Band-pass filtering structure and band-pass filter

Abstract

The band-pass filtering structure comprises a T-type inductor and a capacitance network, the T-type inductor is composed of a first inductor and a second inductor, one end of the second inductor is coupled to the center tap position of the first inductor, the other end of the second inductor is coupled to the reference ground, and the capacitance network is connected with the first inductor. The center tap divides the first inductor into two parts with equal effective inductance values, the capacitor network comprises a first resonant capacitor and a second resonant capacitor, the first resonant capacitor is coupled to one end of the first inductor, and the second resonant capacitor is coupled to the other end of the first inductor; the band-pass filter is provided with an inductor, a capacitor and a grounding layer, the inductor forms a T-shaped inductor, and the grounding layer and the capacitor provide a low-impedance grounding point to improve out-of-band performance; according to the T-type inductor, the scheme that two inductors are jointly designed to replace the scheme that three inductors are connected in series and combined is adopted, so that the layout area of a device is further reduced under the condition of the same working frequency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of filter design, in particular to a bandpass filter structure and a bandpass filter. BACKGROUND

[0002] As an indispensable part of the transceiver system link, the filter has always been a hot device in the research of radio frequency circuit. In the sub-6GHz frequency band transceiver system, the passive devices based on PCB, low temperature co-fired ceramic technology (LTCC) and other processes can achieve extremely excellent radio frequency performance. The size of these passive devices is often related to the wavelength of the working frequency. The lower the working frequency, the longer the wavelength, and the larger the size of the device is required. However, in the low frequency band or the intermediate frequency band of the transceiver, it is difficult to integrate the filter inside the chip due to the constraints of size, performance and cost. Therefore, the design of the filter focuses on reducing the size-to-wavelength ratio.

[0003] In the prior art, Yi-Chyun Chiang of Chang Gung University and others designed a miniaturized filter structure composed of microstrip resonators, with a size-to-wavelength ratio of 0.17, and Chin-Lung Yang designed a transmission zero adjustable on-chip filter with a size-to-wavelength ratio of 0.018. However, these miniaturized structures, especially in the bandpass filter structure, still have a large size with the existing T-shaped inductor composed of three inductors. Considering the factors of half-wavelength array, cost and others, it is difficult to integrate on-chip. Therefore, the size of the passive filter structure needs to be further compressed. CONTENT OF THE INVENTION

[0004] Embodiments of the present application provide a bandpass filter structure and a bandpass filter to further reduce the size of the filter structure.

[0005] To solve the above technical problems, embodiments of the present application disclose the following technical solutions:

[0006] In a first aspect, the application provides a band-pass filter structure, comprising a first port, a second port, a T-shaped inductor and a capacitor network, the T-shaped inductor is composed of a first inductor and a second inductor, the first inductor has a first end, a second end and a center end, the second inductor has a first end and a second end, the first end of the second inductor is coupled to the center end of the first inductor, and the second end of the second inductor is coupled to a reference ground; the capacitor network comprises a first resonant capacitor and a second resonant capacitor, and a first ground capacitor and a second ground capacitor, the first resonant capacitor is coupled between the first port and the first end of the first inductor, and the second resonant capacitor is coupled between the second port and the second end of the first inductor; the first ground capacitor is coupled between the first end of the first inductor and the reference ground, and the second ground capacitor is coupled between the first end of the second inductor and the reference ground; wherein in the first inductor, the effective inductance value from the center end to the first end is equal to the effective inductance value from the center end to the second end.

[0007] Further, the first ground capacitor and the second ground capacitor each have a first end and a second end; the first end of the first ground capacitor is coupled between the first resonant capacitor and the first inductor, and the second end is coupled to the reference ground; the first end of the second ground capacitor is coupled between the second resonant capacitor and the first inductor, and the second end is coupled to the reference ground.

[0008] Further, the capacitor network further comprises a coupling capacitor; the coupling capacitor is coupled between the first port and the second port.

[0009] In a second aspect, the application provides a band-pass filter, comprising an inductor and a capacitor, and a ground layer, the ground layer has a hollow area corresponding to the layout area of the inductor and the capacitor; the inductor comprises a first inductor and a second inductor, the first inductor and the second inductor are each a planar coil-shaped inductor, one end of the planar coil is an outer end point, and the other end is an inner end point, the planar coil is arranged in parallel above the ground layer; the first inductor further has a center connection point connected to the outer end point of the second inductor, and the inner end point of the second inductor is connected to the ground layer, or the center connection point is connected to the inner end point of the second inductor, and the outer end point of the second inductor is connected to the ground layer; the capacitor comprises a first capacitor and a second capacitor, the first capacitor and the second capacitor each have a first end plate and a second end plate arranged in parallel above the ground layer; the first end plate of the first capacitor forms a first port of the band-pass filter, and the second end plate is connected to the outer end point of the first inductor, the first end plate of the second capacitor forms a second port of the band-pass filter, and the second end plate is connected to the inner end point of the first inductor; the first capacitor and the second capacitor serve as resonant capacitors and form a resonant structure of the band-pass filter together with the first inductor and the second inductor.

