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, and in particular to a bandpass filter structure and a bandpass filter. Background Art

[0002] As an indispensable part of the transceiver system link, filters have always been a hot device in RF circuit research. In sub-6GHz band transceiver systems, passive devices based on PCB, low-temperature co-fired ceramic technology (LTCC) and other processes can achieve extremely excellent RF performance. The size of these passive devices is often related to the wavelength of the operating frequency. The lower the operating frequency, the longer the wavelength, and the larger the device size is required. However, in the low-frequency band or the medium-frequency band of the transceiver, it is difficult to integrate 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, for example, a miniaturized filter structure composed of microstrip resonators designed by Yi-Chyun Chiang et al. of Chang Gung University has a size-to-wavelength ratio of 0.17, and an on-chip filter with adjustable transmission zero designed by Chin-Lung Yang et al. has a size-to-wavelength ratio of 0.018. However, these miniaturized structures, especially in the bandpass filter structure, the existing T-type inductor composed of three inductors, still have a large size, and considering the factors of half-wavelength array and cost, it is difficult to integrate on chip. Therefore, the size of the passive filter structure needs to be further compressed. Summary of the invention

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

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

[0006] In a first aspect, the present application provides a bandpass filtering structure, comprising 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 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, 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; 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] Furthermore, the capacitor network also includes a first grounding capacitor and a second grounding capacitor; the first grounding capacitor and the second grounding capacitor both have a first end and a second end; the first end of the first grounding 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 grounding capacitor is coupled between the second resonant capacitor and the first inductor, and the second end is coupled to the reference ground.

[0008] Furthermore, the capacitor network also includes a coupling capacitor; the coupling capacitor is coupled between the first port and the second port.

[0009] In a second aspect, the present application provides a bandpass filter, comprising an inductor, a capacitor and a grounding layer, wherein the grounding 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, wherein the first inductor and the second inductor are both planar coil-shaped inductors, wherein one end of the planar coil is an outer endpoint and the other end is an inner endpoint, and the planar coil is arranged in parallel above the grounding layer; the first inductor also has a central connection point connected to the outer endpoint of the second inductor, and the inner endpoint of the second inductor is connected to the grounding layer; the capacitor comprises a first capacitor and a second capacitor, wherein the first capacitor and the second capacitor both have a first end plate and a second end plate arranged in parallel above the grounding layer; the first end plate of the first capacitor forms a first port of the bandpass filter, and the second end plate is connected to the outer endpoint 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 is connected to the inner endpoint of the first inductor; the first capacitor and the second capacitor serve as resonant capacitors and constitute a resonant structure of the bandpass filter with the first inductor and the second inductor.

[0010] Furthermore, the capacitor also includes a third capacitor and a fourth capacitor, and the third capacitor and the fourth capacitor both have a first end plate and a second end plate arranged in parallel above the grounding 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 grounding 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 grounding layer; the third capacitor and the fourth capacitor serve as grounding capacitors to provide a low-impedance grounding point for the bandpass filter.

[0011] Furthermore, the capacitor also includes a fifth capacitor, which has 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 parameters are adjusted, the bandpass filter can adjust the passband frequency and out-of-band suppression performance.

[0012] Furthermore, the fifth capacitor is an interdigitated capacitor, the first end plate is a first interdigitated plate, the second end plate is a second interdigitated plate, and the multilayer structure of the first interdigitated plate and the second interdigitated plate is located below the plane where the ground layer is located.

[0013] Furthermore, the size-to-wavelength ratio of the first inductor is less than or equal to 3.3×10 -5 , wherein the size of the coil of the first inductor corresponds to the length of 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 coil length 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 bandpass filter.

[0014] Furthermore, the size-to-wavelength ratio of the second inductor is less than or equal to 3.3×10 -5 , wherein the size of the coil of the first inductor corresponds to the length of 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 coil length 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 bandpass filter.

