A miniaturized, high-selectivity bandpass filter for multi-path transmission

Abstract

This invention discloses a miniaturized, highly selective bandpass filter chip for multipath transmission, comprising an input port, an output port, a port matching network, five octagonal inductors (L1~L5), seven MIM capacitors (C1~C7), and one ground inductor Ls1. It includes a conventional filtering path (Path A) and a compact coupling path (Path B) connected in parallel between the input and output ports. The port matching network is composed of capacitors C4 and C7. Path A forms three resonant units by connecting capacitors C1~C3 in parallel with inductors L1~L3, which, together with capacitor C5, inductor L4, and ground inductor Ls1, constitute a basic bandpass structure and generate low-frequency transmission zeros. Path B forms a compact coupling network by connecting symmetrically coupled inductor L5 in parallel with capacitor C6, utilizing mutual inductance coupling to generate additional high-frequency transmission zeros. The filter chip is implemented using GaAs-based IPD technology to achieve fully lumped component integration, possessing advantages such as compact structure, high selectivity, stable performance, and high integration density.

Description

Technical Field

[0001] This invention relates to the field of radio frequency filter technology, and in particular to a miniaturized, highly selective bandpass filter for multipath transmission, specifically applied to miniaturized radio frequency front-end devices such as 5G terminals, portable WiFi devices, and IoT modules that have strict requirements for selectivity, size, and integration. Background Technology

[0002] With the rapid development of technologies such as 5G communication, the Internet of Things, and portable electronic devices, the electromagnetic interference faced by radio frequency front-end systems is becoming increasingly complex, placing higher demands on the selectivity and stopband coverage of filtering devices. At the same time, the trend towards miniaturization of equipment requires filtering devices to balance low insertion loss, wide stopband suppression, and high selectivity within a limited space, which has become a core technical challenge in the industry.

[0003] In existing RF filters, traditional single-channel lumped filters struggle to simultaneously achieve wide stopband and high selectivity. Optimization using only a single channel's resonant unit limits the number of transmission zeros, resulting in insufficient suppression of interference signals across a wide frequency band. Distributed filters, while offering better bandwidth performance, are too large to meet miniaturization integration requirements. Some improved filters attempt to increase the filter order to enhance selectivity, but this leads to a significant increase in insertion loss, and the stopband extension capability remains limited, making them unsuitable for multi-band interference scenarios.

[0004] Therefore, developing a highly selective bandpass filter that achieves multiple transmission zeros through innovative topology, expands the stopband bandwidth through multi-path collaboration, and simultaneously achieves miniaturization and low insertion loss is key to solving current technical pain points and is of great significance for promoting the performance upgrade of miniaturized RF front-ends. Summary of the Invention

[0005] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a miniaturized, highly selective bandpass filter for multipath transmission. By using a dual parallel filtering channel design to generate multiple transmission zeros, it achieves a synergy between high selectivity and wide stopband suppression, while ensuring miniaturized integration and low insertion loss, thus solving the performance limitations of existing filters in complex interference scenarios.

[0006] Technical solution: A miniaturized, highly selective bandpass filter for multipath transmission includes: octagonal inductors L1-L4, compactly coupled inductor L5, capacitors C1-C7, and grounding inductor Ls1. Capacitor C1 and inductor L1 are connected in parallel to form resonator one; capacitor C2 and inductor L2 are connected in parallel to form resonator two; and capacitor C3 and inductor L3 are connected in parallel to form resonator three. One end of capacitor C5 is connected to the input terminal of resonator one, and the other end is connected to the input terminal of resonator two. One end of inductor L4 is connected to the input terminal of resonator two, and the other end is connected to the input terminal of resonator three. The output terminals of the three resonators are short-circuited to each other, forming a basic bandpass structure. One end of grounding inductor Ls1 is connected to the common node of the output terminals of resonators one and two, and the other end is grounded.

[0007] The coupled inductor pair consists of two symmetrically arranged coupled inductors L5 with equal inductance values, and there is a mutual inductance M between the two inductors; the capacitor C6 is connected in parallel with the coupled inductor pair to form a compact coupled network, forming a second parallel filter channel; through the mutual inductance coupling effect and capacitor impedance adjustment, an additional transmission zero is generated outside the high-frequency band, realizing high-frequency stopband extension.

