JPH0870236A - Double tuning circuit - Google Patents

Abstract

PURPOSE: To minimize the stray capacity between the tuning coils of tuning circuits on the primary side and secondary side and to enable adjustment of sufficiently inductive coupling between the tuning circuits by dividing the tuning coil of tuning circuit either on the primary side or on the secondary side into two and connecting them in parallel. CONSTITUTION: Separated tuning coils being a lst coil 21a and a 2nd coil 21b of a secondary tuning circuit B are connected in parallel. Then the separated 2nd coil 21b is arranged in a direction in a manner that its center axis is at a right angle to a center axis of the tuning coil 11 of a primary tuning circuit A. Thus, the inductance of the lst coil 21a is increased more than that of the tuning coil of a conventional secondary tuning circuit (similarly the inductance of the 2nd coil 21b is increased), then the inductive coupling between the primary and secondary tuning circuits A, B is easily adjusted without approaching the tuning coil 11 of the tuning circuit A and the tuning coil 21a of the tuning circuit B with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a double-tuned circuit,
More specifically, it relates to an improvement in adjusting means for inductive coupling of the primary side and secondary side tuning circuits in an interstage coupling circuit of a tuner used for a television receiver or the like.

[0002]

2. Description of the Related Art Generally, the overall response characteristic of a double-tuned circuit is often used to obtain a characteristic in which the bandwidth is wider than that of a single-tuned circuit and the waveform has a steeper slope. As a means for adjusting the inductive coupling of the primary side and secondary side tuning circuits, the tuning coil of the primary side tuning circuit is different from the tuning coil of the primary side tuning circuit formed in an air-core circle. There is known a method of installing a tuning coil of a secondary side tuning circuit formed in an air-core circle so as to be the same axis as the central axis of the. This method has the advantage that it has the simplest structure and that the inductive coupling can be adjusted easily.

Specifically, as an adjusting means for the inductive coupling, an adjusting operator inserts the adjusting rod or the like directly into the tuning coils of the tuning circuits on the primary side and the secondary side, and moves the adjusting rod or the like. By expanding the tuning coil,
Alternatively, it is tuned so as to obtain a desired tuning frequency of the tuning circuits on the primary side and the secondary side while taking necessary inductive coupling between the tuning coils of the tuning circuits on the primary side and the secondary side by contracting. This is done by changing the inductance value of the coil for use. That is, the tuning coils of the primary side and secondary side tuning circuits are adjusted together by inductive coupling, and two adjustments for adjusting the tuning frequency of their own tuning circuits are performed together.

However, in a double-tuned circuit that is tuned to a relatively high frequency such as the UHF band, the inductance of the tuning coils of the primary side and secondary side tuning circuits becomes small, so that the necessary induction is required. To obtain the coupling, the tuning coils of the tuning circuits on the primary side and the secondary side must be very close to each other. When the tuning coils of the primary side and secondary side tuning circuits are brought close to each other in this way, the stray capacitance between the tuning coils of the primary side and secondary side tuning circuits increases, and the stray capacitance Therefore, a problem arises in that the amount of attenuation in the non-pass band of the total response characteristic cannot be obtained sufficiently.

These characteristics will be described in detail with reference to FIGS. 4 and 5. First, FIG. 4 is a general response characteristic diagram of a general double tuning circuit, and FIG.
FIG. 6 is a comprehensive response characteristic diagram showing a state in which a sufficient amount of attenuation in the non-pass band of the overall response characteristic cannot be obtained due to stray capacitance between the tuning coils of the primary side and secondary side tuning circuits.

In the double tuning characteristics of FIG. 4, (a) shows a steep slope of the waveform, and (b) shows a skirt of the slope. The total response characteristic shown in FIG. 4 is characterized by being particularly excellent in selection characteristic. The slope (c) of the waveform of the total response characteristic in FIG. 5 shows a steep characteristic to some extent, but its skirt (d) shows a large spread. This is because when the tuning coils of the primary side and secondary side tuning circuits are brought close to each other and inductively coupled, the stray capacitance between the tuning coils of the primary side and secondary side tuning circuits increases. Occurs in In other words, since the stray capacitance couples the tuning circuits on the primary side and the secondary side, the tail of the waveform is widened as in the overall response characteristic of FIG. A sufficient amount of attenuation in the pass band cannot be obtained.

