JPH08168036A - White peak control circuit - Google Patents

Abstract

PURPOSE: To provide a white peak control circuit which never varies the limit level of a white peak projected on an image receiving tube even when the brightness is adjusted. CONSTITUTION: The voltage which determines the white peak limit level of a white peak limiter circuit 5 is varied by a white peak control means 8 associatively with the control voltage for brightness adjustment from a control means 4. Consequently, the brightness is adjusted by a brightness adjusting circuit 3 provided in front of the white peak limiter circuit 5. Even if the level of an illuminance signal inputted to the limiter circuit 5 varies, the white peak limit level set in the limiter circuit 5 varies as the illuminance signal level varies, so the amplitude from the black level of the illuminance signal to the white peak limit level is held invariably ideal and neither white blurring nor blooming is caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white peak control for the purpose of limiting the white peak in order to suppress the underexposure and blooming of an image displayed on a picture tube in a luminance signal processing system such as a television receiver. Regarding the circuit.

[0002]

2. Description of the Related Art Conventionally, in a television receiver, after a contrast adjustment and a brightness adjustment in a luminance signal processing system, whitening and blooming of an image displayed on a picture tube (a phenomenon that an image is blurred when the luminance is increased) are prevented. Therefore, a limiter circuit that suppresses the signal peak on the white side is provided.

FIG. 3 is a block diagram showing a conventional white peak control circuit.

In FIG. 3, a luminance signal is input to the input terminal 1, the amplitude of the luminance signal is adjusted by the contrast adjusting circuit 2, and the signal level is adjusted by the brightness adjusting circuit 3. After being adjusted, the brightness-adjusted signal is supplied to the white peak limiter circuit 5 and is limited so that the white peak of the luminance signal does not exceed a preset value, and the output terminal 7 transfers the signal to the subsequent circuit. It is configured to be output.

The brightness adjustment of the brightness adjustment circuit 3 is performed by an adjustable bright control voltage output from the brightness control means 4. The white peak limiter circuit 5 limits the white peak by applying a fixed limit voltage to the voltage input terminal 6 to determine the white peak limit level.

However, in the above circuit, since the white peak limit level (DC voltage) is fixed, the signal level is adjusted by the brightness adjustment performed at the time of shipment of the television receiver or the brightness adjustment by the user after the shipment. However, there is a problem in that the limit level of the white peak actually displayed on the picture tube changes due to the change.

Problems in the case where such brightness adjustment is performed will be described with reference to FIGS. 4 (A) to 4 (C).

FIG. 4A shows a state when the bright is in the center. In this state, the amplitude a from the black level to the white peak limit level is ideal, and neither whitening nor blooming occurs. .

FIG. 4 (B) shows a state in which the brightness is lowered from the state of FIG. 4 (A). In this state, the amplitude b from the black level to the white peak limit level is wide and a large amplitude signal is obtained. Cause blooming.

FIG. 4C shows a state in which the brightness is raised from the state of FIG. 4A. In this state, the amplitude c from the black level to the white peak limiting level is narrow, and white crushing occurs.

As described above, in the conventional circuit, when the brightness is adjusted, there is a problem that whitening or blooming occurs and the image displayed on the picture tube is deteriorated.

[0012]

As described above, in the conventional white peak limiting means, the limiting level of the white peak actually displayed on the picture tube changes due to the brightness adjustment, causing whiteout or blooming, and thus the image reception. There was a problem that the image on the tube deteriorated.

Therefore, in view of the above problems, the present invention does not change the limit level of the white peak displayed on the picture tube even if the brightness is adjusted, and the white peak control can maintain the picture of the picture tube in a good state. It is intended to provide a circuit.

[0014]

A white peak control circuit according to a first aspect of the present invention comprises a brightness adjusting circuit for inputting a brightness signal and adjusting the level of the brightness signal, and a control voltage for adjusting the brightness. First control means that is generated and supplied to the brightness adjustment circuit, a limiter circuit that limits the white peak level of the brightness signal after brightness adjustment so as not to exceed a set value, and this limiter circuit The set value of the first
The second control means for changing the control voltage according to the control voltage from the second control means.
And a control means of.

