JPH10207424A - Agc circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the collapse of a high luminance part by controlling the amplitude of an input video signal to be within the dynamic range of an A/D conversion section. SOLUTION: Video signals of R, G and B from terminals 1a to 1c are amplified by amplifier sections 4a to 4c and impressed to voltage control amplifier sections 9a to 9c. A reference pulse generation section 5 generates a reference pulse having a required amplitude during blanking of the video signals, this reference pulse is synthesized into the video signal G or the like from the amplifier section 4b by a reference pulse synthesizing section 6, a peak is detected by a peak detecting section 7, this peak value is held by a peak holding circuit 8, the amplifying degrees of the voltage control amplifier sections 9a to 9c are controlled based on this peak value and exceeding of the dynamic range of A/D conversion sections 10a to 10c is prevented. Signals from the A/D conversion sections are processed by a signal processing panel driving section 11 and, by driving a PDP 12, the videos are displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AGC circuit,
The present invention relates to an apparatus for controlling the amplification degree of an input video signal so as to effectively use a dynamic range of an A / D converter.

[0002]

2. Description of the Related Art PDP (Plasma Display Panel)
In an image display device using the method, an analog image signal is converted into a digital signal and applied to a PDP. That is, as in the example shown in FIG. 4, analog R (red), G (green) and B (blue) video signals from input terminals 1a, 1b and 1c are amplified by amplifiers 4a, 4b and 4c, respectively. The A / D converters 10a, 10b and 10c respectively convert the signals into digital signals, perform necessary signal processing for display on the PDP by the signal processing / panel driver 11, drive the PDP 12, and display an image. However, there is a problem that the amplitude of the input video signal varies depending on the signal source, and when the signal amplitude is large and exceeds the dynamic range of the A / D converter, the high-luminance portion is crushed (gradation is compressed). On the other hand, in the case of a video signal source having a small amplitude, there is a problem that the dynamic range of the A / D converter is not effectively used.

[0003]

SUMMARY OF THE INVENTION In view of the above, the present invention is directed to a case where the amplitude of an input video signal does not exceed the dynamic range of the A / D converter and the amplitude of the input video signal is small. Another object of the present invention is to control the amplitude of a video signal input to the A / D converter so that the dynamic range of the A / D converter can be used effectively.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an apparatus for converting a video signal into a digital signal by an A / D converter, performing required signal processing, and digitally driving a display. A voltage control amplifier for amplifying an input video signal with an amplification factor based on a control signal at a stage preceding the A / D converter, and a reference pulse having a required amplitude triggered by a horizontal synchronization signal synchronized with the video signal; A reference pulse generating unit, a reference pulse synthesizing unit that synthesizes a pulse from the reference pulse generating unit during the blanking period of the video signal, and a peak detecting unit that detects a signal from the reference pulse synthesizing unit. It is an object of the present invention to provide an AGC circuit that controls the voltage control amplifier based on a signal from a peak detector.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an AGC circuit according to the present invention, R
(Red), G (green) and B (blue) video signals or a video signal composed of a luminance signal and a color difference signal (or a color signal) are input to the voltage control amplifier, and are amplified at a required amplification degree. The digital signal is converted by a / D conversion unit, signal processing for display on a PDP is performed by a signal processing and panel driving unit, and the PDP is driven to display an image. The reference pulse generation unit generates a reference pulse having a required amplitude by using a horizontal synchronization signal synchronized with the video signal as a trigger, and synthesizes this pulse with the input video signal by the reference pulse synthesis unit. This signal is subjected to peak detection by a peak detection unit, and the detected value is held for a required time by a peak hold circuit or a time constant circuit, applied to a voltage control amplifier, and the output signal amplitude is adjusted to the dynamic range of the A / D converter. Control the gain to be within the corresponding amplitude.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an AGC circuit according to the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an AG according to the invention.
It is a principal part block diagram of one Example of a C circuit. In the figure, 1a, 1b and 1c are video signal input terminals for inputting R, G and B video signals, 2 is a horizontal synchronizing signal (HD) input terminal, and 3 is a vertical synchronizing signal (VD) input terminal. . Reference numerals 4a, 4b, and 4c denote amplification units that amplify video signals from the terminals 1a, 1b, and 1c. Reference numeral 5 denotes a reference pulse generator, which generates a reference pulse having the same polarity as the video signal and a required amplitude during a blanking period of the video signal by using the HD from the terminal 2 as a trigger. The amplitude of the reference pulse is controlled by voltage control amplifiers 9a, 9b, and 9c described later.
The maximum amplitude of the output signal of A / D converters 10a and 10b and
This is a reference value for controlling so that it is within the maximum input value (dynamic range) that can be processed linearly at 10c.
Reference numeral 6 denotes a reference pulse synthesizing unit, which synthesizes a pulse from the reference pulse generating unit 5 during a blanking period of the video signal from the amplifying unit 4b. Reference numeral 7 denotes a peak detector, which detects a signal from the reference pulse synthesizer 6 by peak detection. 8 is a peak hold circuit,
The signal level from the peak detector 7 is held until the next signal input. Alternatively, the peak detection unit 7 is provided by a time
Signal is integrated with a required time constant. 9a,
Reference numerals 9b and 9c denote voltage controlled amplifiers, and a peak hold circuit 8
The signals from the amplifying units 4a, 4b, and 4c are amplified with the amplification degree based on the signals from the same. A / D converters 10a, 10b and 10c convert signals from the voltage control amplifiers 9a, 9b and 9c into digital signals. Reference numeral 11 denotes a signal processing / panel driving unit.
Processing for displaying the signals from the D conversion units 10a, 10b and 10c on the PDP 12 is performed, and the PDP 12 is driven to display an image.

