JP2001024481A - Composite tuning transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite tuning transformer for uniformly suppressing the image frequency of a wide reception band in a simple circuit constitution. SOLUTION: An antenna turning transformer T1 is arranged at an input side, and a load tuning transformer T2 is arranged at an output side in this composite transformer. In this case, in the antenna tuning transformer T1, a primary input coil N1 for impedance matching and a primary tuning coil N2 with a tap (a) for tuning are transformer-coupled, and a variable capacitance element C and an additional capacitance element C1 are connected in parallel with the primary tuning coil N2 so that a primary resonance circuit can be formed. In the load tuning transformer T2, a coupled coil N3 with a tap (b) and a secondary tuning coil N4 with a tap (c) are coiled so as to be shared, and the tap (b) is directly connected with the secondary tuning coil N4, and the tap (c) is connected through an additional capacitance element C2 with the coupled coil N3. Then, this is connected with a variable capacitance element C in parallel so that a secondary resonance circuit can be formed. In the primary tuning coil N2, a coil N21 is serially connected through the tap (a) with a coil N22, and one end is connected with the variable capacitance element C and the additional capacitance element C1, and the other edge is grounded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuning circuit for selecting a received wave and a trap circuit for suppressing an image interference wave while improving the matching between the antenna impedance and the input impedance of the high-frequency amplifier. The present invention relates to a high-frequency double-tuned transformer of a superheterodyne receiver having a function.

[0002]

The image frequency generated by the frequency conversion is an interference wave unique to the superheterodyne system. This image frequency fim is a frequency that is twice the intermediate frequency fi from the reception wave f1, and is fim = f1 + 2fi in the upper heterodyne system, and fim = f1−2fi in the lower heterodyne system.
For example, when receiving an LW band of 288 kHz, assuming that the intermediate frequency is 450 kHz, in the case of the upper heterodyne system, the image frequency is 288 kHz + 450 kHz × 2 = 1188 kHz. Therefore, usually 52
The image frequency enters the MW band wave of 2 kHz to 1710 kHz, which may cause interference.

In order to suppress the image frequency, it is necessary to take measures such as increasing the number of stages of the high-frequency tuning coil and separately providing a trap circuit for the image frequency. However, if the number of stages of the high-frequency tuning coil is increased, the number of variable capacitors and variable capacitance diodes, which are variable capacitance elements constituting the circuit, is increased, thereby increasing the price and complicating the adjustment of the circuit. In addition, when a trap circuit for an image frequency using a fixed capacitance element is separately provided in order to suppress a rise in price, even if a specific image frequency can be removed, an image frequency of a wide reception band that changes according to the reception frequency is used. Cannot be removed by a fixed trap circuit.

Accordingly, an object of the present invention is to provide a double-tuned transformer capable of uniformly suppressing an image frequency in a wide receiving band with as few components as possible and a simple circuit configuration.

[0005]

In order to achieve the above object, the present invention is configured as follows.

That is, the first aspect of the present invention is an antenna tuning transformer having a variable capacitance element connected in parallel with a primary tuning winding having a tap a, a coupling winding having a tap b and a secondary tuning winding having a tap c. A common winding is used for the wire, tap b is connected directly to the secondary tuning winding, tap c is connected to the coupling winding via an additional capacitance element for impedance correction, and a variable capacitance element is connected in parallel with this. , And a load tuning transformer composed of a primary tuning winding tap a connected to the coupling winding, and a secondary tuning winding tap c connected to an additional capacitor for blocking DC current. A double-tuned transformer for a superheterodyne receiver, wherein the transformer is connected to an amplifier via an element. According to a second aspect of the present invention, the coupling winding and the secondary tuning winding of the load tuning transformer are wound around a plurality of brim drum type ferrite cores having two or more winding grooves while arranging the number of turns and the coupling coefficient. The double-tuned transformer according to claim 1, wherein: The invention according to claim 3 is the double-tuned transformer according to claim 1, wherein a coupling coefficient between a coupling winding of the load tuning transformer and a secondary tuning winding is set to 0.1 to 0.7. . Claim 4
2. The double-tuned transformer according to claim 1, wherein the coupling coefficient of the winding connected in series via the tap c of the secondary tuning winding is set to 0.85 to 1.0. . The invention of claim 5 is characterized in that the two windings connected in series via the tap b of the coupling winding form a mutual induction circuit in which the respective winding starts have the same polarity and the magnetic flux is applied. The double-tuned transformer according to claim 1, wherein According to a sixth aspect of the present invention, the three windings connected in series via the taps b and c of the coupling winding and the secondary tuning winding are connected to each other so that the start of each winding has the same polarity and a magnetic flux is applied. 2. The double-tuned transformer according to claim 1, wherein an induction circuit is formed.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a double tuning circuit of a superheterodyne receiver embodying the present invention. The double tuning circuit has an antenna tuning transformer T1 on the input side and a load tuning transformer T2 on the output side. Antenna tuning transformer T
Reference numeral 1 denotes a transformer coupling between a primary input winding N1 for impedance matching and a primary tuning winding N2 with a tap a for tuning, and
The variable capacitance element C and the additional capacitance element C1 are connected in parallel with the next tuning winding N2 to form a primary resonance circuit. The load tuning transformer T2 shares a coupling winding N3 with a tap b and a secondary tuning winding N4 with a tap c, the tap b is directly connected to the secondary tuning winding N4, and the tap c connects the additional capacitive element C2. Connected to the coupling winding N3 via the power supply. Then, a variable capacitance element C is connected in parallel with these to form a secondary resonance circuit.

