JP2633357B2 - High frequency transformer for power divider - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency transformer, and more particularly to a transformer used for a power divider in a TV frequency band.

[Conventional technology]

The frequency handled by the conventional power distributor for television broadcast reception is 5 to 860 MHz, including CATV and UHF, and the transformer used is a conductor wound using a through hole in a columnar ferrite core having a through hole. It is configured by mounting.

Fig. 13 shows a state in which a high-frequency transformer configured using a conventional toroidal-type ferrite core is mounted on a printed circuit board to form a power divider. The input terminal IN and the output terminal provided on the printed circuit board The terminals of the transformers T1 and T2 are connected to OUT, the distribution terminal TAP and the absorption terminal, and the absorption terminal is connected to a resistor R whose other end is grounded.

FIG. 14 shows a circuit configuration of such a power divider, which is configured using two transformers T1 and T2 having the same configuration. Assuming that the turns ratio of these transformers is N, the voltage of each part in this transformer is, for example, TV Communications,
As described in April 1967 P80, the relationship is as follows. If the input voltage is Ei, the output voltage is Eo, and the transformer primary winding voltage is Ek, Eo = Ei−Ek (1) Therefore, Ek = Ei−Eo (2) Here, the voltage between both ends of the absorption resistor r in the figure. If Er = 0, Ei / N = N · Ek (3) Ek = Ei / N ² (4)

Substituting this equation (4) into equation (1) gives Eo = Ei−Ei / N ² Ei (1-1 / N ² ) (5), and substituting equation (5) into equation (2) , Ek = Ei / N ² (6) From the figure, Et = Ei / N = N · Ek (7). By substituting equation (2) into equation (7), Et = N · Ek = N (Ei−Eo) (8) Here, assuming Ei = 1, equations (5), (6),
Substituting into (7), Et = 1 / N Eo = 1-1 / N ² Ek = 1 / N ² , and the characteristics as a transformer are determined by the turns ratio of the primary to secondary windings of the transformer. Will be.

[Problems to be solved by the invention]

Compared to the above ideal transformer, the actual transformer is
Inferior in characteristics. That is, since the secondary winding of the transformer T1 is inserted in parallel between the input and output as shown in FIG. 14, sufficient electric characteristics cannot be obtained by simply setting the winding ratio. If the winding ratio is not maintained and the impedance of the secondary winding is not sufficiently increased, insertion loss increases and input impedance deteriorates.

For this purpose, the number of turns of the secondary winding must be increased. However, if this is done, the line capacitance increases, the actual impedance does not increase, and resonance occurs due to stray capacitance and inductance, and the upper limit of the operating frequency is determined. Resulting in.

Fig. 15 shows the transformer of Fig. 14 with a thickness of 3mm,
This figure shows the electrical characteristics of a toroidal ferrite core having a length of 5 mm, a hole diameter of 1 mm, and an initial magnetic permeability of 3000 and a primary winding of 0.5 and a secondary winding of 55 (turning ratio of 11). That is, the signal transmission characteristics among the input terminal IN, the output terminal OUT, and the distribution terminal TAP show deterioration at a frequency of about 1200 MHz or more for the reason described above. In particular, the isolation characteristics between the output terminal OUT and the distribution terminal TAP significantly deteriorate.

Here, in recent years, with the start of satellite broadcasting, distribution at the intermediate frequency has been required, and it has become necessary for power distributors for television broadcast reception to handle higher frequencies, especially in Europe up to 1750 MHz. Characteristics are required.

In order to handle such a high frequency, the power distributor using the conventional high-frequency transformer is insufficient. In other words, a conventional transformer with a configuration in which a conductive wire is wound around a ferrite core not only has a large stray capacitance between the windings but also has an indefinite value, and requires work to adjust the difference in characteristics between products, and cannot adjust the stray capacitance. The characteristic is degraded as the frequency becomes higher.

The present invention has been made in consideration of the above points, and has as its object to provide a transformer for a power divider in which characteristics are not deteriorated up to a frequency band exceeding a conventional frequency band for television broadcasting.

[Means for solving the problem]

A columnar ferrite core having a central through-hole, and a plurality of peripheral through-holes disposed substantially concentrically with respect to the central through-hole; at least one conductive wire is inserted into the peripheral through-hole; and The center hole includes a winding wound so that all of the conductors of the peripheral through-hole are inserted, and a conductive element provided to cover the entire outer peripheral surface of the ferrite core and connected to ground. And a high-frequency transformer for a power distributor.

(Operation)

The ferrite core has a central through-hole and a plurality of peripheral through-holes arranged substantially concentrically around the central through-hole, and at least one conductive wire is inserted into the plurality of peripheral through-holes. Then, all the conductors are inserted into the center through hole.

When the conductor is inserted, the guide groove provided on the inner wall of the through hole guides the conductor and holds the conductor at a predetermined position. The magnetic flux generated by the conductive wire inserted into each through-hole passes through the magnetic path closed in the ferrite core, so that it does not leak to the outside, and the leakage magnetic flux does not affect the characteristic impedance. Therefore, the characteristic impedance of the high-frequency transformer is a predetermined value determined by the outer shape of the conductive element and the conductor, the distance between them, the magnetic permeability and the dielectric constant of the core interposed therebetween.

Moreover, the stray capacitance is stable, and there are few uncertainties due to the stray capacitance.

〔The invention's effect〕

According to the present invention, the winding is substantially accommodated in the ferrite core, and the outer peripheral surface of the ferrite core is covered with the conductive element, so that the leakage magnetic flux from the winding is small, so that the characteristic impedance is kept constant. In addition, since the windings are precisely arranged at individual positions using the through-holes for winding the ferrite core, the stray capacitance between the windings is reduced, and the operating frequency band can be greatly expanded. Further, there is no variation in the stray capacitance between the windings, and the characteristics caused by the stray capacitance are constant, which is suitable for mass production. In addition, since only one winding is inserted into each through hole, workability is good and it is optimal for mass production.

〔Example〕

FIG. 1 shows the appearance of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a columnar ferrite core, which has one through hole 2 at the center, and is located at a peripheral position on the concentric circle. 6
A plurality of through holes 3 are formed, and a conductive layer 4 is provided on the outer periphery. Then, the primary winding is inserted into the center through hole 2,
A secondary winding is radially wound between the central through-hole 2 and the surrounding through-hole 3. Therefore, one conducting wire of the primary winding and seven conducting wires of the secondary winding are inserted into the through hole 2 at the center.

FIGS. 2 (a) and 2 (b) and FIGS. 3 (a) and 3 (b) show that a conductor 5 or 6 is inserted into the center through hole 2 or the peripheral through hole 3 of the ferrite core and one end thereof is provided with a signal source SG.
And a magnetic circuit-like behavior in the ferrite core when the terminal resistor R is connected to the other end. First, in the case of FIG. 2, when a current i is passed through the conducting wire 5 through the center through hole 2, a magnetic flux shown by a broken line in FIG. 2B passes.
On the other hand, in the case of FIG. 3, when a current flows through the conducting wire 6 between the center through hole 2 and the peripheral through hole 3, a magnetic flux shown by a broken line in FIG. That is, the magnetic flux by the conductor 5 and the magnetic flux by the conductor 6 have the same magnetic path.

FIG. 4 shows a single high-frequency transformer in which the windings shown in FIGS. 2 and 3 are wound around the same core. As shown in the figure, conducting wires 5 and 6 are inserted into through holes 2 and 3 provided in the ferrite core 1, respectively, and the outer peripheral surface of the ferrite core 1 is covered with a conductive coating layer 4.

FIGS. 5 (a), (b), 6 (a), (b) and 7 (a), (b) show an equalizer circuit diagram and an external view of a transformer according to the present invention, respectively. It is.

FIGS. 5A and 5B show an example of a high frequency transformer for polarity reversal, which is used as a component of a balun transformer or a hybrid circuit in the field of CATV.
The winding usually uses a parallel two-wire or coaxial cable.

FIGS. 6 (a) and 6 (b) show a high frequency transformer for impedance conversion configured in an auto-transformer format, and FIGS. 7 (a) and 7 (b) show an impedance conversion configured as a two-winding transformer. For high frequency transformers. CA
In the field of TV, it is frequently used as a 75 ohm to 37.5 ohm 2: 1 impedance converter.

FIGS. 8 (a) and 8 (b) show a distributor constituted by using two high-frequency transformers shown in FIG. 1 and a circuit thereof. As shown in FIG. 2A, one end a1 of the primary winding of one transformer T1 is connected to the input terminal IN, and the other end a1 '.
To the output terminal OUT, and connect one end b1 of the secondary winding to the conductive layer 4
And the other end b1 'is connected to the absorption terminal DUM, and the absorption terminal DUM is grounded via the resistor R. Another transformer T
2, one end a2 'of the primary winding is grounded via an absorption resistor R,
The other end a2 is connected to the distribution terminal TAP, one end b2 'of the secondary winding is connected to the output terminal OUT, and the other end b2 is grounded. As a result, a distributor as shown in FIG.

FIG. 9 shows an example of a core used in the embodiment of the present invention, and has a contour shape in a state where six wires are bundled so that six wires are inserted into the center position of the ferrite core 1. Are provided, and each peripheral hole 3 is six for one.

FIG. 10 shows a state in which the embodiment of the present invention is mounted, in which two transformers T1 and T2 are connected to an input terminal IN, an output terminal OUT and a distribution terminal TAP provided on a printed circuit board, and to an absorption terminal. A resistor R is connected.

FIG. 11 shows the signal transmission characteristics of the power divider using the high-frequency transformer according to the present invention, and has a diameter of 5 mm and a height of 3 mm.
The diameter of the center through hole is 1.5mm and the diameter of the surrounding through hole is 1.0m
A high-frequency transformer is formed by winding a polyurethane wire having a diameter of 0.18 mm around a ferrite core of m, μi = 3000.

It is clear from comparing the characteristics of FIG. 11 with the characteristics of FIG. 15 described above, but the transmission characteristics between the output terminal OUT and the distribution terminal TAP are flat up to 2000 MHz, and the isolation characteristics are greatly improved. ing.

FIG. 12 shows another example of the core used in the embodiment of the present invention.
Is provided, and the peripheral through-holes 3 are arranged so as to form a sector around the center through-hole 2.

[Brief description of the drawings]

FIG. 1 is an external view showing an embodiment of the present invention, FIGS. 2 and 3 are diagrams for explaining the operation of a winding in the ferrite core of FIG. 1, and FIG. 4 is a diagram of FIG. FIGS. 5 (a) and (b) to FIGS. 7 (a) and 7 (a) show a high-frequency transformer in which the windings and the windings of FIG. 3 are wound around the same core.
(B) is a diagram showing a configuration example of a transformer according to the present invention, FIG.
FIGS. 2A and 2B show the high-frequency transformer shown in FIG.
FIG. 9 is a diagram illustrating a distributor configured by using a plurality of ferrite cores, and FIG. 9 is a diagram illustrating an example of a ferrite core used in the present invention.
FIG. 10 is a view showing a state where a distributor constituted by using the high-frequency transformer according to the present invention is mounted on a printed circuit board,
The figure shows the signal transmission characteristics of the distributor according to the invention, FIG.
The figure shows another example of the core used in the embodiment of the present invention.
FIG. 13 is a diagram showing a state of mounting a power divider using a conventional high-frequency transformer on a printed circuit board, FIG. 14 is a circuit diagram of a general high-frequency power divider, and FIG. 15 is a diagram of a conventional high-frequency power divider. FIG. 3 is a diagram illustrating signal transmission characteristics. 1 ... ferrite core, 2 ... center through hole, 3 ... peripheral through hole, 4 ... conductive layer, 5, 6 ... wire, T ... transformer, R ... absorption resistance.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshiyuki Naito 8-9-29 Tsukimino, Yamato-shi, Kanagawa (56) References JP-A-62-71206 (JP, A) JP-A-61-295610 (JP, A) ) Japanese Utility Model Showa 63-134512 (JP, U) Japanese Utility Model Showa 63-33610 (JP, U)

Claims (4)

(57) [Claims] 1. A columnar ferrite core having a central through hole, and a plurality of peripheral through holes arranged substantially concentrically with respect to the central through hole, at least one ferrite core in the peripheral through hole. A winding is inserted into the center through-hole so that the entire conductor is inserted into the center through-hole, and is provided so as to cover the entire outer peripheral surface of the ferrite core, and is connected to ground. A high-frequency transformer for power dividers with conductive elements. 2. The high frequency transformer for a power distributor according to claim 1, wherein said conductive element is a metal pipe. 3. The high frequency transformer according to claim 1, wherein said conductive element is a metal plate or a foil. 4. The high frequency transformer for a power distributor according to claim 1, wherein the conductive element is formed by printing or depositing a conductive material.