JP2644899B2 - Automatic white balance adjustment circuit and device using the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance adjustment circuit for a color television receiver and other devices requiring white balance stabilization.

[Conventional technology]

FIG. 5 shows an example of a conventional automatic white balance adjusting device described in Japanese Patent Publication No. 1-26355.

In FIG. 5, reference numeral 10 denotes an antenna.
Are supplied to the television signal processing circuit 11. From the output terminals 11R, 11G, 11B of the signal processing circuit 11, color difference signals R-Y, G-Y, BY are obtained and supplied to the matrix circuits 12R, 12G, 12B, respectively. A video signal including a luminance signal -Y is obtained from an output terminal 11Y of the signal processing circuit 11, and is passed through a synthesizing circuit 13 to each of the matrix circuits 12R, 12R.
G, 12B, and combines the color difference signal and the video signal to form color signals R, G, B. The output terminal 1 of the signal processing circuit 11
From 1S, a blanking pulse BLK is obtained, separated into vertical and horizontal blanking pulses by a separation circuit 14, and then vertically and signally sent to a signal generation circuit 17 through a vertical blanking pulse shaping circuit 15 and a horizontal blanking pulse shaping circuit 16. Horizontal blanking pulses VB and HB are supplied. The signal generating circuit 17 outputs a signal for inserting a reference pulse into a part of one horizontal period in a predetermined section other than a picture signal, with respect to a video signal supplied to a color picture tube (described later). Terminal 17
A gate pulse which is generated from A and coincides with the insertion timing of the pulse is generated from the output terminal 17B.

A signal (hereinafter referred to as a reference insertion pulse) obtained at an output terminal 17A of the signal generation circuit 17 is inserted into a video signal in a synthesis circuit 13 acting as an analog switch,
The signals are supplied to the matrix circuits 12R, 12G, and 12B, respectively. The outputs of these matrix circuits 12R, 12G and 12B further pass through level correction circuits 18R, 18G, 18B, picture tube drive circuits 19R, 19G, 19B and output circuits 20R, 20G, 20B, respectively, and cathodes 21R, 21G of the color picture tube 21. , 21B. The output voltages of the level correction circuits 18R, 18G, and 18B are controlled to increase and decrease by DC control voltages supplied to control terminals 22, 23, and 24. The picture tube drive circuits 19R, 19G, and 19B are:
As shown in the blue axis drive circuit 19B as a representative, the transistor 2
The signal from the level correction circuit 18B is applied to the base of the transistor 25, the collector is connected to the voltage source VCC via the resistor 26, and the emitter is connected to the circuit 5 via the resistor 27.
0 is connected to the emitter of the transistor 51. Then, the output from the collector of the transistor 25 is supplied to the next-stage output circuit 20B.

Similarly, the output circuit 20R, 20G, 20B has a transistor 28 whose base is connected to the collector of the transistor 25 as a representative of the output circuit 20B on the blue axis. Grounded via a resistor 29, the emitter is the cathode 21B of the color picture tube 21
It is connected to the.

Since the current flowing through each cathode of the color picture tube 21 flows through the transistor 28 and the resistor 29, the current flowing through the resistor 29 is proportional to the cathode current, and the voltage appearing at the resistor 29 is supplied to the sampling circuit 33B through the line 32. . Further, voltages proportional to the cathode currents from the output circuits 20R and 20G are also supplied to the sampling circuits 33R and 33G through the lines 30 and 31, respectively. These sampling circuits 33R, 3
In 3G and 33B, a gate pulse synchronized with the generation timing of the reference insertion pulse is supplied from the output terminal 17B of the signal generation circuit 17 via a line 34, and a voltage proportional to the cathode current during the insertion pulse is sampled. ,
The capacitors Cr, Cg, and Cb have a filtering function so as to hold the voltage sampled by each of the capacitors Cr, Cg, and Cb. The outputs of the sampling circuits 33R, 33G, 33B are supplied to one input terminal (-) of the comparators 35R, 35G, 35B, respectively.

