JPS6230337Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a tuning device for a television receiver. The present invention is an electronic tuning television receiver that has a preset variable resistor that sets a selected channel by varying the voltage applied to a variable capacitance diode and another finely tuned variable resistor. By connecting a tuning variable resistor, even in low frequency channels,
Even in high channels, the variable range of the fine tuning frequency is made to be approximately the same. Televisions, radio receivers, and the like use electronic tuners that tune channels by adjusting the voltage applied to a variable capacitance diode to change the capacitance value to select the channel of incoming radio waves. A variable resistor is used to preset the voltage applied to the variable capacitance diode to select a channel in these electronic tuners. Conventionally, presets for this type of channel selection include, as shown in FIG. As the tuning voltage V, a voltage divided and varied by a preset variable resistor 5 connected to a power source 4 is supplied to a tuning voltage input terminal 6 of the electronic tuner 3.
This voltage is connected to the preset variable resistor 5 and the input terminal 6.
to select frequencies over a wide range of the receiver frequency band. On the other hand, a fine tuning variable resistor 8 is further connected to the power supply 4 in parallel with the preset variable resistor 5, and the voltage of the movable piece of this fine tuning variable resistor 8 is supplied to the tuning voltage input terminal 6 via a high resistance 9. be done. This fine tuning variable resistor 8 allows finer frequency selection near the selected frequency band. However, this is because the preset variable resistor 5 cannot be changed in the tuning voltage curve of an electronic tuner, where the horizontal axis shows the frequency (MHz) and the channel, and the vertical axis shows the tuning voltage V (volts), as shown in Figure 2. For example, the tuning voltage V is selected to have a voltage value at the X position or a voltage value at the Y position, and the fine tuning variable resistor 8 adjusts the respective variable differences x ₁ to x ₂ in X or Y. , or y ₁ ~
It will show the voltage difference of y ₂ . In addition, the tuning voltage curve shown in Figure 2 is the L of 9 channels ranging from A to I in the MID band, 7 channels ranging from 7 to 13 in the VH band, and 14 channels ranging from J to V in the SUPER band. Although it is almost a straight line up to the L channel, the tuning voltage increases rapidly beyond the L channel. Therefore, in the conventional method as shown in FIG. 1, the fine tuning variable resistor 8 is used to make the voltage of the power supply 4 variable, so that the voltage deviations x ₁ to x ₂ and y ₁ to y ₂
are almost equal. For voltage deviations from x ₁ to _{x 2} , the straight line part of the tuning voltage curve will change, so in the example in Figure 2, from channel 11 to channel 3 of J channel.
It is possible to give a tuning change comparable to that of a channel. However, for the voltage deviation between y ₁ and _{y 2} , the non-linear part of the curve will change, so V in Figure 2
Tuning changes can only occur near the channel. Therefore, the conventional circuit has the drawback that the range of fine tuning varies depending on the channel. The present invention relates to a tuning device for a television receiver in which a fine tuning variable resistor is connected to one movable side of a preset variable resistor to overcome the drawbacks of the prior art. As shown in FIG. 3, the present invention connects a fine tuning variable resistor 8 to a movable piece 10 of a preset variable resistor 5 connected to a power source 4, and tunes the electronic tuner 3 through the movable piece through a high resistance 9. Connect to voltage input terminal. In the case of this circuit, as shown in the example in Figure 2,
When presetting a low frequency range by applying a low voltage at the position of the conventional tuning voltage
The voltage at 0 will be varied. For example, if the voltage of tuning voltage
Fine tuning is performed for presets in the high frequency range. For example, if the tuning voltage Y is
When set to 20V, the fine tuning voltage width changes over a wide range of 0 to 20V. Since a low resistance 7 and a high resistance 9 are respectively inserted between the tuning voltage input terminal 6 of the electronic tuner 3, the width of the voltage change is x at low tuning voltage, as shown in FIG. The voltage change width in the range of ₃ to _x4 can be made narrower than before, and at high tuning voltages, the voltage change width can be made almost unchanged in the range of _y3 to _y4 . . In other words, in the channel-tuning voltage curve in Figure 2, the range of change in x ₃ to _{x 4} at low voltages only changes the frequency or a narrow frequency range near channel 13 in the channel, and conversely, the range of change in x 3 to x 4 at low voltages only changes the narrow frequency range near channel ₁₃ ;
Since the range of variation of ~y ₄ is wide, it results in varying the high frequencies of the non-linear part of the characteristic curve or a narrow frequency range near the V channel of the channel. Furthermore, the other embodiment shown in FIG. 4 has a loop shape including grounding on the circuit or wiring between the preset variable resistor 5 and the fine tuning variable resistor 8 in FIG. This prevents mutual interference due to current flow. In the figure,
A transistor buffer is provided in which the base of a buffer transistor 11 is connected to the movable piece 10 of the preset variable resistor 5, the fine tuning variable resistor 8 is connected to the emitter, and the collector is connected to the power source 4. If the transistor 11 is kept active, only a small amount of the base current of the transistor 11 flows from the preset variable resistor 10, so that no mutual interference occurs between the preset variable resistor 5 and the fine tuning variable resistor 8. Also, only a slight voltage difference between the base and emitter of transistor 11 is lower than the voltage at movable piece 10. Table 1 shows experimental examples of frequency variable ranges in arbitrary channels with respect to changes in the fine tuning variable resistor for the conventional circuit shown in FIG. 1 and the circuit shown in FIG. 3 of the present invention described above.

[Table] As is clear from this table, in the conventional circuit shown in Fig. 1, the frequency variable width is small in channels with high frequencies, but in Fig. 3 according to the present invention, the frequency is almost variable regardless of the channel. It can be seen that the range is constant. As described above, the present invention eliminates the difficulty of making fine adjustments to the preset tuning depending on the channel, without making any major changes to the component parts, and makes it possible to adjust the preset tuning uniformly for each channel. It is possible to make fine adjustments to almost the same frequency deviation, making preset operations easy.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a tuning device for a conventional electronically tuned television receiver, Fig. 2 is a curve diagram showing the relationship between television frequency or channel and tuning voltage, and Fig. 3 is a circuit diagram showing a tuning device of a conventional electronically tuned television receiver. Circuit Diagram of Embodiment FIG. 4 is a circuit diagram of another embodiment of the tuning device of the present invention. Note that the symbols shown in the drawings indicate the following. 1... Television frequency signal input, 2... Intermediate frequency signal output, 3... Electronic tuner, 4...
Power supply, 5... Preset variable resistor, 6... Tuning voltage input terminal, 7, 9... Resistor, 8... Fine tuning variable resistor, 10... Movable piece.

Claims (1)

[Claims for Utility Model Registration] (1) An electronically tuned television in which each movable piece of a finely tuned variable resistor connected in parallel with a preset variable resistor for tuning a reception channel is connected to a tuning voltage input terminal of an electronic tuner. In the receiver, both ends of the fine tuning variable resistor are connected between the movable piece of the preset variable resistor and ground, and the movable pieces of both of the variable resistors are connected to a tuning input terminal of an electronic tuner. Tuning device for television receivers. (2) a transistor buffer circuit in which a transistor whose base is connected to the movable piece of the variable resistor and a fine tuning variable resistor are connected in series in parallel to the preset variable resistor; A tuning device for a television receiver according to claim 1, wherein each movable piece of the receiver is connected to a tuning voltage input terminal of an electronic tuner.