[0015] Furthermore, the size-to-wavelength ratio of the bandpass filter is less than or equal to 3.3×10 -5 The size-to-wavelength ratio represents the ratio of size to 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 of the bandpass filter.

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

[0017] Furthermore, when the preset operating frequency of the bandpass filter is 12 GHz, the width of the layout occupied by the inductor and the capacitor is less than or equal to 130 μm and the length is less than or equal to 160 μm, or the area is less than or equal to 20800 μm. 2 .

[0018] One or more of the above technical solutions have at least the following advantages or beneficial effects: In the present technical solution, two inductors are selected to be used in the constituent device of the T-type inductor, and 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 is used to replace the two inductors connected in series in the three-inductor solution, thereby further reducing the overall size of the T-type inductor by utilizing the self-inductance effect of the first inductor, and further reducing the size-to-wavelength ratio of the bandpass filter structure.

[0019] The above-mentioned further technical solutions also have the function of improving the out-of-band characteristics of the bandpass filter through grounding capacitors and coupling capacitors, so that in the application scenario of intermediate frequency signals, the products corresponding to these technical solutions still have good passband characteristics and out-of-band suppression performance when the size-to-wavelength ratio is further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

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

[0022] Figure 2 is a schematic diagram of a bandpass filter structure with a grounded capacitor provided according to an embodiment of the present application;

[0023] Figure 3 is a schematic diagram of a bandpass filter structure with coupling capacitors provided according to an embodiment of the present application;

[0024] Figure 4 is a comparison diagram of a single inductor and a series inductor provided in this application, wherein Figure 4 -a is the layout of two series inductors. Figure 4 -b is the layout of a single inductor;

[0025] Figure 5 This application provides Figure 4 -a shows the series inductor and 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;

[0026] Figure 6 This application is based on Figure 3 Schematic diagram of even mode extraction and odd mode extraction provided by the illustrated embodiment;

[0027] Figure 7 This application is based on Figure 3The layout of the bandpass filter provided by the bandpass filtering structure shown;

[0028] Figure 8 This application is based on Figure 7 The bandpass filter model diagram provided by the bandpass filter layout shown;

[0029] Fig. 9 This application is based on Figure 8 A schematic diagram of the structure of a fourth capacitor C4 provided by the model shown;

[0030] Fig.10 This application is based on Figure 8 The bandpass filter model diagram shown provides a side view;

[0031] Fig.11 This application is based on Figure 3 The bandpass filter structure shown and Figure 8 The simulation data graph provided by the bandpass filter layout shown;

[0032] Fig.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 adjustment S21 simulation data diagram. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and beneficial effects of this application more clear, the following further describes this application in detail in conjunction with the accompanying drawings and specific implementation methods. It should be understood that the specific implementation methods described in this specification are only for explaining this application, not for limiting this application.

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

[0035] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying 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 specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" refers to two or more, unless otherwise clearly and specifically defined.

[0036] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0037] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0038] In a first aspect, the present application provides a bandpass filtering structure, comprising 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 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, 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; 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 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 comprises 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; a 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 grounded capacitors provided according to an embodiment of the present application, such as Figure 2 As shown, in Figure 1 Based on the embodiment shown in the figure, in the bandpass filter structure of this embodiment, the capacitor network further includes a first grounding capacitor C 21 and the second grounding capacitor C22 ; The first grounding capacitor C 21 It has a first end and a second end, wherein the first end is coupled to the first resonant capacitor C 11 The second end of the first inductor L1 is coupled to the reference ground GND; the second grounding capacitor C 22 has a first end and a second end, wherein the first end is coupled to the second resonant capacitor C 12 and the first inductor L1, the second end is coupled to the reference ground GND; the impedance matching is Figure 1 The first grounding capacitor C 21 and the second grounding capacitor C 22 A low-impedance grounding point is provided for the bandpass filtering structure to reduce reflection of high-frequency signals, enhance filtering effects, and improve out-of-band suppression performance and return loss.

