JPS6211075Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a tuning device using an electronic tuner.

[Conventional technology]

As shown in FIG. 1, in the conventional tuning device, when the tuning switch SW ₁ is turned on, the band switching voltage switched by the band switching switch SW ₂ is transferred from the band switching voltage generating circuit BV to the electronic tuning tuner TU.
At the same time, the tuning voltage of the tuning voltage generating circuit TV is applied to the tuning voltage input terminal BT of the electronically tuned tuner TU. The electronic tuning tuner TU will tune to the frequency of a specific channel of a specific receiving band in response to the applied band switching voltage and tuning voltage. In this case, when the band selection switch SW ₂ is switched to the a side, the electronic tuning tuner TU selects the low band, and when it is switched to the b side, the electronic tuning tuner TU selects the low band.
TU selects high band. In addition, the tuning voltage generation circuit
In the TV, the tuning voltage set by the variable resistor _R1 is applied to the tuning voltage input terminal BT via the transistor _TR1 , and the maximum value of the tuning voltage is set by the semi-fixed resistor.
It can be set to any value using R ₂ , but the lowest value is zero and cannot be set to any value. Note that D ₁ , D ₂ and D ₃ are diodes, C ₁ is a capacitor, and R ₃ and R ₄ are resistors. Further, six to eight of these channel selection devices are built into a television receiver, and by turning on the channel selection switch _SW1 , the channel corresponding to the channel selection switch _SW1 is selected.

[Problem that the invention attempts to solve]

In this tuning device, the relationship between the tuning voltage and the tuning frequency is as shown in FIG. That is, the second
In the figure, curves A and B show tuning voltage versus tuning frequency characteristics in the low band and high band, respectively, and regions E and F show the bandwidths of the low band and high band, respectively. As can be seen from this figure, the tuning frequency range of the electronically tuned tuner TU in the high band extends beyond the high band lower limit frequency. The reason for this is that the variable range of the tuning voltage applied to the tuning voltage input terminal BT of the electronically tuned tuner TU is the same for both the low band and the high band, and the lowest value of the tuning voltage when the high band is selected is approximately 0 volts. This is because the tuning frequency of the electronically tuned tuner TU when the high band is selected exceeds the lower limit frequency of the high band. In other words, if the tuning voltage is set so that the bandwidth of the low band matches the tuning frequency range of the electronically tuned tuner TU when the low band is selected, the bandwidth of the high band and the tuning frequency range of the electronically tuned tuner TU when the high band is selected are the same. This means that the tuning frequency ranges of the TUs do not necessarily match.

However, such a conventional channel selection device could not be used if the bandwidth of each receiving band and the receiving frequency range of that receiving band were limited to match.

The purpose of this invention is to provide a tuning device that can match the bandwidth of each receiving band with the tuning frequency range of an electronically tuned tuner when selecting that receiving band.

[Means for solving problems]

The tuning device of this invention includes an electronic tuning tuner that can be tuned in two reception bands, a band switching voltage generation circuit that provides a band switching voltage to the electronic tuning tuner, and a tuning voltage generation circuit that provides a tuning voltage to the electronic tuning tuner. a channel selection voltage generating circuit; a band switching switch that changes the band switching voltage generated from the band switching voltage generating circuit to switch the reception band; and a voltage adjustment circuit that adjusts the lowest value of the channel selection voltage generated from the local voltage generation circuit to a voltage at which the tuning frequency of the electronically tuned tuner matches the lower limit frequency of the one reception band.

[Effect]

According to the configuration of this invention, the voltage adjustment circuit adjusts the lowest value of the tuning voltage to the voltage at which the tuning frequency of the electronic tuning tuner matches the lower limit frequency of one of the receiving bands. The bandwidth of the receiving band can be matched with the tuning frequency range of the electronically tuned tuner when selecting the receiving band. Therefore, even if the bandwidth of each receiving band is limited to match the receiving frequency of that receiving band, it can be used without any problem.

[Example] A first example of this invention will be described based on FIG. 3. This tuning device is obtained by adding a voltage adjustment circuit _S1 to the tuning device shown in FIG. 1 to adjust the lowest value of the tuning voltage generated from the tuning voltage generating circuit TV when selecting a high band. In this voltage adjustment circuit _S1 , when the band selection switch _SW2 is switched to the b side (high band selected), the switch transistor _TR2 is turned on and the base bias current set by the variable resistor _R5 is transferred to the transistor _TR1. By adding to
The tuning voltage generation circuit TV generates a tuning voltage that is the sum of the voltage set by the variable resistor _R1 and the voltage set by the variable resistor _R5 . In this case, the semi-fixed resistance R ₂
There is no effect on the maximum value of the tuning voltage set by . In other words, the operating point of transistor TR ₁ is almost in the saturation region when the bias voltage set by variable resistor R ₁ is maximum (when variable resistor R ₁ is turned all the way down in the figure), so the base voltage is almost at the selected level. This will be the same as the local voltage, which is higher than the voltage supplied from the 12V line and set by variable resistor _R5 , so the base current will no longer be supplied from variable resistor _R5 .
It does not affect the tuning voltage either. That is, variable resistance R ₅
No matter what position is set, there is no effect on the maximum value of the tuning voltage when selecting a high band. Note that R ₆ , R ₇ , R ₈ and R ₉ are resistors, D ₄ and D ₅ are diodes, and in particular, resistor R ₉ is a variable resistor R ₁
When the midpoint terminal is set to the ground side (when the channel selection voltage is the lowest), the voltage set by variable resistor _R5 is applied to the base of transistor TR ₁ , preventing the base impedance of transistor TR ₁ from decreasing. is used for.

