Wide-stop-band 5G frequency band LTCC filter based on frequency-variable coupling technology

Abstract

The invention belongs to the technical field of band-pass filters, and discloses a wide-stop-band 5G frequency band LTCC filter based on a frequency-variable coupling technology, and the frequency-variable coupling technology is used in the design, and four transmission zeros are introduced in different frequency bands, namely, a near-end stop band and a far-end stop band; according to the LTCC band-pass filter, the transmission zeros generated on the two sides of the pass band improve the selectivity of the filter, two transmission zeros are introduced into the far-end stop band, the stop band bandwidth of the LTCC band-pass filter is improved, and the LTCC miniaturized filter with the large bandwidth and high selectivity of the pass band of 3-5 GHz and the ultra-wide stop band of 15 GHz is achieved for the N77 + N79 frequency band of the 5G application frequency band.

Description

Technical Field

[0001] This invention relates to the field of bandpass filter technology, and more specifically to a wide-stopband 5G band LTCC filter based on frequency-variable coupling technology. Background Technology

[0002] With the rapid development of wireless communication systems, radio frequency (RF) filters, as key components for signal selection and interference suppression, face increasingly stringent performance requirements. Planar bandpass filters, due to their compact structure, ease of integration, and excellent microwave characteristics, have become an important part of modern communication systems. However, achieving wide-bandwidth, high-selectivity, and low-insertion-loss filter designs while simultaneously miniaturizing remains a significant research challenge. Low-temperature co-fired ceramic (LTCC) technology, with its multilayer integration capabilities, excellent thermal stability, and three-dimensional circuit layout advantages, provides an ideal solution for realizing high-performance RF filters. Current LTCC filters are limited by the construction method of transmission zeros, hindering the flexible implementation of high selectivity and wideband suppression; therefore, an LTCC bandpass filter with an ultra-wide stopband is urgently needed.

[0003] Existing technologies and their problems: A paper titled "Compact5G n77 Bandpass Filter Utilizing LTCC Heterogeneous Integration Technology," presented at the IEEE Asia-Pacific Conference on Antennas and Propagation, introduces transmission zeros on both sides of the passband using a cross-coupling method. While this method improves the filter's roll-off factor, it fails to meet the requirements for a wide stopband.

[0004] A published patent for an LTCC bandpass filter and its fabrication method uses inductive coupling to achieve flexible adjustment of the transmission zeros, introducing two transmission zeros on each side of the passband to improve the filter's selectivity. However, the generated transmission zeros only focus on near-end suppression and do not achieve a wide stopband.

[0005] A published patent for an ultra-miniature high-Q bandpass filter based on LTCC technology describes how, by rationally selecting the equivalent element values ​​of the filter resonant unit and optimizing the coupling relationship of its equivalent elements in vertical space, transmission zeros can be introduced near both ends of the passband to achieve a high rectangular coefficient. However, its vertical coupling is mainly used to construct transmission zeros at fixed positions, and the position of the transmission zeros cannot be independently controlled, thus failing to achieve transmission zeros in the far-end stopband. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems by providing a wide-stopband 5G band LTCC filter based on frequency-variable coupling technology. By employing frequency-variable coupling technology in the design, four transmission zeros are introduced in different frequency bands, namely the near-end stopband and the far-end stopband. The transmission zeros generated on both sides of the passband improve the filter's selectivity, and the introduction of two transmission zeros in the far-end stopband enhances the stopband bandwidth of the LTCC bandpass filter. For the N77+N79 frequency band in 5G applications, this invention achieves a miniaturized LTCC filter with a large bandwidth of 3-5GHz, high selectivity, and an ultra-wide stopband of 15GHz.

[0007] The technical solution adopted in this invention is as follows: A wide-stopband 5G band LTCC filter based on frequency-conversion coupling technology, the bandpass filter includes an LTCC ceramic body, external electrodes, and several circuit layers distributed within the LTCC ceramic body. The external electrode is provided in three parts, with two external electrodes distributed on both sides of the LTCC ceramic body and the other arranged at the bottom of the LTCC ceramic body. The external electrode is connected to the metal ground and the circuit layer through metal vias.

