JPH05300429A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To reduce the number of the external parts and pins of an IC in the case of making into the IC by adjusting the chroma signal level of a slave picture corresponding to the level detecting output of a chroma signal for master picture. CONSTITUTION:For a video signal for master picture from an input terminal 1, only the chroma signal component is extracted by a BPF 2 and impressed to a first VCA(voltage controlled amplifier circuit) 16. The level of an output signal from the VCA 16 is detected by a level detection circuit 5 and corresponding to the detecting output, the gain of the VCA 16 is controlled. Therefore, the chroma signal for master picture at a fixed level is obtained at the output terminal of the VCA 16. A PLL circuit 11 generates output signals synchronized with input signals. On the other hand, the output signal of a memory 8 is D/A converted 9 and modulated by a modulation circuit 10, and the modulated chroma signal is impressed to a second VCA 17. Then, the gain relation of third and fourth VCA 18 and 19 is made inversely proportional. Thus, the gains of the VCA 16 and 17 can be exactly made inversely proportional. Therefore, no low-pass filter is required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing circuit of a dual screen TV (television) receiver capable of aligning chroma levels of a main screen and a sub screen.

[0002]

2. Description of the Related Art A so-called PIP (picture-in-picture) is known in which two image contents are displayed on one screen. As described in, for example, Japanese Patent Application Laid-Open No. 61-194983, the PIP is designed so that the image content of the main screen and the image content of the child screen are switched by a change-over switch to be displayed on one screen.

FIG. 2 is a circuit diagram showing such a dual-screen TV receiver. The parent-screen video signal from the input terminal (1) is
The chroma signal and the luminance signal are separated by the BPF (2) and the LPF (3), and the chroma signal is obtained at the output end of the BPF (2) and the luminance signal is obtained at the output end of the LPF (3). The chroma signal is supplied to the ACC amplifier circuit (4) and AC.
After being adjusted to a constant level by an ACC (automatic color control) circuit (6) composed of a C detection circuit (5), it is applied to a first mixing circuit (7) and mixed with a luminance signal from the LPF (3). It Therefore, at the output terminal of the first mixing circuit (7), a parent screen video signal having a constant chroma signal level can be obtained.

On the other hand, the output signal of the memory (8) in which the contents of the sub-picture video signal are stored is applied to the DA conversion circuit (9) and DA converted. Then, the D-A conversion circuit (9) generates BY and RY color difference signals, which are applied to the modulation circuit (10). The modulation circuit (10) has the A
The output signal (subcarrier) of the PLL circuit (11) synchronized with the output burst signal of the CC circuit (6) is applied,
This is modulated with the BY and RY color difference signals. Then, a chroma signal is generated at the output end of the modulation circuit (10) and mixed with the luminance signal from the DA conversion circuit (9) in the second mixing circuit (12). Therefore, a sub-screen video signal is obtained at the output terminal of the second mixing circuit (12). The switch circuit (13) is controlled so as to switch according to a switching control signal for inserting the child screen into the parent screen from the terminal (14). Therefore, according to the circuit of FIG. 2, a two-screen television image can be obtained at the output terminal (15).

By the way, in the circuit of FIG. 2, the chroma signal level of the parent screen is controlled to a constant level by the action of the ACC circuit (6). Therefore, the input signal level applied to the modulation circuit (10) is adjusted so that the chroma signal level of the child screen becomes equal to the above-mentioned constant level, and the chroma levels of both signals are aligned.

[0006]

However, in the circuit of FIG. 2, the video signal for the main screen is once separated into the luminance signal and the chroma signal in order to keep the chroma signal level of the main screen constant, and then mixed again. Therefore, there is a problem that a low-pass filter for separating the luminance signal is required. Since the low-pass filter requires a capacitor and an inductor, the low-pass filter is externally attached to the IC, which causes a problem of increasing the number of external components and pins of the IC.

[0007]

The present invention has been made in view of the above points, and is a video signal processing circuit for making the levels of the chroma signal for the main screen and the chroma signal for the sub screen coincide with each other. Variable gain amplifying circuit for adjusting the level of the chroma signal for use with the first and second variable gain amplifying circuits having the same configuration as the first variable gain amplifying circuit for adjusting the level of the chroma signal for the small screen
A variable gain amplifying circuit, a level detecting circuit that detects the output chroma signal level of the first variable gain amplifying circuit, and applies the detected output to the first variable gain amplifying circuit, and a detection output that is the reverse of the detecting output of the level detecting circuit. Create a proportional control signal,
And a control circuit for applying the control signal to the second variable gain amplifier circuit.

[0008]

According to the present invention, the gain of the second variable gain amplifier circuit to which the chroma signal for the child screen is applied is controlled according to the level detection output of the chroma signal for the parent screen. The chroma level of the screen will always follow the chroma level of the parent screen, and the chroma levels of both chroma signals can be aligned. At this time, the video signal for the main screen does not need to have a constant chroma level, so there is no need to separate and mix, and a low pass filter is not required. Further, according to the present invention, a gain control signal having an inversely proportional relationship can be accurately obtained from the control circuit, so that the same circuit can be used as the first and second VCAs, which is suitable for IC integration and an accurate chroma signal. Adjustment is possible.

