A high performance lc high pass filter

Abstract

This invention proposes a high-performance LC high-pass filter, comprising a signal input terminal, a signal output terminal, and a common ground terminal, and further comprising a first resonant unit, a second resonant unit, a third resonant unit, a fourth resonant unit, and a fifth resonant unit connected in sequence. This invention can be used in carrier aggregation scenarios to suppress blocking interference caused by low-frequency transmitted signals to high-frequency receivers, while allowing high-frequency signals to pass through without distortion. Its steep stopband characteristics ensure extremely high suppression even at frequencies very close to the passband, effectively protecting sensitive receiving circuitry. By employing a Π-type capacitor network structure, the bandwidth of the high-pass filter is extended by 6%. Furthermore, the integrated design reduces its physical size by approximately 10%, making it highly suitable for space-constrained system applications.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication, specifically to a high-performance LC high-pass filter. Background Technology

[0002] In wireless communication, radio frequency systems, and high-speed digital circuits, high-pass filters are crucial passive devices widely used to suppress low-frequency interference, isolate DC components, and retain useful high-frequency signals. Traditional high-pass filter designs are primarily based on LC (capacitor-inductor) networks, which are simple in structure, low in cost, and easy to integrate. However, with the development of modern communication systems towards multi-band and broadband directions (such as 5G, millimeter-wave communication, and ultra-wideband radar), traditional LC high-pass filters face the following significant challenges in terms of broadband performance, high-frequency cutoff characteristics, and low-frequency suppression depth:

[0003] 1. The contradiction between broadband and low-frequency suppression: The transition band of a single-pole LC high-pass filter (such as a first-order RC / RL or a second-order Π-type / T-type structure) is relatively wide, and the suppression in the low-frequency region is insufficient (such as stopband attenuation <20dB), which makes it difficult to meet the application requirements in high-interference environments. Although increasing the number of stages can improve the suppression depth, it will lead to an increase in passband insertion loss and a deterioration in high-frequency cutoff characteristics.

[0004] 2. High-frequency parasitic parameter limitations: In the microwave band (>1GHz), the parasitic resistance and distributed capacitance / inductance effects of inductors (L) and capacitors (C) are significant, causing the actual response of the filter to deviate from the ideal characteristics. Especially at high frequencies, parasitic effects can lead to increased passband ripple, cutoff frequency drift, and degraded out-of-band rejection, making it difficult to achieve a flat response over a wide bandwidth.

[0005] 3. Multi-frequency interference: Broadband systems often have multiple nearby low-frequency interference sources (such as power supply resonance and fundamental noise). Traditional narrowband high-pass filters cannot achieve a steep transition band in the wide frequency domain, resulting in insufficient stopband suppression and affecting the system signal-to-noise ratio.

[0006] 4. Trade-off between size and performance: To achieve high bandwidth suppression, existing solutions often use multi-stage cascaded or hybrid structures (such as LC + transmission line), but this increases circuit complexity and physical size, making it difficult to meet the requirements of miniaturized RF modules (such as MMIC, SIP).

[0007] To overcome the aforementioned shortcomings, the industry has attempted to use active filters, acoustic wave filters (SAW / BAW), or LTCC multilayer structures, but these suffer from high power consumption, high cost, limited power capacity, or insufficient design flexibility. Therefore, an innovative design based on passive LC topology is needed that can maintain low cost, high suppression, and low insertion loss while adapting to the application requirements of high-frequency, broadband systems. Summary of the Invention

[0008] To address the aforementioned problems, this invention proposes a high-performance LC high-pass filter that can improve bandwidth while also considering size, insertion loss, and out-of-band rejection. The technical solution provided by this invention is as follows:

[0009] A high-performance LC high-pass filter includes a signal input terminal, a signal output terminal, and a common ground terminal. It also includes a first resonant unit, a second resonant unit, a third resonant unit, a fourth resonant unit, and a fifth resonant unit connected in sequence and electrically, wherein:

[0010] The first resonant unit is connected in series between the signal input terminal and the first internal node, and is composed of a first capacitor and a first inductor connected in series in sequence.

[0011] The second resonant unit is connected in parallel between the first internal node and the common ground terminal, and is composed of a second inductor and a second capacitor connected in series.

[0012] The third resonant unit is a symmetrical Π-type capacitor network connected between the first internal node and the second internal node. It includes a third capacitor connected in series between the first internal node and the second internal node, a fourth capacitor connected in parallel between the first internal node and the common ground terminal, and a fifth capacitor connected in parallel between the second internal node and the common ground terminal. The capacitance values ​​of the fourth capacitor and the fifth capacitor are equal.

