JPH0678328A - Color television receiver - Google Patents

Abstract

PURPOSE:To prevent a picture tube from being excessively biased and the screen from being blanked undesirably longer by displaying immediately a video image when a time from application of power till an output of a sampling circuit exceeding a reference voltage is shorter than a prescribed time. CONSTITUTION:A CPU 23 outputs a control signal to a blanking circuit 24 just after application of power to blank the screen. The state is maintained till the sampling output exceeds a 2nd reference voltage (E2). When it is detected that the sampling output exceeds the voltage E2 and the output of a comparator 18 is decreased to be a low level, it is judged how many seconds elapses from application of power, and when the time is within a prescribed time (A sec), a control signal is immediately given to a blanking circuit 24 to stop the blanking of the video image. When the time is not within the A sec, after the blanking is maintained for a prescribed period (B sec) from this point of time and the video image is displayed through the control of the circuit 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color television receiver, and more particularly to a color television receiver having an automatic white control circuit.

[0002]

2. Description of the Related Art Generally, a color television receiver includes a means for adjusting a bias of a color picture tube in order to set a reference white color which is a reference for color reproduction.

As such adjusting means, there is a circuit including a so-called service switch. In such a circuit, by switching the service switch to the "service" position, the picture tube is separated from the video signal to stop the vertical scanning, and in this state, the cutoff voltage of each electron gun is adjusted. ing. However, such adjustment requires skill and it is impossible to make such adjustment in a general household. For this reason, the reference white is displaced due to aging due to long-term use of the color television receiver, and an unnatural color may be reproduced.

For these reasons, recently, a reference signal is inserted into a part of the blanking period of the color television signal supplied to the color picture tube, and the picture tube current flowing through the color picture tube during the insertion period. Detection means for detecting,
An automatic white control circuit has been proposed which comprises a means for controlling the bias of the picture tube according to the output level of the detection means.

However, even such an automatic white control circuit has the following problems. That is, since the cathode temperature of the picture tube is low immediately after turning on the power of the image receiver,
There is no emission of electrons from the cathode and no cathode current flows. Therefore, the output level of the detecting means for detecting the picture tube current becomes the lowest, and the bias of the picture tube is controlled according to this level, so that the picture tube always outputs from the maximum transfer state. Is shortened, the reference white is deviated, and the viewer is uncomfortable.

An automatic white color control circuit for solving the above problems is disclosed in Japanese Patent Laid-Open No. 60-18086 (H04N).
9/73). The circuit block is shown in FIG. 2, and this operation will be described below.

In FIG. 2, reference numeral 1 is an antenna, and 2 is a television signal processing circuit for processing a signal received by the antenna 1. The demodulated chrominance signals RY, BY, GY and luminance signal-Y. Is output. Reference numeral 3 denotes a matrix circuit which synthesizes each color difference signal and a luminance signal and outputs primary color signals R, G and B. Further, 4 is a separation circuit, which obtains a blanking pulse output from the television signal processing circuit 2 and separates it into vertical and horizontal blanking pulses, and a vertical blanking pulse shaping circuit 5 and a horizontal blanking pulse. Vertical and horizontal blanking pulses are supplied to the signal generating circuit 7 via the shaping circuit 6.

The signal generating circuit 7 has a blanking period of 1
A signal for inserting the reference pulse in the horizontal period is output to the synthesizing circuit 8, and a gate pulse that coincides with the reference pulse insertion timing is output to the sampling circuit 9.
The synthesizing circuit 8 operates as an analog switch, receives a signal from the signal generating circuit 7, inserts a reference pulse in a predetermined period of the video signal, and supplies the reference pulse to the matrix circuit 3. The outputs of these matrix circuits 3 are supplied to a picture tube drive circuit 12 and an output circuit 13 via each level correction circuit 11 whose output is controlled by a DC control voltage supplied to a control terminal 10 to drive a color picture tube 14. To do. Note that the picture tube drive circuit 12 and the output circuit 13 show the B-axis circuit in detail, and the other axes are similar circuits, so only the blocks are shown.

