JPH06303556A - Automatic luminance controller - Google Patents

Abstract

PURPOSE:To obtain an automatic luminance controller in which a range where the adjusting function of luminance such as contrast and brightness, etc., remains unchanged in spite of the change of display size and also, the luminance of a display image remains unchanged in the video signal processing of a color television receiver. CONSTITUTION:This controller is comprised by providing a size detection circuit 30 which detects the display size of an image, a conversion circuit 40 which outputs an input voltage by applying level conversion according to the control signal of the size detection circuit 30, and a limitation circuit 50 which detects beam current quantity and applies limitation to the output of the conversion circuit 40 by comparing it with a reference voltage outputted from the size detection circuit 30. Therefore, the effective operating range of a contact volume remains unchanged even when the change of surface size such as that of an aspect ratio is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic brightness control device in video signal processing of a color television receiver.

[0002]

2. Description of the Related Art A conventional automatic brightness control device is disclosed, for example, in Japanese Patent Application Laid-Open No. 2-312442. Figure 8
Shows a block diagram of this conventional automatic brightness control device, 1 is an input terminal, 2 is a signal processing circuit, 3 is an amplifier, 4
Is a cathode ray tube (CRT), 5 is an electron gun, 6 is a deflection circuit, 7
Is a deflection yoke, 8 is a flyback transformer, 9 is a diode, 10 is an anode, 13, 14, 16 are resistors, 1
5 is an ABL circuit, 17 is a voltage source, 18 is a transistor,
Reference numeral 19 is a control terminal.

In the conventional automatic brightness control device configured as described above, the image signal supplied to the input terminal 1 is supplied to the amplifier 3 through the signal processing circuit 2, and the signal from the amplifier 3 is supplied to the electronic device of the CRT 4. Supplied to the gun 5. Further, the signal processing circuit 2 separates the horizontal and vertical synchronization signals,
The deflection signal formed by the deflection circuit 6 is supplied to the deflection yoke 7. Further, the high voltage obtained at one end of the secondary coil of the flyback transformer 8 is supplied to the anode 10 through the diode 9. As a result, an image based on, for example, an image signal of a cinemascope size supplied to the input terminal 1 is projected on the screen 12 via the lens 11.

At the same time, the other end of the secondary coil of the flyback transformer 8 is grounded through a resistor 13,
The voltage (negative voltage) obtained from the resistor 13 is the resistor 1
4 is supplied to the ABL circuit 15. And this A
The control signal formed by the BL circuit 15 is supplied to the gain control terminal of the amplifier 3.

Therefore, in this circuit, for example, when the display brightness increases and the current flowing through the anode 10 increases,
When the potential of the other end of the secondary coil of the transformer 8 increases in the negative direction, and the potential exceeds a predetermined value, a control signal is output from the ABL circuit 15 to reduce the gain of the amplifier 3 and reduce the display brightness. It has become so.

Further, in this circuit, the ABL circuit 15
Is connected to the negative voltage source 17 via the resistor 16 and the both ends of the voltage source 17 are connected via the switching transistor 18, and controls the deflection width of the deflection circuit 6. The terminal 19 is connected to the base of the transistor 18.

Therefore, in this circuit, for example, a cinemascope-size image signal is supplied, and the deflection circuit 6 is deflecting the maximum width, so that the ABL circuit 15 operates as a secondary coil at a luminance level at which the circuit is operated. Flowing current 3
Assuming mA and the resistance value of the resistor 13 being 4.7 kΩ, the potential of the other end A of the secondary coil at this time becomes -14.1V. At the same time, the resistance values of the resistors 14 and 16 are both set to 47 kΩ, and at this time, the transistor 18 is turned on and the other end C of the resistor 16 is set.
Is grounded, the input terminal B of the ABL circuit 15
Potential is -7V. In this state, the ABL circuit 15 is made to operate.

On the other hand, when a normal television signal is supplied, a signal is supplied to the control terminal 19 to cause the deflection circuit 6 to operate.
The deflection width at is set to 1 / 1.77 only in the horizontal direction.
Therefore, in this state, the current flowing through the secondary coil at the brightness level for operating the ABL circuit 15 is 1 / 1.77.
Of about 1.7mA, and the potential at point A is -7.9V. Therefore, in this state, in order to set the potential of the point B to -7V, the potential of the point C may be set to -6.1V, that is, the voltage of the voltage source 17 is set to -6.1V so that the transistor 18 is turned off. To

Therefore, in this circuit, when the cinemascope size is used, the current flowing in the secondary coil is 3 mA or more and is AB.
The L circuit 15 operates so as to reduce the gain of the amplifier 3, and in the case of a normal TV signal, the ABL circuit 1 operates at 1.7 mA or more.
5 operates so as to reduce the gain of the amplifier 3, and ABL can be performed in each state.

