JPS6013566B2 - input tuning circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an input tuning circuit for high frequency signals used in tuners of television receivers and the like.

Tuners for television receivers and the like must be able to receive signals over a wide frequency band.

For example, television broadcast channels span both the VHF and UHF bands, and in order to be able to receive these signals, it must be possible to tune over a wide frequency range. Since the frequencies of the VHF band and the UHF band are significantly different, 1
reception is difficult with two tuner circuits, so typically V
Different tuner circuits had to be used for the HF band and the UHF band. In recent years, varactor diodes and the like have been used as tuned circuit elements.

So-called electronic tuners have come into use, and although it is natural that the VHF band tuner circuit and the UHF band tuner circuit have different circuit constants, the circuit configuration is different. Since they are almost the same, if high-frequency amplification circuits, frequency conversion circuits, local oscillation circuits, etc. can be shared between VHF and UHF bands, one tuner circuit can receive both VHF and UHF signals. It is possible to reduce costs and improve reliability due to the simplification of the configuration. In such a tuner that shares the tuner circuit between the VHF band and the UHF band, the inductance element of the tuning circuit is
A device that can switch between the HF band and the UHF band is known.

However, in such a tuner, a high frequency switch diode is required to switch the inductance element, and when switching to the UHF band, this switch diode is connected in series with the inductance element for the UHF band, and the tuning circuit is changed. It will be included in

At this time, the inductance of the inductance element is approximately 1000m, which is a very large value, and the high frequency resistance of the switch diode is inserted in series with it, but in the UHF band. Since the high frequency resistance of the switch diode is a fairly large value of 0.5 to 10, the loss in the tuning circuit becomes quite large, making it almost impractical.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques, and to
To provide an input tuning circuit which enables configuration of a tuner which can share a tuner circuit for F band and UHF band and can receive VHF band and UHF band without switching circuit elements.

To achieve this objective, the present invention provides a so-called two-point tuning circuit for signal selection, which has two different resonant frequencies and is capable of simultaneously tuning to signals of two different frequencies. It is characterized by the following points.

First, a two-point tuning circuit, which is the basis of the present invention, will be explained.

FIG. 1 is a diagram for explaining the principle of a two-point tuning circuit according to the present invention, in which the portion indicated by 7 is a two-point tuning circuit, 8 is a signal source, and 9 is a load.

The two-point tuning circuit 7 is a two-terminal circuit having terminals 1 and 2, and consists of a first capacitor 3, a second capacitor 4, a first coil 5, and a second coil 6. A series circuit of the first capacitor 3 and the first coil 5 is further connected in parallel to the parallel circuit of the first capacitor 3 and the second coil 6.

Characteristic curve 1 shown by the broken line in Figure 2 shows how the actasos between terminals 1 and 2 of this two-point tuned circuit 7 changes depending on the frequency based on the transmission characteristics to the load.
0, the reactance is infinite at two different frequencies, that is, the signal attenuation is close to zero, indicating resonance.

This resonant frequency can be made to fall within each of the VHF high band and UHF band of television broadcasting by appropriately determining circuit constants. In addition, the resonance frequency at these two points can be changed as shown in the characteristic curve 11 shown by the solid line by changing the capacitance C2 of the second capacitor 4, and this two-point tuning circuit 7 can be used for television broadcasting. VH of
Tuning can be achieved for both F/-band and UHF band signals without switching circuits. The characteristic curve 10 in FIG. 2 shows that when the capacitance C2 of the capacitor 4 is 1 F, the characteristic curve 11 is 2. Since this capacitance value and its variation range can be sufficiently obtained from the varactor diode used in ordinary television receivers, there is no problem in configuring it as an electronically tuned tuner. do not have.

Therefore, if a tuner for a television receiver is constructed using this two-point tuning circuit, tuning can be achieved for both the VHF high band and the UHF band without switching the tuning circuit. Tuners can be shared without causing problems such as increased loss due to switching of tuning circuits.

