KR970007481B1 - Voltage transformer of aft(automatic fine tuning) for pip television system - Google Patents

Abstract

An apparatus for switching AFT(Automatic Fine Tuning) voltage of a television having a PIP(Picture in Picture) function is disclosed. An AFT voltage change unit(40) switches AFT voltage provided from a main tuner(20) or a sub tuner(30) according to a tuner selection signal of a timer(10) based on a feedback tuner AFT voltage. Thereby, the implement of the circuit is simple and the operation of AFT is easily processed.

Description

Automatic Fine Tuning (AFT) Voltage Changer for Televisions with Sub-Screen Functions

1 is a schematic block diagram of an AFT voltage switching device of a television having a sub picture function according to an embodiment of the present invention;

FIG. 2 is a circuit diagram showing an example of the AFT voltage switching means shown in FIG.

* Explanation of symbols for main parts of the drawings

10: timer 20: main tuner

30: Stun tuner 40: AFT voltage switching means

40a: main AFT voltage output section 40b: sub AFT voltage output section

40c: switching part

The present invention relates to an AFT (Automatic Fine Tuning) voltage switching device of a television having a picture in picture (PIP) function, and in particular, an AFT voltage output from two tuners of a television having a sub picture function. The present invention relates to an AFT voltage switching device of a television having a sub picture function which outputs the signal through a predetermined switching switching means and feeds the output AFT voltage to a single AFT input port in a timer.

In general, to get the best picture, the local oscillation frequency must always be precisely adjusted so that the median frequency at the output of the tuner is 58.75 MHz. The adjustment for this purpose is called fine tuning, and the local oscillation frequency is converted by ambient temperature or change over time, so that a fine tuning mechanism or an automatic fine tuning (AFT) circuit is attached to maintain the correct frequency. As a fine tuning mechanism of a mechanical tuner, many preset methods are used. This preset method adjusts the core in the local oscillation coil by engaging the gear to change the inductance. If you do so, the texture remains intact even if the channel is changed.

In addition, the automatic fine tuning (AFT) circuit detects a change in the oscillation frequency of the local oscillation circuit, thereby automatically controlling the oscillation frequency, and always preserves it at the correct frequency.

On the other hand, TV currently being commercialized and released has a sub-screen function, that is, a smaller screen size than the main screen so that viewers can see which broadcast program is in progress while other channels are watching as a main screen. The ability to be displayed at a predetermined position of the CRT has been reduced to allow more efficient viewing.

As described above, in a television having a sub picture function, a sub picture is displayed on a main screen due to a difference between a main screen and a sub picture channel, and thus, a channel frequency of the main picture and a channel frequency of the sub picture are different. The channel frequency must be maintained accurately according to each screen. For that reason, two televisions equipped with a sub picture function are provided with two tuners for outputting an AFT signal (i.e., a predetermined AFT voltage) for mutually accurate tuning of the channels of the main picture and the sub picture. .

As described above, a television having a sub picture function already includes a timer dedicated to the sub picture function (that is, a timer provided with two AFT input terminals). Not only is it complicated, but there is an inconvenience of having a separate tuning circuit for each tuner in a product not equipped with the timer for the sub picture function.

Accordingly, the present invention has been made in view of the above circumstances, and an object thereof is to output the AFT voltages from the two tuners through the switching switching means according to the tuner selection signal of the timer, and to output the AFT voltages of the single tuner within the timer. The present invention provides an AFT voltage switching device for a television having a sub picture function that is fed back to an AFT input port.

In order to achieve the above object, an AFT voltage switching device of a television having a sub picture function according to an embodiment of the present invention is an AFT of a predetermined tuner fed back with a single AFT input port in a television having a sub picture function. AFT voltage switching means for switching the AFT voltage output from the main tuner or the sub tuner in accordance with the tuner selection signal of the timer for outputting a predetermined tuner selection signal based on the voltage is further provided.

According to a preferred embodiment of the present invention, the AFT voltage switching means includes a main AFT voltage output unit for outputting a predetermined AFT voltage according to the main tuner selection signal output from the timer, and a subtuner selection signal output from the timer. The sub-AFT voltage output section outputs a predetermined AFT voltage, and a switching section for switching and outputting the AFT voltage from the main AFT voltage output section or the sub-AFT voltage output section according to the tuner selection signal from the timer.