FIG. 9 shows the case where another circuit is used instead of the voltage source 17. In FIG. 9, 21 is a terminal to which a normalized horizontal width signal is input, 22 is a terminal to which a normalized vertical width signal is input, 23 is a multiplier,
Reference numeral 24 is a bias circuit. Terminal 2 as shown in FIG.
The normalized horizontal and vertical deflection widths supplied to 1 and 22 are multiplied by a multiplier 23, and the multiplied value is supplied to the other end of the resistor 16 through an arbitrary bias circuit 24. This makes it possible to automatically correct the ABL control for an image having an arbitrary aspect ratio.

[0011]

However, in the conventional configuration as described above, for example, in the case where the brightness of an image of a cinemascope size is low and the current flowing through the secondary coil is 1 mA, a normal 4: 3 television is used. Even if you change the size
The BL circuit does not operate and the gain of the amplifier 3 does not change. Therefore, in such a case that the brightness before the display size change is low and the ABL circuit is not controlled even after the display size is reduced, the beam current amount before and after the size change does not change. Since the amount of beam current does not change and the display area decreases, the brightness of the display image increases.

In view of the above point, the present invention has an object to provide an automatic brightness control device in which the brightness of a display image does not change regardless of the display size and the effective operation range of contrast control does not change.

[0013]

SUMMARY OF THE INVENTION According to the present invention, a size detection circuit for detecting a display size of an image based on a signal related to the display size and a control voltage for controlling the brightness of the display image are controlled according to the control signal of the size detection circuit. It includes a conversion circuit for converting the level and outputting it, and a limiting circuit for comparing the beam current amount with the reference voltage output from the size detection circuit to limit the output of the conversion circuit. Instead, the brightness of the displayed image is stabilized.

[0014]

According to the present invention, even if the display area is changed by changing the aspect ratio and the like, the image brightness is always kept constant and the effective range of the contrast volume does not change. In addition, since the beam current is limited according to the display area, it is possible to prevent seizure of the tube surface, blooming and the like.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an automatic brightness control device according to the first embodiment of the present invention.

In FIG. 1, 30 is a size detection circuit for detecting the size of the display image, 40 is a conversion circuit for converting the level of the input voltage according to the control signal output from the size detection circuit 30, and 50 is a beam current and size detection circuit. A limiting circuit that limits the output voltage of the conversion circuit 40 by comparing it with a reference voltage output from 30, a calculating circuit, 32 a reference voltage generating circuit, 33 a level signal generating circuit, 51 a comparing circuit, 52 a It is a subtraction circuit. The size detection circuit 30 includes a calculation circuit 31, a reference voltage generation circuit 32, and a level signal generation circuit 33, and the limit circuit 50 includes a comparison circuit 51 and a subtraction circuit 52.

FIG. 2 is a block diagram of an example when the first embodiment is used for contrast control. The same functions as those in FIG. 1 are represented by the same numbers. In FIG. 2, 70 is a contrast control circuit that controls the amplitude of the video signal, 80 is a brightness control circuit that performs DC reproduction of the video signal, and 90 is a drive circuit for driving the CRT.
0 is a current detection circuit for detecting the beam current, 110 is a CR
T and 120 are deflection circuits, and 130 is a deflection coil.

In FIG. 2, the current detection circuit 100 is a CR.
The amount of beam current flowing through T110 is detected, current-voltage conversion is performed, and V _B is output to the limiting circuit 50. On the other hand, the voltage V given from the contrast volume is converted into the conversion circuit 40.
_Is converted to V _i and output to the limiting circuit 50. Limit circuit 5
0 compares the voltage V _B given by the current detection circuit 100 with the voltage V _f given by the size detection circuit 30 and calculates V _i
And limit it to V _o . V _o is the contrast control circuit 7
It is inputted to the control terminal of 0 and controls the amplitude of the video signal.