[0010] Further, the capacitor further comprises a third capacitor and a fourth capacitor, both of which have first end plates and second end plates arranged in parallel above the ground layer; the first end plate of the third capacitor is connected to the second end plate of the first capacitor, and the second end plate is connected to the ground layer; the first end plate of the fourth capacitor is connected to the second end plate of the second capacitor, and the second end plate is connected to the ground layer; the third capacitor and the fourth capacitor serve as ground capacitors to provide a low-impedance grounding point for the band-pass filter.

[0011] Further, the capacitor further comprises a fifth capacitor, which has first end plates and second end plates parallel to the ground layer, the first end plate is connected to the first end plate of the first capacitor, and the second end plate is connected to the first end plate of the second capacitor; the fifth capacitor serves as a coupling capacitor between the first port and the second port of the band-pass filter, and when its capacitance parameter is adjusted, the band-pass filter can adjust the passband frequency and the out-of-band suppression performance.

[0012] Further, the fifth capacitor is an interdigital capacitor, the first end plate is a first interdigital plate, and the second end plate is a second interdigital plate, and the multi-layer structure of the first interdigital plate and the second interdigital plate is located below the plane where the ground layer is located.

[0013] Further, the size-to-wavelength ratio of the first inductor is less than or equal to 3.3x10 -5 , wherein the size is the length of the coil corresponding to the effective inductance value of the first inductor, and the size-to-wavelength ratio represents the ratio of the size to the wavelength, wherein the size represents the length of the coil corresponding to the effective inductance value of the first inductor, and the wavelength represents the signal wavelength corresponding to the center frequency point of the band-pass filter.

[0014] Further, the size-to-wavelength ratio of the second inductor is less than or equal to 3.3x10 -5 , wherein the size is the length of the coil corresponding to the effective inductance value of the first inductor, and the size-to-wavelength ratio represents the ratio of the size to the wavelength, wherein the size represents the length of the coil corresponding to the effective inductance value of the first inductor, and the wavelength represents the signal wavelength corresponding to the center frequency point of the band-pass filter.

[0015] Further, the size-to-wavelength ratio of the band-pass filter is less than or equal to 3.3x10 -5 , and the size-to-wavelength ratio represents the ratio of the size to the wavelength, wherein the size represents the total layout area occupied by the inductor and the capacitor, and the wavelength represents the square of the signal wavelength corresponding to the center frequency point of the band-pass filter.

[0016] Further, the inductor and the capacitor are manufactured by a SiGe-BiCMOS process and are connected to the ground layer.

[0017] Further, when the preset operating frequency point of the band-pass filter is 12GHz, the layout occupied by the inductor and the capacitor has a width less than or equal to 130μm and a length less than or equal to 160μm, or an area less than or equal to 20800μm 2 .

[0018] The one or more of the above technical solutions have at least the following advantages or beneficial effects: in the technical solution, two inductors are selected for the T-shaped inductor, one end of the second inductor is coupled to the center tap position of the first inductor, instead of using three inductors, and the center tap of the first inductor replaces two inductors in series in the three-inductor scheme, so that the self-induction effect of the first inductor is further utilized to reduce the overall size of the T-shaped inductor, and the size-to-wavelength ratio of the band-pass filter structure is further reduced.

[0019] The further technical solution has the effect of improving the out-of-band characteristics of the band-pass filter by the ground capacitance and the coupling capacitance, so that in the application scenario of intermediate frequency signals, the corresponding product of the technical solution has good passband characteristics and out-of-band suppression performance while the size-to-wavelength ratio is further reduced. BRIEF DESCRIPTION OF DRAWINGS

[0020] The technical solutions and other beneficial effects of the present application will become apparent from the following detailed description of specific embodiments of the present application, combined with the accompanying drawings.

[0021] Figure 1 is a schematic diagram of a basic band-pass filter structure according to an embodiment of the present application;

[0022] Figure 2 is a schematic diagram of a band-pass filter structure with a ground capacitance according to an embodiment of the present application;

[0023] Figure 3 is a schematic diagram of a band-pass filter structure with a coupling capacitance according to an embodiment of the present application;

[0024] Figure 4 is a comparison layout of a single inductor and a series inductor provided by the present application, wherein Figure 4 (a) in FIG. is a layout of two series inductors, Figure 4 (b) in FIG. is a layout of a single inductor;

[0025] Figure 5 is a comparison layout of a single inductor and a series inductor provided by the present application, wherein Figure 4 the series inductor shown in (a) in FIG. Figure 4Simulation data graph of the single inductor in (b), wherein Figure 5 (a) is an inductance value simulation data graph, Figure 5 (b) is a quality factor simulation data graph;

