JPH07123436A - Automatic white balance control circuit - Google Patents

Abstract

PURPOSE:To provide stable white balance by detecting the beam value in each primary color of a cathode-ray tube, storing that value as a control value, comparing a beam current detected value with the control value at the time of control and controlling a primary color drive value. CONSTITUTION:A reference voltage generating circuit 1 generates a reference voltage during a vertical blanking (BL) period. A switching circuit 2 selects a primary color signal excepting for the vertical BL term and outputs a normal video signal. During the vertical BL period, a reference voltage 1 is selected to one of three primary color signals in manner of time division, two remaining primary color signals are switched to a BL level, and only one of three primary color signals outputs the reference voltage. That primary color signal passes through an amplifier circuit 3, and the beam current in each primary color of the cathode-ray tube is detected by a beam current detection circuit 4. At the time of assembly control, the detected value of the circuit 4 is held in a storage means 5 as the control value and after the control, this value is defined as a set value. At the time of drive control, the detected current value is compared with the preceding detected current value stored in a storage means 6 by a comparing means 7, and the primary color drive value is controlled by control circuits 7 and 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance adjusting circuit for a television receiver.

[0002]

2. Description of the Related Art Recently, some television receivers have an automatic white balance adjusting circuit. The automatic white balance adjustment circuit can also be classified into the following two categories.

1. It operates so that white balance adjustment is not required during assembly adjustment. 2. White balance adjustment is necessary during assembly adjustment, but the adjustment value is stored and it operates to suppress temperature changes and aging changes.

The automatic white balance adjustment circuit described here belongs to the latter one. Some of the latter automatic white balance adjusting circuits have already been proposed, but one disclosed in "Automatic White Balance Adjusting Device" of Japanese Patent Publication No. 63-25558 is one of those already known as prior art. Is one. In the above-mentioned technique, the beam current measurement pulse is red, green, and
It is generated in one of the primary colors of blue and its beam current is A /
It operates so as to maintain the initial white balance by comparing the content read by the D converter with the value stored in advance in the initial state. Furthermore, it is not absolutely adjusted to the initial state, It is characterized by matching the ratio or offset of the primary color beam current. As a result, when the white balance is adjusted during the assembly adjustment, the detected data of the beam current at that time is stored and the temperature change and the secular change are suppressed.

[0005]

In such an automatic white balance adjusting circuit, the beam currents of the other two primary colors are controlled with reference to the beam current of one of the three primary colors. When the function was activated, the white balance was lost if the cutoff or drive control range was exceeded.

[0006]

In order to solve the above problems, the present invention provides a reference voltage generating circuit for generating a reference voltage in a vertical blanking period and a vertical color signal by selecting a primary color signal in a period other than the vertical blanking period. In the blanking period, a switching circuit that selects the reference voltage for one of the three primary color signals in a time division manner and switches to the blanking level for the remaining two primary color signals is connected to the output of the switching circuit. A primary color signal amplification circuit that amplifies each primary color signal of red, blue, and green, and that can independently change the DC level and amplification degree for each primary color signal, and the output of this primary color signal amplification circuit is input to input a color image. Beam current detection circuit for detecting the beam current of each primary color of the color cathode ray tube for reproducing, and one kind of each of the above-mentioned beam current detection circuit at the time of assembly adjustment,
First storage means for holding the detected current values of blue and green as set values, and each red of the beam current detection circuit during normal use,
Second storage means for temporarily holding one type of detected current value of blue and green, a detected current value measured corresponding to the voltage of the reference voltage generation circuit during drive control, and another primary color measured immediately before. Comparing means for comparing the detected current value stored in the second storage means, and if the detected current value is larger than the adjustment value stored in the second storage means by the output of the comparing means, the drive value of the primary color Is decreased by a predetermined amount, and if it is equal or smaller, it is controlled so as to be increased by a predetermined amount, and if the drive control means of the primary color signal amplification circuit becomes maximum, the drive value is stopped increasing. It has a configuration of control means.

