Passive bandpass filter circuit and RF circuit

Abstract

The present application provides a passive bandpass filter circuit and a radio frequency circuit, the passive bandpass filter circuit comprising: a first resonator branch, comprising a plurality of first-type resonators connected in series in sequence along a radio frequency signal transmission direction; a second resonator branch, comprising at least one second-type resonator and two third-type resonators, the second-type resonator being connected between the input end of the LC resonant circuit of the middle first-type resonator and an electrode ground, the third-type resonator being respectively connected between the input end of the LC resonant circuit of the first and last first-type resonators and an electrode ground, the second-type resonator comprising a series-connected LC resonant circuit and a capacitor, the third-type resonator comprising a series-connected LC resonant circuit and an inductor, in this way, the one-to-one corresponding arrangement of the types and quantities of the resonators in the first resonator branch and the second resonator branch is conducive to improving the compactness of the layout, setting more high-frequency transmission zero points, and making the stopband suppression range wider and the suppression degree better.

Description

Technical Field

[0001] The present application relates to the field of radio frequency technology, and in particular to a high-suppression wide-stopband passive bandpass filter and a radio frequency circuit. Background Art

[0002] The filter is one of the most important passive components in the RF circuit. Its function is to select useful spectrum and suppress unnecessary spectrum from passing through the system. It can allow a specific signal frequency range to pass through, while attenuating signal frequencies outside the passband to ensure that the working frequency band is clean and avoid interference. It is widely used in RF transceiver systems such as broadcast communications, mobile communications, satellite communications, navigation, remote sensing and radar.

[0003] As a frequency selection device, the performance of the filter affects the entire transceiver link system. In the process of designing and researching the filter, the inventor of the present application conducted the following research and analysis on the relevant technologies in the technical field of the filter:

[0004] Filters are classified in different ways according to different classification standards. According to the filter circuit structure, they can be divided into two categories: passive filter circuits and active filter circuits. There are many types of passive filters. According to the process, they can be divided into piezoelectric filters (including SAW and BAW), low temperature co-fired ceramic (LTCC) filters, integrated passive bandpass device (IPD) filters, etc.; according to the design method of passive circuits, they can be divided into distributed parameter structure filters and lumped parameter structure filters; in addition, distributed parameter structure filters include microstrip filters, cavity filters, waveguide filters, etc.

[0005] With the continuous development of communication technology, the system integration is getting higher and higher, and the demand for high out-of-band suppression, wide stopband, and miniaturized filters is getting higher and higher. Among them, although the cavity filter has good performance, it is difficult to meet the requirements of miniaturization and low cost due to its large size and high cost; although the piezoelectric filter has a high Q value and a good rectangular coefficient, it is widely used in narrowband communication systems, but it is difficult to meet the requirements of high relative bandwidth and wide stopband suppression. IPD (Integrated Passive Devices) integrated passive devices can use advanced semiconductor manufacturing processes, including thin film processes and photolithography processes. The IPD process has the characteristics of high substrate resistivity and high metal conductivity. For example, high-resistance silicon, glass, gallium arsenide, etc. can realize high Q value and low loss passive devices. Compared with the LTCC process, it has finer line width and smaller line spacing characteristics. The IPD process has better performance in miniaturization, easy integration, high yield, high precision, low cost, product chain supply and better reliability. Summary of the invention

[0006] In order to solve the existing technical problems, the present application provides a passive bandpass filter circuit and a radio frequency circuit with high suppression in a wide stopband range.

[0007] In a first aspect, a passive bandpass filter circuit is provided, comprising:

[0008] The first resonator branch comprises a plurality of first-type resonators connected in series in sequence along a transmission direction of the radio frequency signal; the first-type resonator comprises an LC resonant circuit and a capacitor connected in series;

[0009] The second resonator branch includes at least one second type resonator and two third type resonators, wherein the second type resonator is connected between the input end of the LC resonant circuit of the middle first type resonator and the electrode ground, and the third type resonator is respectively connected between the input end of the LC resonant circuit of the first type resonator at the head and the tail and the electrode ground; the second type resonator includes a series-connected LC resonant circuit and a capacitor, and the third type resonator includes a series-connected LC resonant circuit and an inductor.

[0010] In a second aspect, a radio frequency circuit is provided, comprising the passive bandpass filter circuit described in any embodiment of the present application.