In this way, in the tuning device of this embodiment, the lowest value of the tuning voltage can be arbitrarily adjusted using the variable resistor _R5 in response to switching of the band selection switch _SW2 . electronic tuning tuner
The lowest tuning frequency of the TU can be matched to the lower limit frequency of the high band, that is, the bandwidth of each receiving band and the tuning frequency range of its electronically tuned tuner TU can be matched, so that the receiving frequency range It can also be used in restricted situations.

A second embodiment of this invention will be explained based on FIG. This tuning device is obtained by adding a voltage adjustment circuit _S2 to the tuning device shown in FIG. 3 for adjusting the maximum value of the tuning voltage generated from the tuning voltage generating circuit TV when selecting a high band. In this voltage adjustment circuit _S2 , when the band selection switch _SW2 is switched to the b side (high band selected), the switch transistor _TR3 is turned on, and the variable resistor _R10 is connected in parallel to the semi-fixed resistor _R2 . As a result, the maximum value of the tuning voltage when the high band is selected is made higher than the maximum value of the tuning voltage when the low band is selected. In this case, there is no influence on the minimum value of the tuning voltage set by the variable resistor _R5 . In addition,
R ₁₁ is a resistor and D ₆ is a diode.

In this way, the tuning device of this embodiment can arbitrarily set the minimum and maximum values of the tuning voltage when selecting a high band using the variable resistors R ₅ and R ₁₀ in response to switching of the band selection switch SW ₂ , respectively. Since it is adjustable, it is possible to adjust the minimum and maximum values of the tuning frequency of the electronically tuned tuner TU when selecting a high band.

A third embodiment of this invention will be explained based on FIG. This channel selection device is the same as the channel selection device shown in Fig. 3, with the addition of a voltage adjustment circuit _S3 that adjusts the maximum value of the channel selection voltage generated from the channel selection voltage generation circuit TV when selecting a high band. be. In this voltage adjustment circuit _S3 , when the band selection switch _SW2 is switched to the b side (high band selected), the switch transistor _TR3 is turned on, and the variable resistor _R10 connected in series with the semi-fixed resistor _R2 is turned on. are short-circuited, so that the maximum value of the tuning voltage can be made lower than the maximum value of the tuning voltage when the low band is selected, as in the embodiment shown in FIG.
However, the voltage value itself is higher than the voltage value in the embodiment shown in FIG. 4 (provided that the resistance values of the resistors R ₂ are equal).

Note that the other configurations and effects are the same as those of the second embodiment.

[Effect of idea]

According to the tuning device of this invention, the voltage adjustment circuit adjusts the lowest value of the tuning voltage to a voltage at which the tuning frequency of the electronic tuning tuner matches the lower limit frequency of one receiving band. , it is possible to match the bandwidth of each receiving band with the tuning frequency range of the electronically tuned tuner when selecting that receiving band. Therefore, even if the bandwidth of each receiving band is limited to match the receiving frequency of that receiving band, it can be used without any problem.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional tuning device, Fig. 2 is its tuning voltage versus tuning frequency characteristic, Fig. 3 is a circuit diagram of the first embodiment of this invention, and Fig. 4 is a diagram of the tuning frequency characteristic of this invention. The circuit diagram of the second embodiment, FIG. 5, is the third embodiment of this invention.
FIG. 3 is a circuit diagram of an embodiment of the invention. BV...band switching voltage generation circuit, TU...electronic tuning tuner, TV...tuning voltage generation circuit, SW ₂
... Band selection switch, S ₁ ... Voltage adjustment circuit.

Claims (1)

[Scope of utility model registration request] an electronic tuning tuner capable of tuning in two reception bands; a band switching voltage generation circuit for supplying a band switching voltage to the electronic tuning tuner; a tuning voltage generation circuit for supplying a tuning voltage to the electronic tuning tuner; A band switching switch changes the receiving band by changing the band switching voltage generated from the band switching voltage generating circuit, and a selecting voltage generated from the tuning voltage generating circuit in response to switching to one receiving band by the band switching switch. A channel selection device comprising: a voltage adjustment circuit that adjusts a minimum value of a station voltage to a voltage at which a tuning frequency of the electronically tuned tuner coincides with a lower limit frequency of the one reception band.