A reference voltage from a reference voltage source 36 is supplied to the other input terminal (+) of each of the comparators 35R, 35G, and 35B, and is compared with the sampling circuits 33R, 33G, and 33B. Then, it rises, and conversely, falls when the sampling output rises, and stabilizes where the difference between the sampling output and the reference voltage becomes zero.

The outputs of these comparators 35R, 35G, and 35B are line 37, respectively.
Control terminal 2 of level correction circuit 18R, 18G, 18B through 38, 39
2,23,24.

The circuit shown in the frame 50, the base voltage E ₂ from the voltage source 52 is supplied to the collector of the transistor 51 is grounded through the resistor 53, the emitter bias than the emitter of the transistor 51 to the transistor 25 It is being supplied.

The sampling circuit 54 is connected to the collector of the transistor 51.
Is controlled by a signal from the output terminal 17B. The output of the sampling circuit 54 is supplied to one input terminal of the comparator 55 (+), the other input terminal of the comparator 55 - reference voltage E ₃ of the voltage source 56 is supplied to the () . The output of the comparator 55 is supplied to the output terminal 57 of the circuit 50. The comparator 55 compares the voltage E ₃ and the output of the voltage source 56 of the sampling circuit 54, when the sampling output is E ₃ or more next-stage switching means Sr, Sg, Sb
When the switch means Sr, Sg, Sb are on, the filter capacitors Cr, Cg, Cb are connected to the voltage source 58 via the resistors Rr, Rg, Rb, respectively. The switch means Sr, Sg, Sb are all electronic switches.

A high voltage is supplied from the anode terminal 40 of the picture tube 21,
Horizontal and vertical deflection currents are supplied to the deflection coil 41 from terminals 42 and 43.

The operation of the automatic white balance adjusting device thus configured will be described with reference to the waveform diagram of FIG.

In FIG. 6, A indicates a video signal at the output terminal 11Y of the television signal processing circuit 11, VB indicates a vertical blanking signal, HB indicates a horizontal blanking signal, and L indicates a picture signal.

FIG. 6B shows the output waveform of the vertical blanking pulse shaping circuit 15 and C shows the output waveform of the horizontal blanking pulse shaping circuit 16, respectively.
B and HB are supplied to the signal 17, and a reference insertion pulse as shown in FIG. 6D is obtained from the output terminal 17A. This insertion pulse is generated in a part (period T ₁ ) of the horizontal blanking pulse HB section other than the picture signal section, and can be easily obtained, for example, by providing counter means in the signal generation circuit 17.

6D is synthesized with the video signal (FIG. 6A) in the synthesizing circuit 13 to obtain the signal shown in FIG. 6E. This composite signal passes through a matrix circuit 12, a level correction circuit 18, a drive circuit 19, and an output circuit 20, and the picture tube 21
Of the cathode. For example, taking the circuit of the blue axis as an example, the current flowing through the cathode 21B of the picture tube 21 passes through the emitter-collector path of the transistor 28,
Flow to 29. The resistor 29 detects a cathode current, and a voltage proportional to the amount of the current is detected from a connection point between the resistor 29 and the collector of the transistor 28, and is supplied to the sampling circuit 33B. The sampling circuit 33B is that the gate pulse synchronized from the output terminal 17B to the generation timing of the reference insertion pulse (period T ₁₎ of the signal generating circuit 17 is supplied to the cathode current of the kinescope 21 in the period T ₁ The proportional voltage is sampled, and the sampled output is applied to one input terminal (-) of the comparator 35B.

This comparator 35B has characteristics as shown in FIG. 7, the reference voltage applied to the other input terminal (+) is E1, the input voltage applied to _one input terminal (-) is the horizontal axis, and the output is When the voltage is plotted on the vertical axis, the output voltage decreases as the input voltage increases, and conversely, the output voltage increases as the input voltage decreases. Also, the characteristic of the level correction circuit 18B to which the output of the comparator 35B is supplied is such that the output level increases as the DC control voltage applied to the control terminal 24 increases, and conversely, the output level decreases as the DC control voltage decreases. It has become.

