JPH0243367B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a high frequency tuning circuit for suppressing image signals in a superheterodyne receiver.

[Prior art and its problems]

In order to suppress image signals in a superheterodyne receiver, it is necessary to increase the number of high-frequency tuning filter stages, configure the tuning coil to have an anti-resonance point, and provide a separate trap circuit for image signals. This method is conventionally used.

However, increasing the number of stages of a tuned filter increases the number of coils, variable capacitance elements such as variable capacitors, and variable capacitance diodes that make up the tuning filter, which not only increases the price, but also complicates the adjustment of the circuit by increasing the number of stages. . In the case where the tuned filter is configured with a parallel resonant circuit and the coil has an anti-resonance point, it is difficult to adjust the tap position and the coupling coefficient of the coil, which is undesirable because the degree of freedom in circuit design is restricted. In addition, since the positional relationship between the frequencies of the anti-resonance point and the resonance point is fixed, even if the image signal corresponding to a specific reception frequency is suppressed, it will not be effective if the frequency of the image signal moves as the reception frequency changes. Moreover, at frequencies past the anti-resonance point, by providing the anti-resonance point, the amount of signal attenuation decreases rapidly, as if a rebound occurs, and the suppression state of the image signal often worsens.

Trap circuits can also suppress only image signals of specific frequencies.

As described above, conventionally, there has been no completed method for uniformly suppressing image signals whose frequencies vary depending on the reception frequency using a simple circuit configuration.

〔the purpose〕

An object of the present invention is to connect an untuned transformer to a tuned transformer so that the output phases of both transformers are added in opposite phases at the frequency of the image signal, so that the image can be imaged almost uniformly over a wide receiving band. An object of the present invention is to provide a high frequency tuning circuit that can suppress signals.

[Technical means to solve problems]

The present invention connects a variable capacitance element to the primary winding on the input side to form a series resonant circuit, and comprises a tuned transformer that obtains a high frequency output from the secondary winding on the output side, and a tuned transformer connected to the input side of the tuned transformer. It consists of an untuned transformer connected in parallel with the resonant circuit and whose output side is connected in series with the secondary winding, and the phase of the output voltage of the tuned transformer and the untuned transformer is on the side where the frequency of the image signal is higher than the tuning frequency of the tuned transformer. They are connected so that they are in opposite phases to each other and in the same phase on the side where the image signal does not have a frequency, and when the tuning frequency is changed according to the receiving frequency, the image signal corresponding to a specific receiving frequency A high frequency tuning circuit for a superheterodyne receiver is characterized in that the amplitude level of the output voltage of each transformer is adjusted to be approximately equal at the frequency of .

The frequency of the image signal corresponding to this specific reception frequency is selected so that the deviation between the frequency at which the amplitude levels of the output voltages of the tuned transformer and the untuned transformer are equal throughout the entire reception band and the frequency of the image signal is minimized. More specifically, the higher the reception frequency within the reception band, the smaller the difference between the reception frequency and the frequency of the image signal, and the more difficult it is to suppress the image signal, so the frequency of the image signal at a relatively high reception frequency is selected. This is desirable for image signal suppression in the entire reception band.

〔Example〕

The following description will be made with reference to the circuit diagram of FIG. 1 showing a basic embodiment of the high frequency tuning circuit of the present invention, and FIGS. 2 to 4 showing its characteristic diagrams.

In FIG. 1, T1 is a tuned transformer and T2 is an untuned transformer.

The tuning transformer T1 has a primary winding L11 on the input side,
It consists of a secondary winding L12 on the output side, and a primary winding L1.
Both ends of the secondary winding L12 are connected to terminals 1 and 2, and both ends of the secondary winding L12 are connected to terminals 3 and 4, respectively. The side connected to terminal 1 of the primary winding L11 and the side connected to the terminal 1 of the secondary winding L12
The side connected to terminal 3 has the same polarity. A variable capacitance diode D1 is connected between terminal 2 and the ground, and a variable capacitance diode D1 is connected between the primary winding L11 and the variable capacitance diode D1.
A series resonant circuit is formed. An input signal applied to terminal 1, which also serves as the hot side input terminal of the high frequency tuning circuit, is tuned by this series resonant circuit.