However, conventionally, even in the case of a double tuning circuit that tunes to a relatively high frequency such as the UHF band, since the same double tuning circuit as described above is employed, the tuning of the double tuning circuit is performed. The inductance value of the coil for use becomes small, and the shape of the air-core circular coil that forms this inductance value is, for example, a wire diameter: 0.3 mm, a winding diameter: 3 in consideration of the adjustment by the above-mentioned adjustment operator. The shape is limited to about 0.0 mm and the number of turns: 1. In addition, the tuning coils of the primary side and the secondary side tuning circuits formed by the coil having such a shape must be brought very close to each other for inductive coupling. Therefore, as described above, the stray capacitance between the tuning coils of the primary side and secondary side tuning circuits increases, and due to the stray capacitance, sufficient attenuation in the non-pass band of the overall response characteristics is obtained. There was a problem of disappearing. Therefore, as a solution to the above-mentioned problem, even if the inductance value of the tuning coil of the tuning circuit on the primary side and the secondary side is small, the shape of the tuning coil can be set relatively large. A tuning coil is formed by using a resonance line formed in a loop shape, and the inductive coupling can be adjusted between the tuning coils formed by the resonance line.
As described above, when the resonance line is used as the tuning coil, inductive coupling can be achieved without bringing the resonance line very close to each other unlike the conventional tuning coil.

However, if the resonance line as described above is used for the tuning coil, it becomes easy to adjust the inductive coupling between the tuning circuits on the primary side and the secondary side, but the desired tuning frequency of each tuning circuit is set. In order to do so, the number of man-hours for designing the resonance line was large, and it was difficult to develop the tuner. Further, since the precision of the external dimensions is the most important for this resonant line, the material cost, the die manufacturing cost, etc. are high, so the unit cost of the resonant line itself is inevitably high. Therefore, it was one of the factors that the price of the tuner finally increased.

Next, the structure of the double tuning circuit in the inductive coupling adjusting means of the conventional inter-stage coupling circuit of the television tuner will be described. FIG. 6 is a circuit diagram of a conventional double tuning circuit, FIG. 7 is a diagram showing the actual arrangement of each component in the circuit diagram shown in FIG. 6, and FIG. FIG. 3 is an equivalent circuit diagram equivalently shown as A and B, respectively.

In FIG. 6, reference numerals 11, 12, and 13 denote tuning coils formed by the resonant lines of the tuning circuit on the primary side, respectively.
A variable voltage diode and a tuning capacitor,
The cathode side of the voltage variable capacitance diode 12 and the tuning capacitor 13 are connected in series. The series connection circuit of the voltage variable capacitance diode 12 and the tuning capacitor 13 is connected in parallel to the tuning coil 11 to form a parallel tuning circuit. This parallel tuning circuit is called a tuning circuit A on the primary side. Further, R1 is a resistor whose one end is connected to a connection point between the cathode side of the voltage variable capacitance diode 12 and the tuning capacitor 13 and the other end is connected to TU1. TU1 is a terminal for applying a tuning voltage for changing the tuning frequency of the tuning circuit A on the primary side.

Reference numerals 21, 22 and 23 denote a tuning coil, a voltage variable capacitance diode and a tuning capacitor formed by the resonance line of the secondary side tuning circuit, respectively, for tuning with the cathode side of the voltage variable capacitance diode 22. The capacitor 23 is connected in series. The series connection circuit of the voltage variable capacitance diode 22 and the tuning capacitor 23 is connected in parallel to the tuning coil 21 to form a parallel tuning circuit. This parallel tuning circuit is called a tuning circuit B on the secondary side. R2 is a resistor having one end connected to the connection point between the cathode side of the voltage variable capacitance diode 22 and the tuning capacitor 23, and the other end connected to TU2. TU2 is a terminal for applying a tuning voltage for changing the tuning frequency of the tuning circuit B on the secondary side.

FIG. 8 shows an equivalent circuit for the tuning circuits A and B on the primary side and the secondary side described above. In FIG. 8, C1 and C2 are the series connection capacitance of the voltage variable capacitance diode 12 and the tuning capacitor 13 and the series connection capacitance of the voltage variable capacitance diode 22 and the tuning capacitor 23 described above. Further, the tuning coils 11 and 21 of the tuning circuits A and B on the primary side and the secondary side have substantially the same inductance value.