Therefore, when the cathode current decreases due to, for example, a decrease in the emission of the cathode 21B of the picture tube 21 or a drift in a related circuit, the input voltage to the sampling circuit 33B decreases. The output of the sampling circuit 33B so is proportional to the cathode current sampling only the voltage in the sampling period T ₁ of the above picture period regardless sampling output is reduced. On the other hand, in the comparator 35B, the reference voltage E ₁
Compared to the output of the comparator 35B according to the characteristics of FIG. 7 according to the difference between E ₁ is increased. As a result, the control voltage applied to the control terminal 24 of the level correction circuit 18B increases, and the output level thereof also increases. As a result, the transfer voltage of the picture tube 21 increases, and the cathode current increases. Conversely, when the cathode current increases, the above operation is performed in reverse to reduce the cathode current.
The difference between the input voltage and the reference voltage E ₁ of the 33B is stabilized where becomes zero.

The same operation is performed not only for the correction of the blue axis but also for the red and green axes so that the difference between the input voltage of the comparator and the reference voltage becomes zero in the state where the initial reference white is adjusted. If a circuit is set for the CRT, the CRT bias is automatically adjusted even if the cathode emission of the CRT is reduced or a circuit drift occurs, and correction can be made so that there is no deviation of the reference white at all times.

The operation described above is for normal operation,
Although there is no particular problem, the operation described above causes the following problem.

When the color television receiver is turned off for a long time, the temperature of the cathode of the picture tube is almost the same as the room temperature. If the power is turned on in this state, the temperature required for the cathode to emit electrons will not reach the temperature until a predetermined time has elapsed. For this reason, no cathode current flows because no electrons are emitted from the cathode during this time. This is because the output of the sampling circuit becomes the lowest, the output of the comparator increases, the output level of the level correction circuit also increases, the transfer voltage of the picture tube rises, and the dynamic range of the control system increases, as is apparent from the above operation. It saturates to the maximum value. Then, when the temperature of the cathode rises in this state, the cathode current starts to flow, the transfer voltage of the picture tube decreases, and the normal operation value is converged. That is, when the power is turned on, the picture tube picture is output from the maximum picture tube transfer state, so that the life of the picture tube is shortened and the viewer is discomforted.

A circuit for solving the above problem is a circuit part shown by a frame 50 in FIG. 5, switch means Sr, Sg, Sb, resistors Rr, Rg, Rb.
It is. The operation of this part will be described below.

During the above-described normal operation, the switch means Sr, Sg, Sb are off. Next, in the operation when the power is turned on, as described above, since the cathode current does not flow, the base potential of the transistor 25 of the drive circuits 19R, 19R, and 19B increases. Then, the emitter current of the transistor 25 increases and the transistor
The emitter current of 51 increases. Therefore, the collector current of the transistor 51 increases, the input voltage of the sampling circuit 54 increases, and the (+) input terminal voltage of the comparator 55 increases.
And this voltage is comparator 55 (-) switch means Sr, Sg, Sb is turned on by the output from the comparator 55 to become larger than the reference voltage E ₃ is the input voltage. As a result, the capacitors Cr, Cg, and Cb are charged from the voltage source 58 via the resistors Rr, Rg, and Rb, and the voltages of the capacitors rise. Therefore, the outputs of the comparators 35R, 35G, 35B decrease, and the level correction circuit 18
The output levels of R, 18G and 18B decrease. That is, when the picture tube drive circuit current exceeds a predetermined level, control is performed so as to suppress the supply of the video signal to the picture tube to a certain level or less. Then, when the electron emission capability of the cathode becomes stable, a video signal can be supplied at a predetermined level.

[Problems to be solved by the invention]

FIG. 5 showing an example of the above-mentioned prior art shows a case where the number of reference insertion pulses is one, and controls one of the picture tube biases of a black level or a white level. FIG. 4 shows an example of the application of the prior art in which two types of reference insertion pulses, that is, black level and white level reference pulses, are inserted to control the picture tube bias. This figure will be described below.

