JPS6027452B2 - Double tuned circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a double-tuned circuit suitable for the construction of a tube for a television receiver.

With the increase in the number of television broadcast channels, television receivers must also be able to receive UHF bands in addition to the conventional VHF band, and their tuners are also configured to support both VHF and UHF. Something has become necessary.

However, providing independent tuners for each of the VHF and UHF bands poses problems in terms of cost and space, so some or all of the tuner functions are shared between the VHF and UHF bands. The so-called all-channel tuner is known. FIG. 1 shows an example of a tuning circuit used in such an all-channel tuner.

This circuit is a so-called electronic tuning circuit that uses a variable capacitance diode as a tuning element. 1 is a coupling capacitor to form the tuning circuit, 2 is a tuning variable capacitance diode, and 3, 4, and 5 are inductance elements. , 6 and 7 are switching diodes, 8 and 9 are capacitors for cutting DC components, 10, 11 and 12 are bias resistors for blocking high frequencies, 13 is a terminal for applying a tuning voltage, 14, 15 is a terminal for applying voltage for the switch.

Next, the operation will be explained.

First, by applying a negative voltage to terminals 14 and 15, the diode 6
, 7 are cut off, the tuned circuit consists of inductance elements 3, 4, and 5, capacitor 1, and variable capacitance diode 2, and the inductance of the tuned circuit is the sum of inductance elements 3, 4, and 5. This value and the capacitance of capacitor 1 and diode 2 determine the resonance frequency.

Next, a positive voltage is applied to the terminal 14, and the terminal 15 remains at a negative voltage.

As a result, the diode 6 becomes conductive, the diode 7 remains cut off, and the inductance element 5 is short-circuited by the diode 6 at high frequency, leaving only the inductance elements 3 and 4 forming the tuned circuit. High resonant frequency.

Finally, a positive voltage is applied to terminal 15. At this time, either positive or negative voltage may be applied to the terminal 14. As a result, the diode 7 becomes conductive, so that the inductance elements 4 and 5 are short-circuited at high frequency, and the inductance of the tuned circuit becomes the value of only the inductance element 3, resulting in an even higher resonant frequency.

Therefore, by setting the inductance values of inductance elements 3, 4, and 5 to appropriate values and switching the voltages applied to terminals 14 and 15, inductance element 3 can be used for UHF band, and inductance elements 3 and 4 can be used for VHF band. band /・i band, and further inductance elements 3, 4, 5
This allows tuning to all of the low band of the VHF band.

It goes without saying that the capacitance of the variable capacitance diode 2 can be changed by applying a predetermined positive voltage to the tuning terminal 13.

In this way, a tuned circuit can be obtained that can be used in an all-channel tuner.

However, in the tuned circuit shown in Fig. 1, when switching to the high band of the VHF band and the UHF band, the inductance due to the lead wires of the switching diodes 6 and 7 will be added to the tuned circuit. It will be included. Further, the inductance due to this IJ-wire portion includes a high frequency resistance, and furthermore, there is a drawback that the Q value of the tuning circuit is lowered due to the on-resistance of the switching diode. In particular, in the UHF band, the inductance of the tuned circuit is as small as 1 mH, so the inductance due to the switching diode 7's glue line reaches 5 to 6 mH. Therefore, the Q value of the tuning circuit including the loss due to the on-resistance of the fitting diode is further reduced.

Therefore, when the tuning circuit is a double tuning circuit, the loss increases further, and it is extremely difficult to use both UHF and VHF as a tuner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a double-tuned circuit that eliminates the drawbacks of the prior art described above and can constitute an all-band tuner with low loss.

To achieve this objective, the present invention provides a UHF
It is characterized by the use of a two-point tuning circuit that has tuning points for both the VHF band and the VHF band at the same time. First, FIG. 2 shows a two-point tuning circuit used in the double tuning circuit of the present invention,
Its operation will be explained using the characteristic curve shown in FIG.

This figure shows how the IJ actance between terminals 20 and 21 changes depending on the frequency in a circuit in which a parallel resonant circuit is formed by a capacitor 16 and coils 17 and 18, and a variable capacitance element 19 is connected in parallel with the coil 18. and the third
As shown in the figure, the reactance x becomes almost infinite at two points where the frequencies are fL and fH, and the
It can be configured to have a tuning point at a point.

The resonant frequency fL and f day are the same as those of the variable capacitance element 1.
9 can be changed at the same time.