The untuned transformer T2 has a primary winding L2 on the input side.
1. Consists of a secondary winding L22 on the output side, both ends of the primary winding L21 are terminals 5 and 6, and the secondary winding L22
Both ends are connected to terminal 7 and terminal 8, respectively. The side connected to terminal 5 of the primary winding L21 and the secondary winding L22
The side connected to the terminal 8 has the same polarity. and,
Terminal 6 and terminal 8 are grounded, and terminal 5 and terminal 7 are connected to terminal 1 and terminal 4 of tuning transformer T1, respectively.

In this way, the primary winding L21 of the untuned transformer T2 is connected in parallel to the series resonant circuit formed in the tuned transformer T1, consisting of the primary winding L11 and the variable capacitance diode D1, and the secondary winding L22 is It is connected in series to the secondary winding L12 of the tuning transformer T1.
Further, the terminal 3 also serves as the hot side output terminal of the high frequency tuning circuit.

By the way, FIG. 2 is a characteristic diagram showing the output voltage characteristics of the tuned transformer T1 and the untuned transformer T2 when they are not connected to each other as shown in FIG. 1. The horizontal axis represents frequency, and the vertical axis represents voltage level.

|V _3-4 | is the output terminal 3 and terminal 4 of the tuning transformer T1 when the frequency of the input signal changes.
This is the amplitude of the output voltage V _3-4 obtained during this period, and the voltage level is highest at the tuning frequency f ₀ .

|V _7-8 | is shown by a dotted line, and is the amplitude of the output voltage V 7-8 obtained between terminals 7 and 8 on the output side of the non-tuned transformer T2, and is the amplitude of the output voltage V _7-8 obtained between terminals 5 and 6 on the input side. Even if the frequency of the input signal applied between them changes, the voltage level remains flat without depending on the frequency. f ₁ is the amplitude of the output voltage V _3-4 |V _3-4 |
This is a frequency higher than the tuning frequency f ₀ at which the amplitude |V _7-8 | of the output voltage V _7-8 becomes equal. This frequency f ₁
As will be described later, corresponds to the frequency of the image signal corresponding to a specific reception frequency.

FIG. 3 is a characteristic diagram showing the state of the phase of the output voltage with respect to the input signal when they are not connected to each other.

φ _3-4 is the output voltage obtained between terminal 3 and terminal 4
It is the phase with respect to the input signal of V _3-4 , and changes near the tuning frequency f ₀ . The side lower than the tuning frequency f ₀ is almost 180 degrees ahead, and the side higher than it is in phase. On the other hand, φ _7-8 indicated by a dotted line is the output voltage obtained between terminals 7 and 8 on the output side when an input signal is applied between terminals 5 and 6.
It has a phase of V _7-8 , always leads the input signal by 180°, and does not change with frequency.

Such a phase relationship of the output voltages can be obtained by setting the polarities of the primary and secondary windings in each transformer as shown in FIG.

By connecting the tuned transformer T1 and the untuned transformer T2, which exhibit output voltage characteristics as shown in Figures 2 and 3, as shown in Figure 1, terminal 3, which serves as the output terminal of the high frequency tuning circuit, and ground In between, output voltage characteristics as shown in the characteristic diagram of FIG. 4 are obtained.

Amplitude of output voltage V _3-0 between terminal 3 and ground |
V _3-0 | is the sum of output voltage V _3-4 and output voltage V _7-8 , which have different amplitude and phase relationships. Therefore, between the tuning frequency f ₀ and the frequency f ₁ , the voltage level of the amplitude |V _3-0 | decreases more rapidly than the output voltage V _3-4 , becomes the lowest at the frequency f ₁ , and then increases slightly. As is clear from the explanation of FIGS. 2 and 3, this means that at frequencies higher than the tuning frequency f ₀ , the output voltage V _3-4 of the tuned transformer T1 and the output voltage V _7-8 of the untuned transformer T2 are different. This is because they are 180° out of phase and out of phase, and the amplitudes of both voltages are essentially subtracted.

When the amplitude of the output voltage V _3-4 and the output voltage V _7-8 exceed the same frequency f ₁ , the amplitude |V _7-8 | becomes the amplitude |V _3-4 |
Since it becomes larger, the voltage level of the amplitude |V _3-0 | also increases slightly. However, since the falling state of the amplitude |V _3-4 | is saturated, the amplitude |V _3-4 | and the amplitude |V _7-8
The difference between | is not very wide. Therefore, the increase is only slight, and does not increase dramatically as in the case where the anti-resonance point is exceeded in the conventional case.

