JPH05284440A - Brightness adjustment circuit - Google Patents

Abstract

PURPOSE:To provide the brightness adjustment circuit by which brightness information is added to a video signal without changing its DC component and in which the added brightness information is not lost by AC coupling at a post-stage. CONSTITUTION:The circuit is provided with a 1st clamp circuit 9 arranging pedestal level of an inputted video signal to a constant level, an adding circuit 13 adding a DC voltage for brightness adjustment for a horizontal flyback time of the video signal outputted from a 1st clamp circuit 9 and a 2nd clamp circuit 18 arranging DC voltages added to the video signal by the adding circuit 13 to be a constant voltage level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bright adjusting circuit used in a television receiver or the like.

[0002]

2. Description of the Related Art Conventionally, for example, a brightness adjusting circuit of a television receiver is constructed as shown in FIG. 3, in which 1 is an input terminal for receiving or inputting a video signal from an external video device or the like, and 2 is an input terminal. A DC voltage control circuit for adjusting the DC component of the video signal input to the input terminal 1 on the basis of the control voltage applied to the control terminal 2A, 3 is a brightness adjustment potentiator 4 according to the brightness adjustment, that is, the brightness adjustment. A voltage generation circuit 5 for generating a DC voltage corresponding to a bright control voltage VBR given from a control volume 4 is a comparator which performs a comparison operation only when a gate pulse GP0 synchronized with a horizontal synchronizing signal of a video signal is applied. The device 5 compares the pedestal level of the video signal output from the DC voltage control circuit 2 with the DC voltage from the voltage generation circuit 3 based on the gate pulse GP0. Being adapted to produce an output voltage corresponding to the difference, the output voltage is to be supplied to the DC voltage control circuit 2 as a control voltage. Incidentally, 6 is a holding capacitor for holding the output voltage until the next output voltage is supplied from the comparator 5, and 7 is an output terminal for outputting a video signal from the DC voltage control circuit 2.

Therefore, in such a circuit configuration, the pedestal level of the video signal output from the DC voltage control circuit 2 is compared with the DC voltage from the voltage generation circuit 3, and the DC voltage control is performed so that the difference becomes zero. Since it is controlled by the circuit, the unevenness of the pedestal level is eliminated and the brightness-adjusted video signal is output from the output terminal 7.

For example, the direct current voltage from the voltage generating circuit 5 according to the brightness adjustment is Vo, and when the video signal S1 for direct current as shown in FIG. 4 is input, the pedestal level thereof becomes the direct current voltage Vo. Matched, that is, DC voltage Vo
When the video signal S2 for the DC component as shown in FIG. 4 is input, the pedestal level of the pedestal level is matched with the DC voltage Vo,
That is, the output is lowered to Vo.

[0005]

However, in such a brightness adjusting circuit having the conventional structure, the DC voltage from the voltage generating circuit, which is compared with the pedestal level, changes in accordance with the brightness adjustment, thereby changing the DC voltage of the video signal. However, if one or several circuits for performing other signal processing are to be connected in the subsequent stage, the circuit that allows for the DC component change of the video signal due to the brightness adjustment It was necessary to design it, which was a major obstacle to lowering the voltage of the circuit power supply. Further, when connecting the signal processing circuit in the subsequent stage by AC coupling (CR coupling), there is a problem that the bright information is lost and the bright adjustment of the corner is wasted.

The present invention has been made in view of the above points, and bright information is added to a video signal without changing the direct current component thereof, and the added bright information is obtained by AC coupling in a subsequent stage. It is an object of the present invention to provide a bright adjustment circuit that is prevented from being lost.

[0007]

In order to achieve the above object, the present invention provides a first clamp circuit for aligning a pedestal level of an input video signal to a constant level, and an output from the first clamp circuit. A configuration including an additional circuit for adding a DC voltage for brightness adjustment within a horizontal blanking period of the video signal, and a second clamp circuit for aligning the DC voltage added to the video signal by the additional circuit to a constant level. It is what Specifically, the additional circuit includes a voltage generation circuit that generates a DC voltage according to the brightness adjustment,
And a switch circuit for supplying the DC voltage from the voltage generating circuit to the second clamp circuit within the horizontal blanking period in place of the video signal output from the clamp circuit.

[0008]

According to this structure, the direct current component of the video signal is reproduced by the first clamp circuit, and the direct current voltage corresponding to the brightness adjustment is added by the additional circuit within the horizontal blanking period of the video signal. Therefore, the relative voltage relationship between the video signal and the DC voltage is changed by the brightness adjustment. Then, the direct current voltage added to the video signal by the second clamp circuit is adjusted to a constant level, so that the direct current component of the video signal is set to a level according to the relative voltage relationship with the direct current voltage. ..

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the bright adjusting circuit of the present invention will be described below with reference to the drawings. In FIG. 1, 8 is an input terminal to which a video signal received or input from an external video device is input, and 9 is a first clamp circuit for aligning the pedestal level of the video signal input to the input terminal 8 to a constant level. Reference numeral 10 is a first DC voltage control circuit for adjusting the DC component of the video signal input to the input terminal 8 based on the control voltage applied to the control terminal 10A, and 11 is a first gate synchronized with the horizontal synchronizing signal of the video signal. The first comparator 11 performs a comparison operation only when the pulse GP1 is applied, and the first comparator 11 operates based on the first gate pulse GP1.
The pedestal level of the video signal output from the first reference voltage V1 is compared with the first reference voltage V1, and an output voltage corresponding to the difference is generated.
It is supplied to the DC voltage control circuit 10 and controlled so that the difference becomes zero. Here, 12 is a holding capacitor for holding the output voltage until the next output voltage is supplied from the first comparator 11.

