JP3517166B2 - Double-tuned transformer - Google Patents

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 interfering wave as well as matching the antenna impedance and the input impedance of a high frequency amplifier to increase the receiving efficiency. The present invention relates to a high-frequency double-tuned transformer for a super-heterodyne receiver that also has the function.

[0002]

The image frequency generated by the frequency conversion is an interference wave peculiar to the superheterodyne system. The image frequency fim is a frequency twice the intermediate frequency fi from the received wave f1, and fim = f1 + 2fi in the upper heterodyne system and fim = f1-2fi in the lower heterodyne system. For example, 28
When receiving an 8 kHz LW band wave, the intermediate frequency is set to 45
At 0 kHz, in the case of the upper heterodyne system, a frequency of 288 kHz + 450 kHz × 2 = 1188 kHz becomes an image frequency. Therefore, usually 52
The image frequency may enter 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 high frequency tuning coils and providing a trap circuit separately for the image frequency. However, when the number of stages of the high frequency tuning coil is increased, the number of variable capacitors and variable capacitance diodes which are the variable capacitance elements that configure the circuit increases, the price increases, and the circuit adjustment becomes complicated. In addition, if a trap circuit for the image frequency that uses a fixed capacitance element is provided separately to suppress the price increase, even if the specific image frequency can be removed, the image frequency in a wide reception band that changes according to the reception frequency Is impossible to remove with a fixed trap circuit.

Therefore, the present invention has been made for the purpose of providing a double-tuned transformer capable of uniformly suppressing an image frequency in a wide reception band with a minimum number of parts and a simple circuit configuration.

[0005]

In order to achieve the above object, the present invention has the following constitution.

That is, the invention of claim 1 is an antenna tuning transformer formed by connecting a variable capacitance element in parallel with a primary tuning winding with a tap a, a coupling winding with a tap b and a secondary tuning winding with a tap c. The wire is shared, the tap b is directly connected to the winding start of the secondary tuning winding, and the tap c is connected to the winding start of the coupling winding via an additional capacitance element for impedance correction, and in parallel with this. A load tuning transformer formed by connecting variable capacitance elements is arranged on each of the input side and the output side, and the tap a of the primary tuning winding is connected to the winding start of the coupling winding. A double-tuned transformer for a superheterodyne receiver, characterized in that tap c is connected to an amplifier via an additional capacitance element for blocking DC. 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 drum type ferrite core having a plurality of flanges 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 According to a third aspect of the present invention, the coupling coefficient between the winding start side winding and the secondary tuning winding that are connected in series via the tap b of the coupling winding is set to 0.1 to 0.7. The double-tuned transformer according to claim 1. According to a fourth aspect of the invention, the coupling coefficient of the windings connected in series via the tap c of the secondary tuning winding is 0.85 to 1.
The double-tuned transformer according to claim 1, wherein the double-tuned transformer is set to 0. According to a fifth aspect of the present invention, the winding start side winding and the secondary tuning winding, which are connected in series via the tap b of the coupling winding, are connected to each other such that the respective winding starts have the same polarity and the magnetic flux is applied. The double-tuned transformer according to claim 1, wherein the double-tuned transformer forms an induction circuit.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows 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
1 is a transformer-coupled primary input winding N1 for impedance matching and primary tuning winding N2 with tap a for tuning,
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 the coupling winding N3 with tap b and the secondary tuning winding N4 with tap c, the tap b is directly connected to the winding start of the secondary tuning winding N4, and the tap c is the additional capacitance. Element C
2 to the winding start of the coupling winding N3. Then, the 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.

In the primary tuning winding N2, the windings N21 and N22 are connected in series via the tap a, the N22 side is connected to the variable capacitance element C and the additional capacitance element C1, and the N21 side is grounded.

The coupling winding N3 is connected to the winding N via the tap b.
31 and N32 are connected in series, and the winding start of N32 is 2 via the tap a of the primary tuning winding N2 and the additional capacitance element C2.
Connect to the tap c of the next tuning winding N4 and ground the N31 side.

In the secondary tuning winding N4, windings N41 and N42 are connected in series via a tap c, and the winding start is coupled winding N4.
The end of winding is connected to the variable capacitance element C. The windings N32, N41, N42 form a mutual induction circuit of connection in which the respective winding starts have the same polarity and the magnetic fluxes of N32, N41, N42 are added. In addition, in order to clarify the polarity of each winding, the start position of the winding is indicated by a dot in the figure.

The output is drawn from the tap c of the secondary tuning winding N4, and the IC is supplied via an additional capacitance element C'for DC blocking.
It is connected to a terminal 2 which is connected to an amplifier (not shown). Further, the winding start of the coupling winding N3 and the tap a of the primary tuning winding N2 are also connected via the additional capacitance element C2. As a result, a trap circuit for the image frequency is formed by the windings N31, N32, N41, N42, the additional capacitance element C2, and the variable capacitance element C. The additional capacitance element C2 has one end connected to the tap a (or the winding start of the coupling winding N3) and the other end to the tap c in the figure, but one end thereof is coupled to the coupling winding N3.
, And the other end may be connected to any one point in the secondary tuning winding N4. Further, although the winding start of the winding N41 is connected to the tap b in the figure, it may be directly grounded.