[0013] The fourth resonant unit is connected in parallel between the second internal node and the common ground terminal, and is composed of the third inductor and the sixth capacitor connected in series.

[0014] The fifth resonant unit is connected in series between the second internal node and the signal output terminal, and is composed of the seventh capacitor and the fourth inductor connected in series.

[0015] The third resonant unit is used to provide multiple transmission poles in the passband, thereby widening the effective bandwidth of the high-pass filter; the second and fourth resonant units each resonate in series at a preset stopband frequency, exhibiting low impedance and deeply attenuating the stopband signal to the ground terminal.

[0016] Preferably, the first resonant unit and the fifth resonant unit are stacked in a mirror image to form a symmetrical impedance matching network for input and output, which is used to achieve impedance matching with external circuits in the passband.

[0017] Preferably, the first resonant unit and the fifth resonant unit further include a grounded eighth capacitor and a ninth capacitor.

[0018] Preferably, the second resonant unit and the fourth resonant unit have the same topology and component parameters, and are respectively symmetrically arranged about the third resonant unit.

[0019] Preferably, the series resonant frequencies of the second inductor and the second capacitor in the second resonant unit, and the series resonant frequencies of the third inductor and the sixth capacitor in the fourth resonant unit, are all set to be equal to or close to the stopband center frequency that the high-pass filter needs to suppress.

[0020] Preferably, the capacitance values ​​of the third, fourth, and fifth capacitors satisfy one of the following relationships:

[0021] The three capacitances are equal, forming a symmetrical broadband matching network;

[0022] The fourth and fifth capacitors have the same capacitance value, which is greater than that of the third capacitor, and are used to adjust the frequency response flatness within the passband.

[0023] Preferably, it includes at least one additional resonant unit, which is a branch of an inductor and a capacitor connected in series and connected in parallel between the first internal node and / or the second internal node and the common ground terminal.

[0024] The additional resonant unit is configured to resonate at a stopband frequency different from the resonant frequencies of the second and fourth resonant units, thereby introducing at least one additional attenuation pole within the stopband of the high-pass filter.

[0025] Preferably, at least one inductor is an adjustable inductor, or at least one capacitor is an adjustable capacitor, such that the cutoff frequency or stopband rejection frequency of the high-pass filter can be electrically tuned.

[0026] Preferably, the high-pass filter is integrated into a multilayer low-temperature co-fired ceramic, a monolithic microwave integrated circuit, or a printed circuit board process, wherein the inductor is implemented through a planar spiral inductor, a transmission line, or a high-impedance line, and the capacitor is implemented through a metal-insulator-metal capacitor, a gap capacitor, or a finger-crossed capacitor.

[0027] Preferably, the high-pass filter is used in RF front-end modules, multiplexers, or carrier aggregation systems to suppress low-frequency interference signals and allow high-frequency communication signals to pass through with low loss.

[0028] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: This invention can be used in carrier aggregation scenarios to suppress blocking interference caused by low-frequency transmitted signals to high-frequency receivers, while allowing high-frequency signals to pass through without distortion. Its steep stopband characteristics ensure extremely high suppression even at frequencies very close to the passband, thereby effectively protecting sensitive receiving circuits. By employing a Π-type capacitor network structure, the bandwidth of the high-pass filter is extended by 6%. Furthermore, the integrated design reduces its physical size by approximately 10%, making it highly suitable for space-constrained system applications. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0030] Figure 1 This is a simplified circuit topology diagram of the present invention;

[0031] Figure 2 This is the circuit schematic diagram of the present invention;

[0032] Figure 3 This is the overall layout of the high-pass filter of the present invention;

[0033] Figure 4 This is a simulation data diagram of the high-pass filter layout of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] To make the above-mentioned objectives, features and effects of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Example 1: Reference Figures 1 to 4 This invention provides a broadband high-pass filter with steep stopband suppression characteristics. The high-pass filter includes a signal input terminal (Port1, the first terminal), a signal output terminal (Port2, the second terminal), and a common ground terminal (GND). The main circuit topology of the filter consists of five cascaded resonant units, exhibiting a symmetrical structure to achieve good input-output impedance matching.

[0037] The first resonant unit is connected in series between the signal input terminal Port1 and the first internal node A, and is composed of a first capacitor C1 and a first inductor L1 connected in series. This unit mainly participates in determining the initial roll-off characteristics of the high-pass filter and provides necessary impedance transformation. The first resonant unit may also include a grounded eighth capacitor 8.

