a first capacitor and a first inductor which are connected in series, the second resonant cavity comprises a second capacitor and a second inductor which are connected in parallel, and the third resonant cavity comprises a third capacitor and a third inductor which are connected in series; the second end of the second resonant cavity is connected with a fourth capacitor; the band-pass filter is further provided with a fifth capacitor and a sixth capacitor which are connected in series. The first end of the third resonant cavity is connected to the joint between the fifth capacitor and the sixth capacitor. Wherein the zero frequency transmitted by the first resonant cavity is higher than the zero frequency transmitted by the second resonant cavity, and the zero frequency transmitted by the second resonant cavity is higher than the zero frequency transmitted by the third resonant cavity. The invention also provides the electronic equipment with the band-pass filter. The insertion loss of the band-pass filter can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a bandpass filter and an electronic device having the bandpass filter. Background Art

[0002] As electronic devices become smaller, the various devices used inside them also need to be continuously miniaturized. However, the miniaturization of electronic devices often leads to a decline in communication quality. In microwave systems, the balance between the size and performance of RF devices becomes particularly important. The performance of RF devices represented by filters directly affects the indicators of the entire microwave system. The performance of filters mainly has two indicators: in-band insertion loss and stop-band attenuation, and the quality factor Q of the filter will directly affect the in-band insertion loss.

[0003] At present, high-precision passive integrated components are generally made using low-temperature co-fired ceramic technology. The passive devices mainly produced using this technology include filters, duplexers, baluns, antennas, couplers, etc. Compared with the existing mainstream production processes, such as silicon wafer semiconductor processes, the main raw material of the low-temperature co-fired ceramic process is ceramics. Its biggest advantage is that ceramics have low thermal expansion, which is conducive to the high-density multi-layer process design of large-scale integrated circuit devices. In addition, the devices made using this process have the advantage of low transmission loss, making this process the biggest highlight in high-frequency communications. In general, the main advantages of the low-temperature co-fired ceramic process are good compatibility, excellent high-frequency transmission characteristics, multi-level layout and wiring in a small volume, high integration and flexible space design, high reliability and relatively low cost, and short production cycle.

[0004] However, the in-band insertion loss of filters currently made based on the low-temperature co-fired ceramic process is relatively high, and insertion loss is extremely critical in distortion-free transmission systems. Excessive insertion loss will affect the communication performance of electronic equipment. Therefore, how to reduce the insertion loss of filters made using the low-temperature co-fired ceramic process is a key issue that needs to be broken through in circuit and space design and technology. In addition, the existing passive RF products are relatively large in size, which is not conducive to the design of modules in integrated circuits. Summary of the invention

[0005] A first object of the present invention is to provide a bandpass filter with low insertion loss.

[0006] A second object of the present invention is to provide an electronic device having the above-mentioned bandpass filter.

[0007] To achieve the first purpose of the present invention, the bandpass filter provided by the present invention includes a signal input end and a signal output end; the circuit between the signal input end and the signal output end forms a first resonant cavity, a second resonant cavity and a third resonant cavity; the first resonant cavity includes a first capacitor and a first inductor connected in series, the second resonant cavity includes a second capacitor and a second inductor connected in parallel, and the third resonant cavity includes a third capacitor and a third inductor connected in series; the second end of the second resonant cavity is connected to a fourth capacitor; the bandpass filter is also provided with a fifth capacitor and a sixth capacitor connected in series, and the first end of the third resonant cavity is connected to the connection between the fifth capacitor and the sixth capacitor; wherein the zero-point frequency transmitted by the first resonant cavity is higher than the zero-point frequency transmitted by the second resonant cavity, and the zero-point frequency transmitted by the second resonant cavity is higher than the zero-point frequency transmitted by the third resonant cavity.

[0008] It can be seen from the above scheme that the bandpass filter is provided with three resonant cavities, and the zero-point frequencies transmitted by the three resonant cavities are not the same. Specifically, the zero-point frequency transmitted by the first resonant cavity is relatively high, which is used to control the out-of-band suppression of the high-end frequency band. The zero-point frequency transmitted by the second resonant cavity is slightly lower, which mainly affects the passband and the high-end frequency band. The zero-point frequency transmitted by the third resonant cavity is relatively low, which mainly affects the low-end passband and out-of-band suppression.

