CN103138705A - Band-pass filter - Google Patents

Abstract

The present invention provides a bandpass filter, comprising an input signal electrode P1; an output signal electrode P2; a ground electrode P3; a first series LC resonant circuit, including a first inductor L1 and a first capacitor C1 connected in series, wherein , the input signal electrode P1 is connected to the input terminal of C1, and the output terminal of C1 is connected to the input terminal of L1; the second series LC resonant circuit includes a second inductance L2 and a second capacitor C2 connected in series, wherein the input terminal of L2 is connected to the output terminal of L1, The output terminal of L2 is connected to the input terminal of C2, and the output terminal of C2 is connected to the output signal electrode P2; the feedback capacitor C3, the input terminal of C3 is connected to the input terminal of the input signal electrode P1 and C1, and the output terminal of C3 is connected to the output signal electrode P2 and the output terminal of C2; the parallel inductor L3, the input terminal of L3 is connected to the output terminal of L1 and the input terminal of L2, and the output terminal of L3 is connected to the ground electrode P3. The bandpass filter has the advantages of small size, good frequency selection performance, small in-band insertion loss, strong out-of-band suppression, simple and effective method, wide application, low manufacturing cost, suitable for mass production and the like.

Description

a bandpass filter

technical field

The invention belongs to the field of electronic technology, and relates to a band-pass filter, in particular to a novel band-pass filter with two transmission zeros based on multi-layer low temperature co-fired ceramic technology (Low Temperature Co-fired Ceramic, LTCC). device.

Background technique

With the increasing trend of IC integration, the proportion of system-on-chip (SOC) and system-in-package (SIP) applications in communication systems is increasing. In this case, the area occupied by passive components in the system Relatively improved, so how to improve the performance of components while reducing the size of passive components has become a core technology.

In a wireless communication system, a band-pass filter (BPF) is an indispensable component of the RF pre-stage. Bandpass filter is the basic unit of RF/microwave transceiver components. As a frequency selection component, it is used to select or limit the frequency range of RF signals, and plays an important role in many RF fields.

At present, the RF/microwave system is developing towards multi-function and miniaturization. Based on multi-layer circuit lamination technology, such as the multi-chip module (Multi-Chip Module, MCM) technology of low temperature co-fired ceramic (Low Temperature Co-fired Ceramic, LTCC) technology has been obtained. Widely concerned, it can completely bury various passive devices, such as capacitors, inductors, antennas, filters, etc. Highly integrated, low-cost low-power RF and microwave functional modules.

Ceramic substrates with high dielectric constants have certain advantages for designing and processing single bandpass filter components, but they are not suitable for designing and processing multi-chip components. The main reason is that they are not suitable for processing and the insertion loss of radio frequency/microwave signals is large.

Contents of the invention

Therefore, considering the technical problems in the above-mentioned prior art, the object of the present invention is to provide a bandpass filter with miniaturization, low insertion loss, wide frequency band and high performance. The present invention combines the characteristics of multi-layer circuit lamination technology on the basis of analyzing the type and characteristics of the prototype equivalent circuit of the band-pass filter, uses the T-shaped equivalent circuit model, and proposes to add a feedback capacitor at the input and output ports, and use the connection between the two capacitors The mutual coupling between them realizes a simple new band-pass filter with two transmission zeros, which effectively solves the performance and area problems of the integrated band-pass filter.

In order to achieve the above object, the technical scheme adopted in the present invention is:

An embodiment of the present invention provides a bandpass filter, including:

An input signal electrode P1 through which electrical signals are input;

An output signal electrode P2 through which electrical signals are output;

a ground electrode P3 through which it is connected to the reference ground;

The first series LC resonant circuit includes a first inductor L1 and a first capacitor C1 connected in series, wherein the input signal electrode P1 is connected to the input terminal of C1, and the output terminal of C1 is connected to the input terminal of L1;

The second series LC resonant circuit includes a second inductor L2 and a second capacitor C2 connected in series, wherein the input end of L2 is connected to the output end of L1, the output end of L2 is connected to the input end of C2, and the output end of C2 is connected to the output signal electrode P2 ;

The feedback capacitor C3, the input end of C3 is connected to the input end of the input signal electrode P1 and C1, and the output end of C3 is connected to the output end of the output signal electrode P2 and C2;

An inductor L3 is connected in parallel, the input terminal of L3 is connected to the output terminal of L1 and the input terminal of L2, and the output terminal of L3 is connected to the ground electrode P3.