[0011] The passive bandpass filter circuit provided in the above embodiment is designed with a first resonator branch and a second resonator branch. The first resonator branch includes first-type resonators connected in series in sequence along the transmission direction of the radio frequency signal. The first-type resonator includes a series-connected LC resonant circuit and a capacitor. The second resonator branch includes a second-type resonator and a third-type resonator respectively connected to the input ends of each first-type resonator. The second-type resonator includes a series-connected LC resonant circuit and a capacitor. The third-type resonator includes a series-connected LC resonant circuit and an inductor. In this way, the one-to-one correspondence between the type and number of resonators in the first resonator branch and the second resonator branch is conducive to supporting the first resonator branch and the second resonator branch to include a larger number of resonators to set more high-frequency transmission zeros while achieving a compact layout of the passive bandpass filter circuit. The stopband suppression range is wider and the suppression degree is better.

[0012] The radio frequency circuit provided in the above embodiment has the same concept as the corresponding passive bandpass filter circuit embodiment, and thus has the same technical effect as the corresponding passive bandpass filter circuit embodiment, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the structure of a passive bandpass filter circuit in one embodiment.

[0014] Figure 24 is a topological diagram of a passive bandpass filter circuit in one embodiment.

[0015] Figure 3 for Figure 2 The layout diagram of the passive bandpass filter circuit is shown.

[0016] Figure 4 This is an electromagnetic simulation S-parameter curve diagram of the passive bandpass filter circuit provided in an embodiment of the present application.

[0017] Figure 5 This is a graph of the S parameters of the passive bandpass filter circuit provided in an embodiment of the present application at 0-12 GHz.

[0018] Figure 6 This is an S parameter curve diagram within the 0.4-1.6 GHz band of the passive bandpass filter circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0020] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. The described embodiments should not be regarded as limiting the present application. All other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of this application.

[0021] In the following description, the expression "some embodiments" is involved, which describes a subset of all possible embodiments. It should be noted that "some embodiments" may be the same subset or different subsets of all possible embodiments, and may be combined with each other without conflict.

[0022] It should also be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may also be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "inside", "outside", "left", "right" and similar expressions used herein are only for the purpose of explanation in conjunction with the embodiments of the accompanying drawings and do not represent the only implementation method.

[0023] Please refer to Figures 1 to 3, an embodiment of the present application provides a passive bandpass filter circuit, comprising: a first resonator branch 11, comprising a plurality of first-type resonators 111 connected in series in a direction of transmission of radio frequency signals; the first-type resonator 111 comprises a series-connected LC resonant circuit and a capacitor. A second resonator branch 12, comprising at least one second-type resonator 112 and two third-type resonators 113, the second-type resonator 112 being connected between the input end of the LC resonant circuit of the middle first-type resonator 111 and the electrode ground, and the third-type resonator 113 being respectively connected between the input end of the LC resonant circuit of the first and last first-type resonators 111 and the electrode ground; the second-type resonator 112 comprises a series-connected LC resonant circuit and a capacitor, and the third-type resonator 113 comprises a series-connected LC resonant circuit and an inductor.

[0024] Among them, the LC resonant circuit refers to a circuit composed of an inductor and a capacitor, which generates oscillation through the interaction between the capacitor and the inductor, and is used to tune and select a specific frequency signal.

[0025] The input end of the LC resonant circuit refers to the end of the LC resonant circuit for the RF signal to be incident on. In this embodiment, it refers to the end of the LC resonant circuit that is relatively closer to the RF signal input end along the RF signal transmission direction.

[0026] In the above embodiment, by designing the first resonator branch 11 and the second resonator branch 12, the first resonator branch 11 includes first-type resonators 111 connected in series in sequence along the transmission direction of the radio frequency signal, the first-type resonator includes an LC resonant circuit and a capacitor connected in series, the second resonator branch 12 includes a second-type resonator 112 and a third-type resonator 113 respectively connected to the input ends of each first-type resonator 111, the second-type resonator includes an LC resonant circuit and a capacitor connected in series, and the third-type resonator includes an LC resonant circuit and an inductor connected in series. In this way, the one-to-one correspondence between the type and number of resonators in the first resonator branch 11 and the second resonator branch 12 is conducive to supporting the first resonator branch 11 and the second resonator branch 12 to include a larger number of resonators to set more high-frequency transmission zeros, and the stopband suppression range is wider and the suppression degree is better, while achieving a compact layout of the passive bandpass filter circuit.