Further, in FIG. 6, reference numeral 1 is an input terminal for inputting an output signal of a television reception signal (not shown) through an antenna tuning circuit, and 2 is an appropriate amplification of the reception signal input to the input terminal 1. An RF amplifier 3, which couples the RF amplifier 2 and the tuning circuit A on the primary side, and a capacitor which blocks a DC current, 4 couples the frequency mixing circuit 6 and the second tuning circuit B, and a DC A capacitor for blocking the current, 5 is a local oscillation circuit, 6 is a frequency mixture of the local oscillation signal from the local oscillation circuit 5 and the reception signal selected and passed by the second tuning circuit B and outputs an intermediate frequency signal. Frequency mixing circuit. An output terminal 7 outputs the intermediate frequency signal output from the frequency mixing circuit 6.

Next, referring to FIG. 7, the double tuning circuit composed of the above-mentioned two tuning circuits A and B is provided on the printed circuit board housed inside the tuner and has wiring patterns 15-19.
And 25 to 29.

To further explain these contents in detail, the tuning coil 11 of the tuning circuit A on the primary side is a wiring pattern 15 of the tuning circuit A on the primary side formed on a printed circuit board housed inside the tuner. , 16 and the tuning coil 21 of the secondary side tuning circuit B is connected between the wiring patterns 25, 26. In FIG. 7, reference numeral 15 denotes a hot side pattern for connecting the tuning coil 11 of the tuning circuit A on the primary side to the capacitor 3 and the voltage variable capacitance diode 12, and 16 denotes the tuning coil 11 on the primary side and the capacitor 13. Is a ground pattern for connecting the. Further, 17 is a pattern to which the capacitor 3 is connected and is further connected to the RF amplifier 2 not shown, and 18 is a hot side pattern for connecting the voltage variable capacitance diode 12, the tuning capacitor 13 and the resistor R1.
Reference numeral 19 is a terminal TU to which the resistor R1 is connected and to which a control voltage for controlling the tuning circuit A on the primary side (not shown) is applied.
It is a pattern connected to 1.

Similarly, in FIG. 7, 25 is a hot side pattern for connecting the tuning coil 21 of the tuning circuit B on the secondary side to the capacitor 4 and the voltage variable capacitance diode 22, and 26 is the tuning on the secondary side. It is an earth pattern which connects the coil 21 and the capacitor 23. Further, 27 is a pattern to which the capacitor 4 is connected and is further connected to the frequency mixing circuit 6 not shown, and 28 is a hot side pattern for connecting the voltage variable capacitance diode 22, the tuning capacitor 23 and the resistor R2. , 29 are connected to a resistor R2, and a secondary side tuning circuit B (not shown) is provided.
This is a pattern connected to the terminal TU2 to which a control voltage for controlling is applied.

[0017]

However, in such a conventional double-tuned circuit that tunes to a relatively high frequency such as the UHF band, in order to obtain sufficient inductive coupling, the resonance lines are respectively tuned. Since the tuning coil 11 of the tuning circuit A on the primary side and the tuning coil 21 of the tuning circuit B on the secondary side are placed close to each other for inductive coupling,
It is easy to adjust the inductive coupling between the tuning circuits A and B on the primary side and the secondary side, but the number of man-hours for designing the resonance line is large in order to set the desired tuning frequency of each tuning circuit, and it is difficult to develop a tuner. I was expecting.

Further, since the precision of the external dimensions is most important for this resonant line, the material cost and the die manufacturing cost are high, so that the unit cost of the resonant line itself is inevitably high. As a result, the price of the tuner finally becomes high.

Therefore, an object of the present invention is to solve the above-mentioned problems, and the tuning coil of the secondary side tuning circuit is divided into a first coil and a second coil. , The first coil and the second coil are connected in parallel, and the first coil and the second coil are arranged in a direction in which the central axis of the second coil is perpendicular to the central axis of the tuning coil of the tuning circuit on the primary side. Of the tuning circuit of the tuning circuit and the first tuning circuit of the secondary side
It is an object of the present invention to provide an inexpensive double-tuned circuit in which the stray capacitance between the coils is minimal and sufficient inductive coupling can be achieved.

[0020]

In order to solve the above-mentioned problems, a double tuning circuit of the present invention is characterized in that, in claim 1, a tuning circuit on a primary side and a secondary tuning circuit each comprising a capacitor and a tuning coil connected in parallel. A tuning circuit on one side of the tuning circuit, the tuning coil of at least one of the tuning circuit on the primary side or the secondary side is formed by connecting a first coil and a second coil in parallel. The first coil and the tuning coil of the other tuning circuit of the tuning circuit formed by the first coil are inductively coupled to each other.

