JPH0346589Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is applicable to television receivers (hereinafter referred to as TV), VTRs, etc.
This invention relates to an automatic frequency tuning circuit used in equipment equipped with a TV signal reception function.

(Prior art) In equipment equipped with a TV signal reception function,
Generally, an automatic frequency tuning circuit (hereinafter, automatic frequency tuning is abbreviated as AFT) is used to generate a voltage generated by an automatic frequency tuning control voltage generation circuit in response to a frequency deviation between the frequency value of an intermediate frequency signal and a predetermined intermediate frequency value. By applying the automatic frequency tuning control voltage to the local oscillator, an intermediate frequency signal having a predetermined intermediate frequency value is always stably obtained from the mixing stage to which the received input TV signal and the oscillation wave of the local oscillator are supplied. TV signals are received in a state where the

Figure 4 shows the frequency-control voltage characteristics (curve A) of the AFT circuit that generates the AFT control voltage corresponding to the frequency deviation between the frequency value of the intermediate frequency signal and the predetermined intermediate frequency value, and the AFT output from the AFT circuit. FIG. 4 is a diagram showing the controlled characteristics (straight line B) of a local oscillator to which a control voltage is supplied, and the frequency-control voltage characteristic of the AFT circuit is as exemplified by curve A in FIG. It has characteristics that are approximately point symmetrical with respect to the intermediate frequency value o.

The intersection o' between the curve A and the straight line B in FIG. 4 indicates the stable point when the AFT control loop is operated, that is, the attained frequency o'.

In the AFT circuit, even if the controlled characteristic of the local oscillator moves parallel to straight line B due to temperature change, for example, the controlled characteristic of the local oscillator will show the frequency-control voltage characteristic of the AFT circuit. This is to ensure that a stable intermediate frequency can be obtained as long as the part of curve A between points a1 and a2 intersects curve A, but in reality The range in which the AFT circuit operates stably is the range in which the controlled characteristic B of the local oscillator moves between the straight line B1 and the straight line B2 shown by the dotted line in Fig. o →
l, the upper side is o→h. It is desirable that the above-mentioned pull-in range be in a state in which the upper part and the lower part of the above-mentioned frequency o are approximately equal, that is, in a balanced state.

FIG. 5 is a diagram showing the output circuit of the AFT circuit, and in this FIG. is a reference voltage source having the same voltage value as the static voltage Vo of the AFT control voltage, and 6 is a control voltage supply terminal (input section for the defect control voltage) for controlling the switching operation of the changeover switch 4. When the movable contact c of the changeover switch 4 is switched to the fixed contact a side, the AFT control voltage output from the AFT circuit is sent out from the output terminal 3, and the movable contact c of the changeover switch 4 is switched to the fixed contact a side. is switched to the fixed contact b side, the reference voltage Vo output from the reference voltage source 5 is sent out from the output terminal 3.

In the state where the movable contact c of the changeover switch 4 is switched to the fixed contact b side as described above, the reference voltage Vo to be output from the reference voltage source 5 is
The voltage value is set to be equal to the static voltage Vo of the circuit, and as a result, when the movable contact c of the changeover switch 4 is switched to the fixed contact b side, the controlled characteristic of the local oscillator is as shown in Fig. 4. It is moved parallel to straight line B in FIG. 4 to a position passing through o, and the retraction range is approximately balanced vertically with respect to o. Then, the aforementioned changeover switch 4 stops the AFT operation by switching its movable contact c to the fixed contact b side, and
It functions as a default switch that returns the local oscillator to its initial setting.

However, the frequency-control voltage characteristic of an AFT circuit is generally different from the frequency-control voltage characteristic as shown in curve A in FIG. 4 mentioned above, and as exemplified in curve A in FIG. , the lower side (lower frequency side) and the upper side (higher frequency side) are not balanced, and therefore the pull-in range is also unbalanced, so the quality usually deteriorates.

As a solution to the above problem, the frequency of the intermediate frequency signal obtained based on the oscillation wave sent out from the local oscillator when that reference voltage is supplied to the local oscillator as the reference voltage to be output at the time of defect. It is conceivable to set the voltage value to a frequency that is approximately in the middle of the pull-in range of the AFT circuit.

