JP6845540B2 - Single layer thin film common mode filter - Google Patents

Description

The present disclosure relates to a common mode filter used for high frequency differential transmission.

In 5G, which is the next-generation communication standard, in addition to the UHF band (0.3 to 3 GHz) of the conventional communication band, the SHF band (3 to 30 GHz) or higher frequency band is examined, and the LTE-Advanced communication standard is applied. May be done. That is, the introduction of carrier aggregation and MIMO (Multi Input Multi Output) technology is being considered.

Especially in MIMO technology, it is expected that a maximum of 4 antennas and a maximum of 8 antennas will be used, and if this is the case, a wireless circuit will be required for each antenna. In addition, there is a need for multi-band to support international roaming, and the internal circuit scale of mobile terminals such as mobile phones is on the rise. On the other hand, there is still a strong need for further miniaturization and lower profile of mobile terminals, and there is an urgent need for further miniaturization and integration of circuits.

On the other hand, since the 5G standard handles signals with higher frequencies, electromagnetic interference (EMI) inside the mobile terminal housing becomes more apparent as circuits are integrated and miniaturized. The differential signal transmission method is effective as one of the EMI countermeasures. This differential signal transmission method is currently used for USB, HDMI (registered trademark), etc., and is mainly used in digital circuits, especially transmission lines between liquid crystal displays and CPUs in the mobile communication field (Non-Patent Document 1). .. Further, not only in digital transmission but also in analog circuits, a differential signal transmission method may be used as a transmission line connecting elements.

The differential signal transmission method is a method in which signals having opposite phases are input to each of the two transmission lines for communication, and in principle, noise (in-phase component) from the outside of the transmission line is canceled. In addition, the electromagnetic field emitted from the transmission line is also canceled, and it is said that there is no noise radiation to the outside. However, in reality, unbalanced components occur due to deviations in signals and amplitudes, distortions in differential signals, and slight variations in signal lines. Therefore, the signals of the two transmission lines do not become completely out-of-phase signals, and a so-called common (in-phase) mode current flows, which becomes a source of noise and affects peripheral devices and circuits. Therefore, a common mode filter that suppresses this common mode noise is indispensable for the differential signal transmission method.

Currently, in the common mode filter that is in practical use, many chip parts and the like using a common mode choke coil (hereinafter referred to as CMC) are used. CMC is an electronic component that uses magnetic coupling by winding two conductors around a magnetic core in the same direction. It occurs in the core when a differential signal current flows through the winding and when a common mode current flows. The coupling of magnetic flux acts in the opposite direction, causing a large difference in impedance. Therefore, the current of the differential signal having low impedance passes as it is, the common mode current having high impedance is suppressed, and the generation of noise can be prevented (Non-Patent Document 2). However, the above-mentioned CMC device requires two thin film coils to be stacked, and there is a problem that integration, particularly low profile, is structurally difficult.

Therefore, the inventors have proposed a thin film common mode filter that utilizes the difference in equivalent circuit characteristics between the differential (differential) transmission mode and the in-phase (common) transmission mode depending on the combination of the inductor and the capacitor formed in the thin film. Good operation in the 1.8 to 2.0 GHz band was demonstrated (Patent Document 1).

Japanese Unexamined Patent Publication No. 2016-144115

Satoru Saito; "EMC Design of Differential Interfaces", TDK EMC Technology, https: // products. tdk. com / info / ja / products / emc / guidebook / index. html (accessed 2016-04-19) Yoshikazu Fujishiro; "Analysis of Common Mode Filters by S-Parameters", Institute of Electronics, Information and Communication Engineers, EMCJ2000-60, pp.25-30 (Sep.2000)

However, the frequency at which the conventional common mode filter operates with practically sufficient performance such as differential mode attenuation of 3 dB or less and common mode attenuation of 15 dB or more is generally up to the UHF band, and the conventional extension line configuration is higher than this. However, it was very difficult to secure the same performance in the SHF band, which is an order of magnitude higher.

Therefore, the inventors have conducted extensive research, and as a result, they have realized a common mode filter that is composed of a single-layer thin film, operates well even in the SHF band, and has a compact and simple configuration.