Reference numeral 13 is an additional circuit for adding a DC voltage for brightness adjustment within the horizontal blanking period of the video signal output from the first clamp circuit 9, and 14 is for adjusting the brightness adjustment by the brightness adjustment volume 15. That is, the bright control voltage VB given from the bright adjusting volume 15
A voltage generation circuit for generating a DC voltage V3 according to R, 16
Is a switch circuit that performs a switching operation based on a switching pulse SP that is synchronized with a horizontal synchronizing signal of the video signal. The switch circuit 16 normally outputs the video signal output from the first DC voltage control circuit 10 to a signal processing circuit at a subsequent stage. However, it is switched only when the switching pulse SP is applied, that is, only in the horizontal synchronizing signal within the horizontal retrace line period of the video signal and its back porch portion, and the voltage generating circuit 14 replaces it. The DC voltage V3 is supplied to the signal processing circuit 17 in the subsequent stage. Here, the signal processing circuit 17 is AC-coupled to the switch circuit 16, and is adapted to perform signal processing necessary for obtaining a good image, for example, band characteristic correction.

Reference numeral 18 denotes a signal processing circuit 17 from the additional circuit 13.
A second clamp circuit 19 that adjusts the DC voltage added to the video signal supplied through the control signal to a constant level, and a second DC voltage 19 that adjusts the DC component of the video signal based on the control voltage applied to the control terminal 19A. The control circuit 20 is a second comparator which performs a comparison operation only when the second gate pulse GP2 (in this case, having the same timing and pulse width as the switching pulse SP) synchronized with the horizontal synchronizing signal of the video signal is applied. Then, the second comparator 20 outputs the second gate pulse GP
Based on 2, the DC voltage added to the video signal output from the second DC voltage control circuit 19 is compared with the second reference voltage V2 to generate an output voltage according to the difference. The output voltage is supplied to the second DC voltage control circuit 19 as a control voltage and controlled so that the difference becomes zero. Here, 21 is a holding capacitor for holding the output voltage until the next output voltage is supplied from the second comparator 20, and 22 outputs the video signal from the second DC voltage control circuit 19. It is an output terminal.

Therefore, the video signal input to the input terminal 8 first has its pedestal based on the first gate pulse GP1 applied at the timing shown in FIG. 2B by the first clamp circuit 9. After the direct current component is regenerated by adjusting the reference voltage V1 to 1 (see FIG. 2A),
Based on the switching pulse SP applied at the timing shown in FIG. 2D by the additional circuit 13 in the next stage, the DC voltage V3 corresponding to the brightness adjustment is generated within the horizontal blanking period.
Is added (see FIG. 2C), and the relative voltage relationship between the video signal and the DC voltage V3 is determined by the brightness adjustment.

After the signal processing in the signal processing circuit 17 of the next stage, the second clamp circuit 18 has the second gate pulse having the same timing and the same pulse width as the switching pulse SP as shown in FIG. 2D. By aligning the DC voltage V3 added to the video signal on the basis of GP2 with the second reference voltage V2, the lost DC component is reproduced and the DC component corresponds to the relative voltage relationship with the DC voltage V3. The level is set (see FIG. 2E), that is, the brightness is adjusted and the output terminal 22
Will be output from.

As described above, in the present embodiment, the horizontal synchronizing signal and the back porch portion are switched to the DC voltage for brightness adjustment, but the invention is not limited to this, and the color burst signal is taken out in advance. However, it is necessary to prevent the switching to the DC voltage from reaching the back porch portion before the color burst signal is taken out.

[0015]

As described above, according to the brightness adjusting circuit of the present invention, the relative voltage relationship between the DC voltage added within the horizontal blanking period of the video signal and the video signal is changed by the brightness adjustment. Since the bright information is added by means of the bright information, the direct current component of the video signal does not change due to the addition of the bright information, and even if a circuit for performing other signal processing after adding the bright information is connected by AC coupling. Bright information is never lost. Therefore, when connecting another signal processing circuit after adding bright information, it is possible to eliminate the restrictions on the circuit design associated with the addition of bright information, and also to easily reduce the voltage of the circuit power supply. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration example for realizing the present invention.

FIG. 2 is a signal waveform diagram in each part thereof.

FIG. 3 is a diagram showing a conventional circuit configuration example.

FIG. 4 is a diagram for explaining the operation.

[Explanation of symbols]

 9 1st clamp circuit 13 Additional circuit 14 Voltage generation circuit 16 Switch circuit 18 2nd clamp circuit

Claims (2)

[Claims] 1. A first clamp circuit for adjusting a pedestal level of an input video signal to a constant level, and the first clamp circuit.
An additional circuit that adds a DC voltage for brightness adjustment within the horizontal blanking period of the video signal output from the clamp circuit of
A bright adjustment circuit comprising: a second clamp circuit for adjusting the DC voltage added to the video signal by the addition circuit to a constant level. 2. The additional circuit includes a voltage generating circuit for generating a DC voltage according to the brightness adjustment and a voltage generating circuit within the horizontal blanking period in place of the video signal output from the first clamp circuit. 2. The bright adjusting circuit according to claim 1, further comprising: a switch circuit that supplies the DC voltage of 2 to the second clamp circuit.