Moreover, the resonance frequencies fL and fH are the same as those of the coils 17 and 18.
By selecting appropriate values for the inductance and the capacitance of the capacitor 16, it is possible to set one frequency fL to be within the VHF band and the other frequency fH to be within the UHF band. For example, a capacitor
The capacitance of coil 17 is 5.2 F, and the inductance of coil 17 is 34. On the same day, the inductance of the coil 18 was set to 48. The day before, the capacitance of the variable capacitance element 19 was set to 2. When it is tsubo F, fL=22 sacroelbow z, fH=770MHz,
This corresponds to the highest reception frequency (TV channel in Japan) in the VHF band and the UHF band, respectively, and the capacitance of the variable capacitance element 19 is set to 11. If it is tsubo F, then fL=17
The skin level z, fH=47 blood level z, which corresponds to the lowest receiving frequency in each band.

Therefore, the circuit shown in FIG. 2 provides a two-point tuning circuit that can simultaneously tune to the high bands of the UHF and VHF bands without switching. Note that in the above example, the range of change in the capacitance of the variable capacitance element 19 is 2.
11 from Tsubo F. Although it is marked F, this can be easily obtained with a normal variable capacitance diode, and there is no problem in using it as a so-called electronic tuning circuit.

FIG. 4 shows a double tuning circuit using a two-point tuning circuit, where 23 and 32 are coupling capacitors, 24 and 31 are resonance capacitors, 25 and 29 are tuning coils that become the first inductance element, 26 and 30 are tuning coils which are second inductance elements, 27 and 28 are tuning variable capacitance diodes, 33 and 34 are bypass capacitors, 35,
36 is a high frequency blocking resistor. Further, 22 and 28 are input and output terminals, and 37 is a tuning voltage application terminal. The part surrounded by a dotted line indicated by 39 indicates one two-point tuning circuit constituting the double tuning circuit, and this part is equivalent to the circuit shown in FIG. 2.

These coils 25, 29 and 26, 30 are inductively coupled as shown by arrows M, and constitute a double-tuned circuit as a whole. Next, the operation of this circuit will be explained. As already explained in connection with the circuit shown in FIG. 2, each two-point tuning circuit constituting the double tuning circuit has tuning points at both the high band frequencies of the UHF band and the VHF band at the same time.

Therefore, now the capacitance of capacitors 23 and 32 is set to 1.5p.
F, capacitors 24 and 31 are 3. Tsubo F, tuning coil 25
, 29 inductance of approximately 34NH, tuning coil 26
, 30 is set to approximately 5mH, and the input terminal 2
When the transmission characteristics between the output terminal 2 and the output terminal 38 are determined using a 500 impedance measuring device, the characteristics shown in the characteristic curve of FIG. 5 can be obtained.

That is, by setting the positive voltage applied to the terminal 37 to an appropriate value, the capacitance of the variable capacitance diodes 27 and 28 is set to 11. When it is set to tsubo F, the characteristics will be as shown by the dotted line,
The capacitance of variable capacitance diodes 27 and 28 is set to 2. When the area is set to F, the characteristics shown by the solid line are obtained.

Now, returning to the two-point tuning circuit in FIG. 2, the inductance of the coil 17 is L, the coil 18 is -, the capacitance of the capacitor 16 is C, and the capacitance of the variable capacitance element 19 is C.
2, C. , L, is naturally V
Since the frequency is selected to be higher in the HF band, the reactance of the part consisting of C, , and L is VH
In the F band, it is capacitive.

Therefore, the resonant frequency in the VHF band is the equivalent capacitance of the capacitive reactance consisting of C, , L and the variable capacitance element 1.
9, and the inductance L2 of the coil 18.
It is determined by On the other hand, in the UHF band, L
Since the resonance frequency of and C2 is selected to be lower than the UHF band, its reactance is also capacitive (
), and in the UHF band, this capacitive reactance, the capacitance C of the capacitor 16, and the coil 1
It is determined by the inductance L of 7. That is,
In this two-point tuned circuit, the coil 18 is primarily responsible for the tuning action at the lower resonant frequency, and the coil 17 is primarily responsible for the tuning action at the higher resonant frequency.

Therefore, returning to FIG. 4 again, the coupling of each tuned circuit as determined by the nature of the double tuned circuit is the coil 25, 2, respectively.
This is done with the connection M between 9 and 26, 30.

However, as mentioned above, in the VHF band, the coils 26 and 30
Also, since the tuning action is performed by coils 25 and 29 in the UHF band, coil 2 is used for operation in the VHF band.
The coupling M between coils 26 and 30 has little effect, and the coupling M between coils 26 and 30 has little effect on operation in the UHF band.

Therefore, the coupling characteristics as a double-tuned circuit in the VHF band and the coupling characteristics as a double-tuned circuit in the UHF band can be separately adjusted and arbitrarily determined.