The single-layer thin film common mode filter according to one aspect of the present disclosure is a single-layer thin film common mode filter having a substrate and a group of thin film conductors on the surface of the substrate and outputting a differential signal to a differential signal input. Therefore, the conductor group includes at least a first inductor portion in the path between the differential signals on the input side and a second inductor portion in the path between the differential signals on the output side, and the first inductor The portion and the second inductor portion are made of non-linear striped conductor lines having the same shape as each other, and are housed in rectangular regions separated from each other and provided in parallel with each other.

The first inductor portion and the second inductor portion may be a meander-shaped striped conductor line.

Further, the conductor group includes an end portion provided for each of the differential inputs of the first inductor portion, an end portion provided for each of the differential outputs of the second inductor portion, and the first inductor portion. a first input terminal adjacent to each other via the one end portion and the slit of the differential input, a second input terminal adjacent via the other end portion and the slit of the differential input of the first inductor section, the first a first output terminal adjacent to each other via the one end portion and the slit of the differential output of the second inductor section, the second output terminal adjacent to each other via the other end portion and the slit of the differential output of the second inductor section And may be included.

The first inductor portion and its input side end are formed as a first conductor, the second inductor portion and its output side end are formed as a second conductor, and the end portions on both sides of the first conductor are formed. A first grounding terminal adjacent to each other via a slit and a second grounding terminal adjacent to both ends of the second conductor via a slit may be included.

The surface of the substrate and the conductor group may be coated with a dielectric material.

The line lengths of the first and second inductors may be 10% to 40% of the signal wavelength.

The first inductor portion and the second inductor portion may be separated by 80 μm or more, and the width of the meander-shaped striped conductor line may be 5 μm to 40 μm.

The folding interval in the meander-shaped striped conductor line may be 50 μm or more.

According to one aspect of the present disclosure, a common mode filter can be configured with a thin film single-layer structure, and not only is it significantly smaller and thinner than the prior art, but also excellent filter performance is exhibited. Furthermore, since it is composed of a single layer, not only the design is facilitated, but also vias between layers are not required, so that the yield can be improved and the manufacturing cost can be reduced.

Top view of one aspect of the present disclosure Sectional view of one aspect of the present disclosure Part diagram of one aspect of the present disclosure Equivalent circuit diagram of one aspect of the present disclosure Equivalent circuit diagram of one aspect of the present disclosure (in the case of common mode) Characteristic diagram of one embodiment of the present disclosure

Hereinafter, embodiments according to one aspect of the present disclosure will be described in detail with reference to the drawings.

FIG. 1 is a top view of a single-layer thin film common mode filter according to an embodiment of the present disclosure (hereinafter referred to as the present embodiment), FIG. 2 is a sectional view of cross-sections AA, and FIG. 3A, FIG. Parts drawings are shown in (b) and (c).

In FIGS. 1 and 2, reference numeral 1 denotes a substrate, and for example, a polyimide resin is used. A group of thin-film conductors made of, for example, copper is provided on the surface of the substrate 1. Of the conductor group, 13 is a first input terminal and 14 is a second input terminal, to which a differential input signal is supplied. 24 first output terminal, 23 is a second output terminal element, signal filtering processing is output in the differential signal.

Reference numeral 11 denotes a first conductor, which has a first inductor portion 112 and ends 111 and 113 on both sides thereof. Reference numeral 21 denotes a second conductor, which has a second inductor portion 212 and end portions 211 and 213 on both sides thereof. The ends 211 and 213 are adjacent to the ends 111 and 113 of the first conductor via slits 101 and 201, respectively. Further, a first ground terminal 15 adjacent to the ends 111 and 113 of the first conductor via slits 104 and 105, respectively, is provided. Similarly, the end portions 211 and 213 of the second conductor are provided with the adjacent second grounding terminals 25 via the slits 204 and 205, respectively.

Further, in the present embodiment, one end 111 of the first conductor passes through the slit 102 to the first input terminal 13, and one end 211 of the second conductor passes through the slit 202 to the first output terminal 24. And they are adjacent to each other. Further, the other end 113 of the first conductor is adjacent to the second input terminal 14 via the slit 103, and the other end 213 of the second conductor is adjacent to the second output terminal 23 via the slit 203.