[0009] By setting three different resonant cavities corresponding to different out-of-band zero frequencies, and selecting appropriate parameters of the three resonant cavities, the insertion loss of the bandpass filter can be made very small, meeting the communication quality requirements of high-performance electronic equipment.

[0010] In some embodiments, the first end of the first resonant cavity is connected to the first end of the second resonant cavity, and the second end of the first resonant cavity is grounded.

[0011] It can be seen that since the second resonant cavity is the main resonant cavity, it mainly affects the passband and the high-end frequency band. By reasonably setting the circuit relationship between the second resonant cavity and the first resonant cavity, the performance requirements of the bandpass filter can be ensured.

[0012] In some embodiments, the second end of the third resonant cavity is grounded.

[0013] In some embodiments, the bandpass filter includes a ceramic body, and the first resonant cavity, the second resonant cavity, the third resonant cavity, and the fourth capacitor, the fifth capacitor, and the sixth capacitor are encapsulated in the ceramic body.

[0014] It can be seen that three resonant cavities and multiple capacitors are encapsulated in a ceramic body, and the bandpass filter is made by low temperature co-fired ceramic process. By setting three resonant cavities, the bandpass filter made by low temperature co-fired ceramic process has lower insertion loss.

[0015] In some embodiments, the first inductor, the second inductor, and the third inductor are all vertical spiral coil inductors.

[0016] In this way, the bandpass filter can be manufactured by adopting the lamination technology, and it is beneficial to manufacture the first inductor, the second inductor and the third inductor.

[0017] In some embodiments, in the ceramic body, the second inductor is packaged above the first inductor, and the first inductor and the third inductor are packaged on the upper part of the ceramic body.

[0018] In the low-temperature co-fired ceramic process, the factors that affect inductance are the effective value, quality factor and self-resonant frequency of the inductance, and the inductance of the present invention exists in the form of a vertical spiral coil. Therefore, when it is equivalent to a circuit structure in three-dimensional space, it not only has inductance, but also generates parasitic capacitance to the ground and parasitic coupling capacitance between the coils. The parasitic capacitance has a great influence on the inductance of the circuit, so the second inductor and the third inductor are arranged in the upper area of ​​the ceramic body, which can improve the quality of the bandpass filter.

[0019] In addition, arranging the first inductor below the second inductor is beneficial to reducing the volume of the band-pass filter, for example, reducing the size of the band-pass filter in the length direction.

[0020] In some embodiments, the second capacitor is packaged below the second inductor, and the second capacitor is electrically connected to the second inductor via a filler filled in the via hole.

[0021] It can be seen that, in a ceramic body, by providing a via hole and filling the via hole with a conductive material, the connection between the capacitor and the inductor can be achieved.

[0022] In some embodiments, in the length direction of the ceramic body, the second inductor and the third inductor are respectively packaged at two ends of the ceramic body.

[0023] Through the above arrangement, the space in the length direction of the ceramic body can be fully utilized to avoid the bandpass filter being too high and resulting in an excessively large volume.

[0024] In some embodiments, two external terminals are disposed on the bottom surface of the ceramic body; and / or a ground terminal is disposed on the bottom surface of the ceramic body.

[0025] By setting external terminals and grounding terminals, the bandpass filter can be connected to external electrical signals, thereby realizing signal input and output.

[0026] To achieve the second objective of the present invention, the present invention provides an electronic device having the above-mentioned bandpass filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1 is an electrical schematic diagram of a bandpass filter embodiment of the present invention.

[0028] Figure 2It is a structural diagram of a bandpass filter embodiment of the present invention from a first viewing angle.

[0029] Figure 3 It is a structural diagram of the second viewing angle of the bandpass filter embodiment of the present invention.

[0030] Figure 4 It is a structural diagram of a bandpass filter embodiment of the present invention from a third viewing angle.

[0031] Figure 5 It is a structural diagram of a bandpass filter embodiment of the present invention from a fourth viewing angle.

[0032] Figure 6 It is an insertion loss curve diagram of a theoretical simulation of a bandpass filter embodiment of the present invention.

[0033] Figure 7 It is an insertion loss curve diagram of a three-dimensional simulation of a bandpass filter embodiment of the present invention.

