KR950015101B1 - If processing circuit for tv receiver - Google Patents

Abstract

The IF signal processor has higher sensitivity and broad automatic gain control range. The IF signal processor includes an IF signal amplifier(100) for amplifying an input IF signal in a preset range, a filter(200) for filtering output signal of the IF signal amplifier(200), a video signal amplifier(300) for amplifying video signal output from the filter(200), a first automatic gain controller(400) for controlling amplification gain of the IF signal amplifier(100), and a second automatic gain controller(500) for controlling the video signal amplifier according the level of the synchronous signal.

Description

Intermediate frequency processing unit

1 is a block diagram of a conventional intermediate frequency processing apparatus.

2 is a view for explaining the automatic gain range and sensitivity according to the input and output signals.

3 is a block diagram according to an embodiment of an intermediate frequency processing apparatus according to the present invention.

4 is a view for explaining the characteristics of the output signal of the image signal amplifier shown in FIG.

* Explanation of symbols for main parts of the drawings

100: intermediate frequency amplifier 200: detector

300: image signal amplifier 400: first automatic gain control unit

500: second automatic gain control unit

The present invention relates to an intermediate frequency processing apparatus in a television signal processing system, and more particularly to an intermediate frequency processing apparatus having a high sensitivity and a wide automatic gain control (AGC) range.

In general, in a television signal processing system, the intermediate frequency processing has an important effect on the image and sound characteristics of the entire TV, and among them, the sensitivity characteristic of the image signal is fundamental to the TV image quality.

The sensitivity of the video signal is determined by the signal-to-noise ratio (S / N), the noise figure (NF) of the receiver, the bandwidth and the input voltage in the video output.

Even if the input is very low S / N ratio below the noise sensitivity, if the contrast is enough, the video can be viewed as it is. Therefore, the lowest input voltage at which the specified output is obtained even if the S / N ratio is ignored is referred to as the maximum sensitivity.

Therefore, in a color television receiver, when the S / N ratio is bad, noise (color noise) from the color circuit also appears, so that the image quality deteriorates.

An intermediate frequency processing apparatus of such a conventional television signal processing system is shown in FIG.

As shown in FIG. 1, the conventional intermediate frequency processing apparatus is an intermediate structure consisting of first to third amplifiers 11-13 each having three stages for amplifying a video signal output from a tuner (not shown). The frequency amplification unit 10 and the amplified signal are AM and / or FM modulated signals during transmission, so that a detection unit 20 for detecting them and an image signal amplification for finally amplifying the output of the detection unit 20 again. The input 30 uses the output of the image signal amplifying unit 30 to automatically control the gain of the receiver according to the strength and weakness of the received radio wave so that a constant image detection output is always output from the image signal amplifying unit 30. Automatic gain control unit 40 for controlling the gain of the intermediate frequency amplifier 10 by determining the strength and weakness of the.

That is, the level of the synchronous signal of the signal output from the image signal amplifier 30 is sensed and fed back to the AGC unit 40. The AGC unit 40 senses the level of the synchronous signal of the fed-back signal and determines that the signal is large and small, and outputs the result of the determination to the first to third amplifiers 11-13 to control the gain.

At this time, the image sensitivity and the automatic gain control range have characteristics that are opposite to each other, that is, if the sensitivity is improved, the automatic gain control range is narrowed.

That is, as shown in FIG. 2, the automatic gain control unit 40 adjusts the output signal from the image signal output unit 30 at a constant voltage Vo with respect to the input video signal. ① It has an automatic gain control range (AGC RANGE1) that is always output as a constant output signal Vo for the input video signals V1 to V2 as a curve.

In this case, when the input video signal V3 smaller than V1 to improve the sensitivity is output to Vo, the range (V4-V2) where the automatic gain control range is reduced like the curve (V4-V1) is higher than the range (V3-V1). As a result, when the sensitivity is improved, there is a problem that the automatic gain control range is reduced.

This is because the gain range of the intermediate frequency amplifier 10 composed of transistors (not shown) cannot be increased to a predetermined value or more (about 60 Hz). That is, as the gain of the transistor increases, the capacitance of the parasitic capacitor of the transistor also increases due to the miller effect, and this parasitic capacitor has a specific characteristic of passing the high frequency signal to the output terminal instead of outputting it to the ground.

Intermediate frequency signal (e.g. SIF: 65.75MHz, VIF: 61.25MHz for 3 channels) is a high frequency signal.

In order to overcome the above problems, it is an object of the present invention to provide an intermediate frequency processing apparatus for improving the sensitivity.

Another object of the present invention is to provide an intermediate frequency processing apparatus having a wide automatic gain control range.