FIG. 4 shows the processing after the color signals R, G, B output from the matrix circuits 12R, 12G, 12B of FIG. In FIG. 4, the same portions as those in FIG. 5 are denoted by the same reference numerals, and detailed description will be omitted.

The color signals R, G, and B are supplied to gain correction circuits 181R, 181G, and 181B, and the white level is controlled by a control signal applied to control terminals 221, 231 and 241.
The control of the black level is performed by a control signal supplied to 182R, 182G, 182B and applied to control terminals 222, 232, 242. These control signals are supplied to the sampling circuits 331R, 331G, 331B, 332R,
332G, 332B and comparators 351R, 351G, 351B, 352R, 352G, 352B.

Here, a reference voltage is applied to the (−) input terminals of the comparators 351R, 351G, 351B from the reference voltage source 361 corresponding to the detection of the white level, and to the (−) input terminals of the comparators 352R, 352G, 352B. Has a reference voltage applied from a reference voltage source 362 corresponding to the detection of the black level.

The control circuit at power-on has two systems since it is necessary to detect the current of the picture tube drive circuit at each of the white level and the black level. The white level control system is a sampling circuit
541, comparator 551, white level corresponding reference voltage source 561 generates a control signal, and switches S ₁ r, S ₁ g, S via line 571.
Control ₁ b. The black level control system is a sampling circuit 54
2, a control signal is generated by the comparator 552 and the reference voltage source 562 corresponding to the black level, and the switch circuits S ₂ r, S ₂ g, S
To control the ₂ b. Here, a gate pulse synchronized with the generation timing of the white level reference insertion pulse is supplied to 171B, and the sampling circuit is controlled via the line 341.A gate pulse synchronized with the generation timing of the black level reference insertion pulse is supplied to 172B. The sampling circuit is controlled via a line 342. With the above configuration, the white level and the black level suppress the transfer voltage of the picture tube to a predetermined level or less when the power is turned on.

 The conventional technique shown in FIG. 4 has the following problem.

1. Two circuits of the picture tube transfer voltage suppression circuit at power-on are required, and the circuit scale increases.

2. Since the current detection of the picture tube drive circuit is performed using a mixture of three channels of R, G, and B, if there is a variation between the channels, the transfer voltage of the picture tube of a single color is reduced to a predetermined suppression value of 3
In this case, when the power is turned on, the image may start with a single color or become saturated with a single color. In order to avoid this, the current detection of the picture tube drive circuit should be 3 times.
When each channel is provided, transistor 51, resistor 5
3. Sampling circuits 541 and 542 and comparators 551 and 552 are required for three channels, which increases the circuit scale.

3. To integrate iC and integrate the stage before the picture tube drive circuit, input terminals of sampling circuits 541 and 542 are required. Further, in the case of item No. 2, three input terminals are required, and the number of iC terminals increases.

 An object of the present invention is to improve the above problem.

[Means for solving the problem]

In order to achieve the above object, a first configuration of an automatic white balance adjustment circuit according to the present invention includes a gain correction circuit provided on a signal transmission line and a drive circuit that drives a picture tube in response to an output of a DC level correction circuit. Current detection means for inserting a white level reference signal and a black level reference signal into a part of the signal and detecting a picture tube current during the insertion period, and the current detection means according to the detection value corresponding to the white level. In an automatic white balance adjustment circuit configured to control the gain correction circuit in a closed loop and to control the DC level correction circuit in a closed loop in accordance with a detection value corresponding to the black level, an input voltage or an output voltage of the drive circuit is adjusted. Voltage detecting means for detecting, and when the detection output of the voltage detecting means at the time of the black level exceeds a predetermined value, the DC level correcting circuit is controlled to display the image on the picture tube. Characterized by comprising control means for suppressing the dc bias level of the signal below a predetermined value, and means for setting the gain of the gain correction circuit to a predetermined value.