The operation of the automatic brightness control device of this embodiment constructed as described above will be described below. Figure 1
First, the calculation circuit 31 receives two signals of the horizontal size Dh and the vertical size Dv of the display image from the deflection circuit 120, calculates the area of the display screen, and normalizes it with the reference display area. With the area output standardized by the calculation circuit 31, the reference voltage generating circuit 32 outputs the reference voltage V _f , for example, when the display screen area decreases, and when the display screen area increases, the reference voltage V _f also increases. Works to increase. Further, the level signal generation circuit 33 outputs a signal for controlling the conversion level of the conversion circuit 40 by the standardized area output of the calculation circuit 31.

The comparison circuit 51 compares V _B sent from the current detection circuit 100 with the reference voltage V _f sent from the reference voltage generation circuit 32, and when V _B exceeds the reference voltage V _f , the subtraction circuit 52 subtracts it. The voltage amount V ^- is output. Here the output voltage V _o increases, the amplitude of the video signal increases CRT
As the beam current through 110 increases, so does V _B. When the output voltage V _o on the opposite decreases, also reduces V _B decreases the amplitude of the video signal decreases the beam current. This operation will be described using a graph.

FIG. 3 is an example of a diagram showing the relationship between the voltage V _i input to the limiting circuit 50, the output voltage V _o output from the limiting circuit 50, and the output V _B of the current detection circuit 100. Figure 3
As between the O-A, V _B is the input voltage V _i is up to V _a is does not exceed the reference voltage V _f, also increases the output voltage V _o with increasing input voltage V _i. However, since V _B begins to exceed the reference voltage V _f when V _a is exceeded, the comparison circuit 51 outputs V ⁻ and works to suppress the increase in the output voltage V _o ,
_It operates until _B does not exceed the reference voltage V _f . As a result, even if the input voltage V _i is increased to V _a or higher, the output voltage V _o can be suppressed to a constant value. Therefore, the beam current flowing through the CRT 110 does not flow more than a certain amount of V _B = V _f .

Here, consider a case where the display size is changed with the reference voltage V _f being a fixed value, for example, the aspect ratio of 16: 9 is contracted in the horizontal direction to be changed to the aspect ratio of 4: 3. Since the horizontal size is reduced, the display area is 0.
75 times, and the average brightness L of the displayed image is the beam current amount I.
Since the display area S can be expressed by L = I / S, the average luminance becomes 1.33 times as the aspect ratio is changed. However, the beam current amount does not change even if the aspect ratio is changed because the amplitude of the video signal does not change. Therefore, V ⁻ output from the comparison circuit 51 does not change and the output voltage V _o does not decrease, so that the brightness increases 1.33 times.

On the other hand, in this embodiment, the reference voltage V _f is a variable value controlled by the size detection circuit 30. In this case, if the horizontal deflection is reduced and the aspect ratio is changed in the same manner as described above, the calculation circuit 31 detects the change in the display area and the reference voltage generation circuit 32 lowers the reference voltage V _f output to V _f '. To do. Even _if V _B does not change because the reference voltage has dropped to V _f ', the comparison circuit 51 outputs V ⁻ and decreases the output voltage V _o . As a result, as shown in FIG. 3, the contrast control voltage V _o, which was suppressed at the point A, is suppressed at the point B, the amount of beam current is also suppressed, and burning of the tube surface is prevented.

Next, the operation of the conversion circuit 40 will be described with reference to FIGS. 4 and 5 show the voltage V from the contrast volume and the voltage V _o input to the control terminal of the contrast control circuit 70 and the current detection circuit when the video signal with APL (average level of the video signal) of 100% is input. is a diagram showing an example of the relationship between the 100 output V _B. Figure 4
Is a diagram of V-V _o -V _B when the display size of the underlying, FIG 5 is a diagram of a V-V _o -V _B when reducing the display size when there is no conversion circuit 40.

Now the voltage V from the contrast volume
Will be directly input to the limiting circuit 50. In the state of FIG. 4, V _B is effectively changed up to the maximum voltage V _max of the contrast volume. Then, it is assumed that the display state operating in the state of FIG. 4 is changed to the display state of FIG. 5 by reducing the deflection. As described above, the reference voltage generation circuit 32 reduces the reference voltage V _f to V _f ′, and as a result, image sticking due to an increase in brightness is suppressed.

However, as shown in FIG. 5, when the voltage V of the contrast volume is V _T or more, the change of the control voltage V _o is suppressed by the operation of the limiting circuit 50. Therefore, even if the contrast volume is turned within the range of V _T or more, nothing happens. The brightness does not change. That is, as the deflection is reduced and the display size is reduced, the effective range of the contrast volume becomes narrower. Further, the limiting circuit 5 is used even after the size of the position of the contrast volume is changed to V _1.
In the range where 0 is not restricted, the amount of beam current does not change, and the brightness increases in inverse proportion to the rate of reduction in size.