[0008] Furthermore, the circuit layers, from bottom to top, include a GND layer and five other circuit layers, specifically: The GND layer includes a metal ground located at the bottom of the LTCC ceramic body; The first circuit layer includes five metal equivalent capacitor sheets, namely the first capacitor, the second capacitor, the third capacitor, the fourth capacitor and the fifth capacitor. The GND layer and the first circuit layer form a plate-like capacitor structure. The second circuit layer includes a mirror-distributed sixth capacitor, a seventh capacitor, and a metal ground layer. The third circuit layer includes a fourth inductor, a fifth inductor, a sixth inductor, and a seventh inductor; The fourth circuit layer includes the second inductor and the ninth inductor, and also includes parts of the circuitry of the fourth, fifth, sixth, and seventh inductors; The fifth circuit layer includes a first inductor, a third inductor, an eighth inductor, and a tenth inductor, with the first inductor and the tenth inductor connected to the external electrodes on both sides of the LTCC ceramic body; The above components are all connected by metal through-holes across layers and corresponding connecting lines.

[0009] Furthermore, slots are mirror-image-opened on both sides of the GND layer, and the slots are respectively provided with a first high-frequency suppression capacitor and a second high-frequency suppression capacitor.

[0010] Furthermore, the first high-frequency suppression capacitor is connected to the first inductor through the first metal via, the second inductor is connected to the metal ground and the first capacitor through the second and third metal vias respectively, the fourth inductor is connected to the metal ground through the fourth metal via, and the fourth inductor is connected to the second capacitor through the fifth metal via, the third capacitor and the fifth inductor are connected through the sixth metal via, the fifth inductor, the metal ground supplement layer, the ninth inductor and the eighth inductor are grounded through the seventh, eighth, and ninth metal vias and the eleventh metal via respectively, the eighth inductor is also connected to the fifth capacitor through the tenth metal via, and the second high-frequency suppression capacitor is connected to the tenth inductor through the twelfth metal via.

[0011] Furthermore, a portion of the structure of the second and third inductors overlaps in the vertical direction to form an adjustable electromagnetic coupling. The electromagnetic coupling point is connected to the sixth capacitor to form a parallel resonant structure, generating a transmission zero point at a low frequency in the near band. The structures of the eighth and ninth inductors overlap vertically to form a controlled electromagnetic coupling. The electromagnetic coupling is connected to the seventh capacitor to form a parallel resonant structure, generating a transmission zero at a near-band high frequency.

[0012] Furthermore, by adjusting the proportions of overlapping and non-overlapping portions of the second and third inductors, and the eighth and ninth inductors, the positions of the transmission zero points at near-band low frequencies and near-band high frequencies can be independently controlled.

[0013] Furthermore, the side portions of the external electrodes on both sides of the LTCC ceramic body are respectively connected to the first inductor and the tenth inductor to form a signal path; the bottom portions of the external electrodes on both sides of the LTCC ceramic body are respectively coupled to the first high-frequency suppression capacitor and the second high-frequency suppression capacitor in the vertical direction to form another signal path. The two signal paths form a parallel resonant structure, which can form another pair of independent and controllable far-end suppression transmission zeros.

[0014] Furthermore, all inductor elements are planar spiral coil inductors. As described above, due to the adoption of the above technical solution, the beneficial effects of this invention are: The bandpass filter of this invention introduces independently controllable transmission zeros at the near end of the passband and the far end of the high frequency range through frequency-variable coupling technology, thereby realizing a large bandwidth, high selectivity, and ultra-wide stopband LTCC bandpass filter with a passband of 3-5GHz.

[0015] The bandpass filter of this invention is based on a frequency-variable coupling structure, which enables independent and flexible control of the transmission zero position and avoids the parasitic effect problem caused by cross-coupling.

