JPS6074792A - Brightness adjusting circuit - Google Patents

Abstract

PURPOSE:To prevent deterioration of white balance on screen by amplifying a brightness control signal in common to all cathodes with respectively corresponding gain to superpose the result on a cut-off set voltage of each cathode in a cathode clamp system. CONSTITUTION:The gain of a variable gain amplifier 6 for adjusting brightness is set independently for R, G, B depending on the difference of gradient of an optical output characteristics of R, G, B so as to change respectively the transmission rate transmitted from a common brightness adjusting voltage 2 superposed on a cut-off level setting voltage 5 for R, G, B respectively. Thus, the deterioration of white balance on the screen is prevented by using the brightness adjusting voltage 2 in common to the R, G, B.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention differs in the light output characteristics of each of 几(red), G(green), and B(T).

This relates to a brightness adjustment circuit that keeps the white balance of the screen constant regardless of the brightness in a video output circuit for television receivers in which unique cutoff voltages are set for each of the cathodes G and 13. .

[Background of the Invention] FIG. 1 shows the threshold voltage ( 3 is a graph showing optical output characteristics with respect to Vx-o+).

In the tJ1 diagram, red (几), green (G), ff (
The order of B) differs depending on each CPT. Also, EK
CO is called a cathode cutoff voltage and indicates the rising stain pressure of optical output. In order to achieve good white balance when the screen is dark, it is necessary to match the black level of the drive voltages of 几, G, and B with the respective Rxcos. This is generally called cutoff adjustment, and the cathode voltages of R, (+, and H are each independently shifted by 1 DC), and as mentioned above, the darkest part of the drive voltage of JG and B is adjusted to that voltage. This is to match the corresponding &co.

FIG. 2 shows an example of a conventional circuit for adjusting screen brightness in a wideband video output circuit in which cutoff voltages are set independently for R, U, and B at cathode terminals. Below, the circuit operation will be explained using FIG.
We will also discuss the shortcomings of the circuit example shown in the figure.

In Fig. 2, 1 is an integrated electron gun structure (only the cathode electrodes H, G, B are independent, and the other electrodes are R).

CPT with G and B common),
GI is the first grid (control grid), G! indicates the second grid (screen grid). 2 indicates a brightness adjustment voltage, 6 indicates a video output amplifier, 4 indicates a clamp transistor, and 5 indicates a cut-off level setting voltage. The subscripts of 几, G, and H are 几 and G, respectively.
, means B-only.

In FIG. 2, the video signal input to the video output amplifier 5 is
The light is amplified to the extent that sufficient brightness can be obtained and output to the cathode terminal of CI'T10. Here, the video signal is subjected to direct current generation by the clamp transistor 4 during the black level (or blanking) period, and a direct current potential equal to the cutoff voltage of each cathode of IL, G, and B is applied to the cathode. The DC potential of the cathode is determined by the cutoff level setting voltage 5 iL, (,i,B
It can be set independently and can be matched with the CPT10 cutoff voltage EKCO. As described above, cutoff adjustment, which is an important item in CPT white balance adjustment, can be performed without any problems.

However, the circuit shown in FIG. 2 has a serious drawback in ensuring white balance when adjusting brightness. Deterioration of white balance during brightness adjustment in the circuit shown in FIG. 2 will be described below.

In Fig. 1, as the brightness increases, t, (i,
It is sufficient to bring VK-at of B close to zero potential. In the circuit shown in Fig. 2, this operation is performed by changing the potential of G to 11 with a brightness adjustment voltage of 2.
・, G, 13 are commonly changed.

Although this method has a simple configuration and allows brightness adjustment to be performed using a DC power source, deterioration of the white balance due to brightness adjustment is unavoidable. This is done by changing part of the cut-off voltage setting voltage 5 to R and G in the circuit shown in FIG.

The same applies to a method in which B is shared and the brightness is adjusted by changing the common potential. Hereinafter, the cause will be explained using FIG. 1.

In Fig. 1, when Vx-o+ is uniformly changed for each of 几, Q, and H, even if the black level of the video signal matches the cutoff level, )J
Since the inclinations (gradients) of the VK-o+ optical output characteristics of G and 33 are different, the uniformity of the optical output cannot be maintained after and before changing VK-o+. This is a very serious problem for color displays because the color tone of the display screen changes depending on the state of brightness adjustment.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a brightness adjustment circuit in a video output circuit of a television receiver that can maintain a good white balance regardless of the brightness adjustment state of the screen. .

[Summary of the invention]

In order to achieve the above-mentioned object, in the present invention, R.G.

B: A method in which one common brightness adjustment voltage is manually operated.

