KR19980050202A - Automatic gain adjusting device for two-tuner television receivers - Google Patents

Abstract

In the two-tuner television, when the level of gain-adjusted image detection output through the main image processing system is low, the gain can be broadened by additionally passing through an intermediate frequency amplifier provided in the sub image processing system. An automatic gain adjustment device for a two-tuner television receiver is provided that allows sufficient contrast even when the input signal is very weak.

Description

Automatic gain adjusting device for two-tuner television receivers

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain adjustment apparatus for a television receiver. In particular, in a two-tuner television, when the level of the image detection output gain-adjusted through the main image processing system is low, an intermediate frequency automatically provided in the sub image processing system It relates to an automatic gain adjusting device for a two-tuner television receiver in which the gain is widened by further passing through an amplifier section.

In general, if the television receiver is weak in radio waves induced by the antenna, the image detection output is changed in the same manner, and the contrast of the reproduced screen changes every moment. In order to solve this problem, a conventional television receiver is provided with an automatic gain control circuit (hereinafter, simply referred to as an AGC circuit). FIG. 1 shows a block of the automatic gain adjustment apparatus of the conventional television receiver. It is a block diagram. As shown in Fig. 1, in the conventional automatic gain adjusting apparatus of a television receiver, the antenna 1 is a broadcast wave signal of several channels emitted from the transmitting station into the air (because it is a high frequency signal, it is referred to as RF (Radio Frequency) in the following). Is called a signal). The remote control device 7 encodes the volume key signal or channel key signal selected by the user (hereinafter, only the channel key signal will be described as an example of the invention) and converts it into infrared rays and launches the receiver. Converts the infrared signal emitted from the remote control device 7 into a corresponding electrical signal and provides it to the microprocessor 13 which controls the overall operation of the television receiver. The microprocessor 13 receives the channel key signal provided from the receiver 8 to identify a channel to be tuned in at present, and reads the corresponding frequency from the channel memory 9 to control the PWM generator 10. Output the signal. Next, the PWM generator 10 outputs a predetermined Pulse Width Modulation (PWM) signal in accordance with the control signal from the microprocessor 13, and in the integrating circuit 11, the PWM generator 10 receives a signal from the PWM generator 10. Integrating the output PWM signal generates a voltage control signal corresponding to the channel selected by the user, and outputs it to the local oscillation circuit 12.

On the other hand, the RF amplifier 2 amplifies the RF signal induced by the antenna 1 to increase the sensitivity, and then delivers it to the mixer 3, the mixer 3, the RF signal output from the RF amplifier 2 And a high frequency emitted from the local oscillation circuit 12 to be described later to output a constant intermediate frequency signal (hereinafter simply referred to as IF signal). The local oscillation circuit 12 outputs a frequency signal that changes in accordance with the channel selected based on the voltage control signal output from the above-described integrating circuit 11.

Next, the IF amplifier 4 amplifies the IF signal output from the mixer 3 to increase the sensitivity and selectivity, and the image detector 5 detects the IF signal output from the IF amplifier 4 and combines it. Obtain a video signal.

Thereafter, the obtained composite video signal is a primary color signal sequentially through an image processor and an image amplification unit (not shown), and the screen for the finally tuned channel is output by driving a CRT (Cathode Ray Tube) by the primary color signal. Will be.

On the other hand, in the television receiver, the magnitude of the input signal received through the antenna 1 is changed due to the strength or fluctuation of the reception signal. In the AGC circuit 8, the composite image detected by the image detector 5 is detected. The level of the composite video signal detected by the image detector 5 is always kept constant by automatically adjusting the amplification degree, that is, the gain of the RF amplifier 2 and the IF amplifier 4 based on the signal level. .

However, in the above-described automatic gain adjustment apparatus of a conventional television receiver, the width in which the gain can be adjusted in the AGC circuit is limited, so when the level of the input signal is very weak, even though the AGC circuit passes through the AGC circuit, There was a problem of insufficient contrast.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In the two-tuner television, when the level of the gain-adjusted image detection output through the main image processing system is low, the intermediate frequency amplification provided in the sub image processing system is automatically provided. It is an object of the present invention to provide an automatic gain adjusting device of a two-tuner television receiver, in which a gain can be obtained by additionally extending the gain to obtain sufficient contrast even when the input signal is very weak.