[0034] The present invention is described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0035] The bandpass filter of the present invention is a bandpass filter made by low temperature co-fired ceramic technology, and the insertion loss of the bandpass filter is reduced by setting three resonant cavities corresponding to different out-of-band zero-point frequencies. The electronic device of the present invention is an electronic device with communication function, and is provided with the above-mentioned bandpass filter.

[0036] See also Figure 1 The bandpass filter of this embodiment has a signal input terminal 51 and a signal output terminal 52, and is also provided with three resonant cavities, namely, a first resonant cavity, a second resonant cavity and a third resonant cavity, wherein the first resonant cavity includes a first inductor L1 and a first capacitor C1 connected in series, the second resonant cavity includes a second inductor L2 and a second capacitor C2 connected in parallel, and the third resonant cavity includes a third inductor L3 and a third capacitor C3 connected in series. In addition, the bandpass filter is also provided with three capacitors, namely, a fourth capacitor C4, a fifth capacitor C5 and a sixth capacitor C6.

[0037] from Figure 1 It can be seen that the first end of the first resonant cavity is connected to the signal input terminal 51, and the first end of the first resonant cavity is also connected to the first end of the second resonant cavity, and the second end of the first resonant cavity is grounded, that is, one end of the first capacitor C1 is grounded. The second end of the second resonant cavity is connected to the first end of the fourth capacitor C4, and the second end of the fourth capacitor C4 is grounded. In addition, the second end of the second resonant cavity is also connected to the fifth capacitor C5, the fifth capacitor C5 and the sixth capacitor C6 are connected in series, and the second end of the sixth capacitor C6 is connected to the signal output terminal 52. The first end of the third resonant cavity is connected to the connection between the fifth capacitor C5 and the sixth capacitor C6, and the second end of the third resonant cavity is grounded.

[0038] In this embodiment, the zero-point frequencies transmitted by the three resonant cavities are different. Specifically, the zero-point frequency transmitted by the first resonant cavity is higher than the zero-point frequency transmitted by the second resonant cavity, and the zero-point frequency transmitted by the second resonant cavity is higher than the zero-point frequency transmitted by the third resonant cavity. In other words, the zero-point frequency transmitted by the first resonant cavity is relatively high, which is used to control the out-of-band suppression of the high-end frequency band. The zero-point frequency transmitted by the second resonant cavity is slightly lower, which mainly affects the passband and the high-end frequency band. The zero-point frequency transmitted by the third resonant cavity is relatively low, which mainly affects the low-end passband and out-of-band suppression. It can be seen that the second resonant cavity is the main resonant cavity, which mainly realizes the control of the passband frequency band of the bandpass filter. Therefore, the bandpass filter of this embodiment uses three resonant cavities to generate three zero points respectively, and connects two capacitors in series and one capacitor in parallel on the main circuit of the bandpass filter, so that the bandpass filter has the advantages of reducing insertion loss, and has the advantages of widening the bandwidth and optimizing the attenuation characteristics.

[0039] According to the above theoretical circuit diagram, when the bandpass filter is applied to production, this embodiment is made by low temperature co-fired ceramic process, see Figures 2 to 5 , multiple capacitors and inductors of the bandpass filter are encapsulated in a ceramic body 40. Specifically, the ceramic body 40 can be made of stacked sheets, that is, metal lines are printed on each layer of ceramic insulator, and each capacitor and inductor is formed by these metal lines. Therefore, in this embodiment, the first inductor 11, the second inductor 12 and the third inductor 13 are all vertical spiral coil inductors, and multiple inductors can be efficiently manufactured in this way.

[0040] As can be seen from the figure, in the height direction of the ceramic body 40, the second inductor 12 is packaged above the first inductor 11, and the second inductor 12 and the third inductor 13 are respectively at the left and right ends of the length direction of the ceramic body 40, that is, the second inductor 12 and the third inductor 13 are arranged along the length direction of the ceramic body 40.

[0041] In addition, six capacitors are also encapsulated in the ceramic body 40. Specifically, each capacitor is a sheet capacitor, that is, two metal layers parallel to each other are formed in the ceramic body 40 for each capacitor. For example, two metal layers of the first capacitor 21 are formed below the first inductor 11, thereby forming the first capacitor 21. In addition, the first capacitor 21 is electrically connected to the first inductor 11 through metal conduction. In the present embodiment, a plurality of vias 41 are provided in the ceramic body 40, each of which extends along the height direction of the ceramic body 40, and each of which is filled with a filler. In some embodiments, the filler is a filler with conductive properties, such as a metal. Since when making a bandpass filter, each capacitor and each capacitor are made by printing silver and other metals on each layer of insulating ceramic board, the filler in the via 41 is the same as the metal on each layer of insulating ceramic board, such as silver.