Figure 7 shows the result of implementing the above solution.
This is a configuration example of an AFT circuit, and in this FIG. 7, 1 is an AFT circuit, 2 is an input terminal for an intermediate frequency signal,
3 is the output terminal of the AFT control voltage, 4 is the changeover switch, and 5' is the voltage value shown by Vo' in Figure 6.
Assuming that the reference voltage source that generates Vo′, that is, the reference voltage, is supplied to the local oscillator, the frequency value of the intermediate frequency signal obtained based on the oscillation wave sent from the local oscillator is
A reference voltage source 6 is set to a voltage value Vo' that can set the frequency o to approximately the middle of the pull-in range of the AFT circuit. This is a supply terminal (input section for day-feet control voltage). When the movable contact c of the changeover switch 4 is switched to the fixed contact a side, the AFT control voltage output from the AFT circuit is sent out from the output terminal 3,
Further, when the movable contact c of the changeover switch 4 is switched to the fixed contact b side, the reference voltage Vo' output from the reference voltage source 5' is sent out from the output terminal 3. When the reference voltage Vo' is output at the time of defect as described above, the pull-in range can be approximately balanced between the upper side and the lower side of the frequency o.

(Problem that the invention aims to solve) Incidentally, in recent years, AFT circuits and intermediate frequency amplification circuits have been integrated into ICs in the form of being mounted in a common IC package.
With the increasing integration of functions, integrated circuits that do not generate the AFT control voltage during the AFT circuit's failure but instead generate a static voltage Vo have become commercially available as integrated circuits, and are used in TV signal receiving equipment. It started to be done.

Figure 8 is a block diagram showing the functions of the parts corresponding to the AFT circuit section and the defective circuit section in an IC having the above-mentioned configuration. When a control voltage is supplied to the terminal 6 of the AFT circuit to perform the day-to-day operation, the output from the AFT circuit has a voltage value equal to the quiescent voltage Vo of the AFT circuit, so the amplifier in the pull-in range as described above is There will be a problem of balance.

Therefore, in this case as well, the solution as explained with reference to FIG. By attaching this externally to the IC so that the aforementioned predetermined voltage value Vo' is outputted by the changeover switch 4 at the time of defect, it is possible to balance the pull-in range between the upper and lower sides. However, applying such a solution would not only result in the use of an IC without taking advantage of its inherent day-to-day functionality, but would also result in higher costs due to the increased number of components. occurs.

(Means for Solving the Problems) The present invention provides an automatic frequency tuning control voltage generation circuit that generates a local oscillation frequency control voltage corresponding to a frequency deviation between the frequency of an intermediate frequency signal and a predetermined intermediate frequency value; the automatic frequency tuning control voltage generation circuit, and causes the automatic frequency tuning control voltage generation circuit to output a predetermined constant static voltage Vo from the output terminal of the automatic frequency tuning control voltage generation circuit. A circuit including a resistance element is connected between the input part of the day-to-day operation control voltage for controlling the operation of the day-to-day circuit in the circuit arrangement and the output terminal of the automatic frequency tuning control voltage generation circuit, and The day-to-day operation control voltage applied to the input section of the day-to-day operation control voltage is outputted from the output terminal of the above-mentioned automatic frequency tuning control voltage generation circuit via the circuit including the above-mentioned resistance element. The present invention provides an automatic frequency tuning circuit for equipment equipped with a TV signal receiving function, in which the resistance value of the resistor element is determined so as to be added as a correction voltage to the voltage Vo.

(Example) Hereinafter, specific details of the automatic frequency tuning circuit of the device having a TV signal receiving function according to the present invention will be explained in detail with reference to the accompanying drawings. 1 to 3 are block diagrams of different embodiments of automatic frequency tuning circuits for devices equipped with a TV signal receiving function according to the present invention, and the frame indicated by the symbol IC in FIGS. is an integrated circuit that includes an AFT control voltage generation circuit that has a built-in defect function that can output a static voltage Vo during a defect operation, and 1' in the figure indicates a block that has the function of the AFT circuit. 2 is an input terminal for the intermediate frequency signal, 3 is an output terminal for the AFT control voltage, 4' is a block showing a functional part of the AFT defect circuit, and 6 is an input terminal for the defect control voltage. R is a resistor connected between the output terminal 3 of the AFT control voltage and the input section 6 of the defective control voltage.

In Figure 2, AFT control voltage output terminal 3
and the day-feet control voltage input section 6,
A series connection circuit of a resistor R and an inverter INV is provided.

The above-mentioned input section 6 for the day-to-day control voltage has two cases: one in which the portion 4' having the function of the AFT day-to-day circuit in the integrated circuit IC is made to perform the day-to-day operation, and the other in which the day-to-day control voltage input section 6 is made to perform the day-to-day operation. , control voltages having different voltage levels are supplied respectively.