[0007]

According to the present invention, the drive value of one specific primary color can be fixed and the automatic white balance adjusting circuit which is stable even if the drive values of the other two primary colors exceed the control range. It will be possible.

[0008]

Embodiment 1 First, an embodiment of the first invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the first invention.

In FIG. 1, reference numeral 1 is a reference voltage generating circuit for generating a reference voltage during a vertical blanking period. 2 selects a primary color signal in a period other than the vertical blanking period, selects one of three primary color signals in the vertical blanking period from the reference voltage in a time division manner, and blanks the remaining two primary color signals. This is a switching circuit for switching to the level. Reference numeral 3 denotes a primary color signal amplifier circuit which is connected to the output of the switching circuit 2 to amplify each primary color signal of red, blue and green and to independently change the DC level and the amplification degree for each primary color signal. Reference numeral 4 denotes a beam current detection circuit which receives the output of the primary color signal amplification circuit 3 and detects the beam current of each primary color of the color CRT which reproduces a color image.

Reference numeral 5 designates a first storage means for holding the respective detection current values of red, blue and green of the beam current detection circuit 4 as set values during assembly and adjustment. Reference numeral 6 denotes a second storage means for temporarily holding the red, blue, and green detection current values of the beam current detection circuit during normal use. Reference numeral 7 is a comparison for comparing the detected current value measured corresponding to the reference voltage of the reference voltage generating circuit 1 during drive control with the detected current value stored in the second storage means of another primary color measured immediately before. It is a means. Reference numeral 8 indicates that when the detected current value is larger than the detected current value of the immediately preceding primary color stored in the second storage means 6 by the output of the comparison means 7, the drive value of the primary color is lowered by a predetermined amount, and if equal or smaller, The control means controls to increase by a predetermined amount and stops increasing the drive value when the drive control means of the primary color signal amplification circuit becomes maximum.

Next, the operation will be described. In FIG. 1, a reference voltage generating circuit 1 generates a reference voltage during a vertical blanking period. In the switching circuit 2, the primary color signal is selected and the normal video signal is output except during the vertical blanking period. In the vertical blanking period, one of the three primary color signals is selected by time-divisionally selecting the reference voltage 1 for one of the three primary color signals and switching to the blanking level for the remaining two primary color signals. Only the reference voltage is output. This is the AD of the beam current detection circuit
This is because the beam current is measured in a time-division manner because only one converter is used. If an AD converter independent of the three primary colors is prepared, the switching circuit 2 only has to switch between the reference voltage and the video signal.

Next, the output of the switching circuit 2 is input to the primary color signal amplifying circuit 3 so that the primary color signals of red, blue and green are amplified and the direct current level and the amplification degree can be independently changed for each primary color signal. To do. The output of the primary color signal amplification circuit 3 is input to the beam current detection circuit 4 to detect the beam current of each primary color of the color CRT which reproduces a color image. Here, the beam current is detected by the collector by the PNP transistor, converted into a voltage by the resistor, and then captured as digital data by the AD converter. At the time of assembly and adjustment, the red, blue, and green detection current values of the beam current detection circuit 4 are held as adjustment values in the first storage means 5, and after adjustment, these values are used as set values. During normal use, the red, blue, and green detection current values of the beam current detection circuit are stored in the second storage means 6.
Temporarily hold. This is because the beam current of each primary color is measured in a time division manner, and the detected current cannot be compared with other primary colors unless the detected current is held.

During drive control, the comparison means 7 detects the detected current value corresponding to the voltage of the reference voltage generating circuit and the detection current value stored in the second storage means 6 of another primary color measured immediately before. Compare with. In the control means 8, when the detected current value by the output of the comparison means 7 is larger than the detected current value of the immediately preceding primary color stored in the second storage means 6, the drive value of the primary color is lowered by a predetermined amount to determine whether it is equal. If it is small, the white balance is automatically adjusted by controlling it so that it is increased by a predetermined amount. At this time, if the drive control means of the primary color signal amplifying circuit is maximized, the drive value is stopped increasing.

