JPS6010113Y2 - Electronic tuner operation circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an operating circuit for an electronic tuner, and its purpose is to enable tuner voltage jump operation with a single variable resistor.

In general, the VHF band 0 tuner voltage in television receivers is 90 to 108M R2 Low.
It is divided into a high band of 170 to 222 MHz, and in order to make it into one band, the actance of a resonant circuit using an integrated circuit can be switched, and a broadband oscillation circuit can be used to cover the low band and high band. Then, the tuner voltage was switched using a dual volume control.

However, in the former case, two resonant circuits are required, one for the low band and one for the high band, which complicates the circuit configuration.On the other hand, in the latter case, the relationship between using a double polyus However, there is a problem in that it is difficult to match the tolerance of the volume itself, and it is difficult to reliably switch the tuner voltage between the low band and high band.

The present invention solves these conventional drawbacks, and the present invention will be described below with reference to drawings of embodiments.

The drawing shows an example of the operation circuit of the electronic tuner of the present invention, in which R1 is a semi-fixed resistor for setting the upper limit voltage, R2 is a variable resistor for tuner voltage, R3 is a semi-fixed resistor for setting the lower limit voltage, R2 is an interlaced voltage width setting resistor, which are connected in series and inserted between the positive power source and the negative power source.

R5 and tortoise are comparative voltage setting resistors, which are connected in series and in parallel to the series connection of the resistors R□, R2, and R3.

TR1 is a comparison transistor whose emitter is connected to the connection point O of the resistors R5 and R6, whose base is connected to the movable terminal of the resistor R2 via the bias resistor R7, and whose coctor is connected to the short-circuit voltage. Setting resistor R8,
It is connected to the negative power supply via the series connection body of R9.

TR2 is a switching transistor whose collector is connected to the connection point P of the resistors R3 and R1, its emitter is connected to the negative power supply, and its base is connected to the connection point Q of the resistors R8 and R9. ing.

Then, the tuner voltage is taken out from the movable terminal of the resistor R2.

In the operating circuit having such a configuration, the resistor R
When the movable terminal of No. 2 is at the lower limit position, the base voltage of the comparison transistor TR□ is the same as that of the resistors R3 and R.
On the other hand, the switching transistor TR2 has its base voltage set by the resistors R8 and R9 connected to the collector of the comparison transistor TR5 and is in the ON state.

From this state, the movable terminal of the resistor R2 is moved to the upper limit side, and when the base voltage of the comparison transistor TR1 reaches the voltage set by the resistors R5 and R6, the comparison transistor TR□ is turned off. On the other hand, the switching transistor TR2 is also turned off.
state.

At this time, the resistor R1 is inserted into the resistor R2 via the resistor R3, so the tuner voltage taken out to the movable terminal of the resistor R2 is equal to the voltage set by the resistor R1. It will rise rapidly.

Further, when the movable terminal of the resistor R2 is moved from the upper limit side to the lower limit side and the base voltage of the comparison transistor TR1 becomes equal to or lower than the voltage set by the resistor Rs=R6, the comparison transistor TR1 On the other hand, the switching transistor TR2 is turned on due to the pressure set by the resistors R8 and R9 connected to the comparison transistor TR, and the tuner voltage taken out to the movable terminal of the resistor R2 is applied to the resistor. The voltage is lowered by the voltage set by the voltage regulator R2.

At this time, since a bias voltage is constantly applied to the collector of the switching transistor TR by the resistors R6 and R6, the comparison transistor TR
, respond promptly to the actions of

Here, the above operation circuit is connected to the V of the television receiver.
When using HFHF heavy duty electronic tuner, use the above resistor R.
It goes without saying that the value of 4 is set as the jump voltage width between the Low band and the High band.

Figure 4 shows the relationship between the frequency of the VHFTV band in Japan and the tuner voltage.

In Figure 4, 90~108MHz is the LOW band, 1
70~222MHz is divided into HIGH band, and the tuner voltage is 90MHz V g g 108M
Hz to V F, 170MHz to Vc g 222MH
If z is ■8, other than vHFTv band (7) 108
Since it is not necessary to receive up to 170 MHz, it is necessary to skip vF to Vc in a one-band configuration, and the relationship between the scale movement of the tuning volume and the tuner voltage is shown in FIG.

FIG. 1 shows an equivalent circuit of the operating circuit of the electronic tuner of the present invention.