Now, the input section 6 of the above-mentioned day-feet control voltage
within the integrated circuit IC as a control voltage supplied to the
When the section 4' having the function of the AFT day-to-day circuit is not to perform a day-to-day operation, a low-level voltage is supplied, and when it is to be made to perform a day-to-day operation, a high-level voltage is supplied. In the embodiment shown in the first figure, a low level voltage is applied to the input section 6 of the defect control voltage in order to prevent the portion 4' having the function of the AFT defect circuit in the integrated circuit IC from performing the defect operation. is supplied, the integrated circuit IC generates an AFT control voltage and sends it to the output terminal 3 of the AFT control voltage.
When a high-level voltage is supplied to the input section 6 of the defect control voltage in order to cause the portion 4' having the function of the AFT defect circuit to perform defect operation, the integrated circuit IC
Due to the operation of the part 4' having the function of the AFT defect circuit in the IC, the static voltage Vo generated in the integrated circuit IC is applied to the output terminal 3 of the AFT control voltage.
is sent to the AFT control voltage output terminal 3, and at the same time, the high level voltage supplied to the input section 6 of the day-to-day control voltage is applied to the AFT control voltage output terminal 3 via the resistor R.
The voltage appearing at the control voltage output terminal 3 is higher than the static voltage Vo mentioned above. This is from the AFT control voltage output terminal 3 of the integrated circuit IC to the integrated circuit.
This is because the impedance seen inside the IC is high.

In this case, AFT control voltage output terminal 3
Since the voltage value generated in the AFT circuit can be changed by changing the resistance value of the resistor R mentioned above, the frequency value of the intermediate frequency signal obtained based on the oscillation wave sent out from the local oscillator is The voltage value Vo' that allows the frequency o to be set approximately in the middle of the pull-in range is the static voltage mentioned above.
If the voltage Vo′ is higher than Vo,
By varying the resistance value of the resistor R mentioned above,
AFT the voltage that indicates the required voltage value Vo′.
It can be set at the control voltage output terminal 3.

In the embodiment shown in FIG.
The voltage value required to generate a voltage value Vo' at the AFT control voltage output terminal 3 that can make the frequency o approximately in the middle of the pull-in range of the AFT circuit is higher than the above-mentioned static voltage Vo. If the voltage Vo' is a low voltage value, or it is necessary to generate a voltage value Vo' at the AFT control voltage output terminal 3 that can make the frequency o approximately in the middle of the pull-in range of the AFT circuit. The voltage value that is applied is a voltage Vo′ that is higher than the static voltage Vo mentioned above,
When the control voltage supplied to the input section 6 of the aforementioned day-to-day control voltage does not cause the section 4' having the function of the AFT day-to-day circuit in the integrated circuit IC to perform the day-to-day operation, a low level voltage is required. If a high-level voltage is supplied to perform the day-to-day operation, the inverter INV is connected directly to the resistor R as shown in the second diagram. It may be a circuit layout.

Figure 3 shows a video intermediate frequency stage integrated circuit M51307ASP (manufactured by Mitsubishi Electric Corporation) with a built-in AFT circuit.
In this figure, the IC is the above-mentioned integrated circuit M51307ASP, and pins 9 and 10 of this IC are shown as examples.
An intermediate frequency signal is input to pin No. 50, an AFT control voltage is output from pin No. 50, and a resonant circuit that determines the AFT control center frequency is connected to pin No. 47.
TC is connected.

The above-mentioned resonant circuit TC is constituted by a coil L and a capacitor C, and a DC-blocking capacitor 7 is grounded between the resonant circuit TC and the ground. The collector of a transistor 8 is connected to the connection point between the non-grounded terminal of the capacitor 7 and the resonant circuit TC, and the emitter of the transistor 8 is grounded, and furthermore, resistors 9 and 10 are connected to the base. one end of each is connected,
The other end of the resistor 9 described above is grounded, and the other end of the resistor 10 is connected to the input section 6 for the defect operation control voltage, and also to one end of the resistor R. The other end of the resistor R is connected to pin 50 of the IC.

IC used in the embodiment shown in Figure 3
By grounding pin 47 DC
Since the configuration is such that the AFT operation in the IC is stopped and the static voltage Vo of the AFT circuit is output to pin 50, a high-level voltage is applied to input section 6 of the day-to-day operation control voltage in Figure 3. When input is input, transistor 8 becomes conductive and the 47th pin of the IC is DC grounded via the resonant circuit TC.
The quiescent voltage Vo in the AFT circuit of the IC is output to pin 50 of the IC, but in this state, a high-level voltage is input to the input section 6 of the defect operation control voltage, so By applying the high level voltage supplied to the above-mentioned day-to-day control voltage input section 6 to the AFT control voltage output terminal 3 via the resistor R,
The voltage appearing at the AFT control voltage output terminal 3 is higher than the static voltage Vo mentioned above. this is,
This is because the impedance when looking inside the integrated circuit IC from the AFT control voltage output terminal 3 of the integrated circuit IC is high.