The second configuration includes a drive circuit for driving the picture tube in response to the outputs of the gain correction circuit and the DC level correction circuit provided on the signal transmission line, and a white level reference signal and a black level Current detection means for inserting the reference signal of the above and detecting the picture tube current during the insertion period, and controls the gain correction circuit in a closed loop in accordance with the detection value corresponding to the white level, and corresponds to the black level. An automatic white balance adjustment circuit configured to perform closed loop control of the DC level correction circuit in accordance with the detected value, wherein voltage detection means for detecting an input voltage or output voltage of the drive circuit; A control means for controlling the gain correction circuit when the detection output at the level exceeds a predetermined value to suppress the drive bias level of the video signal to the picture tube to a certain value or less. When, characterized by comprising a means for setting the gain of the level correcting circuit to a predetermined value.

[Action]

In the first configuration, the voltage detecting means detects a voltage corresponding to a black level. When the detection value exceeds a predetermined value, the control means controls the DC level correction circuit to suppress the DC bias level applied to the picture tube to a predetermined value or less, and sets the gain of the gain correction circuit to a predetermined value. When the power is turned on, the rise of the transfer voltage of the picture tube drive circuit is suppressed until the picture tube current starts flowing.

In the second configuration, the voltage detection means detects a voltage corresponding to a white level. When the detection value exceeds a predetermined value, the control means controls the gain correction circuit to suppress the drive bias level applied to the picture tube to a predetermined value or less, and sets the correction level of the DC level correction circuit to a predetermined value. Then, when the power is turned on, the rise of the transfer voltage of the picture tube drive circuit is suppressed until the picture tube current starts flowing.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
In FIG. 1, the same portions as those in FIG. 4 are denoted by the same reference numerals, and the detailed description is omitted.

The color signals R, G, B are supplied to the DC bias correction circuits 183R, 183G, 183B via the clamp capacitors CiR, CiG, CiB. This DC bias correction circuit is constituted by a clamp circuit, and switches charging / discharging currents to the capacitors CiR, CiG, CiB by a binary voltage supplied to the control terminals 223, 233, 243. When the control terminal is at a high voltage, it is charged and the DC potential rises, and when the control terminal is at a low voltage, it is discharged and its DC potential falls. This charge / discharge operation is performed at the timing of inserting the black level of the gate pulse supplied through the line 342, and the period is maintained.

The picture tube drive circuits 19R, 19G, and 19B have transistors 25 and 64, as shown by the blue axis drive circuit 19B, and the signal from the gain correction circuit 181B is added to the base of the transistor 25. The emitter is connected to a constant current source 62 via a resistor 61. A constant voltage source 65 is added to the base of the transistor 64,
The collector is connected to a voltage source VCC2 via a resistor 66, and the emitter is connected to the constant current source 62 via a resistor 63. The output from the collector of the transistor 25 is supplied to the output circuit 20B of the next stage, and the output from the collector of the transistor 64 is supplied to the (+) input of the comparator 552B.

The operation will be described below. First, during normal operation, the control system for the black level uses the signals of the current detection lines 30, 31, and 32 to output the signals from the comparators 353R and 353R.
The reference voltage source 362 supplied to the (−) input of the 53G, 353B and applied to the (+) input is compared. The result is a switching output, and a high or low voltage is output. These outputs are connected to the control terminals 223, 233, 24 of the DC level correction circuits 183R, 183G, 183B via switching means S ₃ r, S ₃ g, S ₃ b.
3 and is controlled during the period of the black level reference insertion pulse. Here the switching means S ₃ r, S ₃ g, comparators 552R for controlling the S ₃ b, 552G, the output of 552B switch becomes low voltage is left as Figure 1 are selected in the black level insertion period. Next, the white level control system operates in the same manner as in FIG. 4 except that the outputs of the comparators 351R, 351G, and 351B and the gain correction circuit 18
1R, 181G, switching means S ₄ r, S ₄ g, is S ₄ b is inserted between the control terminal 221, 231 and 241 of 181B. These switching means are controlled by the outputs of the hold circuits 59R, 59G, 59B, and these hold circuits are provided by the comparators 552R, 552G,
The potential of the 552B output during the black level period is held. Therefore hold circuit output becomes a low voltage, the switching means _{S 4 r, S 4 g,} S 4 b the left is selected as the first view. As described above, normally, the bias control is applied to both the white level and the black level by the current of the picture tube.