In addition, since there is no need to use a switch for operation in the UHF band and VHF band, there is no risk of the Q of the tuning circuit decreasing, and as is clear from Figure 5, the loss in the UHF band is
It is approximately 4 dB, and when used alone in a ^/4 type resonant circuit (
Characteristics comparable to those of the UHF band double-tuned circuit (without switching in the VHF band) having a loss of about 4 to 61 were obtained.

Therefore, by using this double tuning circuit, it is possible to construct an all-channel tuner with excellent characteristics that allows the high frequency stage and the frequency conversion stage to be shared without switching. FIG. 6 shows an embodiment in which the double tuning circuit of the present invention is applied to an all-channel electronic tuner.

In this figure, 40 is an antenna input terminal, 41 is an input tuning circuit, 42 is a high frequency amplification section, 43 is a double tuning circuit, 4
4 is a frequency conversion section, 45 is a VHF oscillation circuit, and 46 is a UH
F oscillation circuit, 47 is an intermediate frequency output terminal.

The double-tuned circuit 43 in this embodiment is different from the circuit shown in FIG. 4 in that a cutout circuit for the low band of the VHF band is provided, and other aspects are the same as in the case shown in FIG.

That is, the parts from 23 to 32 are the same as in FIG. 4, including DC blocking capacitors 71 and 72, tuning coils 73 and 80 which are the third inductance elements, high frequency blocking resistors 74 and 75, and switching diode 78. , 79 are inductive coupling coil 82 and bypass capacitors 81 and 83.
, and that a high frequency blocking resistor 84 is provided.

Note that 58 is a field effect transistor (F) for high frequency amplification.
ET), 60 is a choke coil, 90 is a field effect transistor (FET) for frequency conversion, 91 is an intermediate frequency transformer, 10 river AGC signal terminal 101 is a terminal for applying tuning voltage, 102 is a terminal for applying tuning voltage A switching voltage terminal 103 is a power supply terminal for switching between a low band and a high band.

Next, the operation will be explained.

First, when receiving the UHF band, a positive voltage is applied to the switching terminal 102, and the switching terminals 78 and 79
is in a conductive state and the coils 26 and 30 and the coils 73 and 8
The connection point of 0 is grounded at high frequency via capacitors 71 and 72.

At the same time, only the UHF oscillation circuit 46 is activated. Therefore, the UHF band signal from the antenna input terminal 40 passes through the input tuning circuit 41 to the first gate G of the FET 58.
is added to and amplified, coupled to the double tuning circuit 43 by the coupling capacitor 23, selectively tuned and transmitted via the coupling M between the tuning coils 25 and 29 as explained in the embodiment of FIG. F for frequency conversion from capacitor 32
A kamasha will be provided at the first gate G of ET90.

At the same time, the local oscillator signal from the UHF oscillation circuit 46 is also transmitted to the FET90.
Since the frequency-converted intermediate frequency signal passes through the intermediate frequency transformer 91 and appears at the output terminal 47, signal reception in the UHF band is performed. At this time, selective tuning of the channels is performed by changing the equivalent capacitance of the variable capacitance diodes 27 and 28 by the tuning voltage applied to the terminal 101, as explained in the case of FIG.

Incidentally, a signal in the VHF band/-band is also transmitted to the FET 90 via the coupling M between the coils 26 and 301 of the double-tuned circuit 43.
is applied to the first gate G of the VHF oscillation circuit 45.
is not operating, there is no possibility that the receiving operation will be performed.

Next, when receiving the VHF band, the terminal 102
The point of applying a positive voltage to the diodes 78 and 79 to short-circuit the coils 73, 80, and 82 is similar to the above-mentioned U.
Same as when receiving HF band, but this time UHF oscillation circuit 4
6 is stopped, and only the VHF oscillation circuit 45 is left operating.

As a result, the UHF band and VH selected by the double tuning circuit 43
Of the F-band high band signals, only the latter signal is converted into an intermediate frequency signal by the frequency converter 49 and sent to the output terminal 47.
VHF band/... band signals are received. When receiving low band VHF band, terminal 10
2, diodes 78 and 79 are cut off, and only VHF oscillation circuit 45 is operated.

As a result, the tuned coils constituting the double-tuned circuit 43 are coils 25, 26, and 73, and coils 29, 30, and 8, respectively.
By selecting the inductances of the coils 73 and 80 to appropriate values, the capacitances of the capacitors 24 and 31 and the variable capacitance diodes 27 and 28 can be reduced.
The resonant frequency formed by the series inductance of the coils 25, 26, 73 and the coils 29, 30, 80 can be made to fall within the VHF low band, and the double tuning circuit 4
3, only the VHF low band signal is selected. At this time, channel tuning is performed by applying a tuning voltage to the terminal 101 in the UHF band, VHF band/.
This is similar to the case of the index band. Since the UHF oscillation circuit 46 is not operating and only the VHF oscillation circuit 45 is operating, only the VHF low band signal among the signals appearing at the antenna input terminal 40 is obtained as an intermediate frequency signal at the output terminal 47. It will be done.