In this case, AFT control voltage output terminal 3
Since the voltage value generated in the AFT circuit can be changed by changing the resistance value of the resistor R mentioned above, the frequency value of the intermediate frequency signal obtained based on the oscillation wave sent out from the local oscillator is The voltage at the AFT output voltage output terminal 3 can be set to a voltage value Vo' that allows the frequency o to be approximately in the middle of the pull-in range.

When a low level voltage is input to the input section 6 of the defective operation control voltage in Fig. 3, the transistor 8 becomes non-conductive, and a DC bias appears at pin 47 of the IC, which is grounded in terms of DC. hand,
The AFT control voltage is output from the IC's AFT circuit to pin 50 of the IC. In this state, since a low level voltage is input to the input section 6 for the defect operation control voltage, the AFT control voltage is sent out from the AFT control voltage output terminal 3.

(Effects) As is clear from the detailed explanation above, the automatic frequency tuning circuit of the device equipped with the TV signal reception function of the present invention is capable of adjusting the frequency difference between the frequency of the intermediate frequency signal and the predetermined intermediate frequency value. An automatic frequency tuning control voltage generation circuit that generates a local oscillation frequency control voltage corresponding to an input section for a day-to-day operation control voltage for controlling the operation of the day-to-day circuit, and an automatic frequency tuning circuit; A circuit including a resistance element is connected between the output terminal of the control voltage generation circuit and the day-to-day operation control voltage applied to the input section of the day-to-day operation control voltage is passed through the circuit including the resistance element to generate the above-mentioned automatic control voltage. Since the resistance value of the resistance element is determined so as to be added as a correction voltage to a predetermined constant static voltage Vo output from the output terminal of the frequency tuning control voltage generation circuit, the present invention For example, the automatic frequency tuning circuit of a device equipped with a TV signal reception function has functions corresponding to the AFT circuit part and the day-to-day circuit part, and when the day-to-day circuit is operating, the output from the AFT circuit is connected to the AFT circuit. Even for integrated circuits and other AFT circuits that are configured to have a voltage value equal to the static voltage Vo of By applying the defective control voltage to the AFT control voltage output terminal 3 via the resistor R, the voltage appearing at the AFT control voltage output terminal 3 is an intermediate value obtained based on the oscillation wave sent out from the local oscillator. It is possible to set the frequency value of the frequency signal to a voltage value Vo' that can make the frequency o approximately in the middle of the pull-in range of the AFT circuit. The problem is successfully resolved.

[Brief explanation of drawings]

1 to 3 are block diagrams of different embodiments of the automatic frequency tuning circuit for equipment equipped with a TV signal receiving function according to the present invention, FIGS. 4 and 6 are characteristic curve examples, and FIG. 5 7 and 8 are block diagrams of conventional circuits. 1...AFT circuit, 2...Intermediate frequency signal input terminal, 3...AFT control voltage output terminal, IC...
AFT has a built-in day-to-day function that can output static voltage Vo during day-to-day operation.
Integrated circuit including control voltage generation circuit, 1'...AFT
Blocks 4' indicating functional parts of the circuit...
...Block showing a part having the function of the AFT defective circuit, 6... Input section of the defective control voltage, R... Resistor, INV... Inverter.

Claims (1)

[Scope of utility model registration request] an automatic frequency tuning control voltage generation circuit that generates a local oscillation frequency control voltage corresponding to a frequency deviation between the frequency of the intermediate frequency signal and a predetermined intermediate frequency value;
and a day-to-day circuit that stops the original operation of the automatic frequency tuning control voltage generation circuit and sends out a predetermined constant static voltage Vo from the output terminal of the automatic frequency tuning control voltage generation circuit. A circuit including a resistive element is connected between the input part of the day-to-day operation control voltage for controlling the operation of the day-to-day circuit in the configured circuit arrangement and the output terminal of the automatic frequency tuning control voltage generation circuit. , the day-to-day operation control voltage applied to the input section of the day-to-day operation control voltage is outputted from the output terminal of the above-mentioned automatic frequency tuning control voltage generation circuit via the circuit including the above-mentioned resistance element. The resistance value of the resistance element is determined so as to be added as a correction voltage to the static voltage Vo.
Automatic frequency tuning circuit for equipment with the ability to receive TV signals.