1 is a block diagram of an automatic gain adjusting device of a conventional television receiver;

2 is a block diagram of an automatic gain adjusting device of a two-tuner television receiver according to a preferred embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

1: antenna, 2: RF amplifier,

3: mixer, 4: IF amplifier,

5: video detector, 6: AGC circuit,

7: remote control unit, 8: receiver,

9: channel memory, 10: PWM generator,

11: integrating circuit, 12: local oscillating circuit,

13: microprocessor, 21: antenna,

22: first RF amplifier, 23: first mixer,

24: first IF amplifier, 25: first switching unit,

26: second switching unit, 27: first image detector,

28: AGC circuit, 29: A / D converter,

30: second RF amplifying unit, 31: second mixer,

32: third switching portion, 34: fourth switching portion,

35: second image detector, 36: remote control device,

37: receiver, 38: microprocessor.

The automatic gain adjusting device of the two-tuner television receiver of the present invention for achieving the above object comprises a first RF amplifier, a first mixer, an IF amplifier, and a first detector for detecting an image signal for a main channel captured by an antenna. An image detector, a first RF amplifier, a first mixer, an IF amplifier, and a first image detector configured to detect an image signal of a subchannel captured by an antenna, provide simultaneous viewing of a main channel and a subchannel on a screen. And a two-tuner television receiver which automatically adjusts the gain of the first IF amplifier based on the detection output level of the first image detector, wherein the output of the first IF amplifier is directly output to the first image detector. A plurality of switching units configured to output the first image detector through a second IF amplifier unit; If the A / D converter and A / D converter for A / D converting the output voltage of the AGC circuit are not tuned simultaneously, the input signal of the main channel induced by the antenna based on the output of the A / D converter Determine the level of the input signal, and when the level of the input signal is equal to or greater than a predetermined reference value, the output of the first IF amplifier part is output to the first image detector through the second IF amplifier part until the reference value is equal to or less than the reference value. And a microprocessor for controlling the switching unit.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to an accompanying drawing, the automatic gain adjustment apparatus of the 2-tuner television receiver of the television receiver of this invention is demonstrated in detail.

First, it is clear that the two-tuner television receiver used in the present specification requires not only the two-tuner but also two other image processing systems. An example of such a television receiver is a commercially available sub-screen television receiver. Can be mentioned. In addition, the sub-screen television receiver refers to a television receiver that divides a part of the CRT screen into one or more and simultaneously watches two or more channels.

2 is a block diagram of an automatic gain adjusting device of a two-tuner television receiver according to a preferred embodiment of the present invention. 2, in the automatic gain adjusting apparatus according to the present invention, an antenna 21, a first RF amplifier 22, a first mixer 23, a first IF amplifier 24, and a radio frequency signal for a main channel are processed. The first image detector 27 performs the same function as the corresponding circuit configuration of the conventional automatic gain gain device as described above, and in addition, the AGC circuit 28, the remote control device 36 and the receiver 37 Since the same function as the conventional circuit configuration described above is performed, a detailed description thereof will be omitted.

On the other hand, the second RF amplifier 30 amplifies the RF signal induced by the antenna 1 to increase the sensitivity, and transfers it to the second mixer 31, the second mixer 31 in the second RF amplifier 30 The IF signal is output by mixing the RF signal outputted from the PB and the local oscillation frequency from the second local oscillator circuit (not shown) to be described later. As described above, the second local oscillating circuit outputs a frequency signal that changes in accordance with the selected subchannel based on the voltage control signal output from the integrating circuit (not shown). Next, the second IF amplifier 33 amplifies the IF signal output from the second mixer 31 to increase sensitivity and selectivity, and the second image detector 35 outputs from the second IF amplifier 33. The IF signal is detected to obtain a second composite video signal.

Meanwhile, in the present invention, in addition to the first to fourth switching units 25, 26, 32, and 34, the first switching unit 25 and the fourth switching unit 34 are further provided. Each has a single common input terminal and two output terminals switched by the control signal SW of the microprocessor 38. On the other hand, the second switching unit 26 and the third switching unit 32 each have two input terminals and a single common output terminal switched by the control signal SW of the microprocessor 38. An input terminal of the first switching unit 25 is connected to an output terminal of the first IF amplifier 24, and two output terminals are connected to an input terminal of the second switching unit 26 and an input terminal of the third switching unit 32, respectively. . The other input terminal of the second switching unit 26 is connected to the output terminal of the fourth switching unit 34, and the output terminal thereof is connected to the first image detector 27. The remaining input terminal of the third switching unit 32 is connected to the output terminal of the second mixer 31, and the output terminal thereof is connected to the input terminal of the second IF amplifier 33. Finally, the remaining output terminal of the fourth switching unit 34 is connected to the input terminal of the second image detector 35. In the figure, reference numeral 29 denotes an A / D converter which converts the AGC control voltage (analog voltage signal) output from the AGC circuit 28 into a corresponding digital signal P1 and provides it to the microprocessor 38. .