[0009]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
(16) is a first VCA (voltage control amplifier circuit) whose gain α changes according to the detection output of the level detection circuit (5), (1
7) is a second VCA having the same circuit configuration as the first VCA (16), (18) has the same circuit configuration as the first VCA (16), and has a gain depending on the detection output of the level detection circuit (5). The third VCA in which α changes, (19) is the third VC
The fourth VCA that further increases the output signal of A (18) by β, (2
0) compares the output signal of the fourth VCA (19) with a reference signal and controls the gain of the fourth VCA (19) according to the difference between them, and (21) outputs from the second VCA (17). This is a mixing circuit that mixes the chroma signal for the sub-screen and the luminance signal from the DA conversion circuit (9) and outputs the video signal for the sub-screen.

In FIG. 1, the same circuit elements as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted. In the parent screen video signal from the input terminal (1), only the chroma signal component is extracted by the BPF (2) and applied to the first VCA (16). The output signal of the first VCA (16) is level-detected by the level detection circuit (5), and the gain of the first VCA (16) is controlled according to the detected output. Therefore, the chroma signal for the parent screen of a constant level is obtained at the output terminal of the first VCA (16). The PLL circuit (11) is composed of a phase comparator, a low pass filter and a VCO, and generates an output signal synchronized with the input signal. At that time,
The input signal to the PLL circuit (11) preferably has a constant level, and the first VCA (16) is necessary for this purpose.

On the other hand, the output signal of the memory (8) is DA
The conversion circuit (9) performs D-A conversion, the modulation circuit (10) modulates, and the modulated chroma signal is the second VCA (17).
Applied to. Now, assuming that the output current of the third VCA (18) in the non-controlled state is I ₀ , the output current in the controlled state is αI ₀ . Therefore, the output current of the fourth VCA (19) is βαI ₀
Becomes Here, the reference signal current of the comparison circuit (20) is set to K
If I ₀ (where K is less than 1), the comparison circuit (2
Β) αI ₀ = K · I ₀ (1) is established by the negative feedback action of ( ₀ ), and the gains of the third and fourth VCAs (18) and (19) are obtained from the equation (1). The relationship is β = K / α ………………………… (2). From the equation (2), it is understood that the gain relationships of the third and fourth VCAs (18) and (19) are inversely proportional. Therefore, by using the output control signal of the comparison circuit (20), the second
If the gain of VCA (17) is controlled, the first VCA (1
6) and the gain of the second VCA (17) can be made to have an exact inverse proportional relationship.

Therefore, the chroma signal level for the sub-screen is adjusted in accordance with the chroma signal level for the main screen, and a dual-screen television signal with a uniform chroma level is obtained at the output terminal (15). Be done. FIG. 3 shows the first to fourth VCAs (16), (17), (18) and (19) of FIG.
And a specific circuit diagram of the comparison circuit (20), in which a chroma signal for the parent screen is applied to the first input terminal (22),
A chroma signal for the child screen is applied to the second input terminal (23). Then, the level-adjusted chroma signal for the parent screen is obtained at the first output terminal (24), and the level-adjusted chroma signal for the child screen is obtained at the second output terminal (25). The description of the operation is omitted.

[0013]

As described above, according to the present invention, when the chroma signal level of the main screen and the chroma signal level of the sub screen are aligned, the chroma of the sub screen is detected according to the level detection output of the chroma signal for the main screen. Since I am adjusting the signal level,
It is not necessary to apply ACC to the chroma signal of the main screen, and the separation / mixing of the luminance signal is not necessary. Therefore, a low pass filter is not required. Therefore, when integrated into an IC, the number of external parts and pins of the IC can be reduced. Further according to the invention, the first
Since the gain control signals for the variable gain amplifying circuit and the second variable gain amplifying circuit can be provided in inverse proportion to each other, a general differential amplifier having the same configuration can be used. Therefore, the chroma signal levels of the parent and child can be accurately aligned from the small level to the large level.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a video signal processing circuit of the present invention.

FIG. 2 is a circuit diagram showing a conventional video signal processing circuit.

FIG. 3 is a circuit diagram showing a specific circuit example of FIG.

[Explanation of symbols]

 (5) Level detection circuit (16) First VCA (17) Second VCA (18) Third VCA (19) Fourth VCA (20) Comparison circuit

Claims (2)

[Claims] 1. A video signal processing circuit for matching the levels of a master-screen chroma signal and a child-screen chroma signal,
A first variable gain amplifying circuit for adjusting the level of the chroma signal for the main screen, and a second variable gain amplifying circuit for adjusting the level of the chroma signal for the small screen, which has the same configuration as the first variable gain amplifying circuit A level detection circuit that detects the output chroma signal level of the first variable gain amplification circuit and applies the detection output to the first variable gain amplification circuit; and a control signal that is inversely proportional to the detection output of the level detection circuit. And a control circuit for applying the control signal to the second variable gain amplifier circuit, and a video signal processing circuit. 2. The control circuit further comprises a third variable gain amplifier circuit whose gain changes according to the detection output of the level detection circuit, and a fourth variable gain amplifier circuit which further amplifies the output signal of the third variable gain amplifier circuit.
A variable gain amplifier circuit; and a comparator circuit that performs level comparison between the output signal of the fourth variable gain amplifier circuit and a reference signal, and controls the gain of the fourth variable gain amplifier circuit according to the difference between them. 2. The video signal processing circuit according to claim 1, wherein the gain control of the second variable gain amplifier circuit is performed according to the comparison output signal of the comparison circuit.