[0042] As can be seen from the figure, the second capacitor 22 is formed directly below the second inductor 12, and the second capacitor 22 and the second inductor 12 are electrically connected through the filler in the via 41. In this way, the electrical connection between the second capacitor 22 and the second inductor 12 can be achieved. In addition, a third capacitor 23 is also provided directly below the third inductor 13, and a via 41 is also provided between the third inductor 13 and the third capacitor 23. The via 41 is also filled with a filler, such as silver, and the electrical connection between the third inductor 13 and the third capacitor 23 is achieved through the filler.

[0043] In addition, the fourth capacitor 24, the fifth capacitor 25 and the sixth capacitor 26 are also packaged in the ceramic body 40, the fourth capacitor 24 is located below the fifth capacitor 25, and the sixth capacitor 26 is located below the third capacitor 23. It can be seen that in this embodiment, the second inductor 12 and the third inductor 13 are arranged at the top of the ceramic body 40. This is because in the low-temperature co-fired ceramic process, the factors affecting the inductance are the effective value, quality factor and self-resonant frequency of the inductance, and each inductor of this embodiment exists in the form of a vertical spiral coil, so when it is equivalent to a circuit structure in three-dimensional space, it is not only an inductor, but also a parasitic capacitance to the ground and a parasitic coupling capacitance between the coils. The parasitic capacitance has a great influence on the inductance of the circuit, so the second inductor 12 and the third inductor 13 are arranged in the upper area of ​​the ceramic body, which can improve the quality of the bandpass filter.

[0044] In addition, two external terminals 31, 32 are arranged on the bottom surface of the ceramic body 40, and the two external terminals 31, 32 are respectively used as the signal input terminal 51 and the signal output terminal 52 of the bandpass filter, and are used for signal transmission with the outside. Therefore, the two external terminals 31, 32 are exposed on the outer surface of the bandpass filter. In addition, since each external terminal 31, 32 is also electrically connected to the corresponding inductor or capacitor through the filler in the corresponding via hole. In addition, a grounding terminal 33 is also arranged on the bottom surface of the ceramic body 40 to provide a grounding signal for the bandpass filter. When the bandpass filter is mounted on the circuit board, the grounding terminal 33 is electrically connected to the grounding pad on the circuit board, thereby ensuring that the grounding signal of the bandpass filter is at the same level as the grounding signal on the electronic device. Therefore, the grounding terminal 33 is also exposed on the outer surface of the ceramic body 40.

[0045] Since the bandpass filter needs to have many devices grounded, another grounding terminal 34 is provided in the ceramic body 40. The grounding terminal 34 is encapsulated in the ceramic body 40, that is, it is not exposed on the outer surface of the ceramic body 40, but inside the ceramic body 40, the grounding terminal 34 is connected to the grounding terminal 33 through the filler in the via, so that the potential of the grounding terminal 34 is the same as the potential of the grounding terminal 33.

[0046] When making a bandpass filter, each layer of insulating ceramic plates is made respectively, and corresponding circuits are formed on each layer of insulating ceramic plates according to the arrangement of each capacitor and inductor, for example, a strip circuit required for a spiral inductor is formed, or a capacitor sheet required for each capacitor is formed. In addition, a through hole that runs through the insulating ceramic plate is started at the position where a via hole is required to be set. In this way, after each layer of ceramic insulating plates forms circuits and through holes, each layer of ceramic insulating plates is laminated in a fixed order, filled in each via hole, and then sintered. In order to realize the miniaturization of the bandpass filter, it is necessary to control the size of the ceramic body 40, for example, the length of the ceramic body 40 is 1.6 mm, the width is 0.8 mm, and the height is 0.577 mm. Therefore, after the ceramic body block is cut and sintered, the size of each product is 1.6 mm × 0.8 mm × 0.577 mm.