The windings N31, N32, N41, N42 are
As shown in FIG. 2, the three-flange drum core D having the cap core CA is wound around the first groove D1 and the second groove D2. 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 of the windings N32 and N4 is set to 0.
1 to 0.7, and the coupling coefficient of the windings N41 and N42 is set to 0.85 to 1.0.

The double-tuned circuit embodying the present invention is configured as described above, and guides the input signal applied to the terminal 1 to the primary resonant circuit and the secondary resonant circuit, and changes the variable capacitance element C to achieve a specific reception. Tune to frequency. At the same time, the image interfering waves mixed in the input signal are generated by the windings N31, N32, N41, N.
42, the additional capacitance element C2 and the variable capacitance element C are used for the attenuation.

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 band. Suppress the frequency.

The reason why the resonance frequency of the trap circuit moves according to the reception frequency will be specifically described below. Figure 1
In order to make it easier to think of the secondary resonance circuit of the load tuning transformer T2, the circuit is simplified as follows. First, FIG.
As shown in, the taps b and c are commonly used for input and output to form the 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 winding N43, and the windings N43 and N42 are connected in series via the tap c. Further, the AC bypass capacitor C'has an impedance within the band band of about 0 and can be ignored, and the winding N21 is omitted on the assumption that the inductance is infinite. Further, the additional capacitive element C2 will be excluded for the time being.

When a current is applied to the windings N43 and N42, the self-inductances L43 and L42 of the windings N43 and N42 are changed to L43 'and L42', and the mutual inductance of the windings N43 and N42 is changed to M (M > 0)
Then, L43 '= L43 + M L42' = L42 + M. Here, since L43 = L43'-M L42 = L42'-M, the windings N43 and N42 are equivalently 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, in series with -M, L43 'and L42' +
A parallel circuit of C is connected to form a trap circuit of -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 maximum (denominator = 0) is the reception frequency f0, and the frequency at which the impedance Z is minimum (numerator = 0) is the resonance frequency f0 ′ of the trap. 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 reception frequency f0 in which the impedance changes according to the frequency and the reactances of the variable capacitance element C and the windings N31, N41, N42 are equal, and the variable capacitance element is tuned. Damping is applied at the resonance frequency f0 'of the trap where the reactance of C42 and the coupling coefficient K or the reactance of N42 in which the number of turns is 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 according to the change of the variable capacitance element C. Move in parallel. As a result, it is possible to suppress the image frequency that changes according to the reception frequency f0.

From the calculation formula, the reactance of the trap circuit is smaller than that of the tuning circuit. Therefore, in the low frequency region where the capacitance of the variable capacitance element C is large, the movement width of the resonance frequency f0 'of the trap is small, but the variable capacitance element is small. In the high frequency region where the capacity of C is small, the antenna tuning transformer T1
Coupling greatly affects the impedance and changes the trap of the image frequency with respect to the reception frequency f0.

Therefore, as shown in FIG. 1, the additional capacitance element C2 for impedance correction is connected in parallel with the windings N32 and N41. This makes it possible to correct the impedance of the tuning circuit and bring the attenuation band of the trap closer to the image frequency.

When the additional capacitance element C2 is added, the reception frequency f0 of the load tuning transformer T2 moves to a slightly lower range, so the reception frequency f0 of the antenna tuning transformer T1 is also lowered accordingly, and therefore the additional capacitance element C1 is set. to add. When the capacitance of the additional capacitance element C2 is small, the reception frequency f0 also hardly changes, so the additional capacitance element C1
May not be added. In addition, the additional capacitance element C2 may not be added depending on the degree of influence of the coupling of the antenna tuning transformer T1, and in that case, the additional capacitance element C1 is not necessary.

Further, the resonance frequency f0 'of the trap should be moved to a high range because the denominator of the calculation formula becomes small when the coupling coefficient K is increased, and should be moved to a low range because the denominator becomes large when the coupling coefficient K is made small. I understand. Alternatively, if the coupling coefficient K is fixed and the number of turns of the winding N42 is increased, the denominator of the calculation formula becomes large, so that it moves to the low range, and if the number of turns of the winding N42 is reduced, the denominator becomes small, so move to the high range. I understand. Thus, the resonance frequency f0 'of the trap can be adjusted to the image frequency band by providing the coupling coefficient K or the number of turns of the winding N42 with a width.

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 characteristic is attenuated near the image frequency and the result measured in the MW band is 30 dB within the band band. An improvement of ~ 45 dB was seen. Further, the reception sensitivity is at the same level as that of the conventional circuit, and the image frequency is suppressed without deteriorating other electric characteristics. In addition, one of the load tuning transformers of the double tuning transformer is a common winding, so the number of turns is significantly reduced compared to the conventional one, and the size and weight of the double tuning transformer is reduced.