[0026] Figure 6 is a schematic diagram of even mode extraction and odd mode extraction provided by the embodiment shown in Figure 3 is a schematic diagram of even mode extraction and odd mode extraction provided by the embodiment shown in

[0027] Figure 7 is a layout of a bandpass filter provided by the bandpass filter structure shown in Figure 3

[0028] Figure 8 is a model diagram of a bandpass filter provided by the bandpass filter layout shown in Figure 7

[0029] Figure 9 is a structure schematic diagram of a fourth capacitor C4 provided by the model shown in Figure 8

[0030] Figure 10 is a side view provided by the model diagram of the bandpass filter shown in Figure 8

[0031] Figure 11 is a simulation data graph provided by the bandpass filter structure shown in Figure 3 Figure 8

[0032] Figure 12 is a coupling capacitance tuning S21 simulation data graph provided by the bandpass filter structure shown in Figure 3 Figure 8 DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and beneficial effects of the present application clearer, the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described in the present specification are only for the purpose of explaining the present application, and are not intended to limit the present application.

[0034] ​​​​​​​​In the description of the present application, it should be noted that the term "tap" refers to a connection point on a portion of winding or resistance value of an inductor, transformer or resistor, etc. in the field of circuit or filter, which is used to change the characteristics of the circuit or realize special functions. In filter design, the selection of tap position can be used to adjust the impedance matching, gain or frequency response, and the tap is usually connected to the circuit to adapt to different impedance or frequency requirements. In the present application, the meaning of "center tap" is a connection point located at the midpoint of the inductance value of the inductor.

[0035] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified and limited.

[0036] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, it can be direct connection, or indirect connection through intermediate medium, it can be the communication between two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0037] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the "upper", "above" and "on" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "below", "under" and "under" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0038] In a first aspect, the present application provides a bandpass filter structure, including a first port, a second port, a T-type inductor, and a capacitor network, wherein the T-type inductor is composed of a first inductor and a second inductor, the first inductor having a first end, a second end, and a center end, the second inductor having a first end and a second end, the first end of the second inductor being coupled to the center end of the first inductor, and the second end of the second inductor being coupled to a reference ground; the capacitor network includes a first resonant capacitor and a second resonant capacitor, the first resonant capacitor being coupled between the first port and the first end of the first inductor, and the second resonant capacitor being coupled between the second port and the second end of the first inductor; wherein, in the first inductor, the effective inductance value from the center end to the first end is equal to the effective inductance value from the center end to the second end.

[0039] Figure 1 This is a schematic diagram of a basic bandpass filter structure provided according to an embodiment of the present application, wherein the basic bandpass filter structure includes a first port 1 and a second port 2, a T-type inductor L T and capacitor network. Figure 1 As shown, the T-type inductor L T The first inductor L1 and the second inductor L2 are composed of a first end, a second end and a center end Tap. C The second inductor L2 has a first end and a second end. The first end of the second inductor L2 is coupled to the center end of the first inductor L1, and the second end of the second inductor L2 is coupled to the reference ground GND. The capacitor network includes a first resonant capacitor C 11 and the second resonant capacitor C 12 , the first resonant capacitor C 11 The second resonant capacitor C is coupled between the first port 1 and the first end of the first inductor L1. 12 is coupled between the second port 2 and the second end of the first inductor L1; the center end Tap of the first inductor L1 C The effective inductance to the first terminal and the center terminal Tap C The effective inductance values ​​to the second end are equal, that is, the first inductor L1 is divided into two parts with equal effective inductance values ​​by the center tap. In one embodiment, the input impedance Rin of the first port 1 and the second port 2 is set to 50Ω to indicate that the impedance matching of the bandpass filter structure is ideal.

[0040] Figure 2 is a schematic diagram of a bandpass filter structure with a grounded capacitor according to an embodiment of the present application. Figure 2 As shown, in Figure 1 Based on the embodiment shown in FIG, in the bandpass filter structure of this embodiment, the capacitor network further includes a first grounding capacitor C 21and a second ground capacitor C 22 ; the first ground capacitor C 21 has a first end and a second end, wherein the first end is coupled between the first resonant capacitor C 11 and the first inductor L1, and the second end is coupled to the reference ground GND; the second ground capacitor C 22 has a first end and a second end, wherein the first end is coupled between the second resonant capacitor C 12 and the first inductor L1, and the second end is coupled to the reference ground GND; the impedance matching is the same as that of the embodiment shown in Figure 1 ; the first ground capacitor C 21 and the second ground capacitor C 22 provide a low-impedance grounding point for the band-pass filter structure to reduce the reflection of high-frequency signals, enhance the filtering effect, and improve the out-of-band rejection performance and return loss.