Preferably, the bandpass filter is formed by stacking multiple dielectric substrates.

Preferably, the bandpass filter includes an uppermost first dielectric substrate and a lowermost second dielectric substrate;

Metal conductor sheets are arranged on the surfaces of the first and second dielectric substrates.

Preferably, the metal conductor sheet of the first dielectric substrate is the upper plate of capacitors C1 and C2;

The metal conductor sheet of the second dielectric substrate is a ground plate.

Preferably, the bandpass filter further includes a third dielectric substrate with a metal conductor sheet disposed on its surface, disposed between the first dielectric substrate and the second dielectric substrate;

The third dielectric substrate is a reference metal ground, and the reference metal ground is electrically connected to the metal conductor sheet of the second dielectric substrate through a metal via.

Preferably, a rectangular slot is dug in the middle of the metal reference ground for providing the metal conductor sheet forming L1 and the metal conductor sheet of the C1 lower plate, and the metal conductor sheet of L2 and the metal conductor sheet of the C2 lower plate.

Preferably, the bandpass filter further includes a fourth dielectric substrate provided with a metal conductor sheet on its surface;

The fourth dielectric substrate is disposed between the third dielectric substrate and the second dielectric substrate;

A metal conductor sheet L3 is provided on the side of the fourth dielectric substrate facing the third dielectric substrate.

Preferably, the material of the multilayer dielectric substrate is low temperature co-fired ceramics.

Preferably, a metal tray is arranged in the multi-layer dielectric substrate.

Preferably, the C1, C2, and C3 are parallel plate capacitors;

The L1, L2, and L3 are planar spiral inductors, and L1, L2 are on the same dielectric substrate, and L1, L2, and L3 are on different dielectric substrates.

It can be seen from the above that the bandpass filter provided by the embodiment of the present invention includes an input signal electrode P1 through which an electrical signal is input; an output signal electrode P2 through which an electrical signal is output; a ground electrode P3 , connected to the reference ground through this electrode; the first series LC resonant circuit includes a first inductance L1 and a first capacitor C1 connected in series, wherein the input signal electrode P1 is connected to the input terminal of C1, and the output terminal of C1 is connected to the input terminal of L1; the second Two series LC resonant circuits, including a second inductance L2 and a second capacitor C2 connected in series, wherein the input end of L2 is connected to the output end of L1, the output end of L2 is connected to the input end of C2, and the output end of C2 is connected to the output signal electrode P2; Feedback capacitor C3, the input terminal of C3 is connected to the input terminal of input signal electrode P1 and C1, the output terminal of C3 is connected to the output terminal of output signal electrode P2 and C2; the parallel inductor L3, the input terminal of L3 is connected to the output terminal of L1 And the input terminal of L2, the output terminal of L3 is connected to the ground electrode P3. The bandpass filter has the advantages of small size, good frequency selection performance, small in-band insertion loss, strong out-of-band suppression, simple and effective method, and can be widely used in multi-chip components (MCM) and monolithic microwave integrated circuits (MMIC). Moreover, the novel bandpass filter provided by the embodiment of the present invention is based on the LTCC process, has low manufacturing cost, and is suitable for mass production. The bandpass filter can be widely used in radio frequency wireless communication fields such as mobile phones, bluetooth systems, and wireless local area networks.