[0016] The bandpass filter of this invention utilizes LTCC multilayer integration technology and electromagnetic coupling formed by vertically overlapping metal coils, which reduces the space occupied by the actual metal structure and achieves further miniaturization of the filter while maintaining excellent performance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the packaging structure of the bandpass filter of the present invention; Figure 2 This is a three-dimensional structural diagram of the internal component arrangement of the bandpass filter of the present invention; Figure 3 This is a schematic diagram of the internal metal circuit layer of the bandpass filter of the present invention; Figure 4 This is a three-dimensional structural schematic diagram of the internal component arrangement of the bandpass filter of the present invention from another perspective; Figure 5 This is a front view schematic diagram of the internal electrical component arrangement of the bandpass filter of the present invention; Figure 6 This is a schematic diagram of the bottom assembly disk of the bandpass filter of the present invention; Figure 7 This is a schematic diagram of the vertical electromagnetic coupling structure of the internal metal coil of the bandpass filter of the present invention; Figure 8 This is a schematic diagram of the circuit principle of the bandpass filter of the present invention; Figure 9 This is a simulation S-parameter curve of the bandpass filter model of the present invention.

[0018] In the diagram, 1-LTCC ceramic body, 2-metal ground, 3-first capacitor, 4-second capacitor, 5-third capacitor, 6-fourth capacitor, 7-fifth capacitor, 8-sixth capacitor, 9-seventh capacitor, 10-first inductor, 11-second inductor, 12-third inductor, 13-fourth inductor, 14-fifth inductor, 15-sixth inductor, 16-seventh inductor, 17-eighth inductor, 18-ninth inductor, 19-tenth inductor, 20-first high-frequency suppression capacitor, 21-second high-frequency suppression capacitor. Capacitor, 22-First external electrode, 23-Second external electrode, 24-External ground electrode plate, 25-Metal ground supplement layer, 26-First metal via, 27-Second metal via, 28-Third metal via, 29-Fourth metal via, 30-Fifth metal via, 31-Sixth metal via, 32-Seventh metal via, 33-Eighth metal via, 34-Ninth metal via, 35-Tenth metal via, 36-Eleventh metal via, 37-Twelfth metal via. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings.

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Example Compared with the transmission zeros generated by frequency-varying coupling in this embodiment, the transmission zeros generated by existing cross-coupling cannot be controlled independently and are not flexible enough. Furthermore, in physical implementation, the cross-coupling elements are prone to parasitic effects that affect the high-frequency far-end suppression of the filter.

[0022] Existing filters do not address high-frequency far-end suppression, and their cross-coupling and ability to introduce transmission zeros only in the near band cannot meet the high-frequency far-end suppression requirements. The frequency-variable coupling structure in this embodiment can achieve transmission zeros at high-frequency far ends and suppress parasitics.

[0023] This embodiment of the bandpass filter uses a frequency-variable coupling structure, where the coupling coefficient is a function of frequency. It can produce distinctly different and controllable coupling effects in different frequency bands, such as the near-end stopband (2GHz, 6GHz) and the far-end stopband (above 10GHz), thereby independently and flexibly introducing transmission zeros at specific locations. This allows the LTCC bandpass filter to achieve both high near-band selectivity and wide stopband suppression; the specific structure is as follows: like Figure 1 and Figure 4 As shown, this embodiment provides a wide-stopband 5G band LTCC filter based on frequency-variable coupling technology, including an LTCC ceramic body 1 and a metal ground 2. Two external electrodes are provided on both sides of the LTCC ceramic body 1, including a first external electrode 22 and a second external electrode 23. The external electrode at the bottom of the LTCC ceramic body includes an external ground electrode piece 24; as shown... Figure 6 The metal ground 2 shown is located at the bottom layer inside the ceramic body, which is the GND layer. The GND layer and the metal equivalent capacitance sheet of the first circuit layer above it form a parallel plate capacitor structure, as shown. Figure 2 , Figure 3 and Figure 5The first circuit layer includes a first capacitor 3, a second capacitor 4, a third capacitor 5, a fourth capacitor 6, and a fifth capacitor 7; the second circuit layer above the first circuit layer contains a sixth capacitor 8, a seventh capacitor 9, and a metal ground layer 25; the third circuit layer above the second circuit layer contains a fourth inductor 13, a fifth inductor 14, a sixth inductor 15, and a seventh inductor 16; the fourth circuit layer above the third circuit layer also contains portions of the circuits of the inductors in the third circuit layer, and the fourth circuit layer also contains a second inductor 11 and a ninth inductor 18; in the fourth circuit layer... The fifth circuit layer above the circuit layer is equipped with a first inductor 10, a third inductor 12, an eighth inductor 17, and a tenth inductor 19. The first inductor 10 and the tenth inductor 19 are connected to the first external electrode 22 and the second external electrode 23 on both sides of the LTCC ceramic body 1. The bottom of the LTCC ceramic body 1 has an external ground electrode plate 24. The first high-frequency suppression capacitor 20 and the second high-frequency suppression capacitor 21 are mirror-distributed on the left and right sides inside the LTCC ceramic body 1, located at the slot of the GND layer. The above components are connected to each other through metal vias across layers and corresponding connecting lines.

