KR101067670B1 - Low pass filter and layout structure thereof - Google Patents

Abstract

The present invention is to provide a low pass filter capable of improving the stopband characteristics, and the present invention provides a first and a second inductor connected in series between the first and second stages, and the first and second At least any one of first and second capacitors connected in parallel with an inductor, between the first end and the ground end, between the connection point between the first and second inductors and the ground end, or between the second end and the ground end. Provided is a low pass filter comprising a parasitic capacitor formed in one place.

Low Pass Filters, LPFs, Inductors, Capacitors, Parasitic Capacitors, Ground Plates

Description

LOW PASS FILTER AND LAYOUT STRUCTURE THEREOF}

The present invention relates to a low pass filter and its arrangement, and more particularly, to a low pass filter and its arrangement that can improve the stopband characteristics.

In general, a filter that functions to select only a desired frequency in a communication system has become a very important factor. The filter is classified into four types according to the pass band: low pass filter, high pass filter, band pass filter, and band stop filter. Among them, a band pass filter that passes only a specific frequency band and a low pass filter that passes only a specific frequency with a stopband frequency are most commonly used.

FIG. 1 is an equivalent circuit diagram illustrating a low pass filter according to the prior art, and FIG. 2 is a view illustrating an arrangement structure of the low pass filter shown in FIG. 1.

1 and 2, a low pass filter according to the related art includes a connection point and a ground terminal between first and second inductors L1 and L2 connected in series and first and second inductors L1 and L2. And a capacitor C11 connected in parallel between (GND). The first and second inductors L1 and L2 are wound in a coil shape, and the capacitor C11 is a structure in which two plates face each other.

However, the low pass filter according to the prior art having such a structure exhibits poor stopband characteristics. In this structure, in order to improve the stopband characteristic, a parallel-connected capacitor and a series-connected inductor are additionally required, so that the order of the filter increases, so that the elements of the filter increase and the insertion loss of the pass band increases.

In addition, in the arrangement of the low pass filter according to the prior art as shown in FIG. 2, since only one ground plate serving as a ground end (GND) is disposed at the bottom of the arrangement, when another part or structure is arranged on the filter, the filter The characteristics of fluctuate, causing incorrect results. For this reason, the existing embedded filter must be in a fixed position, and there is a disadvantage that no other components exist on the top thereof.

Accordingly, the present invention has been proposed to solve the above problems according to the prior art, and has the following objects.

First, an object of the present invention is to provide a low pass filter capable of improving stopband characteristics.

Second, another object of the present invention is to provide an arrangement structure of a low pass filter which can improve the arrangement margin by increasing the independence of the embedded filter.

According to an aspect of the present invention, a first and a second inductor connected in series between first and second stages, and first and second in parallel with the first and second inductors, respectively, are provided. A low pass filter comprising a capacitor and a parasitic capacitor formed between at least one of a connection point between the first and second inductors, a connection point between the first and second inductors and the ground end, or between the second end and the ground end. To provide.

In addition, the present invention according to another aspect for achieving the above object is the first and second inductors connected in series between the first and second stages, and the first and second inductors connected in parallel with the first and second inductors respectively; Formed between at least one of a second capacitor and the first terminal and the first ground terminal, a connection point between the first and second inductors and the first ground terminal, or between the second terminal and the first ground terminal. A first parasitic capacitor and a second parasitic capacitor formed between at least one of the first end and the second ground end, between the connection point and the second ground end, or between the second end and the second ground end. Provide a low pass filter.

In addition, the present invention according to another aspect for achieving the above object is a first and second ground plate disposed respectively in the upper and lower parts so as to be spaced apart from each other, and is connected between the first end and the connection point and the first ground plate and A first wiring for a first inductor together to form a parasitic capacitor, a second wiring for a second inductor connected between the connection point and the second end to form a parasitic capacitor together with the first and second ground plates; A third wiring connected to the first end to function as an upper electrode of the first capacitor, a fourth wiring connected to the connection point to function as a lower electrode of the first capacitor, and an upper electrode of the second capacitor connected to the connection point. A fifth wiring connected to the second end and a sixth wiring connected to the second end to serve as a lower electrode of the second capacitor, and a first wiring board connected to the first end to form a parasitic capacitor. An arrangement structure of a low pass filter including a seventh wiring to be provided is provided.

According to the present invention, the following effects can be obtained.