In addition, according to the present invention, the main AFT voltage output unit may be switched on / off according to a first switching device switched on / off according to an AFT voltage output from an AFT output terminal of the main tuner and a tuner selection signal from the timer. A second switching element for controlling the output path of the AFT voltage through the first switching element, and a first attenuating element for attenuating the AFT voltage output through the first switching element under the control of the second switching element. do.

On the other hand, the sub-AFT voltage output unit is switched on / off in accordance with the AFT voltage output from the AFT output terminal of the sub-tuner, and switched on / off in accordance with the tuner selection signal from the timer to the third switching device And a fourth switching element for controlling the output path of the ART voltage through the second switching element, and a second attenuating element for attenuating the AFT voltage output through the third switching element under the control of the fourth switching element.

In addition, the second switching device of the main AFT voltage output unit and the fourth switching device of the sub AFT voltage output unit perform on / off operations in reverse.

According to the present invention configured as described above, the AFT voltage output to the main tuner or the sub-tuner according to the tuner selection signal output from the timer is switched through the AFT voltage switching means and the output AFT voltage is a single of the timer. By feeding back to the AFT input terminal, the timer outputs a tuner selection signal based on the input AFT voltage.

Hereinafter, the present invention will be described in more detail with reference to the attached drawings.

1 is a block diagram of an AFT voltage switching device of a television having a sub picture function according to an embodiment of the present invention, reference numeral 10 denotes a single AFT input port and is based on a previous feedback AFT voltage. After the tuner selection signal is output, another tuner selection signal is outputted while the AFT voltage of the corresponding tuner is fed back through the AFT voltage switching means 40, and the fed back AFT voltage is inputted to the AFT input port. The timer determines whether the voltage is the AFT voltage output from the main tuner 20 or the AFT voltage output from the subtuner 30, and outputs a predetermined tuner selection preference.

20 outputs a predetermined AFT voltage so that the viewer of the television having the sub picture function selects an arbitrary channel as the main channel so that the screen state of the main picture displayed on the CRT (not shown) can maintain an optimal state. This is a main tuner with AFT circuit.

30 outputs a predetermined AFT voltage so that a viewer watching a television having a sub picture function selects an arbitrary channel as a sub channel so that the screen state of a sub picture displayed on a CRT (not shown) can maintain an optimal state. A subtuner with an AFT circuit.

40 is an AFT voltage switching means for switching the AFT voltage from the main tuner 20 or the sub tuner 30 based on the tuner selection signal output from the timer 10.

Here, as shown in FIG. 2, when the timer 10 outputs the main tuner selection signal, one of the AFT voltage switching means 40a generates and outputs a predetermined AFT voltage according to the main AFT voltage. The output unit 40a, the sub-AFT voltage output unit 40b for generating and outputting a predetermined AFT voltage according to the output of the sub-tuner selection signal from the timer 10, and the output from the timer 10. As the tuner selection signal is changed, a switching unit made of, for example, a switching transistor for switching the AFT voltage output from the main AFT voltage output unit 40a or the AFT voltage output from the sub AFT voltage output unit 40b at high speed. 40c).

In addition, the main AFT voltage output unit 40a has a first terminal (base) connected to the AFT output terminal of the main tuner 20 via a resistor R4, and the second terminal (collector) of, for example, about 9V. A first switching element Q1 connected to an operating power supply terminal Vcc and switched on / off according to the AFT voltage output from the AFT output terminal of the main tuner 20; The first terminal (base) is connected to the tuner select signal output terminal (not shown) of the timer 10, and the third terminal (emitter) is connected to the third terminal (emitter) of the first switching element Q1. The AFT voltage from the main tuner 20 connected to the third terminal of the first switching element Q1 is turned off when the timer 10 outputs the main tuner selection signal. When the timer 10 outputs the sub-tuner selection signal, the timer is turned on to cut off the AFT voltage from the main tuner 20 by grounding a predetermined AFT voltage applied to the third terminal of the first switching element Q1. 2 switching elements Q2 and; The first switching element Q1 is connected to an intermediate node between the third terminal of the second switching element Q2 and the third node of the first switching element Q1 and the second switching element Q2 is turned off. And a first attenuating element TQ1 that attenuates the AFT voltage from the main tuner 20 output by the predetermined value.

In addition, the sub AFT voltage output unit 40b has a first terminal (base) connected to the AFT output terminal of the sub tuner 30 via a resistor R4 ', and the second terminal (collector) is, for example, about 9V. A third switching element Q3 connected to an operating power supply terminal Vcc and switched on / off according to the AFT voltage output from the AFT output terminal of the subtuner 30; A first terminal (base) is connected to a tuner selection signal output terminal (not shown) of the timer 10 via a diode D1, and a second terminal (collector) is connected to a third of the third switching element Q3. AFT voltage from the subtuner 30 connected to a terminal (emitter) and turned off when the timer 10 outputs the subtuner selection signal to the third terminal of the third switching element Q3 On the other hand, when the timer 10 outputs the main tuner selection signal, the timer 10 is turned on to ground the predetermined AFT voltage applied to the third terminal of the third switching element Q3 from the subtuner 30. A fourth switching element Q4 for blocking the AFT voltage; The third switching element Q3 is connected to the intermediate node between the second terminal of the fourth switching element Q4 and the third terminal of the third switching element Q3 and the fourth switching element Q4 is turned off. And a second attenuating element TQ2 that attenuates the AFT voltage from the sub-tuner 30 output by the predetermined value.

According to a preferred embodiment of the present invention, the first attenuating element TQ1 of the main AFT voltage output section 40a is composed of a plurality of resistors R1, R2, R3, and the sub-AFT voltage output section 40b. The second attenuating element TQ2 is composed of a plurality of resistors R1 ', R2', and R3 ', and the resistors R1, R2, and R3 and the resistors R1', R2 ', and R3' are mutually opposite. The resistance values of the corresponding resistors, that is, the resistors R1 and R1 ', the resistors R2 and R2', and the resistors R3 and R3 'are the same.

Referring to the AFT voltage switching operation by the AFT voltage switching device of a television having a sub-screen function according to an embodiment of the present invention configured as described above are as follows.

In FIG. 1, a viewer once watching a television with a sub picture function displays a main picture on a CRT using the main tuner 20, and then, for example, shows a broadcast program that is being broadcast on another channel. If the sub-tuner 30 wants to see the image and displays the sub-screen on the CRT, the AFT voltage switching means 40 is a tuner selection signal output from the timer 10 (here, the tuner selection signal is a main tuner). Means a selection signal and a sub tuner selection signal, and the main tuner selection signal and the sub tuner selection signal are alternately outputted from the tuner selection signal output terminal of the timer 10) from the main tuner 20. A AFT voltage and the AFT voltage from the sub-tuner 30 are switched by a high speed switching operation, and a switching operation is performed.

In the above AFT voltage switching operation, for example, when the main tuner selection signal is first output from the timer 10, the switch S of the switching unit 40c is connected to the terminal A and the sub-AFT voltage output. As the fourth switching element Q4 in the part 40b is turned on, the AFT voltage from the subtuner 30 is grounded through the fourth switching element Q4, so the AFT voltage output from the subtuner 30 is Is blocked. In this case, since the second switching element Q2 in the main AFT voltage output unit 40a is turned off and the first switching element Q1 is turned on, the AFT voltage output from the main tuner 20 is the first switching. The element Q1 outputs an AFT voltage whose predetermined voltage value is attenuated after a predetermined voltage increase in the plurality of resistors R1, R2, and R3 in the first attenuating element TQ1. The attenuated AFT voltage from the main tuner 20 is fed back to a single AFT input port of the timer 10. During the feedback, the sub-tuner selection signal is output from the tuner selection signal output terminal of the timer 10 so that the switch S of the switching unit 40c is connected to the terminal B and the main AFT voltage output unit. Since the second switching element Q2 in the 40a is turned on and the AFT voltage from the main tuner 20 is grounded through the second switching element Q2, the AFT voltage output from the main tuner 20 is blocked. do. In this case, since the fourth switching device Q4 in the sub-AFT voltage output unit 40b is turned off and the third switching device Q3 is turned on, the AFT voltage output from the subtuner 30 is controlled by the third switching. The device Q3 outputs an AFT voltage whose predetermined voltage value is attenuated after a predetermined voltage increase in the plurality of resistors R1 ', R2', and R3 'in the second attenuating element TQ2. The attenuated AFT voltage from the subtuner 30 is fed back to a single AFT input port of the timer 10.

As such, while the AFT voltage from the sub tuner 30 is fed back to the single AFT input port of the timer 10, the AFT voltage from the main tuner 20 is fed back to the AFT input port of the timer 10. Therefore, the timer 10 outputs a main tuner selection signal, and while the AFT voltage from the main tuner 20 is fed back to the AFT input port of the timer 10, the timer 10 The sub-tuner selection signal is output, and while the AFT voltage from the sub-tuner 30 is fed back, the timer 10 performs an operation of outputting the main tuner selection signal.

As described above, since the AFT voltage output through the AFT voltage means 40 is alternately fed back to the timer 10, the timer 10 alternately outputs a tuner selection signal based on the fed back AFT voltage. The AFT voltage switching means 40 performs a switching operation so that the AFT voltage of the tuner is output.

According to the present invention as described above, when two tuners are used, the AFT voltages from the main tuner and the sub tuner are switched through the integrated circuit (IC) AFT voltage switching means, and the output AFT voltages of the single By feeding back to the AFT input port the timer to alternately output the tuner selection signal, the circuit implementation is much simpler than the conventional method, and the AFT (automatic fine tuning) operation is easily performed. .

Claims (8)

In a television having a sub-screen function, the main tuner 20 according to the tuner selection signal of the timer 10 for outputting a predetermined tuner selection signal based on the AFT voltage of a predetermined tuner fed back with a single AFT input port. Or AFT voltage switching means (40) for switching the AFT voltage output from the sub-tuner (30). The main AFT voltage output unit 40a of claim 1, wherein the AFT voltage switching unit 40 outputs a predetermined AFT voltage according to a main tuner selection signal output from the timer 10. A sub-AFT voltage output section 40b for outputting a predetermined AFT voltage according to the sub-tuner selection signal outputted from the < RTI ID = 0.0 >), < / RTI > An AFT voltage switching device for a television having a sub picture function, comprising: a switching unit (40c) for switching and outputting the AFT voltage from the sub-AFT voltage output unit (40b). The main AFT voltage output unit 40a of claim 2, wherein the main AFT voltage output unit 40a is switched on / off according to the AFT voltage output from the AFT output terminal of the main tuner 20, and the timer 10 Control of the second switching element Q2 and the second switching element Q2 on / off-switched according to the tuner selection signal) to control the output path of the AFT voltage through the first switching element Q1. And a first attenuating element (TQ1) for attenuating a predetermined value of the AFT voltage output through the first switching element (Q1) under the AFT voltage switching device of a television having a sub picture function. The sub-AFT voltage output unit 40b includes a third switching element Q3 switched on / off according to the AFT voltage output from the AFT output terminal of the sub-tuner 30, and the timer 10. Of the fourth switching element Q4 and the fourth switching element Q4 which are switched on / off in accordance with a tuner selection signal from the control circuit 131 to control the output path of the AFT voltage through the third switching element Q3. And a second attenuating element (TQ2) for attenuating a predetermined value of the AFT voltage output through the third switching element (Q3) under control. 4. The AFT voltage switching device of a television with a sub picture function according to claim 3, wherein the first attenuating element (TQ1) comprises a plurality of resistors (R1, R2, R3). 5. The AFT voltage switching device of a television with a sub picture function according to claim 4, wherein the second attenuating element (TQ2) comprises a plurality of resistors (R1 ', R2', R3 '). The AFT of a television having a sub picture function according to claim 3 or 4, wherein the second switching element Q2 and the fourth switching element Q4 are configured to perform an on / off operation opposite to each other. Voltage switching device. 7. The display device according to claim 5 or 6, wherein the resistance values of the resistors R1: R1 ', the resistors R2: R2', and the resistors R3: R3 'are equal to each other. AFT voltage switching device for televisions.