The present invention is characterized by an effective and specific circuit configuration when applying this so-called two-point tuning circuit to an input tuning circuit of a tuner of a television receiver.

When operating a so-called two-point tuning circuit as an input tuning circuit for a tuner, the most important thing to be careful about is how to couple the high-frequency signal source in the VHF and UHF bands with the input impedance of the high-frequency amplifier circuit that serves as the load. . In other words, the matching condition is satisfied and VH
It must be ensured that the signal input sections in each of the F and UHF bands do not affect each other.

In each of the VHF and UHF bands, methods for coupling the antenna input and load include capacitive coupling (C coupling) and inductive coupling (M coupling).

Note that the inductive coupling includes coupling by inductance (L coupling). Which of these coupling methods to select cannot be determined unambiguously, as it must be selected by considering factors such as the load condition, the load condition, the damping characteristics, etc., but a combination of these coupling methods In V
The object of the present invention is to propose a coupling method with less mutual interference between HF input and UHF input, and to provide an all-channel input tuning circuit that can receive from VHF to UHF without switching the tuning circuit.

Now, before explaining the present invention, an example of an input tuning circuit using a two-point tuning circuit will be explained with reference to the connection diagram in FIG. 3 and the equivalent circuit diagram in FIG. 4. In these figures,
12 is a high frequency signal input terminal, 13 is an output terminal, 14 is a power supply terminal, 15 is a tuning voltage application terminal, 16 is a band switching voltage application terminal, 17 is an FET serving as a high frequency amplification element, 18
19 is a varactor diode for tuning, 19 is a switch diode for switching between VHF low band and/or low band, 20 to 22 are tuning coils, 23 is a choke coil, 24 is a tuning capacitor, 25, 26 27 to 31 are bypass capacitors, 32 to 37 are bias resistors, and 39 is a terminal to which an AGC signal is applied. In addition, 40 in FIG. 4 is an equivalent resistance of the input signal source connected to the input terminal 12, a capacitor 38 and a resistor 41 are F through the coupling capacitor 26.
These are the equivalent capacitance and equivalent resistance on the output side including the gate G of ET17.

Then, the coil 20 becomes the first coil of the two-point tuned circuit,
The coils 21 and 22 correspond to the second coil, the same capacitor 24 corresponds to the first capacitor of the two-point tuned circuit, and the varactor diode 18 corresponds to the second capacitor.

Next, the operation will be explained. First, when receiving the VHF band and the UHF band, a positive voltage is applied to the band switching voltage application terminal 16 to make the diode 19 conductive and the coil 22 short-circuited.

In this state, the switch diode 19 shown in FIG.
It has the same configuration as the two-point tuning circuit 7 shown in the figure.

Therefore, since resonance occurs at two points with different frequencies, by setting the constants of the coils 20, 21, the capacitors 24, 25, 38, and the varactor diode 18 to appropriate values, the characteristic curves 10, 11 in FIG. As shown in , tuning can be achieved at two points: the VHF high band and the UHF band.

By changing the voltage applied to the varactor diode 18 from the terminal 15, it is possible to tune to any frequency within each band and receive signals.

Next, when receiving VHF low band, a negative voltage is applied to the terminal 16 to turn off the diode 19.

This state corresponds to the case where the switch 19 in FIG. 4 is open, and the coil 22 is inserted in series with the coil 21 and the first
This means that the inductance L2 of the coil 6 in the figure has increased, and by selecting an appropriate value for the inductance of the coil 22, the resonance point at the low frequency of the two-point tuned circuit can be placed within the VHF low band, and the Tuning to VHF low band signals can be achieved by changing the voltage applied to the VHF low band diode 18. In this way, according to the circuit shown in FIG.
By turning only one switch diode 19 on and off and switching only one coil 22, it is possible to switch from VHF low band to VHF high band and UHF of television broadcasting.
An input tuning circuit capable of receiving all of the bands can be obtained. Moreover, at this time, since a cutting wire, such as a diode, is not connected in series with the coil 20, which mainly determines the resonant frequency in the UHF band, there is no possibility that disadvantages such as increased loss in the tuning circuit due to band switching will occur. Not at all.