The voltage generated in the resistor 15 in the output circuit 13 in which a current proportional to the current flowing in each cathode of the color picture tube 14 flows is supplied to each sampling circuit 9. These sampling circuits 9 sample a voltage proportional to the cathode current during the gate pulse period supplied from the signal generating circuit 7 and hold it in each capacitor 16. The voltage sampled and held in this way is supplied to the comparator 17
It is input to one input terminal (-) and compared with the reference voltage (E1) supplied to the other input terminal (+). The outputs of these comparators 17 are supplied to the level correction circuit 11 as control voltages. In this way, the feedback loop of the automatic white control circuit is configured, and automatic control is performed so that the cathode current during the reference pulse insertion period becomes constant.

Further, in this circuit, the output of the R-axis sampling circuit 9 is supplied to one input terminal (-) of the second comparator 18 and is input to the other input terminal (+) of the second comparator 18. It is compared with the reference voltage (E2). The output of the second comparator 18 opens and closes the switch means 19 in the next stage, and when the sampling output is equal to or lower than the second reference voltage (E2), the switch means 19 is turned off and the second reference voltage (E2). In the above cases, it is turned on.

The switch means 19 has one end connected to a power source via a resistor and the other end grounded via a charging / discharging capacitor 20. The voltage generated across the capacitor 20 is supplied to one input terminal (−) of the third comparator 21 and compared with the third reference voltage (E3) supplied to the other input terminal (+). . The output of the third comparator 21 is supplied to the mute circuit 22.
When the voltage of the capacitor 20 is lower than the third reference voltage (E3), the passage of the video signal to the synthesis circuit 8 is blocked, and the voltage of the capacitor 20 is changed to the third reference voltage (E3).
When it is higher than 3), the video signal is passed.

Next, the operation of this circuit will be further described with reference to FIG. In FIG. 3, (a) shows a change in electron emission capability of the cathode of the picture tube, (b) shows a change in sampling output of the sampling circuit 9, and (c) shows a change in output of the second comparator 18. Show. Further, (d) shows a change in the charging voltage of the capacitor 20, and (e) shows a change in the output of the third comparator 21. The abscissas of (a) to (e) represent time changes starting from the time point t0 when the power of the receiver is turned on.

In FIG. 3A, the cathode temperature is low and the electron emission capability is extremely low from t0 to t1 for a while after the power is turned on, and the electron emission capability starts to increase after time t1. Since the output of the sampling circuit 9 is proportional to the cathode current, the curve of (b) shows a rising characteristic similar to that of (a). Therefore, during this period t0 to t1, the sampling output is low, the output of the second comparator 18 is high, the switch means 19 is off, and the output of the third comparator 21 is also high. Therefore, the video signal is blocked by the mute circuit 22 and is not transmitted to the subsequent stage.

Next, at time t2, when the output of the sampling circuit 9 exceeds the second reference voltage (E2), the output of the second comparator 18 falls to low as shown in FIG. To turn on. When the switch means 19 is turned on, the capacitor 20 starts charging, and the voltage across the capacitor 20 gradually rises as shown in (d). Further time t
When the voltage reaches 4, the voltage across the capacitor 20 exceeds the third reference voltage (E3), and as shown in (e), the third comparator 21
Output drops low. Therefore, after time t4, the video signal is transmitted to the subsequent stage. Since this circuit operates as described above, it is possible to prevent an excessive transfer voltage to the picture tube when the power is turned on.

[0015]

The characteristic of the electron emission capability shown in FIG. 3 (a) changes depending on the state of the picture tube. For example, when the power is turned off and then immediately turned on, the picture tube warms up. Therefore, the period from t0 to t1 becomes shorter, and the rising characteristic becomes steeper.

However, in the television receiver provided with the automatic white control circuit as described above, the charging time constant of the capacitor 20 is constant, so that FIG.
The rising characteristics from time t2 to time t4 are constant. Therefore, regardless of the state of the picture tube, the image does not appear until a certain time has elapsed after the sampling output exceeds the second reference voltage, and as described above, the picture tube has already warmed up and is stable in a short period of time. Even if it is in the state, there is a problem that the screen is muted unnecessarily long. The present invention is intended to solve the problems of the prior art.