[0041] Figure 3 is a schematic diagram of a bandpass filter structure with coupling capacitors provided according to an embodiment of the present application, such as Figure 3 As shown, in Figure 2 Based on the embodiment shown in the figure, in the bandpass filter structure of this 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 and Figure 1 The embodiment shown is the same; the coupling capacitor C0 directly participates in the signal transmission between the first port 1 and the second port 2, and has a significant impact on the passband and high sideband out-of-band suppression of the filter. By adding the coupling capacitor C0, the frequency characteristics of the filter can be more conveniently adjusted by adjusting its parameters.

[0042] The T-type inductor L in the above embodiments T The first inductor L1 and the second inductor L2 are both 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 of the first inductor L1. C That is, the center tap position of the inductor, the second end is coupled to the reference ground GND, compared with the structure of the T-type inductor composed of three inductors, the T-type inductor L T By utilizing the self-inductance effect of the first inductor L1, the first inductor L1 replaces two series inductors with equal inductance values, such as two series inductors with an inductance value of half of L1, thereby further reducing the layout area occupied by the T-type inductor. Since the jointly designed T-type inductor must take the self-inductance effect into consideration, it is impossible to directly determine the effective inductance value of each inductor through the schematic layer, and it is necessary to accurately determine the structure of the inductor and the connection position of the coil in the layout design. Figure 4 is a comparison diagram of a single inductor and a series inductor provided in this application, wherein Figure 4 -a is the layout of two series inductors. Figure 4-b is the layout of a single inductor.

[0043] like Figure 4 -a, the two series inductors are L1 / 2, both are coil-shaped inductors, represented by two continuous coils in the layout, wherein 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, and 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 width w1 of the total layout is 80μm, the length l1 is 113μm, and the area is 80μm*113μm=9040μm 2 ;

[0044] like Figure 4 -b, a single inductor is L1, which is also a coil-shaped inductor, represented by a single continuous coil in the layout, and the coil is wound counterclockwise from the outer end point to the inner end point. In one embodiment, the width w2 of the layout is 50μm, the length l2 is 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 -a, because the wires of the coils on the left and right sides are parallel to each other and the currents are in opposite directions, 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 -b, in a single coil L1, the currents in the parallel wires have the same direction, which will generate magnetic flux lines with the same direction. The superposition of each other will enhance the magnetic field strength of L1. For the corresponding layout, under the conditions of the same effective inductance 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 -a shows the series inductor and 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, such as Figure 5 -a, two series-connected L1 / 2 and a single L1 achieve roughly the same inductance conditions at 0-50GHz; Figure 5 -b shows that under 0-50GHz conditions, a single L1 has a higher quality factor than two series-connected L1 / 2.

[0047] Combination Figure 4 The comparison diagram shown is Figure 5It can be seen from the simulation data shown that the T-type inductor provided in the present application is structurally improved to be composed 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. A smaller layout area can be used in the layout design to realize an inductor device with the same inductance and a higher quality factor. Compared with a 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 is derived by using the even mode extraction and odd mode extraction methods. It is necessary 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 equations (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), a fourth-order polynomial can be obtained:

[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 know 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 band-pass filter provided by the band-pass filter structure shown in the figure, 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, that is, the center end Tap C The coil is conductively connected at the position, and the inner end of 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 first inductor L1 is connected to the inner end point of the first inductor L2, and the first grounding capacitor C 21 The upper end of 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 C 12The 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 of the first inductor L1 is conductively connected; 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, such as Figure 8 As shown, combined Figure 7 It is observed that in this embodiment, the XY plane is parallel to the plane where the grounding layer 3 is located, the Z-axis direction is perpendicular to the grounding 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 grounding layer 3 has a hollow area 31 corresponding to the layout area of ​​the inductor and the 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 in parallel above the grounding 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 grounding 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 grounding layer 3; the capacitor includes a first capacitor C1 and a second capacitor C2, and the first capacitor C1 and the second capacitor C2 both have a first end plate and a second end plate arranged in parallel above the grounding layer 3; the first end plate C11 of the first capacitor C1 forms the first port 1 of the band-pass 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 band-pass 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 band-pass filter with the first inductor L1 and the second inductor L2.