[0027] In order to improve such an operation, the conversion circuit 40, as the ratio of the display area and the beam current is always constant, suppressing an increase in brightness performs conversion to V _o from V. For example, consider the case where the size is changed from the reference display area to a display area that is α times larger. The beam current I and the voltage V _s input to the cathode (V _s is a voltage based on the cutoff) have a relationship of (Equation 1), and the relationship between V _s and the contrast control voltage V _o is generally. Since there is a proportional relationship, it becomes (Equation 2). (Number _{1) I = k · V s} a (km 2 1: am 2 3) in equation _{(2) V s = k 1 ·} V o + b ( number 2), b but is the bias component of the contrast control voltage , The contrast control circuit 70 operates with the bias component = 0, or the contrast control circuit 70
Assuming that there is a function to add a bias component at, b =
The description will proceed assuming 0. Further, the relationship between the beam current I and the output V _B of the current detection circuit 100 is also a proportional relationship, which is (Equation 3). (Equation 3) V _B = k ₂ · I Further, from (Equation 1) to (Equation 3), the relationship between V _B and V before the size change is (Equation 4). (Equation 4) V _B = k ₂ · I = k ₂ · k · V _sa ^a = k ₂ · k · k ₁ ^a · V _o ^a = k ′ · V _o ^a (k ′ = k ₂ · k · k) ₁ ^a ) Since the conversion circuit 40 operates so as to keep the ratio of the display area and the beam current constant, the beam current I ′ when the area is changed to α times also becomes α times the beam current I before the change. Therefore, the output V _B 'of the current detection circuit 100 after the change also becomes (Equation 5). The relationship between (number _{5) V B '= α ·} V B also the relation of V-V _o of the resized by the conversion circuit 40 V _o' V than when the equation (4) _B 'and V _o' ( Equation 6) is obtained. (Equation 6) From V _B '= k' · V _o ' ^a (Equation 4) to (Equation 6), V _o ' can be expressed by (Equation 7). (Equation 7) V _B '= k' ・ V _o ' ^a = α ・ V _B = α ・ k' ・ V _o ^a Therefore, V _o ' ^a = α ・ V _o ^a V _o ' = α ^{1 / a}・ V _As can be seen from _o (Equation 7), the operation of the conversion circuit 40 can be converted to the desired V-V _o ′ relationship by multiplying the V-V _o relationship before size change by α ^{1 / a} . The signal for increasing the V-V _o relationship by α ^{1 / a} is the control signal output from the level signal generating circuit 33.

FIG. 6 is a graph showing the conversion when the display size is reduced by half. In FIG. 6, the line A has a relationship of V _o -V _B , and is plotted with k = k ₁ = k ₂ = 1 and a = 3. The B line before the change size V-V _o
Therefore, the output V _BX of the current detection circuit 100 when V _o = V and the maximum value V _max of the volume voltage is set to the reference voltage V _f so that the effective operation range of the volume is set to O−V _max . C line is V-V after the display area is changed to 1/2
_This is the relationship of _o ', which is a line obtained by multiplying the B line by α ^{1 / a} (m ² 0.79).

In FIG. 6, the output V _BX 'of the current output circuit 100 with respect to the maximum voltage value V _max of the volume after the size change is V _BX / 2. Further, looking at the outputs V _B1 and V _B1 ′ of the current detection circuit 100 before and after the size change at the voltage V ₁ in the middle of the volume, it is found that V _B1 ′ = V _B1 / 2, which also reduces the display area. The beam current also decreases at the same rate as, so the brightness of the displayed image does not change.

Further, since the output V _BX 'of the current detection circuit 100 after the size conversion with respect to the maximum voltage V _{max of the} volume does not exceed the reference voltage V _f ' = V _f / 2 after the size change, the output V of the conversion circuit 40. _o'is not limited by the limiting circuit 50 and is input as it is to the control terminal of the contrast control circuit 70. Therefore, the change of the contrast control voltage V _o 'or the output V _B of the current detection circuit 100 with respect to the change of the volume voltage V is uniformly increased, and the change of the volume voltage V occurs between V _{T and} V _{max in} FIG. On the other hand, there is no range in which the output V _B of the current detection circuit 100 does not change, that is, the brightness does not change, and the effective operation range of the volume remains O−V _max even after the display size is changed.