Next, an operation at the time of power-on, which is a feature of the present invention, will be described. The features of the circuit are the circuit part indicated by the box 50 and the switch means S ₄ r, S ₄ controlled by the output of this circuit 50.
g, S ₄ b, and that the (+) input of the comparators 552R, 552G, 552B for detecting an excessive bias of the picture tube is used as the collector of the transistor 64 to detect the voltage.

The circuit 50 detects the output equivalent voltage of the picture tube drive circuit 19R, 19G, 19B during the black level reference insertion pulse period,
When these voltages exceed a predetermined value, the comparators 552R and 552
G and 552B become high-potential outputs, respectively, and switch means S ₃ r,
The selection of S ₃ g and S ₃ b selects the right side in FIG. 1, that is, the ground (low potential). Therefore, the DC level correction circuit
182R, 182G, 182B operate so as to lower the DC level and make the detection voltage of the picture tube drive circuit equal to or lower than a predetermined value. Here, the difference from FIG. 4 is that the comparators 552R, 552G, 552B
Means 59R for holding the output of, 59G, provided 59B, the these output switch means S ₃ r, S ₃ g, there is to be controlled switching the S ₃ b.

That is, when the outputs of the comparators 552R, 552G, and 552B are at a low voltage, the operation is in a normal operation state in which a cathode current is flowing.
At this time, the outputs of the holding means 59R, 59G, and 59B also become low-voltage outputs, and the switching means S ₄ r, S ₄ g, and S ₄ b
Select the output of 51R, 351G, 351B. Therefore, the gain correction circuit 1
81R, 181G, and 181B operate under normal control. Next, when the outputs of the comparators 552R, 552G, and 552B are at a high voltage, this means that the power is turned on and the cathode is not yet warmed up. The potential becomes high, and the switch means S ₄ r, S ₄ g, and S ₄ b switch respectively to select the ground side. Therefore, the gain correction circuits 181R, 181G, and 181B operate at the minimum gain, and the cathode drive voltage is minimized.

As described above, the transfer voltage of the picture tube drive circuit can be suppressed for both the black level and the white level for each channel by detecting the output equivalent voltage of the picture tube drive circuit only during the black level reference insertion pulse period.

According to the present embodiment, the number of elements constituting the circuit can be reduced, and there is an effect that simplification can be achieved.

Another embodiment of the present invention will be described with reference to FIG. still,
In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the detailed description is omitted.

The feature of the present invention is the detection location of the over bias of the picture tube. In FIG. 2, the picture tube drive circuits 19R, 19G, 19
Although the emitter of the transistor 25 of B is used, the same applies when the base is used. The emitter voltages of the transistors are input to the (+) input terminals of the comparators 552R, 552G, and 552B, respectively. In these comparators, the voltage is compared with the voltage of the reference voltage source 564 input to the (-) input terminal, and the same operation as in FIG. 1 is performed.

According to this embodiment, a transistor constituting a circuit for detecting an output equivalent voltage of the picture tube drive circuit shown in FIG.
64, resistors 63 and 66, and constant current source 62 can be individually controlled for three channels without providing them for three channels, and the above-mentioned problems such as monochromatic saturation caused by variations in operation between channels can be improved with a small number of elements. Can be. When iC is considered, considering that the parts excluding the picture tube drive circuits 19R, 19G, and 19B and the output circuits 20R, 20G, and 20B are integrated,
When the (+) input of the comparators 552R, 552G, and 552B is used as the base line of the transistor 25, this line can be built in the iC, and the number of iC terminals is reduced as compared with the method of FIG. be able to.

Another embodiment of the present invention will be described with reference to FIG. still,
In FIG. 3, the same portions as those in FIG. 2 are denoted by the same reference numerals, and detailed description will be omitted.