The high frequency tuning circuit of the present invention exhibiting the output voltage characteristics shown in _FIG .
When the amplitudes of V _7-8 are equal in opposite phase, the _amplitude of the output voltage V _3-0 |V _3-0 | By making it consistent with the above, the suppression effect will be exerted. The reception frequency is the tuning frequency f ₀
It goes without saying that we must respond to this.

As is well known, in the case of the upper heterodyne system,
Since the frequency of the image signal is equal to the received frequency plus twice the intermediate frequency, it is easy to set the relationship between the tuning frequency f ₀ and the frequency f ₁ that matches the frequency of the image signal. However, when the receiving frequency changes, the frequency of the image signal also moves, so the frequency f ₁ and the frequency of the image signal are slightly different. However, as is clear from Fig. 2, as the tuning frequency f ₀ changes, the amplitude |V _3-4
The frequency f ₁ , which is the intersection of | and amplitude |V _7-8 |, also moves, so it does not deviate significantly. Therefore, by selecting a specific reception frequency so that the deviation is small in the entire reception band and matching the frequency f ₁ to the frequency of the image signal, the tuning frequency can be adjusted.
Even if f ₀ changes, the frequency f ₁ follows the frequency of the image signal and moves throughout the reception band, making it possible to suppress the image signal.

In addition, in the non-tuned transformer T2, the polarity and turns ratio of the primary winding L21 and the secondary winding L22 are determined in order to set the frequency _f1 , but the inductance value on the input side is determined by the input of the entire high frequency tuning circuit. The impedance only needs to be to the extent that it does not overload the circuit, and if the receiving band is a medium wave band, the impedance is several tens of microns to several mm.
It can be used at about H. Further, the no-load Q may be about 10 to 20. Note that even if the non-tuning transformer T2 has a tuning point at a frequency that is sufficiently lower or higher than the band in which the reception frequency and image signal frequency exist,
There is no problem as long as the phase and amplitude are constant within the band.

The primary winding L21 and the secondary winding L22 are insulated, but as shown in the wiring diagram in Figure 10, the secondary winding on the output side is drawn out from the primary winding L21 on the input side with a tap. You may. Conversely, the primary winding on the input side may be pulled out from the secondary winding on the output side by a tap. In either case, the polarity of either the primary winding L11 or the secondary winding L12 of the tuning transformer T1 is reversed to obtain the same phase relationship. Furthermore, in the case of the lower heterodyne method,
The frequency of the image signal is the received frequency minus twice the intermediate frequency, but in that case, the phases Φ _3-4 and Φ _7-8 are in opposite phase on the side lower than the tuning frequency f ₀ . Therefore, it is sufficient to set the phase to be the same on the higher side.

FIG. 5 is a circuit diagram showing another embodiment of the high frequency tuning circuit of the present invention, which is applied to a vehicle-mounted medium wave band receiver.

This high frequency tuning circuit is of a double tuning type, with 2
It consists of one tuned transformer T3, one tuned transformer T4, and one untuned transformer T5.

Both ends of the primary winding L31 of the tuned transformer T3 are connected to the terminals 9 and 10, and both ends of the secondary winding L31 are connected to the terminals 11 and 12. Primary winding L3
1 and the polarity of the secondary winding L32 does not matter. Terminal 1
0, terminal 12 is grounded, and terminal 9 serves as the hot side input terminal of the high frequency tuning circuit.

Terminal 11 is capacitor C1, resistor R1, resistor R
2. Connect to terminal 13 of tuning transformer T4 via capacitor C2. A variable capacitance diode D is connected between the connection point of capacitor C1 and resistor R1 and ground.
2. A variable capacitance diode D3 is connected between the connection point of the resistor R2 and the capacitor C2 and the ground. A connection point between the resistor R1 and the resistor 2 is connected to a terminal 21 for supplying a bias voltage.

Both ends of the primary winding L41 of the tuned transformer T4 are connected to the terminals 13 and 14, and both ends of the secondary winding L42 are connected to the terminals 15 and 16. Terminal 14 is connected to tap 22 of secondary winding L32 of tuning transformer T3.
Connect to. Terminal 15 serves as the hot side output terminal of the high frequency tuning circuit. The side connected to terminal 14 of primary winding L41 and terminal 1 of secondary winding L42
The side connected to 5 has the same polarity.