Description of drawings

FIG. 1 is a schematic diagram of an equivalent circuit of a bandpass filter provided by an embodiment of the present invention;

Fig. 2 is the exploded and perspective schematic diagram of the bandpass filter provided by the embodiment of the present invention;

FIG. 3 is a schematic diagram of actual test results and three-dimensional electromagnetic field simulation results of the bandpass filter provided by the embodiment of the present invention.

Detailed ways

The embodiment of the present invention provides a novel bandpass filter with two transmission zeros. As shown in the electrical equivalent circuit diagram of a novel band-pass filter with two transmission zeros illustrated in accompanying drawing 1, the band-pass filter may specifically include:

An input signal electrode P1 through which electrical signals are input;

An output signal electrode P2 through which electrical signals are output;

a ground electrode P3 through which it is connected to the reference ground;

A first series LC resonant circuit (comprising a first inductor L1 and a first capacitor C1 connected in series), wherein the input signal electrode P1 is electrically connected to the input terminal of C1, and the output terminal of C1 is connected to the input terminal of L1;

A second series LC resonant circuit (comprising a second inductance L2 and a second capacitor C2 connected in series), wherein the output terminal of L1 in the first series LC resonant circuit (L1, C1) is connected to the second series LC resonant circuit (L2, C2) The input terminal of L2, the output terminal of L2 is connected to the input terminal of C2, and the output terminal of C2 is connected to the output signal electrode P2;

The feedback capacitors C3 and C3 are set between the two ports of the input signal electrode P1 and the output signal electrode P2, that is, the input terminal of C3 is connected to the input terminals of the input signal electrodes P1 and C1, and the output terminal of C3 is connected to the output signal electrodes P2 and C2 The output terminal of the feedback capacitor C3 utilizes the mutual coupling between the two capacitors (C1, C2);

A parallel inductor L3 is connected in parallel between the first series LC resonance circuit (L1, C1) and the first series LC resonance circuit (L2, C2). Specifically, the input end of L3 is connected to the output end of L1 and the output end of L2 The input terminal, the output terminal of L3 is connected to the ground electrode P3;

Reference ground, through the reference ground, introduces ground voltage.

Further, the bandpass filter provided by the embodiment of the present invention may be formed by stacking multiple dielectric substrates. Wherein, the uppermost layer and the lowermost dielectric substrate surface are respectively provided with metal conductor sheets, the metal conductor sheet of the uppermost dielectric substrate is the upper plate of capacitors C1 and C2, and the lowermost dielectric substrate metal conductor sheet is the grounding plate.

Further, the capacitors ( C1 , C2 , C3 ) are realized by parallel plate capacitors, wherein the upper plates of C1 , C2 have larger areas and are closer to each other, and can form a coupling capacitor C3 .

Further, the inductors (L1, L2, L3) are realized by planar spiral inductors, the inductors L1, L2 are on the same layer of dielectric substrate, and the two and L3 are on different layers of dielectric substrates, and they use through holes to realize different Connectors between layers of metal conductors.

Furthermore, in one layer of the dielectric substrate among the multilayer dielectric substrates, a layer of metal conductor plate is set as a reference metal ground, which is electrically connected to the bottom metal ground plate through a through hole.

In the embodiment of the present invention, a metal conductor sheet may be provided on the upper surface or the lower surface of the intermediate dielectric substrate provided with electrical components (capacitors, inductors) (except for the uppermost and lowermost dielectric substrates, if the intermediate dielectric substrate is If the upper surface is provided with a metal conductor sheet, the uppermost dielectric substrate can be provided with a metal conductor sheet on the upper surface, while the lowermost layer can be provided with a metal conductor sheet on both sides or on the upper surface. If the middle layer dielectric substrate is provided with a metal conductor sheet on the lower surface sheet, the uppermost dielectric substrate can be provided with metal conductor sheets on both sides or the lower surface, and the lowermost layer can be provided with metal conductor sheets on the lower surface) to play the role of isolation and protection.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

In a specific embodiment, as shown in FIG. 2, the bandpass filter provided by the embodiment of the present invention can be provided with a total of 7 layers of dielectric substrates, the thickness of the dielectric substrate is about 84.5 μm, and the thickness of each layer of conductor sheet is about 12 μm. Considering the processing technology, a metal tray with a diameter of 250 μm must be added at the connection between the metal microstrip line and the metal cylinder. In order to facilitate the description of the connection relationship, the distance between the layers is kept as far as possible. Therefore, FIG. 2 cannot represent the proportional relationship of the actual size of the novel bandpass filter with two transmission zeros of the present invention.

