KR940010614B1 - Image intermediate frequency signal processing unit - Google Patents

Abstract

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Description

Image Intermediate Frequency Processing Circuit

1 is a block diagram showing an image intermediate frequency processing circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a balanced input amplifier used in the image intermediate frequency processing circuit of FIG. 1. FIG.

FIG. 3 is an explanatory diagram illustrating band characteristics in the main portion of FIG. 1. FIG.

4 is a block diagram showing a conventional image intermediate frequency processing circuit.

FIG. 5 is an explanatory diagram illustrating band characteristics in the main portion of FIG. 4. FIG.

* Explanation of symbols for main parts of the drawings

1: antenna 2: tuner

3: first filter (PSF-1 circuit) 4: second filter (PSF-2 circuit)

5: first image intermediate frequency amplifier circuit (VIF-1 circuit)

6: tank circuit 7: first detection circuit (DFT-1 circuit)

8: output terminal 9: AGC circuit

10: second image intermediate frequency amplifier circuit (VIF-2 circuit)

11: second detection circuit (DET-2 circuit)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to video intermediate frequency processing circuits used in TV receivers, video tape recorders, and the like. In particular, high bandwidth of video signal components, in-phase distortion improvement of color signal components, and buzz reduction of audio signal components are provided. An image intermediate frequency processing circuit is designed.

Background Art Conventionally, in an inter-carrier system TV receiver, an image carrier component, a color carrier component and an audio carrier component frequency-converted by a tuner are amplified by one intermediate frequency processing circuit having one kind of common pass band. And detection was carried out. Therefore, in the intercarrier method, the intermediate frequency processing circuit can be simplified, but there is a drawback that interference between the video signal and the audio signal is unlikely to occur. As a countermeasure, an audio trap corresponding to the beat frequency between video and audio carriers is provided in order to lower the audio signal level than the video signal level and to prevent the audio signal from being mixed into the video. 4 is a block diagram showing a conventional image intermediate frequency processing circuit. In this figure, the TV signal from the antenna 21 is converted into an intermediate frequency signal (hereinafter referred to as IF signal) by the tuner 22, and then an elastic surface and a filter having a predetermined band characteristic (Picture Surface acoustic wave Filter). The intermediate frequency amplifier circuit (hereinafter referred to as VIF circuit) 24 through the PSF circuit (23). The IF amplified signal from the VIF circuit 24 is supplied to an image detection circuit 26 (hereinafter referred to as a DET circuit) 26 having a tank circuit 25 for synchronous detection, and an output terminal 28. Obtain a synchronously detected image detection output, that is, a composite image signal. Between the DET circuit 26 and the VIF circuit 24, the AGC voltage proportional to the amplitude of the IF signal is fed back to the VIF circuit 24 based on the image detection output, so that the VIF circuit becomes constant. An AGC circuit 27 for controlling the gain of the circuit 24 is provided. The tank circuit 27 is composed of a parallel circuit of an inductance element and a capacitor, and is inserted between the power supply terminal + Vcc and the DET circuit 26.

In the above configuration, the band characteristic of the PSF circuit 23 is as shown in FIG. 5A. That is, the response of the video carrier component P and the color carrier component C is 6 dB lower than the response in the pass band, and the response of the audio carrier component S is reduced by about 18 dB. As for the band characteristic of the composite video output obtained by the output terminal 28, as shown in FIG. 5B, the response of the color component C is decreasing. When the composite image output passes through a color component band pass filter (not shown) having a band characteristic as shown in FIG. 5C, the color component C is separated. In Fig. 5C, the diagonal line indicates the cross color component (high band component of the luminance signal, etc.) entering the color band. 5A, B, and C, the horizontal axis represents the relative frequency relationship between the video carrier component P, the color carrier component C, and the audio carrier component S. In FIG.

The conventional circuit has the following problems.

First, due to the 6 dB reduction of the color carrier identification, the video band is insufficient and the bandwidth of the image carrier component is reduced. Second, since the audio carrier component is degraded by about 18 dB, the buzz sound increases due to the incorporation of the video carrier component, and in particular, the sound quality during de-tuning is deteriorated. Third, the color component and the carrier bits of the voice enter the video band, resulting in color / audio bit interference. Fourth, the in-phase distortion of the color component is large, and the cross color component in the color band is large.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image intermediate frequency processing circuit which aims at high bandwidth of image components, reduction of audio buzz, reduction of color / audio bit interference, improvement of in-phase distortion of color components, and improvement of cross color disturbance.

