JPH11219825A - Surface mounting type balun transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface mounting type balun transformer the mounting area of which is small. SOLUTION: This is a surface mounting type balun transformer, in which dielectric sheets carrying single spiral inductors L1 -L4 are laminated. Then, a capacitor formed between a capacitor electrode 3 and a ground electrode layer 6 is connected with an unbalanced terminal 4 in parallel with a primary balun line. That is, frequency characteristic can be adjusted so as to be made lower by the capacitor, and the strip line length of each spiral inductor L1 -L4 can be made shorter than λ/4. Thus, areas carrying the spiral inductors L1 -L4 can be reduced, and each sheet can be obtained with a small area. Then, when the dielectric sheets carrying the single spiral inductors are laminated, the mounting area can be made as small as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface mount type balun transformer used as an impedance converter in a portable transceiver such as a portable telephone or a car telephone.

[0002]

2. Description of the Related Art A balun transformer, which is a balanced-unbalanced conversion element, has an unbalanced terminal on a primary balun line X and two balanced terminals on a secondary balun line Y, as shown in FIG. An unbalanced transmission line is connected to the unbalanced terminal, and two signal lines of the balanced transmission line are respectively connected to the two balanced terminals to form a balun circuit (Marchand Balun). Then, the unbalanced signal input from the unbalanced terminal of the primary balun line X is converted and output from the two balanced terminals of the secondary balun line Y, and a balanced signal is output based on the phase difference. Conversely, the balanced signal from the balanced terminal is converted into an unbalanced signal and output from the unbalanced terminal.

[0003]

As a balun transformer applied to a high-frequency circuit, a balun transformer formed by winding a conductive wire around a magnetic core such as ferrite has conventionally been used. By the way, this configuration has a problem that conversion loss is large in a high-frequency band equal to or higher than the UHF band, and the shape becomes large.

In order to solve this problem, a balun transformer having a coaxial structure effective in a high frequency band has been used. However, this configuration is long and is required to be miniaturized such as a mobile radio device. Is not appropriate.

Therefore, a balun transformer having a laminated structure disclosed in Japanese Patent Application Laid-Open No. Hei 8-191016 has been proposed. In this configuration, two spiral inductors are arranged in parallel on the surface of a dielectric sheet, and a balanced line and an unbalanced line are formed for each dielectric sheet. However, this balun transformer having a laminated structure is suitable for miniaturization, but has a problem that the mounting area is large when mounted on a printed circuit board.

Therefore, the present inventors have proposed a spiral inductor in which a strip line is spirally wound and formed by laminating a plurality of dielectric sheets each carrying one of them. By the way, in such a configuration, the plane area is determined by the length of the strip line line,
This line length is set to λ / 4, and the problem that the mounting area is restricted by the line length remains. The present invention makes it possible to shorten the line length of the spiral inductor,
It is an object of the present invention to provide a surface mount type balun transformer whose mounting area can be further reduced.

[0007]

According to the present invention, a capacitor electrode is formed on a connection sheet having unbalanced terminals formed on the surface thereof by connecting the unbalanced terminals to the connection sheet, and a ground electrode layer is formed on the connection sheet. And a capacitor formed between the capacitor electrode and the ground electrode layer, and a primary dielectric sheet carrying a spiral inductor is disposed on the upper and lower surfaces of the sheet pair so as to be circumscribed, respectively. Configure the primary balun line by connecting the outer ends of the spiral inductors of the dielectric sheet to each other and connecting the inner end of the spiral inductor of the primary dielectric sheet circumscribing the connection sheet to the unbalanced terminal on the connection sheet Then, two secondary-side dielectric sheets carrying the spiral inductor are disposed on each of the primary-side dielectric sheets so as to be circumscribed respectively, and further, a ground electrode layer is provided outside thereof. Ground sheets formed on the surfaces are circumscribed, respectively, and the inner ends of the spiral inductors of both secondary dielectric sheets are connected to the ground electrode layers of the circumscribed ground sheets, respectively, and the outer ends are connected to the sheet. A surface-mount balun transformer characterized in that a secondary-side balun line is formed by extending to the side edge of the balun.

In this configuration, the unbalanced signal input from the unbalanced terminal on the central connection sheet is determined by the fact that the spiral inductors on the primary dielectric sheet are located above and below the connection sheet on the secondary dielectric sheet. Electromagnetically coupled with the spiral inductor of the above, and is taken out as a signal from both balanced terminals. The phase difference between the two balanced terminals is 180 degrees, so that noise is canceled. Note that the balanced signal from the balanced terminal can be converted and output as an unbalanced signal from the unbalanced terminal. In this configuration, since a single spiral inductor is carried for each dielectric sheet, there is an advantage that the area is small.