[0038] The second resonant unit, serving as the first parallel grounding branch, is connected between the first internal node A and the common ground terminal GND. It is composed of the second inductor L2 and the second capacitor C2 connected in series. The series resonant frequency of the second resonant unit is... It is precisely designed near the stopband center frequency where the high-pass filter needs deep suppression. At this resonant frequency, the impedance of this branch is close to zero, which is equivalent to directly short-circuiting the signal at node A to ground, thereby creating a transmission zero at this specific frequency and achieving strong attenuation of the stopband signal.

[0039] The third resonant unit is a key broadband component, employing a symmetrical Π-type capacitor network structure connected between the first internal node A and the second internal node B. This network includes: a third capacitor C3 connected in series in the main path; a fourth capacitor C4 connected in parallel between the first internal node A and ground; and a fifth capacitor C5 connected in parallel between the second internal node B and ground. The Π-type capacitor network can introduce multiple transmission poles within the passband, effectively extending the filter's -3dB bandwidth and improving insertion loss and return loss performance within the passband. In a preferred embodiment, C4 = C5, and together with C3, they form a specific capacitance ratio to optimize passband flatness.

[0040] The fourth resonant unit, serving as the second parallel grounding branch, has a topology completely symmetrical to the second resonant unit. It is connected between the second internal node B and the common ground terminal GND, and is composed of the third inductor L3 and the sixth capacitor C6 connected in series. Similarly, its series resonant frequency... Designed and The two symmetrical transmission zeros, being equal or nearly equal, create a second transmission zero within the stopband. The combined effect of these two symmetrical transmission zeros makes the suppression curve of the filter stopband (especially near the cutoff frequency) extremely steep.

[0041] The fifth resonant unit is connected in series between the second internal node B and the signal output terminal Port2, and is composed of the seventh capacitor C7 and the fourth inductor L4 connected in series. The fifth resonant unit may also include a grounded ninth capacitor 9. This unit is mirror-symmetrical to the first resonant unit 101, together completing the output impedance matching of the filter and ensuring the symmetrical transition characteristics of the signal from the passband to the stopband.

[0042] After high-frequency signals within the passband are input at Port1, they are primarily transmitted to Port2 via a low-loss path consisting of a series path of C1-L1, C3, and L4-C3, and parallel capacitors of C8, C9, C2, and C6. The Π-shaped network (C3, C4, C5) effectively widens the passband. For low-frequency interference signals within the stopband, when their frequency approaches the resonant frequency of the L2-C2 and L3-C6 branches, the impedance of these two branches drops sharply, efficiently discharging the signal energy to ground. This results in two deep attenuation zeros on the frequency response curve, achieving steep stopband suppression.

[0043] The passband of the high-pass filter covers a frequency range from a first cutoff frequency to a second cutoff frequency, wherein the first cutoff frequency is mainly determined by the parameters of the first resonant unit, the third resonant unit, and the fifth resonant element; the stopband suppression range covers a frequency point from DC to a frequency point below the first cutoff frequency.

[0044] Example 2: Building upon Example 1, to achieve high suppression over a wider stopband, additional resonant units can be added at node A and / or node B. For example, an additional branch consisting of an inductor Lx and a capacitor Cx connected in series can be connected in parallel between node A and ground. This is achieved by setting the resonant frequencies of Lx and Cx to be different from those of other elements. Another stopband frequency (such as the second harmonic or a specific interference frequency) can be used to introduce a third transmission zero at that frequency without affecting the passband performance, thereby extending the stopband rejection width.

[0045] Example 3: The filter of the present invention can be easily implemented using various modern integrated circuit processes. For example, in the multilayer low-temperature co-fired ceramic (LTCC) process, inductors L1-L4 can be implemented using three-dimensional spiral inductors or high-impedance transmission lines; capacitors C1-C9 can be implemented using interlayer parallel plate capacitors (MIM capacitors) or vertically interleaved finger capacitors. All components are integrated inside a multilayer ceramic dielectric block and vertically interconnected through vias, ultimately forming a high-performance, small surface-mount integrated filter module.

[0046] Furthermore, to meet the requirements of reconfigurable systems, one or more capacitors (such as C2 and C6) can be replaced with varactor diodes, or one or more inductors (such as L2 and L3) can be replaced with adjustable inductors (such as an inductor array switched by MEMS switches). By changing the values ​​of these adjustable components through external control voltage or digital signals, the frequency of the filter's stopband attenuation point can be dynamically adjusted, realizing a frequency-tunable high-pass filter.