[0008] One end of the matching capacitor C4 is connected to the input port, and the other end is connected to the input of both Path A and Path B. One end of the matching capacitor C7 is connected to the output port, and the other end is connected to the output of both Path A and Path B.

[0009] Furthermore, all inductors L1 to L5 adopt an octagonal structure design, with traces only running in the middle and top metal layers. This structure improves the Q value by reducing the parasitic capacitance and resistance of the inductors, ensuring the accurate and stable resonance point of the resonant unit, providing a reliable basis for the formation of transmission zeros and poles, and reducing the impact of parasitic losses on in-band flatness.

[0010] Furthermore, in the conventional filter channel Path A, resonators 1, 2, and 3 form three independent resonant poles through the parameter combination of capacitors C1~C3 and inductors L1~L3, which together constitute a wideband pass response. Capacitor C5 and inductor L4 adjust the pole spacing through impedance coupling to make the passband curve smoother. The impedance characteristics of ground inductor Ls1 are coordinated with those of resonators 1 and 2. When the frequency is lower than the self-resonant frequency of resonator 1, resonator 1 becomes inductive and forms a series LC notch structure with ground inductor Ls1, generating a stable transmission zero outside the low-frequency band and enhancing low-frequency interference suppression.

[0011] Furthermore, when the frequency is higher than the passband upper limit of Path A, the mutual inductance effect of the coupling inductor L5 makes the channel as a whole inductive, forming a parallel LC notch structure with capacitor C6, thus creating the first high-frequency transmission zero. At the same time, the mutual inductance coupling effect of the coupling inductor pair changes the impedance phase of the channel, and works in conjunction with the capacitive reactance of capacitor C6 to form a second additional transmission zero at a higher frequency band. This, combined with the low-frequency zero of Path A, achieves high selectivity across the entire frequency band.

[0012] Furthermore, the port matching capacitors C4 and C7 are designed with precise capacitance values ​​to achieve efficient matching between the input port, the output port and the Z0 characteristic impedance. This design avoids dual-path signal reflection, ensures that the pole and zero characteristics of the two channels are not affected by the signal, guarantees the suppression effect of multiple transmission zeros and the stability of poles, and improves the signal transmission efficiency within the passband.

[0013] Furthermore, Path A, through the impedance coordination of the grounding inductor Ls1 and the resonant unit, forms at least one transmission zero outside the low-frequency band; Path B, by utilizing the mutual inductance effect of the coupled inductor pair and the parallel adjustment of capacitor C6, forms at least two additional transmission zeros outside the high-frequency band. The reasonable distribution of multiple transmission zeros across the entire frequency band significantly improves the ability to suppress out-of-band interference signals, giving the filter high selectivity.

[0014] Furthermore, Path A focuses on basic bandpass characteristics and low-frequency suppression, while Path B focuses on high-frequency stopband extension. The impedance characteristics of the two channels complement each other, ensuring low-loss transmission of signals within the passband while achieving comprehensive suppression of wide-band interference signals, thus resolving the contradiction between "passband loss" and "stopband suppression" in traditional single-channel filters.

[0015] Furthermore, all inductors L1 to L5 adopt an octagonal structure design, which has a higher space utilization rate compared to traditional square or round inductors. By optimizing the metal line width and spacing, the inductor Q value is improved and parasitic losses are reduced. Capacitors C1 to C7 adopt a MIM structure, which is small in size and high in precision, ensuring the accuracy of dual-path impedance adjustment.

[0016] Furthermore, based on GaAs-based IPD technology, it achieves integrated full-lumped components, a compact dual-path layout, no distributed transmission line structure, and a chip physical size of only 1030μm×620μm, meeting the integration requirements of miniaturized RF front-end.

[0017] Beneficial effects Compared with existing technologies, the present invention has the following significant advantages: 1. By generating multiple transmission zeros through dual-path collaboration, a strong suppression notch structure is formed both outside the low-frequency band and outside the high-frequency band, which has excellent suppression capability for interference signals in a wide frequency band and its selectivity is significantly better than that of traditional single-channel filters.

