KR900007329Y1 - Aft control circuit - Google Patents

Abstract

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Description

AFT control circuit

1 is a circuit diagram according to the present invention.

* Explanation of symbols for main parts of the drawings

MP: One-chip Microprocessor TN: Tuner

AD: Image Detection and AFT Detection Circuit CP1, CP2: Comparator

P1, P2: One-chip microprocessor input stage IFT: Interface

[Industrial use]

The present invention relates to an AFT control circuit of a television receiver, and more particularly, to an AFT control circuit capable of maintaining the best automatic fine adjustment state by controlling an AFT voltage according to a channel selected from a tuner unit in a microprocessor.

[Traditional Technology and Problems]

In general, an AFT (Auto Fine Tuning) control circuit installed in a television receiver adopts a one-chip microprocessor for AFT voltage input according to a channel selected from a tuner. The analog-to-digital converter is used to convert the digital signal and then decode the digital signal to control the AFT voltage according to the channel selection.

However, as the functions of television receivers are becoming more diversified, there are many cases where one-chip microprocessors dedicated to AFT voltage control, which do not have an analog-to-digital converter, are used in conventional hand microprocessors used for AFT control. In this case, since the analog-to-digital converter must be separately provided in the one-chip microprocessor, the structure of the product is complicated and the price is increased.

[Purpose of designation]

The present invention was devised in consideration of the above-described circumstances. The comparator was installed at the front end of a one-chip microprocessor which does not have an analog-to-digital converter used for AFT voltage control and a dedicated terminal for AFT. It provides AFT control circuit of television receiver that compares voltage signal according to intermediate frequency input from and applies it to one chip microprocessor so that one chip microprocessor can control local oscillation frequency of tuner and execute automatic fine adjustment. There is a purpose.

[Composition of design]

The present invention for achieving the above object is a television receiver equipped with a tuner (TN) and an image detection and AFT detection circuit (AD), the non-inverting terminal (+) at the output side of the projection detection and AFT detection circuit (AD) ) Is connected to the inverting terminals (-) of the comparators (CP1, CP2) to which the reference voltage setting resistors (R1, R2, R3) are connected, and on the output side of the comparators (CP1, CP2) of the one-chip microprocessor (MP). Input terminals P1 and P2 are connected to each other, and the one-chip microprocessor MP has a structure in which the tuner TN is connected through a conventional interface IFT.

(Action)

FIG. 1 shows a circuit diagram of the present invention having the above-described structure. When the dominant user adjusts the tuner TN and selects a desired channel, the tuner TN selects a channel among the high frequency signals RF. In addition to tuning the frequency of the designated channel, the PLL control voltage corresponding to the designated channel from the tutor TN is applied to the microprocessor MP, and the microprocessor MP interfaces a predetermined voltage according to the designated channel. A VCO (Voltage Cscillator (not shown)) inside the tuner TN is applied through the ITF to generate a local oscillation frequency corresponding to the designated channel.

Subsequently, the tuner TN generates an intermediate frequency IF based on the tuned channel frequency and the local oscillation frequency of the VCO, and applies the intermediate frequency IF to the image detection and the AFT detection circuit AD. The AFT detection circuit AD outputs an image signal VS and outputs a voltage corresponding to the value of the input intermediate frequency IF, that is, a voltage inversely proportional to the value of the intermediate frequency IF. It is applied to the inverting terminal (-) of CP2).

Here, the voltage input to the non-inverting terminal (+) of the comparator CP1 is the voltage input to the non-inverting terminal (+) of the comparator CP2 to the non-inverting terminal (+) of the comparators CP1 and CP2. When is denoted by C2, the divided voltage by the resistors R1 to R3 represented by the following equation is applied. In other words,

Here, the value of the resistors R1 to R3 is the output of the comparator CP1 when the AFT adjustment state is normal, that is, when the intermediate frequency IF is a predetermined value, and the output of the comparator CP2 is It is set to be low level.

Therefore, the intermediate frequency IF is higher than the predetermined frequency, that is, the tuner TN is tuned to a high frequency so that the voltage output from the image detection and AFT detection circuit AD is higher than R3 · Vcc / (R1 + R2 + R3). If it is small, the voltage inputted to the inverting terminal (-) of each comparator (CP1, CP2) is lower than the reference voltage inputted to the non-inverting terminal (+) so that the output from the comparators (CP1, CP2) becomes the mode high level. Tutor TN is properly tuned and the voltages output from the image detection and AFT detection circuits are R3, Vcc / (R1 + R2 + R3) and (R2 + R3), Vcc / (R1 + R2 + R3). If the value is between, the level is output from the comparator CP1 and the low level is output from the comparator CP2, and the tuner TN is tuned to a low frequency and output from the image detection and AFT detection circuit AD. When the voltage becomes greater than (R2 + R3) Vcc / (R1 + R2 + R3), both low levels are output from the comparators CP1 and CP2.

On the other hand, the microprocessor MP performs the AFT control by increasing or decreasing the control voltage for controlling the VCO of the tuner TN based on the voltage applied from the comparators CP1 and CP2 to the input terminals P1 and P2. do.

For example, when the voltages applied to the input terminals P1 and P2 are all at a high level, the microprocessor MP determines that the intermediate frequency IF is tuned to be high and the data is tuned to a lower side than the present. In this case, the interface ITF changes the oscillation control voltage of the VCO according to the data from the microprocessor MP so that the local oscillation frequency is adjusted in a direction in which the intermediate frequency is lowered so as to perform normal tuning. That is, the control is performed so that the intermediate frequency IF becomes a predetermined value. However, the above operation is continuously performed until the high level is output from the comparator CP1 and the low level is output from the comparator CP2.

In addition, the above operation is performed in the same manner even when the tuner TN is tuned to a low frequency so that both low levels are output from the comparators CP1 and CP2.

[Effect of design]

As described above, according to the AFT control circuit according to the present invention, even in the case of a television receiver in which a one-chip microprocessor without an AFT dedicated input terminal is used, AFT control can be realized with a simple circuit configuration.

In addition, the present invention is not limited to a television receiver, but can be effectively applied to a case of reproducing a video signal in a magnetic recording / reproducing apparatus (VTR) or the like.

Claims (1)

In a television receiver equipped with a tour (TN) and an image detection and AFT detection circuit (AD), the non-inverting terminal (+) at the output side of the image detection and AFT detection circuit (AD) has a resistance for setting a reference voltage (R1). , The inverting terminals (-) of the comparators CP1 and CP2 to which R2 and R3 are connected are connected, and the input terminals P1 and P2 of the one-chip microprocessor MP are connected to the output side of the comparators CP1 and CP2, respectively. In the one-chip microprocessor MP, the tuner TN provides an interface ITF to control the AFT voltage according to the outputs of the input comparators CP1 and CP2 and the PLL voltage of the tuner TN. AFT control circuit, characterized in that configured through.