JPS6237846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tuning device for a television receiver using an electronic tuner, which changes the power supply voltage for tuning in response to band switching between VHF and UHF, and widens the variable range of the tuning voltage. As if switching,
The purpose is to prevent public radio waves adjacent to television signals from being received.

For example, due to national circumstances or other reasons, there are markets that require that public radio waves adjacent to television waves cannot be received, and it is technically difficult to satisfy this requirement by improving the tuners themselves, and the number of varieties of tuners is increasing. The problem is that standardization is not possible.

The present invention attempts to satisfy this requirement without improving the tuner itself.

One embodiment will be described below with reference to the accompanying drawings. In FIGS. 1 and 2, 1 is a power supply terminal to which a DC power supply voltage of 110V is applied; 2 and 3 are resistors and Zener diodes connected to this power supply terminal 1 to supply a stabilized voltage of 30V; 4, 5
A resistor and a diode are used to equalize the current when a switching transistor 6 is turned on and the current when a switching transistor 7 is turned on, which will be described later.A band identification signal appears on the cathode side of the diode 5. 8, 9, 10, 11 are
A VHF and UHF band switching switch, each with a VHF terminal and a UHF terminal as fixed terminals.
The VHF terminal is left open, and the UHF terminals are commonly connected to the cathode of the diode 5. Each movable terminal of the band changeover switches 8 to 11 is connected to a backflow prevention diode 1.
2, 13, 14, 15, the channel selection switch 1
6 and the connection point of the tuning variable resistors 17, 18, 19, and 20.

Diodes 21, 22, 23, and 24 are connected to the movable terminals of the tuning variable resistors 17, 18, 19, and 20, respectively, and serve to prevent backflow and to compensate for the temperature of a transistor 25, which will be described later. This transistor 25 functions for impedance conversion, and has its emitter connected to a tuning voltage output terminal 26.

The switching transistors 6 and 7 each have their collectors connected to a 30V voltage terminal, and their emitters connected to the terminals of the tuning variable resistors 17, 18, 19, and 20 that are not connected to the tuning switch 16. ing. The switching transistor 6
A diode 27 for reverse protection of the transistor 6 and bias resistors 28 and 29 are connected to the base of the transistor 6, and a connection point between the diode 27 and bias resistors 28 and 29 is connected to a band switching circuit via a resistor 30. Connected to the UHF terminals of switches 8 to 11. On the other hand, switching transistor 7
A bias resistor 31 is connected between the base and collector, a reverse protection diode 32 is connected between the base and emitter, and the base is further connected to a variable resistor 34 via a temperature compensation diode 33. .

35 is a switching transistor for supplying power supply voltage to a VHF tuner (not shown);
The output terminal 36 is connected to the emitter, and the base is connected to the 30V voltage terminal via a diode 37 and a resistor to completely cut off the transistor 35, and the switching diode 3
8 to the band identification signal line.

Further, 39 is a switching transistor for supplying power supply voltage to a UHF tuner (not shown), whose collector is connected to an output terminal 40, and whose base is connected to the band identification signal line via a switching diode 41. are doing.

42 is a terminal to which a 15V DC voltage is applied.

In the above configuration, the band changeover switch 8
~11 are in the state shown in the figure, and the channel selection switch 1 is
6, the first terminal is selected (for example, the first channel). At this time, the band selection switch 8 is connected to the vacant VHF terminal, and the band identification signal line is disconnected from the ground, so the transistor 6 is turned on.
A voltage of 30V appears on the band identification signal line. This voltage is applied to the tuning variable resistor 17,
The voltage set by this variable resistor 17 passes through a diode 21, is impedance-converted by a transistor 25, is outputted to an output terminal 26 as a tuning voltage Vt, and is applied to an electronic tuner (not shown).

On the other hand, at this time, the switching diode 38 becomes conductive, the transistor 35 turns on, the power supply voltage is supplied from the output terminal 36 to the VHF tuner, and the first channel is selected. Note that at this time, the diode 41 is non-conductive and the transistor 39 is in a cut-off state.

Next, when the tuning switch 16 is switched to the second terminal, since the band selection switch 9 is connected to the UHF terminal, the band identification signal line becomes low level (forward voltage of the diode 13 is about 0.6V). As a result, transistor 6 is cut off and transistor 7 is turned on.

Therefore, the emitter of the transistor 7 is adjusted by the variable resistor 34 (between 30V and 0V).
A voltage approximately equal to the voltage appears and is applied to the tuning variable resistor 18. The equivalent circuit at this time is shown in FIG.

On the other hand, at this time, in the switching circuit, the transistor 35 is cut off, the transistor 39 is turned on, and the power supply voltage is supplied from the output terminal 40 to the UHF tuner. Incidentally, FIG. 3A shows an equivalent circuit when the first terminal is selected by the channel selection switch 16.

Next, when the channel selection switch 16 is switched to the third terminal, a voltage approximately equal to the voltage adjusted by the variable resistor 34 is applied to the variable resistor 19, as in the case described above.

As described above, according to the above configuration, when receiving UHF broadcasting, it is possible to adjust the upper limit of the tuning variable range with high accuracy, and reception of unnecessary radio waves can be reliably prevented. Although the above embodiment describes the case where the tuning switch 16 is switched in four stages, the present invention is not limited to this, and in this embodiment, the upper limit of the voltage applied to the tuning variable resistor in the UHF band is suppressed. However, this point is not limited to this either.

As explained above, according to the present invention, it is possible to adjust the upper limit of the tuning variable range with high precision, and it is also possible to set the tuning voltage variable range for each band. Any reception band can be selected, and it can be easily adapted to the national conditions of special broadcast bands. Furthermore, since a dedicated special tuner is not required, there is an advantage that the total cost is reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a tuning device according to an embodiment of the present invention, Fig. 2 is a circuit diagram of the main part of the same device, and Fig. 3 A and B are equivalent circuit diagrams for explaining the functions of the same device. be. 6, 7...transistor, 8, 9, 10, 11
...Band changeover switch, 12, 13, 14, 1
5... Diode for backflow prevention, 16... Tuning switch, 17, 18, 19, 20... Tuning variable resistor, 25... Impedance conversion transistor, 26... Tuning voltage output terminal, 34... Variable Resistor.

Claims (1)

[Claims] 1. A first switching circuit that conducts when the band switching identification signal voltage generated by band switching is a high level value close to a reference voltage, and a first switching circuit that conducts when the band switching identification signal voltage is a low level value close to OV. 2 switching circuits are connected in parallel, a band switching reference voltage point and a tuning voltage adjustment circuit are connected through this parallel circuit, and the band switching identification signal voltage makes the first and second switching circuits conductive. What is claimed is: 1. A tuning device that controls cut-off and is configured such that the variable range of the tuning voltage is arbitrarily set within the range of the reference voltage by the switching circuit.