Here, the first inductor portion 112 and the second inductor portion 212 are non-linear striped conductor lines, and have the same shape as each other.

In particular, in the present embodiment, the first inductor portion 112 and the second inductor portion 212 have a meander shape and are provided parallel to each other as shown in FIG.

Further, in the present embodiment, as shown in FIG. 2, the surface of the substrate 1 and the conductor group are covered with the dielectric 2. It is assumed that the dielectric 2 also enters the slits (105, 204, etc.) between the conductors.

The functions of the single-layer thin film common mode filter according to the present embodiment configured as described above will be described below.

First, the first inductor section 112 and the second inductor section 212 generate inductance based on self-induction action, respectively. The first and second inductor portions are each composed of a meander-shaped (or comb-shaped) striped conductor line as shown in FIG. 3 (a). The inductance of the meander-shaped conductor line changes depending on the number of turns, the length of the turn-back section, the interference from the adjacent inductor portion, etc., but the inductance increases roughly in proportion to the total length of the conductor line.

In the examples described later, in the optimum design when the signal frequency is 28 GHz (wavelength 10.7 mm), the constant of each inductor section is 0.64 nH, and the conductor line length of the inductor section that realizes this is 2.12 mm. there were. This corresponds to about 20% of the above signal wavelength. Although it depends on the filter specifications, in the case of a common mode filter as in this embodiment, it is necessary to secure an inductor corresponding to a lead wire having a length of about 10% to 40% of the signal wavelength as the line length of each inductor section. Conceivable.

Further, in the same embodiment, a 9-fold back mianda shape is used, and a striped conductor having a line length of 2.12 mm is contained in a region of 680 μm × 180 μm. If this is a linear striped inductor, at least the vertical dimension needs to be 2.12 mm or more. As for the horizontal dimension, it is necessary to keep a space from the other inductor portion as described later, and the horizontal dimension cannot be shortened by the lengthening of the vertical dimension. That is, if an attempt is made to secure the same degree of inductance without using the meander shape, the area of the entire filter will surely increase.

Even if the striped conductor line constituting the inductor is not a meander shape but a non-linear shape, a certain inductance-to-area ratio can be obtained. For example, instead of the mianda shape, it may be serrated or sine wavy. Further, even if it has a meander shape, it may be folded back in the direction perpendicular to the meander shown in FIG. 1, that is, in the y-axis direction. Further, the folded portion of the mianda does not have to be at a right angle as shown in FIGS. 1 and 3 (a), and may be folded back in an arc shape.

The greater the number of folds of Mianda, the longer the wire can be stored in the same area. That is, inductance can be earned. However, on the other hand, the interval between folds becomes narrower, and the parasitic capacitance cannot be ignored. Considering that the capacitor (20 to 40 fF) described later is made of a slit having a width of 5 μm, it is desirable that the folding interval is 10 times that, that is, 50 μm or more.

The width d (FIG. 3A) of the striped conductor line should be thick enough that the resistance component can be ignored. However, if it is too thick, the parasitic capacitance between the adjacent folded parts will increase. In the examples described later, d = 20 μm, but it is preferable to design in the range of 5 μm to 40 μm according to the required specifications.

The overall chip area will be smaller if the distance between the first inductor section 112 and the second inductor section 212 is as close as possible. However, if it is packed too much, the mutual inductance between both inductors cannot be ignored. In the meander type coil, the mutual inductance becomes a negative value and acts to reduce each inductance. It is necessary to determine the optimum interval in consideration of the chip area and inductance.

In order to reduce the influence of the mutual inductance as much as possible, it is preferable to arrange the first inductor portion 112 and the second inductor portion 212 having the same shape in parallel with each other. On the contrary, when both are provided so as to be symmetrical with each other, adjacent portions and separated portions are alternately generated, and mutual inductance appears stronger in the close portions.

As described above, by providing two inductor portions 112 and 212 having the same shape and a non-linear shape, particularly a meander shape, in parallel, it is possible to realize a desired inductance in a single-layer structure with an almost minimum area. it can.