As shown in Figure 2, the novel bandpass filter with two transmission zeros provided by the embodiment of the present invention comprises a first dielectric substrate 1 on which a metal conductor sheet 9 is provided as a ground plate; a sixth dielectric substrate 6 , there is a metal conductor piece on it, as another metal reference ground 8, wherein a rectangular slot is dug in the middle of the metal reference ground 8, which is used to provide the planar spiral inductance L1 forming the first series LC resonant (L1, C1) circuit The metal conductor sheet 22 of the metal conductor sheet 22 and the metal conductor sheet 21b of the lower plate of the parallel plate capacitor C1 and the metal conductor sheet 25 of the plane spiral inductor L2 of the second series LC resonant (L2, C2) circuit and the metal of the parallel plate capacitor C2 lower plate The conductor sheet 24b, and the metal reference ground 8 and the ground plate 9 are connected together by metal through holes to realize a unified reference ground. The fifth dielectric substrate 5 is provided with a metal conductor piece 23 parallel connected to the ground plane spiral inductor L3. A seventh dielectric substrate 7 on which the metal conductor sheet 21a forming the upper plate of the parallel plate capacitance C1 of the first series LC resonance (L1, C1) circuit and the parallel plate of the second series LC resonance (L2, C2) circuit are provided The metal conductor piece 24a on the upper plate of the capacitor C2, and the metal conductor piece 21a and the metal conductor piece 24a are capacitively coupled to form a coupling capacitor C3.

The metal on each layer of the first dielectric substrate 1, the sixth dielectric substrate 6, the fifth dielectric substrate 5, and the seventh dielectric substrate 7 is printed on the upper surface of the dielectric substrate by the LTCC printing process. The metal conductor is covered with silver and has a thickness of 12 μm. The remaining dielectric substrates have no metal conductor sheets on them, but only metal trays, such as dielectric substrates 2, 3, and 4, on which a plurality of metal sheets constituting the metal tray are provided. The dielectric substrate material used It is LTCC ceramic Ferro-A6S/M, the dielectric constant is 5.9, the dielectric loss tangent is 0.002, and the thickness of each layer is 84.5 μm.

The first dielectric substrate 1, the sixth dielectric substrate 6, the fifth dielectric substrate 5, and the seventh dielectric substrate 7 are electrically connected through metal through holes. Considering the processing technology, the diameter of all metal through holes is 175 μm, and If the metal microstrip of each layer is to be connected to the metal via, a metal tray with a diameter of 250 μm must be added at the position of the metal layer where the metal microstrip is connected to the via. The thickness of the metal tray is the same as that of the metal layer. The thickness is the same, and both are 10 μm.

The upper plate metal conductor sheet 21a of the parallel plate capacitor C1 and the upper plate metal conductor sheet 24a of the parallel plate capacitor C2 on the fourth dielectric substrate 7 respectively provide lead electrodes, and the lead electrodes connect respective input and output electrodes to corresponding external electrodes Input and output ports.

Fig. 3 is a schematic diagram of the actual test results and three-dimensional electromagnetic field simulation results of the invented novel bandpass filter with two transmission zeros. The center frequency of the novel band-pass filter of the present invention is 1.61GHz, and the bandwidth is 260MHz. out-of-band suppression characteristics. It can be seen from the test results that the insertion loss and reflection loss are slightly larger than the simulation results, and the center frequency and bandwidth have no change. The test results show that the present invention adopts the T-type equivalent circuit of the feedback capacitor to realize the low dielectric loss with two transmission zero points. Electricity constant LTCC bandpass filter is a simple and effective method.