The primary input winding N1 has one end connected to a terminal 1 connected to an antenna (not shown) and the other end grounded. The primary input winding N1 may receive the high impedance of the rod antenna and the FET.

The primary tuning winding N2 has a winding N21 and a winding N22 connected in series via a tap a, one end connected to the variable capacitance element C and the additional capacitance element C1, and the other end grounded.

The coupling winding N3 is connected to the winding N through a tap b.
31 and N32 are connected in series, one end of which is connected to the tap a of the primary tuning winding N2 and the secondary tuning winding N via the additional capacitive element C2.
4 and connected to the other tap c, and the other end is grounded. Winding N3
1 and N32 have the same polarity at the beginning of each winding, and N3
1. The mutual induction circuit of the connection to which the magnetic flux of N32 is added is formed.

The secondary tuning winding N4 has the windings N41 and N42 connected in series via a tap c, one end of which is connected to the tap b of the coupling winding N3, and the other end of which is connected to the variable capacitance element C.
The windings N31, N41, and N42 form a mutual induction circuit in which the magnetic fluxes of the windings N31, N41, and N42 are added with the respective winding starts having the same polarity. In order to clarify the polarity of each winding, the starting position of the winding is indicated by a dot in the figure.

The tap c is pulled out from the vicinity of the maximum available power level of the secondary tuning winding N4 while also performing impedance matching with the load circuit, and is connected to an IC amplifier (shown in FIG. No) is connected to terminal 2. In addition, one end of the coupling winding N3 and the tap a of the primary tuning winding N2 are connected via the additional capacitance element C2. Thereby, the windings N31, N32, N41, N
42, a trap circuit for an image frequency by the additional capacitance element C2 and the variable capacitance element C is formed. The additional capacitance element C2 has a tap a (or a coupling winding N) at one end in the figure.
Although one end of (3) and the other end are connected to tap c, one end may be connected to any one point between taps a and b and the other end may be connected to any one point between taps b and c.

The windings N31, N32, N41 and N42 are
As shown in FIG. 2, it is wound around the first groove D1 and the second groove D2 of the three-flange drum core D having the cap core CA. At this time, the number of turns and the degree of interference of the windings N31, N32, N41, and N42 are arranged, and the coupling coefficient between the windings N3 and N4 is set to 0.1.
To 0.7, and the coupling coefficient between the windings N41 and N42 is set to 0.85 to 1.0.

The double-tuned circuit embodying the present invention has the above-described configuration, and the input signal applied to the terminal 1 is led to the primary resonance circuit and the secondary resonance circuit, and the specific capacitance is changed by changing the variable capacitance element C. Tune to frequency. At the same time, the image interference wave mixed into the input signal is transmitted to the windings N31, N32, N41,
Attenuation is caused by a trap circuit including N42, the additional capacitance element C2, and the variable capacitance element C.

When the capacitance of the variable capacitance element C is changed, as shown in FIG. 3, the entire frequency characteristic moves substantially in parallel according to the reception frequency, and the resonance frequency of the trap circuit also moves in parallel within the band. Suppress frequency.