[0027] See also Figure 3In some embodiments, in the first resonator branch 11, the capacitor of each first type resonator 111 is formed as a microstrip line extending along the transmission direction of the radio frequency signal, and the inductors in the first resonator branch 11 and the second resonator branch 12 are arranged on opposite sides of the microstrip line. In this embodiment, the layout design of the first resonator branch 11 and the second resonator branch 12 is to form the capacitors of the plurality of first type resonators 111 as microstrip lines extending along the transmission direction of the radio frequency signal, and the inductors in the first resonator branch 11 and the second resonator branch 12 are arranged on opposite sides of the microstrip line. In this way, the compactness of the layout of the passive bandpass filter circuit can be effectively improved, which is conducive to miniaturization and low cost of the overall size of the filter.

[0028] See also Figure 2 In some embodiments, the first type resonator 111 includes a first resonator 21, a second resonator 22, and a third resonator 23 connected in series in the direction of RF signal transmission; wherein the first resonator 21 includes a first LC resonant circuit and a first capacitor Cv1 connected in series, and the first LC resonant circuit includes a first resonant capacitor C1 and a first resonant inductor L1 connected in parallel; the second resonator 22 includes a second LC resonant circuit and a second capacitor Cv2 connected in series, and the second LC resonant circuit includes a second resonant capacitor C2 and a second resonant inductor L2 connected in parallel; the third resonator 23 includes a third LC resonant circuit and a third capacitor Cv3 connected in series, and the third LC resonant circuit includes a third resonant capacitor C3 and a third resonant inductor L3 connected in parallel. In this embodiment, in order to take into account miniaturization and high suppression of the wide stopband suppression range as the design purpose, the first resonator branch 11 is set to include a first resonator 21, a second resonator 22, and a third resonator 23 connected in series in sequence. The first resonator 21, the second resonator 22 and the third resonator 23 have the same structure, and respectively include an LC resonant circuit and a capacitor connected in series with the LC resonant circuit. In this way, it is easier to form the capacitors in the first resonator 21, the second resonator 22 and the third resonator 23 into microstrip lines extending along the transmission direction of the RF signal, thereby simplifying the molding process and reducing costs.

[0029] In some embodiments, the second resonator branch 12 includes a fourth resonator 24, a fifth resonator 25 and a sixth resonator 26 connected to the input ends of the first LC resonant circuit, the second LC resonant circuit and the third LC resonant circuit, respectively; wherein the fourth resonator 24 includes a fourth LC resonant circuit and a fourth inductor Lv4 connected in series, and the fourth LC resonant circuit includes a fourth resonant capacitor C4 and a fourth resonant inductor L4 connected in parallel; the fifth resonator 25 includes a fifth LC resonant circuit and a fifth capacitor Cv5 connected in series, and the fifth LC resonant circuit includes a fifth resonant capacitor C5 and a fifth resonant inductor L5 connected in parallel; the sixth resonator 26 includes a sixth LC resonant circuit and a sixth inductor Lv6 connected in series, and the sixth LC resonant circuit includes a sixth resonant capacitor C6 and a sixth resonant inductor L6 connected in parallel. In the present embodiment, in order to take into account both miniaturization and a high suppression range of a wide stopband, the second resonator branch 12 is further configured to include resonators corresponding one-to-one to each resonator in the first resonator branch 11, and in the second resonator branch 12, the third type of resonators corresponding to the first and tail resonators of the first resonator branch 11 are symmetrically arranged relative to the second type of resonator corresponding to the middle resonator of the first resonator branch 11. Taking the first resonator branch 11 including the first resonator 21, the second resonator 22 and the third resonator 23 connected in series in sequence as an example, the second resonator branch 12 includes a fourth resonator 24, a fifth resonator 25 and a sixth resonator 26 corresponding to each other. The fourth resonator 24 and the sixth resonator 26 respectively adopt a structural form in which an LC resonant circuit is connected in series with an inductor, and the fifth resonator 25 adopts a structural form in which an LC resonant circuit is connected in series with a capacitor. In this way, in the first resonator branch 11 and the second resonator branch 12, the total number of inductors occupying a larger layout size can be evenly arranged on opposite sides of the microstrip line, which is conducive to optimizing the layout layout of the passive bandpass filter circuit, improving the compactness of the layout while taking into account a larger number of transmission zeros, and is conducive to miniaturization and low cost of the overall size of the filter.