[0041] Figure 3 is a schematic diagram of a band-pass filter structure with a coupling capacitor according to an embodiment of the present application, as shown in Figure 3 , based on the embodiment shown in Figure 2 , in the band-pass filter structure of the present embodiment, the capacitor network further includes a coupling capacitor C0; the coupling capacitor C0 is coupled between the first port 1 and the second port 2; the impedance matching is the same as that of the embodiment shown in Figure 1 ; the coupling capacitor C0 directly participates in the signal transmission between the first port 1 and the second port 2, has a significant impact on the passband and high-side out-of-band rejection of the filter, and by adding the coupling capacitor C0, the frequency characteristics of the filter can be more conveniently adjusted by adjusting the parameters of the coupling capacitor C0.

[0042] The T-shaped inductor L T in each of the above embodiments is composed of the first inductor L1 and the second inductor L2, the first end of the second inductor L2 is coupled to the center end Tap C of the first inductor L1, i.e., the center tap position of the inductor, and the second end is coupled to the reference ground GND; compared with the structure of the T-shaped inductor composed of three inductors, the T-shaped inductor L T uses the self-induction effect of the first inductor L1 to replace two series inductors with equal inductance values, such as two series inductors with an inductance value of two-thirds L1, thereby further reducing the layout area occupied by the T-shaped inductor. Since the self-induction effect must be considered in the joint design of the T-shaped inductor, the effective inductance value of each inductor cannot be directly determined by the schematic layer, and the structure of the inductor and the connection position of the coil need to be accurately designed in the layout design, Figure 4 is a comparison layout of a single inductor and a series inductor provided by the present application, wherein Figure 4 (a) is a layout of two series inductors,Figure 4 (b) is the layout of a single inductor.

[0043] like Figure 4 As shown in (a), the two series inductors are L1 / 2, both of which are coil-shaped inductors. They are represented by two continuous coils in the layout. L1 / 2 on the left side of the layout is wound counterclockwise from the outer end point of the coil to the inner end point of the coil, and L1 / 2 on the right side of the layout is wound counterclockwise from the inner end point of the coil to the outer end point of the coil. L1 / 2 on the left side of the layout and L1 / 2 on the right side of the layout are conductively connected through their respective inner end points of the coil. In one embodiment, the total layout width w1 = 80 μm, length l1 = 113 μm, and area is 80 μm * 113 μm = 9040 μm 2 ;

[0044] like Figure 4 As shown in (b), a single inductor is L1, which is also a coil-shaped inductor. The layout is represented by a single continuous coil, which is wound counterclockwise from the outer end point to the inner end point. In one embodiment, the width of the layout is w2 = 50μm, the length is l2 = 90μm, and the area is 50μm*90μm = 4500μm 2 , less than Figure 4 One-half of the total layout area of ​​the series inductor shown in (a);

[0045] Figure 4 In (a), since the wires of the left and right coils are parallel to each other and the currents are in opposite directions at the positions close to each other, magnetic flux lines in opposite directions will be generated, weakening the magnetic field strength generated by L1 / 2 on the left and right sides of the layout. Figure 4 In the single coil L1 in (b), the currents in the parallel wires have the same direction, which will generate magnetic flux lines with the same direction. The superposition of these lines enhances the magnetic field strength of L1. For the corresponding layout, under the conditions of the same effective inductance value and roughly the same coil structure, the width w2 is smaller than the width w1, and the length l2 is also smaller than the length l2.

[0046] Figure 5 This application provides Figure 4 The series inductor shown in (a) is connected to Figure 4 (b) shows the simulation data of a single inductor, where Figure 5 (a) is the inductance simulation data diagram, Figure 5 (b) is the quality factor simulation data diagram, as shown in Figure 5 As shown in (a), two series-connected L1 / 2 and a single L1 achieve roughly the same inductance conditions under 0-50GHz conditions; Figure 5 As shown in (b), under 0-50GHz conditions, a single L1 has a higher quality factor than two series-connected L1 / 2.

[0047] Combine Figure 4 The comparison diagram shown is Figure 5 It can be seen from the simulation data shown that the T-type inductor provided in the present application is structurally improved to consist of the first inductor L1 and the second inductor L2, and one end of the second inductor L2 is connected to the center tap position of the first inductor L1. In the layout design, a smaller layout area can be used to realize an inductor device with the same inductance and a higher quality factor. Compared with the filter using three inductors to form a T-type inductor, the filter using the T-type inductor provided in the present application has lower loss and better rectangular coefficient.