First, according to the present invention, a low pass filter is implemented by combining a parallel capacitor and at least one parasitic capacitor in a basic unit structure of a low pass filter to achieve a stopband characteristic compared to a low pass filter according to the prior art having a basic unit structure. Can be improved.

Secondly, according to the present invention, the ground plate is disposed up and down, and the inductor and capacitor wirings are formed therebetween, and the low pass filter is separately embedded by implementing a low pass filter using a parasitic capacitor formed between the wirings and the ground plate. The advantage of improving the stopband characteristics without increasing the number of elements (wiring) of the filter can be obtained.

Third, according to the present invention, the ground plate may be disposed on the upper and lower portions of the filter, respectively, to increase the independence of the filter, thereby increasing the degree of freedom of the filter arrangement, thereby implementing a more compact and integrated product. In addition, by being disposed on the ground plate on the top of the filter, it is possible to embed other components or elements on top of it, which is a great advantage in terms of area utilization.

Hereinafter, the most preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art can easily implement the technical idea of the present invention. In addition, the parts denoted by the same reference numerals (or reference numerals) throughout the specification represent the same elements.

Example

3 is an equivalent circuit diagram illustrating a low pass filter according to an embodiment of the present invention.

As shown in FIG. 3, a low pass filter according to an embodiment of the present invention includes first and second inductors L1 and L2 connected in series between first and second stages P1 and P2, and a first pass filter. And first and second capacitors C21 and C22 connected in parallel with the first and second inductors L1 and L2, respectively, between the second stages P1 and P2. Further, between the connection point N and the ground terminal GND between the first terminal P1 and the ground terminal GND, the first and second inductors L1 and L2, or the second terminal P2 and ground. Parasitic capacitors C11, C12, and C13 formed in at least one of the stages GND.

In the embodiment shown in FIG. 3, the parasitic capacitors C11, C12, C13 are connected to the connection point N between the first terminal P1 and the ground terminal GND and between the first and second inductors L1 and L2. Although illustrated as an example, all formed between the ground terminal (GND), the second stage (P2) and the ground terminal (GND), even if only at least one of them is formed in the low-frequency according to the prior art shown in FIG. An effect that can significantly improve the stopband characteristics than the pass filter can be obtained.

As will be described later, the parasitic capacitors C11, C12, and C13 are not formed by using separate conductive wires, but form the first and second inductors L1 and L2 and the first and second capacitors C21 and C22. It is formed by using a ground plate that functions as a wiring and a ground terminal (GND). Accordingly, separate wirings for forming the parasitic capacitors C11, C12, and C13 are not required, thereby reducing the number of elements (wirings) embedded on the substrate.

FIG. 5 is a graph illustrating simulation results for comparing and comparing stopband characteristics of a low pass filter according to an exemplary embodiment of the present invention and a low pass filter according to the related art.

Referring to FIG. 5, 'LPF_ORG' is a characteristic waveform for the low pass filter according to the related art shown in FIG. 1, and 'LPF_R1' is a low pass filter according to another embodiment of the present invention. It is a characteristic waveform for the low pass filter having, and 'LPF_R2' shows a characteristic waveform for the low pass filter according to the embodiment of the present invention shown in FIG.

Parameters for the simulation result graph of the low pass filter illustrated in FIG. 5 are shown in Table 1. In Table 1, the value in '()' indicates the capacitance of the corresponding capacitor of 'LPF_R2'.

L1 L2 C11 C12 C13 C21 C22 nH 1.296 1.318 - - - - - pF - - 0.6 (0.7) 0.283 0.317 0.097 (0.161) 0.161 (0.309)

In FIG. 3, the low pass filter according to the embodiment of the present invention includes parallel capacitors C21 and C22 and three parasitic capacitors C11, C12, and C13 in the basic unit structure of the low pass filter according to the related art illustrated in FIG. 1. ). In FIG. 4, the low pass filter according to another embodiment of the present invention is configured by adding parallel capacitors C21 and C22 and one parasitic capacitor C11 to the basic unit structure. The low pass filter shown in FIGS. 1, 3 and 4 is designed to have a characteristic impedance of 50 Ω in the first and second stages P1 and P2.

Referring to FIG. 5, a cutoff frequency based on a -10 dB reference for each low pass filter is shown in FIG. 1. The low pass filter LPF_ORG illustrated in FIG. 1 has a value of 11 GHz or more, and the low pass filter LPF_R1 illustrated in FIG. 4. In this case, the value is approximately 8 GHz to 9 GHz, and the low pass filter LPF_R2 illustrated in FIG. 3 has a value of 7 GHz to 8 GHz.