In order to achieve the above objects, the intermediate frequency processing apparatus according to the present invention includes a tuner for outputting a received high frequency broadcast signal as an intermediate frequency signal, wherein the intermediate frequency signal is amplified with a predetermined amplification gain having a minimum value and a maximum value. A television broadcast signal processing system for outputting a video signal afterwards, comprising: an intermediate frequency amplifying means for amplifying an intermediate frequency signal output from the tuner within the set amplification gain range having a minimum value and a maximum value greater than the minimum value and the maximum value. ; Detection means for detecting an amplified intermediate frequency signal outputted from the intermediate frequency amplifying means and outputting it as an image signal; Video signal amplifying means for amplifying the video signal output from the detecting means; First automatic gain adjusting means for detecting the level of the synchronization signal loaded on said video signal amplifying means and adjusting the gain of said intermediate frequency amplifying means; And second automatic gain control means for detecting the level of the synchronization signal loaded on the video signal amplification means and operating only when the level of the synchronization signal is low to adjust the gain of the video signal amplification means.

3 is a circuit diagram according to an embodiment of an intermediate frequency processing system according to the present invention.

According to FIG. 3, the image intermediate frequency amplification unit 100 is composed of three stages of amplifiers 101-103, an input terminal of which is connected to an output terminal of a tuner (not shown), and an output terminal of which is configured as a multiplier. It is connected to the input of the detector 200.

The input terminal of the image signal amplifier 300 is connected to the output terminal of the detector 200, and the output terminal is connected to the input terminal of the signal processor (not shown) and the input terminals of the first and second automatic gain control units 400 and 500, respectively. do.

The control signal output terminal of the first automatic gain adjusting unit 400 is connected to the control signal input terminal of the first to third amplifiers 101 to 103, and the control signal output terminal of the second automatic gain adjusting unit 500 is used to amplify the image signal. It is connected to the control signal input terminal of the unit 300.

Next, the operation of FIG. 3 will be described.

In order to facilitate understanding of the present invention, an intermediate frequency (IF) signal will be described by dividing it into a large case and a small case.

(1) IF signal is small

After the intermediate frequency amplifier 100 amplifies the IF signal, the amplified IF signal is output through the detector 200. Here, the amplification gain range of the intermediate frequency amplification unit 100 is set differently from the minimum value and the maximum value, even though they are the same as the conventional amplification gain range. That is, the minimum value is higher than the conventional minimum value by a predetermined value, and the maximum value is increased by the higher predetermined value. For example, in the prior art, the present invention is set to have an amplification gain range of 60 dB as -5 dB to 55 dB, provided that it is -10 dB to 50 dB.

If the IF signal is small, since the level of the synchronization signal of the video signal output from the video signal amplifier 300 is high as shown in FIG. 4B, the second automatic gain control unit 500 does not operate.

As shown in FIG. 4A, when the standard video signal output from the video signal amplifier 300 has 2Vp-p, the sync signal level SYNC TIP is maintained at 2.3V.

Therefore, only the first automatic gain adjusting unit 400 operates to set the gain of the intermediate frequency amplifier 100 to the maximum.

That is, when the input IF signal is very small, only the first automatic gain control unit 400 operates to maximize the gain of the image signal intermediate frequency amplifier 100 so that the conventional amplification of the intermediate frequency amplifier 100 is performed. The image sensitivity is improved because it has a maximum value greater than the maximum value of gain.

(2) IF signal is large

When a large IF signal is input, it is amplified by the intermediate frequency amplifier 100 and input through the detector 200 to the image signal amplifier 300. At this time, the level of the synchronization signal of the image signal is shown in FIG. Since it is lowered together, both the first and second automatic gain control units 400 and 500 are operated at the same time.

The first automatic gain control unit 400 reduces the gain of the image signal intermediate frequency amplifier 100 to a minimum, and at the same time, the second automatic gain control unit 500 also lowers the gain of the amplifier 300.

In this case, even if an IF signal larger than the gain of the second automatic gain control unit 500 is input than the conventional first automatic gain control unit 400 operates, the output can be output as an image signal having a constant output. The adjustment range is widened. Therefore, when the IF signal is large, it has a wider automatic gain adjustment range.

As described above, the intermediate frequency processing apparatus according to the present invention has an effect of improving sensitivity and having a wide automatic gain adjustment range.

Claims (2)

A television broadcast signal processing system comprising a tuner for outputting a received high frequency broadcast signal as an intermediate frequency signal, wherein the intermediate frequency signal is amplified with a predetermined amplification gain having a minimum value and a maximum value and then output as an image signal. Intermediate frequency amplifying means for amplifying the intermediate frequency signal outputted from the predetermined amplification gain range having the minimum value and the maximum value and the predetermined minimum value and the maximum value; Detection means for detecting an amplified intermediate frequency signal outputted from the intermediate frequency amplifying means and outputting it as an image signal; Video signal amplifying means for amplifying the video signal output from the detecting means; First automatic gain adjusting means for detecting the level of the synchronization signal loaded on said video signal amplifying means and adjusting the gain of said intermediate frequency amplifying means; And second automatic gain control means for detecting the level of the synchronization signal loaded on the video signal amplification means and operating only when the level of the synchronization signal is low to adjust the gain of the video signal amplification means. Device. The intermediate frequency processing apparatus according to claim 1, wherein the first and second automatic gain adjusting means controls the gains of the intermediate frequency amplifying means and the image signal amplifying means to be low when the intermediate frequency signal is large. .