Both ends of the primary winding L51 of the untuned transformer T5 are connected to the terminals 17 and 18, and both ends of the secondary winding L52 are connected to the terminals 19 and 20. The side connected to terminal 17 of the primary winding L51 and the secondary winding L52
The side connected to terminal 20 has the same polarity, and terminal 1
7 and terminal 19 are connected to terminal 14 and terminal 16, respectively, of tuning transformer T4. Terminal 18 and terminal 20 are grounded.

Resistor R1 and resistor R2 are bias resistors, and capacitor C1 and capacitor C2 serve to cut off direct current.

In the high frequency tuning circuit shown in FIG. 5, a parallel resonant circuit is formed by the secondary winding L32 of the tuning transformer T3 and the variable capacitance diode D2, and a parallel resonant circuit is further formed by the primary winding L41 of the tuning transformer T4 and the variable capacitance diode D.
3 forms a series resonant circuit.

The primary winding L51 of the untuned transformer T5 is connected in parallel to the series resonant circuit of the tuned transformer T4, and the secondary winding L52 is connected in series to the secondary winding L42 of the tuned transformer T4. The input signal from the terminal 9 is double tuned by two resonant circuits, but by connecting the tuning transformer T4 and the non-tuning transformer T5 as described above, an image can be generated in the same manner as in the embodiment shown in FIG. The signal is suppressed.

In addition, in the embodiment shown in Fig. 5, the intermediate frequency is set to 450KHz in the output voltage characteristic obtained between the terminal 15, which serves as the output terminal of the high frequency tuning circuit, and the ground.
The image signal frequency of 2300KHz is suppressed the most when the tuning frequency is 1400KHz, which is relatively high. In other words, in the respective output voltage characteristics of the tuned transformer T4 and the untuned transformer T5,
The amplitude level of the output voltage is made the same at the image signal frequency of 2300KHz corresponding to one reception frequency of 1400KHz. The frequency of 2300 KHz corresponds to frequency f ₁ in the embodiment of FIG. The turns ratio of the primary winding L41 and the secondary winding L42 of the tuned transformer T4 is 6:1, and the primary winding L51 of the untuned transformer T5
The turns ratio of the secondary winding L52 and the secondary winding L52 may be approximately 5:1.

6, 7, and 8 are characteristic diagrams showing the output voltage characteristics of the high frequency tuning circuit shown in FIG. 5, where the vertical axis represents the output voltage V _15-0 obtained between the terminal 15 and the ground.
The level of the amplitude |V _15-0 | is expressed as the amount of attenuation.
Tuning frequency is 1400KHz, 600KHz, 1600KHz respectively
It is. The dotted line is the amplitude of the conventional output voltage without the untuned transformer T5 connected. If the untuned transformer T5 is not connected, terminal 16 is grounded.

In FIG. 6, the frequency corresponding to the frequency f ₁ in the embodiment of FIG. 1 is set to 2300 KHz, so the frequency of the largest amount of attenuation matches the frequency of the image signal, and the image signal is completely suppressed.

In FIG. 7, the frequency of the image signal, 1500 KHz, is shifted higher than the frequency near 1100 KHz, which is the frequency with the largest amount of attenuation, but it is attenuated by 20 dB or more compared to the case indicated by the dotted line.

In FIG. 8, the frequency of the image signal, 2500 KHz, is shifted lower than the frequency with the largest amount of attenuation, but it is attenuated by 30 dB or more compared to the case indicated by the dotted line.

As is clear from this example in the medium wave band, in the upper heterodyne system, the frequency of the image signal is lower than the frequency with the largest attenuation on the relatively high frequency side of the receiving band, and On the low frequency side, it is desirable to set the output voltage characteristics of the high frequency tuning circuit so that the frequency of the image signal is higher than the frequency with the largest amount of attenuation. To do this, we set the frequency of the image signal corresponding to a specific reception frequency to 2300KHz.
However, by comparing the image signal that moves with the reception frequency in the medium wave reception band,
This can be improved by increasing the amount of attenuation from 20dB to 40dB. Depending on the relationship with other circuit parts, the frequency of the image signal when the reception frequency is 1000KHz
Similar desirable results can be obtained by selecting one point of the image signal in a range from 1900 KHz to about the frequency of the image signal of the embodiment.