Hereinafter, the reason why the resonance frequency of the trap circuit moves according to the reception frequency will be specifically described. FIG.
In order to make it easy to think of the secondary resonance circuit of the load tuning transformer T2, the circuit is simplified as follows. First, FIG.
As shown in (1), taps b and c are used as a common input and output to make tap c, and the winding N32 of the coupling winding N3 is omitted. As a result, the windings N31 and N41 are replaced with the single winding N43, and the winding N43 and the winding N42 are connected in series via the tap c. The impedance of the AC bypass capacitor C 'in the band is almost zero and can be ignored, and the winding N21 is omitted on the assumption that the inductance is infinite.
Further, the additional capacitive element C2 is considered for the time being excluded.

Here, when a current flows through the windings N43 and N42, the flowing current flows in the same direction, and a magnetic flux is added.
Accordingly, the self-inductances L43 and L42 of the windings N43 and N42 are changed to L43 'and L42', and assuming that the mutual inductance of the windings N43 and N42 is M (M> 0), L43 '= L43 + M L42' = L42 + M . Here, since L43 = L43'-M L42 = L42'-M, the windings N43 and N42 are equivalent to L4
A circuit for connecting -M in series with 3 'and L42' is formed.

As described above, when the circuit of FIG. 4 is replaced with an equivalent circuit and the capacitance of the variable capacitance element C is C,
As shown in FIG. 5, L43 'and L42' +
A parallel circuit of C is connected to form a trap circuit between -M, L43 ', L42', and C between the input signal and the ground circuit.

When the impedance Z of this equivalent circuit is calculated,

(Equation 1) Becomes The frequency at which the impedance Z of the equivalent circuit is maximized (denominator = 0) is the reception frequency f0, and the frequency at which the impedance Z is minimum (numerator = 0) is the resonance frequency f of the trap.
0 '. Therefore, the reception frequency f0 is

(Equation 2) And the resonance frequency f0 'of the trap is

(Equation 3) Becomes

As described above, the double-tuned circuit of the present invention tunes at the receiving frequency f0 where the impedance changes according to the frequency and the reactance of the variable capacitance element C and the windings N31, N41 and N42 becomes equal. Attenuation is given at the resonance frequency f0 'of the trap where C and the coupling coefficient K or the reactance of N42 with the number of turns arranged are equal. Therefore, when the variable capacitance element C is changed, as shown in FIG. 3, the entire frequency characteristic moves substantially in parallel according to the reception frequency f0, and at this time, the resonance frequency f0 ′ of the trap also changes in accordance with the change in the variable capacitance element C. To translate. This makes it possible to suppress an image frequency that changes according to the reception frequency f0.

From the calculation formula, the reactance of the trap circuit is smaller than the reactance of the tuning circuit. Therefore, in the low frequency region where the capacitance of the variable capacitor C is large, the movement width of the resonance frequency f0 'of the trap is small. In the high-frequency region where the capacitance of C is small, the movement width becomes large and moves to a higher region. For example, reception frequency f0 = 999k
And the resonance frequency f0 'of the trap in Hz is 1899 kHz
, For a higher reception frequency f0 = 1404 kHz, the resonance frequency f0 ′ of the trap = 2304 kHz
z or more. For this reason, the attenuation band becomes higher than the image frequency, and the trap becomes sweet.

Therefore, as shown in FIG. 1, the additional capacitance element C2 is connected in parallel with the windings N32 and N41. The reactance of the trap circuit and the tuning circuit both increases due to the addition of the additional capacitance element C2, but the trap circuit becomes larger, so that the resonance frequency f0 'of the trap moves to a lower range than the reception frequency f0. I do. This allows the trap attenuation band to approach the image frequency.

When the additional capacitance element C2 is added, the reception frequency f0 of the load tuning transformer T2 moves to a low frequency.
The reception frequency f0 of the antenna tuning transformer T1 is also lowered accordingly, and an additional capacitance element C1 is added for that purpose. When the capacitance of the additional capacitance element C2 is small, the reception frequency f0 also hardly changes.
May not be added.

The resonance frequency f0 'of the trap is
It can be seen that when the coupling coefficient K is increased, the denominator of the calculation formula becomes smaller, and thus the denominator moves to a higher frequency. Alternatively, when the number of turns of the winding N42 is increased while the coupling coefficient K is fixed, the denominator of the calculation formula becomes large, so that the denominator becomes smaller when the number of turns of the winding N42 is reduced. I understand. Thus, the coupling coefficient K or the winding N42
, The resonance frequency f0 'of the trap can be adjusted to the image frequency band.