[0048] Figure 6 This application is based on Figure 3 The embodiment shown provides a schematic diagram of even mode extraction and odd mode extraction to illustrate Figure 3 The bandpass filter structure shown has a basic bandpass filter function, where for ease of explanation Figure 3 The principle of the bandpass filter structure shown in the figure, and the frequency characteristic curve of the bandpass filter structure derived by applying the even mode extraction and odd mode extraction methods, need to let C 11 =C 12 =C1, C 21 =C 22 = C2, the transmission zero point is obtained according to the transmission coefficient model, and the transmission coefficient model is:

[0049]

[0050] Among them, S 21 Characterizing the signal transmission strength from the first port 1 to the second port 2, the reflection coefficient is:

[0051]

[0052] Wherein, Z0 is the terminal impedance, which represents the characteristic impedance of the first port 1 and the second port 2 and is generally 50 ohms. and They are Figure 3 The even-mode input impedance and odd-mode input impedance of the bandpass filter structure are shown in FIG. Figure 6 As shown, the even-mode input impedance It can be expressed as L1 / 2 and 2L2 in series, C2 in parallel, and finally C1 in series; odd-mode input impedance It can be expressed as the parallel connection of C2 and L1 / 2, the series connection of C1, and finally the parallel connection of 2C0. That is, equations (3) and (4):

[0053]

[0054] According to formulas (1) and (2), let S 21 =0 can be deduced

[0055]

[0056] Thus, the transmission zero point is obtained. Substituting equations (3) and (4) into (5), we can obtain a fourth-order polynomial:

[0057] f 4 k1+f 2 k2+k3=0 (6)

[0058] in:

[0059]

[0060] The transmission zero point is:

[0061]

[0062] From the transmission zero point, we can see that Figure 3 The bandpass frequency in the bandpass filter structure shown is related to the parameters of the first inductor L1, the second inductor L2 and each capacitor in the capacitor network. Figure 3 The layout, model diagram and simulation data of the bandpass filter designed with the bandpass filter structure shown.

[0063] Figure 7 This application is based on Figure 3 The layout of the bandpass filter structure shown in FIG. 1 shows a layout of a bandpass filter, wherein the first inductor L1 and the second inductor L2 are both planar coil inductors, represented by two continuous coils in the layout, and the winding direction from the outer end point of the coil to the inner end point of the coil is counterclockwise, and the outer end point of the coil of the second inductor L2 is connected to the center tap of the first inductor L1, i.e., the center end Tap. C The coil is conductively connected to the reference ground GND; the capacitor network includes a first resonant capacitor C 11 , the second resonant capacitor C 12 , the first grounding capacitor C 21 , the second grounding capacitor C 22 and coupling capacitor C0, the first resonant capacitor C 11 The left end of the first port 1 is used as the first port 1, and the right end is conductively connected to the outer end of the coil of the first inductor L1. The second resonant capacitor C 12 The right end point of the second port 2 is used as the left end point of the first inductor L1 and the first grounding capacitor C is conductively connected to the inner end point of the first inductor L1. 21 The upper end of the conductive connection is connected to the first resonant capacitor C 11 The right end of the first inductor L1 is connected to the outer end of the coil, and the lower end is conductively connected to the reference ground GND. The second grounding capacitor C 22 The upper end of the conductive connection is connected to the second resonant capacitor C12 The left end of the coupling capacitor C0 is connected to the inner end of the coil of the first inductor L1, and the lower end is conductively connected to the reference ground GND. The left end of the coupling capacitor C0 is connected to the resonant capacitor C 11 The left end is conductively connected, and the right end is connected to the resonant capacitor C 12 The right end of the first inductor L1 is conductively connected; the center end Tap C The effective length of the coil of the first inductor L1 is divided into two parts with equal effective inductance values; Figure 7 As shown, the width of the layout is w3 = 130 μm, the length is l3 = 160 μm, and the area is 130 μm * 160 μm = 20800 μm 2 .

[0064] Figure 8 This application is based on Figure 7 The bandpass filter model diagram provided by the bandpass filter layout shown in FIG. Wherein, the bandpass filter includes an inductor and a capacitor and a ground layer 3, as shown in FIG. Figure 8 As shown, combined Figure 7 Observation, in this embodiment, the XY plane is parallel to the plane where the ground layer 3 is located, the Z axis direction is perpendicular to the ground layer 3, the X axis direction is parallel to the width direction of the band-pass filter, and the Y axis direction is parallel to the length direction of the band-pass filter; the ground layer 3 has a hollow area 31 corresponding to the layout area of ​​the inductor and capacitor; the inductor includes a first inductor L1 and a second inductor L2, the first inductor L1 and the second inductor L2 are both planar coil inductors, one end of the planar coil is the outer endpoint, and the other end is the inner endpoint, and the planar coil is arranged parallel to the ground layer 3; the first inductor L1 also has a central connection point L13, which is connected to the outer endpoint L21 of the second inductor L2, and the inner endpoint L22 of the second inductor L2 is connected to the ground layer 3. In one embodiment, the central connection point L13 of the first inductor L1 is connected to the The inner endpoint L22 of the second inductor L2 and the outer endpoint L21 of the second inductor L2 are connected to the ground layer 3; the capacitor includes a first capacitor C1 and a second capacitor C2, each of which has a first end plate and a second end plate arranged parallel to the ground layer 3; the first end plate C11 of the first capacitor C1 forms the first port 1 of the bandpass filter, the second end plate C12 of the first capacitor C1 is connected to the outer endpoint L11 of the first inductor L1, the first end plate C21 of the second capacitor C2 forms the second port 2 of the bandpass filter, and the second end plate C22 of the second capacitor C2 is connected to the inner endpoint L12 of the first inductor L1; the first capacitor C1 and the second capacitor C2 serve as resonant capacitors and form a resonant structure of the bandpass filter with the first inductor L1 and the second inductor L2.