FIG. 9 is a sectional view of cores around which a tuned transformer and an untuned transformer are wound, which are connected to each other.

The drum-shaped core 30 with a three-piece brim has two winding grooves 31 and 32, and the winding groove 31 has the primary winding L41 and the secondary winding L42 of the tuned transformer T4, and the winding groove 3.
2, the windings of the tuned transformer T4 and the untuned transformer T5 are wound in separate winding grooves, such as the primary winding L51 and the secondary winding L52 of the untuned transformer T5. 33 is a concave-shaped core that covers the core 30, and is moved up and down to adjust the characteristics of the tuning transformer T4.

In this way, if the tuned transformer and the untuned transformer that are connected to each other are wound around the same core 30,
Even if a new untuned transformer is connected, the shape and especially the size of the high-frequency tuned circuit will hardly change, and the price will not increase due to the extra core. Furthermore, assembly of the high frequency tuning circuit becomes easier.

Note that although the tuned transformer and the untuned transformer in the present invention have windings wound around them, there is also a known technique for constructing a transformer by forming a conductor pattern on a circuit board that plays the same role as the winding. It may be configured using other techniques.

〔effect〕

As described above, the high frequency tuning circuit of the present invention connects an untuned transformer to at least one tuned transformer, and the output voltages of each transformer have opposite phases on the side where the frequency of the image signal is higher than the tuning frequency of the tuned transformer. and on the side where there is no image signal, they are added in the same phase.

When the tuning frequency is changed in accordance with the receiving frequency, the amplitude levels of the output voltages of both transformers are made equal for the image signal corresponding to a specific receiving frequency. As a result, even if the frequency of the image signal moves together with the tuning frequency, a large deviation from the most attenuated frequency in the output voltage characteristic, for example, the frequency f ₁ in the embodiment of FIG. 1, does not occur. Therefore, it is possible to suppress image signals in the vicinity of the frequency that is most attenuated over a wide band.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the high frequency tuning circuit of the present invention, Fig. 2 is a characteristic diagram showing the output voltage characteristics of the tuned transformer and untuned transformer shown in Fig. 1, and Fig. 3 is the tuning diagram shown in Fig. 1. A characteristic diagram showing the phase of the output voltage of a transformer and an untuned transformer, FIG. 4 is a characteristic diagram showing the output voltage characteristics of the high frequency tuning circuit of FIG. 1, and FIG. 5 is another embodiment of the high frequency tuning circuit of the present invention. FIGS. 6, 7, and 8 are characteristic diagrams showing the output voltage characteristics of the high frequency tuning circuit of FIG. 5, and FIG.
The figure is a sectional view of the cores around which the tuned transformer and the untuned transformer are wound, and FIG. 10 is a wiring diagram showing another configuration of the untuned transformer of FIG. 1. 1 to 21: terminals, T1, T3, T4: tuned transformer, T2, T5: untuned transformer.

Claims (1)

[Claims] 1. A tuned transformer in which a variable capacitance element is connected to the primary winding on the input side to form a series resonant circuit, and a high frequency output is obtained from the secondary winding on the output side; It consists of an untuned transformer connected in parallel with the series resonant circuit, and whose output side is connected in series with the secondary winding, and the phase of the output voltage of the tuned transformer and the untuned transformer is higher than the tuned frequency of the tuned transformer, which is the image signal of the reception frequency. They are connected so that they are in opposite phase to each other on the side where the frequency of the image signal is present, and are in the same phase on the side where the frequency of the image signal is not present.Moreover, when the tuning frequency is changed according to the receiving frequency, A high frequency tuning circuit for a superheterodyne receiver, characterized in that the amplitude level of the output voltage of each transformer is adjusted to be approximately equal at the frequency of an image signal corresponding to the frequency. 2. The high frequency tuning circuit according to claim 1, wherein the secondary winding on the output side of the non-tuned transformer is drawn out from the primary winding on the input side by a tap. 3. The high frequency transformer according to claims 1 and 2, wherein the tuned transformer and the untuned transformer are configured by winding the core separately around each winding groove of a three-flange core having two winding grooves. Tuned circuit.