When the characteristics of the double-tuned circuit embodying the present invention are compared with those of the conventional circuit shown in FIG. 6, as shown in FIG. 7, the characteristics are attenuated near the image frequency and measured in the MW band. An improvement of ~ 45 dB was seen. Also, the receiving sensitivity is at the same level as that of the conventional circuit, and the image frequency is suppressed without deteriorating other electric characteristics. Furthermore, the load tuning transformer, one of the double-tuned transformers, uses a common winding, so the number of turns is greatly reduced compared to the conventional type, realizing a compact and lightweight double-tuned transformer.

8 to 11 show modified examples of the double tuning circuit of the present invention. The double tuning circuit of FIG. 8 has two taps b and b '.
The next tuning winding N5 and the output tuning winding N41 are transformer-coupled,
The primary tuning winding N2 and the secondary tuning winding N5 are connected via taps a and b '. The tap b 'is connected to one end of the output tuning winding N41 via the additional capacitance element C2, and the tap b is connected to the other end of the output tuning winding N41.
A secondary resonance circuit is formed by connecting a variable capacitance element C in parallel with the next tuning winding N5. The position of the tap b may be changed in the range up to the tap b 'for correcting the trap position.

The double-tuned circuit shown in FIG. 9 is obtained by connecting a capacitance element C0 for tracking correction in parallel with the variable capacitance element C of the circuit shown in FIG.

The double-tuned circuit shown in FIG. 10 is a circuit in which the winding N21 of the circuit shown in FIG. 1 is independently wound, and the tap a is omitted, and the winding is directly connected to the coupling winding N3.

The double tuning circuit shown in FIG. 11 is obtained by connecting the additional capacitance element C2 of the circuit shown in FIG. 1 between taps b and c.

[0031]

As described above, the double-tuned transformer according to the present invention comprises an antenna-tuned transformer having a variable capacitance element connected in parallel with a primary tuning winding having a tap a, and a tap b.
And the secondary tuning winding with tap c are commonly used, the tap b is connected directly to the secondary tuning winding, and the tap c is connected to the coupling winding via an additional capacitance element for impedance correction. And a load tuning transformer comprising a variable capacitance element connected in parallel to the input and output sides, a tap a of a primary tuning winding connected to the coupling winding, and a secondary tuning winding connected. The tap c of the winding is connected to an amplifier via a DC blocking additional capacitance element. Therefore, according to the present invention, since a trap circuit is formed by the mutual inductance M and LC by mutual induction of the common winding of the load tuning transformer, when the variable capacitance element is changed, the resonance frequency of the trap circuit is interlocked with the reception frequency. Also changes, and the image frequency that changes according to the reception frequency can be suppressed.
Further, since the additional capacitance element for impedance correction shifts the resonance frequency of the trap to a low frequency, the attenuation band of the trap can be made closer to the image frequency.
Further, since the load tuning transformer is commonly wound and the mutual inductance M is drawn out, no new components for trapping are required, and the economy and reliability are improved.

Further, in the double-tuned transformer of the present invention, the common winding of the load-tuned transformer is wound around a plurality of brim drum type ferrite cores having two or more winding grooves while arranging the number of turns and the coupling coefficient. . Further, the common windings of the load tuning transformer form a mutual induction circuit in which the magnetic flux is applied with the respective winding starts having the same polarity. Therefore,
According to the present invention, since the resonance frequency of the trap changes depending on the number of turns and the coupling coefficient of the common winding of the load tuning transformer, the number of turns and the coupling coefficient are arranged together with the additional capacitance element for impedance correction to appropriately adjust the resonance frequency of the trap. Can be adjusted to the vicinity of the image frequency.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a double tuning circuit embodying the present invention.

FIG. 2 is a winding diagram of a tuning coil embodying the present invention.

FIG. 3 is a frequency characteristic diagram of a double tuning circuit embodying the present invention.

FIG. 4 is a simplified circuit diagram of FIG.

FIG. 5 is an equivalent circuit diagram of FIG.

FIG. 6 is a circuit diagram of a conventional double tuning circuit.

FIG. 7 is a diagram comparing characteristics of a double-tuned circuit embodying the present invention and a conventional circuit.

FIG. 8 is a modified example of the double tuning circuit embodying the present invention.

FIG. 9 is another modified example of the double tuning circuit embodying the present invention.

FIG. 10 is another modified example of the double-tuned circuit embodying the present invention.