The slits 101, 102, 103, 104, 105, 201, 202, 203, 204, 205 function as capacitors together with the conductors sandwiching them. Especially the slit 102,103,202,203 capacity _{C L} type capacitor (FIG. 3 (b)), the slits 104,105,204,205 capacity _{C R} of the type of the capacitor (FIG. 3 (c)) the Each is configured. Slits 101 and 201 are incorporated combined so capacity is _C L / 2.

In the present embodiment, the slit also has a comb shape like an inductor portion, but the capacitance value of the capacitor is determined not only by the length of the slit but also by the width w (FIG. 3B). Therefore, the degree of freedom in design is higher than that of the inductor section. For example, in Examples (20 to 40 fF) described later, w = 5 μm, but if the design rule allows the width w to be narrowed, it is possible to obtain the same capacitance even if it is linear.

The first and second inductors and peripheral capacitors form a common mode filter shown by the equivalent circuit of FIG. The numbers in parentheses in the figure are on the circuit diagram corresponding to the first input terminal 13, the second input terminal 14 , the first output terminal 24 , the second output terminal 23, the first ground terminal 15, and the second ground terminal 25. Represents a node.

Further, in the case of the common mode, the equivalent circuit of FIG. 4 can be rewritten by omitting the inductor as shown in FIG.

_{The characteristic impedance Z 0 of} the equivalent circuit shown in FIGS. 4 and 5, the transmission coefficient of the differential mode | S _21D |, and the transmission coefficient of the common mode | S _21C | are expressed by the following equations (1) to (3). Can be done.

Hereinafter, examples of the common mode filter in the present embodiment will be described.

In this embodiment, a design example of a common mode filter for the 27.9 to 28.1 GHz (SHF) band and an electromagnetic field analysis result will be described. First, as a design guideline, the characteristic impedance Z ₀ , the transmission coefficient of the differential mode | S _21D |, and the transmission coefficient of the common mode | S _21C | shall satisfy the following specifications.
Z ₀ = 50 ± 5Ω ・ ・ ・ (4)
| S _21D |> 0.89 (-1dB) ... (5)
| S _21C | ≤0.1 (-20 dB) ... (6)
The equivalence coefficients of equations (5) and (6) are represented by voltage ratios, respectively.

Practically, it is said that the differential mode attenuation should be within 3 dB and the common mode attenuation should be 15 dB or more. However, errors due to parasitic capacitance of wiring and skin effect are assumed, and in particular, | S _21D | is larger than the design value. Because there is a tendency to become, we dared to set strict specifications.

In the present embodiment, first a suitable parameter _{(L L, C L, C} R) is an expression (1) to the characteristic impedance _{Z 0} with _(3), the transmission coefficient _{| S 21D} |, transmission coefficient | S _21C | is calculated, and a plurality of candidates satisfying all the conditions of the equations (4) to (6) are narrowed down. Next, from these candidates, the _{parameter that minimizes | S 21D} | is selected. Next, the selected parameters are modeled with electromagnetic field analysis software, and the characteristics of the full device whose structure is designed by combining them are analyzed. From the analysis result, it is determined whether or not the transmission coefficient satisfies the target value, and if it is satisfied, the device design is completed. If not, the device structure and parameters are modified and the above process is repeated. The high-frequency three-dimensional electromagnetic field analysis software ANSYS-HFSS (registered trademark) was used for the electromagnetic field analysis.

As a result, the parameters satisfying the conditions of the above equations (4) to (6) converged to the following values.
L _L = 0.32 nH (2 L _L = 0.64 nH)
C _L = 40fF
C _R = 30fF

The actual size of the parts on the common mode filter at this time was as follows.
x2L _L = 180 μm
y2L _L = 680μm
xC _L = 80 μm
yC _L = 205μm
xC _R = 145μm
yC _R = 65μm
The material of the substrate 1 and the dielectric 2 is polyimide, and the conductor group is all made of copper having a thickness of 5 μm. Further, the line width d of each inductor portion is 20 μm, and the slit width w is 5 μm.

The frequency characteristics of the common mode filter of this embodiment designed as described above are shown in FIG. FIG. 6B shows the frequency characteristics of the differential mode transmission coefficient | S _21D | and the common mode transmission coefficient | S _21C |, and FIG. 6A shows the frequency characteristics of the differential mode transmission coefficient | S _21D | near a frequency of 28 GHz. An enlarged view of is shown.