[0017]

To this end, according to the present invention, a reference signal is inserted into a part of a blanking period of a color picture tube and a color television signal supplied to the color picture tube, and the inserting period is set. In a television receiver provided with an automatic white control circuit comprising a detecting means for detecting a picture tube current flowing through the color picture tube and a means for controlling a bias of the picture tube according to an output level of the detecting means. A control signal generating means for generating a control signal by detecting that the output level of the detection signal exceeds a predetermined reference value; and the control signal after a lapse of a first predetermined time from the power-on of the television receiver. When it occurs, the image is blocked from being projected for a second predetermined time from that point, and when the control signal is generated within the first predetermined time, the image is immediately projected. Consisting of a signal control means.

[0018]

According to the present invention, the picture tube is already warmed when the time from when the power is turned on to when the output of the sampling circuit exceeds the second reference voltage is shorter than the predetermined time. The rising edge of the emission capacity curve is steep and it is judged that the stable state has been reached immediately, and the image is immediately displayed.

[0019]

1 is a block diagram showing an embodiment of the present invention, in which the same components as those in FIG. 2 are designated by the same reference numerals and their description is omitted. In FIG. 1, reference numeral 23 denotes a CPU 23 that mainly performs channel selection processing, remote control signal reception processing, and control of brightness and contrast of video signals, and supplies various control signals to the television signal processing circuit 2. The CPU 23 is also connected to the second comparator 18 and inputs its output. Further, 24 is a blanking circuit, which replaces the mute circuit 22 of FIG.
The screen is blanked according to an instruction from the CPU 23. However, a gate pulse that coincides with the reference pulse insertion timing is given to the blanking circuit 24, and the signal is passed to the subsequent stage only during the reference pulse insertion period.

FIG. 4 shows a flowchart of a portion of the operation of the CPU 23, which is relevant to the present invention. The operation will be described based on this figure.

Immediately after the power is turned on, the CPU 23 outputs a control signal to the blanking circuit 24 to blank the screen.
(Step 1) This state is continued until the sampling output exceeds the second reference voltage (E2). When it is detected that the sampling output exceeds the second reference voltage (E2) and the output of the second comparator 18 falls low (step 2), it is determined how many seconds have elapsed since the power was turned on. It is determined (step 3), and if it is within a predetermined period, that is, within A seconds in this embodiment, a control signal is immediately output to the blanking circuit 24 to stop the blanking of the image. (Step 4) If it is not within A seconds, blanking circuit 24 is controlled so as to display an image after continuing blanking for a predetermined period (B seconds) from this point (Step 5). Here, the values of A to B differ depending on the characteristics of each picture tube and are set arbitrarily, but according to the experiment by the applicant, about 2 seconds is suitable for both A and B. .

[0022]

As described above, according to the present invention, it is possible to prevent the screen from blanking for an unnecessarily long time in order to prevent the picture tube from being excessively biased when the power is turned on.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional technique.

FIG. 3 is a waveform diagram for explaining the operation of FIG.

FIG. 4 is a flowchart for explaining the operation of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 antenna 2 television signal processing circuit 3 matrix circuit 4 separation circuit 5 vertical blanking pulse shaping circuit 6 horizontal blanking pulse shaping circuit 7 signal generation circuit 8 synthesis circuit 9 sampling circuit 10 control terminal 11 level correction circuit 12 picture tube drive circuit 13 Output Circuit 14 Color Picture Tube 15 Resistor 16 Capacitor 17 Comparator 18 Second Comparator 19 Switch Means 20 Capacitor 21 Third Comparator 22 Mute Circuit 23 CPU 24 Blanking Circuit

Claims (1)

[Claims] 1. A color picture tube and a reference signal inserted into a part of a blanking period of a color television signal supplied to the color picture tube, and a picture tube current flowing through the color picture tube during the insertion period. In a television receiver provided with an automatic white control circuit comprising a detecting means for detecting and a means for controlling the bias of the picture tube according to the output level of the detecting means, the output level of the detection signal is a predetermined reference level. Control signal generating means for generating a control signal upon detecting that the value has been exceeded, and when the control signal is generated after a lapse of a first predetermined time after the power of the television receiver is turned on, a second signal is generated from that point. Of the color television projector for preventing the image from being projected for a predetermined time and immediately displaying the image when the control signal is generated within the first predetermined time. Receiver.