[0018] 2. The low-frequency suppression of Path A and the high-frequency extension of Path B complement each other, greatly expanding the stopband coverage and effectively filtering out multi-band interference signals, making it suitable for complex electromagnetic environments.

[0019] 3. The optimized structure of the octagonal inductor and MIM capacitor, combined with the integration advantages of the IPD process, results in a chip size of only 1030μm×620μm, while ensuring low insertion loss in the passband, meeting the performance and space requirements of miniaturized devices.

[0020] 4. The dual-path topology design is simple, the component parameters can be flexibly adjusted, and it is compatible with PCB mounting or IPD process mass production. It can be directly adapted to various RF front-end scenarios such as 5G terminals, portable WiFi devices, and IoT modules, and has a wide range of applications. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the circuit structure of the present invention; Figure 2 This is a schematic diagram of the layout of the present invention (size: 1030μm × 620μm). Figure 3 The graph shows the EM simulation test results of this invention (horizontal axis is frequency / GHz, vertical axis is amplitude / dB, including S). 11 (Return loss) and S 21 (Insertion loss / out-of-band rejection) curve, with the locations of multiple transmission zeros marked. Detailed Implementation

[0022] The present invention will now be explained in more detail with reference to the accompanying drawings.

[0023] A miniaturized, highly selective bandpass filter for multipath transmission, fabricated using GaAs-based IPD technology, has the following circuit structure: Figure 1 As shown, it mainly includes input ports, output ports, port matching networks (C4, C7), traditional filter channels (Path A), compact coupling channels (Path B), and grounding inductor Ls1. All components are integrated within a 1030μm × 620μm chip layout (e.g., Figure 2 (As shown).

[0024] Capacitor C1 and inductor L1 are connected in parallel to form resonator one; capacitor C2 and inductor L2 are connected in parallel to form resonator two; and capacitor C3 and inductor L3 are connected in parallel to form resonator three. One end of capacitor C5 is connected to the input terminal of resonator 1, and the other end is connected to the input terminal of resonator 2. One end of inductor L4 is connected to the input terminal of resonator 2, and the other end is connected to the input terminal of resonator 3. The output terminals of resonator 1, resonator 2, and resonator 3 are connected. This structure constitutes the traditional filter channel Path A. The grounding suppression branch is a grounding inductor Ls1, one end of which is connected to the connection node between the output terminals of resonator one and resonator two, and the other end is grounded. The coupled inductor pair consists of two coupled inductors L5 with equal inductance values ​​arranged symmetrically, with mutual inductance M between the two inductors. Capacitor C6 is connected in parallel with the compact coupled inductor pair to form a compact coupling channel Path B. One end of the matching capacitor C4 is connected to the input port, and the other end is connected to the input of both Path A and Path B. One end of the matching capacitor C7 is connected to the output port, and the other end is connected to the output of both Path A and Path B. The traditional filtering channel Path A and the compact coupling channel Path B form a dual parallel filtering channel, which is connected in parallel between the matching capacitors C4 and C7.

[0025] Furthermore, both the input and output ports of the filter adopt a ground-signal-ground (GSG) structure, with the center signal patch and the two side ground patches symmetrically distributed. The ground patches are reliably connected to the bottom ground plane through metallized grounding holes. When a signal is input from the input port, the matching capacitor C4 evenly distributes the signal to Path A and Path B. The impedance characteristics of the two channels work together to ensure that the signal phase in the passband is consistent and the loss is superimposed and canceled. Meanwhile, the out-of-band interference signal forms a suppression superposition at the low-frequency transmission zero of Path A and the high-frequency transmission zero of Path B, further enhancing the high selectivity, while avoiding the influence of signal reflection between channels on pole stability.

[0026] The compact coupling channel (Path B) of this invention does not use the traditional single inductor structure. Instead, it uses two coupling inductors L5 with equal inductance values ​​to form a coupling inductor pair. By reducing the distance between the two inductors, the mutual inductance M effect is enhanced. Combined with the parallel MIM capacitor C6, a compact coupling network is formed, which realizes the accurate generation of high-frequency out-of-band additional transmission zeros.