In this configuration, the unbalanced terminal has a capacitor C formed between the capacitor electrode and the ground electrode layer.
Are connected in parallel with the primary-side balun line. By providing the capacitor C, it is possible to shift the reflection characteristic to the lower frequency side. Therefore, if the strip line length of each spiral inductor is shorter than λ / 4, the frequency increases and a deviation from the target frequency occurs. However, by providing such a capacitor C, the frequency is adjusted to be shifted to the higher side, and the target frequency is adjusted. Frequency can be achieved. This is understood from the fact that the frequency can be kept constant by disposing the capacitor C even if L becomes small, because of the relationship of f = 1 / 2π (LC) ^1/2. You.

Therefore, the provision of the capacitor C makes it possible to make the length of the strip line of each spiral inductor smaller than λ / 4, thereby reducing the area for supporting the spiral inductor. This makes it possible to reduce the mounting area by making each sheet a small area.

In addition, since the ground electrode layer on the ground sheet adjacent to the connection sheet is disposed at the center, the presence of the ground electrode layer causes electromagnetic shielding above and below the ground electrode layer, thereby achieving stable signal conversion with little noise. It becomes possible.

[0012]

1 and 2 show a surface mount type balun transformer 1 according to the present invention. This surface mount type balun transformer 1 is formed by spirally winding a strip sheet toward a center, a connection sheet 2 disposed adjacent to the connection sheet 2, and a center disposed above and below the connection sheet 2. a plurality of dielectric sheets 7a having the spiral inductor L ₁ ~L ₄ comprising, 7b, 13a, and 13b, ground sheet 18a disposed outside position, and 18b, formed by stacking an exterior sheet 25 uppermost Things. Each sheet is formed of a dielectric material such as ceramic or resin.

The structure of each sheet will be described in more detail.
A rectangular capacitor electrode 3 is formed on the upper surface of the connection sheet 2, and the capacitor electrode 3 extends to a side edge to form an unbalanced terminal 4. As shown in FIG. 1, the unbalanced terminals 4 are vertically extended by the conductive layer 23 in a state where the respective sheets are stacked.

On the ground sheet 5 adjacent to the lower surface of the connection sheet 2, a ground electrode layer 6 is formed over almost the entire surface. On both side edges of the ground electrode layer 6, ground connection terminals 6a extend to the side surfaces. Then, between the capacitor electrode 3 of the connection sheet 2 and the ground electrode layer 6 of the ground sheet 5, the capacitor C according to the main part of the present invention is formed.

Primary-side dielectric sheets 7a and 7b are laminated on the front and back sides of the sheet pairs 2 and 5, respectively. On the primary dielectric sheets 7a and 7b, spiral inductors L ₁ and L ₂ each formed by spirally winding a strip line are formed. The winding directions of the spiral inductors L ₁ and L ₂ are opposite, but may be the same. Then, connected to the capacitor electrode 3 an inner end of the spiral inductor L ₁ of the upper portion of the primary dielectric sheet 7a through via hole 8 penetrating the center of the seat 7a. The outer ends of the spiral inductors L ₁ and L ₂ are connected to each other through a via hole 9 that penetrates through the primary dielectric sheet 7 a and the sheets 2 and 5. As a result, a line extending from the inner end of the upper spiral inductor L ₁ to the open inner end of the spiral inductor L ₂ via the strip lines of the spiral inductors L ₁ and L ₂ is formed. I have.

Outside the primary dielectric sheets 7a and 7b, secondary dielectric sheets 13a and 13b are circumscribed. Spiral inductors L ₃ and L ₄ wound in a spiral shape are formed on the secondary dielectric sheets 13a and 13b, respectively. The outer ends of the spiral inductors L ₃ and L ₄ extend to the edges of the secondary dielectric sheets 13a and 13b, and the edges serve as balanced terminals 14a and 14b.
As shown in FIG. 1, the balanced terminals 14a and 14b are also vertically extended by the conductive layer 23 in a state where the sheets are stacked.

The ground sheet 18 further disposed outside.
Ground electrode layers 19a and 19b are formed on the electrodes a and 18b. The ground electrode layers 19a and 19b are
a and the spiral inductors L via the via holes 20a and 20b penetrating the secondary dielectric sheet 13b, respectively.
_3, connected to the inner ends of the L _4. In addition, each ground electrode layer 19
a and 19b are partially grounded sheets 18a and 18b, respectively.
Of the left side edge in FIG.
21 is also formed, and the ground connection terminal 2 is similarly provided at the center of the left edge.
1 is formed. These ground connection terminals 21 and 21
Reference numeral 21 denotes a laminated state of sheets, which is vertically continued by a conductive layer 23 as shown in FIG.