In claim 2, referring to claim 1,
The second coil is arranged such that the central axis of the second coil is perpendicular to the central axis of the tuning coil of the other tuning circuit of the tuning circuit. .

A third aspect of the present invention is based on the first or second aspect, wherein the double-tuned circuit is used in the UHF band.

[0023]

The above technical means operates as follows. At least one tuning coil of the tuning circuit on the primary side or the secondary side is divided into a first coil and a second coil, and the first coil and the second coil are connected in parallel. First, because the inductance value of the coil can be increased
It is possible to easily adjust the inductive coupling without bringing the coil of No. 1 and the tuning coil of the other tuning circuit of the tuning circuit formed by the first coil close to each other.

Further, the second coil is arranged in a direction in which the central axis of the second coil is perpendicular to the central axis of the tuning coil of the other tuning circuit of the tuning circuit formed by the second coil. By doing so, it is possible to prevent inductive coupling between the second coil and the tuning coil of the other tuning circuit of the tuning circuit formed by the second coil.

By using this double-tuned circuit in the UHF band, the stray capacitance between the tuning coils of the tuning circuits on the primary side and the secondary side can be adjusted to a minimum to adjust the inductive coupling. is there.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A double-tuned circuit according to the present invention will be described below with reference to the drawings showing the construction of the present invention. FIG. 1 is a circuit diagram showing a double tuning circuit according to an embodiment of the present invention, and FIG. 2 shows an arrangement of tuning coils of a primary side and a secondary side tuning circuit according to the embodiment. It is a map of the actual situation. 3 is an equivalent circuit diagram equivalently showing the tuning circuit portion of the double tuning circuit of the present invention.

In these figures, the same components as those of the conventional example and the embodiment of FIGS. 1 to 3 of the present invention are designated by the same reference numerals and the description thereof will be omitted. The present invention shown in FIG.
3 is different from the embodiment shown in FIG. 3 in that the tuning coil 21 of the tuning circuit B on the secondary side of the conventional example has two coils.
That is, the first coil 21a and the second coil 21b are divided and these two coils are connected in parallel, and the central axis of the tuning coil 11 of the tuning circuit A on the primary side is perpendicular to the central axis. In addition, the configuration of disposing the divided second coil 21b is different. The other structure is the same as the conventional example. An equivalent circuit of the tuning circuit portion of the double tuning circuit according to the present invention is shown in FIG. In FIG. 3, reference numeral 24 is, as described above, the tuning coil 21 of the conventional tuning circuit B on the secondary side is divided into two coils, a first coil 21a and a second coil 21b, and the two coils are connected in parallel. This is a tuning coil of the secondary side tuning circuit B equivalently shown.

As described above, since the tuning coil 21 of the tuning circuit B on the secondary side of the conventional example is divided into the first coil 21a and the second coil 21b and connected in parallel, the conventional example is shown. Since the inductance of the first coil 21a can be made larger than that of the tuning coil 21 of the tuning circuit B on the secondary side (similarly, the inductance of the second coil 21b also becomes larger), the tuning circuits A on the primary side and the secondary side The inductive coupling between B and B can be easily adjusted without bringing the tuning coil 11 of the tuning circuit A on the primary side and the first coil 21a of the tuning circuit B on the secondary side close to each other. Therefore, the tuning circuit A on the primary side
Since the stray capacitance between the tuning coil 11 and the first coil 21a of the tuning circuit B on the secondary side can be minimized, a sufficient amount of attenuation in the non-pass band can be obtained. The second coil 21b of the secondary side tuning circuit B can prevent inductive coupling with respect to the tuning coil 11 of the primary side tuning circuit A and the first coil 21a of the secondary side tuning circuit B.

Further, in the present invention, the first coil 21a of the tuning circuit B on the secondary side has the second coil 21b connected between the wiring patterns 30 and 31. The second coil 21b is connected so that the wire diameter, the winding diameter, and the number of windings can be changed so that the frequency can be adjusted, for example, and the second coil 21b is also connected. The mounting position of can be changed appropriately.
Therefore, the coupling of this double-tuned circuit can be easily adjusted by selecting the second coil 21b having an appropriate constant and connecting it in parallel to the first coil 21a of the secondary side tuning circuit B. . Also, according to the present invention, the tuning coil of the secondary side tuning circuit is divided into two coils, the first coil and the second coil, but the tuning coil of the primary side tuning circuit is also divided into two as described above. It may be divided into two coils.