Next, a description will be given of how the coupling condition between the signal source and the load is satisfied in the circuit shown in FIG.

As is clear from the equivalent circuit in FIG. 4, the equivalent resistance ye on the load side is coupled to the tuning circuit via the equivalent capacitor 38, and the resistance ys of the signal source is also coupled to the tuning circuit via the capacitor 25. .

Therefore, the coupling format on the input side and the output side is exactly the same, and the equivalent resistance ys of the input side, that is, the signal source, and the equivalent resistance ye of the output side, that is, the load, are usually on the order of several hundred, and there is almost no difference between them. Coupling capacitors 25 and 2
By appropriately selecting the capacitance value of 6, the frequency characteristics become almost the same, and good matching can be provided over the entire reception band. In addition, the capacitances of the capacitors 25 and 38 are included in the capacitance of the tuning circuit, but since these are only inserted in parallel with the first capacitor 24, the capacitance of the capacitor 24 is set in advance to the capacitance of the capacitors 25 and 38.
The presence of these capacitors 25 and 38 has very little adverse effect, such as narrowing the range of change in the tuning frequency.

However, in the circuit as explained in Fig. 3, a single coupling capacitor is used to
Since extremely wideband signals up to the HF band are input to the load, depending on the type of high-frequency amplification element used as the load, it may be difficult to always satisfy the optimal matching conditions for all bands. Ta.

The present invention further improves this point so that matching can be arbitrarily optimized for each band of VHF and UHF bands.Embodiments of the present invention will be described below with reference to FIGS. 5 to 7.

FIG. 5 shows a first embodiment of the present invention, in which the same or equivalent parts as the input tuning circuit shown in FIG. I'll omit it here.

42 and 43 are switch diodes which correspond to the diode 19 in FIG. 3 and are used for band switching;
~47 is a tuning coil, which also corresponds to coils 21 and 2 in Fig. 3.
2, 48 is a choke coil for applying DC bias, 49 is a coupling capacitor, 50 is a bypass capacitor, 51' is a bias resistor, 52 is a band switching voltage application terminal, 53 is a UHF band signal input terminal,
54 is a VHF band signal input terminal, 55 is a switch diode, and 56 and 56' are bypass capacitors.

Note that in this embodiment, the amplification element 17 and its associated circuits are omitted.

Next, the operation will be explained.

During UHF band reception, a positive voltage is applied to the terminal 16 and a negative voltage is applied to the terminal 52.

As a result, the diodes 42 and 43 become conductive, and the diode 55 is cut off. Therefore, input state 5
The UHF band signal applied to 3 is coupled to the subsequent point of the coil 20 and capacitor 24 via a capacitor 49, and the 2 In addition to the point tuning circuit, the tuning voltage applied from the terminal 15 changes the capacitance of the varactor diode 18 to achieve tuning.

At this time, the coils 45 and 46 are short-circuited by the conductive diodes 42 and 43, and are no longer included in the tuned circuit. Furthermore, although a VHF band signal source is coupled to the terminal 54, the impedance of the signal source is converted by the coils 44 and 47, resulting in a relatively large impedance, as shown in the equivalent circuit of FIG. It is coupled in parallel with the impedance represented by the capacitor 38 and resistor 41 on the load side, and since the impedance on the load side is kept quite low in the UHF band, the UHF band coupled to the terminal 53 is has almost no effect on the signal source. And UH seen from terminal 53
The matching conditions viewed from the load side in the F band are also similar to those of the circuit shown in FIG. 3, and are maintained in a sufficiently good condition. Next, when receiving VHF high band, the positive voltage at the terminal 16 remains as is, and only the voltage at the terminal 52 is switched from a negative voltage to a positive voltage.