An image intermediate frequency processing circuit of the present invention includes a first band having a first band characteristic of a wide band through which a filter for selectively passing an intermediate frequency signal frequency-converted by a tuner passes an image carrier component and a color carrier component of the intermediate frequency signal. And a second filter having a predetermined second band characteristic for passing the filter and the color carrier component and the voice carrier component of the intermediate frequency signal, wherein a detection circuit for detecting the intermediate frequency signal passing through the filter provides a first filter. A first detection circuit for detecting the video carrier component of the intermediate frequency signal that has passed, and a second detection circuit for detecting the color carrier component and the audio carrier component of the intermediate frequency signal that has passed through the second filter; It is characterized by.

1 is a block diagram showing a first embodiment of an image intermediate frequency processing circuit according to the present invention.

In this figure, the received TV signal from the antenna 1 is frequency-converted by the tuner 2 and becomes an IF signal so that an elastic surface for image processing and a first filter of a filter (hereinafter referred to as a PSF-1 circuit) ( 3) and a second filter (hereinafter referred to as a PSF-2 circuit) 4 which is a surface acoustic wave filter for color and sound processing. The PSF-1 circuit 3 and the PSF-2 circuit 4, respectively, show the first-band characteristics and the IF of the broadband to pass the image carrier component and the color carrier component of the IF signal as shown in FIGS. 3A and 3B. And has a predetermined second band characteristic for passing the color carrier component and the voice carrier component of the signal. The IF signal passing through the PSF-1 circuit 3 passes through a first intermediate frequency amplification circuit (hereinafter referred to as a VIF-1 circuit) 5 and has a first detection having a tank circuit 6 for synchronous detection. A circuit (hereinafter referred to as a DET-1 circuit) 7 is entered, and the output terminal 8 obtains an image detection output (synthetic video output). Between the DET-1 circuit 7 and the VIF-1 circuit 5, an AGC voltage proportional to the amplitude of the IF signal is generated and fed back to the VIF-1 circuit 5 to control the gain to be constant. The AGC circuit 9 is provided. On the other hand, the IF signal passing through the PSF-2 circuit 4 passes through a second video intermediate frequency amplifier circuit (hereinafter referred to as a VIF-2 circuit) 10 and is referred to as a second detection circuit (hereinafter referred to as a DET-2 circuit). (11), the output terminal 12 obtains the detection output of the color component and the audio component. The AGC voltage of the AGC circuit 9 is also used to control the gain of the VIF-2 circuit 10.

The VIF-1 circuit 5 and the VIF-2 circuit 10 are both composed of a balanced (balanced) input amplifier as shown in FIG. 2A. The amplifier of FIG. 2A includes two transistors Q1 and Q2 forming a differential band, a transistor Q3 forming a current source connected to a common emitter of transistors Q1 and Q2, and a transistor Q1. And resistors R1 and R2 connected between each collector of Q2 and the power supply terminal 16, and resistors R3 connected between the emitter of the transistor Q3 and the reference potential point. The DC power supply + Vcc is supplied to the power supply terminal 16. Signals from the PSF-1 circuit 3 or the PSF-2 circuit 4 are input to the input terminals 13 and 14 connected to the bases of the transistors Q1 and Q2, and connected to the base of the transistor Q3. The AGC voltage is input to the terminal 15, and an amplified signal is obtained from the output terminals 17 and 18 connected to the collectors of the transistors Q1 and Q2. The signal amplified in this way is supplied to the DET-1 circuit 7 or the DET-2 circuit 11 of the next stage. Alternatively, a plurality of amplifier circuits as shown in FIG. 2A may be combined in multiple stages to obtain an amplified signal and then supplied to the DET-1 circuit 7 or the DET-2 circuit 11 in the next stage.

By using such a balanced input amplifier, when the input signal is applied between the bases of the two transistors Q1 and Q2, the output signal becomes the transistors Q1 and Q2 due to the difference in the collector current of the transistors Q1 and Q2. Since it appears as a difference voltage between the collector outputs of, the noises are erased from the collector outputs even if noise is a chip from the outside, and noise does not appear in the output signal. The gain can be easily controlled by applying an AGC voltage to the base of the transistor Q3 and changing the collector current of the transistors Q1 and Q2. Although the circuit of Fig. 2A has been described with respect to the balanced input type by the two transistors Q1 and Q2, a double balanced amplifier using four transistors may be used.

The unbalanced input amplifier has an amplifier configuration including transistors Q4 and resistors R4 and R5 as shown in FIG. 2B. Here, an emitter grounding type amplifier is shown. The gain control is performed by supplying an input signal to the base of the transistor Q4 and taking an output signal at the collector, and controlling the collector current by applying an AGC voltage to the base. However, there is a drawback in that the rejection performance against external noise is poor in its construction.

