JPH0289490A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To effectively execute an automatic gain control by providing with a variable gain amplifier, an arithmetic circuit and a control circuit, and decreasing the fluctuation of an output when a burst gain position dislocates with respect to a burst. CONSTITUTION:A chrominance signal is amplified by a variable amplifier 1. The output signal of the variable amplifier 1 is inputted to a burst gate circuit 13, and the burst in a fixed period is extracted. For the burst signal, the square root of a mean square is calculated by a circuit 2, which detects a square root rms value of the mean square, and sent to a control circuit 3 consisting of a subtracting circuit 5 and an integrating circuit 4. Since the control circuit 3 integrates the difference between the output of an rms circuit 2 and a reference level, and controls the variable gain amplifier 1, as a result, the amplitude of the output of the variable gain amplifier 1 is controlled so that the rms of the burst level may be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applied to an ACC (Automatic chroma
The present invention relates to an automatic gain control device such as a control1) circuit.

2. Description of the Related Art A conventional ACC circuit will be described with reference to FIG. The carrier color signal is amplified by variable gain amplifier 20. The output signal of the variable gain amplifier 20 is sent to the burst gate circuit 21
is input and a burst of a certain period is extracted. This burst signal is averaged by an averaging circuit 22, and a control circuit 23 controls the gain of the variable gain amplifier 20 so that the level of the burst obtained at the output of the averaging circuit 22 is constant. As a result, the output level of variable gain amplifier 20 is kept constant. Examples like this can be found in the Televisiron Engineering Handbook pp.
989.

Problem to be Solved by the Invention However, in the above configuration, when the color signal has a narrow band like the playback signal of a video tape recorder, the envelope of the burst signal is not a rectangular wave but is distorted, so the position of the burst gate is different from the burst. When there is a deviation, the output of the averaging circuit 22 cannot calculate the correct amplitude of the burst, resulting in a drawback that the output level of the ACC fluctuates.

Means for Solving the Problems In order to solve the above problems, an automatic gain control device of the present invention includes a variable gain amplifier that controls the gain of a color signal to which a burst signal is added, and a variable gain amplifier that controls the gain of the burst signal from the output of the variable gain amplifier. rms of the amplitude for a certain period (root mean
It is comprised of an arithmetic circuit that calculates a 5quare (square root of the mean square) value, and a control circuit that controls the gain of the variable gain amplifier according to the output of the arithmetic circuit.

Effect of the Invention With the above-described configuration, the present invention can reduce fluctuations in output when the position of the burst gate shifts.

Embodiments The automatic gain control device of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. The chrominance signal is amplified by a variable gain amplifier 1. The output signal of the variable gain amplifier 1 is input to a burst gate circuit 13, and a burst of a certain period is extracted. The root mean square of this burst signal is calculated by an rms circuit 2 and sent to a control circuit 3 consisting of a subtraction circuit 5 and an integration circuit 4. The control circuit integrates the difference between the output of the rms circuit and the reference level to control the variable gain amplifier 1, so that the amplitude of the output of the variable gain amplifier 1 is controlled so that the rms of the burst level is constant. .

Next, the effect of controlling the rms value to be constant will be explained with reference to FIG.

FIG. 2(a) shows the waveform of a burst signal subjected to band limitation, such as a playback signal of a video tape recorder.

If the color signal is a color difference signal, it indicates the amplitude of the burst signal,
In the case of a carrier color signal, it shows the envelope of the burst signal. This signal is extracted with a burst gate pulse of width T shown in (b), and the average absolute value during that period is rm in (C).
The s value is (d). In both cases, the horizontal axis indicates the position of the burst gate with respect to the burst, and time 1=0 is when the center of the burst gate pulse and the center of the burst coincide. In other words, (C) and (d) respectively show the output of the average value with respect to the deviation of the burst gate. As can be seen from (C) and (d), the change in output due to burst gate deviation is smaller in rmS. For example, the output when shifted is 0.8, rms in absolute value average
Then, it is 0.91. Therefore, an automatic gain control device using rms can reduce fluctuations in output due to burst gate deviation.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram showing the configuration of a second embodiment of the present invention. This embodiment is an example of the configuration of an automatic gain control device in which the color signals are two color difference signals, an RY signal and a BY signal. The R-Y signal and the B-Y signal are amplified by a variable gain amplifier 12, and respective bursts are extracted by a burst gate circuit 14 and input to an rms circuit 11. rms circuit 11, 2 east circuits 9 and 10, adder circuit 8
, an averaging circuit 7, and a square root circuit 6. Since the R-Y signal and the B-Y signal are orthogonal, the 2 east circuits 9 and 10
By squaring the squared value and adding it in the adding circuit 8, a value of the square of the burst amplitude is obtained. Therefore, by averaging this output using the averaging circuit 7 and taking the square root using the square root circuit 6, the rms value of the burst can be calculated.

2 East circuits 9 and 10 and square root circuit 6 are ROM (read only me) when digitally processing this embodiment.
m.

ry) table. If this output is given to the control circuit 3 as in the first embodiment and the variable gain amplifier 12 is controlled, the amplitude of the output color difference signal can be made constant. Further, in this embodiment, the burst gate circuit 14 is placed in front of the two east circuits 9 and 10, but if the averaging circuit 7 averages only the burst gate period, the burst gate circuit may be omitted.

Effects of the Invention As described above, by using the automatic gain control device of the present invention, it is possible to construct an automatic gain control device in which output gain fluctuation is small when the position of the burst gate deviates from the burst.

Furthermore, the present invention can be applied both when the input color signal is a carrier color signal and when it is a color difference signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention, FIGS. 2(a) and (b) are waveform diagrams showing the waveforms of burst and burst gate pulses, respectively, and FIG. ),
(d) is a graph showing the average absolute value and rms value of bursts, FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention, and FIG. 4 is a block diagram showing the configuration of the conventional example. It is a diagram. 1...variable gain amplifier, 2...r
ms circuit, 4...Integrator circuit, 5...
・Subtraction circuit, 6...Square root circuit, 7.
...Average circuit, 8...Addition circuit, 9
, 10... Square circuit. Name of agent: Patent attorney Shigetaka Awano (1 person)

Claims (5)

[Claims] (1) A variable gain amplifier that controls the gain of the chrominance signal to which the burst signal is added;
An automatic gain control device comprising: an arithmetic circuit that calculates a square root of the mean square value; and a control circuit that controls the gain of the variable gain amplifier according to the output of the arithmetic circuit. (2) The automatic gain control device according to claim 1, wherein the control circuit comprises a subtraction circuit that calculates the difference between the output of the arithmetic circuit and the reference value, and an integration circuit that integrates the output of the subtraction circuit. (3) The automatic gain control device according to claim (1), wherein the color signal is a carrier color signal. (4) The automatic gain control device according to claim 1, wherein the color signal is a color difference signal. (5) The arithmetic circuit includes two squaring circuits that square the levels of the burst signals of the two color difference signals, an addition circuit that calculates the sum of the two squaring circuits, and an average of the output of the addition circuit for a certain period of time. 2. The automatic gain control device according to claim 1, comprising: an averaging circuit for calculating the square root of the output of the averaging circuit; and a square root circuit for calculating the square root of the output of the averaging circuit.