Compared with the prior art, the present invention has the following advantages:

1) Adding the feedback capacitor C3 introduces two transmission zeros and realizes strong out-of-band suppression, which can be completed without increasing the number of stages, effectively reducing the number of components and the area of the device.

2) In forming the feedback capacitor C3, the coupling capacitor C3 is simply formed by coupling the first conductor surface layer constituting the capacitor 1 and the first conductor surface layer constituting the capacitor C2, and two transmission zeros are simply introduced.

3) The circuit is simple, the frequency selectivity is good, the insertion loss is low, and the performance is superior, which effectively solves the performance and area problems of the set bandpass filter.

The above is only the embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be regarded as Be the protection scope of the present invention.

Claims (10)

1. A bandpass filter, characterized in that, comprising: An input signal electrode P1 through which electrical signals are input; An output signal electrode P2 through which electrical signals are output; a ground electrode P3 through which it is connected to the reference ground; The first series LC resonant circuit includes a first inductor L1 and a first capacitor C1 connected in series, wherein the input signal electrode P1 is connected to the input terminal of C1, and the output terminal of C1 is connected to the input terminal of L1; The second series LC resonant circuit includes a second inductor L2 and a second capacitor C2 connected in series, wherein the input end of L2 is connected to the output end of L1, the output end of L2 is connected to the input end of C2, and the output end of C2 is connected to the output signal electrode P2 ; The feedback capacitor C3, the input end of C3 is connected to the input end of the input signal electrode P1 and C1, and the output end of C3 is connected to the output end of the output signal electrode P2 and C2; An inductor L3 is connected in parallel, the input terminal of L3 is connected to the output terminal of L1 and the input terminal of L2, and the output terminal of L3 is connected to the ground electrode P3. 2. The band-pass filter according to claim 1, characterized in that, the band-pass filter is formed by stacking multiple layers of dielectric substrates. 3. The bandpass filter according to claim 2, wherein the bandpass filter comprises a first dielectric substrate of the uppermost layer and a second dielectric substrate of the lowermost layer; Metal conductor sheets are arranged on the surfaces of the first and second dielectric substrates. 4. The bandpass filter according to claim 3, wherein the metal conductor sheet of the first dielectric substrate is an upper plate of capacitors C1 and C2; The metal conductor sheet of the second dielectric substrate is a ground plate. 5. The bandpass filter according to claim 4, characterized in that, the bandpass filter also includes a third dielectric substrate with metal conductor sheets on the surface, arranged on the first dielectric substrate and the second dielectric substrate between; The third dielectric substrate is a reference metal ground, and the reference metal ground is electrically connected to the metal conductor sheet of the second dielectric substrate through a metal via. 6. The bandpass filter according to claim 5, wherein a rectangular slot is dug in the middle of the metal reference ground for providing the metal conductor sheet forming L1 and the metal conductor sheet of the lower plate of C1, and The metal conductor sheet of L2 and the metal conductor sheet of the lower plate of C2. 7. The bandpass filter according to claim 4, wherein the bandpass filter further comprises a fourth dielectric substrate having a metal conductor sheet on its surface; The fourth dielectric substrate is disposed between the third dielectric substrate and the second dielectric substrate; A metal conductor sheet L3 is provided on the side of the fourth dielectric substrate facing the third dielectric substrate. 8. The bandpass filter according to any one of claims 2 to 7, wherein the material of the multilayer dielectric substrate is low temperature co-fired ceramics. 9. The bandpass filter according to any one of claims 2 to 7, wherein a metal tray is arranged in the multilayer dielectric substrate. 10. The bandpass filter according to any one of claims 1 to 7, wherein said C1, C2, and C3 are parallel plate capacitors; The L1, L2, and L3 are planar spiral inductors, and L1, L2 are on the same dielectric substrate, and L1, L2, and L3 are on different dielectric substrates.

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