JP2001095006A - Acc circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ACC circuit characterized by having effect of not greatly enhancing noise greatly, even if the burst level becomes small. SOLUTION: In this ACC circuit, there are provided a first multiplication circuit 101, second multiplication circuit 102, first low-pass filter circuit 103, burst-level detection circuit 104, comparison circuit 105, second low-pass filter circuit 106, clipping circuit 107 and APC(auto phase control) circuit 108.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ACC circuit for providing an effect that noise is not greatly increased even when a burst level is reduced.

[0002]

2. Description of the Related Art In recent years, with the spread of large-screen television receivers, ACC circuits have been required to have high image quality, and have been regarded as one of the high image quality circuits.

Hereinafter, an example of the above-described conventional ACC circuit will be described with reference to the drawings.

FIG. 2 shows a block diagram of an ACC circuit proposed in Japanese Patent Application Laid-Open No. Hei 6-253324, which will be described below. Bandpass not shown
The carrier chrominance signal from which the luminance component has been removed from the composite signal by the filter is amplified by the carrier chrominance signal amplification circuit 101. Next, one of the carrier color signals supplied to the next-stage ACC amplifier circuit 200 and amplified by the first ACC amplifier circuit 201 or the second ACC amplifier circuit 202 is
The signal is transmitted to the burst amplifier 103 and the chroma amplifier 104. Here, the first ACC amplifier circuit 201 has a large gain and a narrow input dynamic range, and the second ACC amplifier circuit 202 has a small gain and a wide input dynamic range.

The output of the first ACC amplification circuit 201 is selected by the ACC amplification switching circuit 203 at the next stage in the state of the small input color burst level, and in the state of the large input color burst level, the second ACC amplification circuit 201 has the small gain. Of the ACC amplifying circuit 202 is selected. The chroma amplifying circuit 104 separates and amplifies only the chroma signal of the carrier chrominance signal, and performs RY, BY demodulation and G in the next stage.
-Input to the Y matrix 109.

The burst amplification circuit 103 extracts and amplifies only the color burst from the carrier chrominance signal and transmits it to the ACC detection circuit 105. The ACC detection circuit 105 generates an ACC control voltage that is inversely proportional to the amplitude of the color burst, and controls the ACC amplification circuit 200. This ACC control voltage is applied to the first and second ACC amplifier circuits 20 respectively.
1, ACC amplification switching circuit 203, and controls the gains of the first and second ACC amplification circuits 201, 202, and the first ACC amplification circuit 201 or Second amplifier circuit 202
Is switched and output.

The ACC-controlled color burst output is supplied to an ACC detection circuit 110 and a killer detection circuit 111.
Is input to Reference subcarrier generation circuit (VCXO) 10
6 generates a 3.58 MHz reference sub-carrier signal, which is converted into a reference sub-carrier signal having an appropriate phase relationship by 90 ° phase amplification and hue control 107. This reference subcarrier signal is further amplified by 90 ° phase amplification and matrix 108 and input to the other ends of APC detection circuit 110 and killer detection circuit 111, respectively.

[0008] The APC detection circuit 110 performs phase detection of the color burst, 90 ° phase amplification, and the reference subcarrier signal from the matrix 108. With this phase detection output, the reference subcarrier signal of the VCXO 106 is pulled into the frequency of the color burst of the carrier chrominance signal. The killer detection circuit 111 determines whether to receive a color broadcast or a black and white broadcast based on the presence or absence of a color burst.

At the time of black and white broadcast reception, the chroma amplification circuit 104
Stop the operation of. The 90 ° phase amplification and the reference subcarrier signal from the matrix 108 are input to the RY, BY demodulation and GY matrix 108, where they are phase-detected with the chroma signal from the chroma amplifier circuit 104, and the color difference signal R- Y, GY, and BY are output. Considering the above-described ACC control state of the color signal reproducing circuit, for example, when the color burst level of the carrier color signal is low, it is handled by the first ACC amplifier circuit 201, and when the color burst level becomes high, Switching is performed by the ACC increase switching circuit 203 so as to be handled by the ACC amplification circuit 202 of No. 2. Compared to the conventional ACC amplifier circuit, the first ACC amplifier circuit 201
Reduces the rate of change from amplifier to attenuator,
The S / N of the entire C amplification circuit 200 is hardly deteriorated.

[0010]

However, the above configuration has the following problems. Although the above circuit certainly has an S / N improvement effect, it is
This is effective in the case where noise is output by the C amplification circuit 200 itself (in the case of an analog circuit or the like), and a large effect cannot be expected when an ACC circuit is formed by digital signal processing that does not generate noise.

[0011]

In order to solve the above-mentioned problems, an ACC circuit according to the present invention has a configuration in which an ACC control voltage can be clipped to change ACC characteristics.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is an ACC circuit characterized by the effect that the noise is hardly increased even if the burst level is reduced.
This has the effect of allowing the ACC characteristic to be changed by clipping the ACC control voltage.