According to a second aspect of the present invention, in the white peak control circuit according to the first aspect, the limiter circuit inputs the luminance signal from the brightness adjusting circuit to one base,
The white peak limiting level is input to the other base, the emitters are commonly connected, and the collectors are both connected to the reference potential point. The first and second transistors form a differential pair, the DC power supply, and the first and second transistors. A first current source connected between the common emitter of the second transistor and supplying a constant current to either one of the first and second transistors, and a base of the first and second transistors. A third emitter for inputting the output of the common emitter, connecting the collector to the DC power supply, connecting the emitter to the reference potential point via the second current source, and outputting the white peak limited luminance signal from the emitter. And a second current source connected to the direct current power source, and a constant current output from the third current source via a resistor. Connect to the control voltage output terminal of Wherein the third current source and said first voltage obtained at the connection point of the resistors, which is a supply arrangement to one of the base of the second transistor as a white peak limit level.

[0016]

According to the first aspect of the invention, the voltage determining the white peak limit level of the limiter circuit is changed in conjunction with the control voltage for brightness adjustment. As a result, even if the level of the brightness signal changes due to the brightness adjustment, the white peak limit level of the limiter circuit also changes in accordance with the change of the brightness signal level, and the black level of the brightness signal is always changed to the white peak. Since the amplitude up to the limit level can be maintained in an ideal state, neither whiteout nor blooming occurs.

[0017]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a block diagram showing a white peak control circuit according to an embodiment of the present invention. The same elements as those of FIG. 3 are described with the same reference numerals.

In FIG. 1, a luminance signal is input to an input terminal 1, the amplitude of the luminance signal is adjusted by a contrast adjusting circuit 2, and the contrast adjusted luminance signal is brightness adjusted. It is supplied to the circuit 3, where the level of the luminance signal is adjusted by the bright control voltage from the brightness control means 4 as the first control means. The brightness signal whose brightness has been adjusted is further supplied to the white peak limiter circuit 5. In the white peak limiter circuit 5,
The white peak of the luminance signal is limited so as not to exceed the white peak limit level given from the white peak control means 8 as the second control means, and is output from the terminal 7 to the circuit in the subsequent stage.

The brightness adjustment of the brightness adjustment circuit 3 is performed by an adjustable bright control voltage output from a variable DC source as the brightness control means 4.

The white peak limiting operation by the white peak limiter circuit 5 is performed by the white peak limiting voltage output from the white peak control means 8. This white peak limiting voltage is linked to the magnitude of the bright control voltage. And it is changing.

The brightness control voltage may be changed by an adjustment knob provided in the brightness control means 4, or by a brightness adjustment key provided by a remote control transmitter (not shown).

According to the above configuration, the white peak limiting voltage in the white peak limiter circuit 5 is changed to the brightness adjusting circuit 3
Since it is changed in conjunction with the bright control voltage in
When the brightness is adjusted and the brightness is increased by increasing the brightness control voltage, the level of the luminance signal input to the white peak limiter circuit 5 increases, but the white peak supplied to the white peak limiter circuit 5 increases. Since the limit voltage also rises, the limit level of the white peak of the image does not change. Therefore, the luminance signal output from the white peak limiter circuit 5 to the subsequent circuit has an ideal amplitude from the black level to the white peak limit level. The condition is maintained, and neither whitening nor blooming occurs.

FIG. 2 shows a concrete configuration example of the brightness control means 3, the white peak limiter circuit 5 and the white peak control means 8, which are the main parts of FIG.

In FIG. 2, the brightness adjusting terminal of the brightness adjusting circuit 3 is provided with a variable DC source D as brightness controlling means 4.
Bright control voltage V1 from C is supplied, and the brightness is adjusted by this control voltage V1.
The luminance signal output from the brightness adjusting circuit 3 is supplied to the base of the transistor Q1 forming the white peak limiter circuit 5.

In this white peak limiter circuit 5, the emitters of two PNP type transistors Q1 and Q2 forming a differential pair are commonly connected, and the output signal from the brightness adjusting circuit 3 is input to the base of the transistor Q1. Then, the white peak limiting voltage from the white peak control means 8 is supplied to the base of the transistor Q2. The collectors of the transistors Q1 and Q2 are both connected to the reference potential point GND, and the constant current source I2 is connected between the DC power supply line Vcc and the common emitter of the transistors Q1 and Q2 to connect the transistors Q1 and Q2.
The output available at the common emitter of the is supplied to the base of an NPN transistor Q3. The collector of the transistor Q3 is connected to the DC power supply line Vcc, and the transistor Q3
Between the emitter of 3 and the reference potential point GND, a constant current source I
3 is connected and the luminance signal output from the emitter of the transistor Q3 is taken out from the terminal 7.

The white peak control means 8 has a constant current source I1 between the DC power source line Vcc of the white peak limiter circuit 5 and the output terminal of the variable DC source DC as the brightness control means 4. The resistor R1 is connected in series, and the voltage obtained at the connection point of the constant current source I1 and the resistor R1 is supplied to the base of the transistor Q2 as a white peak limiting voltage.