(Embodiment 2) An embodiment of the operation of the control means of the present invention will be described with reference to the drawings. The control means determines the specific primary color so that the drive value of the specific primary color is constant, and when the specific drive value is different from the set value, it controls the specific drive value and the drive value of the specific primary color is When they match the set value, the control means controls the drive value of another primary color compared. FIG. 2 is a flow chart showing an embodiment of the operation of the present invention.

The flowchart of FIG. 2 shows the main routine of the control means 8 of the automatic white balance adjusting circuit. It is determined which primary color the detected current data read is, and each primary color is selected. It is distributed to control subroutines. The red, green and blue subroutines are shown in FIGS. 3, 4 and 5, respectively. For convenience of explanation, a specific primary color is determined to be green, and an algorithm for keeping the green drive value constant will be described.

FIG. 3 shows a subroutine for controlling the drive value when the red detected current value is read. First, normalization is performed by multiplying the read detected current data by specific data so that it can be easily compared with other primary colors. As this specific data, the reciprocal of the set value of the red detected current data stored in the first storage means 5 is used. Next, the normalized red detected current data is compared with the blue detected current data stored in the second storage means 6, and if the red detected current data is large, the red drive value is lowered by one step and the red drive value is decreased. If it is one step larger.

FIG. 4 is a subroutine for controlling the drive value when the green detected current value is read. Similar to the case of red, the detected current data for green is normalized and then compared with the detected current data for red. At this time, the aim is to keep the green drive value constant, so determine whether the green drive value matches the target setting value, and if it does not match, set the green drive value. Control, and if they match, control the red drive value.

FIG. 5 is a subroutine for controlling the drive value when the blue detected current value is read. As with the green subroutine, after normalizing the read current value,
It is determined whether or not the green drive value matches the target setting value. If they do not match, the green drive value is controlled, and if they match, the blue drive value is controlled.

With the above algorithm, the green drive value can be kept constant. (Embodiment 3) Another embodiment of the present invention will be described. The control means 8 has an algorithm that determines a certain specific primary color among the three primary colors and makes the drive value of the specific primary color constant, and the drive value of any one of the other two primary colors. If exceeds the control range, the algorithm for keeping the drive value of the specific primary color constant is stopped so that the drive values of the three primary colors are all within the control range.

(Embodiment 4) The control means 8 controls the reading order of the three primary colors in the same order. However, if the reading order is different, an algorithm is added to wait until the correct primary color data arrives. There is. This is an algorithm based on the assumption that the current detection data comes in the order of red, green, and blue in the algorithm described in the second embodiment.

However, for example, when the green data continues for some reason, the red detected current data stored in the second storage means 5 is not updated, and therefore even if the red drive is raised, the red drive current is increased by this algorithm. The red drive value may continue to increase without knowing that the detected current data has increased. Therefore, if the control means side always executes the following primary color subroutine, this can be avoided.

[0022]

As described above, the reference voltage generating circuit for generating the reference voltage in the vertical blanking period of the present invention and the primary color signal are selected in the periods other than the vertical blanking period, and three of the three are selected in the vertical blanking period. A switching circuit that selects the reference voltage for one primary color signal in a time division manner and switches the remaining two primary color signals to the blanking level and the output of the switching circuit are connected to each of red, blue, and green. A primary color signal amplification circuit that amplifies the primary color signal and allows the DC level and amplification degree to be changed independently for each primary color signal, and each primary color of the color CRT that inputs the output of this primary color signal amplification circuit and reproduces a color image. Beam current detection circuit for detecting the beam current of the above, and a first description for holding the detection current values of the red, blue, and green of one kind of the beam current detection circuit as set values at the time of assembly adjustment. Means, second storage means for temporarily holding one type of detection current value of each of red, blue and green of the beam current detection circuit at the time of normal use, and a voltage of the reference voltage generation circuit at the time of drive control. Comparing means for comparing the detected current value measured correspondingly with the detected current value stored in the second storage means of another primary color measured immediately before, and the detected current value of the second detected current value by the output of the comparing means. If it is larger than the adjustment value stored in the storage means, the drive value of the primary color is lowered by a predetermined amount, and if it is equal or smaller, it is controlled so as to be raised by a predetermined amount. A stable automatic white balance adjusting circuit can be obtained by the configuration of the control means that stops increasing the drive value at the maximum.

