KR20050109578A - Balun - Google Patents

Abstract

This invention is the balun which made the deviation of a phase significantly small. The balun of the present invention is a balun having three tracks of the first track (b), the second track (a) and the third track (c) arranged parallel to the ground plane, and the second track (a) and the first track (b). The three lines b are arranged at the same height from the ground plane GC, and the lengths in the longitudinal direction of the first line b, the second line a, and the third line c are all centered in the operating band. The capacitance Ca between the second line a and the ground plane GC is set to 1/4 of the wavelength of the frequency, and the capacitance Cab between the second line a and the first line b is obtained. And the ground plane GC on the side close to the center of the height direction of the second line (a) and the third line (c) and the second line (a) and the third line (c); The distance h3 is longer than the distance h2 between the center of the height direction of the first line b and the center of the height direction of the second line a and the third line c or the dielectric D3 ) Is smaller than the dielectric constant of the dielectric (D2).

Description

Balun {BALUN}

The present invention relates to a balun having three tracks arranged parallel to the ground plane.

In the recent high speed LSI for wireless LAN and Bluetooth, a balanced mode signal is often output to increase the noise margin of the signal.

On the other hand, since a non-balanced circuit is generally used for a wireless circuit, a balun (balanced unbalanced conversion circuit) for this conversion is required.

The balun can be configured by branching into a quarter-wave line and a three-quarter-wave line.

However, when branching into a 1 / 4-wavelength line and a 3 / 4-wavelength line, the line lengths are different. Therefore, even if the phase is 180 degrees with respect to the center frequency, the deviation of the phase increases even when the frequency is out of band.

Then, in view of the above point, an object of this invention is to provide the balun which drastically reduced the phase deviation.

1 is a cross-sectional view showing an example of the balun of the present invention. In the figure, a is a second line, b is a first line, c is a third line, and GC is a ground plane. Wa is the length in the width direction of the second line (a) and the third line (c), Wb is the length in the width direction of the first line (b), t is the first line (b), and the second line (a) And thickness in the height direction of the third line c. Sac is a space | interval of the width direction of a 2nd track a and 3rd track c, and Sab is the width | variety of the one end of the 2nd track a in the case where the one end of the 1st track b is reference | standard. Direction position. In addition, when Sab is positive, one end of the second line is outward from one end of the first line, and when Sab is negative, one end of the second line is inward of one end of the first line. do. The second line a and the third line c are symmetrical with respect to the line AA '. h is the distance between the ground plane GC, h1 is the distance between the center of the height direction of the first line b and the ground plane GC close to the first line b, and h2 is the first line b The distance between the center of the height direction and the center of the height direction of the second line (a) and the third line (c), h3 is the center of the height direction of the second line (a) and the third line (c) It is the distance from the ground plane GC near the 2nd line a and the 3rd line c. D1 is dielectric 1, D2 is dielectric 2, and D3 is dielectric 3.

2 is a plan view showing one example of an equivalent circuit diagram of the balun of the present invention. In the figure, P _in 1 is input terminal 1, P _out 2 is output terminal 2, P _out 3 is output terminal 3, and u, v, w, x, y and z are six terminals. In addition, the length of the longitudinal direction with respect to the 1st line (b), the 2nd line (a), and the 3rd line (c) is 1/4 of the wavelength of the center frequency in an operating band.

3 is a graph showing a change in capacitance when the distance between the second line and the third line at h2 = h3 is changed.

4 is a graph showing a change in capacitance when the distance between the second line and the third line in h2 <h3 is changed.

Fig. 5 shows the interval Sa, the capacitance Ca + Cac, and the input / output impedance Z _in × Z _out satisfying the condition Ca = Cab when the lengths in the width direction of the second line and the third line are changed. ^It is a graph showing the change of each value for ^1/2 .

6 is a graph showing the transmission characteristics S ₂₁ to the output terminal 2 and the transmission characteristics S ₃₁ to the output terminal 3.

FIG. 7 is a graph showing the phase difference between the output terminal 2 and the output terminal 3 when a signal is input from the input terminal 1. FIG.

FIG. 8 is a graph showing the reflection when the differential amplitude is put into the reflection coefficient S ₁₁ of the input terminal 1 and the output terminal 2 and the output terminal 3.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, as a result of earnest research, the conventional wire length of the three lines which comprise a balanced circuit was made into 1/4 of the wavelength of the center frequency in an operating band, etc. It was found that the problem can be solved, and the present invention was completed.