[0030] Please refer to Figure 3In an optional specific example, the fourth inductor Lv4, the first resonant inductor L1, the second resonant inductor L2 and the third resonant inductor L3 are located on one side of the microstrip line; the fourth resonant inductor L4, the fifth resonant inductor L5, the sixth inductor Lv6 and the sixth resonant inductor L6 are located on the other side of the microstrip line. In this embodiment, the fourth resonator 24 and the sixth resonator 26 respectively adopt a structural form in which an LC resonant circuit is connected in series with an inductor, while the fifth resonator 25 still adopts a structural form in which an LC resonant circuit is connected in series with a capacitor. In this way, in the first resonator branch 11 and the second resonator branch 12, the six resonators include a total of eight inductors, which can be evenly arranged on opposite sides of the microstrip line and arranged in sequence along the transmission direction of the RF signal, which is conducive to more reasonable use of the layout space and realizing the miniaturization and low cost of the overall size of the filter.

[0031] In an optional specific example, the fourth resonator 24 is connected between the input end of the LC resonant circuit of the first resonator 21 and the electrode ground; the fourth inductor Lv4 and the fourth resonant inductor L4 are respectively located on opposite sides of the microstrip line, and are respectively located in front of the first resonant inductor L1 and the fifth resonant inductor L5 along the transmission direction of the RF signal. In this embodiment, the form of the fourth inductor Lv4 and the fourth resonant inductor L4 is further designed based on the inductance values ​​of the fourth inductor Lv4 and the fourth resonant inductor L4, and the fourth inductor Lv4 with a relatively smaller size is arranged on the same side of the microstrip line as the multiple inductors in the first resonator branch 11, while the fourth resonant inductor L4 with a relatively larger size is located on the opposite side thereof, which is conducive to more reasonable use of the layout space and realizing miniaturization and low cost of the overall size of the filter.

[0032] It should be noted that in the first resonator branch 11 and the second resonator branch 12, the inductors are both octagonal spiral inductors, which can make the filter as a whole have a higher Q value and achieve better suppression capability compared to conventional quadrilateral inductors.

[0033] In some embodiments, for the design of the second resonator branch 12, the capacitors in the fourth resonator 24, the fifth resonator 25 and the sixth resonator 26 are further arranged to be located on the same side of the microstrip line, and are respectively formed as microstrip branches extending vertically relative to the microstrip line. In this way, the passive bandpass filter circuit as a whole uses microstrips to form a capacitor lumped element, and uses microstrips to complete the electrical connection between other non-capacitive lumped elements in the passive bandpass filter circuit, further optimizing the layout. In this embodiment, the size of the filter can be only 1mm*2mm, effectively achieving the design purpose of miniaturization and low cost of the overall size of the filter.

[0034] In an optional example, the passive bandpass filter circuit is a high-suppression wide-stopband miniaturized passive bandpass filter applied in the L-band frequency range of 0.85GHz-1.25GHz. On the basis of designing that the first resonator branch 11 includes the first resonator 21, the second resonator 22 and the third resonator 23; the second resonator branch 12 includes the fourth resonator 24, the fifth resonator 25 and the sixth resonator 26, five transmission zeros are formed in the high-stop band through six resonators, wherein the first resonator 21 forms the fourth transmission zero and the fifth transmission zero of the high-stop band; the second resonator 22 forms The third resonator 23 constitutes the second transmission zero of the high stop band; the third resonator 23 constitutes the fourth transmission zero of the high stop band; the fourth resonator 24 constitutes the fourth transmission zero of the high stop band; the fifth resonator 25 constitutes the transmission zero of the low stop band and the third transmission zero of the high stop band; the sixth resonator 26 constitutes the first transmission zero of the high stop band. In this way, the filter can achieve a narrower passband, a higher relative bandwidth, more high-frequency transmission zeros and a wider stopband suppression range at a relatively lower frequency. Combined with the optimization of the layout, the filter has a smaller size and a lower cost, so that a narrow-band high-suppression wide-stopband passive bandpass filter can be obtained.

[0035] See also Figures 4 to 6 , which is a schematic diagram of the electromagnetic simulation results of the passive bandpass filter circuit provided in the embodiment of the present application. From the simulation results, it can be seen that six resonators are used to form five transmission zeros in the high stop band, and the suppression degree reaches a wide stop band suppression range of -50dB in the range of 3.5GHz-10.6GHz, and a wide stop band range of -40dB is achieved in the range of 1.9GHz-11.3GHz; and the passband achieves a relative bandwidth of up to 40%, and a high suppression of about 30dB is achieved 300MHz outside the passband.

[0036] In another aspect of the embodiments of the present application, a radio frequency circuit is provided, including the passive bandpass filter circuit of any embodiment of the present application. The radio frequency circuit can be applied to radio frequency transceiver systems such as broadcast communication, mobile communication, satellite communication, navigation, remote sensing and radar to select useful spectrum and suppress unnecessary spectrum from passing through the system.