In FIG. 1, 1 is a voltage comparator whose output is turned OFF when the tuner voltage at the movable terminal of the variable resistor VR1 is higher than the voltage at the voltage dividing point of the voltage dividing resistor.

■Power supply voltage. , the voltage applied to voltage comparator 1 is VA-R
If the voltage applied to the jump part of 4 is ■8, then (1) W
Since the voltage comparator 1 is ON when the voltage is in the band, the switching transistor TR2 is ON, and the transistor T
■ of R2.

Since 2 is sufficiently small, ■8=O [■], so vA”V
c.

Divide the resistance value of the tuning volume at the center and set R
2□, R2□ (naturally R2□+R2□=constant), then vll: of 90 MHz is due to R22=0 [Ω].

Next, 108 when the LOW band and HIGH band change
Since VP of MHz is the same as the comparison voltage, (2)=(31).

Next, when the tuner voltage exceeds Vp, voltage comparator 1 turns OFF.
F and transistor TR2 turns OFF, so it becomes HI.
This will be the GH band.

When in the HIGH band, it becomes Vc”V-10Vs, so 17
Vc at 0 MHz is also the same as equation (3), so equation (4)=(5).

■ of 222MH2.

It is represented by .

Here, from the above equation (2+(31(4)(5)), the ratio is constant, and if the comparison voltage is set in parallel with the tuner voltage, the LOW band or HIGH band region or H
It is possible to jump from the IGH band to the LOW pad, resulting in stable operation.

Also, the potential difference Vpc that jumps from VF to Vc is ■8=Vo
−V, and can be easily expressed by equations (5) and (3).

In the above embodiment, if the tuner voltage appearing at the movable terminal as the resistor R2 moves to the upper limit side exceeds the allowable voltage between the base and emitter of the comparison transistor TR1, the comparison transistor TR □ may be destroyed, and as a countermeasure for this, a diode D□ may be inserted in the forward direction at the base of the comparison transistor TR1 as shown in FIG.

As described above, according to the present invention, a resistor is added to the variable resistor for setting the tuner voltage, and this resistor is connected intermittently by a switching transistor whose operation is controlled by a voltage comparator installed in parallel with the variable resistor. Even if the Low band and H1 node band are located in Miyagi apart from each other during one band setup, the tuner voltage can be taken out from one variable resistor, making it easy to operate the electronic tuner. The circuit can be significantly simplified.

Moreover, from the above variable resistor, there are two types: Low band and High band.
This has great practical effects, such as being able to extract two types of tuner voltages for the h-band in a continuous manner, and greatly improving operability itself.

[Brief explanation of the drawing]

Fig. 1 is a circuit wiring diagram showing one embodiment of the operating circuit of the electronic tuner of the invention, Fig. 2 is a circuit wiring diagram showing another embodiment of the operating circuit of the electronic tuner of the invention, and Fig. 3 is the electronic tuner of the invention. The equivalent circuit diagram of the tuner operation circuit, Figure 4 is the VH of the same circuit.
FIG. 5 is a characteristic diagram of the relationship between the frequency of the FTV band and the tuner voltage, and FIG. 5 is a characteristic diagram of the relationship between the running scale and the tuner voltage. R1...variable resistor, R4...resistor, TR,...comparison transistor, TR2...
...Switching transistor, D□...
·diode.

Claims (3)

[Scope of utility model registration request] (1) A resistor for skipping unnecessary frequency bands is connected to one fixed terminal of the variable resistor for setting the tuner voltage, and a voltage dividing resistor is connected in parallel to the variable resistor. Connect one input of the voltage comparator to
The other input of the voltage comparator is connected to the movable terminal of the variable resistor, and when the tuner voltage taken out from the movable terminal of the variable resistor reaches a predetermined value, a switch circuit is connected in parallel to the resistor. an electronic tuner operating circuit configured to turn on and off by the voltage comparator and connect and disconnect the resistor to the variable resistor. (2) The voltage comparator is a comparison transistor whose emitter is connected to the voltage dividing point of a voltage dividing resistor connected in parallel to the variable resistor, and whose base is connected to the movable terminal of the variable resistor via the base resistor. characterized in that it is configured to control the base voltage of the switching transistor for connecting and disconnecting the resistor added to the variable resistor by means of a voltage dividing resistor connected to the collector of the comparison transistor. An operating circuit for an electronic tuner according to claim 1 of the utility model registration claim. (3) The operating circuit for an electronic tuner according to claim 2, wherein a diode is inserted in the forward direction between the base of the comparison transistor and the movable terminal of the variable resistor.