Further, an exterior sheet 25 is provided on the ground sheet 18a such that the ground electrode layer 19a is not exposed. The unbalanced terminal 4 at the center and the ground connection terminals 2
1, 21 are exposed, and the right side edge has a central ground connection terminal 2.
1 and balanced terminals 14a and 14b are formed on both sides thereof.
Each terminal is connected to the corresponding terminal formed on each sheet via the conductive layer 23. Thus, the spiral inductors L ₃ and L ₄ constitute a secondary balun line Y.

The pair of spiral inductors L ₁ and L ₃ adjacent above the connection sheet 2 and the pair of spiral inductors L ₂ and L ₄ adjacent below the connection sheet 2 are wound in the same direction. Thus, the direction in which the current flows due to the electromagnetic action is defined, and the secondary signals are output to the balanced terminals 14a and 14b, respectively.

In such a configuration, the line length of each of the spiral inductors L _{1 to} L ₄ is appropriately designed such as λ / 4. The central unbalanced signal inputted from the unbalanced terminal 4 on the connecting sheet 2 is input to the inner end of the spiral inductor L ₁ on the primary side dielectric sheet 7a, the spiral inductor L ₁ and the upper in It is taken out from the electromagnetic coupling to the secondary side dielectric sheet 13a of the spiral inductor L ₃ to the balanced terminal 14a of the signal of the secondary side is generated. Similarly, primary-side signal unbalanced spiral inductor L ₂ is applied to be connected to the outer end of the spiral inductor L _1, a spiral inductor on the secondary side dielectric sheet 13b electromagnetically coupled with the lower and the spiral inductor L ₂ L
_A secondary side signal is generated at ₄ and is extracted from the balanced terminal 14b. The signals at the balanced terminals 14a and 14b are 1
Since the phases are different by 80 degrees, noises are canceled and output as a balanced signal.

In such a configuration, the balanced terminals 14a, 1
By applying a balanced signal to 4b, an unbalanced signal may be converted from the unbalanced terminal 4 and extracted.

Thus, as shown in FIG.
And a primary balun line X in which primary spiral inductors L ₁ and L ₂ are connected in series, and secondary spiral inductors L ₃ and L ₄ in a non-connected state. The surface mount type balun transformer 1 is composed of a secondary side balun line Y which is 14b and is formed by electromagnetically coupling the spiral inductors L ₁ and L ₃ and the spiral inductors L ₂ and L _{4 respectively} . Then, an unbalanced transmission line is connected to the unbalanced terminal 4 and the two balanced terminals 14 are connected.
Two signal lines of a balanced transmission line are connected to a and 14b, respectively. Further, the ground connection terminals 6a of the ground sheet 6 and the ground connection terminals 21 and 21 of the dielectric sheets 13a and 13b are provided.
Are connected vertically by the conductive layer 23 as shown in FIG. 1, and a grounding electric circuit is connected to this.

In this configuration, a single spiral inductor L _{1 to} L ₄ is carried for each dielectric sheet, so that each sheet carries two inductors as compared with the conventional structure in which two inductors carry two inductors. It is half the area.

Incidentally, the spiral inductor L ₁
The length of ~L ₄ stripline are usually designed so that the input and output signals lambda / 4. By the way, in such a configuration, the capacitor C formed between the capacitor electrode 3 of the connection sheet 2 and the ground electrode layer 6 of the ground sheet 5 is connected in parallel with the primary side balun line X. It is possible to make it shorter than λ / 4.

That is, the provision of the capacitor C makes it possible to shift the reflection characteristic to a lower frequency side. For this reason, if the strip line length of each of the spiral inductors L _{1 to} L ₄ is made shorter than λ / 4, the frequency becomes higher and a deviation from the target frequency occurs, but by providing such a capacitor C, the frequency becomes higher. The offset is adjusted so that the target frequency can be achieved. This can be understood from the relationship of f = 1 / 2π (LC) ^1/2 .

This means that the provision of the capacitor C makes it possible to make the length of the strip line of each of the spiral inductors L _{1 to} L ₄ smaller than λ / 4. The area for supporting the spiral inductor can be reduced, and the mounting area can be reduced by reducing the area of each sheet.