[0065] Further, in this embodiment, the design size of the first inductor L1 is less than or equal to 3.3×10 -5 The conditions and the preset working frequency point are set, that is, the coil length of the first inductor L1 should be less than or equal to the wavelength corresponding to the preset working frequency point and 3.3×10 -5 Similarly, the coil length of the second inductor L1 can also be less than or equal to the wavelength corresponding to the preset operating frequency and 3.3×10 -5 It should be understood that the size-to-wavelength ratio can also be expressed by the ratio of the layout area to the square of the wavelength. When designing the inductance parameters, the coil length is used for calculation to facilitate the parameterized design of the model.

[0066] Furthermore, the capacitor further includes a third capacitor C3 and a fourth capacitor C4, and the third capacitor C3 and the fourth capacitor C4 both have a first end plate and a second end plate arranged in parallel above the ground layer 3. In this embodiment, the third capacitor C3 and the fourth capacitor C4 both use MIM capacitors (Metal-Insulator-Metal, metal-insulator-metal). Fig. 9 This application is based on Figure 8 The schematic diagram of the structure of the fourth capacitor C4 provided by the model shown in FIG. 1 , wherein the second end plate C42 of the fourth capacitor C4 is formed by the first metal plate M1, the via 5 and the second metal plate M2, and the insulating layer Ci is a thin layer disposed between the first end plate C41 of the fourth capacitor C4 ... Figure 8 It can be seen that the second end plate C42 of the fourth capacitor C4 is connected to the grounding layer 3 through the via 5, the metal layer 4 and the grounding column 6; the first section plate C41 of the fourth capacitor C4 and the second end plate C22 of the second capacitor C2 share the same plate, thereby realizing the second grounding capacitor C 22 The first end of the second resonant capacitor C 12 and the first inductor L1. In this embodiment, the structures of the first capacitor C1, the second capacitor C2, and the third capacitor C3 are similar to the structure of the fourth capacitor C4, and are not described in detail.

[0067] Furthermore, the capacitor also includes a fifth capacitor C5, the fifth capacitor C5 having 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 bandpass filter, and when its capacitance parameters are adjusted, the bandpass filter can adjust the passband frequency and out-of-band suppression performance.

[0068] Preferably, the fifth capacitor C5 is an interdigitated capacitor, i.e., a MOM capacitor (Metal-Oxide-Metal), the first end plate C51 of the fifth capacitor C5 is a first interdigitated plate, and the second end plate C52 of the fifth capacitor C5 is a second interdigitated plate. T The bandpass filter has high requirements for device parameter accuracy. When the coupling capacitor uses the MIM capacitor in the SiGe-BiCMOS process, the layout size is too small, and the error control difficulty in the process is large, resulting in a relatively large deviation between the actual capacitance of the coupling capacitor and the designed capacitance. Therefore, in the preferred embodiment, the fifth capacitor C5 uses cross-finger capacitors to design the layout and model, which can further improve the robustness of the bandpass filter. At the same time, since the MOM capacitor can increase the capacitance by setting a multi-layer interdigital plate superposition mode, the relative MIM capacitor increases the capacitance by expanding the plate area, and the use of MOM capacitors can improve the compactness of the device layout when the parameter requirements of the coupling capacitor are large, and reduce the layout area of ​​the bandpass filter. It should be understood that the coupling capacitor in the present embodiment, that is, the fifth capacitor C5 uses cross-finger capacitors to design only as a preferred technical solution, and all capacitors that can achieve improved out-of-band suppression performance and affect passband performance can be used as optional devices for those skilled in the art to design the bandpass filter layout.