As is clear from FIG. 6, in the vicinity of the frequency of 28 GHz, the transmittance in the differential mode is −2.1 dB, which is slightly lower than the target specification (-1 dB). One reason for this is considered to be an error due to an increase in resistance due to the skin effect of conductors (copper) such as striped conductor lines. However, since the result exceeds -3 dB, it is considered that there is no problem in practical use. It should be noted here that the common mode transmission coefficient is −34 dB, which is 14 dB lower than the target (-20 dB) (common mode noise is suppressed).

As described above, according to the present embodiment, by using a capacitor composed of a non-linear shape, particularly a meander-shaped inductor and a slit between conductors, the configuration is small and simple, and common mode noise is remarkably suppressed in the SHF frequency band. It is possible to realize a common mode filter having a single-layer structure.

In the common mode filter of the present embodiment, the material of the conductor group is copper, but the material is not limited to this, and other metals such as gold and aluminum, or a conductive material that can be thinned may be used. Further, although the substrate 1 and the dielectric 2 are made of polyamide, other insulating materials may be used as long as they can be used in the SHF band. Further, although the common mode filter is an independent chip component in the present embodiment, it may be mounted on a silicon wafer together with other electronic circuits (for example, a high frequency oscillator, an amplifier) and the like. Further, in the embodiment, the center frequency is assumed to be around 28 GH, but the target frequency can be slightly shifted by appropriately reducing or enlarging the overall size within the range where the parasitic capacitance and the skin effect do not become apparent. ..

The present invention can be used for high frequency circuits of information devices using frequencies in the SHF band, particularly mobile terminals such as mobile phones and smartphones of 5G standard. It can also be applied not only to communication equipment but also to all electronic equipment that handles high frequencies such as radar.

1 Substrate 2 Dielectric 11 1st conductor 112 1st conductor 111, 113 Conductor end 21 2nd conductor 212 2nd inductor 211, 213 Conductor end 13 1st input terminal 24 2nd input terminal 14 1st output terminal 23 2nd output terminal 15 1st ground terminal 25 2nd ground terminal 101-105 Slit 201-205 Slit

Claims (8)

A single-layer thin film common mode filter that has a group of thin film conductors on a substrate and the surface of the substrate and outputs a differential signal to a differential signal input.
The conductor group is at least
In the path between the differential signals on the input side , the first inductor and
A second inductor is included in the path between the differential signals on the output side.
The first inductor portion and the second inductor portion are made of non-linear striped conductor lines having the same shape as each other, and are housed in rectangular regions separated from each other and provided in parallel with each other. Common mode filter. The single-layer thin film common mode filter according to claim 1, wherein the first inductor portion and the second inductor portion are formed of a meander-shaped striped conductor line. The above conductor group is further
The ends provided for each of the differential inputs of the first inductor section and
The ends provided for each of the differential outputs of the second inductor section and
The first input terminal adjacent to one end of the differential input of the first inductor section via a slit,
The other end of the differential input of the first inductor section and the second input terminal adjacent to it via a slit,
The first output terminal adjacent to one end of the differential output of the second inductor section via a slit,
The single-layer thin film common mode filter according to claim 1 to 2, wherein the other end of the differential output of the second inductor portion and the second output terminal adjacent to each other via a slit are included. The first inductor portion and the end portion on the input side thereof are formed as the first conductor.
The second inductor portion and its output side end are formed as a second conductor.
The first grounding terminal adjacent to each end of the first conductor via a slit,
A second grounding terminal adjacent to each end of the second conductor via a slit,
3. The single-layer thin film common mode filter according to claim 3. The single-layer thin film common mode filter according to any one of claims 1 to 4, wherein the surface of the substrate and the conductor group are coated with a dielectric material. The single-layer thin film common mode filter according to claim 1, wherein the line lengths of the first and second inductance portions are 10% to 40% of the signal wavelength. The single-layer thin film common mode filter according to claim 2, wherein the first inductor portion and the second inductor portion are separated by 80 μm or more, and the width of the meander-shaped striped conductor line is 5 μm to 40 μm. The single-layer thin film common mode filter according to claim 2, wherein the folding interval in the meander-shaped striped conductor line is 50 μm or more.