[0024] The first high-frequency suppression capacitor 20 is connected to the first inductor 10 through the first metal via 26. The second inductor 11 is connected to the metal ground 2 through the second metal via 27. The second inductor 11 is connected to the first capacitor 3 through the third metal via 28. The fourth inductor 13 is connected to the metal ground 2 through the fourth metal via 29 and is also connected to the second capacitor 4 through the fifth metal via 30. The third capacitor 5 and the fifth inductor 14, located in the middle of the filter, are connected through the sixth metal via 31. The fifth inductor 14 is grounded through the seventh metal via 32. The metal ground supplement layer 25 is grounded through the eighth metal via 33. The ninth inductor 18 is grounded through the ninth metal via 34. The eighth inductor 17 is grounded through the eleventh metal via 36 and is connected to the fifth capacitor 7 through the tenth metal via 35. The second high-frequency suppression capacitor 21 is connected to the tenth inductor 19 through the twelfth metal via 37. The sixth inductor 15 is connected in series between the fifth inductor 16 and the fifth capacitor 7.

[0025] In this embodiment, all inductors are planar spiral coil inductors.

[0026] like Figure 7 and Figure 8As shown, a portion of the second inductor 11 and the third inductor 12 of the planar helical coil overlaps vertically, forming an adjustable electromagnetic coupling. This, along with the sixth capacitor 8, forms a parallel resonant structure, generating a transmission zero at a near-band low frequency of 2GHz. Similarly, a portion of the eighth inductor 17 and the ninth inductor 18 on the left side of the filter overlaps vertically, forming an adjustable electromagnetic coupling. This, along with the seventh capacitor 9, forms a parallel resonant structure, generating a transmission zero at a near-band high frequency of 6GHz. By adjusting the proportion of overlapping and non-overlapping portions of the metal coils, the positions of the two transmission zeros can be independently controlled. The two near-end stopband transmission zeros improve the roll-off coefficient of the LTCC bandpass filter, enhancing selectivity. Figure 9 As shown in the curve, the filter achieves transmission zeros at 2GHz and 6GHz. The near-band suppression is improved specifically: a lower sideband transition bandwidth of 900MHz (45dB) and an upper sideband transition bandwidth of 700MHz (25dB), achieving high-frequency transmission zero suppression. The far-band suppression is also improved, specifically: -35dB suppression in the 6-18GHz band.

[0027] The signal input can be connected to the first inductor 10 and the tenth inductor 19 via the side portions of the first external electrode 22 and the second external electrode 23, respectively. The bottom portions of the first external electrode 22 and the second external electrode 23 are vertically coupled to the first high-frequency suppression capacitor 20 and the second high-frequency suppression capacitor 21, respectively, forming another signal path. The two different paths form a parallel resonant structure, which can generate another pair of independently controllable far-end suppression transmission zeros. This suppresses the harmonic resonance and high-frequency parasitic passband of the filter, giving the LTCC bandpass filter a wide suppression band of 15 GHz.

[0028] This embodiment uses a frequency-variable coupling structure to construct transmission zeros. All equivalent elements are linearly connected in topology, eliminating the need for cross-coupling elements and realizing the filter transmission characteristics of multiple independently controllable transmission zeros.

[0029] The planar metal spiral coil equivalent inductance structure is arranged in an overlapping manner in the vertical direction. This constructs a physical equivalent of the electromagnetic coupling field in the LTCC design, reducing the need for actual metal structures, saving model space, and decreasing the overall size of the filter.