[0065] Further, in the present embodiment, the design size of the first inductor L1 is set according to the condition that the size-wavelength ratio is less than or equal to 3.3x10 -5 , i.e., the coil length of the first inductor L1 should be less than or equal to the product of the wavelength corresponding to the preset operating frequency and 3.3x10 -5 , and the coil length of the second inductor L1 can also be less than or equal to the product of the wavelength corresponding to the preset operating frequency and 3.3x10 -5 It should be understood that the size-wavelength ratio can also be represented by the ratio of the layout area to the square of the wavelength, and when designing the inductance parameters, using the coil length for calculation facilitates the parameterized design of the model.

[0066] Further, the capacitor further includes a third capacitor C3 and a fourth capacitor C4, both of which have first end plates and second end plates arranged in parallel above the ground layer 3. In the present embodiment, the third capacitor C3 and the fourth capacitor C4 both use MIM capacitors (Metal-Insulator-Metal), Figure 9 is a structural diagram of the fourth capacitor C4 provided by the present application according to the model shown in Figure 8 , wherein the second end plate C42 of the fourth capacitor C4 is composed of a first metal plate M1, a via 5 and a second metal plate M2, an insulating layer Ci is a thin layer arranged between the first end plate C41 of the fourth capacitor C4 and the second metal plate M2, and in combination with Figure 8 It can be seen that the second end plate C42 of the fourth capacitor C4 is connected to the ground layer 3 through the via 5, the metal layer 4 and the ground pillar 6; the first end plate C41 of the fourth capacitor C4 and the second end plate C22 of the second capacitor C2 share the same plate material, so as to realize that the first end of the second ground capacitor C 22 is coupled between the second resonant capacitor C 12 and the first inductor L1. In the present embodiment, the structures of the first capacitor C1, the second capacitor C2 and the third capacitor C3 are similar to that of the fourth capacitor C4, and thus are not described herein.

[0067] Further, the capacitor further comprises a fifth capacitor C5, the fifth capacitor C5 has a first end plate and a second end plate parallel to the ground layer 3, the first end plate C51 of the fifth capacitor C5 is connected to the first end plate C11 of the first capacitor C1, and the second end plate C52 of the fifth capacitor C5 is connected to the first end plate C21 of the second capacitor C2; the fifth capacitor C5 serves as a coupling capacitor between the first port 1 and the second port 2 of the band-pass filter, and when the capacitance parameter of the coupling capacitor is adjusted, the band-pass filter can adjust the passband frequency and the out-of-band rejection performance.

[0068] Preferably, the fifth capacitor C5 is an interdigital capacitor, i.e. a MOM capacitor (Metal-Oxide-Metal), the first end plate C51 of the fifth capacitor C5 is a first interdigital plate, and the second end plate C52 of the fifth capacitor C5 is a second interdigital plate. Since the T-shaped inductor L T The band-pass filter with a joint design of the T-shaped inductor L

[0069] Further, in the above embodiment, the size-to-wavelength ratio of the band-pass filter is less than or equal to 3.3x10 -5 , and the size-to-wavelength ratio represents the ratio of the size to the wavelength, wherein the size represents the total layout area occupied by the inductor and the capacitor, and the wavelength represents the square of the signal wavelength corresponding to the center frequency point of the band-pass filter.

[0070] Further, the inductors and capacitors in the above embodiments are manufactured by SiGe-BiCMOS process and connected to the ground layer 3. The SiGe-BiCMOS process combines the SiGe HBT with excellent high-frequency performance and the CMOS process with high integration, realizes miniaturization in high-performance and high-frequency applications, and is the preferred process for high-integration design. This process is widely used in the fields of radio frequency communication, wireless network, filter design, etc.