[0069] Furthermore, in the above embodiment, the size-to-wavelength ratio of the bandpass filter is less than or equal to 3.3×10 -5 The size-to-wavelength ratio represents the ratio of size to 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 of the bandpass filter.

[0070] Furthermore, the inductor and capacitor in the above embodiment are manufactured by SiGe-BiCMOS process and connected to the ground layer 3. SiGe-BiCMOS process combines SiGe HBT with excellent high-frequency performance with high-integration CMOS process, realizes miniaturization in high-performance and high-frequency applications, and is the preferred process for high-integration design. This process is widely used in RF communication, wireless network, filter design and other fields.

[0071] Fig.10 This application is based on Figure 8 The bandpass filter model shown provides a side view of Fig.10 for Figure 8The model in FIG. 1 is a view obtained along the X-axis direction perpendicular to the ZY plane on the side close to the second port 2, wherein the inner end point L22 of the second inductor L2 is connected to the metal layer 4 through the via 5, and the Figure 8 It can be seen 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 grounding column 6. The outer end point L21 of the second inductor L2 is connected to the metal layer 4 through the via 5. The metal layer 4 then extends to below the central end point L13 of the first inductor L2, and is connected to the central end point L13 of the first inductor L1 through the via 5. Figure 8 It can be seen 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 are in the same plane as the second end plates of the third capacitor C3 and the fourth capacitor C4, and the second end plates of the first capacitor C1 and the second capacitor C2 are in the same plane as the first end plates of the third capacitor C3 and the fourth capacitor C4 and the metal layer 4; the fifth capacitor C5 is an interdigitated capacitor in this embodiment, and its first interdigitated plate and the second interdigitated plate are stacked downward from the plane position of the ground layer 3, and the thickness occupied by the capacitor is equivalent to the thickness of the ground layer 3. It should be noted that Fig. 9 The second port 2 shown in the figure is only shown as a rectangular window, and does not indicate the connection relationship between the second port 2 and the ground layer 3 .

[0072] Fig.11 This application is based on Figure 3 The bandpass filter structure shown and Figure 8 The simulation data diagram of the bandpass filter layout shown in the figure uses C0 = 80fF, C 11 =C 12 =1300fF, C 21 =C 22 =380fF, L1 = 280pH, L2 = 190pH, such as Fig.10 As shown, the transmission coefficient 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 21Characterizing the bandpass frequency characteristics of the bandpass filter, the two transmission zero points of the bandpass filter in this embodiment are respectively at 12 GHz and 16 GHz. In the frequency band of 11 GHz to 17 GHz, the insertion loss is about 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] Combination Figure 7 and Fig.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, and the corresponding wavelength is 25 mm. It can be seen that 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] Fig.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 tuning 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 Fig.11 The simulation data shown is the same as Fig.12 As shown in the figure, the three simulation curves show the change of passband and out-of-band suppression performance when the coupling capacitance C0 increases or decreases. When the coupling capacitance C0 increases from 50fF to 110fF, the low-frequency extreme point of the passband is still 12GHz, and the high-frequency extreme point decreases from 17GHz to 16GHz; the out-of-band suppression at 22GHz increases from 8.7dB to 42.5dB; and the out-of-band suppression above 30GHz is reduced by about 6dB overall. According to the above data analysis, increasing the coupling capacitance C0 will reduce the high-frequency extreme point of the filter's passband, effectively improve the stopband suppression at the near end of the high-frequency out-band, and to a certain extent deteriorate the stopband suppression at the far end of the high-frequency out-band. Applying this feature, according to the actual needs of the communication link, the optimal range of the stopband can be designed at the target frequency band.

