JPH066823A - Low light adjustment circuit and low light adjustment method - Google Patents

Abstract

PURPOSE:To decrease a chip area by fixing a cut-off voltage of a G(green) and selecting an adjustment range of the G to be minimum adjustment accuracy of brightness so as to minimize the low light adjustment range of the G and minimizing the number of total bits. CONSTITUTION:A cut-off voltage of the G is set to 160V while a low light of the G is set to a center. Then white balance is matched by using a white balance meter. The dispersion in the cut-off is -1.24V-+1.6V at an IC output point and a minimum adjustment voltage required for white balance adjustment is nearly 6mV. Thus, a 9-bit DAC is required for R(red), B(blue) colors. On the other hand, when the adjustment range of brightness is considered, since an IC output is + or -1.5V or so, the brightness adjustment with a 7-bit DAC calls for 23.4mV at a minimum adjustment range of brightness. Thus, the low light adjustment range of the G is 4 steps, that is, a 2-bit DAC is enough for the adjustment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low light adjusting circuit and a low light adjusting method, and more particularly to a low light adjusting circuit for white balance adjustment by bus control.

[0002]

2. Description of the Related Art The low light adjustment in the white balance adjustment is to adjust the black level points of three tubes of red, green and blue by adjusting the variation of the cutoff level of the CRT. There are basically two types of adjustment methods.

Now, as shown in (FIG. 2), R (red) and G
Consider an example when there is a variation range of the cutoff levels of (green) and B (blue). That is, the cutoff levels of R, G, and B vary between a and a.
Therefore, when the G level is high and R and B are low as shown by A in the figure, the G level is low and R and B are high as shown by A in the figure. If this value is expressed by a specific numerical value, for example, the cutoff voltage of a CRT is 160
Assuming V and cutoff ratio of 1.3, in the case of A, when the cutoff voltage of G is 160V, the cutoff voltages of R and B are 123V, and in the case of A, R and B are
Cutoff voltage of 160V, cutoff voltage of G is 12
It is 3V, and the variation is 37V in both cases.

The first adjustment method is shown in FIG.
In the method shown in A), the low light of R, G, B is set to the center value, and then the one having the highest cutoff voltage of R, G, B is first adjusted to 160V. That is, in the case of the variation of (a) in FIG. 2, G is set to 160 as shown in (FIG. 3).
Adjust to V. Next, the white balance of R and B is adjusted using a white balance meter. At this time, the final state is the cutoff points of R, G, and B shown by A in the figure. Similarly, in the case of (a), R and B are first set to 160V. Next, when the white balance of R and B is adjusted using a white balance meter, the state of (a) in FIG. 3A is finally reached and the white balance is adjusted.

Next, the second adjusting method is shown in FIG.
In the method shown in B), first, the cutoff of G is 160V.
To match. After that, the white balance is adjusted using a white balance meter. In the case of this method, G is 160 when the cutoff voltage of the CRT has a variation of (FIG. 2).
When V, R, and B are 123 V, that is, the white balance is achieved at the cut-off point of (a) in FIG. 3B, and the CRT cut-off voltage is a variation in (a) in FIG. 2, G is 160 V,
White balance is achieved at the 208V point of R and B, that is, at the cut-off point of (a) in FIG. Therefore, the second adjustment method requires about twice the adjustment range as the first method.
However, since the G cutoff voltage is fixed at 160 V, the brightness stability is good.

Considering that this adjustment is performed by bus control, if the amplification factor of the neck circuit is set to 30 times, the cutoff variation of 37V is 1.24V at the IC output point. Normally, when the neck amplification factor is about 30 times, the minimum adjustment voltage required for white balance adjustment is about 6 mV. If the minimum adjustment voltage is 6 mV, the number of steps for adjustment is 207, and the 8-bit DAC (255
Step) is required. Therefore, in the case of the first adjustment method, 8-bit DAC is used for R, G, and B,
In the case of the second adjustment method, the cutoff variation is 8
2. At the IC output point with 5V (+ 48V, -37V).
When the minimum adjustment voltage is 6 mV, the number of steps is 472, and R, G, and B are 9-bit DAC (51
The white balance is adjusted by using (1 step).

[0007]

However, in the above-mentioned structure, a DAC having a large total bit is required, and a chip area is increased in forming an IC, which is also disadvantageous in terms of yield. In addition, this is costly.

In view of the above point, the present invention fixes the G cutoff voltage and minimizes the G low light adjustment range, thereby minimizing the total number of bits and adjusting the low light adjustment in an IC having a small chip area. The purpose is to provide a circuit.