8 to 10 show modified examples of the double-tuned circuit of the present invention. The double-tuned circuit of FIG. 8 has taps b and b'2
The secondary tuning winding N5 and the output winding N41 are transformer-coupled, and the primary tuning winding N2 and the secondary tuning winding N are connected via taps a and b '.
Connect 5. Further, the tap b'is the additional capacitance element C2.
And the tap b is connected to the other end of the output winding N41 through the secondary tuning winding N41.
5, a variable capacitance element C is connected in parallel with 5 to form a secondary resonance circuit.

The double-tuned circuit shown in FIG. 9 has a capacitive element C0 for tracking correction connected in parallel with the variable capacitive element C of the circuit shown in FIG.

In the double-tuned circuit of FIG. 10, the winding N21 of the circuit of FIG. 1 is independently wound, the tap a is omitted, and the coupled winding N3 is directly connected.

[0030]

As described above, the double-tuned transformer of the present invention has an antenna tuning transformer formed by connecting a variable capacitance element in parallel with a primary tuning winding with a tap a and a tap b.
The shared winding and the secondary tuning winding with tap c are shared, and tap b is directly at the beginning of the secondary tuning winding.
The tap c is connected to the winding start of the 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 is arranged on the input side and the output side, respectively. Then, the tap a of the primary tuning winding is connected to the winding start of the coupling winding, and the tap c of the secondary tuning winding is connected to the amplifier via an additional capacitance element for blocking DC. Therefore, according to the present invention, mutual inductances M and L due to mutual induction of the shared windings of the load tuning transformer.
Since the trap circuit is formed by C, when the variable capacitance element is changed, the resonance frequency of the trap circuit also changes in association with the reception frequency, and the image frequency that changes according to the reception frequency can be suppressed. Further, since the additional capacitance element corrects the impedance of the tuning circuit, the attenuation band of the trap can be brought closer to the image frequency. Further, since the load tuning transformer is shared and the mutual inductance M is drawn out, new parts for the trap are not required, and the economy and reliability are improved.

The double-tuned transformer of the present invention is a drum type having a plurality of flanges having two or more winding grooves while arranging the number of turns and the coupling coefficient of the coupling winding and the secondary tuning winding of the load tuning transformer. Wind around the ferrite core. Further, the winding start side winding and the secondary tuning winding, which are connected in series via the tap b of the coupling winding, form a mutual induction circuit of connection in which magnetic fluxes are added with the winding start sides having the same polarity. Therefore, according to the present invention, the resonance frequency of the trap changes depending on the number of turns of the shared winding of the load tuning transformer and the coupling coefficient. Therefore, the resonance frequency of the trap is arranged by arranging the number of turns and the coupling coefficient together with the additional capacitance element for impedance correction. Can be properly tuned near the image frequency.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a double-tuned 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-tuned 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-tuned circuit.

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

FIG. 8 is a modification of the double-tuned circuit embodying the present invention.

FIG. 9 is another modification of the double-tuned circuit embodying the present invention.

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

[Explanation of symbols]

1-2 terminals C variable capacitance element C ', C1, C2 additional capacitance element C0 tracking correction capacitor 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 coupled 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

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 2000-315961 (JP, A) JP 2000-324010 (JP, A) JP 2000-357977 (JP, A) JP 10-209816 (JP , A) JP-A-9-153772 (JP, A) Actual development 5-4639 (JP, U) Actual development 2-137124 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) H03J 3/20-3/24 H03J 5/24 H04B 1/18 H04B 1/26

Claims (5)

(57) [Claims] 1. An antenna tuning transformer formed by connecting a variable capacitance element in parallel with a primary tuning winding with a tap a, a shared winding with a tap b and a secondary tuning winding with a tap c, and a common winding. , Tap b is directly connected to the winding start of the secondary tuning winding, tap c is connected to the winding start of the coupling winding through an additional capacitance element for impedance correction, and a variable capacitance element is connected in parallel with this. And a load tuning transformer consisting of a load tuning transformer and a tap a of the primary tuning winding connected to the winding start of the coupling winding, and a tap c of the secondary tuning winding for DC blocking. A double-tuned transformer for a superheterodyne receiver, characterized by being connected to an amplifier via an additional capacitance element. 2. The coupling winding and the secondary tuning winding of the load tuning transformer are arranged while arranging the number of turns and the coupling coefficient.
The double-tuned transformer according to claim 1, wherein the double-tuned transformer is wound around a drum type ferrite core having a plurality of flanges having the above winding grooves. 3. The coupling coefficient between the winding starting side winding and the secondary tuning winding connected in series via the tap b of the coupling winding is set to 0.1 to 0.7. Item 1
The described double tuning transformer. 4. The double-tuned transformer according to claim 1, wherein the coupling coefficient of the windings connected in series via the tap c of the secondary tuning winding is set to 0.85 to 1.0. 5. A mutual induction circuit in which the winding start side winding and the secondary tuning winding, which are connected in series via the tap b of the coupling winding, have the same winding start and have a magnetic flux applied thereto. The double-tuned transformer according to claim 1, wherein