[0027] When the frequency is lower than the self-resonant frequency of resonator one in Path A, resonator one exhibits inductive characteristics as a whole. It forms a series LC circuit with the ground inductor Ls1, creating a stable notch filter structure and generating the first transmission zero outside the low-frequency band, effectively suppressing interference signals in this frequency band. Similarly, the impedance coupling effect of resonators two and three with capacitor C5 and inductor L4 further optimizes the low-frequency suppression curve, significantly improving the suppression depth of the transmission zero.

[0028] When the frequency is higher than the passband upper limit of Path A, the mutual inductance effect of the coupled inductor L5 in Path B becomes prominent, making the coupled inductor inductive to the whole. It forms a parallel LC circuit with the parallel capacitor C6, forming the first additional transmission zero outside the high-frequency band. This transmission zero complements the high-frequency cutoff characteristic of the passband of Path A, blocking the transmission path of high-frequency interference signals.

[0029] As the frequency continues to increase, the mutual inductance coefficient M of the coupling inductor L5 changes dynamically, forming a secondary impedance resonance with the capacitive reactance of capacitor C6, thus creating a second additional transmission zero at a higher frequency. The distance between the two high-frequency transmission zeros is precisely adjusted by the number of turns of the coupling inductor L5 and the capacitance of capacitor C6, achieving wide-range interference suppression at high frequencies.

[0030] The passband range of the filter is determined by the resonant poles of the three resonators in Path A. The resonant frequencies of resonators 1, 2, and 3 are set by the combination of their respective capacitors C1~C3 and inductors L1~L3. The pole distribution of the three forms a wideband pass response, ensuring low-loss transmission of the target signal.

[0031] The specific values ​​of each inductor and capacitor are given in this embodiment, as shown in Table 1: Table 1. Values ​​of Inductors (nH) and Capacitors (pF)

[0032] Figure 3 The graph shows the EM simulation test results of the filter of this invention at room temperature (the horizontal axis is frequency / GHz, the vertical axis is S-parameter (dB), and the dashed line represents S). 11 (Return loss) curve, the solid line represents S 21 (Insertion loss / out-of-band rejection curve).

[0033] This embodiment uses electromagnetic (EM) simulation software to verify the filter performance, and the results correspond to... Figure 3 The curve shown: S in the figure 21 The high-amplitude region of the curve (solid line) represents the filter's passband. Within this range, the amplitude is close to 0dB, indicating low signal transmission loss and strong penetration within the passband. This perfectly aligns with the "passband signal superposition enhancement" characteristic of dual-path collaborative design; simultaneously, S 11 The amplitude of the curve (dashed line) in the passband is less than -20dB, which proves that the capacitance design of the port matching network is accurate, the matching degree between the input and output ports and the characteristic impedance is high, and the signal reflection is effectively suppressed.

[0034] from Figure 3 S 21The curves show deep valley regions (amplitude below -60dB) on both sides of the passband. These regions correspond to the transmission zero suppression effect of the filter: the deep valley near 4GHz on the left side of the passband is formed by the impedance cooperation of the grounding inductor Ls1 and the resonant unit in the conventional filter channel (Path A). It is a transmission zero outside the low-frequency band and can effectively block interference signals in this frequency band; the deep valley near 8GHz and 10GHz on the right side of the passband is formed by the mutual inductance effect of the coupling inductor L5 and the parallel effect of the capacitor C6 in the compact coupling channel (Path B). It is an additional transmission zero outside the high-frequency band, realizing multi-interference point coverage in the high-frequency band. The distribution of multiple zeros directly reflects the high selectivity of the filter.

[0035] Combination Figure 3 Based on the curve characteristics, the passband of this filter accurately covers the target frequency band (around 6GHz), and the out-of-band suppression maintains a level of ≥30dB across a wide frequency range of 2~12GHz, fully adapting to the interference suppression requirements of scenarios such as 5G terminals and portable WiFi devices; at the same time, S 11 With S 21 The curve trend is consistent with the design logic of the dual-path topology, proving that the design of the component parameters and layout meets the stability requirements and can ensure the reliable operation of the filter in practical applications.