The feature of the present invention is a circuit portion shown by a frame 50,
The emitter line of the transistor 25 is different from the circuit 50 shown in FIG.
The maximum voltage is selected from the three signal lines, and becomes the output signal of the maximum value circuit 60. This output signal is supplied to the (+) input terminal of the comparison circuit 552. The subsequent operation is the same as in FIG. Since the maximum value is detected and controlled by the three signal lines, the transfer voltage of the picture tube drive circuit operates on the channel having the maximum value among the three channels.

According to this embodiment, there is an effect that the circuit scale can be reduced in addition to the effect of FIG.

〔The invention's effect〕

Since the present invention is configured as described above, it has the following effects.

Due to the provision of the automatic white balance adjustment circuit, it is possible to reliably prevent the picture tube from being excessively biased when the power is turned on by using a circuit having a small number of elements.

Also, by changing the method of detecting an over bias of the picture tube, the variation between channels at the time of suppression is suppressed,
Images can be displayed from a stable white color. Furthermore, when iC is used, the number of terminals can be reduced.

Further, the number of elements can be reduced by detecting and controlling the maximum value between the three channels of the excessive bias of the picture tube.

[Brief description of the drawings]

FIGS. 1, 2, and 3 are circuit diagrams showing an embodiment of the present invention, FIGS. 4 and 5 are circuit diagrams showing a conventional automatic white balance adjustment circuit, and FIG. FIG. 5 is a signal waveform diagram of each part for explanation of the operation, and FIG. 7 is a characteristic diagram showing operation characteristics of the comparator used in FIG. 181R, 181G, 181B …… Gain correction circuit, 183R, 183G, 183B ……
DC level correction circuit, 29 ... Cathode current detection resistor, 33
1R, 331G, 331B …… Sampling circuit, 552R, 552G, 552B…
… Comparator, 59R, 59G, 59B …… Hold circuit, S ₃ r, S ₃ g, S
₃ b, S ₄ r, S ₄ g, S ₄ b ...... Switching means.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Kamiya 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Yokohama Plant, Hitachi, Ltd. (72) Koji Kawamoto 3-1-1, Sachicho, Hitachi-shi, Ibaraki Inside Hitachi, Ltd. Hitachi Plant

Claims (4)

(57) [Claims] 1. A drive circuit for driving a picture tube in response to an output of a gain correction circuit and a DC level correction circuit provided in a signal transmission line, and a white level reference signal and a black level reference signal in a part of the signal. Current detecting means for detecting the picture tube current during the insertion period, and controlling the gain correction circuit in a closed loop according to the detected value corresponding to the white level, and detecting the detected value corresponding to the black level. An automatic white balance adjustment circuit configured to perform closed loop control of the DC level correction circuit according to the following: voltage detection means for detecting an input voltage or an output voltage of the drive circuit; Control means for controlling the DC level correction circuit when the detection output exceeds a predetermined value to suppress the DC bias level of the video signal to the picture tube to a certain value or less; and Automatic white balance adjustment circuit, wherein the configuration and means for setting the gain of the gain correction circuit to a predetermined value. 2. A drive circuit for driving a picture tube in response to an output of a gain correction circuit and a DC level correction circuit provided in a signal transmission line, and a white level reference signal and a black level reference signal in part of the signal. Current detecting means for detecting the picture tube current during the insertion period, and controlling the gain correction circuit in a closed loop according to the detected value corresponding to the white level, and detecting the detected value corresponding to the black level. An automatic white balance adjustment circuit configured to control the DC level correction circuit in a closed loop according to the following: voltage detection means for detecting an input voltage or an output voltage of the drive circuit; Control means for controlling the gain correction circuit when the detection output exceeds a predetermined value to suppress the drive bias level of the video signal to the picture tube to a certain value or less; Automatic white balance adjustment circuit for the means for setting the gain of the serial level correction circuit to a predetermined value, a structure having the features. 3. The drive circuit according to claim 1, wherein the drive circuit includes a plurality of channels, and the voltage detection means is configured to detect a maximum value of an input voltage or an output voltage of the plurality of channels. Automatic white balance adjustment circuit. 4. An apparatus using the automatic white balance adjustment circuit according to claim 1.