3 and 4, in the structure in which the parallel capacitors C21 and C22 and at least one parasitic capacitor C11, C12 and C13 are coupled to the basic unit structure shown in FIG. 1, the structure shown in FIG. Compared with the basic unit structure, the cutoff frequency is significantly lowered. In addition, as the number of parasitic capacitors formed as in the structure of FIG.

5, the low pass filter according to the exemplary embodiment of the present invention shown in FIGS. 3 and 4 has a significant stopband characteristic compared to the low pass filter according to the prior art illustrated in FIG. 1. It can be seen that the improved, and as the number of parasitic capacitors added in parallel increases the stopband characteristics.

FIG. 6 is an equivalent circuit diagram of a modified part of the equivalent circuit shown in FIG. 3 to explain the arrangement of the low pass filter according to the exemplary embodiment of the present invention shown in FIG. 3.

In FIG. 3, the parasitic capacitor C12 is equal to the sum of the capacitances of the parasitic capacitors C12 and C31 of FIG. 6, and the parasitic capacitor C11 is equal to the sum of the capacitances of the parasitic capacitors C11 and C32 of FIG. 6. The parasitic capacitor C13 is equal to the sum of the capacitances of the parasitic capacitors C13 and C33 of FIG. 6. Thus, as shown in FIG. 3, two parasitic capacitors connected in series as shown in FIG. 6 may be represented by an equivalent circuit modified by one parasitic capacitor.

FIG. 7 is a plan view as viewed for the actual arrangement of the low pass filter according to the embodiment of the present invention shown in FIG. 6, FIG. 8 is a side perspective view as viewed from the side, and FIG. 9 as shown in FIG. It is the front view which looked at the arrangement structure shown in 7 from the front.

7 to 9, a low pass filter according to an embodiment of the present invention may be a low temperature co-fired ceramics (LTCC), a printed circuit board (PCB), a liquid crystal polymer (LCP) or a silicon (Si) substrate, or the like. It can be embedded in a variety of materials.

In the low pass filter according to the exemplary embodiment of the present invention, first and second ground plates GND1 and GND2 are disposed at upper and lower portions thereof so as to face each other. A dielectric material is filled between the first and second ground plates GND1 and GND2, and is connected between the first end P1 and the connection point N to form a parasitic capacitor together with the first ground plate GND1. First wiring ML1 for one inductor L1 is formed. In addition, a second wiring ML2 for second inductor is formed between the connection point N and the second terminal P2 to form a parasitic capacitor together with the first and second ground plates GND1 and GND2. In this case, the first and second wirings ML1 and ML2 are formed on the same layer, are connected to each other with the boundary of the connection point N, and have at least one bent portion at a specific site to increase the length within a single area. .

In addition, a third wiring ML3 is formed between the first and second ground plates GND1 and GND2 to be connected to the first terminal P1 to serve as an upper electrode of the first capacitor C21. In addition, a fourth wiring ML4 that is connected to the connection point N and functions as a lower electrode of the first capacitor C21 is formed. In this case, the third and fourth wirings ML3 and ML4 are formed to face each other, and the terminal portion has a plate-like structure wider than other portions.

A fifth wiring ML5 is formed between the first and second ground plates GND1 and GND2 to be connected to the connection point N and serve as an upper electrode of the second capacitor C22. In addition, a sixth wiring ML6 is formed to be connected to the second terminal P2 and serve as a lower electrode of the second capacitor C22. In this case, the fifth and sixth wirings ML5 and ML6 are disposed in directions facing each other, and similarly to the third and fourth wirings ML3 and ML4, the terminal portions have a wider plate-like structure. In addition, a seventh wiring ML7 connected to the first end P1 to form a parasitic capacitor together with the first ground plate GND1 is formed.

The first to seventh wirings ML1 to ML7 described above with reference to FIGS. 7 to 9 may be formed of the same conductive material. The first and second ends P1 and P2 and the connection point N are formed of a conductive material similarly to the first to seventh wirings ML1 to ML7. In addition, the first and second ends P1 and P2 and the connection point N are formed in a via structure to connect wires formed in different layers.

In the exemplary embodiment of the present invention, a parasitic capacitor is artificially formed at a portion where the first to seventh wirings ML1 to ML7 and the first and second ground plates GND1 and GND2 overlap with each other, as shown in FIG. 6. Parasitic capacitors C11 to C13 and C31 to C33 having a connection structure can be implemented.