[0075] The introduction provided in the above embodiments is only used to help understand the method, structure and core idea of ​​the present application. For ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A bandpass filter structure, characterized in that: include: A first port and a second port; A T-shaped inductor, consisting of a first inductor and a second inductor, wherein 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; A capacitor network, comprising a first resonant capacitor and a second resonant capacitor, wherein 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; Among them, 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 according to claim 1, characterized in that: The capacitor network also includes a first grounding capacitor and a second grounding capacitor; The first grounding capacitor and the second grounding capacitor each have a first end and a second end; The first end of the first grounded capacitor is coupled between the first resonant capacitor and the first inductor, and the second end is coupled to the reference ground; A first end of the second grounding capacitor is coupled between the second resonant capacitor and the first inductor, and a second end of the second grounding capacitor is coupled to a reference ground.

3. The bandpass filter structure according to claim 1, characterized in that: The capacitor network also includes a coupling capacitor; The coupling capacitor is coupled between the first port and the second port.

4. A bandpass filter, characterized in that: include: An inductor, a capacitor and a ground layer, wherein 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, wherein the first inductor and the second inductor are both planar coil inductors, one end of the planar coil is an outer terminal, and the other end is an inner terminal, and the planar coil is arranged in parallel above the ground layer; The first inductor also has a central connection point connected to an outer end point of the second inductor, and an inner end point of the second inductor is connected to the ground layer; The capacitor comprises a first capacitor and a second capacitor, each of the first capacitor and the second capacitor having 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 is connected to an 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 is connected to an inner end point of the first inductor; The first capacitor and the second capacitor serve as resonant capacitors and together with the first inductor and the second inductor form a resonant structure of the bandpass filter.

5. The bandpass filter according to claim 4, characterized in that: The capacitor further includes a third capacitor and a fourth capacitor, each of the third capacitor and the fourth capacitor having a first end plate and a second end plate disposed 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 grounding capacitors to provide a low-impedance grounding point for the band-pass filter.

6. The bandpass filter according to claim 4, characterized in that: The capacitor further includes a fifth capacitor, the fifth capacitor having a first end plate and a second end plate parallel to the ground layer, the first end plate being connected to the first end plate of the first capacitor, and the second end plate being 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. When the capacitance parameter of the fifth capacitor is adjusted, the bandpass filter can adjust the passband frequency and out-of-band suppression performance.

7. The bandpass filter according to claim 6, characterized in that The fifth capacitor is an interdigitated capacitor, the first end plate is a first interdigitated plate, the second end plate is a second interdigitated plate, and the multilayer structure of the first interdigitated plate and the second interdigitated plate is located below the plane where the ground layer is located.

8. The bandpass filter according to claim 4, characterized in that: The size-to-wavelength ratio of the first inductor is less than or equal to 3.3×10 -5 The size-to-wavelength ratio represents the ratio of the size to the wavelength, wherein the size represents the coil length 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 bandpass filter.

9. The bandpass filter according to claim 4, characterized in that: The size-to-wavelength ratio of the second inductor is less than or equal to 3.3×10 -5 The size-to-wavelength ratio represents the ratio of the size to the wavelength, wherein the size represents the coil length corresponding to the effective inductance value of the second inductor, and the wavelength represents the signal wavelength corresponding to the center frequency point of the bandpass filter.

10. The bandpass filter according to any one of claims 4 to 9, characterized in that: The size-to-wavelength ratio of the bandpass filter is less than or equal to 3.3×10 -5 The size-to-wavelength ratio represents the ratio of size to 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 of the bandpass filter.

11. The bandpass filter according to any one of claims 4 to 9, characterized in that: The inductor and the capacitor are manufactured by SiGe-BiCMOS process and connected to the ground layer.

12. The bandpass filter according to any one of claims 4 to 9, characterized in that: When the preset operating frequency of the bandpass filter is 12 GHz, the width of the layout occupied by the inductor and the capacitor is less than or equal to 130 μm and the length is less than or equal to 160 μm, or the area is less than or equal to 20800 μm. 2 .

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