[0037] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0038] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A passive bandpass filter circuit, characterized in that: include: The first resonator branch comprises a plurality of first-type resonators connected in series in sequence along a transmission direction of the radio frequency signal; the first-type resonator comprises an LC resonant circuit and a capacitor connected in series; The second resonator branch includes at least one second type resonator and two third type resonators, wherein the second type resonator is connected between the input end of the LC resonant circuit of the middle first type resonator and the electrode ground, and the third type resonator is respectively connected between the input end of the LC resonant circuit of the first type resonator at the head and the tail and the electrode ground; the second type resonator includes a series-connected LC resonant circuit and a capacitor, and the third type resonator includes a series-connected LC resonant circuit and an inductor.

2. The passive bandpass filter circuit according to claim 1, characterized in that: In the first resonator branch, the capacitor of each first type resonator is formed as a microstrip line extending along the transmission direction of the radio frequency signal, and the inductors in the first resonator branch and the second resonator branch are arranged on opposite sides of the microstrip line.

3. The passive bandpass filter circuit according to claim 1, characterized in that: The first type of resonator includes a first resonator, a second resonator and a third resonator which are sequentially connected in series along the transmission direction of the radio frequency signal; Wherein, the first resonator comprises a first LC resonant circuit and a first capacitor connected in series, and the first LC resonant circuit comprises a first resonant capacitor and a first resonant inductor connected in parallel; The second resonator includes a second LC resonant circuit and a second capacitor connected in series, and the second LC resonant circuit includes a second resonant capacitor and a second resonant inductor connected in parallel; The third resonator includes a third LC resonant circuit and a third capacitor connected in series, and the third LC resonant circuit includes a third resonant capacitor and a third resonant inductor connected in parallel.

4. The passive bandpass filter circuit according to claim 3, characterized in that: The second resonator branch includes a fourth resonator, a fifth resonator and a sixth resonator connected to input ends of the first LC resonant circuit, the second LC resonant circuit and the third LC resonant circuit, respectively; The fourth resonator includes a fourth LC resonant circuit and a fourth inductor connected in series, and the fourth LC resonant circuit includes a fourth resonant capacitor and a fourth resonant inductor connected in parallel; The fifth resonator includes a fifth LC resonant circuit and a fifth capacitor connected in series, and the fifth LC resonant circuit includes a fifth resonant capacitor and a fifth resonant inductor connected in parallel; The sixth resonator includes a sixth LC resonant circuit and a sixth inductor connected in series, and the sixth LC resonant circuit includes a sixth resonant capacitor and a sixth resonant inductor connected in parallel.

5. The passive bandpass filter circuit according to claim 4, characterized in that: The fourth inductor, the first resonant inductor, the second resonant inductor and the third resonant inductor are located on one side of the microstrip line; The fourth resonant inductor, the fifth resonant inductor, the sixth inductor and the sixth resonant inductor are located on the other side of the microstrip line.

6. The passive bandpass filter circuit according to claim 4, characterized in that: The fourth resonator is connected between the input end of the LC resonant circuit of the first resonator and the electrode ground; The fourth inductor and the fourth resonant inductor are respectively located at opposite sides of the microstrip line, and are respectively located in front of the first resonant inductor and the fifth resonant inductor along the transmission direction of the radio frequency signal.

7. The passive bandpass filter circuit according to claim 4, characterized in that: In the second resonator branch, the capacitors in the fourth resonator, the fifth resonator and the sixth resonator are located on the same side of the microstrip line and are respectively formed as microstrip branches extending perpendicularly to the microstrip line.

8. The passive bandpass filter circuit according to claim 4, characterized in that: The first resonator forms the fourth transmission zero and the fifth transmission zero of the high resistance band; The second resonator forms a second transmission zero in the high-resistance band; The third resonator forms the fourth transmission zero of the high-resistance band; The fourth resonator forms the fourth transmission zero of the high resistance band; The fifth resonator forms a transmission zero in the low resistance band and a third transmission zero in the high resistance band; The sixth resonator forms the first transmission zero of the high-stop band.

9. The passive bandpass filter circuit according to any one of claims 1 to 8, characterized in that: Each inductor in the first resonator branch and the second resonator branch is an octagonal spiral inductor; and / or, The passive bandpass filter circuit is applied in the frequency range of 0.85 GHz to 1.25 GHz in the L band.

10. A radio frequency circuit, characterized in that: The method comprises the passive bandpass filter circuit as claimed in any one of claims 1 to 8.

Images