At this time, the VHF band low band in the double tuning circuit 43. The coupling of the code signals is performed by using the coupling coil 82 as a mutual inductance between the tuning coils 73 and 80 in the VHF low band, and the inductance of this coil 82 can be independently set to an arbitrary value. .

Although the output equivalent (signal source) resistance of the high-frequency amplification FET 58 and the input equivalent (load) resistance of the frequency conversion FET 90 connected to the tuning circuit constituting the double-tuned circuit of this embodiment are different between the VHF band and the UHF band, As mentioned above regarding the basic double-tuned circuit of the present invention shown in FIG. As shown in Figure 2, it is possible to avoid the double bee characteristic, which increases the attenuation at the tuning point, the weak coupling, and narrows the signal passing band width, which increases loss.
It is especially useful as a tuning circuit without the need for a band switching mechanism.
It is possible to obtain an all-channel tuner double-tuned circuit with low loss, including the use of a two-point tuned circuit with low loss in the HF band. Furthermore, since the resistors 74 and 75 are connected in parallel with the coils 73 and 801 through the bypass capacitor 81, it is also possible to damp the tuned circuit by selecting appropriate values for these resistors 74 and 75.

Furthermore, in this embodiment, switching between high band and low band in the VHF band is performed using a switching diode 78,
79, it can be used for all channels, and there is no need for any emergency mechanism between the high frequency amplification section 42 and the frequency conversion section 44, and the connection is simply made via the coupling capacitors 23 and 32. All you have to do is connect it,
These parts 42 and 44 can be easily shared by all bands, and the configuration can be simplified.

As explained above, according to the present invention, it is possible to obtain a double-tuned circuit that has extremely low loss in the UHF band and can perform tuning without switching between the UHF band and the VHF band. It is possible to easily obtain an all-channel tuner that does not have any switching means between the frequency conversion section and the frequency conversion section.

As a result, it is no longer necessary to use different tuners for the UHF band and VHF band as in the past, making it possible to achieve a reduction in size and weight and to obtain a high-performance, low-cost television receiver.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing an example of a conventional tuning circuit used in an all-channel tuner, Fig. 2 is a wiring diagram of a two-point tuning circuit that is the basis of the present invention, and Fig. 3 is a characteristic curve diagram thereof.
Figure 4 is a wiring diagram of a double-tuned circuit using a two-point tuned circuit.
FIG. 5 is a characteristic curve diagram thereof, and FIG. 6 is a wiring diagram showing an embodiment in which the double tuning circuit of the embodiment of the present invention is applied to an all-channel electronic tuner. 25, 29... Tuning coil that is the first inductance element, 26, 30... Tuning coil that is the second inductance element, 27, 28... Variable capacitance diode , 73, 80 . . . a tuning coil serving as a third inductance element, 78, 79 .・・・・・・
・Diode for switch. Figure 2, figure 3, figure 4, figure 5, figure 6

Claims (1)

[Claims] 1. A first inductance element 25, and a second inductance element 25 connected in series to the first inductance element 25.
an inductance element 26, and a third inductance element 7 connected in series with the first inductance element 25 and the second inductance element 26 connected in series with each other.
3, a fourth inductance element 29 inductively coupled to the first inductance element 25, and a fifth inductance inductively coupled to the second inductance element 26 and connected in series to the fourth inductance element 29. Element 3
0, a sixth inductance element 80 with one terminal connected to the fifth inductance element 30 and the other terminal connected to the third inductance element 73, and the third inductance element 73 and the sixth inductance element 80. element 80
a seventh inductance element 82 connected to the connection point of the first, second, third, and seventh inductance elements 25,
The first capacitor 24 is connected in parallel with the fourth, fifth, sixth and seventh inductance elements 29, 30, 80 and 82 in terms of high frequency. a second capacitor 31, a second capacitor 31, a second capacitor 31, a second capacitor 31, a second capacitor 31
a first variable capacitance diode 27 connected in parallel with the inductance elements 26, 73, 82 at high frequency;
, a second variable capacitance diode 28 connected in parallel at high frequency to the sixth and seventh inductance elements 30, 80, 82, and connected in parallel at high frequency to the third and seventh inductance elements 73, 82. and a second switch 79 connected in parallel to the sixth and seventh inductance elements 80 and 82 in terms of high frequency.
When the second switches 78 and 79 are closed, it is tuned to the UHF band frequency and the high band frequency of the VHF band, and when the first and second switches 78 and 79 are open, it is tuned to at least the VHF band frequency. A double-tuned circuit characterized by being tuned to the low band frequency.