FIG. 2 is a block diagram of a main part of another embodiment of the AGC circuit according to the present invention. In the figure, reference numeral 21 denotes a reference pulse generation unit which generates a pulse having the same polarity as the video signal with an amplitude based on the signal from the control unit 29 during a blanking period of the video signal by using the HD from the terminal 2 as a trigger. Reference numerals 22a, 22b and 22c denote reference pulse synthesizers for synthesizing the pulse from the reference pulse generator 21 during the blanking period of the video signal from the amplifiers 4a, 4b and 4c. 23a, 23b and
Reference numeral 23c denotes a peak detector, which detects signals from the reference pulse synthesizers 22a, 22b, and 22c, respectively. 24a,
24b and 24c are peak hold circuits.
The signal levels from 3a, 23b and 23c are held until the next signal is input. Reference numeral 25 denotes a maximum value selection unit for selecting the maximum value of the signal from the peak hold circuit 24a, 24b or 24c. An A / D converter 26 converts the signal from the maximum value selector 25 into a digital signal. A setting unit 27 sets a mode according to the type of the input video signal (mainly a still image, mainly a moving image). Reference numeral 28 denotes a memory unit which stores control data set for each mode (mainly a still image and a main moving image).
A control unit 29 controls the amplitude of the pulse generated by the reference pulse generation unit 21 based on the control data read from the memory unit 28, and controls the voltage control amplification unit 9 via a D / A conversion unit 30.
The following speed of the amplification degree of a, 9b and 9c is controlled. D / A
The converter 30 converts the data from the controller 29 into an analog signal. The other reference numerals are the same as those in FIG.

Next, the operation of the AGC circuit according to the present invention will be described. In the case of FIG. 1, R, G, and B video signals are input terminals.
Input from 1a to 1c, each amplifying unit (buffer amplifier)
The signals are amplified at 4a to 4c and input to the voltage control amplifiers 9a to 9c. The reference pulse generation unit 5 uses the HD from the terminal 2 as a trigger and generates a pulse having the same polarity as the video signal and an amplitude corresponding to the dynamic range of the A / D conversion units 10a to 10c at the position of the blanking period of the video signal. Generate This pulse is input to the reference pulse synthesizing unit 6 and synthesized as shown in FIG. 3 during the blanking period of the G (or R or B) video signal from the amplifying unit 4b. Detect.
The detected value becomes the maximum amplitude value of the video signal when the maximum amplitude of the video signal is larger than the reference pulse as shown in FIG. 3A, and the amplitude of the video signal is smaller than the reference pulse as shown in FIG.
In this case, the amplitude value of the reference pulse is used. The signal level from the peak detector 7 is held by the peak hold circuit 8 until the next detection value is input, or integrated by a time constant circuit with a required time constant.
9c is applied to each control terminal, and the signals from the amplifiers 4a to 4c are amplified with the same amplification based on the voltage of the control terminal. That is, when the video signal of FIG. 3A or FIG. 3B is input to the voltage control amplifiers 9a to 9c, in the case of FIG. 3A, the maximum amplitude (peak value) of the video signal is detected and the amplitude of the reference pulse is detected. Is calculated, and acts on the voltage control amplifiers 9a to 9c based on the difference signal so as to reduce the amplification degree, and as a result, the amplitude becomes within the dynamic range of the A / D converters 10a to 10c. Is controlled. In the case of (b), since the peak detection value is the amplitude of the reference pulse, the voltage control amplifiers 9a to 9c are controlled at the set amplification degree. The signals from the voltage control amplifiers 9a to 9c are supplied to the A / D converter 10
The signals are converted into digital signals at a to 10c, input to the signal processing / panel driving unit 11, perform signal processing for display on the PDP 12, drive the PDP 12, and display an image.