According to a second aspect of the present invention, there is provided a first multiplying circuit for multiplying an input chroma signal and an output signal from a clip circuit described later, and an output signal from the first multiplying circuit. A second multiplication circuit for multiplying a sine wave signal from an APC circuit to be described later, a first low-pass filter circuit for reducing a high-frequency component of an output signal from the second multiplication circuit, and the first low-pass filter Among output signals from the circuit, a burst level detection circuit that outputs a signal level during a burst period, a comparison circuit that compares an output signal from the burst level detection circuit with reference data and outputs the level difference, A second low-pass filter circuit for reducing a high-frequency component of an output signal from the comparison circuit;
A clipping circuit for clipping the High-side level of the output signal from the low-pass filter circuit, and an output signal from the first multiplication circuit, and a SIN wave locked to a subcarrier of the input chroma signal. An ACC circuit comprising an APC (Auto Phase Control) circuit for outputting the signal, and characterized in that the noise is not greatly increased even when the burst level is reduced. The ACC characteristic can be changed by clipping the ACC control voltage. It has the effect of doing so.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 shows an ACC according to an embodiment of the present invention.
FIG. 2 is a block diagram of a circuit. In FIG. 1, reference numeral 101 denotes a multiplication circuit for multiplying an input chroma signal 109 by an output signal from a clip circuit 107 described later, and 102 denotes an output signal from the multiplication circuit 101 and a sine wave signal 110 from an APC circuit 108 described later. Is a low-pass filter circuit that drops the high-frequency component of the output signal from the multiplication circuit 102;
The Y signal 113 is output.

Reference numeral 104 denotes a burst level detection circuit for outputting a signal level during a burst period in the output signal from the low-pass filter circuit 103. Reference numeral 105 denotes a comparison between the output signal from the burst level detection circuit 104 and the reference data 112. A comparison circuit that outputs the level difference, 106 is a low-pass filter circuit that drops high-frequency components of an output signal from the comparison circuit 105, and 107 is a low-pass filter circuit 1.
A clipping circuit that clips the High-side level of the output signal from the control signal 06 and controls the clipping level by the control data 111. A clipping circuit 108 receives the output signal from the multiplication circuit 101 and outputs a subcarrier of the input chroma signal 109. APC (Auto Phase Control) circuit that outputs a sine wave signal 110 locked to the APC.

The operation of the ACC circuit configured as described above will be described below with reference to FIGS.

FIG. 3 is an operation explanatory diagram for explaining the operation of the present embodiment, and is a diagram showing ACC characteristics. The APC circuit 108 is a circuit that outputs a sine wave signal 110 locked to a subcarrier of the chroma signal 109. Multiplication circuits 101, 102, low-pass filter circuits 103, 1
06, burst level detection circuit 104, comparison circuit 10
5. The loop circuit constituted by the clip circuit 107 is a so-called ACC (AutoColor Control).
This circuit operates to keep the subcarrier level of the input chroma signal 109 (actually, the output level of the multiplication circuit 101) constant, but this can be changed by the reference data 112. The characteristics are shown in FIG. 3, where the horizontal axis represents the input level of the chroma signal 109 and the vertical axis represents the B-
The output level of the Y signal 113 is shown, and the chroma signal 1
It can be seen that the output level of the output BY signal is kept constant even when the level of 09 changes.

However, when the input level is considerably reduced, the output level is also reduced in some cases, because the gain of the multiplication circuit 101 is in the MAX state. When the chroma signal 109 decreases, the gain of the multiplication circuit 101 increases.
The noise existing in the image 9 itself is greatly emphasized, and the S / N feeling of the color is deteriorated.

As described above, when the level of the chroma signal 109 is low, the control signal from the clipping circuit 107 increases in order to increase the gain of the multiplication circuit 101.
At this time, if the control data for controlling the clipping circuit 107 is reduced, the output data is clipped, so that small data output from the clipping circuit 107 is output.

Then, the level of the output signal of the multiplication circuit 101 decreases, and as a result, A
Take CC characteristics. That is, when the level of the chroma signal 109 is low, the level of the color difference signal to be output can be reduced, so that color noise is not emphasized more than necessary. Also, when the control data 111 is moved, FIG.
Since the ACC characteristics can be changed as indicated by the solid line and the dotted line, the characteristics can be changed depending on the input signal, and the ACC characteristics optimal for the signal can be created.

[0021]

As described above, according to the present invention, by providing a configuration in which the ACC characteristic can be changed by clipping the ACC control voltage, the noise is not greatly emphasized even when the burst level is reduced. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ACC circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a conventional ACC circuit.

FIG. 3 is an explanatory diagram of an operation of the ACC circuit according to the first embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 101 first multiplication circuit 102 second multiplication circuit 103 first low-pass filter circuit 104 burst level detection circuit 105 comparison circuit 106 second low-pass filter circuit 107 clip circuit 108 APC (Auto Phase Contro)
l) Circuit 109 Chroma signal 110 SIN wave signal 111 Control data 112 Reference data 113 BY signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisao Morita 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 72) Inventor Hitoshi Ando 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. KE03 KF03 KG01

Claims (3)

[Claims] 1. An ACC circuit characterized in that noise is not greatly emphasized even when a burst level is reduced. 2. A first multiplying circuit for multiplying an input chroma signal by an output signal from a clip circuit described later;
A second multiplication circuit for multiplying an output signal from the first multiplication circuit and a sine wave signal from an APC circuit described later;
A first low-pass filter circuit for reducing a high-frequency component of an output signal from the second multiplying circuit; and a burst level detection for outputting a signal level during a burst period among output signals from the first low-pass filter circuit. Circuit, a comparison circuit that compares the output signal from the burst level detection circuit with reference data and outputs the level difference, and a second low-pass filter circuit that drops a high-frequency component of the output signal from the comparison circuit. A clipping circuit for clipping a High-side level of an output signal from the second low-pass filter circuit, and an output signal from the first multiplication circuit, and locking to a subcarrier of the input chroma signal. APC (Auto Pha) that outputs a SIN wave
(ACC) circuit, and has an effect that noise is not greatly emphasized even when the burst level is reduced. 3. The ACC according to claim 2, wherein the clip level of the clip circuit is variable.
circuit.