JPS5827717B2 - Inkiyokusen Kanno Kudousouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode ray tube drive device suitable for application to color television receivers and the like.

In a color television receiver, if the image projected on the cathode ray tube is a black and white image, it is necessary to white balance the entire screen from bright to dark areas.

In this case, the white balance in the dark part of the screen,
The background is adjusted by adjusting the cutoff of the electron gun corresponding to each primary color of R, G, and B, and the gain of the drive circuit related to the rotary drive electrode of the cathode ray tube is adjusted for bright areas. The white balance is adjusted by

FIG. 1 shows a conventional example for performing these white balance adjustments.

In this example, a cathode dosing method is used, and 1
0 indicates the main part of a drive circuit for driving the Cassette cathode ray tube 1. In FIG.

The drive circuits 10 are provided for each of the R, G, and B color signals, but since they have the same configuration, only one of them will be specifically shown.

Ql and Q2 are the final stage drive transistors that constitute the drive circuit 10R, and in this example, one transistor Q is an np transistor.
The other one Q2 is of npn type, and these are connected in series as shown.

As is well known, the input terminal 2a provided on the base side of one transistor Q1 receives a luminance signal sY or (RY').
) color difference signal S.

However, the (R-Y) color difference signal or luminance signal SY is supplied to the other input terminal 2b, and therefore, the R color signal is obtained as an output on the collector side of the transistor Q1. , this primary color signal SR is supplied as a drive signal to the cathode electrode KR, which is a drive signal of the cathode ray tube 1.

Note that 4 represents a power supply terminal, and 5 represents a collector resistor.

Here, in order to adjust the white balance, conventionally, as shown in the figure, a first variable resistor 6 is connected in series in the current path of transistors Q1 and Q2, and a first variable resistor 6 is connected in series between the emitter of transistor Q1 and ground. 2 variable resistor 7 is also connected.

Here, the white balance adjustment in the dark part of the screen can be performed by adjusting the cutoff voltage of the cathode ray tube 1, but this cutoff voltage is
This can be achieved by controlling the collector voltage of 1.

Therefore, if the second variable resistor 7 is adjusted now, the collector current IC of the transistor Q1 can be varied, so that the collector voltage can be controlled as a result, and the cutoff voltage can be adjusted.

Furthermore, by adjusting the first variable resistor 6, the gain G in the drive circuit 10R can be adjusted, thereby making it possible to adjust the white balance in bright areas of the screen.

In principle, each white balance adjustment can be made independently as explained above, but in reality, the results of each adjustment affect the adjustment contents of the other, so-called mutual interference, so the white balance adjustment The adjustment is extremely troublesome, and in particular, it is necessary to perform this adjustment while interrelating all three drive circuits 10R to 10B, which has the disadvantage that the adjustment cannot be performed quickly and accurately.

Therefore, the current flowing through the variable resistors 6 and 7 is 16 si
7, the collector current i.

is given by, and when the resistance values of resistors 5, 6, and 7 are R, , R6, and R7 in order, the gain G is given by:

Therefore, when the second variable resistor 7 is adjusted to adjust the collector current IC, the resistance value R7 is changed at the same time as the collector current IC, so that the gain G is also changed.

On the contrary, if the gain G is adjusted, the collector current IC will also be affected and they will interfere with each other.

The present invention eliminates these drawbacks by simplifying the structure, and the present invention device will be explained with reference to FIG. 2 and subsequent figures.

However, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

In the present invention, as shown in FIG. 2, a variable constant current source 20 is provided, and this is connected to the emitter side of the transistor Q1 instead of the second variable resistor 7.

The variable constant current source 20 has a transistor Q3, which is connected between the terminal of the transistor Q1 and the ground, and whose base is connected to a variable resistor 2 for varying the current 17.
1 to the DC power supply terminal 22.

In this example, in addition to this configuration, a transistor Q is added.

The base biases of Q2 and Q2 are set as described below.

Now, the signal supplied to the terminal 2a is the color difference signal S.

The signal supplied to the terminal 2b is the brightness signal SY.

The black level potential of the luminance signal SY is vl, and the color difference signal S is vl.

When the bias potential is 2, the base biases of the transistors Q1 and Q2 are set in advance so as to satisfy the following equation (2Bo is the voltage between the base and emitter of the transistors Qi and Q2).

24 and 25 indicate bias circuits therefor, respectively.

The circuit configuration described above is similarly applied to the other drive circuits 10B and 10G.

Next, a method for adjusting the white balance using the drive circuits 10RK and 10B will be described. First, to adjust the background, a black level signal, for example, is supplied only to the terminal 2b.

In the case of this black level, since equation (3) holds true,
The potential between the terminals of the variable resistor 6 becomes zero, so the current i
6 is zero.

Therefore, the collector current IC of the transistor Q1 is determined only by the current 17 flowing through the constant current source 20.

Therefore, by adjusting the variable resistor 21 to control the current 17, the collector voltage of the transistor Q1 can be easily made to match the cutoff voltage of the cathode ray tube 1, regardless of the variable resistor 6.

First, the background can be adjusted simply by adjusting the current 17.

To adjust the white balance in bright areas, the variable resistor 6 may be adjusted while the brightness signal SY having a white level potential is supplied to the terminal 2b described above.

In this case, the output impedance of the constant current source 20 is R()
Then, equation (2) becomes as follows.

Then, since the output impedance R8 is sufficiently large compared to the resistance value R5 and can be ignored, if this condition is included, (4)
The formula can be transformed as follows.

As is clear from equation (5), the gain GV'i is constant only by the ratio of the resistance values R5 and R6, and has nothing to do with the variable constant current source 20.

Therefore, gain adjustment has no effect on background adjustment.

As explained above in explanations 1 to 1, since the present invention is designed to adjust the background by providing the variable constant current source 20 and adjusting its current 17, it is necessary to set the collector current IC. Even if 17 is adjusted, each constant for determining the gain G is not affected.

Therefore, it has the feature that the background can be adjusted independently without affecting other parts.

Furthermore, when transistors Q1 and Q2 are connected in series as in this example, if the bias relationship is selected as shown in equation (3), the background adjustment will not be affected during gain adjustment, and mutual interference will be avoided. It has the characteristic of adjusting the white balance independently for each of them without causing any problems.

Therefore, although the adjustment is quick and simple, it is possible to accurately adjust the white balance.

FIGS. 3 to 5 each show other examples of the apparatus of the present invention.

The example shown in FIG. 3 is a case where a variable constant current source 20 is connected between the collector of transistor Q1 and ground.

The example shown in FIG. 4 is a case in which transistor Q4 is cascode-connected to Ql to obtain better frequency characteristics, and the collector of transistor Q4 is connected to terminal 3R of cathode electrode KR.

In the example shown in FIG. 5, a switch 27 is added as shown in the embodiment shown in FIG. 2, and when the switch 27 is turned off, the background is adjusted.

By providing the switch 27 in this way, it is possible to adjust the white balance including the background adjustment by simply supplying only the luminance signal SY including both the black level and the white level as the signal supplied to the terminal 2b.

It goes without saying that this switch 27 can also be used in each of the embodiments shown in FIGS. 2 to 4.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing a conventional example of a cathode ray tube drive device, and FIGS. 2 to 5 are connection diagrams showing an example of a cathode ray tube drive device according to the present invention. 1 is a cathode ray tube, IOR~10B is a drive circuit, 2ay 2
b is a supply terminal for a luminance signal and a color difference signal, 20 is a variable constant current source, and 6 is a variable resistor.

Claims (1)

[Claims] 1 A variable impedance for gain adjustment is provided at the emitter of a transistor forming a drive circuit for driving a cathode ray tube, and a variable constant current source with a sufficiently large output impedance is provided between the collector or emitter of the transistor and ground, and this variable constant current source is provided between the collector or emitter of the transistor and ground. A cathode ray tube driving device, characterized in that the cutoff voltage of the cathode ray tube is adjusted by adjusting the current value of a current source.