When a video signal is input after being separated into a luminance signal and a color difference signal, a luminance signal is input from a terminal 1b, a BY color difference signal is input from a terminal 1a, and an RY color difference signal is input from a terminal 1c. The pulse from the reference pulse generator 5 is combined with the luminance signal from the amplifier 4b. Then, the signal processing / panel driving section 11 matrixes three R, G, and B video signals based on the luminance signals and the color difference signals from the A / D conversion sections 10a to 10c, and drives the PDP 12. When the video signal is input as being separated into a luminance signal and a chrominance signal, a luminance signal is input from a terminal 1b and a chrominance signal is input from a terminal 1a (or 1c), and a pulse from the reference pulse generator 5 is amplified. The signal is synthesized with the luminance signal from the unit 4b. Then, the signal processing / panel driving unit 11 matrixes three R, G, and B video signals based on the luminance signals and the color signals from the A / D conversion units 10a to 10c, and drives the PDP 12.

In the case of FIG. 2, the setting unit 27 sets a mode (mainly a still image = personal computer image, etc., main moving image = television image, etc.) according to the type of input video signal. The control data set for each of these modes is stored in the memory unit 28 in advance, and the corresponding control data is read from the memory unit 28 via the control unit 29 by a signal from the setting unit 27, and based on this data, The amplitude of the reference pulse generated by the reference pulse generator 21 is controlled. The generated reference pulse is input to reference pulse synthesis units 22a to 22c, and amplified by the amplification units 4a to 4c.
Are combined during the blanking period of the video signal
Peak detectors 23a to 23c detect peaks, respectively, and hold these values by peak hold circuits 24a to 24c until the next detection value is input.
Selects the maximum value, converts the digital data into digital data by the A / D converter 26, and controls the controller 29 so that the following speed for the data change from the A / D converter 26 corresponds to the mode set by the setting unit 27. (In the moving image mode, the following speed is increased, and in the still image mode, the following speed is decreased), converted into an analog signal by the D / A converter 30 and applied to the voltage control amplifiers 9a to 9c, and the corresponding gain (voltage control The gains are controlled so as to have the same gain in the amplifiers 9a to 9c. The signals from the voltage control amplifiers 9a to 9c are A / D
The signals are converted into digital signals by the converters 10a to 10c, input to the signal processing / panel driver 11, perform signal processing for display on the PDP 12, drive the PDP 12, and display an image.

The amplitude of the reference pulse (set by the setting unit 27) is, for example, such that the variation range of the video signal at the output terminals of the amplification units 4a to 4c is 0.8V to 1.2Vp-p, and the A / D conversion unit 10a ~Ten
Assuming that the dynamic range of c is 1 Vp-p, if the input video signal is a moving image, the reference pulse is 0.8 V and the peak detector
A / D converters 10a to 10c when outputs of 23a to 23c are 0.8V
If the gain of the voltage control amplifier is set (controlled) so that the peak value of the input signal becomes 1.0 V, the maximum brightness can always be obtained in the PDP within the range of the input variation, and when the input video signal is a still image Indicates that the reference pulse is 1.1 V to 1.2 V, and the output of the peak detectors 23 a to 23 c is 1.1 V to 1.2 V when the A / D converter 10
By setting the peak values of the input signals a to 10c to be 1.0 V, the PDP may not be able to have the maximum luminance, but the fluctuation of the gain can be reduced and the image can be easily viewed.

[0012]

As described above, according to the present invention, A
According to the GC circuit, when the amplitude of the input video signal is larger than the amplitude of the reference pulse added to the video signal, the maximum amplitude is A
The gain of the voltage control amplifier is controlled in accordance with the maximum amplitude of the video signal so as not to exceed the dynamic range of the / D converter, and if the amplitude of the input video signal is smaller than the reference pulse, the amplitude of the reference pulse is used as a reference. Since the gain is controlled, it is possible to prevent the high luminance portion from being collapsed when the amplitude of the video signal is large, and to control A / A when the amplitude of the video signal is small.
The dynamic range of the D conversion unit can be used effectively.

[Brief description of the drawings]

FIG. 1 is a main part block diagram of an embodiment of an AGC circuit according to the present invention.

FIG. 2 is a main part block diagram of another embodiment of the AGC circuit according to the present invention.

FIG. 3 is an example of a waveform of a video signal obtained by combining reference pulses.