[0047] This high-pass filter can be widely used in modern wireless communication systems. For example, in 5G RF front-end modules, it can be used in carrier aggregation scenarios to suppress blocking interference from low-frequency (such as lower frequencies in Sub-6GHz) transmitted signals to high-frequency receivers, while allowing high-frequency signals to pass through without distortion. Its steep stopband characteristics ensure extremely high suppression even very close to the passband frequency, effectively protecting sensitive receiver circuitry.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-performance LC high-pass filter, comprising a signal input terminal, a signal output terminal, and a common ground terminal, characterized in that, It also includes a first resonant unit, a second resonant unit, a third resonant unit, a fourth resonant unit, and a fifth resonant unit that are electrically connected in sequence, wherein: The first resonant unit is connected in series between the signal input terminal and the first internal node, and is composed of a first capacitor and a first inductor connected in series in sequence. The second resonant unit is connected in parallel between the first internal node and the common ground terminal, and is composed of a second inductor and a second capacitor connected in series. The third resonant unit is a symmetrical Π-type capacitor network connected between the first internal node and the second internal node. It includes a third capacitor connected in series between the first internal node and the second internal node, a fourth capacitor connected in parallel between the first internal node and the common ground terminal, and a fifth capacitor connected in parallel between the second internal node and the common ground terminal. The capacitance values ​​of the fourth capacitor and the fifth capacitor are equal. The fourth resonant unit is connected in parallel between the second internal node and the common ground terminal, and is composed of the third inductor and the sixth capacitor connected in series. The fifth resonant unit is connected in series between the second internal node and the signal output terminal, and is composed of the seventh capacitor and the fourth inductor connected in series. The third resonant unit is used to provide multiple transmission poles in the passband, thereby widening the effective bandwidth of the high-pass filter; the second and fourth resonant units each resonate in series at a preset stopband frequency, exhibiting low impedance and deeply attenuating the stopband signal to the ground terminal.

2. The high-performance LC high-pass filter according to claim 1, characterized in that, The first and fifth resonant units are stacked in a mirror image to form a symmetrical impedance matching network for input and output, which is used to achieve impedance matching with external circuits within the passband.

3. A high-performance LC high-pass filter according to claim 2, characterized in that, The first and fifth resonant units also include a grounded eighth capacitor and a ninth capacitor.

4. A high-performance LC high-pass filter according to claim 1, characterized in that, The second and fourth resonant units have the same topology and component parameters, and are respectively symmetrically arranged about the third resonant unit.

5. A high-performance LC high-pass filter according to claim 4, characterized in that, The series resonant frequencies of the second inductor and the second capacitor in the second resonant unit, and the series resonant frequencies of the third inductor and the sixth capacitor in the fourth resonant unit, are all set to be equal to or close to the stopband center frequency that the high-pass filter needs to suppress.

6. A high-performance LC high-pass filter according to claim 1, characterized in that, The capacitance values ​​of the third, fourth, and fifth capacitors satisfy one of the following relationships: The three capacitances are equal, forming a symmetrical broadband matching network; The fourth and fifth capacitors have the same capacitance value, which is greater than that of the third capacitor, and are used to adjust the frequency response flatness within the passband.

7. A high-performance LC high-pass filter according to claim 1, characterized in that, It includes at least one additional resonant unit, which is a branch of an inductor and a capacitor connected in series and connected in parallel between the first internal node and / or the second internal node and the common ground terminal. The additional resonant unit is configured to resonate at a stopband frequency different from the resonant frequencies of the second and fourth resonant units, thereby introducing at least one additional attenuation pole within the stopband of the high-pass filter.

8. A high-performance LC high-pass filter according to claim 1, characterized in that, At least one inductor is an adjustable inductor, or at least one capacitor is an adjustable capacitor, such that the cutoff frequency or stopband rejection frequency of the high-pass filter can be electrically tuned.

9. A high-performance LC high-pass filter according to claim 1, characterized in that, High-pass filters are integrated into multilayer low-temperature co-fired ceramics, monolithic microwave integrated circuits, or printed circuit board processes, where the inductors are planar spiral inductors, transmission lines, or high-impedance lines, and the capacitors are metal-insulator-metal capacitors, gap capacitors, or finger-crossed capacitors.

10. A high-performance LC high-pass filter according to claim 1, characterized in that, High-pass filters are used in RF front-end modules, multiplexers, or carrier aggregation systems to suppress low-frequency interference signals and allow high-frequency communication signals to pass through with low loss.

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