JPS6325559B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an automatic white balance adjustment device in a video reproduction device using a color cathode ray tube, such as a color television receiver or a color monitor television.

Conventional configurations and their problems Traditionally, white balance was adjusted manually or by detecting the beam current and controlling it so that the beam current matched the absolute value of a preset standard. It also has an automatic white balance adjustment device. The latter is very convenient because it can automatically compensate even if the cathode emission of the cathode ray tube changes due to changes over time or temperature, but it cannot be compensated even if the temperature has stabilized. If this was continued, a bright line caused by the beam current measurement signal would always appear on the cathode ray tube, or the white balance would be distorted due to occasional noise or no signal.

OBJECT OF THE INVENTION The present invention eliminates such conventional drawbacks, and the present invention compares the detected beam current with an initial reference beam current value stored in advance to detect variations thereof, and maintains the initial beam current value. As a result of this control, if the fluctuation of the beam current falls within a certain range, the control of the DC level and amplification degree of the video amplification stage is fixed, and the reference voltage for detection is no longer generated. By fixing the control operation in this manner, the above-mentioned inconvenience can be eliminated.

Structure of the Invention The present invention provides a primary color signal amplifier that amplifies red, green, and blue primary color signals and can individually vary the DC level and amplification degree for each primary color signal, and the output of this primary color signal amplifier. a detection circuit that detects the beam current of each primary color of the color cathode ray tube that reproduces a color image by applying a voltage, a reference primary color voltage source that generates a reference primary color voltage for measuring the beam current of each primary color, and a reference primary color voltage source that generates a reference primary color voltage for measuring the beam current of each primary color. and a switching circuit that switches to apply the reference primary color voltage to each primary color signal amplifier instead of each primary color signal. In the initial state, initial beam current data for each primary color measured by the detection circuit when the reference primary color voltage is applied is stored in advance in the initial reference data storage means. On the other hand, in the use state, each beam current is set to the initial value stored in the initial data storage means by the control means based on the beam current for each primary color measured by the detection circuit when the reference primary color voltage is applied. Compared to the beam current,
The DC level and amplification degree of each primary color signal are controlled to correct the fluctuation. Then, by comparing the beam current of each primary color measured by the detection circuit with the initial beam current, and determining that the fluctuation is within a predetermined range, the next power supply is determined based on the output of that determination. The automatic adjustment operation as described above is stopped until the power is turned on or the automatic white balance adjustment is input. That is, control of the DC level and amplification degree of the primary color signal by the control means is stopped to fix the DC level and amplification degree, and application of the reference primary color voltage by the switching circuit is also stopped.

With this configuration, it is possible to automatically adjust the white balance only when necessary, and by stopping the automatic adjustment operation after a certain adjustment state is reached, unnecessary bright lines are prevented from appearing on the cathode ray tube. can be prevented from appearing, and
It is possible to prevent the white balance from collapsing due to unnecessary and inappropriate automatic white balance adjustment operations, and it is possible to always obtain images with a well-balanced white balance while eliminating problems that occur as side effects during automatic white balance adjustment. Can be done.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 depicts the basic part of the overall circuit of this embodiment, and shows only one primary color portion of each primary color in detail. Since the circuits for the other two primary colors are similar, only blocks are shown. Further, FIG. 2 shows a specific example of the control circuit shown in FIG. 1.

The primary color signals of each color are applied to the respective input terminals 1 and are applied to the operational amplifier 8 through the signal switch 18. Resistors 2, 3, 4 and transistor 5
sets the amplification degree and DC bias of the operational amplifier 6 to arbitrary values. The output of the operational amplifier 6 is input to a transistor 7, and is amplified by resistors 8 and 9 to a voltage sufficient to drive a cathode ray tube.

The collector of the transistor 7 is connected to the base of a PNP transistor 10 and drives the cathode of the cathode ray tube through a resistor 11 in the form of an emitter follower. A diode 12 is connected between the base and emitter of the PNP transistor 10.
It operates as a protection device when the base and emitter of the PNP transistor 10 becomes reverse biased when the collector voltage of the transistor 7 rises, and has the function of quickly charging the stray capacitance of the cathode. All cathode beam currents are detected by an A/D converter 14 due to the voltage drop across the collector flow resistance 13 of the transistor 10. The A/D converted data is transmitted to the control circuit 15.

The control circuit 15 is composed of a microcomputer and a memory, and when control is required, transmits data to a D/A converter 16 for offset control and a D/A converter 17 for gain control, and outputs data to the operational amplifier 6. Controls offset voltage and gain. By controlling this offset voltage, the DC level of the primary color signal is controlled, and by controlling the gain, the degree of amplification of the primary color signal is controlled.

On the other hand, the reference primary color voltages for measuring the beam current are usually connected to the low voltage power supply 19 and the high voltage power supply 20.
A type of signal is prepared and added to the signal switch 18 through the signal switch 21.

Next, the operation will be explained with reference to FIG.
First, a color television receiver in its initial state is obtained, with all adjustments including white balance completed in the factory. In the color television receiver in this initial state, by switching the signal switch 21 to the high voltage power supply side and the low voltage power supply side with the signal switch 18 switched to the terminal b side, the low voltage power supply 1
The reference primary color voltages from 9 and the high voltage power supply 20 are applied to the operational amplifier 6 in place of the primary color signals. Each initial beam current at that time is detected as a voltage from one end of the resistor 13, and the A-D converter 1
4, the data is converted into a digital signal and its value is stored in the initial reference data storage means 31. the other 2
Similarly, for the three primary color sections, a low voltage power source and a high voltage power source are applied to an operational amplifier (not shown), and the initial beam currents for each at that time are measured and stored in the initial reference data storage means 31. Therefore, the initial reference data storage means 31 stores reference data of six types of initial beam currents.

When the color television receiver is in use, during the horizontal or vertical blanking period (vertical blanking period in the illustrated example),
The reference primary color voltage control means 32, which operates based on vertical pulses, controls terminal a during periods other than the vertical blanking period.
At the same time, during one blanking period, the signal switch 18 connected to the side is switched to the terminal b side, and the signal switch 21 is switched to the low voltage power supply 19 and the high voltage power supply 20 respectively, and the primary color reference voltage is applied to the operational amplifier 6 instead of the primary color signal. and measure the beam current at that time. Similarly, the beam currents for each of the other two primary color parts during one blanking period are measured. That is, during each blanking period, for example, the beam currents of the three primary color sections at low voltage power supply and high voltage power supply are measured using a time-sharing method, and the respective measured values are passed through the A-D converter 14 to a comparison calculation means. 33, and here a comparison calculation is made with reference data of the initial beam current stored in advance in the storage means 31 to detect a deviation in white balance. If the deviation of any one color is outside a predetermined certain range, the operational amplifier 6 is controlled through the amplification degree/DC bias control means 34 and the D/A converters 16 and 17 to correct the deviation, and the DC level of the primary color signal is adjusted. Control the degree of amplification.
Note that the signal switching device 18 does not need to be switched every horizontal or every vertical blanking period, but may be switched at any period. As a result of such control, if the measured beam current variation falls within a predetermined constant range for all three colors, the comparison output discrimination means 35 issues a comparison discrimination output, and the amplification/DC bias control means 34 and The operation of the reference primary color voltage control means 32 is stopped.

That is, the control of the offset voltage of the operational amplifier 6 via the D/A converter 16 and the control of the gain of the operational amplifier 6 via the D/A converter 17 are stopped, and the control of the DC level and amplification degree of the primary color signal is stopped. To maintain a white balance state at that time by fixing a level and amplification degree. Furthermore, the signal switch 18 is switched to the a side to stop the application of the reference primary color voltage.

Thereafter, the automatic white balance adjustment operation will not be performed until the television receiver or color monitor is turned on again or the user commands the automatic white balance adjustment device to operate again. That is, the white balance adjustment state controlled within a certain range is maintained.

Effects of the Invention As described above, according to the present invention, the automatic white balance adjustment device stops its operation when the white balance falls within a certain range, thereby reducing side effects during automatic white balance adjustment. This eliminates the brightness of the retrace line caused by noise and the minute fluctuations in white balance caused by noise, making it possible to obtain a stable image that always has a good white balance.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a television receiver according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a specific example of the control circuit shown in FIG. 1... Primary color signal input terminal, 6... Operational amplifier,
7, 10...Transistor, 14...A/D converter, 15...Control circuit, 16,17...D/
A converter, 18, 21...Signal switch, 1
9, 20...Reference primary color voltage source.

Claims (1)

[Claims] 1. A primary color signal amplifier that amplifies the red, green, and blue primary color signals and allows the DC level and amplification degree to be individually varied for each primary color signal, and the output of this primary color signal amplifier is applied to create a color image. A detection circuit that detects the beam current of each primary color of the color cathode ray tube to be reproduced; a reference primary color voltage source that generates a reference primary color voltage for measuring the beam current of each primary color; A switching circuit that switches to apply a reference primary color voltage to the primary color signal amplifier, and data of an initial beam current for each primary color measured by the detection circuit when the reference primary color voltage is applied in an initial state are stored in advance. and storing each beam current in the initial data storage means based on the beam current for each primary color measured by the detection circuit when the reference primary color voltage is applied in the use state. a control means for controlling the direct current level and amplification degree of each primary color signal so as to compare the initial beam current with the initial beam current and correct the fluctuation; A comparative output determining means determines whether the output is within a certain range, and this comparative output determining output allows the control means to control the DC level and amplification degree of the primary color signal when the power is turned on next time or when automatic white balance adjustment is performed. An automatic white balance adjustment device comprising means for stopping the application of the reference primary color voltage by the switching circuit to fix the DC level and amplification degree until a command is input.