As a result, the switch diode 55 also becomes conductive.
The terminal 53 to which the UHF band signal source is coupled is grounded at high frequency via the capacitor 50, thereby short-circuiting the UHF band signal. Therefore, the signal from the VHF band signal source coupled to the terminal 54 is impedance-converted by the coils 44 and 47 and connected to two points formed by the coils 20, 44, 47, the capacitor 24, and the varactor diode 18. It will be coupled to a tuned circuit. Generally, the impedance on the load side shown by the capacitor 38 and resistor 41 in the equivalent circuit of FIG. The matching condition in the band can be maintained at the best condition arbitrarily. Further, at this time, since the terminal 53 is grounded at high frequency by the switch diode 55, the impedance of the UHF band signal source coupled to the terminal 53 is VHF.
There is little concern that it will affect operation in the belt.

At this time, the series circuit of capacitors 49 and 50 is connected in parallel to capacitor 24, and this is included in the tuning circuit, but it is sufficient to select the tuning conditions in the VHF band in this way in advance, and there will be no problems. do not become.

Therefore, if the tuning voltage applied to the terminal 15 is adjusted in this state, the capacitance of the varactor diode 18 will change,
It is possible to tune to VHF high band signals.

When receiving VHF low band, the positive fin pressure applied to the fin 52 remains unchanged and a negative voltage is applied to the terminal 16 to turn off the diodes 42 and 43.

As a result, the two-point tuning circuit is composed of the coils 20, 44 to 47, the capacitor 24, and the varactor diode 18, and a resonance point is generated in the low band of the VHF band. Further, at this time, the high frequency input signal supplied to the terminal 54 is transmitted to the coils 44, 45 and the coils 46, 4.
7, the impedance is converted according to the impedance ratio, and the signal is coupled to the tuning circuit. Therefore, it is possible to provide good matching to the load impedance in the VHF low band. As described above, in the embodiment of the present invention shown in FIG. 5, when receiving the UHF band, the UHF band signal is coupled to the two-point tuning circuit via the capacitor 49, and the impedance of the load is reduced at the frequency of this band. A relatively low value provides good matching, and
The influence of the VHF band signal source connected to the terminal 54 has almost no effect on the load due to the impedance conversion effect of the coils 44 and 47 and the existence of the coil 20, which is the dominant impedance of the tuning circuit in the UHF band. There will be no.

When receiving VHF high band and low band,
The UHF band signal is short-circuited by the diode 55, and the conditions necessary for matching are set to the optimum state independently by selecting the ratio of inductance of the coils 44 and 47, 44 and 45, and 46 and 47. I can do it. Another embodiment of the invention is shown in FIG.

The feature of the embodiment shown in FIG. 6 is that inductive coupling is used to couple signals in the UHF band, and capacitive coupling is used to couple signals in the VHF band, resulting in an optimal matching state in both cases. This is what we did.

In FIG. 6, the same or equivalent parts as in FIGS. 3 and 5 are given the same numbers.

In the figure, 57 is a coil for coupling UHF band signals, 58 is a tuning coil corresponding to the two coils in FIGS. VHF band signal coupling capacitor,
60 is a bypass capacitor, 61 is a switch diode, 62 is a bias resistor, 63 is a UHF band high frequency signal input terminal, 64 is a UHF band high frequency signal input terminal, 65 is a choke coil, 66 is a UHF and VHF band conversion This is a voltage application terminal.

Next, the operation will be explained.

During UHF band reception, a positive voltage is applied to terminals 16 and 66 to make diodes 19 and 61 conductive.

As a result, the terminal 64 is grounded at high frequencies via the capacitor 60, and the VHF band signal is short-circuited.