Hereinafter, the operation of the automatic gain adjustment device of the two-tuner television receiver of the present invention having the above-described configuration will be described in detail.

First, when the user wants to simultaneously watch the main channel and the sub channel, the automatic gain adjustment function according to the present invention is stopped, and only the same automatic gain adjustment function as the conventional method is performed.

On the other hand, when the user wants to watch only the main channel, the automatic gain adjustment function according to the present invention becomes possible. In this state, when the level of the input signal received through the antenna 1 is weak and is converted by the A / D converter 29 so that the AGC voltage signal P1 provided to the microprocessor 38 exceeds a predetermined reference value. The microprocessor 38 switches the output terminal of the first switching unit 25 and the input terminal of the third switching unit 32 so that the IF signal output from the first IF amplifier 24 is converted into the second IF amplifier 33. Amplify again. As a result, the IF signal for the main channel is amplified by multiplying the amplification degree of the first IF amplifier 24 and the second IF amplifier 33. At the same time, the microprocessor 38 switches the output terminal of the fourth switching unit 34 and the input terminal of the second switching unit 26 so that the IF signal amplified by the second IF amplifier 34 converts the first image detector 27. To be entered). As a result, since the IF signal is amplified with a high gain, the AGC voltage becomes relatively low, resulting in a sufficient contrast of the screen, and the microprocessor 38 controls each switching unit until such AGC voltage has an appropriate value. The switching states of (25), (26), (32) and (34) are maintained as they are.

On the other hand, when the magnitude of the input signal induced by the antenna 1 is maintained at an appropriate level, since the contrast of the screen is sufficiently satisfied by the conventional automatic gain adjusting device, the microprocessor 38 may include the first switching unit 25. And controlling the second switching unit 26 so that the IF signal output from the first IF amplifier 24 is input to the first image detector 27 as it is.

The automatic gain adjustment apparatus of the two-tuner television receiver of the present invention is not limited to the above-described embodiments, and can be modified in various ways within the scope of the technical idea of the present invention.

According to the automatic gain adjusting apparatus of the two-tuner television receiver of the present invention as described above, when the level of the image detection output gain adjusted through the main image processing system is low, the intermediate frequency automatically provided to the sub image processing system is provided. By further increasing the gain by adjusting the amplifier, a sufficient contrast can be obtained even when the input signal is very weak.

Claims (2)

A first RF amplifier for detecting an image signal for a main channel captured by an antenna, a first mixer, an IF amplifier and a first image detector, and a first RF amplifier for detecting an image signal for a subchannel captured by an antenna And a first mixer, an IF amplifier, and a first image detector to simultaneously watch the main channel and the subchannels on the screen, and obtain a gain of the first IF amplifier based on the detection output level of the first image detector. A two-tuner television receiver that automatically adjusts, A plurality of switching units for outputting the output of the first IF amplifier directly to the first image detector or to the first image detector via a second IF amplifier, If the A / D converter and A / D converter for A / D converting the output voltage of the AGC circuit are not tuned at the same time, they are induced by the antenna based on the output of the A / D converter. Determining the level of the input signal of the main channel, and when the level of the input signal is greater than or equal to a predetermined reference value, the output of the first IF amplifier is detected through the second IF amplifier until the output is less than or equal to the reference value. And a microprocessor for controlling the respective switching units so as to be output to the negative unit. The method of claim 1, wherein the plurality of switching units have a single common input stage and two output stages, and the input stage has a first switching unit, two input stages, and a single common output stage connected to an output stage of the first IF amplifier unit. One input stage has a second switching unit, two input stages and a single common output stage connected to one output stage of the first switching unit, and the one input stage is connected to the remaining output stage of the first switching unit and the other input stage Has a third switching unit connected to the output of the second mixer and a single common input and two outputs, the input being connected to the output of the second IF amplifier, and the one output being connected to the rest of the second switching unit. A two-tuner teller comprising a fourth switching unit connected to an input terminal and the remaining output terminal connected to the second image detector. Automatic gain adjustment device for revision receivers.