[0047] In this embodiment, the second inductor L2 and the second capacitor C2 are connected in parallel to form a second resonant cavity, thereby forming the first transmission zero point and playing the role of dominating the passband together with the fourth capacitor C4. The first inductor L1 and the first capacitor C1 are connected in series to form a second resonant cavity, which dominates the out-of-band suppression of the high-end frequency band. The second transmission zero point generated by the second resonant cavity can optimize the intensity of the out-of-band suppression. The third inductor L3 and the third capacitor C3 are connected in series to form a third resonant cavity and the third transmission zero point formed together with the fifth capacitor C5 and the sixth capacitor C6 affect the low-end passband and out-of-band suppression. It can be seen that the bandpass filter of this embodiment introduces three different transmission zero points with three resonant cavities to maximize the attenuation of the out-of-band; at the same time, multiple capacitors are used to optimize the return loss on the main path and the branch, so as to optimize the insertion loss in the band to the optimal theoretical value.

[0048] Figure 6 is based on Figure 1 The insertion loss curve obtained by theoretical simulation of the circuit diagram shown in the figure is calculated according to the theoretical formula , combined with Figure 6 It can be seen that by selecting appropriate parameters of each capacitor and inductor, in the 3.3 GHz and 4.2 GHz frequency bands, that is, Figure 6 At points m1 and m2 in the figure, the insertion loss of the bandpass filter can be reduced to below 0.8dB within the passband.

[0049] Figure 7 This is a simulation curve diagram for the three-dimensional structure of the bandpass filter. Figures 2 to 5 The three-dimensional structure shown produces a bandpass filter in the 3.3 GHz and 4.2 GHz bands (i.e. Figure 7 Therefore, the bandpass filter of this embodiment has good performance in the 3.3 GHz and 4.2 GHz frequency bands, and can meet the communication quality requirements of high performance of electronic equipment while meeting the requirements of miniaturization.

[0050] Finally, it should be emphasized that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bandpass filter, including a signal input terminal and a signal output terminal; Features: The circuit between the signal input end and the signal output end forms a first resonant cavity, a second resonant cavity and a third resonant cavity; The first resonant cavity comprises a first capacitor and a first inductor connected in series, the second resonant cavity comprises a second capacitor and a second inductor connected in parallel, and the third resonant cavity comprises a third capacitor and a third inductor connected in series; The second end of the second resonant cavity is connected to a fourth capacitor; The bandpass filter is further provided with a fifth capacitor and a sixth capacitor connected in series, and the first end of the third resonant cavity is connected to the connection between the fifth capacitor and the sixth capacitor; Among them, the zero-point frequency transmitted by the first resonant cavity is higher than the zero-point frequency transmitted by the second resonant cavity, and the zero-point frequency transmitted by the second resonant cavity is higher than the zero-point frequency transmitted by the third resonant cavity.

2. The bandpass filter according to claim 1, characterized in that: The first end of the first resonant cavity is connected to the first end of the second resonant cavity, and the second end of the first resonant cavity is grounded.

3. The bandpass filter according to claim 1, characterized in that: The second end of the third resonant cavity is grounded.

4. The bandpass filter according to any one of claims 1 to 3, characterized in that: The bandpass filter comprises a ceramic body, and the first resonant cavity, the second resonant cavity, the third resonant cavity and the fourth capacitor, the fifth capacitor and the sixth capacitor are encapsulated in the ceramic body.

5. The bandpass filter according to claim 4, characterized in that: The first inductor, the second inductor and the third inductor are all vertical spiral coil inductors.

6. The bandpass filter according to claim 5, characterized in that: In the ceramic body, the second inductor is packaged above the first inductor, and the first inductor and the third inductor are packaged on an upper portion of the ceramic body.

7. The bandpass filter according to claim 6, characterized in that: The second capacitor is packaged below the second inductor, and the second capacitor is electrically connected to the second inductor through a filler filled in the via hole.

8. The bandpass filter according to claim 6, characterized in that: In the length direction of the ceramic body, the second inductor and the third inductor are respectively packaged at two ends of the ceramic body.

9. The bandpass filter according to claim 4, characterized in that: The bottom surface of the ceramic body is provided with two external terminals; and / or [NICKY1] A ground terminal is disposed on the bottom surface of the ceramic body.

10. An electronic device, characterized in that The invention comprises a bandpass filter as claimed in any one of claims 1 to 9.

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