The UHF band signal supplied from the terminal 63 is inductively coupled from the coil 57 to the coil 58 and applied to the two-point tuning circuit. Therefore, this coil 57,5
By arbitrarily selecting the degree of yielding coupling M of 8, matching with the load can be maintained in an optimal state. Next, VHF/
- When receiving an i-band, the positive voltage at the terminal 16 remains as it is, and the voltage at the terminal 66 is switched to a negative voltage. This results in V
The HF band signal is coupled from the terminal 64 to the two-point tuning circuit via the capacitor 59, and is tuned to the VHF high band by the coils 58, 21, the capacitor 24, and the varactor diode 18. At this time, the influence of the UHF band from the terminal 63 hardly becomes a problem because the coil 58 hardly contributes to the operation of the tuned circuit in the VHF band.
Therefore, the matching in the VHF band can be independently selected by the capacitance of the capacitor 59, etc., regardless of the matching in the UHF band. And ~ when receiving VHF low band,
The diode 19 is cut off by setting the voltage at the terminal 16 to a negative voltage, the short circuit of the coil 22 is released, and the resonance point of the two-point tuned circuit is moved to the VHF low band. In any case, in order to achieve tuning, it is sufficient to apply a tuning voltage to the terminal 15 and change the capacitance of the varactor diode I8, as in the example already described.

FIG. 7 shows yet another embodiment of the present invention, which is characterized by using the inductance coupling in the embodiment shown in FIG. 5 for coupling VHF band signals, and using the inductance coupling shown in FIG. The inductive coupling shown in the embodiment is used, and the switch diode for signal shorting is omitted by taking advantage of the fact that these coupling methods have little influence on other couplings.

In this Figure 7, the configuration of each part is a combination of the embodiments in Figures 5 and 6, and the same or equivalent parts are given the same numbers, so a detailed explanation will be given. Omitted.

The same applies to the operation; in the UHF band, the coil 58 is dominant in the tuning operation, so the UHF band signal from the terminal 63 is added to the tuning circuit by inductive coupling from the coil 57, and the VHF band signal source is the coil. 44 and 47 or coils 44, 45 and coil 46
, 47, the impedance is converted to a high impedance and does not affect the load exhibiting a relatively low impedance.

In the VHF band, coil 44 is used for tuning operation.
and 45, or the inductance of coils 44 to 47 is dominant, and coil 58 hardly contributes to it, so the inductive coupling with coil 57 is VH
There is almost no problem with F-band signals, and UHF
The impedance of the band's signal source has little effect on matching.

Matching in the VHF band can be arbitrarily and independently maintained at an optimal condition by combining the coils 44 to 47.

Therefore, sufficient characteristics can be obtained without using switches corresponding to the switch diodes 55, 61 in the embodiment of FIG. 5 or 6. Of course,
Depending on the purpose of use, the switch diodes 55, 61 may be omitted in the embodiments shown in FIGS. 5 and 6, or they may be added to the embodiment shown in FIG. 7 for better effects. Also considered is the UHF band and VHF band.
Switch diodes may be provided on both sides of the band, with the other grounded during operation of one to minimize mutual interference.

In the above embodiment, the two tuning frequencies of the two-point tuning circuit are assigned to the VHF high band and the UHF band, respectively. It is obvious that this is a good thing; in this case, the constants of the coils 20, 21, 22, capacitor 24, etc. should be adjusted so that the tuning frequency falls within the VHF low band and UHF band when a negative voltage is applied to the switching voltage application terminal 16. It will not be necessary for those skilled in the art to explain that it is only necessary to select the desired value.

Further, the high frequency amplification element is not limited to the FET17, and the V
It is also unnecessary to explain that any amplification element that exhibits good amplification characteristics in the frequency range from the HF low band to the UHF band can be used.