In the present invention, for the sake of convenience of explanation, only one type of reference voltage is generated by the reference voltage generation circuit because it is limited to the explanation of drive adjustment. However, two types of reference voltages are generated in a time division manner, It goes without saying that the cutoff adjustment can be performed with the lower reference voltage.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic white balance adjustment circuit of the present invention.

FIG. 2 is a flowchart showing an example of the operation of the circuit.

FIG. 3 is a flowchart of a red drive control subroutine that is an example of the operation of the circuit.

FIG. 4 is a flowchart of a green drive control subroutine that is an example of the operation of the circuit.

FIG. 5 is a flowchart of a blue drive control subroutine that is an example of the operation of the circuit.

[Explanation of symbols]

 1 Reference Voltage Generating Circuit 2 Switching Circuit 3 Primary Color Signal Amplifying Circuit 4 Beam Current Detection Circuit 5 First Storage Means 6 Second Storage Means 7 Comparison Means 8 Control Means

Claims (4)

[Claims] 1. A reference voltage generation circuit for generating a reference voltage during a vertical blanking period, and a primary color signal selected during periods other than the vertical blanking period, wherein the reference voltage is applied to one of the three primary color signals during the vertical blanking period. Is selected in a time-divisional manner and the remaining two primary color signals are switched to the blanking level and the output of the above switching circuit is connected to amplify the respective primary color signals of red, blue and green, and at the same time, A primary color signal amplification circuit that allows the DC level and amplification to be changed independently for each signal, and a beam current that detects the beam current of each primary color of a color CRT that inputs the output of this primary color signal amplification circuit and reproduces a color image. A detection circuit, a first storage means for holding the red, blue, and green detection current values of the beam current detection circuit as set values during assembly and adjustment; and the beam during normal use. Second storage means for temporarily holding the red, blue, and green detection current values of the current detection circuit, and the detection current value measured corresponding to the voltage of the reference voltage generation circuit during drive control and the measurement value measured immediately before. Comparing means for comparing the detected current value stored in the second storage means of the different primary color with the detected current value of the immediately preceding primary color whose detected current value is stored in the second storage means by the output of the comparing means. If it is larger, the drive value of the primary color is lowered by a predetermined amount, and if it is equal or smaller, it is controlled to be raised by a predetermined amount.If the drive control means of the primary color signal amplification circuit becomes maximum, the drive value is set there. An automatic white balance adjustment circuit consisting of a control unit that stops raising. 2. The control means controls the specific drive value when the specific drive value is different from the set value so that the specific primary color is determined and the drive value of the specific primary color is constant. 2. The automatic white balance adjusting circuit according to claim 1, which is a means for controlling a drive value of another primary color compared with the drive value of the primary color when the drive value of the primary color is equal to the set value. 3. The control means has an algorithm for determining a specific primary color among the three primary colors, and making the drive value of the specific primary color constant, and also for selecting one of the other two primary colors. 2. If the drive value of the primary color exceeds the control range, the algorithm for stopping the drive value of the specific primary color is stopped, and the drive values of the three primary colors are all within the control range. The automatic white balance adjustment circuit according to claim 2. 4. The control means includes means for controlling the reading order of the three primary colors in the same order, and waiting for correct primary color data if the reading order is different. The automatic white balance adjustment circuit according to claim 2.