That is, the balun of this invention is a balun which has three lines of the 1st line, the 2nd line, and the 3rd line arrange | positioned in parallel with respect to a ground plane, and the said 2nd line and the said 3rd line are the same from the ground plane. The length of the first line, the second line, and the third line in the longitudinal direction are all one quarter of the wavelength of the center frequency in the operating band, and the second line and the ground plane The capacitance is made equal to the capacitance between the second line and the first line.

In the present invention, the distance between the center of the height direction of the second line and the third line and the ground plane on the side closer to the second line and the third line corresponds to the center of the height direction of the first line. The distance between the second line and the center of the height direction of the third line can be longer. In addition, the dielectric constant of the dielectric between the plane formed by the center of the height direction of the second line and the third line and the ground plane close to the second line and the third line is defined as the first line. It may be made smaller than the dielectric constant of the dielectric between the plane formed by the center of the height direction of the line and the plane formed by the center of the height direction of the second line and the third line.

Moreover, the length of the width direction of the said 2nd line and the said 3rd line is made the same, and the said 2nd line and the said 3rd line are bilaterally symmetric with respect to the plane formed by the center of the width direction of the said 1st line. Disposed at a position, and one terminal of the first line is used as an input terminal of an unbalanced signal, the input terminal of the unbalanced signal is connected to one terminal of the third line, and the other terminal and the second terminal of the first line are connected. One terminal of the line is connected to the ground plane, and the other terminal of the second line and the other terminal of the third line are output terminals of the balanced signal, and the impedance of the input terminal of the unbalanced signal and the balance signal The impedance of the output terminal can satisfy the following relationship.

(Ca + Cac) / ε _o = ε _r ^1/2 × Z _air / (Z _in × Z _out ) ^1/2

Where Ca is the capacitance C between the second line and the ground plane, Cac is the capacitance C between the second line and the third line, ε _o is the dielectric constant in vacuum, ε _r is the ratio The dielectric constant, Z _air, is the characteristic impedance (Ω) in vacuum, Z _in is the impedance (Ω) of the input terminal of the unbalanced signal, and Z _out is the impedance (Ω) of the output terminal of the balanced signal.

1 is a cross-sectional view showing one embodiment of the balun of the present invention, and FIG. 2 is a plan view showing one embodiment of the balun of the present invention.

In the present invention, the lengths in the longitudinal direction of the first line (b), the second line (a), and the third line (c) are all 1/4 of the wavelength of the center frequency in the operating band, and the second line ( a) and the third line c are the same height from the ground plane GC, and the capacitance Ca between the second line a and the ground plane GC is the second line a and the first line. It is the same as the capacitance Cab between (b) (hereinafter, it may be called "Ca = Cab").

In the balun of the present invention, the distance between the center of the height direction of the second line (a) and the third line (c) and the ground plane (GC) closer to the second line (a) and the third line (c) (Hereinafter, it may be referred to as “h3.”) The distance between the center of the height direction of the first track b and the center of the height direction of the second track a and the third track c (hereinafter, It is preferable to make it longer than "(h2 may be called.)" (Hereinafter, it may be called "h2 <h3"). In the following description, the distance between the center of the height direction of the first line b and the ground plane GC close to the first line b may be referred to as h1.

In the balun of the present invention, instead of h2 < h3, a plane formed by the center of the height direction of the second line a and the third line c, the second line a, and the third line a. The dielectric constant ε3 of the dielectric (hereinafter sometimes referred to as "D3") between the ground planes GC close to (c) and the plane formed by the center of the height direction of the first line b; It is made smaller than the dielectric constant (epsilon) 2 of the dielectric (henceforth "D2") between the planes formed by the center of the height direction of the 2nd line a and the 3rd line c. May be referred to as "ε3 <ε2". In the following description, the dielectric between the plane formed by the center of the height direction of the first line b and the ground plane GC close to the first line b may be referred to as D1.

In addition, since the balun of the present invention in which h2 < h3 is filled with a dielectric having a relative dielectric constant epsilon _r , the dielectric constants of dielectric 1, dielectric 2 and dielectric 3 are each the same as epsilon _r .

The device simulator is described below for the capacitance Ca between the second line a and the ground plane GC, and the capacitance Ca between the second line a and the first line b. The result of the electromagnetic field analysis used is shown.

First, h2 = h3 = 2 micrometers, change the distance Sac of the 2nd line a and the 3rd line c, and investigate the change of the capacitance Ca and the capacitance Cab. did. The result is shown in FIG.

It can be seen from FIG. 3 that Ca> Cab is in the entire changed interval Sac, and Ca = Cab is not satisfied.

Therefore, when the following conditions are provided, it turns out that Ca = Cab is satisfied at least.

a) h2 <h3

In this case, when the interval Sac is increased, the increase amount of the capacitance Ca becomes larger than the increase amount of the capacitance Cab. If the interval Sac is set to Ca <Cab, when the interval Sac is narrowed, it is changed to Ca <Cab, Ca = Cab, and Ca> Cab when the interval Sac is sequentially expanded, so that the interval satisfying Ca = Cab ( Sac) can be estimated.

Moreover, the aspect of the change of the capacitance Ca and the capacitance Ca in the case where the space | interval Sac is changed with h2 = 1.5 micrometer and h3 = 2 micrometer is shown in FIG. It can be seen from FIG. 4 that Ca = Cab is satisfied when the spacing Sac is about 10.3 micrometers.

b) ε 3 <ε 2

In this case, even if h2 = h3, there exists an interval Sac which satisfies Ca = Cab.

In the case of ε 3 <ε 2, strictly speaking, it is not an isotropic medium, but its effect is small, and the balun can be configured similarly to the case of h 2 <h 3.

In the present invention, the length (hereinafter sometimes referred to as "Wa") in the width direction of the second line a is the same as the length in the width direction of the third line c, and the first line ( It is preferable that it is shorter than the length of the width direction of b) (henceforth "Wb".). It is preferable to make all the thickness (henceforth "t" may be called hereafter) of the height direction of the 1st track | wire b, the 2nd track | wire a, and the 3rd track | wire c.

Moreover, it is preferable that the 2nd line a and the 3rd line c are arrange | positioned at the position left-right symmetric with respect to the line formed by the center of the width direction of the 1st line b, and its extension line, and a 1st line One terminal of the line (b) is an input terminal of the unbalanced signal, and is preferably connected to one terminal of the third line (c), and the other terminal of the first line (b) and the second line ( Preferably, one terminal of a) is connected to the ground plane GC, respectively, and the other terminal of the second line a and the other terminal of the third line c are preferably output terminals of the balanced signal.

The distance Wa in the width direction of the second line a and the third line c, and the interval in the width direction of the second line a and the third line c (hereinafter referred to as "Sac") Is preferably selected appropriately to satisfy the relationship shown below in addition to the condition of Ca = Cab.

(Ca + Cac) / ε ₀ = ε _r ^1/2 × Z _air / (Z _in × Z _out ) ^1/2

Wherein Ca is the capacitance C between the second line (a) and the ground plane (GC), Cab is the capacitance (C) between the second line (a) and the first line (b), Cac is The capacitance C between the two lines (a) and the third line (c), ε _o is the dielectric constant in vacuum, ε _r is the relative dielectric constant, Z _air is the characteristic impedance (Ω) in vacuum, and Z _in is unbalanced The impedance of the input terminal of the signal (Ω), Z _out is the impedance of the output terminal of the balanced signal (Ω).

Below, the process which derived this relationship is shown. In addition, since conductor loss and dielectric loss of a line are small, it is assumed that there is no loss.

The Y matrix (6 rows and 6 columns) of the balun of the three-line line shown in FIG.

Where ω is frequency, u = j × tan (kL), where k is the phase constant in the dielectric and L is the route length.

C is the C matrix of three lines,

However, Cb is the capacitance C between the first line and the ground plane.

Since line length L is 1/4 of the wavelength of the center frequency in the operating band, 1 / u can be approximated to 0, and (1-u ² ) ^1/2 / u to approximate -j. Can be.

Therefore, the Y matrix can be arranged as follows.

As shown in Fig. 2, six terminals are respectively used as the u terminal, the v terminal, the w terminal, the x terminal, the y terminal, and the z terminal, and the v terminal and the third line of the input terminal 1 (P _in 1) and the first line, respectively. The w terminal of the first line and the y terminal of the first line and the u terminal of the second line are respectively connected to the ground plane, and the x terminal and the output terminal 2 (P _out 2) and the third line of the second line are respectively connected. Consider a case where the terminal z and the output terminal 3 (P _out 3) are electrically connected to each other.

Under these conditions, the following equations hold.

Vu (voltage at u terminal) = Vy (voltage at y terminal) = 0

Vv (voltage at terminal v) = Vw (voltage at terminal w) = V1 (voltage at terminal 1)

J1 (current at input terminal 1) = Jv (current at terminal v) + Jw (current at terminal w)

Vx (voltage of x terminal) = V2 (voltage of output terminal 2)

Jx (current at x terminal) = J2 (current at output terminal 2)

Vz (voltage at z terminal) = V3 (voltage at output terminal 3)

Jz (current at z terminal) = J3 (current at output terminal 3)

Therefore, the following equation is established.

J1 (current at input terminal 1) has the following relationship.

J1 = Jv + Jw

J1 = jω {-Cab × V2-Cab × V3-Cac × V2 + (Ca + Cab + Cac) V3} / kz

J1 = jω {-(Cab + Cac) × V2 + (Ca + Cac) V3} / kz

Therefore, the Y-matrix of three terminals is given by the following formula | equation.

Consider the case where the above Y matrix satisfies the condition of the balun. The lossless balun satisfies the following conditions in consideration of the central symmetry.

S ₁₁ = 0

S ₂₁ = -S ₃₁ = 2 ^1/2 × exp (jα) / 2

S ₂₂ -S ₃₂ = S ₃₃ -S ₂₃ = 0

Since it is lossless, the following equation holds.

│S ₂₁ │ ² + │S ₂₂ │ ² + │S ₂₃ │ ² = 1

Sij = Sji i, j = 1, 2, 3

Therefore, the S matrix becomes as follows.

However, S ₂₂ ² = 1/4, and S ₂₂ = exp (jβ) / 2.

The above is an expression in the case where both the input and output terminals are the reference impedances. However, if the above-described S matrix is converted to the Y matrix in the case of Z _in and Z _out / 2, the Y matrix Yb is Become together.

The Y-matrix of three terminals was given by the following formula | equation.

In order for this to be equal to the Y matrix of the input and output terminal impedances Z _in and Z _out / 2, it is necessary that exp (2? J) = -1 and exp (? J) = 1. When α = π / 2 and β = π, Yb can be expressed as follows.

By comparing Y and Yb and designing the structure of the C matrix satisfying the following equation, the balun is achieved.

ω (Cab + Cac) = k _z / (Z _in × Z _out ) ^1/2

ω (Ca + Cac) = k _z / (Z _in × Z _out ) ^1/2

In other words,

ω (Cab + Cac) = ω (Ca + Cac) = k _z / (Z _in × Z _out ) ^1/2

Therefore, necessary conditions are the following two expressions.

Ca = Cab

vp (Ca + Cac) = 1 / (Z _in × Z _out ) ^1/2

Since the specific permeability is almost 1 in a normal metal, the phase velocity Vp can be expressed as follows using Z _air = (μ _o / ε _o ) ^1/2 = 120π.

vp = 1 / (εμ) ^1/2

vp = 1 / (ε _r ε ₀ μ ₀ ) ^1/2

vp = 1 / (ε ₀ × Z _air × ε _r ^1/2 )

Thus, (Ca + Cac) = 1 / vp (Z _in × Z _out ) ^1/2

(Ca + Cac) = ε ₀ × Z _air × ε _r ^1/2 / (Z _in × Z _out ) ^1/2

therefore,

(Ca + Cac) / ε ₀ = ε _r ^1/2 × Z _air / (Z _in × Z _out ) ^1/2

In the present invention, even if the input / output impedance of the balun is specified, the length Wa in the width direction of the second line a and the third line c, the length of the second line a, and the third line c are defined. By selecting the interval Sac, a balun of desired input / output impedance can be produced.

The interval Sac, the capacitance Ca + Cac, and the input / output impedance (Sac) for changing the length Wa in the width direction of the second line a and the third line c and satisfying the condition Ca = Cab Z _in x Z _out ) ^1/2 is shown in FIG. 5. In addition, the length Wb of the width direction of the 1st track | wire b was fixed at 16 micrometers.

It is clear from FIG. 5 that even if the balun's input / output impedance is designated, the balun of the desired input / output impedance can be produced by selecting the length Wa and the spacing Sac in the width direction.

In addition, in the strip line type balun of the present invention, if the aspect ratio is the same, the characteristic does not change even if the absolute dimension is changed.

EMBODIMENT OF THE INVENTION Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to this embodiment, It can change in various aspects in the technical scope grasped | ascertained from description of a claim.

(Example 1)

The performance confirmation experiment was performed about the balun of the 2.45GHz band which becomes this invention which employ | adopted the structure shown in FIG.1 and FIG.2, the input impedance of 50 ohms, and the output impedance of 100 ohms.

(Z _in × Z _out ) ^1/2 = 70.7 Ω, so h2 = 1.5 micrometers, h3 = 2 micrometers, Wa = 3.35 micrometers, Sab = 0.17 micrometers, Sac = 8.96 micrometers, Wb = 16 micrometers Meter.

The length of the line was 2.45 GHz, which was about 15.5 mm, which was roughly equivalent to 1/4 wavelength in the case of permittivity 3.6.

In addition, in an actual printed circuit board, the size is about 100 micrometers, so if it is 100 times, h2 = 150 micrometers, h3 = 200 micrometers, Wa = 335 micrometers, Sab = 17 micrometers, Sac = 896 micrometers, Wb = 1600 micrometers.

6 to 8 show the results of the electromagnetic field simulation.

FIG. 6 is a graph showing the transmission characteristic S ₂₁ to the input terminal 1 which is an unbalanced terminal and the output terminal 2 which is a balanced terminal, and the transmission characteristic S ₃₁ to the output terminal 3 which is a balanced terminal. It can be seen from FIG. 6 that the amplitudes are almost the same at 2.45 GHz.

FIG. 7 is a graph showing the phase difference between the output terminal 2 and the output terminal 3 when a signal is input from the input terminal 1. FIG. It can be seen from FIG. 7 that the phase is almost 180 degrees, and the deviation of the phase is greatly reduced.

8 shows the reflection (S ₂₂ + S ₂₃ -2 × S ₂₃ ) / 2 ^3/2 stages when differential amplitude is put into the reflection coefficient S ₁₁ of the input terminal 1 and the output terminal 2 and the output terminal 3; S ₂₂ is a reflection coefficient of the output terminal 2, and S ₂₃ is a transmission coefficient from the output terminal 3 to the output terminal 2). It can be seen from FIG. 8 that the desired input / output impedance is obtained at 25 dB or less at 2.45 GHz.

As described above, the balun according to the present invention is useful as a balun embedded in a multilayer board because it can obtain the performance of commercially available chip components and can significantly reduce the phase deviation. It is easy to take a countermeasure, and is suitable for the part which requires radical miniaturization.

Claims (4)

A balun having three lines of the first line, the second line, and the third line arranged in parallel with the ground plane, wherein the second line and the third line are arranged at the same height from the ground plane, and the first line is disposed. The lengths in the longitudinal direction of the line, the second line and the third line are all 1/4 of the wavelength of the center frequency in the operating band, and the capacitance between the second line and the ground plane is set to the second line. The balun characterized by the same as the capacitance between the said 1st line. The distance between the center of the height direction of the said 2nd track and the said 3rd track, and the ground plane of the side which is closer to the said 2nd track and the said 3rd track is the center of the said 1st track height direction, The balun which was made longer than the distance from the center of the height direction of a 2nd track and the said 3rd track. The dielectric constant of the dielectric between the plane formed by the center of the height direction of the said 2nd line and the said 3rd line, and the said 2nd line, and the ground plane close to the said 3rd line is said 1st line The balun characterized by being smaller than the dielectric constant of the dielectric between the plane formed by the center of the height direction of and the plane formed by the center of the height direction of the second line and the third line. The width direction of the said 2nd line and the said 3rd line is the same, and the said 2nd line and the said 3rd line are the width directions of the said 1st line in any one of Claims 1-3. Disposed at a position symmetrically with respect to the plane formed by the center of the circuit, and having one terminal of the first line as an input terminal of an unbalanced signal, and connecting the input terminal of the unbalanced signal to one terminal of the third line. And connecting the other end terminal of the first line and one end terminal of the second line with the ground plane, respectively, the other end terminal of the second line and the other end terminal of the third line as the output terminal of the balanced signal, and A balun characterized by satisfying the following relationship between the impedance of the input terminal of an unbalanced signal and the impedance of the output terminal of the balanced signal. (Ca + Cac) / ε ₀ = ε _r ^1/2 × Z _air / (Z _in × Z _out ) ^1/2 Where Ca is the capacitance C between the second line and the ground plane, Cac is the capacitance C between the second line and the third line, ε _o is the dielectric constant in vacuum, ε _r is the ratio The dielectric constant, Z _air, is the characteristic impedance (Ω) in vacuum, Z _in is the impedance (Ω) of the input terminal of the unbalanced signal, and Z _out is the impedance (Ω) of the output terminal of the balanced signal.