In FIG. 6, the effective operating range of the volume is set to O-V _max when the display size is the reference size before changing, but the effective operating range of the volume before changing is O-V.
_{The same} can be considered in the case of _T (V _T <V _max ), that is, in the case where the brightness limitation acts in the middle of the volume voltage.

[0032] Figure 7 is effective when the operating range of the pre-change volume of _{O-V T, V-V} o -V where the display area to 1/2
It is a figure of _B. Lines A, B, and C in FIG. 7 have the same meaning as in FIG. The voltage output from the conversion circuit 40 before the display size is changed is an O-T-X straight line. But,
When the volume voltage is V _T , the output V _BT of the current detection circuit 100 becomes equal to the reference voltage V _f. Therefore, when the volume voltage is V _T or higher, the limiting circuit 50 controls the contrast control voltage V _o to be B in FIG. Bend at the T point like a line.

Similarly, the voltage output from the conversion circuit 40 after the display size is changed is a straight line of OT'-X ', and the control circuit 50 changes the reference voltage V _f ' =
Since it is restricted by V _f / 2, the straight line bends at the point T '. The volume voltage corresponding to the point T ′ is also V _T , and the effective operating range of the volume remains unchanged in this case as well. In addition, the fact that the image brightness does not change after the display size is changed is the same as in FIG. 6 when the C line is between OT ′ and T′−
It is clear from the fact that V _o does not change between X ′.

The relationship between the output V _BX of the current detection circuit 100 and the reference voltage V _f corresponding to the maximum voltage value V _max of the contrast volume before the display size is changed is V _BX <V
_In the case of _f , it is obvious that the effective operation range of the volume and the brightness of the display image after the display size is changed do not change from the case of V _BX = V _f in FIG.

As described above, according to the present embodiment, the size detection circuit for detecting the display area, the conversion circuit for level conversion according to the control signal from the size detection circuit, the beam current and the size detection circuit output. By providing a limiting circuit that compares the output voltage of the conversion circuit by comparing with the reference voltage, the range in which the contrast volume operates effectively does not change even if the display image is changed to an arbitrary display size. Does not change the brightness.

Further, since the beam current corresponding to the display area is limited, seizure of the tube surface, blooming, etc. can be prevented.

In this embodiment, the brightness control based on the contrast has been described, but the brightness control or the signal control relating to other brightness may be used.

Although it has been explained that the area normalization calculation is performed inside the calculation circuit 31, the standardized horizontal size,
The vertical size is used as an input of the calculation circuit 31, and the calculation circuit 31
Then just multiply.

[0039]

As described above, according to the present invention,
Even if the display area is changed, such as when the aspect ratio is changed, the range in which the contrast volume operates effectively does not change. Further, after the display area is changed, it is possible to suppress the change in the brightness of the display image. In addition, since the beam current is limited according to the display area, it is possible to prevent seizure of the tube surface, blooming, etc., and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an automatic brightness control device according to a first embodiment of the present invention.

FIG. 2 is a block diagram when the first embodiment is used for contrast control.

FIG. 3 is a diagram showing an input voltage V _i , an output voltage V _o, and a beam current amount V _B of a limiting circuit 50.

FIG. 4 is a diagram showing a voltage V of a contrast volume, a contrast control voltage V _o, and a beam current amount V _B.

FIG. 5 is a diagram showing the contrast control voltage V, the contrast control voltage V _o, and the beam current amount V _B.

FIG. 6 is a diagram of V-V _o -V _B by the conversion circuit 40.

FIG. 7 is a diagram of V-V _o -V _B by the conversion circuit 40.

FIG. 8 is a block diagram of a conventional example

FIG. 9 is a block diagram of another example of the conventional example.

[Explanation of symbols]

 30 size detection circuit 40 conversion circuit 50 limit circuit

Claims (2)

[Claims] 1. The brightness per unit area on the screen is made substantially equal by controlling at least the amplitude of the video signal based on control information related to the image display size of the cathode ray tube. Automatic brightness control device. 2. A size detection circuit for detecting the display size of an image by a signal related to the display size, and a conversion circuit for level-converting and outputting a control voltage for controlling the brightness of the display image according to the control signal of the size detection circuit. And a limiting circuit that limits the output of the conversion circuit by comparing the beam current amount with a reference voltage output from the size detection circuit, and stabilizes the brightness of the display image regardless of the change in the display size. An automatic brightness control device characterized by: