JPS6244480B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic white balance adjustment circuit for a color television receiver, which allows easy adjustment and always automatically maintains a good white balance by monitoring reproduced images. Regarding.

In a color television receiver, if the color tone of the reproduced color image is not maintained in a good condition, the reproduced image will become unnatural, so the color tone must be adjusted correctly. In particular, if the white parts of an image are colored, the image quality will be significantly impaired, so great care is taken in adjusting the white balance.

As a conventional white balance adjustment method, for example, the video output circuit of a color television receiver is configured as shown in Figure 1, and the white balance is adjusted by setting resistors 1 to 5 as semi-fixed resistors. It is known what has been done.

In this circuit of FIG. 1, 13, 14, 15
are blue, green, and red video output transistors, respectively; 16, 17, and 18 are blue of the color picture tube 22;
Green and red cathodes, 19 are video signal sources, for example, the final stage of a video amplifier, 20
is the chroma signal source. Note that 1 to 12 are resistors, of which resistors 1 to 6 are for white balance, and resistor 7 is for white balance.
-9 are for protection, resistors 10-12 are load resistances of output transistors 13-14, and 21 is a power supply terminal.

To adjust the white balance using this circuit, proceed as follows.

First, a signal corresponding to the dark part of the image is applied from the video signal source 19, and while comparing the reproduced image of the picture tube 22 with the standard white color of the monitor, adjust the reproduced image to the standard white color by appropriately moving the semi-fixed resistors 1 to 3. .

Next, a signal corresponding to the highlight portion of the image is added from the video signal source 19, and the semi-fixed resistors 4 and 5 are adjusted so that the reproduced image matches the standard white color. At this time, since the red phosphor usually has poor luminous efficiency, it is practical to keep the resistor 6 at a minimum amount so that it does not move.

In this way, by adjusting the dark and highlight areas of the reproduced image to the standard white color, it is possible to achieve a sufficient white balance in general cases.

This is because although the gamma characteristics of picture tubes vary numerically, the way they change is almost the same, so if the white balance is maintained between the dark and highlight areas, then almost the entire gradation range will be covered. This is because a sufficient white balance can be obtained throughout.

As is clear from the above description, in conventional color television receivers, white balance must be achieved by adjusting as many as five or six resistors for each receiver.
Furthermore, as is clear from the details of the adjustment, this white balance adjustment is a rather troublesome task, and is a task that requires particularly time and skill among the adjustment tasks for a receiver.

Furthermore, although the gamma characteristics of picture tubes tend to change over time, it is extremely difficult for the user to manually adjust the white balance, so it is generally difficult to adjust the white balance manually. In many cases, images with unbalanced whites are used as is, leading to an increase in the number of users who are dissatisfied with the quality of the receiver.

An object of the present invention is to provide an automatic whitening system for a color television receiver that eliminates the drawbacks of the prior art described above, allows easy white balance adjustment, and can automatically maintain the white balance even if the characteristics of the picture tube change. To provide a balance adjustment device.

In order to achieve this object, the present invention is characterized in that the white balance is automatically corrected according to the state of light emitted from the fluorescent surface of the picture tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments and drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, including resistors 10 to 12, transistors 13 to 15, cathodes 16 to 18 of the picture tube 22, and signal sources 19 and 20.
etc. are the same as the circuit shown in FIG.

37 to 42 are control transistors added in place of the resistors 1 to 6 in FIG. 1, 43 to 48 are switching transistors, and 55 and 56 are picture tubes 2.
2, a phototransistor 57 provided in contact with the fluorescent surface of 2; 57 a Zener diode for keeping the emitter voltages of the transistors 40 to 42 constant; 60;
70 are terminals to which pulse control voltages having waveforms as shown in FIG. 3 are supplied, respectively. Also, 23
- 34 are resistors for operating each transistor appropriately, 35 and 36 are phototransistors 55,
56 is a load resistor, 49 to 54 are signal holding capacitors, 58 and 59 are phototransistors 55,
This is a constant voltage source terminal for operating 56.

The phototransistors 55 and 56 are located at appropriate portions of the fluorescent surface 76 of the picture tube 22, as shown in FIG.
For example, a phototransistor 5 is provided facing the end of the image reproduction part, and a phototransistor 5 is provided in this part of the fluorescent surface 76.
Red phosphor 7 in a size that corresponds to both 5 and 56.
7 is coated, and the shadow mask 74 is also provided with corresponding holes 78 and 79 which are much larger than the hole 75 for image reproduction, so that the shadow mask 74 is provided with holes 78 and 79 which are much larger than the hole 75 for image reproduction. The body 77 is designed to emit light. Note that 71 to 73 are blue, green, and red phosphor stripes for image reproduction, respectively.

Next, the operation will be explained.

First, when comparing the embodiment shown in FIG. 2 with the conventional example shown in FIG. 1, we find that the resistors 1 to 3 in FIG. A phototransistor 5 is connected to the bases of these transistors 37 to 42 via control transistors 43 to 48.
It can be seen that signals from 5 and 56 are added.

First, we will explain the operation of the portion consisting of the transistors 40, 46 and the phototransistor 56.First, a vertical blanking pulse is transformed from the terminal 60 to the video signal source 19, and the second half of the vertical blanking pulse is changed from time _T1 to T. ₂ , the signal a in FIG. 3 is supplied with a step of voltage a' corresponding to the dark part of the image, and voltage a'' corresponding to the highlight part between time _T2 and _T3 , Also, the chroma signal source 20 has a period of voltages a' and a'' of the signal a, that is, from time _T1 to
A color killer signal b for blanking only during T ₃ is supplied from the terminal 61.

Therefore, at time _T1 , the pulse signal f is supplied to the terminal 62 and the pulse signal l is supplied to the terminal 68, and the transistors 13 and 46 become conductive. Therefore, a signal from the phototransistor 56 is applied to the base of the control transistor 40 via the switching transistor 46, and the conductivity of the transistor 40 is changed from the phosphor 77 of the picture tube 22 to the phototransistor 56. Control according to the amount of light.

Now, assume that the voltage of the blue cathode 16 is V, and the blue beam current, that is, the current flowing into the cathode 16 through the resistor 7, is I. Between time T ₁ and T ₂ in FIG. 3, the output from the chroma signal source 20 is 0 due to the killer signal b being supplied to the terminal 61;
A pulse signal f is applied from the terminal 62 to the base of the output transistor 13 for the blue signal, and
The video signal source 19 generates an output corresponding to the dark part of the image according to the voltage a' of the signal a, and this is applied to the emitter of the output transistor 13 via a parallel circuit of a transistor 37 and a resistor 23. . Therefore, the blue cathode 16 is supplied with a beam current I corresponding to the dark part of the image due to the voltage a' of the signal a, and the phosphor 77
emits light. At this time, the green and red cathodes 17,
18 is cut off. Because signal b
is applied to the chroma signal source 20 from the terminal 61 and is in a color killer state, and no signal is applied to the terminals 63 and 64, and the output transistor 1
This is because lines 4 and 15 remain blocked.

Now, when a current I flows through the blue cathode 16 and the phosphor 77 emits light, the light enters the phototransistor 56, and the internal resistance of the phototransistor 56 decreases depending on the intensity of the light. Therefore, the current flowing through the load resistor 35 increases and its voltage drop increases, so the voltage applied to the collector of the switching transistor 46 decreases, and the base voltage of the control transistor 40 also decreases. Therefore, the emitter-collector current of the transistor 13 decreases and the voltage drop due to the load resistor 10 decreases, so the voltage V at the blue cathode 16 increases. That is,
As the beam current I increases, the voltage V at the cathode 16 also increases, and as I decreases, V also decreases.

The above is from time _T1 to _T2 , and at this time, the signal voltage from the phototransistor 56 applied to the base of the control transistor 40 is accumulated in the capacitor 52, and the time constant allows three vertical scanning It is designed to be held for a period of time, ie, from time T ₂ to T ₄ in FIG.

Next, the portion consisting of the transistors 37 and 43 and the phototransistor 55 will be explained.

When the pulse signal i is supplied to the terminal 65 at time _T2 in FIG. 3, the switching transistor 43 becomes conductive. Therefore, the signal from the phototransistor 55 is now supplied from the transistor 43 to the base of the control transistor 37. At this time, from the terminal 60 to the video signal source 1
The voltage of the signal a applied to the terminal 62 is a'', which corresponds to the highlight part of the image. Also, the signal supplied from the terminal 62 to the base of the output transistor 13 is c. , unless the internal resistance of the transistor 37 is considered, the phosphor 77 will emit light with a brightness corresponding to the highlighted area.The intensity of this light is immediately converted into a signal by the phototransistor 55,
3 and is fed back to the base of the transistor 37.
As in the case of transistors 40 and 46, an increase in beam current I results in an increase in cathode voltage V, and the decreasing state changes in a similar manner. The value of the voltage V with respect to the current I is set to 3 by the capacitor 49.
It is held for the vertical scanning period.