[0030] In this embodiment, the metal ground layer of the filter is connected to the six metal disks at the bottom through metal holes, which facilitates assembly onto the PCB board.

[0031] In this embodiment, signals are transmitted at the input and output ends of the filter through two methods: side band coupling and bottom disk coupling, forming a resonant structure to generate independently controllable high-frequency transmission zeros and improve the far-end stopband suppression effect.

[0032] This article uses specific embodiments to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology, characterized in that, The filter includes an LTCC ceramic body, external electrodes, and several circuit layers distributed within the LTCC ceramic body. The external electrode is provided in three parts, with two external electrodes distributed on both sides of the LTCC ceramic body and the other arranged at the bottom of the LTCC ceramic body. The external electrode is connected to the metal ground and the circuit layer through metal vias.

2. The wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to claim 1, characterized in that, The circuit layers, from bottom to top, include a GND layer and five other circuit layers, specifically: The GND layer includes a metal ground located at the bottom of the LTCC ceramic body; The first circuit layer includes five metal equivalent capacitor sheets, namely the first capacitor, the second capacitor, the third capacitor, the fourth capacitor and the fifth capacitor. The GND layer and the first circuit layer form a plate-like capacitor structure. The second circuit layer includes a mirror-distributed sixth capacitor, a seventh capacitor, and a metal ground layer. The third circuit layer includes a fourth inductor, a fifth inductor, a sixth inductor, and a seventh inductor; The fourth circuit layer includes the second inductor and the ninth inductor, and also includes parts of the circuitry of the fourth, fifth, sixth, and seventh inductors; The fifth circuit layer includes a first inductor, a third inductor, an eighth inductor, and a tenth inductor, with the first inductor and the tenth inductor connected to the external electrodes on both sides of the LTCC ceramic body; The above components are all connected by metal through-holes across layers and corresponding connecting lines.

3. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to claim 2, characterized in that, The GND layer has slots on both sides, and the slots are respectively provided with a first high-frequency suppression capacitor and a second high-frequency suppression capacitor.

4. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to claim 3, characterized in that, The first high-frequency suppression capacitor is connected to the first inductor through the first metal via. The second inductor is connected to the metal ground and the first capacitor through the second and third metal vias, respectively. The fourth inductor is connected to the metal ground through the fourth metal via and is also connected to the second capacitor through the fifth metal via. The third capacitor and the fifth inductor are connected through the sixth metal via. The fifth inductor, the metal ground supplement layer, the ninth inductor, and the eighth inductor are grounded through the seventh, eighth, and ninth metal vias and the eleventh metal via, respectively. The eighth inductor is also connected to the fifth capacitor through the tenth metal via. The sixth inductor is connected in series between the fifth inductor and the fifth capacitor. The second high-frequency suppression capacitor is connected to the tenth inductor through the twelfth metal via.

5. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to claim 3, characterized in that, The second and a portion of the third inductor overlap vertically to form an adjustable electromagnetic coupling. The electromagnetic coupling is connected to the sixth capacitor to form a parallel resonant structure, generating a transmission zero at a low frequency in the near band. The structures of the eighth and ninth inductors overlap vertically to form a controlled electromagnetic coupling. The electromagnetic coupling is connected to the seventh capacitor to form a parallel resonant structure, generating a transmission zero at a near-band high frequency.

6. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to claim 5, characterized in that, By adjusting the proportions of overlapping and non-overlapping portions of the second and third inductors, and the eighth and ninth inductors, the positions of the transmission zero points at near-band low frequencies and near-band high frequencies can be independently controlled.

7. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to claim 3, characterized in that, The side portions of the external electrodes on both sides of the LTCC ceramic body are respectively connected to the first inductor and the tenth inductor, forming a signal path; the bottom portions of the external electrodes on both sides of the LTCC ceramic body are respectively coupled to the first high-frequency suppression capacitor and the second high-frequency suppression capacitor in the vertical direction, forming another signal path. The two signal paths form a parallel resonant structure, which can form another pair of independent and controllable far-end suppression transmission zeros.

8. A wide-stopband 5G band LTCC filter based on frequency-variable coupling technology according to any one of claims 2 to 7, characterized in that, All inductors are planar spiral coil inductors.

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