FIG. 4 is an example of a conventional AGC circuit.

[Explanation of symbols]

 1a, 1b, 1c Video signal input terminal 2 Horizontal synchronization signal (HD) input terminal 3 Vertical synchronization signal (VD) input terminal 4a, 4b, 4c Amplification unit 5, 21 Reference pulse generation unit 6, 22a, 22b, 22c Reference pulse Combining section 7, 23a, 23b, 23c Peak detection section 8, 24a, 24b, 24c Peak hold circuit 9a, 9b, 9c Voltage control amplification section 10a, 10b, 10c, 26 A / D conversion section 11 Signal processing / panel driving section 12 PDP 25 Maximum value selection unit 27 Setting unit 28 Memory unit 29 Control unit 30 D / A conversion unit

Claims (11)

[Claims] An A / D converter converts an image signal into a digital signal, performs required signal processing, and digitally drives a display. In the apparatus, an amplitude detector for detecting the amplitude of the image signal is provided. An AGC circuit provided with a voltage control amplifier for amplifying an input video signal with an amplification degree based on a control signal at a stage preceding the A / D converter, and controlling the voltage control amplifier based on a signal from an amplitude detector. . 2. The image processing apparatus according to claim 1, wherein the amplitude detector is configured to generate a pulse having a required amplitude by using a horizontal synchronization signal synchronized with the video signal as a trigger. 2. The AGC circuit according to claim 1, comprising: a reference pulse synthesizing section for synthesizing during a ranking period; and a peak detecting section for detecting a signal from the reference pulse synthesizing section. 3. The video signal is separately input into red, green, and blue, and each of the red, green, and blue video signals is amplified by the voltage control amplifier with the same amplification degree, and the A / D converter is used. 3. The AGC circuit according to claim 1, wherein the AGC circuit performs processing for each of red, green, and blue video signals. 4. The AGC circuit according to claim 3, wherein the pulse from the reference pulse generator is combined with one of red, green and blue video signals by the reference pulse synthesizer. 5. The reference pulse synthesizing section synthesizes a pulse from a reference pulse generating section in a blanking period of each of red, green and blue video signals, and outputs a red, green and blue signal in the peak detecting section.
While detecting each of the green and blue video signals separately,
4. The method according to claim 3, further comprising a maximum value selection section for selecting a maximum value of a red, green or blue signal after the peak detection section, wherein the voltage control amplification section is controlled based on a signal from the maximum value selection section. AGC circuit as described. 6. The video signal is input as a luminance signal and a two-color difference signal, and the reference pulse synthesizing unit synthesizes a pulse from a reference pulse generating unit during a blanking period of the luminance signal, and the voltage control amplifying unit synthesizes a pulse. 3. The AGC circuit according to claim 1, wherein the AGC circuit amplifies the signal and each color difference signal at the same amplification degree, and processes the luminance signal and each color difference signal by an A / D converter. 7. The video signal is input as a luminance signal and a chrominance signal, the reference pulse synthesizing unit synthesizes a pulse from a reference pulse generating unit during a blanking period of the luminance signal, and the voltage control amplifying unit synthesizes a pulse from the luminance signal. 3. The AGC circuit according to claim 1, wherein the AGC circuit amplifies the luminance signal and the chrominance signal with the same amplification degree, and the A / D converter processes the luminance signal and the chrominance signal. 8. The apparatus according to claim 2, further comprising a setting unit for setting an amplitude of a pulse generated by said reference pulse generating unit, wherein the amplitude of the reference pulse is set according to a type of an input video signal. The AGC circuit according to claim 4, claim 5, claim 6, claim 6, or claim 7. 9. A method according to claim 2, wherein a peak hold circuit for holding a signal level from the peak detector is provided at a stage subsequent to the peak detector, and the voltage control amplifier is controlled based on a signal from the peak hold circuit. , Claim 3, claim 4, claim 5, claim 6, claim 7, or claim 8
AGC circuit as described. 10. A time constant circuit for holding a signal level from the peak detector for a required time at a stage subsequent to the peak detector, wherein the voltage control amplifier is controlled based on a signal from the time constant circuit. Claim 2, Claim 3, Claim 4,
A according to claim 5, claim 6, claim 7, or claim 8
GC circuit. 11. A moving picture / still picture discriminating section for discriminating whether an input video signal is a moving picture or a still picture,
A response control unit for controlling the control response speed of the voltage control amplification unit is provided at the subsequent stage of the peak detection unit, and the control response speed is reduced by the determination of the moving image by the moving image / still image determination unit, and the control is performed by the determination of the still image. 11. The AGC circuit according to claim 2, wherein the response speed is increased.