[0036] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A miniaturized, highly selective bandpass filter for multipath transmission, characterized in that, include: Octagonal inductors L1~L4, compact coupled inductor L5, capacitors C1~C7 and grounding inductor Ls1; Capacitor C1 and inductor L1 are connected in parallel to form resonator one; capacitor C2 and inductor L2 are connected in parallel to form resonator two; and capacitor C3 and inductor L3 are connected in parallel to form resonator three. One end of capacitor C5 is connected to the input terminal of resonator 1, and the other end is connected to the input terminal of resonator 2. One end of inductor L4 is connected to the input terminal of resonator 2, and the other end is connected to the input terminal of resonator 3. The output terminals of resonator 1, resonator 2, and resonator 3 are connected. This structure constitutes the traditional filter channel Path A. The grounding suppression branch is a grounding inductor Ls1, one end of which is connected to the connection node between the output terminals of resonator one and resonator two, and the other end is grounded, so that Path A generates a transmission zero outside the low frequency band. The coupled inductor pair is composed of two coupled inductors L5 with equal inductance values ​​arranged symmetrically. There is a mutual inductance M between the two inductors. The capacitor C6 is connected in parallel with the compact coupled inductor pair to form a compact coupled channel Path B, which generates an additional transmission zero outside the high frequency band of Path B. One end of the matching capacitor C4 is connected to the input port, and the other end is connected to the input of both Path A and Path B. One end of the matching capacitor C7 is connected to the output port, and the other end is connected to the output of both Path A and Path B. The traditional filtering channel Path A and the compact coupling channel Path B form a dual parallel filtering channel, which is set in parallel between the matching capacitors C4 and C7. The superposition of multiple transmission zeros achieves high selectivity.

2. The miniaturized, highly selective bandpass filter for multipath transmission according to claim 1, characterized in that, All inductor components adopt an octagonal structure design, with traces only running on the middle and top metal layers. By optimizing the metal line width and spacing, the inductance Q value is improved and parasitic losses are reduced.

3. The miniaturized, highly selective bandpass filter for multipath transmission according to claim 1, characterized in that, In the conventional filter channel Path A, resonators one, two, and three correspond to three resonant points. Wideband pass response is achieved by adjusting the impedance of capacitor C5 and inductor L4. Grounding inductor Ls1 forms a low-frequency suppression notch structure to enhance the suppression effect of transmission zeros outside the low-frequency band.

4. The miniaturized, highly selective bandpass filter for multipath transmission according to claim 1, characterized in that, In the compact coupling channel Path B, the mutual inductance coupling effect of the symmetrical coupling inductor L5 and the impedance adjustment of the capacitor C6 work together to form multiple additional transmission zeros outside the high-frequency band. These zeros are superimposed on the low-frequency transmission zeros of Path A, achieving full-band wide stopband suppression and high selectivity.

5. The miniaturized, highly selective bandpass filter for multipath transmission according to claim 1, characterized in that, The port matching network consists of matching capacitors C4 and C7. Through precise capacitance design, the input port, output port and Z0 characteristic impedance are efficiently matched, ensuring the coordinated transmission efficiency of dual-path signals.

6. The miniaturized, highly selective bandpass filter for multipath transmission according to claims 1-5, characterized in that, The filter chip has a physical size of 1030μm×620μm, adopts a fully lumped component integrated design, has no distributed transmission line structure, and a dual-path compact layout to meet the requirements of miniaturization integration.

7. The miniaturized, highly selective bandpass filter for multipath transmission according to claim 1, characterized in that, The capacitors C1 to C7 all adopt a GaAs-based MIM (metal-insulator-metal) capacitor structure to ensure the impedance matching accuracy of the dual path and the stability of the transmission zero point.

8. The miniaturized, highly selective bandpass filter for multipath transmission according to claim 1, characterized in that, The filter's structure is compatible with PCB mounting or IPD processes for mass production, and its standardized packaging design allows it to be integrated into RF front-end applications such as 5G terminals, portable WiFi devices, and IoT modules.

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