Although the above description has been made of the double tuning circuit for tuning to a relatively high frequency such as the UHF band, it is also applicable to the double tuning circuit for tuning to a relatively low frequency such as the VHF band. It is the same. Then, by applying the double tuning circuit of the present invention, the inductive coupling is adjusted by the tuning coils of the tuning circuits on the primary side and the secondary side, and two tunings for adjusting the tuning frequency of each tuning circuit are adjusted. Since each can be adjusted, adjustments are easier and adjustment work can be done in a shorter time. Also,
Since this tuning coil can use a general air-core circular coil without using an expensive resonance line, the material cost is low, and the cost for manufacturing the tuning coil mold is unnecessary. , Eventually the price of the tuner became cheaper.

[0031]

As described above, according to the present invention, the improved means for adjusting the inter-stage coupling is provided as described below in comparison with the means for adjusting the inter-stage coupling in the related art.

Since the first coil and the second coil of the secondary side tuning circuit are connected in parallel, the inductance value of the first coil can be made larger than that of the tuning coil of the conventional secondary side tuning circuit. Therefore, the inductive coupling between the primary side and secondary side tuning circuits can be easily adjusted without making the tuning coil of the primary side tuning circuit and the first coil of the secondary side tuning circuit close to each other. . The second coil of the secondary tuning circuit can prevent inductive coupling with respect to the tuning coil of the primary tuning circuit and the first coil of the secondary tuning circuit. Therefore, the stray capacitance between the tuning coil of the tuning circuit on the primary side and the first coil of the tuning circuit on the secondary side can be minimized, and a sufficient amount of attenuation in the non-pass band can be obtained. Since it is possible to adjust the inductive coupling by the tuning coils of the primary side and secondary side tuning circuits and the two tunings for adjusting the tuning frequency of the tuning circuit of each side, each adjustment can be performed easily and in a short time. Can be adjusted. Further, as the tuning coil, a general air-core circular coil can be used without using an expensive resonance line, so that the material cost can be reduced. Further, since the cost for manufacturing the tuning coil mold is not required, the cost of the tuner is finally reduced. In particular, this double-tuned circuit is a UH with a relatively high frequency.
When used in the F band, the above effects 1 to 3 are remarkable.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a double tuning circuit of the present invention.

FIG. 2 is an actual view showing an arrangement of respective parts of the primary side and secondary side tuning circuits of the double tuning circuit of the present invention in FIG.

FIG. 3 is an equivalent circuit diagram equivalently showing a tuning circuit portion of a double tuning circuit of the present invention.

FIG. 4 is a general response characteristic diagram of a general double-tuned circuit.

FIG. 5 is a total response characteristic diagram in which sufficient attenuation in the non-pass band cannot be obtained because stray capacitance between the tuning coils of the primary side and secondary side tuning circuits of the conventional example is added. is there.

FIG. 6 is a circuit diagram showing an example of a conventional double-tuned circuit.

FIG. 7 is an actual view showing the arrangement of parts of the primary side and secondary side tuning circuits of the conventional double tuning circuit in FIG.

FIG. 8 is an equivalent circuit diagram equivalently showing a tuning circuit portion of a conventional double tuning circuit.

[Explanation of symbols]

 11 Tuning coil of tuning circuit on primary side 12, 22 Voltage variable capacitance diode 13, 23 Tuning capacitor 21a First coil of tuning circuit on secondary side 21b Second coil of tuning circuit on secondary side A Primary side Tuning circuit B Tuning circuit on the secondary side

Claims (3)

[Claims] 1. A double-tuned circuit in which a primary-side tuning circuit composed of a capacitor and a tuning coil connected in parallel and a secondary-side tuning circuit are arranged, wherein the primary-side or secondary-side tuning circuit is At least one tuning coil is configured by connecting a first coil and a second coil in parallel, and the first coil and the tuning coil of the other tuning circuit of the tuning circuit formed by the first coil. A double-tuned circuit characterized by inductive coupling. 2. The second coil is arranged in a direction in which the central axis of the second tuning circuit is perpendicular to the central axis of the tuning coil of the other tuning circuit formed by the second coil. The double-tuned circuit according to claim 1. 3. The double-tuned circuit according to claim 1, wherein the double-tuned circuit is used in the UHF band.