[0071] Figure 10 is a side view provided by the band-pass filter model diagram shown in Figure 8 , Figure 10 is a view obtained in the X-axis direction perpendicular to the Z-Y plane on the side close to the second port 2 in the model in Figure 8 , wherein the inner end point L22 of the second inductor L2 is connected to the metal layer 4 through the via 5, in combination with Figure 8 , it can be known that the metal layer 4 extends to the edge of the hollow area 31 of the ground layer 3 and is grounded to the ground layer 3 through the ground column 6, the outer end point L21 of the second inductor L2 is connected to the metal layer 4 through the via 5, and the metal layer 4 extends to below the central end point L13 of the first inductor L1 and is connected to the central end point L13 of the first inductor L1 through the via 5; in combination with Figure 8 , it can be known that the planar coils of the first inductor L1 and the second inductor L2 are in the same plane, the first end plates of the first capacitor C1 and the second capacitor C2 and the second end plates of the third capacitor C3 and the fourth capacitor C4 are in the same plane, the second end plates of the first capacitor C1 and the second capacitor C2 and the first end plates of the third capacitor C3 and the fourth capacitor C4 and the metal layer 4 are in the same plane; the fifth capacitor C5 is an interdigital capacitor in this embodiment, and the first interdigital plate and the second interdigital plate are stacked downward from the position of the plane where the ground layer 3 is located, and the thickness occupied by the capacitor is comparable to the thickness of the ground layer 3. It should be noted that Figure 9 , the second port 2 shown in is only a rectangular window as an illustration, and does not represent the connection relationship between it and the ground layer 3.

[0072] Figure 11 is a side view provided by the band-pass filter model diagram shown in Figure 3 and the band-pass filter layout shown in Figure 8 , the simulation data diagram is provided, the parameters adopt C0=80fF, C 11 =C 12 =1300fF, C 21 =C 22 =380fF, L1=280pH, L2=190pH, as shown in Figure 10 , wherein the transmission coefficients S 11 , S 12 , S 21、S 22 are the signal transmission strength from the first port 1 to the second port 2, the signal transmission strength from the first port 2 to the second port 1, the signal transmission strength from the first port 1 to the second port 2, and the signal transmission strength from the first port 2 to the second port 2, respectively. 11 and S 22 Characterize the signal reflection characteristics of the first port 1 and the second port 2 of the bandpass filter, S 12 and S 21 Characterizing the bandpass frequency characteristics of the bandpass filter, the two transmission zeros of the bandpass filter in this embodiment are at 12 GHz and 16 GHz, respectively. In the frequency band of 11 GHz to 17 GHz, the insertion loss is approximately 0.1 dB, the port return loss is better than 14 dB, and in the frequency bands of 0 to 4 GHz and greater than 23 GHz, the out-of-band suppression is greater than 20 dB.

[0073] Combine Figure 7 and Figure 11 The size-to-wavelength ratio of the bandpass filter structure and the bandpass filter provided in this application can be calculated, such as Figure 7 The layout shown in the figure has a layout area of ​​0.13mm×0.16mm=0.0208mm 2 ,like Figure 8 As shown, the operating frequency is 12 GHz, the corresponding wavelength is 25 mm, and the size-to-wavelength ratio is 0.0208 / (25×25)=3.3×10 -5 , where size is the layout area and wavelength is calculated using the corresponding area method. This structure achieves an extremely compact layout size, and its size-to-wavelength ratio is only 6.6% of the filtering structure that uses three inductors to form a T-type inductor.

[0074] Figure 12 This application is based on Figure 3 The bandpass filter structure shown and Figure 8 The bandpass filter layout shown provides the coupling capacitor parameter S 21 Simulation data diagram, where the coupling capacitor C0 is set to 50fF, 80fF and 110fF respectively, and the other parameters are set to the same Figure 11 The simulation data shown is the same as Figure 12As shown, the three simulation curves show the changes of the passband and the out-of-band rejection performance when the coupling capacitor C0 increases or decreases. When the coupling capacitor C0 increases from 50 fF to 110 fF, the low-frequency extreme point of the passband is still at 12 GHz, and the high-frequency extreme point decreases from 17 GHz to 16 GHz; the out-of-band rejection at 22 GHz increases from 8.7 dB to 42.5 dB; and the out-of-band rejection greater than 30 GHz decreases by about 6 dB. According to the above data analysis, increasing the coupling capacitor C0 will decrease the high-frequency extreme point of the passband of the filter, effectively improve the stopband rejection near the high-frequency out-of-band, and to some extent, deteriorate the stopband rejection far from the high-frequency out-of-band. According to the characteristics, the optimal range of the stopband can be designed at the target frequency band according to the actual needs of the communication link.

[0075] The above embodiments are provided only to help understand the method, structure and core idea of the present application. For those skilled in the technical field, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also belong to the scope of protection of the claims of the present application.

Claims

1. A bandpass filter structure, characterized by Comprising: a first port and a second port; a T-shaped inductor, comprising a first inductor and a second inductor, the first inductor having a first end, a second end and a center end, the second inductor having a first end and a second end, the first end of the second inductor coupled to the center end of the first inductor, the second end of the second inductor coupled to a reference ground; a capacitor network, comprising a first resonant capacitor and a second resonant capacitor, and a first ground capacitor and a second ground capacitor, the first resonant capacitor coupled between the first port and the first end of the first inductor, the second resonant capacitor coupled between the second port and the second end of the first inductor; the first ground capacitor coupled between the first end of the first inductor and the reference ground, the second ground capacitor coupled between the first end of the second inductor and the reference ground; wherein in the first inductor, the effective inductance value from the center end to the first end is equal to the effective inductance value from the center end to the second end.