Now, the relationship between these voltage V and current I depends on the characteristics of the transistor used and the values of resistance, etc.
The characteristic curve 3 in FIG. 5 can be obtained.
The gamma characteristics of picture tubes vary considerably, and it is difficult to reduce them for economical reasons, and the gamma characteristics vary within the range shown by characteristic curve 1 or characteristic curve 2, for example. Therefore, when a cathode voltage of V ₁ is applied to a picture tube whose gamma characteristics are as shown in curve 1 and as shown in curve 2, the beam currents become I ₁ and I ₃ , which are greatly different.

However, according to the circuit of this embodiment shown in FIG.
Since the relationship between cathode voltage V and beam current I is as shown in characteristic curve 3, the gamma characteristic is curve 1.
Even if a different picture tube is used as shown in curve 2, the value of the beam current I only changes from I ₁ to I ₂ , which is an almost negligible change.

The above is the operation for the blue cathode 16,
The same goes for green and red cathodes 17 and 18.
In the next vertical scanning period in FIG. 3, pulse signals g and m are first supplied to the terminals 63 and 69, and the transistors 47 and 41 are operated by the signal from the phototransistor 56 to convert the voltage V of the green cathode 17 into the beam current. The pulse signals j and d are then supplied to the terminals 66 and 63, and the signal from the phototransistor 55 is output to the output transistor via the transistors 44 and 38. The voltage V of the green cathode 17 is controlled according to the beam current I by controlling the collector current of the green cathode 14, and this state is maintained by the capacitor 50 for three vertical scanning periods.

Similarly, in the next vertical scanning period, pulse signals h and n are supplied to the terminals 64 and 70, the red cathode 18 is controlled by the phototransistor 56, and then the pulse signal e is supplied to the terminals 64 and 67.
and k are supplied, and the red cathode 18 is controlled by a signal from a phototransistor 55, and both states are maintained by capacitors 54 and 51 for three vertical scanning periods. In any of these cases, the video signal source 19 and the chroma signal source 20 have pulse signals a,
The fact that b is supplied is the same as in the case of the blue cathode 16.

As a result, the blue, green, and red cathodes 16, 17, 18 are sequentially connected to each other, with the vertical scanning period in FIG. 3 as one cycle.
Since the voltage V and current I are controlled to have a predetermined relationship, each terminal 60, 61, 6
Pulse signals a, b, supplied to 2, 63, 64,
Voltage values a′, a″, b, c, c, d, e, fg, h
If you set d, e, f, g, and h in advance to match the standard white color, the white balance will be automatically adjusted according to the gamma characteristics of the picture tube 22 without having to adjust the white balance for each individual receiver. A balance will be achieved.

That is, in this embodiment, since there is almost no possibility that the white balance will be distorted due to the influence of the gamma characteristics of the picture tube used, the voltage value of the pulse signal is set in advance using an arbitrary picture tube to match the standard white color. If the white balance circuit is configured to be driven using a pulse signal having this set value, a good white balance will always be obtained.

As explained above, according to the present invention, there is no need to adjust many resistors etc. in order to obtain white balance, which not only facilitates manufacturing and assembly and greatly reduces costs, but also improves the gamma characteristics of the picture tube. Since it is almost unaffected by changes in color, there is almost no risk of the white balance being distorted during use, and images can always be reproduced in the best condition, allowing the color television receiver to take full advantage of its performance and be used for a long time. Many benefits can be obtained, such as the ability to

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram showing an example of a video output circuit in a color television receiver to explain a conventional white balance adjustment method, and FIG. 2 is an electrical connection diagram of an automatic white balance adjustment device according to an embodiment of the present invention. A circuit diagram, FIG. 3 is a waveform diagram of each operating signal supplied to the electric circuit of FIG. 2, and FIG. 4 is a configuration of a portion that detects light from a fluorescent surface of a picture tube according to an embodiment of the present invention. The schematic perspective view shown in FIG. 5 is a characteristic diagram for explaining the operation of the automatic white balance adjustment device shown in FIG. 2. 13-15...video output transistor, 22
...Color picture tube, 37-42...Control transistor, 43-48...Switching transistor, 55, 56...Phototransistor.

Claims (1)

[Claims] 1. In a color display device equipped with a color picture tube having a plurality of cathodes and a fluorescent surface, and a plurality of color output circuits that supply color signals to each cathode, the white of the video signal is and a reference light detection means for detecting the brightness of the fluorescent surface when the reference signals for each of the primary colors are supplied to the color output circuit. , voltage holding means for holding the output voltage of the reference light detection means, and control means for controlling the color signals supplied to the cathode by the respective color output circuits according to the held voltage. Automatic white balance device.