FIG. 3 shows a spiral inductor L
_{1 to} L ₄ are λ corresponding to a center frequency of 850 MHz by itself.
The length of each strip line is set to L =
Set it to 16.15mm, so that C ≒ 3.395pF,
The thickness of the connection sheet 2 and the area 3 of the capacitor electrode 3 were designed and the reflection characteristics thereof were examined. Here, the thickness of the connection sheet 2 is 0.05 mm, and the capacitor electrode 3 is
0.8 mm x 0.8 mm.

Looking at this reflected waveform, the frequency at which the reflected output was the smallest was 620 MHz. This is the capacitor C
The center frequency is 850 MHz in a state where is not used, which means that the center frequency has been adjusted to 620 MHz by inserting the capacitor C to the lower side. Therefore, even when applied to an input / output signal of 620 MHz, it is possible to use the spiral inductors L _{1 to} L ₄ of L = 16.15 mm, which is the same as the design of 850 MHz. For this reason, the strip line length of the spiral inductors L _{1 to} L ₄ can be shortened as compared with the configuration in which the capacitor C is not inserted, and the formation area can be reduced, so that a sheet having a smaller area as a whole is applied. You will get.

In the above configuration, since the ground electrode layer 6 of the ground sheet 5 is interposed, the spiral inductors L ₁ and L ₃ electromagnetically coupled above the connection sheet 2 by the ground electrode layer 6 and below the connection sheet 2. The spirally coupled spiral inductors L ₂ and L ₄ are electromagnetically shielded and do not interfere with each other.
Therefore, signals having a phase difference of 180 degrees can be respectively taken out from the balanced terminals 14a and 14b, and the balanced signals are output due to the cancellation of the noise.

[0030]

The present invention is directed to a primary dielectric sheet carrying single spiral inductors L ₁ and L ₂ constituting primary balun lines X above and below a connection sheet 2 on which an unbalanced terminal 4 is formed. 7a and 7b are stacked, and a secondary side dielectric sheet 13 carrying single spiral inductors L ₃ and L ₄ constituting a secondary side balun line Y outside thereof is further provided.
a and 13b are circumscribed and spiral inductors L ₃ and L ₄
Are connected to the ground electrode layers 19a, 19b of the ground sheets 18a, 18b disposed on the outermost side, and the capacitor formed between the capacitor electrode 3 and the ground electrode layer 6 is connected to the unbalanced terminal 4. Since C is connected in parallel with the primary side balun line X, the frequency characteristic can be adjusted to a lower side by the capacitor C, and each of the spiral inductors L _{1 to} L
The strip line length of ₄ can be shorter than lambda / 4, Thus, it is possible to reduce the area that carries the spiral inductor L ₁ ~L _4, each sheet can be a small area. Thus, the mounting area can be reduced as much as possible in combination with the lamination of the dielectric sheets carrying the single spiral inductor.

Further, since the ground electrode layer 6 on the ground sheet 5 adjacent to the connection sheet 2 is arranged at the center, electromagnetic shielding is performed above and below the ground electrode layer 6, and stable signal conversion is performed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a surface mount type balun transformer 1 of the present invention.

FIG. 2 is an exploded perspective view of the surface mount type balun transformer 1;

FIG. 3 is a waveform chart showing reflection characteristics.

FIG. 4 is an equivalent circuit diagram.

[Explanation of symbols]

1, 1b Surface mount type balun transformer 2 Connection sheet 3 Capacitor electrode 4 Unbalanced terminal 5 Ground sheet 6 Ground electrode layer 7a, 7b Primary dielectric sheet 13a, 13b Secondary dielectric sheet 18a, 18b Ground sheet 19a, 19b ground electrode layer L ₁ ~L ₄ spiral inductor C capacitors

Claims (1)

[Claims] An unbalanced terminal is formed on a surface of a connection sheet having a capacitor electrode connected to the unbalanced terminal.
Further, a ground sheet having a ground electrode layer formed thereon is laminated on the connection sheet to form a capacitor between the capacitor electrode and the ground electrode layer, and a primary-side dielectric sheet carrying a spiral inductor on the upper and lower surfaces of the sheet pair, respectively. The outer ends of the spiral inductors of both primary dielectric sheets are connected to each other, and the inner ends of the spiral inductors of the primary dielectric sheet circumscribed to the connection sheet are connected to unbalanced terminals on the connection sheet. A primary balun line is formed by connecting the two, and a secondary dielectric sheet carrying a spiral inductor is disposed so as to circumscribe each primary dielectric sheet. Ground sheets formed on the surface are circumscribed respectively, and the inner ends of the spiral inductors of both secondary dielectric sheets are circumscribed. A surface-mounted balun transformer comprising a secondary balun line connected to a ground electrode layer and having an outer end extending to a side edge of the sheet to be a balanced terminal.