[0009]

In order to solve the above problems, the low light adjustment circuit of the present invention ensures the minimum adjustment accuracy of R and B to be the same as the conventional one, and the minimum adjustment accuracy of G is R and B. Although the accuracy equal to is secured, the G adjustment range is set to the minimum brightness adjustment accuracy of G to minimize the G low light adjustment range.

[0010]

With the above-described structure, the present invention can minimize the adjustment range of G, reduce the number of bits of the DAC, reduce the chip area of the IC, and improve the yield.

[0011]

FIG. 1 shows an adjusting method and an adjusting range of white balance adjustment by a bus control circuit in the first embodiment of the present invention. Hereinafter, description will be given according to (FIG. 1).

First, the low light of G is set to the center value, and the cutoff of G is set to 160V. After that, the white balance is adjusted using a white balance meter. At this time, the G adjustment level can be completely adjusted to 160V by the bright and low light adjustments. In the case of this method, when the cutoff voltage of the CRT has a variation in the (FIG. 2), the cutoff point of the (FIG. 3B) is
In the case where the CRT cutoff voltage has a variation (a in FIG. 2), it becomes a cutoff point in (a) in FIG. 3B. Therefore,
The second adjustment method requires twice the adjustment range as the first method. However, the cutoff voltage of G is 1
Since it is fixed at 60V, the brightness stability is good.

When this adjustment is performed by the bus control, if the amplification factor of the neck circuit is set to 30 times, -37V to +
48V cutoff variation at the IC output point
It becomes 1.25V to + 1.6V. Normal neck gain 30
About double the minimum adjustment voltage required for white balance adjustment is 6m
It is about V. If the minimum adjustment voltage is 6 mV, the number of steps for adjustment is ± 207, and 9-bit D
AC (± 255 steps) is required. Therefore, R,
B requires a 9-bit DAC. On the other hand, considering the brightness adjustment range, since the IC output is about ± 1.5 V, the minimum brightness adjustment range is 23.4 mV when brightness adjustment is performed with a 7-bit DAC. Therefore, the low light adjustment range of G is 4 steps, that is, 2-bit DA.
It can be adjusted with C. Therefore, the G DAC can be reduced from the conventional 9 bits to 2 bits.

[0014]

As described above, according to the present invention, the cutoff voltage of G is fixed, the minimum adjustment accuracy of R and B of the low light adjustment circuit is equal to the conventional one, and the minimum adjustment accuracy of G is R. , B, but the adjustment range is set to the minimum adjustment accuracy of bright, and the low-light adjustment range of G is minimized to minimize the total number of bits and reduce the chip area. Since the cost can be reduced and the yield can be improved, its practical effect is very large.

[Brief description of drawings]

FIG. 1 is an adjustment method and an adjustment range for white balance adjustment by a bus control circuit according to an embodiment of the present invention.

FIG. 2 is a white balance and adjustment range of a conventional IC bus control circuit.

FIG. 3 (A) White balance and adjustment range of a conventional IC bus control circuit (B) White balance and adjustment range of a conventional IC bus control circuit

[Explanation of symbols]

 A R, B adjustment range (9-bit DAC) B G adjustment range (2-bit DAC)

Claims (4)

[Claims] 1. In a semiconductor integrated circuit for performing white balance adjustment by bus control, an adjustment range of red and blue pedestal voltages is at least 2 of a cutoff ratio of a CRT.
And the adjustment accuracy required for white balance is double, the adjustment accuracy of green has an adjustment accuracy equal to or higher than that of the red and blue, and the adjustment range of the green is smaller than the adjustment range of the red and blue. A low light adjustment circuit characterized in that 2. The low light adjustment circuit according to claim 1, wherein the adjustment range for green is less than half of the adjustment range for red and blue. 3. In a semiconductor integrated circuit for performing white balance adjustment by bus control, the green low light adjustment range is equal to or twice the minimum brightness adjustment range, and the red and blue pedestal voltage adjustment ranges are set. Is at least twice the cut-off ratio of the CRT, has the adjustment accuracy necessary for white balance, and the green adjustment accuracy has the same or higher adjustment accuracy as the red and blue. circuit. 4. In a semiconductor integrated circuit for performing white balance adjustment by bus control, a green low light adjustment range is equal to or twice as large as a minimum brightness adjustment range, and red and blue pedestal voltage adjustment ranges are set. Is at least twice the cutoff ratio of the CRT, has the adjustment accuracy required for white balance, the green adjustment accuracy is equal to or higher than the red and blue adjustment accuracy, and the bright adjustment and green low adjustment A method for adjusting low light, characterized in that a green cutoff voltage is fixed to a predetermined voltage by light adjustment.