FIG. 11 is another modified example of the double tuning circuit embodying the present invention.

[Explanation of symbols]

 1-2 terminals C Variable capacitance elements C ', C1, C2 Additional capacitance elements C0 Tracking correction capacitance elements D Drum core D1 First groove D2 Second groove CA Cap core L Self-inductance M Mutual inductance N1 Primary input winding N2 1 Secondary tuning winding N3 Coupling winding N4 Secondary tuning winding N41 Output tuning winding N5 Secondary tuning winding a, b, b ', c Tap T1 Antenna tuning transformer T2 Load tuning transformer

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[Procedure amendment]

[Submission date] June 2, 2000 (2006.2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

The primary input winding N1 has the terminal 1 connected to the antenna side (not shown) and the other end grounded.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

The output is drawn from the tap c of the secondary tuning winding N4, and is supplied to the IC via an additional capacitive element C 'for blocking DC current.
Connect to terminal 2 which connects to an amplifier (not shown). Further, one end of the coupling winding N3 and one end of the coupling winding N3 are connected via the additional capacitance element C2.
It is also connected to the tap a of the next tuning winding N2. This allows
Windings N31, N32, N41, N42, additional capacitance element C
2. A trap circuit for an image frequency is formed by the variable capacitance element C. In the figure, the additional capacitance element C2 has one end connected to the tap a (or one end of the coupling winding N3) and the other end connected to the tap c. It may be connected to any point between b and c.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

8 to 11 show modified examples of the double tuning circuit of the present invention. The double tuning circuit of FIG. 8 has two taps b and b '.
The transformer winding is coupled between the secondary tuning winding N5 and the output winding N41, and the primary tuning winding N2 and the secondary tuning winding N are connected via taps a and b '.
5 is connected. The tap b 'is connected to the additional capacitance element C2.
, And a tap b is connected to the other end of the output winding N41, and the secondary tuning winding N
5 and a variable capacitance element C is connected in parallel to form a secondary resonance circuit. The position of the tap b may be changed in the range up to the tap b 'for correcting the trap position.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] Explanation of sign

[Correction method] Change

[Correction contents]

[Description of Signs] 1-2 terminals C Variable capacitance elements C ', C1, C2 Additional capacitance element C0 Tracking correction capacitance element D Drum core D1 First groove D2 Second groove CA Cap core L42, L43 Self-inductance -M Mutual inductance N1 primary input winding N2 primary tuning winding N3 coupling winding N4 secondary tuning winding N41 output winding N5 secondary tuning winding a, b, b ', c tap T1 antenna tuning transformer T2 load tuning transformer

Claims (6)

[Claims] 1. An antenna tuning transformer having a variable capacitance element connected in parallel with a primary tuning winding having a tap a, a coupling winding having a tap b and a secondary tuning winding having a tap c are commonly used. A tap b is directly connected to a secondary tuning winding, a tap c is connected to a coupling winding via an additional capacitance element for impedance correction, and a load tuning transformer formed by connecting a variable capacitance element in parallel with this; Are arranged on the input side and the output side, respectively. The tap a of the primary tuning winding is connected to the coupling winding, and the tap c of the secondary tuning winding is connected to the amplifier via a DC blocking additional capacitance element. A double-tuned transformer for a superheterodyne receiver. 2. The method according to claim 1, wherein the coupling winding and the secondary tuning winding of the load tuning transformer are arranged by changing the number of windings and the coupling coefficient.
2. The double-tuned transformer according to claim 1, wherein said double-tuned transformer is wound around a plurality of brim drum type ferrite cores having said winding grooves. 3. The double-tuned transformer according to claim 1, wherein a coupling coefficient between a coupling winding of the load-tuning transformer and a secondary tuning winding is set to 0.1 to 0.7. 4. The double-tuned transformer according to claim 1, wherein a coupling coefficient of a winding connected in series via a tap c of the secondary tuning winding is set to 0.85 to 1.0. 5. The two windings connected in series via the tap b of the coupling winding form a mutual induction circuit in which the respective winding starts have the same polarity and a magnetic flux is applied. The double-tuned transformer according to claim 1. 6. A mutual induction circuit in which three windings connected in series via taps b and c of the coupling winding and the secondary tuning winding are connected in such a manner that the start of each winding has the same polarity and a magnetic flux is applied. 2. The double-tuned transformer according to claim 1, wherein the transformer is formed.