3A to 3D are graphs showing band characteristics in respective circuit portions of FIG. In each graph, the vertical axis indicates the response (dB), and the horizontal axis indicates the relative relationship between the frequencies of the image carrier component P, the color carrier component C, and the audio carrier component S (MHz). FIG. 3A shows the image band characteristics of the PSF-1 circuit 3, where the PSF-1 circuit 1 has a frequency of the color carrier component C as compared to that of the PSF circuit of the conventional apparatus shown in FIG. It has a first-band characteristic of broadband, which extends to and the voice carrier S becomes zero (zero) response. 3B shows the band characteristics of the PSF-2 circuit 4, wherein the PSF-2 circuit 4 has a narrow band second band characteristic having sufficient response for the color carrier component C and the voice carrier component S. FIG. Has 3C is an output response of the DET-1 circuit 7 and is widened in accordance with the characteristic of (a). FIG. 3D is an output response of the DET-2 circuit 11, and an output response as indicated by a dotted line A is obtained in correspondence with the characteristic of (b). In FIG. 3D, the solid line B is the color band component, the dashed-dot line c is the voice band component, and the diagonal line portion is the cross color component (interference component of the color signal with respect to the luminance signal) that enters the color band.

In the above configuration, the PSF-1 circuit 3 and the PSF-1 circuit 4 each have independent band characteristics, and the positive component interferes with each other by separating and processing the video carrier component and the color / audio carrier component. I can alleviate it. As a result, it is possible to realize the widening of the video component, the high quality of the color (reduction of the image distortion and the cross color disturbance), and the reduction of the buzz component incorporated into the audio component.

In addition, as shown in FIG. 2, by using the VIF stage input method as a balanced input type for both the image processing stage and the color / audio processing stage, it is possible to improve the interference rejection performance against external interference signals. In addition, by controlling the video processing stage and the color / audio processing stage with the same AGC voltage, the same AGC operation can be performed and the disadvantage of the separation processing is not generated.

Therefore, according to the present invention, the image quality such as a TV receiver and the like can be improved.

Moreover, although the elastic surface and the filter are used in the said Example, in this invention, it is not limited to this, What is necessary is just a bandpass filter which has the same band characteristic.

Therefore, the present invention can be modified in various ways without departing from the gist of the invention unless it is limited to the above embodiments.

Claims (4)

An image intermediate frequency processing circuit for processing an intermediate frequency signal frequency-converted by a tuner, comprising: a first filter (3) having a first band characteristic of a wide band through which an image carrier component and a color carrier component of the intermediate frequency signal pass; A second filter 4 having a predetermined second band characteristic for passing the color carrier component and the voice carrier component of the intermediate frequency signal, the image carrier component of the intermediate frequency signal passing through the first filter 3, and A first image intermediate frequency amplification circuit 5 for amplifying a color carrier component, and a second image intermediate frequency amplification for amplifying the color carrier component and the voice carrier component of the intermediate frequency signal passed through the second filter 4. The first detection circuit 7 for detecting the image carrier component of the intermediate frequency signal passed through the first filter 3 and the intermediate frequency signal passing through the second filter 4 The color carrier component And a second detection circuit (11) for detecting the voice carrier component and an AGC signal in response to the detection output of one of the first and second detection circuits (7, 11). And an AGC circuit (9) for feeding back to each of the first and second image intermediate frequency amplification circuits (5,10). 2. The image intermediate frequency processing circuit according to claim 1, wherein at least one of said first and second filters (3,4) comprises an elastic surface and a filter. 2. An image intermediate frequency processing circuit according to claim 1, wherein at least one of said first and second image intermediate frequency amplifier circuits (5,10) comprises a balanced (balanced) input amplifier. 4. The balanced input amplifier of claim 3, wherein the balanced input amplifier comprises a first and a second transistor (Q1, Q2) in which each emitter is connected in common, and a collector and a direct current of the first and second transistors (Q1, Q2). The first and second resistors R1 and R2 connected between the power supply, the third transistor Q3 connected between the common connection emitter of the first and second transistors Q1 and Q2 and the reference potential point, and And a third resistor R3 connected in series with the third transistor Q3, and an intermediate frequency signal is applied to the bases of the first and second transistors Q1 and Q2, and the third transistor ( The AGC voltage from the AGC circuit (9) is applied to the base of Q3), and the amplified signal is taken out from the collectors of the first and second transistors (Q1, Q2).

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