2. The bandpass filter structure of claim 1, wherein: the first ground capacitor and the second ground capacitor each have a first end and a second end; the first end of the first ground capacitor is coupled between the first resonant capacitor and the first inductor, and the second end of the first ground capacitor is coupled to the reference ground; the first end of the second ground capacitor is coupled between the second resonant capacitor and the first inductor, and the second end of the second ground capacitor is coupled to the reference ground.

3. The bandpass filter structure of claim 1, wherein: the capacitor network further comprises a coupling capacitor; the coupling capacitor is coupled between the first port and the second port.

4. A bandpass filter, characterized by, Comprising: an inductor and a capacitor, and a ground layer having a hollow area corresponding to the layout area of the inductor and the capacitor; the inductor comprises a first inductor and a second inductor, the first inductor and the second inductor are both planar coil inductors, one end of the planar coil is an outer end point, the other end is an inner end point, the planar coil is arranged in parallel above the ground layer; the first inductor further has a center connection point connected to the outer end point of the second inductor, the inner end point of the second inductor is connected to the ground layer, or the center connection point is connected to the inner end point of the second inductor, and the outer end point of the second inductor is connected to the ground layer; the capacitor comprises a first capacitor and a second capacitor, the first capacitor and the second capacitor each have a first end plate and a second end plate arranged in parallel above the ground layer; the first end plate of the first capacitor forms a first port of the bandpass filter, and the second end plate of the first capacitor is connected to the outer end point of the first inductor, the first end plate of the second capacitor forms a second port of the bandpass filter, and the second end plate of the second capacitor is connected to the inner end point of the first inductor; the first capacitor and the second capacitor serve as resonant capacitors and form a resonant structure of the bandpass filter together with the first inductor and the second inductor.

5. The bandpass filter of claim 4, wherein: the capacitor further comprises a third capacitor and a fourth capacitor, the third capacitor and the fourth capacitor each have a first end plate and a second end plate arranged in parallel above the ground layer; a first end plate of the third capacitor is connected to a second end plate of the first capacitor, and the second end plate is connected to the ground layer; a first end plate of the fourth capacitor is connected to a second end plate of the second capacitor, and the second end plate is connected to the ground layer; the third capacitor and the fourth capacitor provide a low impedance ground point for the bandpass filter as a ground capacitor.

6. The bandpass filter of claim 4, wherein the capacitor further comprises a fifth capacitor having a first end plate and a second end plate parallel to the ground layer, the first end plate is connected to the first end plate of the first capacitor, and the second end plate is connected to the first end plate of the second capacitor; the fifth capacitor serves as a coupling capacitor between the first port and the second port of the bandpass filter, and when its capacitance parameter is adjusted, the bandpass filter can adjust the passband frequency and the out-of-band rejection performance.

7. The bandpass filter of claim 6, wherein the fifth capacitor is an interdigital capacitor, the first end plate is a first interdigital plate, the second end plate is a second interdigital plate, and the multi-layer structure of the first interdigital plate and the second interdigital plate is located below the plane where the ground layer is located.

8. The bandpass filter of claim 4, wherein, The size-to-wavelength ratio of the first inductor is less than or equal to 3.3x10 -5 , the size-to-wavelength ratio representing a ratio of size to wavelength, wherein the size represents a coil length corresponding to an effective inductance value of the first inductor, and the wavelength represents a signal wavelength corresponding to a center frequency point of the band-pass filter.

9. The bandpass filter of claim 4, wherein, The size-to-wavelength ratio of the second inductor is less than or equal to 3.3x10 -5 , the size-to-wavelength ratio representing a ratio of size to wavelength, wherein the size represents a coil length corresponding to an effective inductance value of the second inductor, and the wavelength represents a signal wavelength corresponding to a center frequency point of the band-pass filter.

10. The bandpass filter according to any one of claims 4-9, characterized in that, The size-to-wavelength ratio of the bandpass filter is less than or equal to 3.3x10 -5 , which represents the ratio of size to wavelength, wherein the size represents the total layout area occupied by the inductor and capacitor, and the wavelength represents the square of the signal wavelength corresponding to the center frequency point of the bandpass filter.

11. The bandpass filter of any one of claims 4-9, wherein the inductor and the capacitor are manufactured by a SiGe-BiCMOS process and are connected to the ground layer.

12. The bandpass filter of any one of claims 4-9, wherein When the preset working frequency point of the band-pass filter is 12GHz, the width of the layout occupied by the inductor and the capacitor is less than or equal to 130μm and the length is less than or equal to 160μm, or the area is less than or equal to 20800μm 2 .

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