JPH04181892A - Contrast adjustment circuit - Google Patents

Abstract

PURPOSE:To easily obtain excellent white balance by devising the circuit such that white balance toward high brightness is adjusted by applying resistance division to a control voltage fed in common and white balance toward low brightness is adjusted by superimposing a low DC voltage onto the control voltage fed in common. CONSTITUTION:A contrast adjustment circuit is provided with a low contrast adjustment variable resistor 7 able to adjust a current Ib of a region of low brightness to each of red, green and blue electron guns only when a contrast variable resistor is adjusted minimum. An emitter level of a transistor(TR) 8 is set as Vout=VE/(1+n)+VbXn/(1+n), where n is a division ratio of a sub- contrast variable resistor 4, Vout is an output, and Vb is a bias voltage. The VE varies with the contrast adjustment variable resistor 7. The effect of the bias voltage Vb is large when the emitter level VE is small, that is, at a low brightness and not almost effected by the Vb when the VE is higher (that is, at high brightness). The white balance at low brightness is adjusted by varying the bias voltage Vb without giving effect on the high brightness.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a color cathode ray tube display device using a video amplifier configured to adjust contrast by varying a DC voltage. The present invention relates to a contrast adjustment circuit that allows good white balance to be obtained over the entire area.

(Prior Art) In recent years, cathode ray tube display devices (hereinafter referred to as CRT displays) have been increasing in frequency as the signals applied to CRT display devices have been increasing year by year in order to meet the demand for displaying more information on the CRT tube surface. has been done.

Therefore, the contrast adjustment of the video amplifier that amplifies these signals is performed by indirectly changing the amplification degree of the video amplifier by changing the DC voltage so as not to affect the frequency characteristics. Moreover, color CRT display devices are red and green.

White balance is maintained by adjusting the amplification of each blue video amplifier to a certain ratio.

An example of a conventional contrast adjustment circuit will be described below with reference to the drawings.

FIG. 4 shows a conventional contrast adjustment circuit. In Figure 4, 1, 2.3 are red and green.

Each blue video amplifier, 4, 5.6 is a sub-contrast volume for white balance adjustment, 7 is a contrast adjustment volume, 8 is a buffer amplifier, 9 to 1
3 is a resistor, C, , C, , C is each video amplifier 1, 2 .
This is a contrast control terminal for inputting the contrast adjustment control voltage of No. 3.

The operation of the conventional contrast adjustment device configured as described above will be explained. Each video amplifier 1.2.3 is
The degree of amplification is changed by the voltage applied to the contrast control terminal C11c and IC3, and the contrast is adjusted by changing the contrast adjustment volume 7.

On the other hand, in a color CRT display device, the color is red.

White color is produced by mixing the three primary colors of green and blue, and the sub-contrast volume is adjusted to a certain ratio according to the luminous efficiency of each color's phosphor using a sub-contrast volume of 4° and 5.6°. The brightness of a cathode ray tube (hereinafter referred to as CRT) is red, green,
It increases in proportion to the current value of each blue electron gun.

Therefore, the white balance is set such that the current ratios of the red, green, and blue electron guns are constant at high brightness (the contrast adjustment volume is at its maximum) in the subcontrast volumes 4 and 5.6.

(Problem to be Solved by the Invention) The current ゎ flowing through the electron gun of a CRT is as follows, where the mutual conductance is gl, and the voltage between the grid and the cathode is Vgk.

Ib=g, XVgk (1) The relationship between the voltage (Vgk) between the grid and the cathode of the CRT and the current (2) is as shown in FIG.

In FIG. 5, the mutual conductance g is Vgk-
It is expressed by the slope of the Iゎ curve.

g□=Δxb/ΔVgk As shown in Figure 5, this Vgk-I curve is not a straight line but near the cutoff voltage V kco (■ b is small→
When the brightness is low), the curve becomes large.

On the other hand, the current {circle around (2)} is as shown in equation ( ), so it does not change linearly with respect to a change in the voltage Vgk between the grid and the cathode. In the contrast adjustment, the voltage Vgk between the grid and the cathode is changed to change the contrast of the CRT display screen.

At this time, in order to obtain a good white balance, red,
It is necessary to make the ratio of the currents of the green and blue electron guns constant throughout the entire range of the contrast adjustment volume.

However, as mentioned above, the Vgk-■1 curve of the VRT is not a straight line, so adjusting the white balance at only one point in a high-brightness area is difficult to achieve by adjusting the cutoff voltage V
In the low-luminance area near kco, the ratio of the currents of the red, green, and blue electron guns changes, causing a problem in which the white balance is disrupted. On the other hand, there is also the problem that in order to obtain a good white balance, it is not possible to increase the variable range of the contrast adjustment volume.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a contrast adjustment circuit that can obtain a good white balance in the entire contrast volume even when contrast adjustment is performed over a wide range.

