A LTCC balun filter

Abstract

The utility model discloses an LTCC balun filter, which adopts a Marchand balun structure and a three-dimensional integrated structure of LTCC. The balun is composed of two symmetrical quarter-wavelength coupled lines, and energy is fed into the unbalanced port, and the quarter-wavelength short circuit is coupled with the half-wavelength open line to obtain energy, resulting in output energy with the same amplitude and 180° phase difference. It is achieved by the strong coupling coefficient of the two coupled lines, and the odd-mode excitation is suppressed by high even-mode impedance to achieve broadband characteristics. The advantages of this structure are wider passband, small insertion loss, and better phase and amplitude balance. At the same time, a large number of lumped elements are not required, thereby reducing the volume of the balun.

Description

Technical Field

[0001] The utility model relates to the technical field of microelectronics, in particular to an LTCC balun filter. Background Art

[0002] With the rapid development of wireless communication technology, people have put forward higher and higher requirements for high-density and small-size electronic products. Low Temperature Co-fired Ceramic (LTCC) technology has been widely used in the field of communications due to its characteristics in terms of integration and Q value. Due to the inherent characteristics of RF passive devices, the system occupies a large volume, and the volume of integrated technology is not far enough to meet engineering requirements. Based on the advanced LTCC multi-layer three-dimensional integration technology, RF passive devices can be miniaturized, high-performance, and low-cost. Balun is a very important device in the differential circuit of modern communication systems.

[0003] Balun is usually used in differential circuits of RF circuits. It is a signal conversion device from a single-ended unbalanced circuit to a double-ended balanced circuit. It is basically a balanced output signal, which divides a single-ended unbalanced input signal into two equal-amplitude reverse signals. On the one hand, it can play the role of impedance conversion, and on the other hand, the two outputs have a phase difference of 180°, which is equivalent to the opposite function of the output of the power divider. Balun is usually designed using microstrip lines or strip lines, with small size and high integration. In practical applications, a variety of balanced-unbalanced converters with different structures have been proposed, such as active baluns, lumped element baluns, ring baluns, microstrip baluns, and LTCC baluns. LTCC baluns are the smallest and most reliable, but with the development of microwave and millimeter circuits, LTCC balun filters have been put forward with requirements for smaller size, wider passband, smaller insertion loss, and better phase and amplitude balance, and the above problems need to be further solved. Utility Model Content

[0004] In view of the shortcomings of the prior art, the present invention proposes an LTCC balun filter, which adopts the vertical interconnection structure unique to LTCC technology, which can significantly reduce the size of components; adopts the Marchand Balun structure and the three-dimensional integrated structure of LTCC, which is realized by the strong coupling coefficient of two coupling lines, and suppresses the odd-mode excitation through high even-mode impedance to achieve broadband characteristics. The advantages of this structure are wider passband, small insertion loss, and better phase and amplitude balance. The specific technical solution is as follows:

[0005] A LTCC balun filter, the filter comprises an input terminal electrode and an output terminal electrode located at both ends of the filter in the length direction and a ground terminal electrode located in the middle of the filter in the length direction, the input terminal electrode, the output terminal electrode and the ground terminal electrode of the filter are printed on the surface of the LTCC ceramic substrate, the three-dimensional structure of the filter is wrapped in the LTCC ceramic body, the circuit structure inside the filter is ten layers, a ceramic diaphragm of a specified thickness is provided between two adjacent layers of circuits, and an LTCC vertical interconnection structure is used to realize the connection of components, wherein the first and second layers are two three-dimensional inductors connected by through holes, one end of the two inductors is They are respectively connected to the input terminal electrode and the output terminal electrode, and the other ends are commonly connected to the ground terminal electrode. The fourth layer is a capacitive coupling layer. The fifth, sixth, seventh, eighth and ninth layers are four three-dimensional inductors connected by through holes, two of which are located in the left half and the other two are located in the right half. The capacitive coupling layer of the fourth layer is also divided into left and right parts. The left half forms a cross coupling with the inductor below it, and the right half also forms a cross coupling with the inductor below it; the third and tenth layers are grounding layers, which are connected to the external circuit through the grounding terminal electrode; the inductor adopts a vertical spiral inductor, and the connection between different layers is realized through vertical through holes.

[0006] Furthermore, the input terminal electrode, the output terminal electrode and the ground terminal electrode are all made of metal silver.

[0007] Furthermore, the ceramic body is an L66 ceramic body with a relative dielectric constant of 66.

[0008] Furthermore, the overall size of the filter is 2.0 mm×1.25 mm×1 mm.

[0009] Furthermore, the width of the inductors of the fifth, sixth, seventh, eighth and ninth layers is 40 μm.

[0010] The beneficial effects of the utility model are as follows:

[0011] Low temperature co-fired ceramic is an electronic packaging technology that uses a multilayer ceramic process to place passive devices inside a ceramic medium. LTCC technology has outstanding advantages in terms of cost, miniaturization, low impedance technology, design diversification and flexibility, and high-frequency performance. LTCC uses a multilayer ceramic lamination process and low temperature co-firing to ensure that the internal circuit can be printed with metals with high conductivity (gold, silver, etc.) inside its medium, thereby ensuring better conductive losses. The LTCC balun filter of the utility model adopts the Marchand balun structure and the three-dimensional integrated structure of LTCC, which is realized by the strong coupling coefficient of two coupling lines, and suppresses odd-mode excitation through high even-mode impedance to achieve broadband characteristics, wider passband, better standing wave performance, reduced insertion loss, and better phase and amplitude balance. At the same time, the large area of ​​ground at the lower end of the model circuit can effectively reduce the influence of the external circuit on the filter, and can effectively shield the interference of the upper inductance of the filter on the lower capacitance and inductance. In addition, a large number of lumped components are not required, thereby reducing the size of the balun, making it light in weight, and having good output amplitude and output 180° phase shift. Therefore, it is easy to produce and can achieve broadband characteristics, and can be widely used in microwave and millimeter wave circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the equivalent circuit principle diagram of the LTCC balun filter of the utility model;

[0013] Figure 2 This is the appearance diagram of the LTCC balun filter of the utility model;

[0014] Figure 3 It is a front view structural diagram of the LTCC balun filter of the utility model;

[0015] Figure 4 This is a first-layer structural diagram of the LTCC balun filter of the utility model;

[0016] Figure 5 This is a second-layer structure diagram of the LTCC balun filter of the utility model;

[0017] Figure 6 It is the third layer structure diagram of the LTCC balun filter of the utility model;

[0018] Figure 7 This is a structural diagram of the fourth layer of the LTCC balun filter of the utility model;

[0019] Figure 8 This is a structural diagram of the fifth layer of the LTCC balun filter of the utility model;

[0020] Fig. 9 This is a sixth-layer structure diagram of the LTCC balun filter of the utility model;

[0021] Fig.10 It is the structure diagram of the 7th layer of the LTCC balun filter of the utility model;

[0022] Fig.11 This is the 8th layer structure diagram of the LTCC balun filter of the utility model;

[0023] Fig.12 It is the ninth layer structure diagram of the LTCC balun filter of the utility model;

[0024] Fig.13 It is the 10th layer structure diagram of the LTCC balun filter of the utility model;

[0025] Fig.14 1 is a diagram showing the phase difference simulation result of the LTCC balun filter in the embodiment;

[0026] Fig.15 1 is a diagram of S-parameter simulation results of the LTCC balun filter in the embodiment;

[0027] Fig.16 Graph showing the amplitude difference simulation result of the LTCC balun filter in the embodiment. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below according to the accompanying drawings and preferred embodiments, and the purpose and effect of the present invention will become more clear. The present invention will be further described in detail below in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Figure 1 The equivalent circuit schematic diagram of the LTCC balun filter of the utility model is as follows: Figure 1 As shown, the LTCC balun filter of the utility model is composed of two symmetrical quarter-wavelength coupled lines, the straight port of the first coupled line is grounded with the coupled port and the isolated port of the second coupled line, and the straight ports of the first coupled line and the second coupled line are two balanced output terminals of the balanced-unbalanced converter. The coupled port of the first coupled line is directly connected to the input end of the second coupled line. Energy is fed into the unbalanced port, and the quarter-wave short circuit of the quarter wavelength is coupled with the half-wavelength open line to obtain energy, so that the output energy obtains the same amplitude and 180° phase difference. It is achieved by the strong coupling coefficient of the two coupled lines, and the odd-mode excitation is suppressed by high even-mode impedance to achieve broadband characteristics. The advantages of this structure are wider passband, better standing wave performance, reduced insertion loss, and better phase and amplitude balance. At the same time, a large number of lumped elements are not required, thereby reducing the volume of the balun.

[0030] Figure 2This is the appearance diagram of the LTCC balun filter. The filter appearance includes an LTCC ceramic substrate 1. A weldable metal conductor strip is printed on the outer side of the middle part of the LTCC ceramic substrate in the length direction as the grounding electrode 2 of the filter; the opposite ends of the filter substrate in the length direction are covered with weldable metal conductors as the input electrode 3 and output electrode 4 of the filter; the input electrode, output electrode and grounding electrode of the filter are made by punching, filling, screen printing, lamination and sintering processes. When using it, you only need to solder the filter to the corresponding circuit board through the metal electrode in the correct way.

[0031] like Figure 3-13 As shown, the three-dimensional structure of the filter is wrapped in the LTCC ceramic substrate 1, the circuit structure inside the filter is ten layers, and a ceramic diaphragm of a specified thickness is between two adjacent layers of circuits. The LTCC vertical interconnection structure is used to realize the connection of components, wherein the first and second layers are two three-dimensional stereoscopic inductors connected by through holes, one end of the two inductors is respectively connected to the input terminal electrode and the output terminal electrode, and the other end is commonly connected to the ground terminal electrode, the fourth layer is a capacitive coupling layer, the fifth, sixth, seventh, eighth, and ninth layers are four three-dimensional stereoscopic inductors connected by through holes, two of which are located in the left half and the other two are located in the right half, the capacitive coupling layer of the fourth layer is also divided into left and right parts, the left half forms a cross coupling with the inductor below it, and the right half also forms a cross coupling with the inductor below it; the third and tenth layers are grounding layers, which are connected to the external circuit through the grounding terminal electrode; the inductor adopts a vertical spiral inductor, and the connection between different layers is realized through vertical through holes.

[0032] The inductors of the first and second layers are realized by spiral wide-side coupling lines, and the width of the inductors of the fifth, sixth, seventh, eighth and ninth layers is 40 μm.

[0033] The value of each component can be adjusted by adjusting the line length and line width of each layer of the spiral inductor; at the same time, the large ground area at the lower end of the model circuit can effectively reduce the impact of the external circuit on the filter, and can effectively shield the interference of the upper inductance of the filter on the lower capacitance and inductance.

[0034] In this embodiment, the LTCC balun filter has an overall size of 2.0 mm×1.25 mm×1 mm, the relative dielectric constant of the LTCC ceramic medium used is 66, the loss tangent is 0.003, the thickness of each layer of the ceramic medium is 0.05 mm, and the metal conductor material is metallic silver.

[0035] Fig.14 , 15 16 are respectively a phase difference simulation result diagram, an S parameter simulation result diagram and an amplitude difference simulation result diagram of the LTCC balun filter in the embodiment, Fig.14It can be seen that the phase difference of the filter is 180° at 2400 ~ 2500 MHz; Fig.15 It can be seen that the filter has an insertion loss of less than 3.2 dB at 2400 ~ 2500 MHz, an unbalanced end standing wave ratio of less than 2.0, a stopband attenuation of more than 48 dB at 880 ~ 960 MHz, a stopband attenuation of more than 25 dB at 1710 ~ 1990 MHz, and a stopband attenuation of more than 35 dB at 3800 ~ 4000 MHz. Fig.16 It can be seen that the absolute value of the amplitude difference of the filter within 2400 ~ 2500 MHz is less than 0.2 dB, indicating that the filter meets the requirements.

Claims

1. An LTCC balun filter, characterized in that: The filter comprises input electrodes and output electrodes at both ends of the filter in the length direction and a ground electrode in the middle of the filter in the length direction. The input electrodes, output electrodes and ground electrodes of the filter are printed on the surface of the LTCC ceramic substrate. The three-dimensional structure of the filter is wrapped in the LTCC ceramic body. The circuit structure inside the filter is ten layers. A ceramic diaphragm of a specified thickness is provided between two adjacent layers of circuits. The LTCC vertical interconnection structure is used to realize the connection of components. The first and second layers are two three-dimensional inductors connected by through holes. One end of the two inductors is respectively connected to the The input terminal electrode and the output terminal electrode are connected to the ground terminal electrode at the other end. The fourth layer is a capacitive coupling layer. The fifth, sixth, seventh, eighth and ninth layers are four three-dimensional inductors connected by through holes, two of which are located in the left half and the other two are located in the right half. The capacitive coupling layer of the fourth layer is also divided into left and right parts. The left half forms a cross coupling with the inductor below it, and the right half also forms a cross coupling with the inductor below it. The third and tenth layers are ground layers, which are connected to the external circuit through the ground terminal electrode. The inductor adopts a vertical spiral inductor, and the connection between different layers is realized through vertical through holes.

2. The LTCC balun filter according to claim 1, characterized in that: The input terminal electrode, the output terminal electrode and the ground terminal electrode are all made of metal silver.

3. The LTCC balun filter according to claim 1, characterized in that: The ceramic body is an L66 ceramic body with a relative dielectric constant of 66.

4. The LTCC balun filter according to claim 1, characterized in that: The overall size of the filter is 2.0 mm×1.25 mm×1 mm.

5. The LTCC balun filter according to claim 1, characterized in that: The width of the fifth, sixth, seventh, eighth and ninth layers of the inductor is 40 μm.

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