As shown in FIG. 2, in the arrangement of the low pass filter according to the related art, the ground plate GND disposed below to form the capacitor C11 connected in parallel with the first and second inductors L1 and L2. ) To form a separate conductive plate. In order to suppress the formation of parasitic capacitors in other areas, the spaces between the wirings used as the first and second inductors L1 and L2 and the ground plate GND are relatively spaced apart.

However, in the arrangement structure of the low pass filter according to the embodiment of the present invention, unlike the arrangement structure of the low pass filter according to the prior art, in order to implement a parasitic capacitor connected in parallel to the basic unit structure of the low pass filter, it is physically separate. Instead of forming a conductive plate to form a parasitic capacitor, the first and second ground plates GND1 and GND2 are disposed up and down, and the first and second inductors L1 and L2 and the first and second inductors are disposed therebetween. The wirings for the second capacitors C21 and C22 are formed, and the parasitic capacitors are formed by spaced apart the gaps between the wirings and the first and second ground plates GND1 and GND2 so that the parasitic capacitors can be formed. The parasitic capacitors formed in this way may be connected in parallel with the first and second inductors L1 and L2 at a specific portion to implement a low pass filter having an equivalent circuit as shown in FIGS. 3 and 6.

In addition, as described above, in the arrangement structure of the low pass filter according to the related art, when the ground plate is disposed only at the lower part of the filter, the characteristics of the filter are changed when other components or elements are disposed on the upper part of the filter, causing incorrect results. You can also However, in the arrangement structure of the low pass filter according to the embodiment of the present invention, the first and second ground plates GND1 and GND2 are disposed on the upper and lower portions of the filter, respectively, to increase the independence of the filter, thereby increasing the degree of freedom of arrangement of the filter. This enables more compact and integrated products.

As described above, although the technical spirit of the present invention has been described in detail in the preferred embodiments, it should be noted that the above-described embodiments are for the purpose of description and not for the purpose of limitation. As such, those skilled in the art may understand that various embodiments are possible within the scope of the technical idea of the present invention.

1 is an equivalent circuit diagram illustrating a low pass filter according to the prior art.

Figure 2 is a side perspective view showing the arrangement of the low pass filter shown in FIG.

3 is an equivalent circuit diagram illustrating a low pass filter in accordance with an embodiment of the present invention.

4 is an equivalent circuit diagram illustrating a low pass filter in accordance with another embodiment of the present invention.

FIG. 5 is a graph showing a simulation result for comparing the stopband characteristics of a low pass filter according to an embodiment of the present invention and a low pass filter according to the prior art. FIG.

FIG. 6 is an equivalent circuit diagram of a partially modified equivalent circuit shown in FIG. 3. FIG.

7 is a plan view as seen for the actual arrangement of the low pass filter according to the embodiment of the present invention shown in FIG.

8 is a side perspective view of the arrangement structure shown in FIG.

9 is a front view of the arrangement shown in FIG. 7 as viewed from the front;

<Explanation of symbols for the main parts of the drawings>

L1, L2: Inductor

C21, C22: Capacitor

C11 ~ C13, C31 ~ C33: Parasitic Capacitors

ML1 to ML7: Wiring

Claims (8)

delete delete First and second ground plates respectively disposed on upper and lower portions of the upper and lower parts so as to be spaced apart from each other; A first wiring for a first inductor connected between a first end and a connection point to form a parasitic capacitor together with the first ground plate; A second wiring for the second inductor connected between the connection point and the second end to form a parasitic capacitor together with the first and second ground plates; A third wiring connected to the first end and serving as an upper electrode of the first capacitor; A fourth wiring connected to the connection point and functioning as a lower electrode of the first capacitor; A fifth wiring connected to the connection point and functioning as an upper electrode of a second capacitor; A sixth wiring connected to the second end to function as a lower electrode of the second capacitor; And A seventh wire connected to the first end to form a parasitic capacitor together with the first ground plate Arrangement structure of the low pass filter comprising a. The method of claim 3, wherein And the first and second wires have at least one bend. The method of claim 3, wherein And the first and second wirings are arranged on the same layer. The method of claim 3, wherein The third to the sixth wiring is a low pass filter arrangement structure of the end portion is formed in a plate-like structure. The method of claim 3, wherein And the first and second ends and the connection point have a via structure for connecting wirings formed on different layers. The method of claim 3, wherein And a low pass filter in which a dielectric material is filled between the first and second ground plates.

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