(Means for Solving the Problems) In order to achieve the above object, in the contrast adjustment circuit of the present invention, the current I in the low brightness area is set to red only when the contrast volume is narrowed down.

A low light adjustment volume that can be adjusted for each of the green and blue electron guns is provided.

(Function) Therefore, according to the configuration of the present invention, even if the contrast volume is changed over a wide range, it is possible to obtain a good white balance in the entire range of the contrast volume, and at the same time, the sub-contrast volume and the low light volume influence each other. Adjustment man-hours can be reduced to avoid this.

(Example) The contrast adjustment circuit of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a contrast adjustment circuit in one embodiment of the present invention. In FIG. 1, the same numbers as in the conventional example indicate the same parts. 20 to 2
7 is resistance, 50.51.52 is red, green.

Transistors 61, 62, and 63 perform emitter follower operation for each color of the lamp, and 61, 62, and 63 are low light adjustment volumes.

FIG. 2 is a diagram for explaining the operating principle of the present invention, and the following explanation will be given based on FIG. 2.

When the emitter potential of the transistor 8 is VE, the division ratio of the sub-contrast volume 4 is n, the output is Vout, and the bias voltage is ■, Vout=VE/(1+n)
+V, Xn/(1+n) where vo changes depending on the contrast adjustment volume 7. Now, normalize each position and give it as follows.

V, = 0.05 to 1.0 n = o, 05, and V is 0,05.0.1.0. ], 5, the ratio changes as shown in FIG. 3 when the bias voltage ゎ=0 is taken as a reference.

In FIG. 3, the emitter potential v8 is novo 1 smaller,
In other words, when the brightness is low, the influence of the bias voltage is large,
This shows that when vo is large (that is, when the brightness is high), it is hardly affected by vb. By installing this circuit in the contrast adjustment circuit of each red, green, and blue video amplifier, red and green on the low brightness side can be adjusted.

You can change the amplification degree of each blue video amplifier.

This result shows that by changing the bias voltage vb, the white balance on the low luminance side can be adjusted without affecting the high luminance side.

In FIG. 1, the potential of El (corresponding to ■ in FIG. 2) is from the base potential of the transistor 50 to the emitter-base voltage ■, as is well known. The value will be much lower.

Therefore, by changing the low light adjustment volume 61, the emitter potential of the transistor 50 changes, and white balance on the low brightness side can be achieved.

(Effects of the Invention) As is clear from the above embodiments, the present invention provides a transistor and a volume for low light adjustment.
The white balance on the low-brightness side near the CRT cutoff can be adjusted without affecting the high-brightness side, and not only can a good white balance be obtained over the entire contrast variable range, but it also reduces the number of adjustment steps and improves productivity. It also has the effect of being measured.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a contrast adjustment circuit according to an embodiment of the present invention, FIG. 2 is an operational principle diagram for explaining FIG. 1, and FIG. 3 is a V of the circuit of FIG. 2. FIG. 4 is a block diagram of a conventional contrast adjustment circuit, and FIG. 5 is a Vgk-Ib characteristic diagram of a cathode ray tube. 1.2.3...Video amplifier, 4,5゜6...Sub contrast volume, 7...Contrast adjustment volume, 8...Buffer amplifier, 9-1
1.20~27...Resistance, 50.51.52...
Transistor, 61°62, 63...Low light adjustment volume, C,,C,,C,...Contrast control terminal. Patent Applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 1.2.3,--BioW/A 4.5.6,
,, Bubukore Trust Nail Sum 71. G) Toraman's so-called vertical claw volume 8-, Hai... Nofu 77-/F9
jO, +1.20.21.22.23.2425.26
．． 27, -lft 50.51.52°゛-tra)
Booster 616263, - Low light adjustment volume C
+, C2, C3 - Ko 7 Trust Tomo 1 Koi Sen Figure 2 Figure 4

Claims (1)

[Claims] It has a color cathode ray tube display device that uses three video amplifiers whose amplification degree can be adjusted by changing the DC voltage for control, and the DC voltage for control is commonly supplied to the three video amplifiers to increase the contrast. In a contrast adjustment circuit configured to adjust the white balance by individually changing the control voltages to the three video amplifiers at the same time, the white balance adjustment on the high brightness side is performed using a commonly supplied control. The voltage is divided by resistance,
On the low-brightness side, the contrast adjustment circuit is configured to adjust white balance by superimposing low-voltage direct current on the commonly supplied control voltage.