JP2900736B2 - Impedance conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impedance conversion element such as a choke coil and a matching strip line used in a high-frequency circuit such as a high-frequency power amplifier and a voltage-controlled oscillator of a radio receiver such as an automobile telephone and a portable telephone.

[0002]

2. Description of the Related Art In recent years, with the spread of small wireless communication devices such as car phones, mobile phones, and cordless phones, miniaturization and high performance of high frequency circuits used in these devices have emerged as research subjects. Research on miniaturization and high quality of circuits such as voltage-controlled oscillators and the like has been actively pursued. In particular, one of the problems to be solved is to improve an element that converts impedance in a distributed manner, such as a strip line occupying a large area, in these circuits.

[0003] In response, many impedance conversion elements have been developed. Examples are shown in FIGS. FIG. 4 is a diagram schematically showing an example of a conventional impedance conversion element. In the impedance conversion element 10 shown in the figure, a thin wire 12 is formed by a thin film on the upper surface of a ceramic plate 11 having a low dielectric constant, and both ends of the thin wire 12 are formed on opposite sides of the ceramic plate 11 as surface mount components. It is connected to the mounting electrode 13.

FIG. 5 is a diagram showing a part of another example of a conventional impedance conversion element using a microstrip line. In the impedance conversion element 20, a microstrip line 22 of a thick film is formed on a low dielectric constant ceramic plate 21 constituting a high frequency circuit such as a high frequency power amplifier or a voltage controlled oscillator, together with mounting electrodes and wiring between components. ing. Micro strip line 2
2, mounting lands 24 for mounting surface mounting components 23 such as a high-frequency power amplifier and a voltage controlled oscillator are formed.

[0005]

However, the impedance conversion element 10 shown in FIG. 4 has the following problems. That is, when this impedance conversion element is mounted on a substrate constituting a high-frequency circuit, the surface of the ceramic plate 11 on which the fine wires 12 are not formed is exposed, so that the substrate on which the impedance conversion element 10 is mounted is exposed. Depending on the state (for example, whether or not there is a ground electrode, and whether or not a signal line is provided), the characteristic impedance of the impedance conversion element 10 changes. Further, since the dielectric constant of the ceramic plate 11 is small, the wavelength shortening rate is small and the distribution constant cannot be controlled.
As a result, long wiring is required, and the impedance conversion element 10 becomes large. In addition, since the fine wire 12 is disposed on the ceramic plate 11, the impedance conversion element 10 has an intermediate characteristic between the distributed constant type and the lumped constant type. Since it is not high and the line length cannot be secured for the wavelength as in the case of the distributed constant strip line, it is impossible to convert the impedance into a desired impedance without causing a substantial phase change. Further, since the thin wire 12 is formed of a thin film, the DC resistance of the impedance conversion element 10 is large.

On the other hand, the impedance conversion element 20 shown in FIG.
However, there is a problem that the microstrip line 22 occupies a large area because it is impossible to dispose a fine wire and the dielectric constant of the substrate must be reduced in order to suppress the stray capacitance. Microstrip line 2
2 is designed with a distribution constant in consideration of the dielectric constant of the ceramic plate 21, so that the impedance conversion element 20 designed for one application cannot be used for another frequency band, and the impedance conversion element is not used for each frequency band. As a result of having to create, there is a problem that costs are increased for needs such as high-mix low-volume production.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a small impedance conversion element having a large characteristic impedance and the characteristic impedance does not change.

[0008]

To achieve the above object, an impedance conversion element according to the present invention comprises a dielectric plate having a high dielectric constant and a microstrip line formed on one surface of the dielectric plate. A magnetic plate having a high magnetic permeability provided on one surface of the dielectric plate so as to sandwich the microstrip line.

In another aspect of the invention, the impedance conversion element is formed on each of the opposing surfaces thereof, and is connected between both ends of the microstrip line. A ground electrode formed so as not to be electrically connected to the electrode.