As explained above, according to the present invention, it is possible to obtain an all-channel input tuning circuit that can obtain sufficiently satisfactory matching from the VHF low band to the UHF band, and can also provide a sufficiently wide frequency change range. A tuner can be obtained in which elements and the like are shared by each of the VHF and UHF bands, and inputs can be separated for VHF and UHF to reduce mutual interference, and optimal reception conditions can be achieved in each band.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram showing an example of a two-point tuning circuit that is the basis of the present invention, Figure 2 is a characteristic diagram of a two-point tuning circuit, and Figure 3 is an example of an input tuning circuit using a two-point tuning circuit. FIG. 4 is an equivalent circuit diagram for explaining its operation, and FIGS. 5, 6, and 7 are wiring diagrams of input tuning circuits showing different embodiments of the present invention. 3...First capacitor, 4...Second capacitor, 5
...First coil, 6...Second coil, 7...
・Two-point tuning circuit, 12... Input terminal, 13...
...Output terminal, 15... Tuning voltage application terminal, 16... Band switching voltage application terminal, 18...
Varactor diode for tuning, 19, 42, 43...Switch diode for band switching, 20~22,44~
47, 58... Tuning coil, 24...
... Tuning capacitor, 53, 63... UHF band signal input terminal, 54, 64... VHF band signal input terminal. Spear! Figure 2 #-・Ma B [j1,-L Kuroo Ota Kuruga, 6 Figure O 7 Ward)

Claims (1)

[Claims] 1. A first capacitive element is connected in parallel with the series circuit of the first and second inductance elements, a second capacitive element is connected in parallel with the second inductance element, and at the same time A resonant circuit configured to resonate at two different frequencies is provided, and by changing the capacitance of the second capacitive element,
An input tuning circuit capable of receiving signals in more than one frequency band has an input terminal into which a UHF band signal is input, and the UHF band signal input to this input terminal is transmitted to the first resonant circuit. UHF signal input means for inputting a UHF signal to a connection point between the capacitive element and the first inductance element through capacitive coupling;
VHF signal input means for dividing the second inductance element and inputting a VHF band signal from the dividing point;
An input tuning circuit comprising means for outputting both F and VHF band signals from a connection point between the first inductance element and the first capacitance element by capacitive coupling. 2. The input tuning circuit according to claim 1, wherein the UHF signal input means includes a switch diode that selectively grounds an input terminal into which a UHF band signal is input at high frequency. . 3. A first capacitive element is connected in parallel with the series circuit of the first and second inductance elements, and a second capacitive element is connected in parallel with the second inductance element, and two different frequencies are simultaneously transmitted. A resonant circuit configured to resonate is provided, and by changing the capacitance of the second capacitive element,
In an input tuning circuit capable of receiving signals in more than one frequency band, the UHF band signal is inputted by inductively coupling it to the first inductance element of the resonant circuit.
It has an HF signal input means and an input terminal into which a VHF band signal is input, and the VHF band signal input to the input terminal is connected to a capacitor at a connection point between the first inductance element and the first capacitance element. It is characterized by having a VHF signal input means for inputting by coupling, and a means for outputting both UHF and VHF band signals from a connection point of the first inductance element and the first capacitance element by capacitive coupling. input tuning circuit. 4. The input tuning circuit according to claim 3, wherein the VHF signal input means includes a switch diode that selectively grounds an input terminal to which a VHF band signal is inputted at a high frequency. 5 A first capacitive element is connected in parallel with the series circuit of the first and second inductance elements, and a second capacitive element is connected in parallel with the second inductance element, thereby simultaneously transmitting two different frequencies. A resonant circuit configured to resonate is provided, and by changing the capacitance of the second capacitive element,
In an input tuning circuit capable of receiving signals in more than one frequency band, the UHF band signal is inputted by inductively coupling it to the first inductance element of the resonant circuit.
HF signal input means, and a VHF device that divides the second inductance element and inputs a VHF band signal from the dividing point.
An input tuning circuit comprising: signal input means; and means for outputting both UHF and VHF band signals from a connection point between the first inductance element and the first capacitance element by capacitive coupling.