The output of each amplifier whose gain can be adjusted independently for G and B is expressed as R,
Superimposed on the cutoff setting voltage of G and B, JL,
Q.13 The difference in the slope of the optical output characteristics is corrected by the gain adjustment function of the amplifier to prevent the white balance of the screen from deteriorating due to brightness adjustment.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a circuit diagram showing one embodiment of the present invention. In this figure, the same parts as in Figure 2 are given the same license number. FIG. 6 shows a variable gain amplifier for brightness adjustment.

The deterioration of white balance due to brightness adjustment, which was a big problem with the brightness adjustment mechanism shown in Figure 2, is caused by the fact that the slopes of the light output characteristics of It, G, and JJ are different from each other.
This was caused by adjusting the brightness using the I3 common voltage.

・ Therefore, in the present invention, as shown in FIG.
The difference in the slope of the optical output characteristics of G and H is set independently for the total gain 1t of the brightness adjustment variable gain amplifier 6, G and B, and the common brightness adjustment voltage 2 to B.,G.

By changing the transmission rate transmitted for superimposition on the cut-off level setting voltage 5 of each B, J, R, G
, B is used to prevent the white balance of the screen from deteriorating.

Next, a specific circuit example of the present invention and its circuit operation will be described using FIG. FIG. 4 is a circuit example specifically showing the vicinity of the clamp transistor 4, cut-off level setting voltage 5, and brightness adjustment variable gain amplifier 6 in FIG. 3.

For the sake of simplicity, only one channel for output is shown in FIG. 4, but in an actual circuit, two additional channels of the same circuit are added for G and H. In FIG. 4, the same parts as in FIGS. 2 and 5 are given the same numbers.

In FIG. 4, numeral 7 indicates a cathode voltage control block including a cut-off level setting voltage 5 and a variable gain amplifier 6 for brightness control. Reference numeral 8 indicates a cutoff voltage setting resistor, and 9 indicates a gain adjustment resistor. The operation of the circuit shown in FIG. 4 will be explained below.

First, in order to cut off the transistor Q1, the voltage of the brightness adjustment voltage 2 is made high enough.

In this state, the static bias current of the transistor is changed using cutoff adjustment resistors 8, the output impedance is lowered using the common collector amplifier of the transistor Qs, the emitter potential of the clamp transistor 4 is fixed, and the cutoff voltage is set.

Note that the transistor Q# can be omitted as long as the clamp voltage is stable.

Next, the transistor Q is activated, and the gain adjustment resistor 9
By changing the temperature, the slope of the J CILT optical output characteristics is corrected.

Through the above operations, the transmission rate to each set voltage sl(, s(j, sB) of the brightness adjustment voltage 2 common to R, G,
, B independent setting text, CPT] VK-o+ It is possible to prevent deterioration of the white balance of the screen due to differences in the slope of the light output characteristics.

[Effects of Hatsu J]

The present invention solves the deterioration of the screen white balance during brightness adjustment, which was a very serious drawback in the cathode clamp method that applies two voltages at the cathode terminal, which is necessary when driving the integrated electron gun CPT with a wideband video signal. It is resolved. According to the present invention, the brightness of a high-resolution display can be changed without deteriorating the color tone, thereby significantly improving marketability.

Furthermore, if CPT beam current information is superimposed on point A in FIG. 4, it also functions as an ABL control loop (controlling the screen brightness so that it does not become brighter than a certain limit).

Furthermore, it is clear that the present invention can be applied to a system in which IL, G, and H cathode ray tube electron guns are each independent.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing an example of the light output characteristics of a color cathode ray tube, and Figure 2 is a television receiver.
10'(11ii1 kta Iz (-νt L 2
tskt /7'N trial 1 alp mW clause 1a swimming momme σ)-A circuit diagram showing an example, Figure 6 is a circuit diagram showing an example of the failure], Figure 4 is the main part of the circuit in Figure 6. This is the schematic circuit diagram of 1... CP T 4... Clamp transistor, 5... Cutoff level setting voltage, 6... Brightness 141 adjustment variable gain amplifier. (゛Pa'・YoI, benyu artist Akira Takahashi-)゛3rd Roo 4 Figure I8I'b

Claims (1)

[Claims] 1) Television receiver with different light output characteristics for 几 (red), q (green), and B (blue), and therefore unique cutoff voltages are set for the cathodes of R, G, and B. In the video output circuit of the machine, each cathode is provided with a dedicated variable gain amplifier whose gain can be set independently, and a brightness control signal common to all cathodes is amplified by each amplifier with a corresponding gain. A brightness adjustment circuit characterized in that the cutoff setting voltage is superimposed on the cutoff setting voltage of each corresponding cathode.