[0010]

The dielectric plate having a high dielectric constant has a large wavelength shortening ratio, so that the impedance conversion element can be downsized and the distribution constant of the microstrip line can be controlled.
Also, by arbitrarily selecting the magnetic permeability of the magnetic plate,
A decrease in characteristic impedance due to the dielectric constant of the dielectric plate is prevented.

[0011]

FIG. 1 is a view showing an embodiment of the impedance conversion element according to the present invention, wherein 1a is a perspective view showing the appearance thereof, and 1b is a perspective view with a part thereof cut away. The impedance conversion element 1 is formed by forming a microstrip line 3 with a thick film or a thin film on a ceramic plate 2 having a high dielectric constant, and laminating a ferrite plate 4 having a high magnetic permeability so as to cover the microstrip line 3.

A surface mounting electrode 5 is formed so as to cover the opposing surface of the unit in which the ceramic plate 2 and the ferrite plate 4 are integrated with the microstrip line 3 interposed therebetween and the peripheral edge thereof. Stripline 3
Are electrically connected to the surface mounting electrode 5. The portion sandwiched between the surface mounting electrodes 5 on both sides is covered with a grounding electrode 6 formed so as not to make electrical contact with these surface mounting electrodes 5.

Next, the manufacturing process of the impedance conversion element 1 will be described. (1) An Ag microstrip line 3 is formed as a thick or thin film on a ceramic plate 2 and fired. (2) The glass paste is thinly printed on the microstrip line 3. (3) A ferrite plate 4 having the same area as the ceramic plate 2 is placed on the printed glass paste.
Are laminated and fired at a temperature higher than the melting point of glass and lower than the melting point of Ag to integrate them. (4) To be connected to the entire periphery of the integrated ceramic plate 2 and ferrite plate 4 and to both ends of the microstrip line 3,
Ag or Ag-Pd paste is dipped and fired. (5) Finally, the above-mentioned paste is removed by a dicing machine except for portions that become the surface mounting electrodes 5 and the grounding electrodes 6.

Since the impedance conversion element 1 formed in this manner uses the ceramic plate 2 having a high dielectric constant and thus has a large wavelength shortening rate, the distribution constant can be controlled and the size can be reduced. The decrease in characteristic impedance can be prevented by the ferrite plate 4 having magnetic permeability. In addition, since the grounding electrode 6 is formed around the impedance conversion element 1, stable characteristics can be obtained regardless of the state of the substrate on which the impedance converting element 1 is mounted.

The reason why the characteristic impedance can be prevented from lowering is mathematically explained as follows. When the capacitance and inductance of the impedance conversion element 1 of FIG. 1 are obtained by coaxial approximation, the capacitance C and the inductance L are expressed as follows:

## EQU1 ## C = (2πε) / log (b / a)

L = (μ / 2π) · log (b / a) where
a is the radius of the coaxial center conductor, b is the distance from the center of the center conductor to the ground plane, ε is the dielectric constant of the ceramic plate 2, and μ is the magnetic permeability of the ferrite plate 4.

Therefore, the characteristic impedance Z of the impedance conversion element 1 is

Z = (L / C) ^1/2 = (1 / 2π) · (μ / ε) ^1/2 · log (b / a) Therefore, by arbitrarily selecting the magnetic permeability of the ferrite plate 4, it is possible to prevent the characteristic impedance from decreasing due to the dielectric constant of the ceramic plate 2.

FIG. 2 schematically shows a circuit when a grounded-emitter type buffer amplifier circuit is formed using the impedance conversion element 1 of FIG. 1 formed as a choke coil. 2, the base input signal of the transistor T _R from the terminal S is the coupling capacitor C _B
Is supplied via The emitter of the transistor T _R is grounded via an emitter resistor R _E and emitter bypass capacitor C _E connected in parallel, the collector of the transistor T _R is connected to the power supply V via the impedance conversion element 1 as a choke coil Z _L, The output signal is taken out to the terminal O via the coupling capacitor _CO . C _V is a capacitor for grounding the power supply.

[0018] FIG. 3 is a Smith chart showing the impedance as seen from the collector side of the transistor T _R of Figure 2. Due to the power supply grounding capacitor C _V , the impedance on the power supply side is at the low impedance point A. on the other hand,
By inserting the choke coil Z _L between the collector of the power supply V and the transistor T _R, it can be seen that is converted to a high impedance point B. At this time, since the characteristic impedance of the choke coil Z _L is large, it can be seen that the high impedance point B does not approach the center of the Smith chart and maintains the high impedance. Also,
Even when the frequency changes, the phase change amount is small and the high impedance is maintained.

[0019] Incidentally, an impedance conversion element 1 can be complexed with an element, for example, it may be to incorporate the ground capacitors C _V a choke coil Z _L in FIG.

As can be understood from the above description, in the impedance conversion element 1, by changing the pattern of the microstrip line 3, the dielectric constant of the ceramic plate 2 or the magnetic permeability of the ferrite plate 4,
An impedance conversion element having a phase change amount and a characteristic impedance corresponding to various frequencies can be manufactured. Therefore, conventionally, when an impedance conversion element was formed by a microstrip line on a ceramics plate, it was necessary to change the impedance conversion element when the frequency band was changed. On the other hand, in the embodiment of FIG. By preparing different impedance conversion element groups in advance, it is sufficient to replace the impedance conversion element according to the application, not only it is easy to cope with high-mix low-volume production, but also various It is possible to shorten the circuit design and development period.
Further, since the central portion of the impedance conversion element is covered with the grounding electrode, the characteristic impedance does not change depending on the state of the substrate on which the impedance conversion element is mounted, and can be used for a wide range of applications.

[0021]

As apparent from the detailed description of the present invention based on one embodiment, the present invention provides:
Since the microstrip line is sandwiched between a dielectric plate having a high dielectric constant and a magnetic plate having a high magnetic permeability, the impedance conversion element can be reduced in size and impedance can be increased. Since different impedance conversion element groups can be prepared in advance, it is possible to use an impedance conversion element according to the application, and it is easy to cope with high-mix low-volume production as well as high-frequency circuits and the like. Can shorten the design and development period of various circuits.

If the central part of the impedance conversion element is covered with a grounding electrode, the characteristic impedance does not change depending on the state of the substrate on which the impedance conversion element is mounted, and it is expected to be used for a wide range of applications.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of an impedance conversion element according to the present invention, wherein 1a is a perspective view showing an appearance thereof, and 1b is a perspective view in which a part thereof is cut away.

FIG. 2 is a diagram schematically showing a circuit when a grounded-emitter type buffer amplifier circuit is configured using the impedance conversion element of FIG. 1 formed as a choke coil.

FIG. 3 is a Smith chart showing the impedance as seen from the collector side of the transistor T _R of Figure 2.

FIG. 4 is a diagram schematically showing an example of a conventional impedance conversion element.

FIG. 5 is a diagram showing a part of another example of a conventional impedance conversion element using a microstrip line.

[Explanation of symbols]

1: impedance conversion element, 2: ceramic plate with high dielectric constant, 3: microstrip line, 4: ferrite plate with high magnetic permeability, 5: surface mounting electrode, 6: grounding electrode.

Claims (3)

(57) [Claims] 1. A dielectric plate having a high dielectric constant, a microstrip line formed on one surface of the dielectric plate, and a ground for forming a microstrip line formed on the other surface of the dielectric plate. An electrode, and a high-permeability magnetic plate provided on one surface of the dielectric plate on which the microstrip line is formed so as to sandwich the microstrip line. element. 2. The semiconductor device according to claim 1, further comprising: mounting electrodes formed on opposite sides of the impedance conversion element so as not to be electrically connected to the ground electrode, and connected to both ends of the microstrip line. The impedance conversion element according to claim 1, wherein 3. The method according to claim 1, wherein the ground electrode is provided around an outer periphery of the impedance conversion element on which the mounting electrode is not formed.
3. The impedance conversion element according to claim 2, wherein the element is covered so as not to be electrically connected to the mounting electrode.