Next, the operation of the circuit shown in FIG. 2 will be described. The brightness signal input to the input terminal 1 is amplitude-adjusted by the contrast adjustment circuit 2, the signal level is adjusted (brightness adjustment) by the brightness adjustment circuit 3, and is input to the white peak limiter circuit 5. .

In the white peak limiter circuit 5, the luminance signal is input from the base of the PNP transistor Q1 and N
The signal is output from the emitter of the PN transistor Q3 to the next stage circuit. Further, the white peak limiting voltage which changes according to the bright control voltage V1 from the variable DC source DC which is the brightness control means 4 is input to the base of the PNP transistor Q1.

When the base voltage of the transistor Q1 is lower than the base voltage (white peak limiting voltage) of the transistor Q2, the current I2 from the constant current source I2 connected to the transistors Q1 and Q2 is all on the side of the transistor Q1. As a result, the transistor Q2 cuts off, that is, becomes inoperative, and the input signal of the base of the transistor Q1 is output to the base of the NPN transistor Q3.

On the contrary, when the base voltage of the transistor Q1 is higher than the base voltage (white peak limiting voltage) of the transistor Q2, the current I2 from the constant current source I2 connected to the transistors Q1 and Q2 is all on the side of the transistor Q2. As a result, the transistor Q1 is cut off, that is, in the non-operating state, and the signal (white peak limiting voltage) of the base of the transistor Q2 is output to the base of the NPN transistor Q3.

As described above, even if the voltage of the luminance signal (base voltage of the transistor Q1) rises, a voltage higher than the base voltage of the transistor Q2 is not output, so that the limiter operation is performed.

In the prior art (FIG. 3), the base voltage (white peak limiting voltage) of the transistor Q2 was a fixed bias voltage, but in the present invention, the bright control voltage V1 is leveled by using the constant current source I1 and the resistor R1. Shift and use that voltage as the base voltage of transistor Q2,
The base voltage (white peak limiting voltage) of the transistor Q2 changes according to the bright control voltage V1. The white peak limiting voltage is given by the following equation.

White peak limiting voltage = V1 + (I1 × R1) where V1 is the bright control voltage from the variable DC source DC, I1 is the current of the constant current source I1, and R1 is the resistance value of the resistor R1.

[0034]

As described above, according to the present invention, the white peak limit level of the limiter circuit for limiting the white peak is changed according to the brightness adjustment. Therefore, the brightness adjustment and the white peak limit are performed. Even if you do, you can obtain a video without whiteout or blooming.

[Brief description of drawings]

FIG. 1 is a block diagram showing a white peak control circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific configuration example of a main part of FIG.

FIG. 3 is a block diagram showing a conventional white peak control circuit.

FIG. 4 is a diagram illustrating a problem of the conventional circuit of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Luminance signal input terminal 3 ... Brightness adjustment circuit 4 ... Brightness control means (first control means) 5 ... White peak / limiter circuit 7 ... Luminance signal output terminal 8 ... White peak control means (second control means) )

Claims (2)

[Claims] 1. A brightness adjusting circuit for inputting a brightness signal, adjusting the level of the brightness signal, and first control means for generating a control voltage for brightness adjustment and supplying the control voltage to the brightness adjusting circuit. And a limiter circuit for limiting the white peak level of the brightness signal after the brightness adjustment so as not to exceed a set value, and the set value of the limiter circuit for the control voltage from the first control means. And a second control unit that changes the white peak control circuit according to the above. 2. The limiter circuit inputs the luminance signal from the brightness adjusting circuit to one base, inputs the white peak limit level to the other base, connects the emitters in common, and references the collectors together. The first and second transistors forming a differential pair, which are connected to the potential point, are connected between the DC power supply and the common emitter of the first and second transistors, and are connected to the first and second transistors. A first current source for supplying a constant current to either one of them, an output of a common emitter of the first and second transistors is input to a base, a collector is connected to the DC power supply, and an emitter is a second current. A third transistor connected to a reference potential point via a power source and outputting a luminance signal subjected to white peak limitation from the emitter, wherein the second control means includes a third current source in the DC power source. Connect The constant current output from the third current source is connected to the control voltage output terminal of the first control means via a resistor, and the voltage obtained at the connection point of the third current source and the resistor is set to the above-mentioned value. The white peak control circuit according to claim 1, wherein the white peak control circuit is configured to supply the white peak limit level to one of the bases of the first and second transistors.